CORAL SEA ATOLL LAGOONS - CLOSED NURSERIES FOR THE LARVAE OF A FEW CORAL-REEF FISHES

Lagoons of two western Coral Sea atolls (Osprey and Holmes Reefs) were sampled with oblique bongo-net tows and neuston tows a total of three times over 3 years. Equivalent samples were taken in the ocean nearby . Concentrations of oceanic larvae in the lagoons were 13-14% of conce ntrations in the ocean, but oceanic taxa constituted less than 1% of t he larvae captured in the lagoons. Concentrations (number.m-3) and abu ndances (number.m-2) of shorefish larvae were 4-10 times higher in the lagoon than in the ocean, but larvae of more shorefish taxa were foun d in the ocean. In the lagoons catches were heavily dominated by larva e of apogonids, clupeids, gobiids, pomacentrids and schindleriids. Tax onomic composition in the lagoons varied little. Based on presence/abs ence, and sizes of the larvae captured, only 33 taxa (of 15 families) complete or probably complete their pelagic larval period within these atoll lagoons. These include (number of species where larvae were ide ntified below family level): Apogonidae (9), Atherinidae (2), Belonida e (1), Blenniidae (4), Bythitidae (1), Clupeidae (1), Gobiidae, Hemira mphidae, Lutjanidae (1), Microdesmidae (1), Nemipteridae (1), Pempheri didae (1), Pomacentridae (3), Pseudochromidae (4), Schindleriidae (1), Tripterygiidae. In contrast, many reef fishes (from 31 families) were found not to complete their pelagic phase in the lagoons. Thus, only a few fish taxa are capable of completing their life cycles in atoll l agoons, but larvae of most of those that do are abundant. These taxa h ave predominately closed populations, demonstrating that, contrary to the current paradigm, not all coral reef fishes live in predominately open populations. Although these taxa have closed lagoonal populations over ecological time scales, the wide distribution of the taxa and th e ephemeral nature of atoll lagoons make it unlikely they have closed populations over evolutionary time scales.