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Notes
- Abstract:
- Energetic responses of zooxanthellate reef corals along depth gradients have relevance to the thermal stress regugia potential of mesophotic coral ecosystems (MCE). Previous observations suggested that MCE in the Caribbean are thermally buffered during the warmest parts of the year and occur within or just below the chlorophyll maximum, suggesting abundant trophic resources. However, it is not known if mesophotic corals can maintain constant energy needs throughout the year with changing environmental and biological conditions. The energetic content of tissues from the stony coral species Orbicella faveolata and Agaricia lamarcki was measured on the southern insular shelf of St. Thomas, US Virgin Islands over five periods from April 2013 to April 2014. Three sites for each species, at depths of 6m, 25m, 38m and 63m, were selected to capture energetic differences across the full vertical range of coral habitats in the USVI. Mesophotic colonies of O. faveolata exhibited a significant reduction in energetic content during the month of September 2013 compared to mid-depth and shallow colonies, whereas A. larmarcki experienced similar energetic variability, but with significant reduction in energy content that occurred in July 2013 for colonies at sites deeper than 25 m. The results o calorimetric analyses indicate that O. faveolata may be at risk during late summer stress events, possibly due to the timing of reproductive activities. The low-point of A. lamarcki energy content, which may also coincide with reproduction, occurs prior to seasonal thermal stress events, thus favoring this species in mesophotic habitats.
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