Generation Lengths of Some Temperate Marine Copepods: Estimation, Prediction, and Implications

Abstract

Only copepodids should be used to trace synchronous cohorts from relative abundance of stages, and only long-lived adults correctly signal new generations from size changes. From extensive published data from Loch Striven, Scotland [UK], life cycles are thus detailed for Pseudocalanus minutus, Microcalanus pygmaeus, Calanus finmarchicus, Centropages hamatus, Temora longicornis, Acartia clausi and Oithona similis. Generation lengths are also estimated for all but M. pygmaeus from temperatures in nature and from laboratory data on food-satiated development. For stage durations (D) at various temperatures (T), Belehradek''s temperature function D = a(T-.alpha.)-b is used. Temperature response can be about the same throughout a species range. With b fixed, .alpha. within a species can be the same for older stages as for embryonic duration, which can thus be used to estimate a for generation length even from a laboratory example at a single temperature. If food-satiated durations are available only for some stages, it can be assumed that other stages are similar (isochronal development). Food-satiated generation lengths predicted thus from the laboratory match those inferred from the Loch Striven samples. Trophic studies may be less revealing than further work on the "intrinsic" determinants of copepod performance. Competition for food should not be assumed in studies of niches and community dynamics of marine copepods.