Virgin Islands National Park: Coral Reef: Recruitment Tiles

In this study, coral recruitment was measured on a kilometer-wide scale onshallow (5–6 m depth) fringing reefs in St. John, US Virgin Islands, with theobjective of determining the extent to which variation in recruitment was affectedby biophysical coupling involving temperature and flow. Coral recruitment wasmeasured using settlement tiles deployed at 10 sites along 10 km of shore. The tileswere first deployed in August 2006, and thereafter replaced every ≈6 months tosample from either August to January, or January to August over 2 years. Seawatertemperature was recorded at the 10 sites using logging thermistors, and flow wasquantified using drogues. Overall, corals recruited at a rate equivalent to 76corals m− 2 6 months− 1, and were represented mostly by poritids (43% of recruits),agaricids (29%), faviids (17%) and siderastreids (7%). Although the density ofrecruits differed among sites in a pattern that varied among periods and years,there was a consistent trend for mean density to decline from ≈ 4 corals tile− 1 ateastern sites, to ≤ 1 coral tile− 1 at western sites. One aspect of seawatertemperature – the daily range – differed among sites and was greater at westerncompared to eastern sites, and while it was related inversely to recruitment overone of the sampling periods, it was equivocal as a physical process affectingrecruitment. Instead, our results are consistent with biophysical coupling involvingpatch depletion and downstream filtering, whereby patches of coral larvae aredelivered to the south shore of St. John and depleted of larvae through settlementas the water progresses westward.