Intertidal habitats and decapod faunal assemblages (Crustacea: Decapoda) of Socotra Island, Republic of Yemen

Abstract

The Socotra Archipelago, situated in the north-western part of the Indian Ocean at the entrance of the Gulf of Aden, has a unique zoogeographical position, as the transition between the Arabian and Red Seas and East African shores. The Socotran marine environment, however, is as yet poorly studied, with only sparse and incomplete reference to the field of crustaceans. The current work presents results from a survey of the intertidal decapod assemblages of Socotra Island conducted in spring 1999.

The information from 185 sites sampled around the island is summarized in a map with short descriptions of representative intertidal habitats, their relative area and distribution. Both rocky shores and cobble beaches have the largest diversity of decapods. Sandy beaches are dominated mainly by Ocypode saratan and Coenobita scaevola, whilst rocky shores are dominated by Grapsus albolineatus, G. tenuicrustatus, Plagusia tuberculata, Pachygrapsus minutus, Metopograpsus messor and Eriphia smithii. In cobble beaches, Pseudozius caystrus, Leptodius exaratus, Xanthias sinensis, Clibanarius signatus and Clibanarius virescens are the most common species. Cardisoma carnifex and Uca inversa are common bordering mud flats and coastal lagoons. As fishing pressure is low, mud flats surrounding wadis and coastal lagoons host small undisturbed populations of Scylla serrata and Fenneropenaeus indicus. There is only a reduced number of mangrove trees and area of mangrove, most of which is already destroyed or under severe human and environmental pressure. The largest and most representative stand has an unusual structure: species diversity is strikingly low, it is disconnected from the sea by a sand bar or dune, and is completely dry.

Interesting zoogeographical findings are detailed, and a list of intertidal decapod fauna, relating each species to its common habitat is presented. This list is compared with previous studies, and other intertidal decapod assemblages from the Arabian Gulf, Red Sea and East Africa.