SMSG Blog

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

Those of you who follow this blog may have read about the settlement panels; squares of plastic that are placed underwater and which allow us to follow how animals settle and grow on the rocks. There are two problems that have to be overcome when deploying anything in the seas around Ascension Island.

Firstly, the panels need to be secured against the affects of the famous Ascension rollers. We came up with several ideas but in the end we decided that no amount of ballast was going to secure the plates against the swell. A colleague of mine at the British Antarctic Survey has tried to use similar panels, held down by ballast, but he lost the lot. We therefore decided that we would strap the plates to objects that had been there for a long, long time.

[caption id="attachment_539" align="aligncenter" width="584"] Stevie Cartwright attaching plates to an old undersea cable.

Secondly, very little grows on the surface of rocks at Ascension as the black trigger fish will eat almost anything that is exposed. The panels, therefore, need to be fixed to a solid surface that would stop trigger fish getting access to the underside of the plates.

[caption id="attachment_541" align="aligncenter" width="584"] These plates are attached to the wreck of the Derby, which sank in 1929, and hopefully will stay in place for at least another year!

We chose to position the first of the three plates on one of the cables in Mitchell’s Bay, the second on the wreck of the Derby and the final plates just off Wigan pier. Stevie Cartwright was in charge of fixing the plates using a selection of cable ties and straps. He also cable tied one temperature logger to each of the plates and a tag that lets anyone who finds them know that these are scientific experiments and should not be disturbed.

[caption id="attachment_536" align="aligncenter" width="584"] Panel in place and waiting for a new community of sealife to move in.

The key to the success of this project is the willingness of local divers Caz, Sam and Nik to visit the panels every 6-8 weeks and take high resolution images of the developing communities. They will post the pictures back to Dr David Barnes in the UK who will identify each of the animals and follow how the panels are colonised through time. This long term project will help us understand the time of year when animals spawn at Ascension and the data loggers also give us one of the first high resolution records of how shallow water sea temperature varies around the Island. These two vital pieces of information can be compared with other parts of the world and will allow us to better manage the Island's marine biodiversity.

We appreciate any of you Ascension divers and snorkellers letting us know if you see any damage to the plates.

- Submitted by Dr Simon Morley