Monitoring Larval Fluxes through the Surf Zones of Australian Coral Reefs

Abstract

The first successful trials with stationary 'crest' nets to monitor the nocturnal fluxes of larval fish crossing reef margins in both eastern and western Australia are described. Lengthy deployments were possible on Ningaloo Reef, north-western Australia, because that system is topographically suitable: i.e. a fringing barrier reef where surf produces a constant flow into a coastal lagoon. Sampling on 85 nights between October 1994 and March 1995 revealed a rich larval fish fauna (56474 individuals) dominated by pelagic juveniles nearing settlement stage. Variations in the daily catches of replicate nets (200 m apart) were highly correlated, showing the suitability of this technique for monitoring larval supply. Another trial (five nights) was made at One Tree Reef, southern Great Barrier Reef. On nocturnal flood tides, when rising water first spilled into the lagoon, triplicate nets caught many presettlement fish (47797 individuals) in this flow. The behaviour of some taxa clearly assisted their transport through the surf. Despite the successful short-term deployments at One Tree, there may be limited potential to deploy this gear elsewhere on the Great Barrier Reef because of unsuitable flow regimes.