The Ba Moussa West Coral fauna, a new Early Carbiniferous Coral assemblage from central Morocco.

Mississippian rocks are common in the Moroccan Meseta. They have been studied and described by French geologists since the beginning of the twentieth century. The Mississippian stratigraphic successions are clearly different in the western and in the eastern parts of the Meseta. The succession was considered quite continuous from the Devonian to the Serpukhovian. However, sedimentation in the eastern part of the central Meseta (Azrou-Khenifra Basin) is more complicated. It took place in both a shallow-water carbonate platform and a deeper water flysch basin, within a tectonically active setting, involving movements of blocks, and transgressions and regressions that produced some gaps and unconformities. Sedimentation during the Tournaisian, early and mid Visean in the basin is regarded as being absent by some authors, whereas continuous or sporadic sedimentation during that time interval is suggested by others.

In a paper published in the Journal of Palaeogeography on 11 February 2020, Sergio Rodríguez of the Universidad Complutense de Madrid and the Instituto de Geociencias at the Consejo Superior de Investigaciones Científicas, Ian Somerville of the School of Earth Sciences at University College Dublin, Pedro Cózar, also of the Instituto de Geociencias at the Consejo Superior de Investigaciones Científicas, Javier Sanz-López of the Departmento de Geología at the Universidad de Oviedo, Ismael Coronado of the Institute of Paleobiology, Felipe González of the Departmento de Ciencias de la Tierra at the Universidad de Huelva, Ismail Said, also of the Universidad Complutense de Madrid, and Mohamed El Houicha of the Laboratoire de Géodynamique et Géomatique at the Université Chouaïb Doukkali, report the recent discovery of a relatively rich Mississippian (early Visean) Coral fauna in the southern part of the Azrou-Khenifra Basin, describe the Corals in detail and their host limestone rocks, and comment on their comparison and affinity with other coeval Coral assemblages in North Africa, Europe and southwest Asia. The microfossil content was also studied to enhance the biostratigraphic discussion and significance of the Coral fauna.

The beginning of Carboniferous sedimentation in the Khenifra region, which lies in the southern part of the Azrou-Khenifra Basin and contains the largest Mississippian outcrops in the eastern central Meseta, is usually considered to occur within the widely known late Visean transgression. However, two early Visean transgressions have been cited. The first one is imprecisely located as “to the north of Ba Moussa (point 1)”. The second one was equated with the base of V2b of mid Visean age.

In the southwestern margin of the Azrou-Khenifra Basin at Sidi Lamine and Tabainout, a thick shallow-water carbonate succession with basal Mississippian conglomerate and sandy limestone can be seen to rest unconformably on older (Ordovician) tilted siltstones and sandstones. A similar relationship is seen at the southeastern margin of the basin at Tiouinine where shallow water sandy limestones rest unconformably on red Ordovician sandstones.

(a) Location of Khenifra in central Morocco; (b) Geological map of Azrou-Khenifra Basin with Ba Moussa West coral fauna locality and other Coral localities mentioned in the text; (c) Simplified geological sketch map of Ba Moussa West area and the location of the studied limestone horizons BMW1 and BMW2. hV-Fm1, Lower Visean; hV-Fm2, Upper Visean. Rodríguez et al. (2020).

The eastern part of the Azrou-Khenifra Basin, northwest of Khenifra, is a region of mostly deep-water rythmic mudstones. However, recent field investigations at Ba Moussa West, northwest of a nappe folded as a north-south trending syncline, and approximately 3 km northwest of Khenifra city margins, have discovered two pale gray weathering limestone units within a thick dark gray siltstone and shale rhythmic succession. These limestones contain abundant corals that form the focus of this paper. The limestone units form two distinct parallel ridges, some 50m apart, and traceable laterally for over 200 m. They form prominent features on the landscape, compared to the subdued topography of the more easily eroded mudstones which encase the limestones. The beds dip steeply to the east (70°) and in places can be vertical. The two ridges expose respectively, 4.90m and 4.10m thicknesses of well-bedded limestones (with beds ranging typically from 10 to 40 cm thick) with thin dark gray shale interbeds.

(a) View looking south of limestone ridge (BMW1) about 5 m thick showing steeply dipping beds overlain and underlain by softer shales; (b) Limestone bed with large angular quartzite and sandstone lithoclasts (beside coin) succeeded by thin laminated sandy limestone and black shales, in turn overlain by bioclastic limestone rich in Corals; solitary Rugose Coral Siphonophyllia (black arrows) and Cerioid Tabulate Coral Turnacipora (white arrow), coin diameter is 2.5 cm; (c) Close-up view of richly bioclastic limestone bed with sharp base, showing abundant transverse sections of Siphonophyllia and Sychnoelasma (black arrows), hammer length is 40 cm; (d) Coarse-grained crinoidal limestone with longitudinal and transverse sections of Siphonophyllia khenifrense; (e) Thin section of rudstone at BMW1 showing bioclasts and lithoclasts. Abbreviations: br, brachiopod; bz, bryozoan; co, coral; cr, crinoid; gr, gastropod; st, sandstone; (f) Thin section of rudstone at BMW2 showing bioclasts and lithoclasts. Abbreviations: br, brachiopod; co, coral; cr, crinoid; sl, siltstone; st, sandstone. Rodríguez et al. (2020).

The limestones are variable in composition and texture, comprising coarse-grained, bioclastic and lithoclastic calcirudites, rich in crinoids, thick-shelled Brachiopods and relatively abundant Corals. The limestone beds consist of numerous sedimentary events. Some have sharp, erosive bases and show grading with laminated tops. Large angular lithoclasts of sandstone and siltstone (up to 20 cm in diameter) occur in some beds. Other limestones are buff weathered, fine-grained, laminated calcarenites. Under the petrological microscope two microfacies are differentiated. The first microfacies, which is less common, is a laminated Crinoidal wackestone-packstone containing small fragments of Crinoidal plates, Corals and Bryozoans. The second one, which is dominant, is a polymictic rudstone with fragmented Corals, Crinoids, Bryozoans, Brachiopods, Trilobites, Gastropods, Bivalves, Foraminifers and angular to subangular grains of quartzite sandstone and siltstone. The disposition of siliciclastic clasts and bioclasts is random in some beds, suggesting rapid sedimentation, but in some beds, most clasts are disposed mainly parallel to the stratification. The fragmentation of bioclasts is also variable.

The limestones can be regarded as proximal debris flow and multistorey high-density turbidite bodies, with numerous event beds, deposited in a prevailing succession of distal turbidite beds. Thus, the coral assemblage is allochthonous and may have been transported far from its original depositional shelf setting.

The two limestone horizons (BMW1 and BMW2) were sampled and corals were collected. Samples from BMW1 contain almost entire Brachiopods and Corals, whereas in BMW2 most bioclasts are completely broken and very few Coral specimens are identifiable at generic or specific level. The coral assemblage is relatively rich, but their diversity is quite low (5 genera and 7 species). The assemblage comprises solitary Rugose Corals and Tabulate colonies. Many corals are well preserved and nearly complete, missing only the apexes and showing sometimes compressed calices when they show few skeletal elements and are filled with muddy sediment. However, others are completely fragmented or crushed or have lost much of their dissepimentaria. Fifty specimens were collected, of which 38 have been definitively identified.

Thin sections of samples were studied to describe the microfossil content. Owing to the brecciated character of many beds, including boulders of large size, only the fine-grained limestones yield Foraminifers. Assemblages are relatively abundant in those fine-grained limestones, although specimens are commonly crushed, and diversity is limited to a few genera. Assemblages from BMW1 are slightly richer than BMW2, although this may be the result of more intense sampling and sectioning.

A large sample from limestone BMW1 (3.8 kg weight) was etched with 8%–10% buffered formic acid solution, following the standard technique to avoid damaging. The low abundance of Conodont elements includes one complete P1 element and six broken elements with upper surface damaged and a few with surface dissolution, which could be in relation to significant transport and resedimentation of elements. The colour of Conodonts shows values of 4.5 to 5 for the alteration index. Reworking of Conodonts may be causing a higher colour alteration index value, but small recrystallised apatite surface is observed in Conodonts. Some specimens preserve a smooth surface, but etched surfaces with pits are often discerned. It suggests short heating on proximity to an igneous intrusion.

Conodonts from samples of BMW1. (a)–(b) Fragment of element of Kladognathus sp., DGO 15624, and detail of the face where breakage shows a lamellar inner structure and small apatite crystal 2–3 μm in size interpreted as recystallized and, later, slight dissolution; (c)–(e) Aboral and oral views of Mestognathus cf. beckmanni, DGO 15625, and detail of the margin of the platform with a strong dissolution located on the ornamentation of ridges and carina causing the inversion of surface relief; (f) Oral view of Polygnathus lobatus with pits due to dissolution of the Conodont surface, DGO 15622; (g) Gnathodus pseudosemiglaber, DGO 15623; (h)–(i) Oral and aboral views of Polygnathus inornatus, DGO 15621. Conodonts are stored in the Museum of Geology of the University of Oviedo. Rodríguez et al. (2020).

The allochthonous shales embedding the limestone horizons were sampled for palynomorphs. A total of 12 shale samples were crushed and dissolved following the classical extraction techniques. After complete removal of carbonate and silicate minerals, the organic remains were oxidized with Fuming Schulze solution and mounted in slides for microscope analysis. Palynomorphs recovered from shales are dominated by phytoclasts and, in minor proportions, by spores, whereas organic-walled marine microphytoplankton and amorphous organic matter are virtually absent. The reduced number of spores and their irregular state of preservation precluded further taxonomic identification. The large proportion of equidimensional to lath-shaped phytoclasts and the absence of marine components may be explained by the intense reworking and effective dilution associated to low-density turbidity currents. The brownish-black to black colour of spores and phytoclasts points to a thermal alteration index which essentially agrees with the colour alteration index values observed for conodonts from the limestone sample.

The Coral assemblage from Ba Moussa West contains a new species of Siphonophyllia, with other solitary Rugose Corals, such as Sychnoelasma urbanowitschi, Cravenia lamellata, Cravenia tela, and Cravenia rhytoides. Colonial Tabulate Corals recorded include Turnacipora megastoma, and Pleurosiphonella crustosa. Themost abundant specimens collected belong to the genus Siphonophyllia (20) and Turnacipora (7). Most other species are represented only by three specimens or less.

The assemblage is similar to that described from lower Visean (Arundian) Moel Hiraddug Formation in North Wales, UK. In both regions the large Siphonophylliid Corals represent the dominant component in dark gray bioclastic limestone and shale lithofacies, in which colonial Rugose Corals are absent. However, the Ba Moussa succession has a lower diversity Coral assemblage and the specimens are not as well preserved. This may be explained by the sedimentological setting at Ba Moussa, with the Corals occurring in graded limestone beds containing large exotic clasts, interpreted as debris flow and proximal turbidite deposits.

The stratigraphic range of Sychnoelasma urbanowitschi, and the three species of Cravenia (Cravenia lamellata, Cravenia tela, and Cravenia rhytoides) is very restricted, typically diagnostic of the early Visean throughout Western Europe. Turnacipora megastoma occurs also, typically in the early Visean.

The Ba Moussa West assemblage has similarities with Tafilalt in Eastern Morocco, where a richer early Visean solitary Rugose assemblage is recorded including Cravenia, Siphonophyllia and Sychnoelasma, but where colonial Rugose genera are also absent. Similar assemblages containing dominant Cyathopsids plus Sychnoelasma, Pleurosiphonella and Micheliniids have been reported in Canada and United States, and in Mid-Asia.

The Ba Moussa limestone beds are clearly older than other Mississippian sections in the Khenifra area, as confirmed by the associated Foraminifers and Conodonts. Coral assemblages from Tabainout and Sidi Lamine, 20 km and 30 km respectively, further west of Ba Moussa West, at the western margin of the Azrou-Khenifra Basin, contain fasciculate and massive colonial Rugose Coral genera (Siphonodendron and Lithostrotion) of late Visean (Asbian) age. Both sections have basal transgressive deposits with in situ shallow-water limestones containing ooids and Calcareous Algae. At Tiouinine, 8 km southeast of Khenifra on the eastern margin of the basin, very rich and diverse late Visean (Brigantian) Coral assemblages form a reefal tract. The early Visean age of the Ba Moussa West limestone correlates with the early Visean age of the transgressive point 1, located to the north of Ba Moussa.

The assemblage in samples from BMW1 contains the Foraminifers Earlandia vulgaris, Earlandia elegans, Endothyra spp., Endothyra similis, Endolaxina sp., Endothyranopsis (Eosinopsis) sp., Eosparastaffella sp., Eosparastaffella concinna, Eosparastaffella evoluta, Eosparastaffella interiecta, Eosparastaffella macdermoti, Eosparastaffella aff. macdermoti, Eosparastaffella ovalis, Eosparastaffella simplex, Eosparastaffella tumida subsp. 1, Eosparastaffella vdovenkoae, Eotextularia diversa, Granuliferella sp., Globoendothyra sp., Lapparentidiscus sp.,? Lituotubella sp., Mediocris mediocris, Mediocris ovalis, Mediocris aff. ovalis, Omphalotis sp., Pseudoplanoendothyra sp., Septabrunsiina sp., Septaglomospiranella sp., Spinobrunsiina sp., Spinolaxina sp., Tetrataxis sp. and Urbanella (Brenckleites) fragilis. The Algospongia recorded are very common Kamaena delicata and Palaeoberesella lahoseni, as well as Stacheoides spissa and Exvotarisella sp.

(a) Eotextularia diversa, BMW1, Pc4367; (b) Latiendothyranopsis sp., BMW2; (c) Omphalotis sp., BMW1, Pc4364; (d) Eoparastaffella tumida, BMW1, Pc4364. (e) Granuliferella sp., BMW1, Pc4364; (f) Mediocris aff. ovalis, BMW1, Pc4366; (g) Eoparastaffella simplex, BMW1, Pc4366; (h) Eoparastaffella ex gr. simplex (Eoparastaffella tumida subsp. 1), BMW1, Pc4367; (i) Eoparastaffella aff. concinna, BMW1, Pc4365; (j) Eoparastaffella evoluta, BMW2; (k) Eoparastaffella vdovenkoae, BMW1, Pc4366; (l) Eoparastaffella macdermoti, BMW1, Pc4364; (m) Eoparastaffella ovalis, BMW1, Pc4367; (n) Endolaxina sp., BMW1, Pc4367; (o) Pseudoplanoendothyra sp., BMW1, Pc4364; (p) Endothyranopsis (Eosynopsis) sp., BMW1, Pc4364. Scale bar same for all figures. Rodríguez et al. (2020).

The assemblage is characterized by a high diversity in Eoparastaffella species, and in particular, the first species with pointed periphery in the last whorl, Eoparastaffella tumida subsp. 1 and Eoparastaffella ex gr. simplex. Although the marker for the base of the MFZ9, as well as the marker for the base of the Visean, Eoparastaffella tumida subsp. 1 is derived from Eoparastaffella simplex from the basal levels of the MFZ9, and thus, the assemblages can be attributed to the base of the Visean. It is noteworthy for the occurrence of Eoparastaffella concinna and Eoparastaffella evoluta, also derived from Eoparastaffella simplex in more advances stages of the MFZ9.

The foraminiferal assemblage recorded in BMW2 is composed of Earlandia minor, Earlandia vulgaris, Endothyra spp., Endothyra ex gr. bowmani, Endothyra prisca, Endothyra similis, Eotextularia diversa, 'Glomospira' sp., Eoparastaffella sp., Eoparastaffella concinna, Eoparastaffella interiecta, Eoparastaffella macdermoti, Eoparastaffella simplex, Eoparastaffella tumida subsp. 1, Eoparastaffella vdovenkoae, Mediocris mediocris, Latiendothyranopsis sp., Omphalotis sp., Plectogyranopsis sp., and Pseudoplanoendothyra sp. This assemblage also contains the pointed and slender Eoparastaffella, including Eoparastaffella. concinna, which is a more evolved form than the ancestral stock of pointed Eoparastaffella. In consequence, the assemblage is also assigned to an advanced stage in the MFZ9. The Algospongia recorded in those levels contain Palaeoberesella lahoseni, Kamaena delicata, Issinella sp., and Exvotarisella sp.

The Conodont fauna studied in samples from BMW1 includes Polygnathus inornatus, Polygnathus lobatus (that is usually related with the first species), and a fragment of Polygnathus sp. These taxa were usually described in the early to mid Tournaisian Siphonodella–Polygnathus inornatus Assemblage Zone in the British Isles. However, it has been indicated that Polygnathus inornatus ranged up to the upper Tournaisian Gnathodus typicus Conodont Zone in Cornwall (UK). Polygnathus inornatus have been reported in the upper Tournaisian Scaliognathus anchoralis Zone of the Moravia-Silesia and the Dinant-Namur basins, and in the earliest Visean, just at the first occurrence of Pseudognathodus homopunctatus in the Belgian area. A late Tournaisian to early Visean age is supported by the occurrences of one P1 element of Gnathodus pseudosemiglaber, one P1 fragment of Mestognathus sp. and one P2 element probably corresponding to Kladognathus sp. The fragment of Mestognathus sp. shows dissolution of the carina and ornamentation of the platform, and the blade and the dorsal part of the platform are broken. The parapet area is close to that described in Mestognathus praebeckmanni. The secondary keel seems to be formed with a basal groove, as in Mestognathus beckmanni, but the specimen is broken. The first occurrence of Mestognathus beckmanni was indicated just below the lower boundary of the Visean Stage at the Global Boundary Stratotype Section in the Pengchong section, South China and in a few localities of Western Europe, although it is often recorded in Visean beds. The early Visean Pseudognathodus homopunctatus species is lacking in Rodríguez et al.'s sample.

The new species of Siphonophyllia is named Siphonophyllia khenifrense, which refers to the town of Khenifra within the Azrou-Khenifra Basin in Morocco. Seventeen whole specimens were recovered, all from Ba Moussa West, as well as 29 transverse sections and 15 longitudinal sections.

The whole specimens are cylindrical Corallites between 20 mm and 40 mm in alar diameter and recorded fragments are up to 20 cm long, often without calice. The dissepimentarium is often abraded. The outer wall is thin.

Siphonophyllia khenifrense. (a)–(c) Holotype DPM BMW1-1: (a) DPM BMW1-1A, transverse section., (b) DPM BMW1-1B, transverse section., (c) longitudinal sections; (d)–(e) DPM BMW1-6: (d) transverse section, (e) longitudinal sections; (f)–(g) DPM BMW1-20: (f) longitudinal sections, (g) transverse section.; (h) DPM BMW2-16, transverse section; (i) DPM BMW2-4, transverse section; (j) Wall microstructure in Siphonophyllia khenifrense, DPM BMW1-1, L, Lamellae; (k) Septal microstructure in Siphonophyllia khenifrense, DPM BMW2-16, Gr, Granular axial septum; F, Fibronormal middle zone; L, Lamellar external zone. Black arrows indicate the position of the cardinal septum. Corals are housed in the Geodinamica, Estratigrafía y Paleontología Department of the Universidad Complutense de Madrid. Rodríguez et al. (2020).

The tabularium diameter varies from 17 mm in immature stage to 31 mm in adult stage. The tabularium is wide, 3/5 to more than 4/5 Corallite diameter; the variation in tabularium width is a function of the age of the specimen (immature vs mature Corallite) and variation in the width of the dissepimentarium, which although generally narrow, can also be variably preserved. The number of major septa ranges commonly between 42 and 61, but up to 68 may be present. The septa are long, almost reaching the axis in immature stage but withdrawn from the centre in mature adult stage. They are straight to slightly flexuous in the tabularium, thinning axially and straight to sinuous in the dissepimentarium. Major septa are strongly thickened in the tabularium but are thin in the dissepimentarium; septa can be slightly thicker in cardinal quadrants and thinner in counter quadrants. The minor septa are also thickened where they penetrate slightly into the tabularium, but not as thick as majors; in the dissepimentarium they are thin. They are variable in length, from 1/4 to 1/3 length of majors. The cardinal septum is slightly shorter in most mature Corallites and located in a closed small cardinal fossula. It is often flanked by two major septa which are shorter than the others. Counter septum is inconspicuous, but shorter in late adult stages.

The dissepimentarium is narrow (typically 1/10 to 1/5 Corallite diameter) and mainly composed of interseptal regular dissepiments. The dissepiments are more irregular in the external part of the dissepimentarium, with occasional lonsdaleoid dissepiments. Typically 3 to 6 rows of slightly angular concentric dissepiments are present in the dissepimentarium. In longitudinal section, the dissepiments are small and elongate. They are declined to the tabularium from 60° to 70°.

The tabulae are mostly complete flat domes with some splitting; horizontal, medially sagging and convex tabulae can be present, sloping down peripherally to prominent gutters. They are relatively widely spaced numbering between 6 and 12 each centimetre.

The wall microstructure is microlamellar, as well as the septal stereoplasm and thickenings of tabulae and dissepiments. The septal mesoplasm is granulofibrous with incipient development of microtrabeculae. The tabulae and dissepiments are microgranular.

At least four transgressive phases have been differentiated in the Azrou-Kenifra Basin which were related with fault activity and resedimentation on the margins of tectonic blocks. The early Visean Corals at Ba Moussa West are the oldest occurrence in this basin, and are an important fauna differentiated from the commonly described faunas in late Visean beds of the western margin of the basin at Sidi Lamine and Tabainout, as well as in the northern part of the basin at Adarouch.

The early Visean age in the MFZ9 is older than the previously considered age for North Ba Moussa point 1 (Zone 11 or equivalent MFZ10), in spite of Foraminifer species that was based on their zonal correlation, Earlandia vulgaris and Eotextularia diversa, are also occurring in samples from BMW1 and BMW2 (assigned here to the MFZ9).

The Ba Moussa West succession is a resedimented body of shale, siltstone and limestone with early Visean microfossils and Corals, indicating that the probable age of sedimentation was very close to that of skeletal growth of the components. The corals and microfossils correspond to shallow-water taxa dwelling on a neighbouring sedimentary relief. The coralline assemblage shows a distinctive dominance of solitary rugosans, the absence of colonial Rugosans and occurrence of colonial Tabulate Corals. Moreover, the solitary forms are dominated by Siphonophyllia khenifrense and Sychnoelasma urbanowitschi, and the Tabulate Coral Turnacipora megastoma. A similar association of Siphonophyllia aff. garwoodi and Sychnoelasma urbanowitschi is known from the early Visean of the Laval syncline in Normandy (north France), although with colonial Rugosans there (Solenodendron spp.). This colonial genus is not recorded in the Azrou-Khenifra Basin first until the late Visean.

This colonial genus is not recorded in the Azrou-Khenifra Basin first until the late Visean. However, none of the seven listed key taxa of this subzone are recorded in Morocco, although the genera Siphonophyllia, Cravenia and Sychnoelasma are present. Perhaps of greater significance though, is that whereas Siphonophyllia hawbankense is only recorded in the underlying upper Tournaisian RC4ß1 subzone, a new taxon Siphonophyllia hawbankense subsp. A which starts in this subzone, extends into RC4ß2 subzone. The strong possibility exists though, that this corresponds to the small Siphonophyllia urbanowitschi of Ba Moussa, which represents the transition to larger typical forms in RC5 Zone.

The Ba Moussa West Coral fauna, although quite restricted in its diversity, nevertheless, contains typical elements of the Western European Coral province (which includes North Africa and Nova Scotia). In particular, the dominance of solitary Rugosa and Tabulate Corals is a feature of the early Visean assemblages which are recognised in northwest Europe: Normandy (north France), southern Belgium, southwest Province, North Wales, Craven Lowlands and South Cumbria (Great Britain), and Dublin Basin (Ireland). Similar early Visean faunas with solitary rugosans are known in the eastern part of the Anti-Atlas region at Tafilalt in eastern Morocco and in the Béchar Basin in Algeria. The late Tournaisian to early Visean Rugose Coral fauna from Tafilalt is richer than that from Ba Moussa. It is dominated by solitary genera, both undissepimented (Sychnoelasma, Cravenia) and dissepimented (Bifossularia, Cyathoclisia, Clisiophyllum, Siphonophyllia, Palaeosmilia, Amygdalophyllum), and is lacking colonial Rugosans.

Palaeogeographic distribution of the Coral taxa recorded in Ba Moussa West in the Palaeotethys region and around Laurentia and Baltica. (s) Siphonophyllia, (u) Sychnoelasma urbanowitschi, (c) Cravenia, (t) Turnacipora, (p) Pleurosiphonella. (1) Ba Moussa West, (2) Tafilalt, (3) Midcontinent, (4) Western Interior, (5) Canadian Rockies, (6) Carnic Alps, (7) Western Europe, (8) Eastern Europe, (9) Moscow Basin, (10) Ural Mountains, (11) Tian-Shan (Northwest China), (12) Turkey, (13) Transcaucasia, (14) Iran, (15) Himalaya, (16) South China. Rodríguez et al. (2020).

It was previously considered that since the Azrou-Khenifra Basin only had late Visean and younger Coral assemblages, so too the Jerada Basin in northeast Morocco, they were isolated from other marine basins in the early Visean. Connections among the Azrou-Khenifra Basin, northwest Europe, Tafilalt, and other Saharian basins in Algeria (Béchar Basin) were open from the Asbian and Brigantian (late Visean). The Ba Moussa West Corals, Foraminifers and Conodonts suggest that marine seaways were available for migrations between the Azrou-Khenifra Basin and other regions from the early Visean. Similar early Visean faunas with solitary Rugosans are known in the eastern part of the Anti-Atlas region at Tafilalt, in eastern Morocco and in the Béchar Basin in Algeria. The marine connections between northwest Europe and the southern part of the Azrou-Khenifra Basin is supported by similar early Visean assemblages recognized in northwest Europe with abundant solitary Rugose and Tabulate Corals, but with colonial Rugosans: Normandy (north France), southern Belgium, southwest Province, North Wales, Craven Lowlands and South Cumbria (Great Britain), and Dublin Basin in Ireland.

In relation to the tabulate corals, the Tabulate Turnacipora megastoma in the Ba Moussa West assemblage was also known from Central Saharian basins, but also from the Chadian-Arundian (early Visean) locations in northwest Europe (UK, Ireland, France, Germany?). The occurrence of Pleurosiphonella crustosa is the first report in North Africa and suggests marine connection with the Urals. It was first described from the upper Tournaisian of Transcaucasia and its age range extends here slightly into the early Visean. The dispersion between southwest Asia (Armenia, Taurides and Alborz) and the Azrou-Khenifra Basin, via Tafilalt, Béchar and Sinai, is poorly established. Some solitary Rugosans (Siphonophyllia) are common to all areas, but others, such as Kueichouphyllum and the colonial form Eokoninkocarinia, indicative of Asiatic affinity are clearly absent in Morocco.

A new early Visean Coral assemblage has been discovered transported in the rhythmic facies deposits of the southern part of the Azrou-Khenifra Basin, northwest of Khenifra, Morroco. The Ba Moussa West coral fauna includes the new species Siphonophyllia khenifrense, as well as Sychnoelasma urbanowitschi, Cravenia lamellata, Cravenia tela, Cravenia rhytoides, Turnacipora megastoma and Pleurosiphonella crustosa. The early Visean age of the Coral assemblage is supported by microfossil data, which confirms a previous hypothesis that indicated a first transgression during the early Visean in the Carboniferous of the Meseta. The allochthonous coral assemblage was recovered from coarse-grained proximal limestone debris flow and turbidite beds within a fault-bounded rhythmic unit in the eastern part of the basin. No evidence remains of the former early Visean shallow-water platform from which the Corals were derived. All other in situ platform carbonate rocks around the southern margin of the Azrou-Khenifra Basin are of late Visean (Asbian–Brigantian) age. The early Visean Ba Moussa West Coral fauna can be compared with that from the Saharian basins of southeast Morocco and Algeria. Most of the genera and species in the Ba Moussa West assemblage are identical to those in Western Europe, indicating possible marine connections. The new Rugose species described, Siphonophyllia khenifrense, is probably endemic to North Africa. Its ecological niche in northwest Europe was occupied by Siphonophyllia cylindrica or Siphonophyllia aff. garwoodi.

The microfossil determinations provide greater precision in the age dating of the Ba Moussa West limestones. The foraminiferal assemblages from BMW1 can be attributed to the lowermost Visean (MFZ9). Similarly, the Conodont fauna recovered from the same beds, although sparse, suggests a late Tournaisian to early Visean age.

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Phestilla fuscostriata: A new species of Nudibranch Sea Slug from the South China Sea.

The Nudibranch superfamily Fionoidea is a highly diverse group of marine Sea Slugs, containing 20 families, 52 genera and 324 species. ike many other nudibranchs, however, there has been some controversy with the systematics and phylogeny of Fionidea. In the family Trinchesiidae, the majority of species are free-living, though some form obligate association with their prey species on which they settle, feed and lay eggs. Among the most well-known examples of such obligate relationship are those between the genus Phestilla, and certain Acroporid, Agariciid, Poritid and Dendrophylliid Coral species: the Nudibranchs live on these Corals, feed on them, and their larvae show host specificity in settlement. Different from other genera of Trinchesiidae, Phestilla does not possess a cnidosac (an anatomical feature in which the Sea Slug stores cnidocytes, Cnidarian stinging cells harvested from its prey and used for its own defence) at the tip of its cerata, but has a glandular region in this location. The genus Phestilla currently has nine recognized species, among which, eight are obligate corallivores. Field observation and laboratory studies have revealed the specificity between Corals and their Nudibranch predators, with a particular species of Phestilla feeding on only one species or genus of Coral, which implies host shifts are associated with speciation.

In a paper published in the journal Zoological Studies on  June 2020, Juntong Hu of the Department of Biology at Hong Kong Baptist University, Yanjie Zhang, also of the Department of Biology at Hong Kong Baptist University, and of the Southern Marine Science and Engineering Guangdong Laboratory, James Yang Xie, again of the Department of Biology at Hong Kong Baptist University, and Jian-Wen Qiu, once again of the Department of Biology at Hong Kong Baptist University, and of the Southern Marine Science and Engineering Guangdong Laboratory, describe a new species of Phestilla from the Coral Pavona decussata, a structure forming Agariciid species in the South China Sea.

Colonies of the Scleractinian Coral Pavona decussata were collected from Sharp Island, Hong Kong, at depths of about 2 m, in August 2018 by SCUBA diving and then cultured in the laboratory in an aquarium system. Nudibranchs and their egg masses, found on the surface of the Pavona decussata in October 2018, were collected from the Coral surface. The specimens were preserved either in 95% ethanol for molecular study or in 4% formaldehyde in seawater for morphological analysis. All specimens examined werer deposited in the collection of the Swire Institute of Marine Science, at the University of Hong Kong.

The new species is named Phestilla fuscostriata, from the Latin 'fuscus' meaning 'brown' and 'striatus' meaning 'streaky', refers to the brown stripes on the body, which is a morphological character of the new species.

A colony of the Coral Pavona decussata showing three adults of the Nudibranch Phestilla fuscostriata  (indicated by red arrows) and many crescent-shaped egg masses of the Nudibranch on the Coral surface. Scale bar is 1.0 cm. Hu et al. (2020).

Living specimens of Phestilla fuscostriata are 2 mm to 8 mm in length. The body excluding the cerata is elongate and dorsal-ventrally flattened. The general body colour is white with dense brown pigmentation on dorsal side of head, tentacles, body and cerata. Ethanol preserved specimens are white due to loss of brown pigmentation.

The oral tentacles and rhinophores are digitiform; in adults the former are approximately twice as long and twice the diameter of the latter. A very small eye is present behind the rhinophore. The cerata are digitiform, swollen distally, and arranged in seven transverse rows in the holotype, each row consisting of 1 to 6 cerata attached laterally on a distinctly raised ridge on each side of the body, with the number of cerata decreasing from anterior to posterior. Fewer rows of cerata and fewer cerata per row are present in juveniles. Within a row, one single pair of dorsal cerata and zero to several pairs of ventral cerata are present. In the holotype, there are seven pairs of dorsal cerata, and six rows of ventral cerata with 5, 5, 4, 3, 2 and 1 pair from first row to the sixth row, respectively. The longest cerata on the second row is approximately 1.5 times as long as the body width. A translucent glandular region present at the tip of each ceras. Comparing adult and juvenile specimens indicates that the dorsal cerata develop earlier than the ventral cerata.

The anus is acleioproctic, located dorsally on right side of body between the third and fourth rows of cerata. The reproductive opening is located anterior to the first row of cerata, on right side of body.

Living specimens of Phestilla fuscostriata. (A) Holotype, SWIMS-Mol-19-001, dorsal view. (B) Holotype, SWIMS-Mol-19-001, ventral view; (C) Paratype, SWIMS-Mol-19-002, dorsal view. (D) Paratype SWIMS-Mol-19-002, ventral view. (E) Paratype, SWIMS-Mol-19-005, dorsal view. (F) Paratype, SWIMS-Mol-19-005, ventral view. Scale bars are 1.0 mm. Hu et al. (2020).

Eggs of Phestilla fuscostriata are white, 0.2 mm in diameter, and clearly observable through translucent body wall on the ventral side. Egg masses are crescent-shaped, about 0.25 cm in diameter, and have a translucent membrane enclosing around 20–50 eggs. At about 24°C, eggs develop into veliger larvae and break through membrane in 2–3 weeks. Veligers have a pair of black eyes and a well-developed swimming velum. Newly settled juveniles are more elongate, the velum is lost, but the oral tentacles or cerata have not yet developed. After roughly one week, juveniles resemble adults, with black eyes, but with tentacle and cerata, although at this stage cerata few and small.

Early developmental stages of Phestilla fuscostriata. (A) Embryos inside egg membrane. (B) Rudimentary veligers without well-formed shells inside egg membrane. (C) Veligers with well-formed shells. (D) Hatched veliger with well-developed velum for swimming. (E) Postlarva, dorsal view. (F) Early juvenile, with the head turned to the left when the photograph was taken. Scale bars: (A)–(C), (F) 500 μm; (D)–(E) = 40 μm. Hu et al. (2020).

Phestilla fuscostriata resembles its host coral P. decussata in the coloration pattern, therefore exhibiting excellent camouflage. Hu et al. were unaware of its presence in our aquarium system until this nudibranch built up a dense population on Pavona decussata, which eventually killed some of the colonies. The only known food source for Phestilla fuscostriata is Pavona decussata. When other species of Scleractinian Coral such as Platygyra carnosa and Acropora digitifera were also present in the same aquarium, the Nudibranch was found only on Pavona decussata, which indicates its host specificity. During reproduction, this Nudibranch deposits egg masses and glues them tightly on the surface of the Coral colonies.

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Spirobranchus spp.: Christmas Tree Worms associated with new hosts found in Puerto Rico and the Netherlands Antilles.

Caribbean Christmas Tree Worms, Spirobranchus spp., are considered host generalists in their associations with Anthozoan (Scleractinia) and Hydrozoan (Millepora) Stony Corals. As planktonic larvae, they settle on Coral surfaces and start secreting a calcareous tube to be used as a dwelling. This tube usually becomes overgrown by the host Coral (except for its opening) and may get encapsulated deep inside the Coral skeleton. In this manner, the well-protected Worms grow and survive predation and other hazards, allowing them to live for over four decades. When the host Corals are overgrown by other organisms, such as Octocorals and Sponges, these may act as secondary hosts.

In a paper published in the journal Diversity on 21 March 2020, Bert Hoeksema of the Taxonomy and Systematics Group at the Naturalis Biodiversity Center, the Groningen Institute for Evolutionary Life Sciences at the University of Groningen, and the Institute of Biology Leiden at Leiden University, Jaaziel García-Hernández of the Marine Genomic Biodiversity Laboratory at the University of Puerto Rico - Mayagüez, Godfried van Moorsel of Ecosub and the ANEMOON Foundation, Gabriël Olthof also of the Taxonomy and Systematics Group at the Naturalis Biodiversity Center, and the Institute of Biology Leiden at Leiden University, and Harry ten Hove, again of the Taxonomy and Systematics Group at the Naturalis Biodiversity Center, report two new primary hosts (Scleractinians) and two new secondary hosts (a Zoantharian Soft Coral and an Ascidian colonial Sea Squirt), discovered during recent surveys (2015–2019) in the southern and eastern Caribbean, as well as in the Greater Antilles.

The Coral–Worm associations occurred in shallow subtidal water (less than 4 m depth), with the Knobby Brain Coral, Pseudodiploria clivosa, hosting Spirobranchus giganteus at St. Eustatius in the northern Leeward Islands, and the Golfball Coral, Favia fragum, hosting both Spirobranchus giganteus and Spirobranchus polycerus at Bonaire in the southern Leeward Islands. The secondary host observations, both for Spirobranchus giganteus, involved the Zoantharian Palythoa caribaeorum at Puerto Rico and the Ascidian Trididemnum solidum at Bonaire and Curaçao. Palythoa caribaeorum represents a first record as a secondary host for a species of the order Zoantharia. Until now, the only other Anthozoan secondary hosts were species in the order Alcyonacea (subclass Octorallia), whereas Trididemnum solidum represents an entirely new host phylum, the Chordata. The only other non-Anthozoan secondary hosts known to date are Sponges (Porifera).

A Coral of Pseudodiploria clivosa at 2 m depth, Scubaqua House Reef, St. Eustatius, Eastern Caribbean (2015) hosting Spirobranchus giganteus: (a) overall view and (b) close-up. Hoeksema et al. (2020).

The two new Scleractinian hosts are both typical for shallow subtidal water near the shoreline (less than 4 m depth), where a lack of previous surveys may explain why they have not previously been reported. The new records of secondary hosts are remarkable because these encrusting Animals are known to be aggressive in competition for space with Scleractinians by allelopathy (the production of harmful biochemicals) and can be abundant on shallow reef flats and slopes, where they usually outcompete and kill Scleractinian Corals by overgrowing them. In both cases, the Christmas Tree Worms survive by withstanding this overgrowth and maintain an open space near the tube opening.

Favia fragum hosting Spirobranchus spp. at 3–4 m depth, dive site 'Front Porch', Bonaire, Southern Caribbean (2019). (a)–(c) Spirobranchus giganteus: overall view (a), overgrown tube section indicated by red arrow (b); antler-shaped opercular spines showing dark pink colouration indicated by yellow arrow (c). (d) Spirobranchus polycerus: two individuals, one showing white spines on its operculum (blue arrow). Hoeksema et al. (2020).

Hoeksema et al.'s new host records confirm two Caribbean Christmas tree worms as generalist symbionts capable of infesting a large spectrum of host Corals. They are also strong survivors when their primary hosts become overgrown by more aggressive competitors for space. Previous host records mostly concern  Spirobranchus giganteus, but Hoeksema et al. also report a new host Coral for Spirobranchus polycerus. This worm species occurs in shallow water (less than 4 m depth), whereas Spirobranchus giganteus is commonly found down to 40 m depth. Both Spirobranchus species can easily be distinguished, as Spirobranchus giganteus shows long dark pink opercular spines, whereas those of Spirobranchus polycerus are short and white. Furthermore, Spirobranchus giganteus may be larger than Spirobranchus polycerus and usually shows six to seven (maximum eight) whorls in its branchial spires, whereas Spirobranchus polycerus has two to three (maximum five).

Palythoa caribaeorum acting as a secondary host for Spirobranchus giganteus at 5 m depth, Cayo Media Luna (La Parguera Natural Reserve), Puerto Rico, Greater Antilles (2017): (a) Worm extended and (b) retracted, showing the tube opening surrounded by dead Coral; damage to the Zoantharian host caused by the operculum of the extended Worm indicated by a black arrow. Hoeksema et al. (2020).

Hoeksema et al.'s observations suggest that future surveys may discover other hosts for both Spirobranchus species with the possibility of more host overlap. Whether such host sharing is related to their phylogenetic affinities or to ecological similarities (e.g., overlapping bathymetric distributions) is an open question that merits assessment.

Trididemnum solidum acting as a secondary host for Spirobranchus giganteus in the Southern Caribbean: (a), (b) dive site 'Thousand Steps', Bonaire (2019); (c) Marie Pampoen, Curaçao, 12 m depth (2017); (d), (e) Daaibooi Bay, Curaçao (2017). Extended Worms (a), (d) and the same individuals retracted, showing an open space in front of the Worm tube mouth (b), (e). Hoeksema et al. (2020).

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Understanding the distribution of Corals on the Venezuelan coast.

The importance of scales in ecology has been largely acknowledged for decades. Many modern ecologists are deeply influenced by he view that ecological processes act at a variety of spatial and temporal scales, and they generate patterns that may differ from those at which processes act. Today it is known that ecological dynamics tend to be stochastic at small scales, but variability is conditional on the resolution of description. Furthermore, there has been an increased recognition that the problem of scale at which ecological processes act, should be considered as critical if it is wanted to produce general predictions about patterns in space and time. Thus, modern ecological thinking agrees that in order to understand a system (e.g., a community), it is important to study it at the appropriate scale. It is clear that increasing consideration of scale is helping to address a key issue in ecology: the question of what influences the distribution and abundance of organisms. Species distributions depend on four important processes: (1) climate, (2) species interactions, (3) habitat structure and (4) dispersal capabilities, each one operating with different strength at a range of spatial scales. Generally, the presence or absence of organisms within a community may depend on rare or large-scale (regionspecific) dispersal and colonization events, while local abundance is more a function of frequent, fine-spatial scale processes such as biotic interactions and habitat heterogeneity. This implies that communities are structured by both abiotic and biotic factors nested along different spatial scales which often occur along environmental gradients. Concomitantly, the species richness of a community is also expected to be highly dependent on spatial scales evaluated.

In a paper published in the journal PeerJ on 4 May 2020, Emy Miyazawa of the Laboratorio de Ecología Experimental at the Universidad Simón Bolivar, Luis Montilla, also of the Laboratorio de Ecología Experimental at the Universidad Simón Bolivar, and of the Integrative Marine Ecology Departmen at Stazione Zoologica Anton Dohrn, Esteban Alejandro Agudo-Adriani, again of the Laboratorio de Ecología Experimental at the Universidad Simón Bolivar, and of the Department of Biology at the University of North Carolina at Chapel Hill, Alfredo Ascanio, again of the Laboratorio de Ecología Experimental at the Universidad Simón Bolivar, and of the Department of Biology at the Miami University of Ohio, Gloria Mariño-Briceño, again of the Laboratorio de Ecología Experimental at the Universidad Simón Bolivar, and Aldo Croquer, once again of the Laboratorio de Ecología Experimental at the Universidad Simón Bolivar, and of the Centro de Innovación Marina, at the Nature Conservancy, present the results of a multi-scale study of the distribution of Coral species on the coast of Venezuala.

Coral Reefs are one of the most complex and diverse ecosystems of the planet. Reef species diversity has been estimated from 600,000 to more than 9 million species worldwide. The habitat and shelter for the majority of these species is largely provided by Scleractinian Corals. There is compiling evidence indicating that ecological processes controlling the structure of Coral assemblages (e.g., substrate availability, recruitment, competition, and herbivory) are strongly dependent on spatial scales. In addition, oceanographic processes which partly define the environmental setting of a reef are also extremely variable within habitats, across sites, reef systems, and regions. Furthermore, biological and environmental factors may interact with each other to produce different patterns in species distribution across several spatial scales. In consequence, understanding the underlying factors controlling the Coral species richness in a reef is not a simple task for it is a multi-scale problem.

Total species richness of a region, frequently named gamma diversity (γ), can be partitioned in two components: (1) α -diversity (i.e., the number of species by site), and (2) β-diversity (i.e., the variation in the species identities from site to site). For decades, ecologist have debated ways to estimate and interpret α and β- diversity; but in recent years, the study of β-diversity has gained a lot of interest for it is what actually makes assemblages of species more or less similar to one another at different places and times. Many different measures of β -diversity have been introduced, but there is no overall consensus about which ones are most appropriate for addressing particular ecological questions. Some authors have distinguished two types of β-diversity: (a) turn-over and (b) variation. Turn-over refers to changes in community structure among sampling units distributed along well-defined environmental gradients, whereas variation portrays variability in species composition among sample units within a given spatial or temporal extent, or within a given category of a factor (such as a habitat type or experimental treatment). On the other hand, some have partitioned the total β-diversity into two components: (1) nestedness, i.e., when the species composition of sample units with low richness represent a subset of the species found in the richest sample units, and (2) species replacement, i.e., a turn-over of species. Regardless the point of view, the study of each of these components is relevant to understand processes that  control ecological communities and a range of ecosystem functions.

While spatial patterns of  γ and α -diversity of Coral assemblages have been studied extensively; only few studies have focused on measuring β-diversity. This is the case of Venezuela, where most of the papers published to date have only been focused on site descriptions based on species composition and abundance, whereas the influence of spatial variation across different scales on coral assemblages remains poorly explored. The Venezuelan coast is highly heterogeneous with clear longitudinal environmental gradients which are deeply influenced by up-welling regimes that play an important role for the distribution of marine biodiversity. In fact, Algal communities in rocky shores and sessile organisms associated to Mangrove roots have been found to vary at different spatial scales along the Venezuelan coast. Thus, it should not be surprising to find Coral assemblages to be extremely variable across spatial scales in Venezuela. Miyazawa et al. expected that greater changes in community structure and β-diversity of Coral assemblages will occur at scales of thousand of kilometers (i.e., between the eastern and western regions) and within sites (i.e., hundreds of meters). This is because of existing contrasting environmental settings driven by upwelling spots that have been described along the Venezuelan coast line. The goal of this study was two-fold: (1) to quantify spatial variation of Coral assemblages from hundreds meters to hundreds of kilometers, and (2) to determine if there are patterns of β -diversity across these scales.

Miyazawa et al. conducted a multi-scale sampling design comprising coastal areas as well as continental and oceanic islands. Specifically, seven localities were sampled along the Venezuelan territory encompassing three contrasting regions. The western region, included two localities: (1) Morrocoy National Park and (2) Ocumare de la Costa. The former is a continental reef system formed by a group of keys and lagoons surrounded by fringing and patch reefs located nearby Mangroves and Seagrass beds; whereas the latter is a small bay protected by reef barriers with Seagrass and Mangroves dominating the inner and shallower habitats. Likewise, the central region, entailed two localities: (3) Los Roques National Park which is an oceanic archipelago with a central lagoon, characterized by extensive reef banks/patches and two large coralline barriers located south and east of the archipelago; and (4) Chichirivivhe de la Costa, a location of rocky reefs with steep slopes and scattered coral assemblages. Finally, in the eastern region three localities were included: (5) Mochima National Park, (6) Los Frailes and (7) Cubagua. In Mochima, Seagrass beds and Mangroves border a rocky coastline with steep slopes and fringing reef communities. Los Frailes and Cubagua are islands lying at the continental shelf and dominated by small patch reefs with scattered Coral assemblages bordering their coastlines. The whole eastern coast of Venezuela and its continental islands are subjected to seasonal upwelling due to its connection with the Cariaco trench. The selection of these locations aimed to cover the vast majority of reef habitats described for Venezuela. Permits for taking pictures at marine protected areas was given by Ministerio del Poder Popular para el Ecosocialismo y Aguas.

Map of the Venezuelan coast with the seven locations used in this study. Western region, represented in blue, include: MOR D, Morrocoy National Park; and OCU D, Ocumare de la Costa. Central region, represented in red, include: ROQ D, Archipielago Los Roques National Park; and CHI D, Chichiriviche de la Costa. Eastern region, represented in green, included MOC, Mochima National Park; CUB D, Cubagua; and FRA D, Los Frailes. Miyazawa et al. (2020).

A fully-nested design encompassing three hierarchical-random factors (i.e., site, locality, and region) was used to determine spatial variation on Coral assemblage structure (i.e., absolute cover of Coral species) and β -diversity from hundreds of meters (sites) to hundreds of kilometers (region). The factor region encompassed three levels (West, Center, and East); nested within region there were two/three localities, four to seven reef sites within each locality, and four 30m-long transects within each site, understood as the operational unit.

At each reef site, benthic surveys were conducted during 2017 and 2018, following the guidelines outlined by the Global Coral Reef Monitoring Network-Caribbean with slight modifications. In order to increase the number of sampled sites, Miyazawa et al. surveyed four instead of five 30 m-long transects parallel to the shoreline following the bottom contour between 8 10 m depth. Transects were set randomly, with the first transect being always layout at the first spot of diving. From that point, each transect was moved up or down from the first transect. Distance among transects varied from 5 to 6 m, so each operational unit was inter-spaced across the sampled reef habitat. For each transect, fifteen 80 x 90 cm photos were taken every other meter to determine the benthic community structure (60 photos per site). A reference frame was used in the field to calibrate each photograph in the laboratory for further analysis of benthic cover.

The photo quadrat analysis was performed using PhotoQuad. For this, every coral was identified to species level and the percentage cover was estimated from 25 points randomly set in an area of approximately 7200 cm². From the analysis of photo quadrats, Miyazawa et al. obtained two matrices: (1) absolute cover of Coral species and (2) Coral species presence/absence. Data cleaning and quality control were performed using R. Thus, Coral cover estimates were done from a randomly-selected sample composed of 375 points per transect (15 photos x 25 points = 375).

The results show that species composition and abundance of corals in Venezuela varied across different spatial scales. The greatest variability was found at the scale of sites. The scale of hundreds of kilometers was the second most important source of variation in the analysis. This result indicates that Coral assemblages in Venezuela only vary by 21.35% at the scale of region. Also, Miyazawa et al. found statistical significance at the scale of locations within regions, explaining 11.42% of the total variance. Thus, their results indicate that Coral assemblages are much variable at small to medium scales (i.e., from hundreds of meters to tens of kilometers) rather than hundreds of kilometers (i.e., regions) alone.

Overall, Western region was largely composed of Orbicella faveolata reefs, whereas the eastern reefs were dominated by Pseudodiploria strigosa. On the other hand, across the Central regions which included Oceanic and Coastal Reefs, mixed Coral communities were found. These species accounted for more than 75% of dissimilarities across localities, sites and regions.

Reefs of the Mountainous Star Coral, Orbicella faveolata, were found to dominate the western region of Venezuela. Evan D'Alessandro/Rosenstiel School of Marine and Atmospheric Science/University of Miami.

Longitude was highly correlated with observed spatial patterns, in contradiction to latitude. This result indicates that the relative position of each site along the Venezuelan coast (i.e., longitudinal variation), is an important factor to determine the features of Coral assemblages in Venezuela, instead of the proximity to the coast (i.e., latitudinal variation).

When assessing β-diversity, Miyazawa et al. found the highest variation in species presence/absence occurring between transect of the same site and between sites of the same locality. On the other hand, at larger scales, they found no significant dispersion in species composition between localities of the same region. In addition, site and locality were the spatial scales with the largest dissimilarity, with turn-over component as the main contributor. Furthermore, at larger scales, dissimilarity decreased and the contribution of turn-over and nestedness became evener. Thus, Miyazawa et al.'s result clearly shows that in Venezuela it is more likely to find changes in Coral species composition at small to medium scales (i.e., hundreds of meters to tens of kilometers) than at larger scales (i.e., hundreds of kilometers). Finally, the results indicate that Coral species found between the western, central and eastern region of Venezuela can result either from species replacement or from species loss, which is interpreted as a subset of a total pool of species.

The Symetrical Brain Coral, Pseudodiploria strigosa, was found to dominate the eastern reefs of Venezuela. Dennis Mahle/Flikr/Wikimedia Commons.

While Coral assemblages have been extensively studied in Venezuela, this is the first multiscale assessment to show the importance of spatial scales in determining the structure of these communities. Overall, Miyazawa et al. found that Coral assemblages in Venezuela are variable from hundreds of meters and hundreds of kilometers. Additionally, the largest changes in the composition of coral species occurred at a small scale with a clear predominance of species turn-overs. Also, longitude and latitude are a good predictors of Coral assemblage structure (i.e., species composition and abundance) further indicating that large-scale processes are also important to determine the structure of these communities.

Previous studies have acknowledged the importance of spatial scales on Coral assemblages in the Caribbean and in Venezuela. Particularly, the effect of upwelling and other related oceanographic processes has been pinpointed as strong factors that shape Coral assemblage structure along the Venezuelan coast where at least 12 upwelling points have been targeted. Miyazawa et al.'s study shows that Coral assemblages in Venezuela are much variable within and between localities than we originally expected. They found two fold higher variability at small to medium scales when compared to regions. However, Coral assemblages between the western, central and eastern regions differed by 21.35%, further indicating that differences at scale of region cannot be neglected. Moreover, about 32% of the total variance in coral species composition and abundance was associated to the residual which indicates that other variables like levels of anthropogenic disturbance, oceanic influence or other intermediate scales between those taken into consideration might also be relevant to determine the structure of these assemblages.

In Venezuela, encrusting communities associated with Mangrove roots have been studied following a spatial hierarchical design. Similar to Miyazawa et al.'s results, higher variation for this assemblages were found at the smallest and biggest scales. Moreover, Algal assemblages associated rocky platforms have previously been found to be highly variable at tens of kilometers and not between localities or regions, further illustrating the importance of local processes in providing structure to different assemblages of sessile organisms in the country.

Only a few numbers of studies encompassing multiple hierarchical spatial scales have been conducted in the Caribbean. For example, a multi-scale study surveyed a series of reef sites across locations and different bio-regions in the Caribbean for three major Coral taxonomic groups: Corals, Sponges and Octocorals. This study concluded these faunas exhibited considerable biogeographical variability at broad spatial scales (hundreds of kilometers). However similar to Miyazawa et al.'s study, it uncovered a higher degree of variability within sites highlighting the relevance of local ecological drivers (e.g., rugosity and wave exposure) in structuring Coral assemblages. Other studies have also taken into account the importance of spatial scales for Coral assemblages, but must of them have focused on total live Coral cover and total abundance of colonies.

Coral formations at Madrisquí Island in the Los Roques National Parl. Anaurora Yranzo in Debrot et al. (2019).

It is widely acknowledged that behind patterns are ecological processes that shape communities. In Coral Reef ecosystems, processes such as predation (e.g., herbivory) and competition have profound impacts on species abundance and composition at scales of a few meters. For example, very high densities or the absence of the Black Sea Urchin, Diadema antillarum, can determine the composition of Corals in patches of few m². Also, reef Fish can preferentially prey on certain Coral species, thus decreasing their abundance or making them less competitive than other neighboring Corals. In addition, the presence of Vermetid Snails could potentially modify the survival rates of Coral species. Furthermore, factors such as structural complexity (e.g., rugosity and micro scale habitat heterogeneity) may influence competition and survival of colonies depending on their sizes. Coral Reefs in Venezuela are known to be highly variable within and between sites but the processes responsible for these patterns have not been firmly established. However, spatial variation of Coral assemblages in Los Roques has been associated to changes in reef slopes.

Various anthropogenic stressors can alter biological interactions thereby affecting the structure of Coral assemblages. For example, overfishing often leads to the dominance of Macroalgae which escape to herbivory control. The selective extraction of species of carnivorous Fish can lead to an increment in the abundance of Echinoderms, which may also steer to increasing erosion, loss of topographic complexity and live Coral cover. Also, high intensity of recreational activities represents an important disturbance to marine communities, for example, Coral cover and the proportion of massive Corals is being found to be lower in places with high recreational diving intensity Thus, spatial variability recorded within sites of Morrocoy and Los Roques National Parks could be explained by their differences in touristic use for not all sites within these Marine Protected Areas are
exposed to the same Human pressures.

Echinoderms such as the Black Sea Urchin, Diadema antillarum, can determine the composition of Corals in patches of few m². Alchetron.

In addition, experimental evidence shows that some Coral species differ in resistance to environmental stressors such as sedimentation which could explain the patterns observed within sites and between locations showing higher sedimentary regimes and river presence (e.g., coastal versus oceanic reef sites). Furthermore, local oceanographic events can generate mortality which leads to changes in the structure of Coral assemblages. Differences between Playa Caimán, Cayo Norte and Sombrero (Morrocoy National Park) represent a example of how abnormal oceanographic conditions can alter benthic communities by killing dominant species in specific sites while promoting stable alternative states which hampers recovery. Miyazawa et al.'s results seem to support that each site/location in Venezuela possess different communities because they may have been affected/unaffected by different stressors and/or mortality events in different times. Thus, high spatial variability on Coral assemblages in Venezuela could be related to the differences in the disturbance regime and local history as noticed in other studies.

Coral bleaching mortality events may be patchy and could potentially affect Coral assemblages at different spatial scales (e.g., within sites, localities and regions). For example, in 2010 an increase in seawater temperature in Los Roques National Park affected 72% of the colonies at the study sites, showing bleaching and prevalence of diseases such as Black Band and White Plague. Extensive mortality caused changes in the community structure a year later. Other bleaching events recorded in Venezuela since 1998 primarily affected reefs in several oceanic islands and the western and central coast of Venezuela, but these events did not produce extensive mortality events like the one reported in 2010.

It is likely that the eastern coast of Venezuela remained less affected by bleaching events because of seasonal upwelling and unique environmental conditions. In fact one study found differences in Coral mortality rates during bleaching events, according to local environmental settings (e.g., light intensity, penetration, temperature and currents). However it has been argued that upwelling does not necessarily guarantee a refuge for Corals. Thus, in Venezuela differences between geographical regions could be strongly influenced by factors such as nutrient input and temperature decrease associated with the upwelling season. In fact, it has been suggested that during these periods the assemblages of Macroalgae become more dominant, which could modify the Coral assemblage structure through competitive processes.

A bleached Coral colony in Venezuela. Tubuceo/Geographical.

The Venezuelan coast is characterised by an upwelling period that occurs between January and June, in particular, the eastern region of the country is characterised by a large area of upwelling. However, various studies did not find an effect of the upwelling on factors such as the reproductive behavior of spawn Corals and the growth rates of colonies. On the other hand, the dynamic of Black Band Disease, one of the most important factors producing rapid Coral mortality in Cubagua has been shown to be deeply influenced by upwelling events. Thus, Miyazawa et al.'s results indicate that upwelling alone is not sufficient to explain the extremely variable nature of Coral assemblage.

Miyazawa et al. found that differences in Coral species composition occurred at spatial scales of hundreds of meters to tens of kilometers. Although it is known that β -diversity depends on the spatial scale at which it is measured, in most studies β -diversity is assumed to be homogeneous at small spatial scales. Changes in species composition at scales of tens of meters often occurs in highly-heterogeneous habitats sampled with enough resolution to detect these changes. In Miyazawa et al.'s study, they found that there was more likely to be different species composition within transects of a single site than between localities belonging to different regions. Thus, their results clearly indicate that Coral habitats in Venezuela are extremely variable at local scales, suggesting significant environmental heterogeneity within reef habitats, with Coral species probably forming mosaics or patches within a single habitat. However, it is not clear what are the conditions favoring this heterogeneity within the reef sites. This variation at the smallest scale could mean that Venezuelan Coral assemblages are in good condition, although there are patches of mortality, with more or fewer species, reflected in a high turnover rate.

At larger scales (i.e., between the eastern, central and western Venezuelan coast) Miyazawa et al. found quite similar and homogeneous Coral species composition, which may be partly due to the reduced pool of species that exist in the Caribbean when compared to the Indo Pacific region. In regions with larger species pools such as the Indo Pacific, β-diversity tends to be higher at larger spatial scales because species represent a subset of a total species pool. In Venezuela, coral reefs located at the oceanic sites and the western coast are dominated by Orbicella, whereas in the eastern coast and the majority of sites located at the central coast Pseudodiploria and Colpophyllia become
more important.

The Boulder Brain Coral is an important species on the eastern and central coasts of Venezuela. Coralpedia/University of Warwick/Darwin Initiative.

Miyazawa et al.'s results indicate that at scales of tens of kilometers species nestedness (loss) becomes as important as species turnover (replacement). These two components arise from different ecological phenomena. Species nestedness occurs when the biotas of sites with smaller numbers of species are subsets of the biotas at richer sites, reflecting a non-random process of species loss as a consequence of any factor that promotes the orderly disaggregation of assemblages. On the other hand, species turn-over (replacement) occurs as a consequence of environmental sorting and spatial and historical constraints (i.e., stochastic process). For example, processes such as settlement selectivity of Coral larvae could explain species turn overs at tens of meters and kilometers. Coral larvae are known to select certain characteristics in the habitat to settle down, e.g., presence of certain species of Coralline Algae or sounds of the reef. Miyazawa et al.'s results therefore indicate that Coral assemblage structure in Venezuela is probably regulated by a series of interconnected processes acting alone and/or in combination at various spatial scales. This result highlights the importance of creating scale-adapted management actions in Venezuela since the smallest scales reflect the greatest variability. However, very small Marine Protected Areas are often ineffective in achieving their conservation goals, so they must necessarily be chained into a large-scale strategy.

In summary, Coral assemblage structure in Venezuela is highly variable at different spatial scales but within locality variability seem to be very important. The processes that could underlie these patterns are diverse and complex and little experimental efforts to untangle the specific contribution of each factor have been conducted. Longitude is a good predictor of Coral assemblages in Venezuela. Upwelling-related processes could be targeted as potential candidates to explain longitudinal variation of Coral assemblages, whereas oceanographic/coastal processes could explain latitudinal variability. Regarding β -diversity, Coral assemblages are fairly homogeneous across the Venezuelan coast, while increasing spatial resolution shows greater heterogeneity, with smaller scales revealing a greater change in species composition. In addition, the replacement of species is a relevant phenomenon to explain these diversity patterns. Results from this study highlights the importance of taking into account local variability during the design and implementation of specific conservation efforts.

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