Off-reef transport of coral fragments at Lizard Island, Australia

The generation and movement of coral rubble is important to the sedimentary budget of a reef, in sediment facies development, and in the promotion of reef growth. This study examined the rate of down-slope transport of live a nd dead coral fragments from shallow reef fronts at Lizard island, on the G reat Barrier Reef, Australia. Ten large (1 m(2)) collecting trays were depl oyed and cleared annually for 4 years at each of two sites at the base (8-1 2 m depth) of the steeply-sloping fringing reef. The rate of export of cora l fragments down the reef slope was very high: an average of 132 fragments weighing 1.87 kg was recorded each year per meter of reef front. A mean of 2.25% of the fragments (representing 43 species) was five in the trays at e ach annual census, yielding an average rate of colonization onto the reef s lope of 2.7 live fragments per meter of reef front per year. Reworking of h ard calcareous substrates towards the slope promotes reef growth by two mec hanisms: (1) passive dispersal of live coral fragments to peripheral, soft- sediment habitats that are unsuitable for larval settlement, and (2) subseq uent colonization of rubble by coral larvae. There were no major storms dur ing the course of the study, indicating that significant down-slope transpo rt of fragments can occur even in the absence of cyclones. (C) 1999 Elsevie r Science B.V. All rights reserved.