Posted on July 18, 2010 by Stacey Harter, Research Ecologist, Panama City Laboratory, National Marine Fisheries
Like shallow tropical coral reefs, mesophotic coral ecosystems support important ecosystem functions, for example, as hotspots for biodiversity and biomass production and as important fish habitat. Like their shallow counterparts, mesophotic ecosystems are affected by human activities. As harvests decline in shallow ecosystems, fishing pressure moves further offshore, thus raising interest in the protection of deep-sea coral ecosystems. This has lead to the increasing use of marine protected areas (MPAs) in recent years. MPAs are areas for which management has implemented fishing restrictions to protect a particular resource. It is our responsibility as researchers to investigate these areas and provide management with the best possible data to determine whether MPAs are an effective management tool.
One such protected area we are examining on this cruise is Pulley Ridge. The coral reef community covering Pulley Ridge is the deepest known light-dependent coral reef on the U.S. continental shelf. Located off the southwest coast of Florida, the ridge is a drowned barrier island approximately 100 km long by 5 km wide, northwest of the Dry Tortugas and running parallel to the Florida peninsula. The shallowest areas on the ridge are about 60 m deep. Surprisingly, at this depth, several species of coral have been located along the ridge even though only 1-2% of surface light is available to the reef community. The coral Agaricia spp. is one of the most abundant hermatypic corals along Pulley Ridge. This coral forms plates up to 50 cm in diameter and are adapted to low-light environments. In excess of 60 fish species have been reported, comprised of a mixture of shallow and deep water species.
Due to the presence of these coral formations, a portion of Pulley Ridge was designated a Habitat Area of Particular Concern (HAPC) in 2005 by the Gulf of Mexico Fishery Management Council (GMFMC) to receive protection from targeted fishing activity, specifically bottom longlines.
As a result of the submersible dives made at Pulley Ridge, we observed distinct habitat differences in habitat type between northern and southern Pulley Ridge. Northern Pulley Ridge sites were comprised of more carbonate rock in the form of outcrops and pavement, while southern Pulley Ridge sites (including the HAPC) were characterized by rock rubble with hermatypic corals and higher fish diversity. Sand tilefish mounds and red grouper pits were also observed inside the HAPC.
A surprising discovery that was made during our submersible dives was the presence of lionfish at Pulley Ridge. Lionfish are an invasive species native to the Indo-Pacific and, like grouper, are structure-oriented fish. They have become established throughout the southeastern Atlantic, juveniles being observed as far north as Rhode Island. Lionfish have just recently begun to make their way around the southern tip of Florida and enter the Gulf of Mexico. Until this cruise, lionfish had not been found this far north in the Gulf.
Information collected during this cruise will be extremely valuable information for the GMFMC as a measure of HAPC effectiveness as well as baseline data should oil affect this area.