Chapter 18 Key Concepts

Past sampling of continental shelf and deep-sea bottoms involved bottom dredges and grabs, which often failed to give a complete picture of sea-bottom diversity.
Submersibles, remote underwater vehicles, underwater video cameras, and other remote devices are crucial tools in investigating the seafloor.
Suspension-feeding benthic animals dominate sandy sediments, whereas deposit feeders dominate muds.
Suspension feeders function poorly in muds, owing to the clogging effect of resuspended particles and to the destabilizing effect of deposit feeders on the sediment.
Modification of the sediment by burrowers and digging predators causes local patches.
Bottom currents disturb the sediment and generate a series of microenvironments.
Organic material is distributed discontinuously, generating local sites of high food value.
Patchy dispersal and recruitment also create spatial change in benthos on the seabed.
Succession of subtidal soft sediments involves colonization of a disturbed and abiotic substrate by rapidly colonizing surface dwellers, followed by colonization and dominance of deeper-burrowing species.
A transect from the shelf to the deep sea defines a shift from shallow-water bottoms with high biomass and productivity to remote, deep-sea bottoms with low biomass and productivity.
The input of organic matter to the deep-sea floor is low because of the distance from the coast and the great depth through which organic particles must travel, but localized areas of the seabed receive pulses of organic matter.
The decline of organic matter input to the deep-sea bottom is accompanied by strong changes in feeding types of the benthic animals there.
The deep-sea bed consists of sediment with little organic matter, and microbial activity is very low relative to upper-slope and shelf bottoms.
As we go from the shelf to the deep sea, we pass from physically variable environments to those that are stable.
Despite the poor food conditions, the deep sea in the vicinity of the continental slope and continental rise actually has more soft-bottom species than do corresponding environments on the inner continental shelf.
Biodiversity of soft bottoms increases with increasing depth, but then declines as depths surpass about 2,000 m.
Because of strong regional and depth differences in environment in the slope and bathyal zones of 200 to 4,000 m, there is much more regional difference and depth difference in species occurrence and genetic differences within species than in the deeper abyssal zones of greater than 4,000 m.
Despite the apparent similarities in sediment properties, there is a prominent latitudinal diversity gradient in deep-sea benthos.
Deep-sea biodiversity may have been promoted by a stable environment, although disturbance and microhabitat heterogeneity also may have promoted diversity.
Deep- and cold-water hard surfaces often contain habitats dominated by stony and soft corals, ranging from a few colonies to enormous mounds of calcium carbonate sediment. Deep-water coral mounds are extremely diverse.
Deep-water coral mounds support important fisheries, which attract damaging trawlers.
Deep-water coral mounds are affected by the ability to secrete aragonite and may be in a danger zone because of increasing carbon dioxide in the atmosphere.
Seamounts are relatively isolated, elevated areas, usually of volcanic origin, rising 1 km or more above the seafloor and whose top does not reach the sea surface.
Seamounts are mapped and observed with multibeam acoustic methods, video taken by ROVs, and direct sampling.
Seamounts are dominated by a large number of sessile invertebrates, but also by a diverse array of fishes and mobile bottom invertebrate species.
Seamounts often have hard substrata on top because deep-sea currents are focused on their summits, preventing accumulation of soft sediments.
Seamounts have been claimed to have highly endemic faunas, but this is not clear.
Seamount biotas are endangered from overfishing and undersea mining.
Hot vents, located near areas of submarine volcanic activity, spew out hot, sulfide-rich water and support unique biotic assemblages.
Hot-vent faunal habitats are ephemeral, and species disperse along ridge systems, often by means of planktonic larvae.
Some cold-seep areas in the Gulf of Mexico and the Florida escarpment are rich in hydrocarbons and also have rich benthic communities based on local food sources.
Fish and whale carcasses on the seafloor are localized deep-sea environments where species successively colonize and dominate as the carcasses decompose.
Hot vents, cold seeps, and fallen carcasses demonstrate a surprising diversity on highly localized and often ephemeral habitats.
The vents and other habitats demonstrate that the deep sea is not constrained to be in slow motion.
Microbial activity and benthic creatures in trenches and other areas with high organic matter input confirm that organic input is a major influence on deep-sea activity.
A bacterial realm has been found deep below the deep-sea floor.
Pressure increases of approximately 1 atmosphere every 10 m of depth strongly affect the biochemistry of deep-sea organisms.