Spatio-temporal variation in coral recruitment at different scales on Heron Reef, southern Great Barrier Reef

Abstract

Recruitment of scleractinian corals on settlement plates at Heron Island, Great Barrier Reef, was examined over four years (September 1991-September 1995) to quantify spatio-temporal patterns at different scales and to assess post settlement mortality. Recruitment was dominated by pocilloporid corals which accounted for 80.1% of the 8627 spat counted, whereas non-isoporan acroporids represented only 16.4%. Poritids, faviids and isoporan acroporids rarely recruited to the plates (3.5%), despite their obvious abundance as adults on the reef. Recruitment patterns on the plates indicate strong space-time interactions as evidenced by patchy recruitment of both pocilloporid and acroporid spat. Interactions were found between space (on the scale of 102 m, i.e. sites within zones, and 101 m, i.e. racks within sites) and time (on the scale of years) for pocilloporids and between space (on the scale of 103 m, i.e. zones, and 102 m) and time (on the scale of years) for acroporids. Post-recruitment mortality of acroporid spat in the period 3-10 months after their major spawning was dependent on their initial recruitment density, but pocilloporid mortality was either independent of initial recruitment density or, more likely, obscured by additional recruitment of pocilloporids to plates between late February and September. High rates of recruitment and growth by other sessile organisms, particularly bryozoans and oysters, appear to result in increased post-recruitment mortality and limit recruitment of scleractinian corals on settlement plates. The work reinforces an emerging picture that coral recruitment patterns are determined by mechanisms that manifest over a large range of spatial scales.