Eruption on La Soufrière volcano, St Vincent Island.

La Soufrière volcano on the island of St Vincent in St Vincent and the Grenadines, part of the Windward Islands group in the Lesser Antilles Islands of the Caribbean, erupted on Friday 9 April 2021, according to the National Emergency Management Organisation. The volcano erupted slightly after 8.40 am local time, producing an ash column that rose about 6000 m above the island. There have been no reports of any casualties associated with this event, but many communities have reported ash-falls, and much of the north of the island has been evacuated as a precautionary measure. 

 

An ash column above the island of St Vincent on 9 April 2021. University of the West Indies Seismic Research Centre.

La Soufrière is a 1220 m stratovolcano (cone shaped volcano made up of layers of ash and lava) situated at the northern end of the island of St Vincent. It is the youngest, and northernmost, of a chain of volcanoes that make up the island, and is thought to have first erupted around 2380 BC.

The Lesser Antilles are located at the eastern fringe of the Caribbean Tectonic Plate. The Atlantic Plate (strictly speaking, an extension of the South American Plate which runs to the northeast of the Caribbean) is being subducted beneath this, and as it sinks into the Earth, is melted by the heat of the planets interior. Some of the melted material then rises up through the overlying Caribbean Plate as magma, fuelling La Soufrière and the other volcanoes of the Lesser Antilles Volcanic Arc. The subduction of the Atlantic Plate beneath the Caribbean Plate is not a smooth process, with the two plates constantly sticking together then breaking apart as the tectonic pressure builds up, causing Earthquakes in the process, though since the boundary between the two plates is some way to the east of the islands, Earthquakes in the Lesser Antilles tend to be both deep and offshore, which lessens their destructive potential.

 

The subduction of the Atlantic Plate beneath the Caribbean Plate fuels the volcanoes of the Lesser Antilles Volcanic Arc. George Pararas-Carayannis.

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Saharan Dust Storm reaches the Lesser Antilles

A dust storm originating in the Sahara Desert has crossed the Atlantic Ocean and reached the Lesser Antilles Islands in the southern Caribbean this week. The Air Quality Index has exceeded 150, a level deemed to be Unhealthy by the Real-time Air Quality Index, in Tobago, Dominica, and on the north coast of Venezuela, due to high levels of fine particulates (particles with diameters of less than 2.5 μm), with other islands recording levels almost as high, and fears that changing wind directions could bring the dust to the Greater Antilles and southern United States.

A dust cloud over the Atlantic Ocean imaged by the GOES-17 Satellite on Monday 22 June 2020. NOAA/RAMMB.

The predominant weather system over North Africa is the Saharan Air Layer, a hot, dry, and often dust-laden air system that prevents moister air from the Atlantic and Mediterranean brining rain to the area. Over the Atlantic this layer is typically forced up, above the moist, but cooler, sea air, carrying dust westward to South America and the Caribbean. This brings with it dust particles that can have an immediate impact on health in the region, but which are also thought to contribute significanly to the soil fertility of tropical South America and the Caribbean Region, and which also help to suppress tropical storm formation at times of high dust transportation.

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Alert level around Kick 'em Jenny raised after sharp rise in seismic activity.

The Granadan National Disaster Management Agency has raised the alert level around Kick 'em Jenny, a submarine volcano about 8 km to the north of Granada, following an abrupt rise in seismic activity in the area. A total of 1384 Earthquakes with a Magnitude greater than 1.0 were recorded in the week 5-12 June 2020, compared to only 29 in the whole of April and May. Such tremors are often caused by the movement of hot water and volcanic gas beneath a volcano, which could indicate that the volcano is about to erupt. As a precaution a shipping exclusion zone surrounds the Kick 'em Jenny to a distance of 1.5 km; this zone has been increased to 5 km until further notice, due to the heightened risk to shipping during periods of activity.

 Map showing the exclusion zone around Kick 'em Jenny. Caribbean 360.

Kick 'em Jenny rises 1300 m above the surrounding seafoor, but remains 180 m below the surface. It was first discovered in July 1939, when an eruption broke the surface and threw material several hundred meters into the air, as well as generating a tsunami which was observed as far away as Barbados, though it was too small to cause any damage. However Kick 'em Jenny is labled on many earlier maritime charts, indiating that people have been aware there was something here for several centuries, even if they did not know the nature of the feature.

5 m lateral resolution digital terrain model  of the Kick ‘em Jenny current edifice. Robertson et al. (2015).

The Lesser Antilles are located at the eastern fringe of the Caribbean Tectonic Plate. The Atlantic Plate (strictly speaking, an extension of the South American Plate which runs to the northeast of the Caribbean) is being subducted beneath this, and as it sinks into the Earth, is melted by the heat of the planets interior. Some of the melted material then rises up through the overlying Caribbean Plate as magma, fuelling Kick 'em Jenny and the other volcanoes of the Lesser Antilles Volcanic Arc. The subduction of the Atlantic Plate beneath the Caribbean Plate is not a smooth process, with the two plates constantly sticking together then breaking apart as the tectonic pressure builds up, causing Earthquakes in the process, though since the boundary between the two plates is some way to the east of the islands, Earthquakes in the Lesser Antilles tend to be both deep and offshore, which lessens their destructive potential.

The subduction of the Atlantic Plate beneath the Caribbean Plate fuels the volcanoes of the Lesser Antilles Volcanic Arc. George Pararas-Carayannis.

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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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Magnitude 5.2 Earthquake between Tobago and Grenada.

The United States Geological Survey recorded a Magnitude 5.2 Earthquake at a depth of 31.0 km roughly half way between the islands of Tobago and Grenada,  slightly after 11.25 pm local time on Monday 6 April 2020 (slightly after 3.25 am on Tuesday 7 April GMT). There are no reports of any casualties or damage associated with this event, though the quake was felt over a large area, with people reporting feeling it across Tobago, Grenada, Trinidad, and St Vincent and the Grenadines.

The approximate location of the 6 April 2020 Tobago and Grenada Earthquake. USGS.

The Lesser Antilles Islands, including Grenada and Tobago are located at the eastern fringe of the Caribbean Tectonic Plate. The Atlantic Plate (strictly speaking, an extension of the South American Plate which runs to the northeast of the Caribbean) is being subducted beneath this, and as it sinks into the Earth, is melted by the heat of the planets interior. Some of the melted material then rises up through the overlying Caribbean Plate as magma, fuelling the volcanoes of the Lesser Antilles Volcanic Arc. The subduction of the Atlantic Plate beneath the Caribbean Plate is not a smooth process, with the two plates constantly sticking together then breaking apart as the tectonic pressure builds up, causing Earthquakes in the process, though since the boundary between the two plates is some way to the east of the islands, Earthquakes in the Lesser Antilles tend to be both deep and offshore, which lessens their destructive potential.

 The subduction of the Atlantic Plate beneath the Caribbean Plate fuels the volcanoes of the Lesser Antilles Volcanic Arc. George Pararas-Carayannis.

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. The University of the West Indies is interested in hearing from people who have felt Earthquake events in the region; if you felt such a quake then you can report it here. 

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Cerrorchestia taboukeli: A new species of Terrestrial Amphipod from Martinique Island.

Amphipods are (mostly) small, laterally compressed Crustaceans with differentiated legs (i.e. not all their legs are the same). Female Amphipods carry their eggs in brood pouches till they hatch; the young resemble the adults and typically reach maturity after about six molts. Amphipods are extremely widespread and numerous, but often overlooked due to their small size, most species being under 10 mm, though giant species exceeding 30 cm are known from the deep oceans. Amphipods are found in almost all modern marine ecosystems, as well as many freshwater environments; most freshwater 'Shrimps' are Amphipods, as are the terrestrial  and semi-terrestrial Taltrids, known variously as Sandhoppers, Beachhoppers, Fieldhoppers, and Foresthoppers.

In a paper published in the European Journal of Taxonomy on 12 December 2019, Christophe Piscart of Université de Rennes, Khaoula Ayati of the Faculté des Sciences de Bizerte at the Université de Carthage, and Mathieu Coulis of Le Lamentin on Martinique, describe a new species of Foresthopper from Martinique.

The Caribbean Region is inhabited by 21 terrestrial or semi-terrestrial species of Talitrids. These species belong to ten genera (Cariborchestia, Caribitroides, Cerrorchestia, Chelorchestia, Floreorchestia, Mexitroides, Platorchestia, Talitroides, and Talorchestia) and can be pooled into three different ecological groups (Beachhoppers, Fieldhoppers and Foresthoppers) according to their environmental distribution and morphological adaptations. Almost half of the Caribbean species belong to the Beachhopper and Fieldhopper groups, with 11 species that could be considered as Foresthoppers, known from the rain and cloud forests of the Greater Antilles islands and Central America. In the Lesser Antilles, six Amphipod species are known (Floresorchestia guadalupensis, Hyalella caribbeana, Platorchestia platensis, Amphiatlantica sulensoni, Tethorchestia antillensis,  and Tethorchestia karukarae), all from sandy beaches, lakes and ponds on Guadeloupe. No terrestrial species are known to date. Moreover, there is no knowledge on the distribution of Amphipods on Martinique Island, prior to the exploration of Pitons du Carbet mountain range carried out in 2017 and 2018, when a new species of Foresthopper was found during samplings of the soil Arthropods of the tropical sub-mountain rainforest.

Amphipods were sampled in the mountain range of Pitons du Carbet on Martinique Island where they
occur above 1000 m in small forest patches distributed around the summits and high plateaus. The vegetation has the characteristic of a cloud forest, i.e., it is subjected to high precipitation (mean annual rainfall above 6000 mm), high nebulosity (mistiness) and epiphytic plants are very abundant. The species was found in the litter layer of the Mountain Mangrove, Clusia mangle, and Umbrella Plant, Schefflera attenuata, which are the two dominant tree species of the area. Amphipods were found at two localities, the pass between the Piton Alma and Piton Dumauzé, at an altitude of 1045 m, and on the top of the Piton Boucher, at an altitude of 1059 m.

The new species is placed in the Foresthopper genus Cerrorchestia, which is otherwise known from similar environments in Panama to Costa Rica, and given the specific name taboukeli, which derives from ‘Taboukéli oüébo’, meaning ‘summit of the mountain’ in the in the Kalinago language of the the pre-Colombian inhabitants of Martinique Island. The species is sexually dimorphic (i.e. the sexes are different in size and shape), with the males having a greatly enlarged second claw, and being slightly larger, with the described male specimen being 11.3 mm in length, while the described female specimen is 9.6 mm. 

Cerrorchestia taboukeli, male specimen in lateral view. Piscart et al. (2019).

Cerrorchestia taboukeli was found in very wet conditions of the Pitons du Carbet Mountain Range (annual precipitation higher than 6000 mm per year) always at an altitude higher than 1000 m. At this altitude, the cloud forest is sparse, alternating with mountain grassland. Cerrorchestia taboukeli was found only under tree patches in a shaded environment where leaves of Mountain Mangroves and Umbrella Plants create a thick litter layer on the soil. During daylight, the animals rest almost motionless under the leaf litter unless disturbed, in which cases they actively jump in search for shelter.

Cerrorchestia taboukeli, live specimen. Piscart et al. (2019).

Using a quadrat of 25 × 25 cm, the population density was estimated to be, on average, 196 individuals per square meter. The sex ratio of adults was biased toward females, and juveniles represented more than 75% of the population during the sampling period. The species live in leaf litter of cloud forest with an andosol developed on volcanic rocks (andesite).

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