Life And Death in the Plankton: Larval Mortality and Adaptation
Marine animals typically release tremendous numbers of larvae or gametes into the surrounding water column. Conventional wisdom purports that few larvae survive long enough to settle into adult habitats except during years when favorable planktonic conditions prevail. This chapter reviews estimated mortality rates, potential sources of larval mortality, and possible adaptations that reduce mortality. Sources of larval mortality that are encountered during larval life will be treated sequentially from release of gametes and larvae into the water column to reinvasion of adult habitats. Although fertilization by most marine invertebrates occurs in the water column, many other marine animals fertilize eggs internally and release free-swimming larvae. Starvation also stresses larvae and may decrease survival or increase development times. Adaptation to constant physical factors, such as gravity, should be least problematic and contribute least to larval mortality. High mortality resulting from “chaotic” planktonic processes implies that larval and adult stages are decoupled.