Virgin Islands National Park: Coral Reef: Recruitment Tiles

In this study, coral recruitment was measured on a kilometer-wide scale on
shallow (5–6 m depth) fringing reefs in St. John, US Virgin Islands, with the
objective of determining the extent to which variation in recruitment was affected
by biophysical coupling involving temperature and flow. Coral recruitment was
measured using settlement tiles deployed at 10 sites along 10 km of shore. The tiles
were first deployed in August 2006, and thereafter replaced every ≈6 months to
sample from either August to January, or January to August over 2 years. Seawater
temperature was recorded at the 10 sites using logging thermistors, and flow was
quantified using drogues. Overall, corals recruited at a rate equivalent to 76
corals m− 2 6 months− 1, and were represented mostly by poritids (43% of recruits),
agaricids (29%), faviids (17%) and siderastreids (7%). Although the density of
recruits 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 at
eastern sites, to ≤ 1 coral tile− 1 at western sites. One aspect of seawater
temperature – the daily range – differed among sites and was greater at western
compared to eastern sites, and while it was related inversely to recruitment over
one of the sampling periods, it was equivocal as a physical process affecting
recruitment. Instead, our results are consistent with biophysical coupling involving
patch depletion and downstream filtering, whereby patches of coral larvae are
delivered to the south shore of St. John and depleted of larvae through settlement
as the water progresses westward.