A diver explores the vertical distribution of corals on a Pacific wall.

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: NOAA RSS 2.0 Feed

Podcasts LOGO NOAA Podcast:
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.

Mission Summary Mission Summary Chief Scientist Marc Slattery reflects on the exciting initial findings of the Cayman Islands Twilight Zone 2007 expedition.

May 31 log May 31 Learn how at least one member of the Cayman Islands Twilight Zone 2007 team has been afflicted with "barophilia," defined as an obsessive love of deep diving.

May 30 log May 30 As part of the expedition team, a high school teacher becomes enlightened as to the very definition of scientific collaboration. Includes camera icon videos.

May 29 log May 29 The Twilight Zone (TZ) appears to be home to one of the most diverse and abundant sponge assemblages in the Caribbean Basin. These TZ sponges make their shallow-water relatives look minuscule; we saw deep-reef species that exceed 12 feet in diameter! Includes camera icon videos.
May 28 log May 28 The ocean is a largely untapped source of important biotechnology products. Join Team TZ scientists as they explore the deep-reef communities in the Cayman Islands, with their uniquely adapted species. Discover why one of the focused drug discovery efforts is on fluorescent proteins.
May 27 log May 27 A primary goal for this Ocean Explorer cruise is to characterize deep coral-reef communities in order to determine whether the patterns found in the Cayman Islands are broadly applicable to the wider Caribbean. Join scientists as they compare prior work on the walls of the Bahamas to the current dive sites on the walls of Little Cayman.
May 26 log May 26 Sessile animals and plants are attached to a surface. They can't move away when a predator tries to take a bite! But they've developed other strategies. Learn more about these defenses. camera icon Includes video
May 25 log May 25 A milliliter (1/1000 of a liter) of seawater contains thousands to millions of bacterial cells. Marine surfaces, from sand particles to corals, also contain large numbers of microorganisms. Discover the ocean’s "invisible" majority.
camera icon Includes video
May 24 log May 24 One reason people enjoy diving under clear blue seas to study, or even just to look at, coral reefs is their incredible diversity. Coral reefs harbor more species of organisms than do tropical rain forests. We've hardly scratched the surface! camera icon Includes videos
May 10 log May 23 Join scientists as they try to better understand the role of Caribbean sponges in coral-reef ecosystems and to determine why deep-water sponges grow larger and faster than those found in shallow water.
May 11 log May 22 "Safety first!" guides the day as scuba divers descend 130 feet below the surface. camera icon Includes video and podcast icon podcast.

May 21 log May 21 For comparison purposes, the team conducts shallow-reef surveys on sites near the Cayman Islands Twilight Zone study area.