RECRUITMENT OF JUVENILE MARINE FISHES TO SEAGRASS HABITAT IN A TEMPERATE AUSTRALIAN ESTUARY

We investigated the relationship between distance from the ocean and t he recruitment of ocean-spawned juvenile fish to seagrass shallows wit hin marine dominated Lake Macquarie, a coastal barrier lagoon in South east Aus tralia. Samples were taken by seine net every 6 wk between Ju ne 1986 and June 1987, at 20 sites established at various distances fr om the entrance channel. The fish fauna was diverse: 80 species from 3 9 families were caught, with the Gobiidae, Monacanthidae, Syngnathidae , Tetraodontidae, Mugilidae, Atherinidae, Clupeidae, Mullidae, Sparida e, and Blenniidae being web represented. Ambassis jacksoniensis, Ather inomorus ogilbyi, and Gerres subfasciatus accounted for 46% of all ind ividuals. Thirty-two species were classified as ocean spawners, 38 as lagoon spawners, and 10 as unknown in terms of spawning area. Newly se ttled juveniles of ocean spawners were concentrated near the lagoon's entrance, where most recruited in spring. This pattern occurred in the absence of a salinity gradient: distance from the ocean coupled with weak internal water circulation appears to limit larval distribution a nd hence juvenile recruitment. Small juveniles of Rhabdosargus sarba w ere sufficiently abundant for their subsequent dispersal to be directl y traced. On the basis of results for this species, and indirect evide nce of dispersal for several others, it is suggested that ocean-spawne d juveniles, after settling near the entrance, gradually disperse as t hey grow and change their habitat. Thus, further from the entrance, th eir recruitment to seagrass shallows is later, at larger sizes, and in smaller numbers. Newly settled juveniles of lagoon spawners, however, were widely distributed within the lagoon. The optimal recruitment of ocean-spawned juveniles to similar coastal lagoons may depend on suit able habitat being available near the entrance.