RELATIVE IMPORTANCE OF BENTHIC MICROALGAE, PHYTOPLANKTON, AND MANGROVES AS SOURCES OF NUTRITION FOR PENAEID PRAWNS AND OTHER COASTAL INVERTEBRATES FROM MALAYSIA

Carbon, sulfur, and nitrogen stable isotope ratio techniques were used in 1989 and 1990 to evaluate the relative importance of algae and of mangrove detritus in the nutrition of two penaeid prawn species on the west coast of Peninsular Malaysia. Mangrove detritus was found to con tribute to the nutrition of juvenile Penaeus merguiensis de Man living within tidal creeks, but not to adult P. merguiensis and juvenile and adult Parapenaeopsis sculptilis (Heller) captured offshore. Results f rom radiotracer feeding studies, with refractory C-14 mangrove lignoce llulose as the food source, indicated that juvenile P. merguiensis fro m tidal creeks assimilated mangrove carbon with an effciency of 13.4%. This did not differ significantly (P = 0.05) from the assimilation ef ficiencies of juvenile and adult P. sculptilis living offshore (10.0 a nd 10.9%, respectively); these values were significantly higher (P < 0 .001) than for adult P. merguiensis (2.1%). Thus, the differential con tribution of mangrove material to the nutrition of prawns in the tidal creeks and offshore was not related to differences in the prawn's abi lity to utilize detritus. Instead, our analysis of C stable isotopes i n sediments indicated that mangrove detritus was generally more abunda nt within the tidal creeks than offshore. Juvenile prawns in the tidal creeks may also utilize mangrove material indirectly by feeding on sm all detritivorous invertebrates. Stable isotope analyses suggest that benthic microalgae constitute the other major dietary component for pr awns living in tidal creeks, Prawns offshore were utilizing mainly phy toplankton-based material.