Reproductive Strategies of Marine Benthic Invertebrates: A Settlement-Timing Hypothesis

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Abstract
Evidence for nudibranch mollusks is presented which shows a clear relationship between egg-size and developmental mode (planktotrophic, lecithotrophic and direct development), egg-size and development time and thereby larval strategy and development time. Egg-to-juvenile periods differ significantly according to strategy, with lecithotrophic pelagic development being the briefest and planktotrophic development the longest. Support of the lecithotrophic strategy necessitates a greater absolute calorific threshold on the part of the adult than the planktotrophic strategy. It is proposed that for a given species there is an optimal time to spawn (when standing crop is at a peak) and an optimal time for the larvae to settle. While accepting that in selecting for a particular strategy a compromise must be struck between such mediating factors as total and relative energy demand on the adult, egg numbers, individual probabilities of larval survival, and especially dispersal requirements, the settlement-timing hypothesis may be instrumental in resolving some paradoxical situations. For example, a species in which 2 or more alternative strategies appear supportable, in energetic terms, may select that strategy which appropriately bridges the period between the optimal time to spawn and to settle.