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 contribute 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 from radiotracer feeding studies, with refractory C-14 mangrove lignocellulose as the food source, indicated that juvenile P. merguiensis from tidal creeks assimilated mangrove carbon with an effciency of 13.4%. This did not differ significantly (P = 0.05) from the assimilation efficiencies of juvenile and adult P. sculptilis living offshore (10.0 and 10.9%, respectively); these values were significantly higher (P < 0.001) than for adult P. merguiensis (2.1%). Thus, the differential contribution of mangrove material to the nutrition of prawns in the tidal creeks and offshore was not related to differences in the prawn's ability to utilize detritus. Instead, our analysis of C stable isotopes in sediments indicated that mangrove detritus was generally more abundant within the tidal creeks than offshore. Juvenile prawns in the tidal creeks may also utilize mangrove material indirectly by feeding on small detritivorous invertebrates. Stable isotope analyses suggest that benthic microalgae constitute the other major dietary component for prawns living in tidal creeks, Prawns offshore were utilizing mainly phytoplankton-based material.