Digestion in relation to feeding strategies exhibited by crustacean larvae

Decapod crustaceans have adopted a full range of reproductive strategies fr om the release of large numbers of small eggs (Penaeoidea) to the release o f relatively low numbers of large advanced larvae (Nephropidae). As larval size determines trophic position in planktonic food webs, all food sources from phyto- to zooplankton are exploited, with many species changing trophi c level during ontogenetic development. Comparative studies on digestive en zymes, levels of activity and changes during ontogeny, together with measur ements of gastroevacuation rates and food energy values appear to reveal a general pattern. While herbivorous decapod larvae adapt to low food energy values with high enzyme activity levels, rapid food turnover and low assimi lation efficiency, carnivorous larvae exhibit low levels of enzyme activity but compensate by extending retention time of high-energy food to maximise assimilation efficiency. New studies on digestive enzyme levels during dev elopment in the penaeid Litopenaeus vannamei, the caridean Lysmata debelius and the cirriped Elminius modestus, appear to agree with previous observat ions. (C) 2001 Elsevier Science Inc. All rights reserved.