A decade of deep reef exploration in the greater Caribbean


Research submersibles allow long-term dives at any depth with panoramic views of little-explored ecosystems. They are also equipped with equipment to collect fish during these dives. Photo credit: D Ross Robertson, Smithsonian Tropical Research Institute

The mysteries of underwater life have long been a source of inspiration for writers, filmmakers and marine biologists. But scientists interested in understanding ocean biodiversity are often limited by the relatively shallow depths accessible by diving. Small research submersibles, while expensive, allow for exploration of much deeper waters. A new paper, co-authored by researchers from the Smithsonian Tropical Research Institute (STRI) and the National Museum of Natural History (NMNH), the University of Washington and the Universidad Nacional Autónoma de Honduras, describes the important contribution of submersibles to expanding our Knowledge of the diversity of deep reef fish in the Greater Caribbean.

In 2010, Smithsonian scientists initiated the Deep Reef Observation Project, or DROP, to explore the ocean around the Caribbean islands of Curacao, Bonaire, Dominica, Sint Eustatius (Statia), and Roatan using two privately owned small submersibles, Curasub and Idabel. These submersibles can dive to 1,000 or 3,000 feet, about two to six times deeper than a technical dive, and they can stay at maximum depth much longer than technical divers, who can rely on tanks of gas mixtures they carry with them.

The new article in frontiers in marine science shows that due to DROP research at three sites in the Greater Caribbean (Curacao, Statia, Roatan), the number of recorded deep-reef fish has increased approximately 9-fold and the total number of these fish is two to four times greater than at three sites with little or no similar research effort: Alligator Reef in the Florida Keys, Bermuda and St. Croix.

“The DROP research yielded two important results: it showed that the reef fish fauna, dominated by families of typical shallow-water reef fish, extends well below the mesophotic zone – to about 300 meters – and that the diversity of the deep-reef fish fauna of the biogeographical The Greater Caribbean region is at least a third larger than previously thought,” said D. Ross Robertson, STRI staff member. “These results come from our collections of such fish with the submersibles, mainly on Curacao and Roatan.”

Although the rate of discovery of new deep-reef fish species began to increase after the advent of scuba diving, it grew dramatically with the use of research submersibles, as they allow longer dives at any depth with panoramic views of underexplored ecosystems and are equipped with fish collection equipment during these dives.

“When DROP started exploring Caribbean deep reefs with submersibles, we saw a lot of fish species that we didn’t know about,” said Carole Baldwin, Chair of Vertebrate Zoology at the NMNH. “Now, after almost a decade of collecting submersibles in places like Curacao, we can identify almost everything we see out of the submarine’s windows, many of which we have collected, named and described as new species.”

The use of research submersibles has revealed that the fish fauna of the deep reefs in the Greater Caribbean is at least a third larger than previously thought. Photo credits: D. Ross Robertson (Smithsonian Tropical Research Institute) Carole Baldwin (National Museum of Natural History) Luke Tornabene (University of Washington) and Barry Brown (Substation Curacao)

However, such dive research is at the expensive end of the range of options. Depending on whether it’s supported by a research vessel or not, a week-long submersible expedition could cost anywhere from $30,000 to $200,000. In comparison, similar research using a small industrial ROV (remotely operated vehicle) operating to a depth of 300 meters and operated from a small fishing vessel would cost about $40,000 for a week of research.

Baited Remote Underwater Videos (BRUVs) are the cheapest technology and can be used anywhere boat support is available. However, because they rely on bait, they tend to attract certain fish over others and may not gather the same data as other methods.

Closed-Circuit Rebreathers (CCR) are a cheaper option. They allow dives with minimal boat assistance and, since divers are highly manoeuvrable, are probably more effective than submersibles at collecting fast-moving bottom fish. However, they are limited by human physiology to dives less than about 150 meters deep and require longer decompression times after short deep dives.

Differences in deep-reef fish discovered on different islands ultimately suggest that many parts of the greater Caribbean are likely harboring a variety of deep-reef fish waiting to be discovered, a process facilitated by increased use of research submersibles, perhaps in combination , could be accelerated with other less expensive underwater exploration methods.

Funding for the DROP project comes from internal sources within the Smithsonian, the Research and Exploration Committee of the National Geographic Society and the Prince Albert II of Monaco Foundation. Fieldwork in Roatan was conducted with additional funding from the University of Washington and the Burke Museum.

Since 2011, the DROP project has published 45 peer-reviewed papers, with more planned. This includes descriptions of 7 new genera and 35 new species of deep reef fish, molluscs, crustaceans and echinoderms, with an additional 10 or so species of fish yet to be named and described. DROP discovered and delineated a new reef-ocean zone, the rariphotic, connecting the mesophosis and the deep sea. It also acquired nearly a decade of temperature data along a reef slope from 15 to 245 meters, documented the first record of invasive Caribbean lionfish preying on previously unknown biodiversity, acquired fundamental data on the cryptic biodiversity of reefs at different depths on a tropical reef slope, and developed Protocols and methods for deployment and retrieval of scavenging devices placed on deep reefs using ROV/submersible robotic arms.

Researchers name new sea zone: Rariphotic

More information:

D. Ross Robertson et al, Submersibles Greatly Enhance Research on the Diversity of Deep-Reef Fishes in the Greater Caribbean, frontiers in marine science (2022). DOI: 10.3389/fmars.2021.800250

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Smithsonian Tropical Research Institute

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