Mesophotic Coral Ecosystems

3.10. La Parguera, Puerto Rico, USA Richard S. Appeldoorn , University of Puerto Rico at Mayagüez, USA David Ballantine , National Museum of Natural History, Smithsonian Institution and University of Puerto Rico at Mayagüez, USA

Studies of the MCEs off La Parguera on the southwest coast of Puerto Rico have been focused along the insular slope, located approximately 10 km offshore (Figure 1). This area is located within the La Parguera Natural Reserve, an area under nominal management by the Puerto Rico Department of Natural and Environmental Resources (Schärer-Umpierre et al. 2014). The insular platform extending to the slope has an average depth of 20 m and supports an extensive development of coral reefs, seagrass beds andmangrove forests.The entire shelf and the shelf edge have karst topography (Morelock et al. 1977). The shelf break occurs at 20–35m in depth and supports a barrier reef with spur and groove formations through which sand is transported over the shelf edge (Morelock et al. 1977). Deep buttresses are common between 45 and 65 m in depth, and a prominent terrace occurs at approximately 80–90 m. Below 90 m, a steep wall drops precipitously to 160 m (Sherman et al. 2010). Ivonne Bejarano , University of Puerto Rico at Mayagüez, USA Héctor Ruiz , University of Puerto Rico at Mayagüez, USA Nikolaos Schizas , University of Puerto Rico at Mayagüez, USA Wilford Schmidt , University of Puerto Rico at Mayagüez, USA Clark Sherman , University of Puerto Rico at Mayagüez, USA ErnestoWeil , University of Puerto Rico at Mayagüez, USA

Geomorphology and geological processes strongly influence the distribution and development of MCEs off La Parguera. Along a 20 km stretch off La Parguera, only five sites were found to have well-developed MCEs (Figures 1 and 2). As with shallow coral reefs, sedimentation and bedload transport can restrict reef development. At mesophotic depths, sedimentation is generally low, but bedload transport down steep slopes plays a significant role, limiting extensive coral development to areas of topographic highs, where benthic organisms can settle and survive. Off La Parguera, southeast-facing slopes were exposed to direct wave impacts during past sea level rise. They consequently have a shallower slope and are less rugose. In contrast, southwest-facing slopes are steeper and have greater rugosity, which helps channel sediment away from coral outcrops. For this reason, well-developed MCEs off La Parguera were found only on southwest-facing slopes (Figure 1).

Puerto Rico - La Parguera shelf edge

Puerto Rico

La Parguera Shelf Edge

Baranca

Buoy

El Hoyo

Black Wall Hole-in-the-Wall

0

1

2

Kilometres

Precipicio

Figure 1. Shelf edge and upper insular slope off La Parguera, Puerto Rico. Red arrows show those sites containing well-developed MCEs. Primary study sites were Hole-in-the-Wall, a southwest-facing slope, and El Hoyo (blue arrow), a southeast-facing slope (sources Richard S. Appeldoorn and Clark Sherman http://www.noaanews.noaa.gov/stories2011/20110104_corals.html).

MESOPHOTIC CORAL ECOSYSTEMS – A LIFEBOAT FOR CORAL REEFS? 45