Ascension’s underwater wonders revealed

Montage showing a big wave breaking over rocks at the top of the picture, and teeming fish underwater at the bottom of the picture

Ascension beneath the waves: Montage by Simon Pipe. All pictures courtesy of the Shallow Marine Survey Group

The thundering Atlantic rollers around Ascension Island make the sea appear hostile and forbidding. But beneath those mighty waves, a very different world is to found: wild and exciting, and home to a dazzling array of sea creatures.

Now a scientific expedition force from the Falklands has brought out the full spectacle of it with new clarity, as well as yielding records of creatures never before seen in the island’s waters.

colourful underwater sceneClick the pic to see a gallery of Ascension’s sea life

The scientists’ underwater photographs present aspects of Ascension that contrast sharply with the tortured lava fields and volcanic rubble above the shoreline. 

The expedition team’s formal name doesn’t quite convey the extent of its adventurous ambition. The Shallow Marine Surveys Group was set up by sealife experts and divers based in Stanley, to explore the little-known waters around the islands of the South Atlantic and the Southern Ocean.

With their local knowledge, island-based divers Drew Avery and Caz Yon became valued members of the team, along with Stedson Stroud and his Saint colleagues in the conservation department.

Earlier in 2012 the scientists carried out the most extensive survey for nearly 90 years of the seas around snow-covered South Georgia. They were accompanied by playful fur seals as they catalogued giant sea spiders, many-hued sea slugs, and starfish.

In August and September 2012, they brought their cameras and experiments to warmer waters. 

A group of people on the foreshore

Stedson Stroud of Ascension Conservation (in green) briefs expedition members

For most people who pass through Ascension, the nearest they come to an encounter with the riches of its seas is watching a big fish being filleted on the pierhead in Georgetown – or the hawksbill turtles that cluster there at night to feed on the discarded scraps.

The big predators are attracted by smaller fish that thrive in Ascension’s thrashing waters: the result of an unusual mid-ocean “collision” between two great equatorial currents. They combine with the rising mass of the island to create turbulent eddies and gyres. 

Underwater, all is excitement for the passing diver-cum-scientist.

As team members arrived in Georgetown from the Falklands and the UK, a laboratory was set up in the conservation offices, to contribute to an international experiment on the effects of global warming on sea life.

Expedition members scoured the island for containers in which to carry sea water to top up the portable fish tanks each day. They even hunted through rubbish tips before a solution was found.

The scientists also set up “artificial sea beds” – flat squares of plastic, secured underwater – to observe their colonisation by larvae. The problem of stopping them being washed away by Ascension’s powerful rollers was solved by strapping some of them to a shipwreck.

Close-up of a turtle's head and front paddle, with giraffe-like markings

A hook near the eye of a hawksbill turtle could not be safely removed

Local divers will visit the plates every six to eight weeks, and take photographs of the creatures on them. These will then by identified by an expert in the UK, and the results compared with other findings around the world.

Another experiment seeks to solve the mystery of where the island’s hawksbill turtles come from – and go to breed. They gather round the pier at Georgetown to feed, attracted by the lights and fish scraps discarded by anglers.

On the second night of trying, the scientists managed to land the biggest hawksbill ever recorded on the island, in order to fit it with a tracker device, to see where it travels across the Atlantic.

DNA samples were also taken by Sam and Nicola Weber of Ascension Island Conservation.

The creature had a fish hook through its head but the scientists were unable to remove it because it passed too close to its eye. They hoped it would rust and work free – along with a plastic bag that was seen to have snagged on it the next day.

The scientists also examined Sally Lightfoot crabs to see how they compare with others around the world, including on the Galapagos Islands of the Pacific Ocean.

“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,” wrote Dr Wetjens Dimmlich in the expedition blog. 

Expedition members gave talks, including at Two Boats School

Children at Two Boats School shared tips on how to remove an unidentified shrimp from its burrow, when two of the scientists gave a talk. Other talks were given during the visit.

Several species were recorded in the island’s waters for the first time, as Wetjens wrote in his online journal: “With so many divers in the water each day, it is no surprise that new records for Ascension Island are pouring in almost daily.”

They included:

  • the tiny dragonet Callionymus bairdi, “which lives on gravel and rather looks like a piece of gravel”
  • a tube anemone, Isarachnanthus maderensis, which had never been recorded on Ascension but can now be seen at night in great numbers
  • the little sea hare, Dolabrifera dolabrifera
  • the sea anemone, Telmatactis cricoides, which was known from St Helena but not previously from Ascension

They have been added to a checklist of Ascension fish compiled in 1980 and added to since by island residents and visitors Jimmy Young, and John and Jane Bingeman, among others.

A highlight for the researchers on Ascension was being taken to rock pools to see creatures that could be “the most vulnerable species on the planet”.

Hard-to-reach rock pools are home to rare and vulnerable shrimps

Saints Jolene Sim and Natasha Williams led two of the scientists on a half-hour trek across a lava field to reach Shelly Bay, wrote Wetjens.

“Rock pools are found here, separated from the sea by 100m of lava platform but replenished with seawater through underground fissures. These pools appear to contain ecosystems probably found nowhere else.

“Of particular interest are two unique species of shrimp (Procaris ascensionis and Typhlatya rogersi) living in these interconnected network of rock pools.It may be that the shrimp are the most vulnerable species on the planet, found only in these pools and only on Ascension Island – completely protected, to the extent that we are only permitted to look but not touch.”

Other distinct species of algal and invertebrate life were spotted in the pools.

The research team members have now dispersed around the globe.  In a final post on the expedition website, Wetjens writes:

bright yellow shrimp

A shrimp at Shelly Pool

“Although all the team have now departed Ascension, loaded down with samples and countless photographs, the work will continue long after our stay on the island.

“With an entire upcoming edition of the Journal of the Marine Biological Association of the UK  to be dedicated to the results of this expedition, there is a tremendous amount of work to be done in order to meet publishing deadlines.

“With this ahead of us, the Shallow Marine Surveys Group would like to take this opportunity to extend our deepest gratitude and appreciation to the Ascension Island Government and Administrator, Colin Wells, for their enthusiastic support and keen interest in this ambitious undertaking.

“Additionally we would also particularly like to thank Ascension Island Conservation Department for making their facilities available to us, despite the chaos and interruptions we brought to their daily lives.”

  • The Ascension expedition was backed by the Falkland Island Dive Team, a group of military and civilian enthusiasts who gave up their time to provide logistical support – and dissect fish.
  • A future expedition to St Helena is possible, offering the prospect of finding out about fish such as the island’s unique wrasse and dragonet, about which little is known.

SEE ALSO:
Picture gallery: underwater Ascension

LINKS:
Expedition blog
Team profile: Stedson Stroud
Team profile: Jolene Sim
Team profile: Caz Yon
Team profile: Drew Avery
Journal of the Marine Biological Association of the UK

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