Aggregation spawning: Biological aspects of the early life history

Abstract

Most reef fishes have bipartite life histories, separate pelagic-oceanic (egg/larvae) and benthic (juvenile/adult) periods. The several-week pelagic period has early planktonic (egg, yolk sac and preflexion larva) and later nektonic components (post-flexion larva to settlement); the plankton-nekton transition timing is variable. For aggregating species, larvae are weak swimmers early in life, but late stages are often strong swimmers able to perhaps influence their settlement locations. No obvious differences were found between larval stages of aggregating and non-aggregating species and both types of spawning are found within single families, and even within a species. There are no egg types, morphologies, feeding strategies or special structures exclusive to aggregating species. Initial dispersal is determined by location and time of spawning. Pelagic eggs are buoyant, keeping them in near-surface waters and away from benthic predators. The larvae go through a series of stages (egg, yolk sac larvae, pre- and post-flexion larvae, pelagic juvenile), becoming larger and more capable over time. Critical periods occur and can cause major mortality of a cohort. Ocean conditions during the early egg and yolk sac stage are critical to survival followed by initiation of feeding as a second critical event. During pelagic life larvae must survive in open water, find appropriate food as larvae and avoid predators. Cohorts from aggregations can recruit as a large pulse, but other fishes may also have such pulses. The mass spawnings of reef invertebrates, such as stony corals, are generally not comparable to those of fishes, while crustaceans (spiny lobsters, marine crabs, terrestrial crabs) have some similarities. There is a need for fisheries oceanography research on aggregation spawning, as well as more work on laboratory culture. The question of potential maternal benefits to larvae needs careful attention.