Does benthic-pelagic coupling control male-female couplings on the deep-sea bed?

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Craig Young
Harbor Branch Oceanographic Institution

Monday, October 26, 1998
3:00 p.m.—Pacific Forum

Among deep-sea megafaunal invertebrates, there is a surprising and consistent correlation between mode of development and timing of reproduction. At a population level, species that produce yolky eggs and non-feeding larvae tend to reproduce throughout the year, whereas species that produce small eggs and feeding larvae reproduce during discrete and predictable seasons. Both kinds of organisms must synchronize gametogenesis and spawning on appropriate time scales to assure reproductive success. The mechanisms by which reproductive processes are synchronized remain unknown for virtually all deep-sea organisms, though detrital falls have been repeatedly implicated as zeitgebers that could entrain seasonal cycles of gametogenesis. In echinoderms, social behaviors play a clear role in assuring spatial concordance during the spawning season. Using an integrated program of laboratory and field experiments, my laboratory is investigating the potential links between detrital falls and reproduction in deep-sea echinoderms and other benthic invertebrates. Reproductive output is shown to depend on both food quality and quantity, though experimental evidence that food falls can control the timing of reproduction remains equivocal.

It has been hypothesized that some deep-sea species spawn seasonally to assure optimal feeding conditions for their larvae. This principle, known as "Crisp's Rule," has good correlative and experimental support in shallow water, but not for deep-sea invertebrates. Crisp's Rule should apply to deep-sea animals only if their larvae require phytoplankton as food and if they can migrate to depths where phytoplankton is sufficiently abundant. Because deep-sea larvae are difficult to find in plankton samples, we have investigated the likelihood of ontogenetic larval migrations by studying the dietary requirements, energetics, physiology, and behavior of cultured deep-sea larvae in vitro and in situ. If it can be shown that larvae migrate to the euphotic zone, then Crisp's Rule is a viable "ultimate" explanation for the evolution of seasonal reproduction in deep-sea animals. Moreover, from an oceanographic standpoint, migrating larvae and buoyant embryos may represent an important mechanism of reverse coupling between the deep-sea floor and the euphotic zone.

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