NCCOS-supported researchers documented that mesophotic coral ecosystems (MCEs) at depths of 50 and 70 m in southwest Puerto Rico experienced significant interannual changes in community composition, demonstrating that caution should be taken when attributing change to benthic communities, as sampling frequency and timing may affect results. Changes were driven by fluctuations in algal abundance (Dictyota spp.).

Hole-in-the-Wall (left) and El Hoyo (right).

The study photographed transects at two sites with differing geomorphology: Hole-in-the-Wall, a steep and irregular southwest facing slope; and El Hoyo, a gentler gradient and lower relief southeast facing slope, every three months from June 2009–2010. The steeper site (Hole-in-the-Wall), which had chutes to funnel sediment away from the benthic communities, experienced less change in algal abundance in comparison to the site with a gentler slope (El Hoyo). At both sites, there was no net change demonstrated between June 2009 and 2010. However, at both sites and depths, the abundance of Dictyota spp. decreased in June and December and increased in March and September, indicating that the driver of Dictyota fluctuations operated on a broad scale. Unfortunately, these fluctuations could not be attributed to seasonal variations in physical conditions, such as light and temperature. For future research, quantifying the scale of interannual variation is essential if long-term changes in community structure are to be interpreted correctly.

This project was part of the Deep Coral Reef Ecosystem Studies program in the Caribbean led by the University of Puerto Rico and the Caribbean Coral Reef Institute. Designed to improve the understanding of MCEs off La Parguera, Puerto Rico, the program goals were to characterize MCE community composition and structure, determine their potential connectivity, and assess their vulnerability to anthropogenic stresses.

Citation:  Appeldoorn, Richard S., David L. Ballantine, Milton Carlo, Juan J. Cruz Motta, Michael Nemeth, Hector J. Ruiz, Nikolaos V. Schizas, Clark E. Sherman, Ernesto Weil and Paul M. Yoshioka. 2021. Intra-annual variation in mesophotic benthic assemblages on the insular slope of southwest Puerto Rico as a function of depth and geomorphology. Frontier in Marine Sciences 8:732926. https://doi.org/10.3389/fmars.2021.732926