Deep ocean urchin and crab. Photo: MBARI
The deep sea is the largest habitat on earth and is home to many relatively unknown biological communities. It is only in the past two decades that better technologies have allowed humans to view previously unseen areas: the development of camera-equipped remotely operated vehicles (ROVs) and manned submersibles provide a new window on this world.
In the "old" days, exploration of deep-sea life involved dragging a net along the bottom or through the open water. Delicate animals such as jellies came back to the ship damaged beyond recognition. Today, ROVs have substantially increased our knowledge because they allow us to observe animals in their natural habitat and better understand how they interact with each other and with their environment.
There are two major habitats in the deep sea:
- The "midwater": Animals such as fishes, squid and jellies live their entire lives floating here, in the vast area where one can see neither the seafloor below nor the sunlight above. Small bacteria and crustaceans are also abundant in this zone.
- The seafloor, or "benthos": This habitat is dominated by microscopic animals living in the mud, a diverse array of larger surface-dwelling invertebrates (sea stars, urchins, sponges, brittle stars, etc.) and fishes that live on or just above the seafloor. The biological diversity of the sanctuary is due, in part, to diverse benthic habitats, ranging from huge expanses of soft sediment to hardened mud and rock. Rock outcrops on deep-sea canyon walls provide a hard surface on which sponges, anemones and other fixed organisms live.
Organisms have adapted in a variety of ways. Natural light penetrates to only about 300 meters, so marine plants, which need sunlight, are absent below this depth. Because it is dark, many animals don't have the ability to see; others have extraordinarily sensitive eyes to pick up what little light is available. Many deep-sea organisms make their own light - a chemical reaction called bioluminescence. Bright displays of light may be used to communicate, attract mates, create confusion (and thus avoid a predator) or lure food.
<em>Microstoma microstoma</em> (Dusky Smelt; Microstomatidae) collected during mesopelagic fishes survey aboard NOAA SHIP Bell M. Shimada, at Davidson Seamount (SESA 16), 0-410 meters, May 2015. Identified by Robert N. Lea (CAS) and Erica J. Burton (MBNMS). Scale: Centimeter ruler.
Sea star (maybe Anteliaster sp.), crinoids, corals, sponge, and cutthroat eel (Family Synaphobranchidae) on the Davidson Seamount at 2498 meters depth. Credit: NOAA/MBARI 2006
Food is generally limited in the deep sea, so finding it and capturing it is more difficult. Many animals feed on an array of discarded biological material called "detritus," which rains down from above as a result of the activities of animals in shallower water.
Whatever these animals discard or shed provides food that sinks to the seafloor for scavengers and mud-feeding organisms like brittle stars and sea cucumbers. On occasion, large "food falls," like dead whales or dead kelp, sink from above, attracting large numbers of animals that come to take advantage of the bounty.
It is essential to monitor human impacts on the ocean so that we can understand how our activities change our environment. A clear understanding of these effects can help resource managers and policy makers develop sound conservation strategies.
Conservation and management issues affecting sanctuary resources in the deep sea include seabed disturbance, non-sustainable fishing and radioactive waste.
- Bottom trawling: This practice is widely believed to have negative impacts on benthic habitats, such as modification of the substrate, disturbance of soft-bottom communities and removal of non-target fish species. The structure of entire seafloor communities is at risk from this fishery practice. Currently, there is an incomplete picture about the extent of these impacts in the sanctuary, but the use of trawl gear is an ongoing source of concern.
- Non-sustainable fishing: In June 2006, the Pacific Fishery Management Council and National Oceanic and Atmospheric Administration (NOAA) Fisheries closed large portions of the continental slope to trawling in order to protect essential fish habitat for groundfishes. In addition, closures called Trawl Rockfish Conservation Areas (RCAs) have been established to minimize the bycatch of overfished rockfishes. RCA boundaries, however, may change during the year. Trawling is not allowed in state waters.
- Radioactive Waste: Approximately 47,800 barrels of low-level radioactive waste were disposed between 1946 and 1970 (before sanctuary designation, in 1981) in the area referred to as the "Farallon Islands radioactive waste dump." Although the containers were to be dumped at three designated sites, they are actually strewn over a 1400-square-kilometer (540-square-mile) area in depths ranging from 100 meters to more than 2,000 meters within the gulf. Research results to date are inconclusive on the impacts from possible radioactive leakage on the marine
ecosystem. The new sanctuary management plan addresses the need to evaluate the
Glass sponge. Photo: MBARI.
MonitoringExperts from many different fields - biologists, geologists, chemists, engineers and physical oceanographers - all study the deep sea, seeking to understand how the ocean works.
This work is important for many reasons; the size of the deep sea (covering 63 percent of the earth's surface) means that we should know as much as possible about this ecosystem. Scientists strive to understand how deep-sea animals are different from shallow-water species and what adaptations they have developed in response to the deep ocean's unique environment.
The deep sea may also provide economic opportunities. Cancer-fighting drugs developed from sea sponges or other marine organisms may some day provide new pharmaceuticals. Researchers are also investigating the seafloor for new forms of energy. However, one of the best reasons to study the deep sea may be simple curiosity about all the amazing creatures and geological features hidden in its depths.