Ascension : Mysterious Seashells of Ascension Island - by Felix Lorenz
Submitted by The Islander (Gavin Yon) 03.02.2005 (Article Archived on 17.02.2005)
Isolate islands often have a unique fauna and flora. Think of the Dodo from Mauritius Island, the Komodo-lizard and the finches of Galapagos.
Isolate islands often have a unique fauna and flora. Think of the Dodo from Mauritius Island, the Komodo-lizard and the finches of Galapagos. When a new island rises from the sea, caused by volcanic activities or earthquakes, it is uninhabited: there are no plants, no coral reefs, and no animals. Then, the barren land becomes populated by plants whose seeds are drifted ashore by the wind or the ocean, by insects, birds and eventually reptiles whose eggs can drift long distances with wood. These animals and plants start to thrive and multiply, and after a short while, adapt to the specific habitats of the new island. They evolve and form new species-communities endemic (restricted in distribution) to their little world. Such processes take millions of years. Once man enters the islands, also rats, cats, dogs, goats, sheep, etc. will eventually be set out. The local fauna is not adapted to these "alien invaders" and mostly becomes extinct. It was the fate of the Dodo (which became extinct because monkeys ate their eggs) and many other "islanders", while those that survived did so only because the managed to find a little nitche not accessible to the "aliens". A good reading about the subject of Island Biogeography is a book by David
Quammen called "The Song of the Dodo" Scribner, New York.
In the sea, the newly formed shallow water habitats around young islands become populated by the free-swimming larvae of marine animals which subsequently become the food of fish. Also marine habitats of islands may bear endemic species, but contrary to the situation to the land, these communities are not endangered directly by the arrival of man and his lifestock. As long as their habitats remain intact, collecting them for food will not wipe them out. As a marine biologist specializing in the study of cowrie-shells (Cypraeidae) my interest is mainly focussed on the fauna of small isolate islands, as these often have peculiar and unique populations of cowries found nowhere else in the world. The islands of St. Helena and Ascension bear two mysterious populations which are of particular interest. One is small brown and gray spotted type, the other is a buish shell with black dots at its ends. The small brown one seems to have reached Ascension from the Caribbean where a close relative is found, whereas the larger one resembles a West African species. So far it is unknown whether these "islanders" have developed into distinct species or just varieties of their mainland relatives. It is also unknown whether those shells from St. Helena are really the same as those from Ascension. The aim of a study project is to verify the status of these creatures. May be Ascension and St. Helena have their own species of cowry-shells!? A sufficient amount of shells and samples of their animals for DNA analysis will help to clarify this. So far, few specimens from Ascension island are available, and I have no animal material at all. Herewith I would like to ask divers, snorklers and beachwalkers who are familiar with these shells to contact me and help me gather the material needed. Your efforts will be rewarded, and may be some time soon I can report about the findings.