Journal of the Marine Biological Association of India

Ichthyofauna of the intertidal reef flats of Minicoy Atoll, Lakshadweep : An analysis of its structure, relative abundance and food

Volume 34 Issue 1&2

C. S. Gopinatha Pillai, G. Gopakumar and Madan Mohan

Abstract

Long term observations, based on day samplings and analysis at Minicoy atoll in Lakshadweep have yielded substantial information on the structure, composition, relative numerical and biomass abundance as well as food of the ichthyofauna inhabiting the windward and leeward sides of the atoll. The leeward reef flat has a greater fish biomass compared to the windward reef lat, the average total weight per one hour sampling with a cast net being 3839.4 gm and 1179.4 gm respectively. The difference in the surface morphology between the windward and leeward sides is found to influence the fish biomass. The leeward side at Minicoy is strewn with loose boulders with profuse algal growth and associated invertebrates, while the windward reef flat is mostly flat and cemented and there are very few loose coral boulders. The loose boulders harbour ample plant and animal food to the fishes as well as dwelling crevices on the leeward side. The extensive sea grass beds along the lagoon shore may also serve as excellent forage ground for lagoon fishes and lagoon reef fishes in the leeward side.

Out of the 21 families and 190 species of resident and migratory fishes hitherto recorded from the reefs of Minicoy, 69 species belonging to 17 families are commonly found in the present samples. Very little qualitative difference in the faunal composition was observed between the windward and leeward sides. The percentage of incidence of different species in the samples varied from 6 to 100%. Bulk of the species occurring belong to families Acanthuridae, Holocentridae, Pomacentridae, Serranidae, Chaetodontidae, KuWidae, Labridae and Callyodontidae. Acanthurus triostegus triostegus. is the richest forming 49% of the total catch. Others in the order of abundance of biomass include Epinephelus hexagonatus (9.6%), Holocentrus lacteoguttatus (8.7%), Abudefduf glaucus (5.1%), Epinephelus caeruleopunctatus (4.1%), Acanthurus lineatus (3.6%), Epinephelus merra (2.9%), Abudefduf cingulum (2.2%), A. septernfasdatus (1.8%), A. zomtus (1.1%), A. sordidus (1.0%) and the rest minor components.

About 60% of the reef flat fishes are carnivorous feeding on benthic invertebrates associated with dead and live coral boulders which include alphids, young crabs, ascidians, bryozoans and gammarid amphipods ; 30% omnivorous and the rest 10% herbivorous. Strictly plankto-phagous forms are not found — a conspicuous contrast to lagoon fishes.

The present study also indicates a more or less stable state in the ichthyofaunal assemblage of Minicoy reef flats as judgjd from the earlier literature and present samplings. In general when large areas are sampled over a long span of time, stability is the norm. But sampling at short intervals on a restricted area displays diversity due to migration or recruitment in reef fish fauna.

Date : 31-10-1992