Macrobenthic functional feeding groups in a microtidal monsoonal estuary (Kodungallur–Azhikode estuary, India)

The functional feeding groups of macrobenthos in the Kodungallur–Azhikode estuary were studied on a monthly basis for a two year period (2009–2011). The main aim of the study was to understand the distribution pattern of macrobenthic functional feeding groups and their relationship to environmental drivers in the estuary. Malacostracan crustaceans dominated the system (60%) by numerical density, while molluscs contributed significantly to macrobenthic biomass (63%). Many species exploit the same class of resources within an assemblage of macrofaunal groups. The suspension feeding corophiid amphipod Americorophium triaeonyx was the most represented macrofaunal species. Other dominant macrofaunal feeding groups were the suspension feeding hydroid colonies of Obelia bidentata, surface deposit feeding polychaetes Prionospio cirrifera, suspension feeding mussels Arcuatula senhousia, carnivorous isopods Cirolana fluviatilis and sub-surface deposit feeding polychaetes Capitella sp. The sampling stations were compared using taxonomic distinctness (AvTD), and variations in taxonomic distinctness (VarTD), the values of AvTD and VarTD for all stations during the entire monthly survey fell within the confidence intervals of probability funnel (95%, p<0.05). However, a significant variation was noticed in the values between stations (AvTD: F (6,161) = 3.105, p = 0.007; VarTD: F (6,161) = 2.489, p = 0.025). The abundance biomass curves were plotted separately for each site as well as combined for the entire estuary. The relatively high negative trend was observed in the station 5 (W = −0.139) which indicates potential for the relatively high disturbance among all other stations. However, the W-value for the entire estuary was -0.079, which depicted moderate disturbance.