Continental Shelf Research, Vol. 9, No. 5, pp. 479-496, 1989. 0278-4343/89 $3.00 + 0.00 Printed in Great Britain. © 1989 Pergamon Press pie. Trapping and dispersion of coral eggs around Bowden Reef, Great Barrier Reef, following mass coral spawning ERIC WOLANSKI,* DEREK BURRAGE* and BRIAN KING* (Received 9 May 1988; in revised form 14 December 1988; accepted 8 February 1989) Abstract--Bowden Reef is a 5 km long kidney-shaped coral reef with a lagoon, located on the mid-shelf of the central region of the Great Barrier Reef. Field studies were carried out, in November 1986, at the time of mass coral spawning, of the water circulation around Bowden Reef and in the surrounding inter-reefal waters. The near-reef water circulation was strongly three-dimensional although the stratification was weak. In calm weather, coral eggs were aggregated in slicks along topographically controlled fronts. In the absence of a longshore current, water and coral eggswere trapped in the lagoon and in a boundary layer around Bowden Reef, by tidally driven recirculating motions. In the presence of a longshore current, some trapping occurred in the lagoon, but the bulk of the coral eggs was advected away from Bowden Reef and reached downstream reefs in a few days. This implies a likelihoodof both self-seedingof reefs, and connectivitybetween reefs. 1. INTRODUCTION THE question of the connectivity between coral reefs is unresolved, since little is known about the water circulation in a topographically complex environment such as the matrix of reefs forming the central region of the Great Barrier Reef (Fig. 1; see review by HAMNER and WOLANSKI, 1988). Yet management decisions for the Great Barrier Reef Marine Park necessitate some knowledge of the processes controlling reef-to-reef connectivity or, alternatively, the degree of self-seeding of reefs. A two-week long experiment entitled CORSPEX (Coral Spawning Experiment), was undertaken jointly with the Department of Marine Biology at James Cook University, in November 1986 during a mass coral spawning event. The aim of CORSPEX was to improve our understanding of the biological and physical processes controlling the fate of coral eggs and subsequently coral planulae for several days following mass spawning of the corals. The study of the oceanography of mass spawning seemed promising because the time of mass spawning could be predicted accurately (WILLIS et al., 1985), and because the coral eggs are released in such large quantities that, once they are aggregated in slicks, these slicks are readily visible (OLIVER and WILLIS, 1987), thereby providing oceanographers with a natural tracer. Results of the physical oceanography component of CORSPEX are presented here. 2. METHODS No bathymetric charts of the CORSPEX study reef, Bowden Reef, were available (see a location map in Fig. 1). A bathymetric chart was drawn from six echo-sounder * Australian Institute of Marine Science, PMB No. 3, Townsville, M.C., 4810 Queensland, Australia. 479