DISCOVRE 2008

Cruise Log: 10/11/2008

Deep-Sea Fishes Associated with Cold Water Corals and Deep Reefs

Steve W. Ross, Chief Scientist

By most definitions the deep sea starts at the continental shelf edge around 200 m (about 600 ft.), which is the beginning of the continental slope. The general thinking has been that going from this realm into deeper and deeper waters, the fishes are less associated with particular habitats than shallow water fishes. So, unlike in shallow coral reefs, where there are fishes that can only live in reefs, the deep sea is host to more generalist species. It has also been reported that there appear to be definite depth zones for deep-sea fishes (vertical zonation) but that fish communities seem very similar over great distances in the same depth range (lack of horizontal zonation). But, such long standing concepts in deep-sea biology usually resulted from sampling gear like trawls and dredges, which are inefficient and only present a partial view of the habitat and its associated animals. While these gears can be very useful, more direct observation data (as from manned submersibles or remote operated vehicles, ROVs) are changing some of these views of deep-sea fish communities. For this reason, we emphasize using research submersibles and ROVs, which provide very good images of the animals as well as collections that are in good condition.

There is considerable deep-sea reef habitat in the form of cold-water corals (hundreds of species), wrecks, and hard rocky outcrops, especially in depths from 200-1000 m. Such habitat is particularly abundant off the southeastern US and to some extent in the Gulf of Mexico. Our research over the last seven years has been focused on characterizing fish assemblages around these reefs, including documenting their use of habitat, feeding relationships, behaviors, and to what extent they form groupings. We asked questions like: Are there true reef fishes in such depths, similar to the shallow reefs? Do they occur on one habitat more than another?

Our results so far were surprising and differ from other data on cold-water coral reefs in other parts of the world. Off the southeastern US and Gulf of Mexico there are over 110 species of fishes we have seen on these reefs, more than reported elsewhere in the world. A high percentage of the fishes were new records to this region, and we have also so far identified four fish species new to science occurring on or near these reefs. This was unexpected in a part of the world that we thought was well known. In addition, many fish species seemed to be only on reef habitat and rarely, if ever, strayed to nearby non-reef bottom. Such species as slimeheads (or roughies), conger eel, some scorpionfishes, wreckfish, and some hakes (see photos) may in fact represent deep-sea reef fishes. We are also documenting the fishes on non-reef (usually soft bottoms) habitats and find that these are often different than those on the reefs.

There are reef fish communities that appear to be unique. For example, there are groupings of deep-reef fishes on deep coral banks off North Carolina (370-450 m deep) that seem to be different from those off South Carolina, Georgia, & north Florida, which are in turn different from those off south FL (600-800 m deep). The Gulf of Mexico reef fish communities that we are now surveying also differ from those in the Atlantic. We think that combinations of habitat structure and type, temperature, depth, and perhaps physical oceanography (currents) play roles in controlling these groupings. We will be investigating these and other factors as agents for structuring deep-sea fish assemblages. Our deep reef fish research will benefit from and collaborate with other components of this multi-investigator study.

Grenadier, Nezumia aequalis. This is one of the common fishes of sandy to muddy habitats. It generally feeds on small invertebrates found in the sediment surface. - (photo credit: USGS DISCOVRE Expedition) - click to enlarge

Roughy, Gephyroberyx darwini. This species and related species are common on deep reef habitats. We often see this fish under rocky ledges. - (photo credit: USGS DISCOVRE Expedition) - click to enlarge