Currents in the Lizard Island region of the Great Barrier Reef Lagoon and their relevance to potential movements of larvae

Abstract

Current data were collected at 3 stations in the Great Barrier Reef Lagoon of Australia between Lizard Island and Carter Reef, an outer ribbon reef, (approximately 14°S) over a 2 year period. During the southeast Trade wind season (March–September), net circulation at all stations was to the northwest, parallel to the coast and reefs, with little cross-shelf movement. This motion was periodic at about 20 days and highly coherent with the wind. During the non-Trade wind season (October–February) the net circulation depended on the variable wind regime and exhibited frequent current reversals and cross-shelf motion. Tidal currents were superimposed on the net circulation and were mainly cross-shelf but with a tidal excursion of only about 5 km on a flood tide. Tidal currents close to Carter Reef were not cross-shelf but remained parallel to the reef, suggesting that the major tidal flux is through the reef passages. Net circulation close to Carter Reef was not coherent with net circulation at the stations in more open waters, during both Trade and non-Trade seasons. Current speeds were typically 10–30 cm s^-1. Passive plankters entering the water from Carter Reef are therefore likely to remain close to the outer ribbon reefs and be moved parallel to them. Based on the above, we predict that in the Trade wind season, passive plankters would be advected further from their point of origin than during the non-Trade wind season, but there would be more cross-shelf advection during the latter.