Estimating biodiversity in the Clarion-Clipperton Zone.

The Clarion-Clipperton Zone is an area of the Pacific seafloor bounded by the Clarion and Clipperton fracture zones to the north and south, and the 115°W and 160°W longitude lines. It has an area of about 6 million km², making it roughly twice the size of India, and is located between Hawai'i, Kiribati, and Mexico, but lies entirely outside the jurisdiction of any nation. Throughout this region the seafloor is between 4000 and 6000 m deep, and mostly covered with muddy sediments with a scattering of Potato-sized polymetalic nodules, making the zone attractive to prospective deep-sea miners. The seafloor here is known to host a diverse community of benthic organisms, albeit at a much lower density than is found on the continental shelves or in coastal regions.

The Clarion-Clipperton Zone has been explored for mineral extraction since the 1960s, a process formalized by the formation of the International Seabed Authority in the 1980s, although the possibility of actual mining operations is only becoming possible now. There are currently 17 mining concessions granted within the Clarion-Clipperton Zone, covering an area of about 1.2 million km². 

Despite decades of exploration work being carried out within the Clarion-Clipperton Zone, very little taxonomic work has been carried out, with large-scale environmental surveys in the 1970s, 1980s and 1990s producing lists of informally named taxa only; i.e. differentiated by morphological or molecular data, but not formally described. This presents challenges for anyone trying to understand the biodiversity of the region, particularly as deep ocean benthic environments are known to be rich in cryptic species, as the constraints of the environment push members of different taxonomic groups towards similar morphologies and lifestyles.

To make matters worse, the data that has been collected isn't to any method, with sampling and data recording being carried out in different ways in different studies. Furthermore, many studies that have been carried out within the Clarion-Clipperton Zone have concentrated on particular taxa, ecological groups or size classes, and have usually covered only small parts of the zone. This greatly hampers the establishment of any overall understanding of biodiversity within the region, making to almost impossible to come up with a coherent environment management policy plan. Without any meaningful understanding of the biodiversity of the area, it is essentially impossible to calculate the range or environmental requirements of individual species, nor to tell which species are common and widespread and which are rare and tied to very specific environments. 

In a paper published in the journal Current Biology on 25 May 2023, Muriel Rabone of the Deep-Sea Systematics and Ecology Group at the Natural History Museum, Joris Wiethase of the Department of Biology of the University of York, Erik Simon-Lledo of the National Oceanography Centre, Aidan Emery, also of the Deep-Sea Systematics and Ecology Group at the Natural History Museum, Dan Jones, also of the National Oceanography Centre, Thomas Dahlgren, of the Department of Marine Sciences at the University of Gothenburg, and the Norwegian Research Centre, Guadalupe Bribiesca-Contreras, again of the Deep-Sea Systematics and Ecology Group at the Natural History Museum, Helena Wiklund, again of the Deep-Sea Systematics and Ecology Group at the Natural History Museum and the Norwegian Research Centre, Tammy Horton, again of the National Oceanography Centre, and Adrian Glover, once again of the Deep-Sea Systematics and Ecology Group at the Natural History Museum, present a synthesis of Metazoan biodiversity within the Clarion-Clipperton Zone, aimed to convey the best currently available information to all stakeholders, ahead of the start of any mining operation within the zone.

Rabone et al. synthesized data from seven different data sources, producing over 100 000 individual records. Although these were assembled over several decades, the majority of the taxonomic work is recent, and much less than five years old. A total of 219 taxa new to science (including species, genera, and families) have been described from the Clarion-Clipperton Zone, again mostly in the recent past; only seven were described prior to the year 2000. The checklist of Animal species assembled by Rabone et al. includes 436 species found within the Clarion-Clipperton Zone, including 185 which were first described from within the zone (31 new genera and 3 new families were also described from within the zone). Of these 185 species, only six have subsequently been discovered living in other areas; two Sea Cucumbers, a Nematode, a Carnivorous Sponge, a Crinoid, and an Antipatharian Coral.

All geolocated published records of benthic Metazoa from the literature and databases Areas of Particular Environmental Interest and exploration mining contract areas, both active and reserved, are shown in outline. The type localities of all species described from the Clarion-Clipperton Zone to date are also shown (185 in total). Rabone et al. (2023).

A total of 27 phyla of Animals have been recorded in the Clarion-Clipperton Zone, as well as 49 classes, 163 orders, 501 families, and 1119 genera. Of the 436 Animals identified to species level, 185 (i.e. 42%) have been identified on the basis of both molecular and morphological data, with 217 (50%) identified only by their morphology. The remaining 34 species were listed with no method of identification given. Of the species described from the Clarion-Clipperton Zone, 51% were identified solely on the basis of morphology; this rises to 86% for meiofauna (species larger than 150 μm but smaller than 300 μm). For the most abundant groups within the Clarion-Clipperton Zone, Tanaid and Isopod Crustaceans and Polychaete Worms, 23% of the species identified were originally described from outside the zone, including some species from other ocean basins. A total of 5367 unnamed species were recorded, although 3.9% of these are species Rabone et al. believe to have been named erroneously; if these are taken out of the equation the number is 5142.

Rates of species descriptions in the Clarion-Clipperton Zone; proportion of species diversity in the Clarion-Clipperton Zone that is undescribed. (A) Rates of new descriptions and publications in the Clarion-Clipperton Zone. Cumulative totals of new taxa (families, genera, and species combined) and new species described from the Clarion-Clipperton Zone and taxonomic publications per year, over the period 1980–2022. Yearly totals of new descriptions also shown. (B) Proportion of recorded benthic Metazoan diversity from the Clarion-Clipperton Zone that is undescribed: named species recorded in red (both those described from the Clarion-Clipperton Zone and elsewhere), unnamed species shown in blue (‘unassigned’ are records not identified to phylum). Depictions of some of the new Clarion-Clipperton Zone species by phyla: Annelida, Neanthes goodayi Drennan; Arthropoda, Siphonis aurreus; Brachiopoda, Oceanithyris juveniformis; Bryozoa, Pandanipora helix; Cnidaria, Abyssopathes anomala; Echinodermata, Psychropotes dyscrita; Kinorhyncha, Meristoderes taro; Loricifera, Fafnirloricus polymetallicus; Mollusca, Ledella knudseni; Nematoda, Odetenema gesarae; Porifera, Chaunoplectella megapora; and Tardigrada, Moebjergarctus clarionclippertonensis. Rabone et al. (2023).

Based upon identified species, the most abundant taxa in the Clarion-Clipperton Zone are the Arthropoda, comprising 27% of the total, followed by the Annelida, 18%, Nematoda, 16%, Echinodermata, 13%, and Porifera, 7%. The proportions appear to be similar for unnamed species, albeit with a slightly higher proportion of Annelid Worms. According to the World Register of Deep-Sea Species (part of the World Register of Marine Species) there are currently 36 579 named species of Animal known to live at depths of greater than 500 m, of which 31% belong to the Phylum Arthropoda, 17% to the Phylum Mollusca, 15% to the Phylum Chordata, and 10% each to the phyla Annelida and Echinodermata. Thus the Clarion-Clipperton Zone appears to have a significantly higher proportion of Annelid, Nematode, and Echinoderm species than the deep ocean as a whole, and slightly higher proportions of Sponges and Bryozoans than the deep ocean as a whole. Conversely, the Clarion-Clipperton Zone has a lower proportion of Molluscs, particularly Gastropods, and Chordates, particularly Teleost Fish. Also notable is that Holothurans (Sea Cucumbers) make up a higher proportion of the total number of Echinoderm species in the Clarion-Clipperton Zone, while Asteroids (Starfish) and Ophiuroids (Brittle Stars) are less numerous. There are also groups, such as the Pycnogonids (Sea Spiders) for which there are no recorded named species within the Clarion-Clipperton Zone, although unnamed species are known.

Classed by size, 50% of identified species from the Clarion-Clipperton Zone are macrofauna (larger than 300 μm but smaller than 10 mm), 28% are megafauna (larger than 10 mm), and 22% are meiofauna (smaller than 300 μm but larger than 150 μm). This reflects the nature of studies carried out in the area, with 46% concentrating on macrofauna, 30% on megafauna, and 22% on meiofauna, What is notable about the Clarion-Clipperton Zone is the nature of the substrate, with the combination of soft mud and hard nodules, meaning that 14% of named species and 13% of unnamed species are hard-substrate species living on nodules, while the remainder are soft substrate species living on or in the mud. Several species of megafauna (Cnidarians and Sponges) have recently been described from nodules in the Clarion-Clipperton Zone, though there have only been two quantitative studies of macrofaunal nodule dwellers to date, revealing that the majority of these are undescribed Sponges and Bryozoans. One monograph on nodule Bryozoans in the Clarion-Clipperton Zone has been published, which described sixteen new species, nine new genera, and two new families. 

Fauna from the Clarion-Clipperton Zone. (A)–(J) All fauna are species described from the region and illustrating a range of phyla and size classes. Row 1 (A) the Sea Cucumber, Psychropotes dyscrita , commonly known as the ‘Gummy Squirrel’ (scale bar is 5 cm); (B) the Primnoid Coral, Abyssoprimnoa gemina, (scale bar is 5 mm); (C) the Antipatharian Coral, Abyssopathes anomala, (scale bar is 2 cm); and (D) the Hexactinellid Sponge, Sympagella clippertonae, (scale bar is 1 cm). Row 2, (E) the Cyclostomatid Bryozoan, Pandanipora helix, (scale bar is 500 μm); (F) the Isopod, Macrostylis metallicola, (scale bar is 0.2 mm); (G) the Polychaete, Neanthes goodayi, and (H) the Mollusc, Ledella knudseni, (scale bar is 0.5 mm). Row 3, (I) the Nematode, Odetenema gesarae, (scale bar is 100 μm); (J) the Kinorhynch, Meristoderes taro, (scale bar is 10 μm); (K) the Loriciferan, Fafnirloricus polymetallicus, (scale bar is 100 μm), and (L) the Copepod, Siphonis aurreus, (scale bar is 100 μm), Rabone et al. (2023).

Rabone et al. used several different mathematical models to attempt to predict the total number of Animal species within the Clarion-Clipperton Zone, producing answers which ranged from 6109 to 8514, with between 947 and 1034 genera, and 406-544 families. Thus, although there are clearly many unidentified species left within the zone, the picture appears to be much more complete for higher level taxonomic categories.

Rabone et al. estimate that 92% of species within the Clarion-Clipperton Zone remain unidentified. The proportion of unidentified species is thought to vary considerably from group to group, with 99.4% of Taneid Crustacean species though to be unidentified, along with 96.6% of Isopod Crustaceans and 87% of Polychaete Worms. An estimate of 92% of species being unidentified is also in line with higher estimates for the proportion of unidentified species in the total ocean.

Sampling efforts cross the Clarion-Clipperton Zone have note been even, with the majority of studies having been carried out in the central and eastern parts of the area, while portions of the zone remain almost totally unexplored. There is a similar unevenness in the depth of sampling, with the majority of sampling having taken place at depths of about 4200 m and about 5000 m. Both the depth and geographical data relate to areas where mining exploration contracts have been granted, mostly in the east-central part of the zone. Data on numbers do not exist for all recorded species, but where they do, 37% are known only from a single specimen, which implies significant undersampling. Again, 91% of the single specimen species have been recorded in areas where mining concessions have been granted, with the area known from Areas of Particular Environmental Interest. Overall, 95% of species recorded (named and unnamed) are unknown in the declared Areas of Particular Environmental Interest.

Heatmap of sampling effort as the density of unique sampling sites. Sampling effort is displayed as two-degree polygons. Rabone et al. (2023).

Rabone et al.'s study provides an estimate of the known and unknown species richness for benthic Animals across the Clarion-Clipperton Zone. This shows sampling to be very incomplete at the species level, but likely to be complete or very nearly complete at the family level. 

Density of sampling by depth. Number of samples by depth, grouped by 10 sample quantiles, all taxa combined. Rabone et al. (2023).

Diversity estimates can be seriously distorted when specimens of the same species are recorded as different species, a problem Rabone et al. believe was present in one of the sources they consulted,, the DeepData Database of the International Seabed Authority, where they suggest about a quarter of records represent duplicates. Further duplications could potentially be present and undetected within the remaining data.

Rabone et al. note that some regions of and habitats within the Clarion-Clipperton Zone remain almost totally unsampled. There have been, for example, only six studies of rocky outcrops and seamounts within the zone, habitats which are known to typically have very different faunas to other deep sea environments. The Clarion-Clipperton Zone is a highly variable area compared to much of the oceans' abyssal plains, with numerous rocky outcrops, and extensive fields of polymetallic nodules. Such a diverse environment ought to support a diverse community of organisms, with a lack of sampling almost certainly leading to a significant deficiency in the available data on biodiversity in the region.

A number of other factors could potentially cause estimates of species richness to be inflated or underestimated. Notably, within the Clarion-Clipperton Zone, many species have been recorded by informal names only, allowing for multiple synonyms for a single species, and variation in naming practices over time. A proportion of the informal names within the consulted data sources will no doubt be wrong; but it is impossible to do more that estimate this inaccuracy.

For the most abundant groups within the Clarion-Clipperton Zone, Tanaid and Isopod Crustaceans, 23% of identified species have type localities outside the zone, many within other ocean basins. These groups are known to include many widespread species, but it is still quite possible that this record could include many cryptic species (i.e. species which appear morphologically identical, but which are genetically distinct) or species complexes (groups of closely related cryptic species), which are known to be particularly prevalent in the deep oceans. Resolving this would require genetic sampling of both specimens from the type locality and the Clarion-Clipperton Zone population(s); without this the diversity of these groups may be underestimated by 20-25%. Most of the new species described from within the Clarion-Clipperton Zone have been described since the advent of molecular taxonomy as a standard method, but 51% are named from morphological data only. This is particularly true for smaller species, with 86% of meiofaunal species described from the Clarion-Clipperton Zone described only on the basis of morphological data. 

Rabone et al. suspect that their figure of 92% of species being unidentified within the Clarion-Clipperton Zone includes an overestimation of the number of species due to different informal names being used for the same species, but an underestimation of the number of species due to undersampling of some regions, and the presence of cryptic species. 

Rabone et al's study produces a species composition for the Clarion-Clipperton Zone with differs from the World Register of Deep-Sea Species estimate for the deep ocean, even at phylum level. Some of the trends produced in the study are likely to be real, such as the higher diversity of Sea Cucumbers in the World Register of Deep-Sea Species than in the deep ocean as a whole, but others are likely to be the result of problems such as uneven sampling within the zone and a shortage of experts working on some taxonomic groups. Rabone et al. also note that the majority of species identified within the Clarion-Clipperton Zone, both named and unnamed, fall into the macrofauna category, which has been the subject of the most studies within the region. Megafauna, which are hard to sample using remote-operated vehicles, are rarely collected, and therefore seldom identified. Meiofauna are thought to make up the majority of the biomass of organisms in the deep sea, but are also thought to be significantly undersampled. This situation is not unique to the Clarion-Clipperton Zone, and the World Register of Deep-Sea Species probably also contains significant biases, given the lack of sampling across much of the deep ocean floor.

Very few estimates of biodiversity across large areas of the deep ocean floor have been carried out. A study of the deep sea floor of the Southern Ocean found 674 species of Isopod Crustacean, 87% of which were new to science. Rabone et al. estimate that 96% of Isopod species within the Clarion-Clipperton Zone will be undescribed from elsewhere, i.e. the 23 species already described from within the zone, plus an estimated 474 species yet to be described. Estimates of the total number of marine Animal species range from 300 000 (likely to be a significant underestimate) to 10 million (likely to be a significant overestimate). Rabone et al. estimate the proportion of undescribed species within the Clarion-Clipperton Zone at 92%, while the number for the total deep ocean has been estimated at 87%, a comparable figure. The named species within the Clarion-Clipperton Zone currently represent about 1% of the total estimated deep sea biodiversity for the planet, while the total number of species probably represents about 15% of that total.

The biodiversity of the Clarion-Clipperton Zone is currently significantly under-described. Thirty one new genera and three new families have been described from the zone to date, and Rabone et al. are aware of several new general and at least one new family of Animals- awaiting description from samples collected within the zone. The area clearly contains a significant amount of unique evolutionary lineages. The Clarion-Clipperton Zone is known to be home to significant Echinoderm novelty not known from elsewhere, and the same is probably true of other groups. Life histories unknown from elsewhere have also been recorded within the Clarion-Clipperton Zone, including organisms associated with the stalks of Sponges, as well as Nematodes, Isopods, and Polychaetes from groups otherwise associated with infaunal sediment-dwelling lifestyles which have adapted to live on the hard surfaces of polymetallic nodules. Suspension feeders are also particularly likely to be associated with nodules, with 60-80% of megafauna (the size range dominated by suspension feeders) within the Clarion-Clipperton Zone living on the surface of nodules. How these nodule-dwelling species (and species living in the nearby sediments) would be affected by deep-sea mining efforts targeting the nodules has never been the subject of any specific study. Little is known about the life-histories of these nodule-dwelling organisms, and any such study is likely to be extremely difficult, given that a third of such species have been observed only once.

Studies of individual taxa within the Clarion-Clipperton Zone have estimated that the proportion of undescribed taxa is in excess of 80%. Rabone et al.'s study provides the first estimate of the area's total biodiversity, and estimates the number of undescribed species to be between 88% and 92%. Despite decades of study in the region, taxonomic studies have only recently begun, leaving much work to be completed, something which Rabone et al. should be treated as a matter of some urgency, given the likelihood of mining operations commencing in the zone in the near future. Biodiversity is often assumed to be low in deep marine environments, but this assumption is at least partly driven by low sampling levels rather than low diversity. The United Nations Convention on the Law of the Sea states that marine mining efforts should cause 'no serious harm', but this term is not defined, and in the absence of reliable data on deep marine ecosystems, could easily become meaningless. 

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Unraveling the relationship between Giant Manta Rays and Cleaner Fish.

Seamounts are widely regarded as hotspots of biodiversity due to the unique oceanographic conditions that they generate and have been identified as important staging areas for migrant marine megafauna. While the ecological mechanisms that attract elasmobranchs to seamounts are poorly understood, it has been suggested that they provide refuge, represent social convergence points, act as navigational waypoints, and function as mating, feeding, and nursery grounds for a variety of pelagic species. The Giant Manta Ray, Mobula birostris, is one of two recognised Manta Ray species. Reaching 6.70 m in total (disc) width, the Ray is popular among tourists for its size and approachable behaviour. Recognised from fisheries and by-catch to frequent tropical and subtropical offshore waters circumglobally, Giant Manta Rays mature late, have low fecundity, and are classified as Vulnerable to Extinction by the International Union for the Conservation of Nature and Natural Resources’ Red List of Species. For the past two decades, Giant Manta Rays have been observed by SCUBA divers on Monad Shoal, which is a shallow coastal seamount in the Central Visayas of the Philippines, where they interact with Blue Streaked Cleaner Wrass, Labroides dimidiatus, and Moon Wrasse, Thalassoma lunare. Rays, including Giant Manta Rays, are known to host Metazoan parasites, and it is proposed that they visit a cleaning station at this site to control infection.

In a paper published in the journal Marine Biology on 7 April 2020, Calum Murie of the School of Environmental Sciences at the University of Liverpool, the Underwater Africa Foundation, and the Department of Biological Sciences at the University of Chester, Matthew Spencer also of the School of Environmental Sciences at the University of Liverpool, Simon Oliver, also of the Department of Biological Sciences at the University of Chester, and of the Thresher Shark Research and Conservation Project, show that Giant Manta Rays interact with cleaners at a seamount in the Philippines and investigate the cleaner–client association.

A Giant Manta Ray, Mobula birostris, at a cleaning station at Hin Daeng off the coast of Thailand. Jon Hanson/Flikr/Wikimedia Commons.

Batoid rays infected with parasites suffer a variety of health consequences. These include skin lesions, necrosis, anaemia, respiratory disease, and chronic Bacterial and Viral infections that have been reported as lethal in some species. Ectoparasitic infections in captive Elasmobranchs cause behavioural modifications such as rubbing against the structures of enclosures and interacting with Cleaner Fish.

The cleaning system is a classic model of cooperative behaviour among species in which Cleaner Fish remove ectoparasites and dead or infected tissue from the surface, gills, and sometimes the mouth of client Fish. Interactions with Cleaner Fish appear to improve the health of teleost clients by reducing their ectoparasite loads, but the benefit of these interactions is less understood amongst Elasmobranchs. Clients will often ‘pose’ near cleaning stations to solicit ‘services’ from Cleaner Fish. There are approximately 130 species of marine cleaners, with ectoparasitic infection being the most likely proximate cue for clients seeking their services. The Blue Streaked Cleaner Wrasse, Labroides dimidiatus, is an obligate cleaner that preferentially feeds on Gnathiid Isopod larvae that are known to infect the gills of Reef Manta Rays. Labroides dimidiatus prefer large clients and interact with Manta Rays at spatially diverse locations across the globe. The Moon Wrasse, Thalassoma lunare, which is less understood as a cleaner species, also provides cleaning services for Manta Rays. Moon Wrasse are facultative cleaners wherein only juveniles clean whilst contemporaneously exploiting alternative food sources.

A Blue Streaked Cleaner Wrasse, Labroides dimidiatus, in the Coral Sea off the coast of Australia. Rick Stuart-Smith/Reef Life Survey.

Cleaners may maximize the profitability of their energy return by selectively foraging on areas of clients where specific types of parasites can be found. When investigating how cleaners forage on Elasmobranchs, it has been shown that Labroides dimidiatus and Thalassoma lunare spent more time inspecting areas of Thresher Sharks, Alopias pelagicus, that were infected by ectoparasitic Digeneans, Paronatrema spp., compared to areas that are known to harbour other types of parasites. They concluded that cleaners may optimise their foraging by selecting areas of a client’s body that are most likely to produce the highest energy reward per unit effort. A cleaner’s foraging behaviour is, therefore, likely to be driven by the quality of the food patch in relation to the ease with which food may be obtained there. Since specific types of parasites infect specific patches of an Elasmobranch’s body, it can be predicted that cleaners will show preferences for foraging in some patches over others.

A Moon Wrasse, Thalassoma lunare, on the Great Barrier Reef, Australia. Leonard Low/Flikr/Wikimedia Commons.

Murie et al. quantified behavioural interactions between Giant Manta Rays and Cleaner Wrasse from remote video observations to address the following hypotheses: (1) the dynamics of the Cleaner–Manta system are driven by environmental factors; and (2) Cleaner Wrasse preferentially forage on specific areas of a Manta Ray’s body. The Cleaner–Manta association is discussed in relation to other known cleaner–client systems in the marine environment.

Monad Shoal is a seamount in the Central Visayan Sea, near Malapascua Island, Cebu, the Philippines. The top of the mount (15–25 m) is formed by a shallow plateau of low-profile Acropora that is fringed on all sides by a Coral Reef which crests and sheers down 250 m to the valley below. An array of cleaning stations lines the southern face of the mount, one of which (Station A) is frequented by Giant Manta Rays.

SCUBA divers initially deployed remote video cameras at five cleaning stations (A–E) on Monad Shoal during a pilot study which ascertained that Station A was the only location on the seamount where Giant Manta Rays could be observed interacting with Cleaner Fish. A total of 1171.45 h of video observations were subsequently recorded from a fixed point on Station A between April 2011 and June 2013, during three field expeditions spanning 262 days over 20 months. A Sony Handycam® HDR-SR8, housed in an Amphibico Elite housing and fitted with a 120° wide-angle lens, with focal range locked to 0.3 m, was pre-set to record for 360 continuous minutes for all camera deployments. The camera was retrieved at the end of each deployment period, and the video data downloaded for analysis.

Environmental data including tidal conditions, water temperature, and the in situ current strength were documented for each camera deployment. Temperature was measured in situ to the nearest degree Celsius using the readouts of a dive computer at the time of the camera deployment. Current strength was measured from a submerged windsock that was fixed to the substrate in the camera’s field of view. Tides were estimated from Admiralty predictions for Bogo Bay, the Philippines.

Murie et al. took still images of the video recordings when a Manta Ray was positioned directly above the camera to capture its ventral surface. They then entered the still images into a photo bank that considered patterning in the manta’s ventral markings to identify a new individual, or a match to an individual that had been previously observed at Station A. Due to the camera’s field of view, it was not always possible to capture the entire ventral surface for each Manta Ray so some mantas could not be individually identified.

To investigate whether cleaners forage selectively on Giant Manta Rays, it was assumed that different areas of a client’s bodyscape host different types of parasites and that some areas represent higher quality food patches for cleaners than others. Eight food patches were outlined on a sketch of a Giant Manta Ray and categorised as ‘gills’, ‘pelvis’, ‘dorsal head’, ‘ventral head’, ‘pectoral’, ‘ventral body’, ‘dorsal body’, and tail. These were then used to document cleaner interactions for each event. The pelvic and tail patches included the cloaca and tail, respectively, the pectoral patch incorporated both pectoral fins, the gill patch included both sets of gill openings, and the head patch consisted of the cephalic lobes, the eyes, and the mouth. The Ray’s dorsal surface was split into two patches, the boundary of which followed the underside of the Ray’s superbranchial region.

The food patches onto which locations of cleaning interactions were mapped during the analysis of the video recordings. Murie et al. (2020).

Cleaning interactions were characterised by a cleaner’s mouth making discernible physical contact with a Manta Ray and were termed ’bites’. Bite locations were individually mapped onto the sketch according to their associated cleaner species, Labroides dimidiatus or Thalassoma lunare, and treated separately in the analyses. Bites were used as a proxy for parasite removal. The number of cleaning inspections may be underestimated because Cleaner Fish activity behind a Manta Ray could not be observed on the video recordings.

Nine Mantas (M2–M10) were first recorded in 2011, four of which were observed revisiting the site in 2012 (M5, M7, M8, M9). Six Mantas (M11–M16) were first observed in 2012, two of which (M12, M13) were observed revisiting the site in 2013. One Manta (M9) was observed every year (2011–2013). Across all observations four Manta Rays were only seen on a single occasion. The remaining eleven had an average return rate of 5.64  across the three observation years.

Comparisons between models of Giant Manta Ray visits showed that the minutes observed, and the minutes after the high tide explanatory variables should be omitted from the final model. Manta Ray visits to the cleaning station varied throughout the year, occurring most frequently between April and September, with visits rare during March and July. Visits were most likely to occur during warmer temperatures and in the afternoon. Visits were also most likely to occur when the current was strong (over 1.5 metres per second) or weak (about 0.2–0.4 metres per second), but they were rare when the current was mild (about 1 metres per second).

There were 32 recorded cleaning events by 11 identifiable Mantas for which all data was available. These events lasted between 41 and 2976 seconds and involved between 1 and 22 discernible cleaning interactions. Comparisons between single-term deletions of the model for cleaning interactions indicated that all of the explanatory variables should remain in the final model.

The rate of interactions varied between individual Manta Rays, with some (for example M8) receiving much more attention from cleaners than others. The current strength was found to constrain the number of interactions a Manta Ray received, and higher water temperatures had a weakly positive effect, The minute after 05:00 had a weak negative effect, and the day of the year had a weakly positive effect.

Single-term deletions of the model for patch preferences by cleaner species indicated that the interaction between the patch and species should be omitted from the final fitted model.

After controlling for differences in patch area and comparing each patch to the ‘dorsal head’, cleaners showed preferences for certain patches. Both species targeted the gills, which received the largest absolute number of cleaning interactions, with both cleaner species also showing a preference for the pelvis. The pectoral fins received large absolute numbers of cleaning interactions by Labroides dimidiatus, which resulted in a slight preference for this patch by this species despite its large value for patch proportion. Thalassoma lunare’s preference for the ventral body could not be estimated since no cleaning interactions were recorded in this patch for this species, even though this parameter was structurally identifiable in the analysis.

While the cleaner–client system amongst reef Teleosts has received considerable attention, the spatially and taxonomically diverse associations between cleaners and Elasmobranchs are less understood. This study represents the first attempt to quantify interactions between Giant Manta Rays
and cleaner wrasse in the natural environment and supports knowledge of the importance of cleaning stations to marine ecosystems.

Our observations of giant manta rays were most likely to occur in the afternoon on a seasonal basis between the months of April and September. Giant Manta Rays’ large body size and planktivorous diet make ocean productivity a key factor in determining their movements and seasonal shifts in food availability encourage them to undertake substantial migrations. Giant Manta Rays are known to frequent cleaning stations in Mozambique, Ecuador, and Indonesia during the austral winter, and their seasonal fidelity to these sites has largely been attributed to increases in local productivity that is driven by oceanographic processes, including currents. It is possible that Giant Manta Rays have limited movements on a regional scale in Murie et al.'s study area and that they are only in the vicinity of Monad Shoal when seasonal oceanographic processes promote shifts in productivity and the consequent availability of food. They may partition their time to converge on Station A during the afternoon when food is scarce and/or when hydrodynamic conditions facilitate cleaning. Similar temporal trends for Giant Manta rays visiting cleaning stations have been observed in Indonesia where they are known to move offshore to forage nocturnally in deep waters after they clean. Mantas’ movements and use of our study area may be part of a strategy that considers both temporal variations in food availability and cleaner services without being mutually exclusive. 

The overall occurrence of Giant Manta Ray cleaning events was strongly influenced by the state of the current on the seamount. Certain hydrodynamic conditions may generate sufficient water flow and lift for Giant Mantas to ‘hover’ over specific topographical features. In Mozambique, Reef Manta Rays are known to clean during moderate strength currents because these conditions are favourable for hovering over cleaning stations. Hovering may facilitate Giant Mantas’ interactions with cleaners since cleaning typically occurs near spatially finite structures that are known as ‘focal points’. Hovering is also likely to be an energetically efficient strategy that makes Giant Manta Rays more accessible to cleaners and, therefore, more attractive as clients. However, even though hydrodynamic flow may provide lift and facilitate a Giant Manta’s hovering behaviour over a cleaning station, cleaning events were not observed on Monad Shoal when the current was strong. Cleaners are known to seek refuge and conserve their energy during strong currents, which stalls the provision of cleaning services for their clients. The reduced availability of cleaners may have decreased the likelihood of a Giant Manta Ray visiting the site during these periods in spite of the energetic benefits provided by strong currents. 

Reef Teleost clients are known to show preferences for specific services that are offered by specific cleaners at specific stations. A client’s fidelity to individual cleaners may be driven by the type and quality of service on offer (parasite removal, wound healing, tactile stimulation), or other clients competing for the same resources. Many of the individual mantas that we observed on Station A had open wounds from bite marks and dismembered cephalic lobes, presumably from encounters with predators and/or fishing gear. Giant Manta Rays’ fidelity to this site may be indicative of a lack of competition from other Elasmobranch clients, and/or specialist wound healing and parasite removal services that are on offer at this particular location.

Higher temperatures were found to influence the frequency with which Giant Manta Rays visited Station A and were also associated with an increase in the frequency of their interactions with cleaners. Digenean Flatworms (Phylum Platyhelminthes) that are known to infect the cloacas of Elasmobranchs on Monad Shoal are typically dioxenous, parasitising two hosts during their life cycle. During reproduction, oviparous Digeneans release their fertilised eggs into the water column where they hatch to produce miracidia. The miracidia swim to find an intermediate Mollusc host where they grow through several life stages until they eventually emerge as cercaria larvae. Larvae live freely in the water column before they attach to their terminal host, which they locate from host-derived chemical or mechanical cues, or shadows. Attachment typically occurs during seasonal epizootic events, which are characterised by cool (roughly 25 °C) or warm (roughly 32 °C) water conditions and may coincide with a time when hosts are particularly vulnerable to infection. 

Murie et al.'s conjecture for further study that the seasonality with which Giant Manta Rays visit Monad Shoal might coincide with ectoparasite attachment events in the area, leading to heightened parasitism and a greater need for interacting with cleaners.

Since Cleaner Fish tend to modify their foraging patterns in response to variations in the quantity and quality of a food resource, Giant Manta Rays with the highest parasite loads are more likely to be attractive clients. Labroides dimidiatus typically favours larger clients with high ectoparasite infections, and a client’s body size has been positively correlated with ectoparasite abundance. The number of cleaning interactions (per unit time) varied substantially among individual Mantas across our observations. Although Murie et al were not able to quantify body size, it is possible that larger Mantas received more attention from cleaners than smaller ones.

Cleaning interactions were patch-specific, suggesting that the cleaners forage selectively across a Giant Manta Ray’s bodyscape. Ectoparasites that attach to Elasmobranchs are site specific and typically infect the same sites across different host species. Platyhelminthes parasitise most Elasmobranchs, and Paronatrema spp. found in and around the cloaca of pelagic Thresher Sharks, Alopias pelagicus, that regularly visit our study site are thought to be the primary driver for cleaners preferentially foraging on their pelvis. Monogenean Flatworms are similarly known to infect the cloaca of Manta Rays in Mozambique, and Gnathiid Isopods, which are a primary food source for the Blue Streaked Cleaner Wrasse, infect their buccal cavities. While it was not possible to verify whether Manta Rays visiting Monad Shoal are infected by Gnathiids, Digeneans, or Monogeneans, Murie et al.'s observations suggest that either parasitic abundance is highest in and around the cloaca and gills, or that Cleaner Fish are selecting parasites, mucus, and/or dead tissue there because they are accessible.

Many large marine organisms visit cleaning stations to have parasites removed and giant manta rays appear to regularly visit cleaning stations on inshore reefs. The Rays may visit cleaning stations to benefit from feeding opportunities nearby or they may migrate inshore to clean after they forage in deep-water. Giant Manta Rays are thought to have limited regional connectivity and so the low number of absolute visits that we recorded either suggests that the habitat no longer supports their requirements, or that they are in regional decline. Cleaning interactions are both spatially and taxonomically diverse and cleaners’ selective foraging on Giant Manta Ray clients demonstrates a level of preference for areas of a Manta’s body where specific types of parasites might be found. Future identification and quantification of parasite loads on Giant Manta Rays would offer further evidence that Elasmobranch clients provide high-quality food patches for cleaners at seamounts. Cleaning stations are key points of convergence for Giant Manta Rays and they may only frequent specific cleaning stations so these spatially finite habitats should be carefully managed.

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Cylisticus masalicus: A new species of Woodlouse from the rainforests of northern Iran.

Woodlice, Oniscidea, are terrestrial Isopod Crustacians with rigin exoskeletons and fourteen limbs. They are found in moist terrestrial environments (and in the case of a few species, dry terrestrial environments) across the globe, being largly active at night, and consuming dead plant matter. Like all Crustaceans (and unlike other terrestrail Arthropods) Woodlice must regularly shed their exoskeletons as they grow. Female Woodlice carry fertilized eggs in a pouch, the marsupium, until they hatch, giving birth to live young; they can also reproduce asexaully if no males are available. Woodlice are known for the ability to enrole into an almost perfect sphere as a defence mechanism (conglobating), though only members of one family, the Armadillidae, can do this, with other Woodlice enroling to a lesser degree, or not at all.

In a paper published in the journal ZooKeys on 21 April 2016, Ghasem Kashani of the Department of Biology at the University of Zanjan describes a new species of Woodlouse from the subtropical rainforests of northern Iran, as part of a wider study of the Isopod family Cylisticidae in Iran.

The new species is placed in the genus Cylisticus, and given the specific name masalicus, in reference to the city of Masal in Gilan Province, the species having first been identified in forests close to this city. Cylisticus masalicus is a slate grey Woodlouse, with pale muscle spots, reaching a maximum length of about 15 mm. It has long, slender antenae, which remain folded along the back when conglobating.

 Active specimen of Cylisticus masalicus. Kashani (2016).

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Parasitic Isopod Crustaceans from the Philippines, Australia and Taiwan.              Bopyrid Isopods are parasites infesting the bodies of other marine (and occasionally freshwater) Crustaceans. About 800 species have been described, with maximum diversity thought be found in the...

Myopiarolis tona: A new species of Isopod Crustacian from the west coast of New Zealand.                                                       The Serolidae are a group of Marine Isopod Crustaceans found predominantly in the Southern Hemisphere. Most species are found between...

A parasitic Cymothoid Isopod from the Virgin Islands.                                                         Cymothoids are Isopod Crustaceans, related...

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Parasitic Isopod Crustaceans from the Philippines, Australia and Taiwan.

Bopyrid Isopods are parasites infesting the bodies of other marine (and occasionally freshwater) Crustaceans. About 800 species have been described, with maximum diversity thought be found in the Indo-Malay-Philippines Archipelago, where it is predicted that many undescribed species will be found. Most Bopyrids are found within the branchial (gill) chambers of their hosts, though members of the subfamily Athelginae attach to the abdomens of Hermit Crabs, a group particularly prone to parasite infections.

In a paper published in the Raffles Bulletin of Zoology on 29 February 2016, Jason Williams of the Department of Biology at Hofstra University and Christopher Boyko of the Department of Biology at Dowling College describe four new species of Athelgine Bopyrid Isopods from the Philippines, Australia and Taiwan.

Williams and Boyko inspected 2175 Hermit Crabs collected from the shallow subtidal zone at several sites in the Philippines, as well as museum specimens from Australia, Papua New Guinea and Taiwan. A total of three new species of Athelgine Bopyrid Isopods were found in the Philippine material, one of which was also found on a museum specimen collected in Taiwan, while a fourth new species was discovered on an Australian Hermit Crab in a musuem collection.

The first new species described is placed in the genus Allathelges, and given the specific name alisonae, in honour of Alison Carson, the wife of Jason Williams, who helped collect much of the Philippine material. This species was found infecting Hermit Crabs of the species Dardanus lagopodes (Hairy Red Hermit Crabs), from Batangas and Cebu provinces in the Philippines. The species is strongly sexually dimorphic (i.e. the different sexes are not the same size and shape), with females reaching a maximum of 11.75 mm in length while males reach only 3.0 mm.

Allathelges alisonae, female in (A) ventral view and (B) dorsal view. Scale bar is 2 mm. Williams & Boyko (2016).

Females of this species lack eyes, and have a pleon (tail section) with unfused segments, while the males retain eyes and have pleons formed of fused pleons.

Allathelges alisonae, male in (A) dorsal view and (B) ventral view. Scale bar is 500 μm. Williams & Boyko (2016).

The second new species described is placed in a new genus, Claustrathelges, which is a combination of Athelges, a previously described species and 'claustrum' a Latin word for prison, in reference to the fact that the parasites are trapped within the Hermit Crab's home. The species is given the specific name macdermotti, in honour of John McDermott, Emeritus Professor of Biology at Franklin and Marshall College in Pennsylvania, for his work on his work on marine invertebrates in general and Bopyrids in particular, and in recognition of the fact that Williams and Boyko found a species previously named after him to be invalid.

Claustrathelges macdermotti, female in (A) ventral view and (B) dorsal view. Scale bar is 2 mm. Williams & Boyko (2016).

The species is decribed from a single female specimen from a museum specimen of Cancellus typus (the Minor Hermit Crab) collected from San Remo Channel in Victoria, Australia, in 1978. The specimen is 14.4 mm in length, and has a maximum width of 8.2 mm. It lacks eyes.

The third species described is placed in the genus Falsanathelges, and given the specific name mariae, in honour of Maria Spector, the wife of Christopher Boyko.  The species was found on several different Hermit Crab species from Oriental Mindoro and Cebu provinces in the Philippines, as well as museum specimens of Calcinus guamensis (the Guam Hermit Crab) from Taiwan.

Falsanathelges mariae, female in (A) ventral view and (B) doesal view. Scale bar is 1 mm. Williams & Boyko (2016).

Females of this species reach 9.67 mm and males 4.47 mm. One of the female specimens examined hosted a smaller parasitic isopod of the genus Cabirops in its brood chamber (parasites which infest other parasites are referred to as hyperparasites).

Falsanathelges mariae, male specimen in (A) dorsal view and (B) ventral view. Scale bar is 500 μm. Williams & Boyko (2016).

The final new species described is placed in the genus Pseudostegias, and given the specific name trisagitta,  meaning 'three-arrows', in reference to a distinctive structure on the ventral surface of one of its segments. This species is described from a single female specimen 8.9 mm in length found on a Crab of the species Calcinus minutus (the Small White Hermit Crab) at Coco Beach in Oriental Mindoro Province.

Pseudostegias trisagitta, female specimen in (A) ventral view, and (B) dorsal view. Scale bar is 1 mm. Williams & Boyko (2016).

See also...

Myopiarolis tona: A new species of Isopod Crustacian from the west coast of New Zealand.                                                       The Serolidae are a group of Marine Isopod Crustaceans found predominantly in the Southern Hemisphere. Most species are found between...

A parasitic Cymothoid Isopod from the Virgin Islands.                                                         Cymothoids are Isopod Crustaceans, related...

A fossil Isopod Crustacean from the Early Miocene of the Vienna Basin.                  Isopods are one of the most numerous and diverse groups of Crustaceans in modern environments, but while preserved specimens are known from as far back as the Carboniferous, they have a limited presence in the fossil record, largely because their exoskeletons are only very lightly mineralized. They are small, flat...

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Myopiarolis tona: A new species of Isopod Crustacian from the west coast of New Zealand.

The Serolidae are a group of Marine Isopod Crustaceans found predominantly in the Southern Hemisphere. Most species are found between the subtidal zone and about 2000, but one species has been found slightly bellow 5000 m. Serolids range in size from a few millimeters in size, to about 5 cm, with the largest species being found in Antarctic waters.

In a paper published in the journal Zootaxa on 10 December 2015, Karen Spong of Coasts and Oceans at the National Institute of Water and Atmospheric Research and Niel Bruce of the Museum of Tropical Queensland, Queensland Museum and College of Marine and Environmental Sciences at James Cook University describe a new species of Serolid Isopod from waters off the west coast of New Zealand.

The new species is placed in the genus Myopiarolis and given the specific name tona, a Maori word meaning 'nodule' in reference to a prominent nodule on a section of fused thoracic segments. The species is described from five male and three female specimens collected from depths of between 634 and 1248 m on the South Lord Howe Rise, Challenger Plateau and waters off the coast of New Plymouth. Males of the species ranged from 7.5 to 8.5 mm in length, females from 9.00 to 10.00.

Myopiarolis tona, male specimen in dorsal view. Spong & Bruce (2015).

See also...

A parasitic Cymothoid Isopod from the Virgin Islands.                                                         Cymothoids are Isopod Crustaceans, related...

A fossil Isopod Crustacean from the Early Miocene of the Vienna Basin.                  Isopods are one of the most numerous and diverse groups of Crustaceans in modern environments, but while preserved specimens are known from as far back as the Carboniferous, they have a limited presence in the fossil record, largely because their exoskeletons are only very lightly mineralized. They are small, flat...

A new Isopod Crustacean from a limestone cave in Brazil.                                          Isopods are small, flat, benthic Crustaceans known from marine, freshwater and terrestrial environments, where they are known as Woodlice or Pill Bugs, due to the tendency of many species to roll up into tight balls resembling pills for defencive purposes. They are a...

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A parasitic Cymothoid Isopod from the Virgin Islands.

Cymothoids are Isopod Crustaceans, related to terrestrial Woodlice and Pill Bugs, but found in marine environments, where they are parasitic on Fish, typically living in the throat or gills, or on the external surface of the skin. Species which infest the gills of their host are often asymmetrical, with a slightly twisted shape that reflects the shape of the gill arches. These Crustaceans are typically quite harmful to their hosts, causing damage to the gills and branchial filaments, often leading to loss of part of the gills, with a subsequent effect on the development of the Fish.

In a paper published in the journal Zookeys on 10 September 2014, Kerry Hadfield of the Water Research Group (Ecology) at the Unit for Environmental Sciences and Management at North West University, Paul Sikkel of the Department of Biological Sciences at Arkansas State University and Nico Smit, also of the Water Research Group (Ecology), describe a new species of Cymothoid Crustacean from the Virgin Islands.

The new species is placed in the genus Mothocya and given the specific name bertlucy, in honour of Ernest H. (‘Bert’) Williams Jr. and Lucy Bunkley-Williams of the University of PuertoRico, on the occasion of their retirement, and in recognition of their contribution to the study of parasitology in the marine ecosystems of the Caribbean. Mothocyabertlucy was found infesting the gills of the Redlip Blenny, Ophioblennius macclurei around St. John Island and St Thomas Island in the US Virgin Islands and Guana Island in the British Virgin Islands.

Mothocya bertlucy(top) female and (bottom) male, both in lateral view. Hadfield et al. (2014).

Mature females of Mothocya bertlucy reach 7.0-9.0 mm in length and are slightly twisted. Males reach about 6.0 mm in length and are untwisted. The species is small compared to other members of the genus, and has small eyes for its size. It is the first species of Mothocyato have been found infecting a Blenny.

Mothocya bertlucy(left) female and (right) male, both in dorsal view. Hadfield et al. (2014).

 

See also…

A fossil Isopod Crustacean from the Early Miocene of the Vienna Basin.

Isopods are one of the most numerous and diverse groups of Crustaceans in modern environments, but while preserved specimens are known from as far back as the Carboniferous, they have a limited presence in the fossil record, largely because their exoskeletons...

A new Isopod Crustacean from a limestone cave in Brazil.                                                                                                                   Isopods are small, flat, benthic Crustaceans known from marine, freshwater and terrestrial environments, where they are known as Woodlice or Pill Bugs, due to the tendency of many species to roll up into tight balls...

Two new species of freshwater Isopod Crustaceans from Lake Pedder in Tasmania.                                                         In 1972 two small shallow lakes in southwest Tasmania, Lake Pedder and Lake Edgar, were inundated to create a reservoir to feed a hydroelectric power scheme, also called Lake Pedder, in the Serpentine River Valley. This was a source of great concern to biologists as the...

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