Macrobenthic community structure of the northeast Indian shelf, Bay of Bengal

Abstract

Knowledge of tropical benthic fauna is limited. Two cruises (January 1999 and July 2000) were made covering 24 stations along 5 transects between 16° and 20°N in shelf waters (depth 30 to 200 m) in the Bay of Bengal off northeast India. Altogether 62 infaunal samples (Smith-McIntyre grab 0.1 m 2) and 32 epibenthos (through a naturalist dredge 40 x 40 cm) were collected that revealed 169 species representing 15 diverse groups. Gastropods, bivalves, polychaetes and decapods constituted the bulk of the population. Polychaetes were by far the most dominant group (64.98 %) among the infauna followed by amphipods (25.23 %), which were numerically more abundant (mean 1080 ± 292 ind. m-2) at 51 to 75 m than at greater depths (345 ± 185 ind. m-2 at > 150 m). Biomass was higher (wet weight 6.94 ± 4.8 g m-2) at 51 to 75 m than at 101 to 150 m (1.08 ± 1.23 g m-2). There was a preponderance of decapods (26 %), gastropods (20.7 %), bivalves (8.3 %) and several (28.3 %) large-sized polychaetes (e.g. Diopatra neapolitana, Eunice indica, Pista sp.) in the dredge hauls (mean abundance 42 ± 8 ind. haul-1). Infaunal diversity (Shannon-Wiener H′) was higher (H′: 2.455 ± 0.18) at 51 to 75 m relative to the sites at > 150 m depth (H′: 0.981 ± 0.17). Multivariate analyses were used to define assemblages named after the most important (determining) taxon. Three epifaunal associations could be recognised off the northeast Indian shelf, namely the Charybdis Assemblage (30 to 50 m), the Liagore Assemblage (51 to 75 m), and the Amygdalum watsoni-Tibia delicatula Assemblage (> 100 m). Infaunal associations consisted of Ampelisca (30 to 75 m), Nephtys (76 to 100 m) and Cossura coasta (> 100 m). Canonical correspondence analysis (CCA) showed that depth, sand, sediment organic matter and sediment mean size influenced epifauna distribution, whereas for infauna, salinity, temperature, mean particle diameter, sand and depth proved important. © Inter-Research 2007.