Recent studies from around the Virgin Islands and Puerto Rico have revealed the existence and condition of huge tracts of light-dependent coral reefs that form between 100 and 350 feet depth. The Marine Conservation District, an area just slightly smaller than St John, was found to be almost 70 percent coral reefs in an unbroken expanse, with most reefs having living coral covering a quarter to a half of the bottom.
Researchers from the Center for Marine and Environmental Studies (CMES) have reported on part of a scientific examination of deep coral ecosystems south of St Thomas and St John, an area known as the southeastern Puerto Rican Shelf.
These reefs, also known as mesophotic (mizo-fotik) coral ecosystems, are only recently drawing the attention of scientists, conservationists and governments, although their existence has been well known to fishermen and adventurous divers. Mesophotic coral reefs are some of the least studied and most poorly understood light dependant coral habitats in the world. These reefs form in deep, dimly lit waters around the globe in what has been called the “Twilight Zone.”
The study, funded by the Caribbean Fishery Management Council and led by Drs Tyler Smith and Richard Nemeth of the CMES, used technical diving capabilities, such as closed circuit rebreathers and mixed gases, to explore these hard-to-reach coral reefs that had previously been scarcely described. What they have described is likely to constitute some of the most extensive and best-developed mesophotic reefs in the Caribbean and, possibly, the world.
Mesophotic coral reefs exist in dimmer and cooler water, which protected them from the worst coral bleaching impacts caused by severe warm water in 2005 and 2010. The most severe warm water on record for the region was recorded in 2005. While 2010 was on the path to surpass 2005, it eventually experienced a strong cooling from the passage of hurricanes and tropical storms.
These deep reefs possess a variety of habitat types that were previously unknown to science. They are also critical as sites of commercially important grouper and snapper spawning aggregations. Recent sea floor mapping efforts by the National Oceanographic and Atmospheric Administration using ships and specially outfitted airplanes have revealed the true extent and structure of these systems in the USVI. These areas are all now sites for direct exploration by scientific divers.
The importance and extent of mesophotic reefs in the USVI, the relative ease with which they can be accessed, and the well-developed infrastructure for conducting deep ecological and oceanographic studies at CMES contribute greatly to local and federal efforts to explore and understand these systems.
Funding for the study was provided by the National Oceanic and Atmospheric Administration’s Caribbean Fishery Management Council and National Ocean Sciences, as well as locally by the Lana Vento Charitable Trust.