SMSG Blog

By Dr Vladimir Laptikhovsky

Most us that have dived in tropical seas have seen parrot fishes. You might have heard them crunching and munching corals before you see them, they are amongst the most common fish in coral reefs all over the World. But not only coral reefs… some species in the genus Sparisoma managed to cross huge oceanic spaces and settled around the small oceanic islands of the Mid-Atlantic ridge, like the Azores. One of them, Sparisoma strigatum, is known to be endemic to Ascension and St. Helena. Around St. Helena, according to Dr Judith Brown, it is a very common species in shallow waters. Occasionally it occurs in groups in rocky areas between 5 and 20 meters depth. Juveniles might be distributed slightly deeper, amongst weed and rubble patches on sand at 15-18 m depth. The species was known around Ascension Island and even pictured on local postage stamp. However, our previous expedition that covered most of shallow waters around this island did not find it. Why are its numbers so low that it is virtually unnoticeable? This SMSG/SAERI expedition of is looking to answer to this question.

Eventually this mystery species was found, south of Catherine Point where a single specimen was seen and photographed by Steve Brown. It was found together with the white spotted filefish (Cantherhines macrocerus), also recorded on our last trip in August 2012. This was indeed quite an unusual site as it had a remarkable abundance of the endemic Ascension Island wrasse too.

The team returns to Shelly Beach

We mentioned in one of our early posts that two of our team members had been fortunate enough to be shown a very special site here on Ascension, the small rock pools at Shelly Beach where two very rare and vulnerable species of shrimp are found.

Yesterday a large number of the team enjoyed a return visit to the pools, escorted by Stedson Stroud and Jolene Sim of Ascension Conservation. This time we were loaded with all the equipment we would need for a survey of the site, including underwater cameras, devices to measure salinity and temperature, GPS units to map the site and, most excitingly, special permission by the Ascension Island Government to collect a small number of samples for further study.

Enjoy this short gallery of images taken at this exceptional location.

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Ascension Island – a lonely piece of land in a seemingly borderless ocean turned out to be the centre of an oceanographic 'collision'  which does not happen very often in featureless seas. Here, the central branch of the Southern Equatorial Current that normally goes on surface meets the Southern Equatorial Counter-Current that normally goes in subsurface layers but right here, between 7 and 8°S, it travels to the surface. Interactions of these two streams give rise to high water turbulence, numerous gyres and eddies and other kinds of water unrest. Those, combined with upwelling areas in inshore waters caused by the bottom topography, are responsible to the high productivity of the area that attracts numerous large predators close to shore that might be seen filleted on Georgetown pier almost every night.

[caption id="attachment_547" align="aligncenter" width="584"] Getting picked up by our research vessel for the circumnavigation of the island, the Queen of Atlantis.

To study the local oceanographic features, a total of 16 oceanographic stations with manually deployed CTD (Conductivity – Temperature – Density) devices were carried out. To complete the picture around the island, Vlad Laptikhovsky, Steve Cartwright, Wetjens Dimmlich, Frithjof Kuepper and Kostas Konstantinos circumnavigated Ascension in the comfort of the Queen of Atlantis. Generally conditions in the voyage were good but did become quite rough along the more exposed coast near Boatswain Bird Island.

The results reveal a complicated oceanographic structure even in the upper 50-m layer, where waters of both the major oceanic currents combined with a mixed layer of local origin.

[caption id="attachment_548" align="aligncenter" width="584"] Vlad deploying the CTD during the 4-hr trip around Ascension.

During the past two weeks the interaction of these currents was quite mobile. The cold productive Counter-Current eventually occupied the surface layer around most of the island, excluding the small offshore part in the north around English Bay. The more saline (because of evaporation) Equatorial Current moved its water mostly deeper than 20 m revealing expected phenomenon of temperature increase with depth, and surfaced only in the very north of the studied area.

- Contributed by Vladimir Laptikhovsky

The Falkland Island Dive Team (FIDT) is a group of Service, Ministry of Defense (MOD) and civilian personnel who have given their time to support this exciting Project.  The team is making a vital contribution to the project by providing logistical support and planning for the delivery of equipment plus booking of flights, accommodation, vehicles and boat.

[caption id="attachment_454" align="aligncenter" width="584"] Sarah Lee in Lava Tunnel, English Bay.

In the first 2 week period of the project the FIDT have assisted SMSG with data collection, critter and fish collection, photographs, transects and inter-tidal surveys. Not only are the team helping collect data but they have also been getting their hands dirty, literally, by helping to process fish specimens, with Simon Plummer, the diving supervisor, measuring, weighing and dissecting fish and to remove the otoliths which are used to tell how old the fish is.

[caption id="attachment_455" align="aligncenter" width="584"] Simon Plummer (centre) with Drs Vlad Laptikhovsky and Judith Brown

The FIDT have enjoyed discussing their findings with the expedition Drs and Professors. This has made the diving and the experience of working, helping and supporting the project a far more broadening experience. It has also made the team even more mindful of the diverse and balanced marine ecology of the Ascension Islands.

[caption id="attachment_456" align="aligncenter" width="584"] FIDT member Simon Browning demonstrate black triggerfish capture techniques, using a bread basket, while Vlad Laptikhovsky and Simon Plummer look on.

[caption id="attachment_409" align="aligncenter" width="584"] The Ascension Island crab, Grapsus adscensionis.
Image: W Dimmlich

Nicknamed “Sally lightfoot” by sailors, there are two crabs of the genus Grapsus which have chosen the tropical eastern parts of oceans as their habitat. One of them, G. grapsus, settled along the Pacific coasts of America and made the long jump to Galapagos where the local population impressed Charles Darwin with their agility and capacity to avoid sailor hands. Apart from their impressive acceleration from a standing start, another notable characteristic is that they perform a valuable service to marine iguanas by removing ticks from them, similar to the role played by cleaner shrimps with fish.

[caption id="attachment_416" align="aligncenter" width="584"] The crabs can be seen clustering on the lava platforms in all sizes.
Image: W Dimmlich

The second species, G. adscensionis, inhabits the east Atlantic and in the historical past also made a long jump - to Ascension and St. Helena islands. The crab inhabits the splash zone though at night they ramble the sand dunes of the island as some ten-legged hosts. Nothing is known about their biology on this spearhead of their westward expansion of the species range (do they target South America as much as Spanish conquistadors?). In respect to feeding habits, for example they were seen to be feeding on a scientist's sandwich as well as witnessed kidnapping a baby green turtle. It is not exactly what Grapsus do with reptiles on Galapagos… However, neither sandwiches or turtle hatchlings could hardly be considered as a staple throughout the year.

[caption id="attachment_408" align="aligncenter" width="584"] Steve Brown and Vlad Laptikhovksy attempting to catch the very speedy subjects of the investigation.
Image: W Dimmlich

Steve Brown challenged the project to study the reproductive biology of the species, particularly size at maturation and fecundity on Ascension Island. The idea is to compare this information with available data on continental populations of the species, as well as with those on G. grapsus from both the American continent and Galapagos (which are pretty much a "Pacific Ascension") and to reveal how this harsh islands’ environment impacted reproductive features. Because of our intensive diving schedule, the sampling usually occurs every day while tanks are being filled. It takes about two minutes for a crab to be caught, measured all across, sexed, cursed for its strong claws and scratchy pointed legs and released back to the shoreline. Some females however are deprived of their broods that would be further investigated in the lab.

[caption id="attachment_414" align="aligncenter" width="584"] Measuring carapace dimensions of G. adscensionis, while keeping careful hold of the claws!
Image: W Dimmlich

Contributed by V. Laptikhovsky

Nothing vulgar about Octopus vulgaris!

The common octopus (Octopus vulgaris) received its unprepossessing name because it is supposedly common everywhere. It occurs in every ocean where the water is warm enough for exploration by wetsuited divers. The vulgar octopus hates cold waters and established itself worldwide between latitudes 50 of both North and South. However, the well established point of view that this species is a cosmopolitan citizen began to be shaken because, one by one, different populations were found to be different species.

The common octopus from Ascension Island was already supposed to be a distinct creature, and was once upon a time described as Octopus occidentalis. However, later on this name was considered to be a junior synonym of Octopus vulgaris though it is still likely to be a new species. The Ascension octopus could be thought of as underscribed … or more precisely, under-described.

[caption id="attachment_337" align="aligncenter" width="584"] The octopus resident in his den during the day. Nicknamed "Roger" by the team, we'll be visiting regularly to see what scraps he leaves outside.

Virtually nothing is known about the biology of this octopus, and because of this when Dr Jude Brown discovered a den during one of her dives surveys, we decided to have a closer look at the behaviour of this animal, and to include repeated return visits to the den when possible. Whenever we arrived at its shelter at each day we would find the creature sitting inside and watching us with its wise and wrinkled eyes of an elderly gentleman.

The den itself consisted of a few random volcanic pebbles scattered around and was a perfect disguise for a predatory ambusher. Leftovers of the day’s food betrayed the fact that this soft bodied animal used to leave its den at night, invisible to predators. With many hungry fish lurking around any camouflage would be useful.

During the first week of observation its daily prey consisted of one to three bivalve molluscs Americardia media, sometimes spiced by some meaty cowrie  Luria lurida. No fish, no crustaceans. Our octopus appears to have a very particular diet but we shall see whether it will change its food preferences during the forthcoming two weeks.

- Post supplied by Dr Vladimir Laptikhovsky.