Intermittent upwelling and subsidized growth of the scleractinian coral Madracis mirabilis on the deep fore-reef slope of Discovery Bay, Jamaica

Abstract

A 1 yr study was conducted across a 45 m depth gradient on the north shore of Jamaica to explore the hypothesis that depth-specific variability associated with thermocline oscillations effects growth rates of the scleractinian coral Madracis mirabilis. Multiple periods of high-frequency temperature variability were detected at 30 to 55 m depth, indicative of vertical transport of subther- mocline water onto the reef slope at semidiurnal and shorter intervals. Cooling, expressed as cumu- lative degree-days below the depth-averaged daily temperature increased from 1.6°C d at 10 m to 50°C d at 45 and 55 m depth. The sum of the daily temperature variance increased almost 3-fold from 3.7 to 9.9°C 2 from 10 to 55 m. Coral growth rates showed a bimodal distribution as a function of depth, with fastest growth (3.86 to 4.12 g yr -1 ) at 10 and 30 m, reduced growth (2.46 to 3.21 g yr -1 ) at 20 and 45 m, and slowest growth (0.97 g yr -1 ) at 55 m. To assess possible differences among sites differing with respect to the intensity of internal-wave forcing, growth rates of M. mirabilis were compared at 20 and 30 m depth in Jamaica with previous results from the Florida Keys. Overall growth rates were greater in Florida than in Jamaica, corresponding to greater internal-wave activity in Florida, and a similar effect of enhanced growth at 30 m was observed at both sites. Vertical oscillations of the thermocline are a widespread phenomenon, and may contribute to patterns of coral growth in a variety of deep reef environments.