A diver explores the vertical distribution of corals on a Pacific wall. Click image for larger view and image credit.
Cayman Islands Twilight Zone 2007
May 21 – 31, 2007
The words "coral reef" and "sunlight" are almost synonymous in the world of marine biology. That's because most corals exist in an unusual symbiosis with microscopic plants, called zooxanthellae. The zooxanthellae provide the coral with foods resulting from photosynthesis, a process that requires light. However, recent evidence indicates that light-limited deep reefs — those located between 50- and 150-meter (m) depth, in a range also known as the “Twilight Zone" — are an important transition habitat, where many shallow-reef and deep-sea organisms coexist with each other and with species unique to this depth range.
To date, deep reefs worldwide have been examined almost exclusively using video photography from remotely operated vehicles (ROVs), since these communities are deeper than the typical safety limits for scuba divers. Recent advances in technical diving procedures, however, have made it safe and practical to explore the deep reefs in person. We have assembled a team of highly trained technical divers and support divers to mount an expedition into the Twilight Zone of the Cayman Islands.
It is important to note that the term "twilight zone" can mean different things, depending on whether you are talking to an oceanographer or a coral reef ecologist. Oceanographers often refer to the mesopelagic zone (from about 200 to 1,000 m depth) as the twilight zone due to the limited light penetration. Coral reef ecologists refer to the depth below about 1% light penetration on the deep reef as the twilight zone; this corresponds to about 50- to 150-m depth on tropical reefs. This Ocean Explorer mission focuses on the latter, and we will refer to it as the Twilight Zone throughout the Web site.
The Cayman Islands Twilight Zone, where we will explore, is an area where unusual sponges and soft corals cling to nearly vertical walls that drop into the abyss of the Cayman Trench, 7,500 m below the crystal-clear surface waters. Identifying the biodiversity and health status of these important transition communities is the first step toward effective management and conservation of these deep-reef habitats. That's one of our goals on this mission. We will also characterize the physical environment of these deep reefs to better understand how factors like water-flow, nutrients, temperature, and light control the distribution of deep-reef species. In addition, we will explore the connectivity between the deep- and shallow-reefs to determine whether organisms from these Twilight Zone communities can “reseed” degraded shallow reefs. Finally, biological adaptations of these organisms make them excellent candidates for biotechnology research efforts, and we will look at their potential to produce new drugs from the sea.
Our research is a collaborative effort by the University of Mississippi, the University of New Hampshire, and the University of Alabama. We are supported with funding from NOAA’s Office of Exploration, and from the National Institute of Undersea Science and Technology’s Ocean Biotechnology Center and Repository. The Little Cayman Research Center provides on-site logistical support, and the Cayman Islands Department of Environment, and the Marine Conservation Board, have graciously provided permits to explore their reefs.
You can access the Ocean Explorer Cayman Islands Twilight Zone 2007 Newsfeed here:
Learn what we hope to discover on this expedition with a video or audio podcast on the mission. (Quicktime7 H.264, 608 Kb.)
Updates & Logs
Click images or links below for detailed mission logs and updates.