Deep Sea Sediments

Deep-sea sediment ecosystems are often ignored when considering the services provided by the ocean. Although human activities continue to expand to greater depths with improved technology, much of the current exploitation (Table 4.2c) is concentrated in the upper 1,000 m. These upper slope sedimentary habitats are repositories for organic carbon moving off the shelf (Walsh et al. 1981) and support expanding commercial and sport fisheries.

Continental slope sediments have higher carbon input and higher abundances of fishes and invertebrates than deeper areas. These are sites of relatively new fisheries for bony fishes such as orange roughy, pelagic armorhead, sablefish, flatfish, and rattails (which occur deeper as well) (Merrett & Haedrich 1997), and for invertebrates such as snow crabs, tanner crabs, golden crabs, northern shrimp, and red crabs (Elner 1982; Otto 1982). Many fisheries have focused on seamounts as well as the continental margin. On seamounts, black and pink corals are harvested for jewelry (Grigg 1993). All of the deepwater fishery taxa are slow-growing, long-lived forms that cannot sustain fishing pressure; most of their populations have declined or will in the near future, and the provisioning of fish secondary production is therefore short-lived and marginal at best (see Snelgrove et al., Chapter 7). Other deep-sea species, such as blue hake, spinetail ray, and spiny eel, have experienced major declines in the past few decades from take as bycatch (i.e., individuals that are removed incidentally as a result of a fishery that is non-selectively targeting some other species) (Baker & Haedrich 2003).

To the extent that biodiversity is considered a valuable resource (e.g., for future uses, scientific interest) in itself, the deep sea functions to maintain and promote high species diversity (Rex 1983; Gage & Tyler 1991). The continental slopes are regions of high diversity, possibly because of the highly heterogeneous environments in space and time. Specific habitats within the deep sea, such as coral (Lophelia) reefs (Fossaa et al. 2002), seamounts (Koslow et al. 2001), and some reducing environments (hydrothermal vents, whale falls, and methane seeps) (Van Dover 2000) are recognized as valuable refugia that are important in the maintenance of diversity. More than 99 percent of the deep-sea floor has yet to be sampled (Snelgrove & Smith 2002), so there is considerable potential for future discovery and uses. One emerging area is the exploitation of micro-bial forms for specific industrial properties, among them their ability to degrade lipids at low temperatures and to break down hydrogen sulfide, and for enzymes to function at high temperatures (Prieur 1997).

Ecological processes that are regulated by deep-sea marine sediment biota include (1) the capture and deposition of organic matter onto the seabed, (2) the transfer of organic matter to higher consumers, (3) the burial of organic matter, and (4) the oxygenation of sediments through bioturbation. In deep-sea sediments, foraminiferans related sarcodines, macrofauna, and nematodes are key bioturbators and regulators of organic cycling. Active suspension and plankton feeders such as sponges, tunicates,

Table 4.2c. The provisioning of goods and services for deep-sea sediment ecosystems.

See Table 4.2a for explanation of ranking scheme.

Biotic

Abiotic

External

Diversity Importance

Rank

Contributors

Regulators

Interaction

Species Functional Habitat

Provisioning Services

Plants as food

0

Animals as food

1 to 2

fish, invertebrates, all benthos

oxygen, circulation, substrate

food, life history

3

2 2

Other biological products

0

Biochemical/medicines/ models for human research

1

microbes, natural products, enzymes

temperature, chemical availability

3

3 3

Fuels/energy

3

microbes

temperature, time

1

1 0

Fiber

1

sponges

1

0 0

C sequestration

1

bioturbators, microbes, infauna

C02, temperature, advection

carbon pump

2

3 3

Nonliving materials (geological effects)

0

Clean seawater

0

Sediment formation: biodeposition 1

Nutrient cycling 1

Biological control: disease, ? invasive species resistance

Detoxification, waste disposal 2

Climate regulation 3 (C sequestration)

Food web support processes 1

Atmosphere composition 1

Flood and erosion control 0

Redox processes 3

microbes, lithothamnia, biogenic sediments microbes, bioturbators, macrofauna, fishes currents, freshwater and land runoff circulation, temperature, tides sinking of particulates resuspension microbes, benthos circulation, bioturbators, microbes, infauna, mobile fauna entire benthos microbes resuspension, sedimentation hydrodynamic processes, upwelling, resuspension, sedimentation hydrodynamic processes, upwelling, resuspension, sedimentation, oxygen oxygen, substrate, turbulent mixing terrestrial & pelagic input terrestrial & pelagic input bioturbators, microbes oxygen carbon flux

Table 4.2c. (continued)

Biotic

Abiotic

External

Diversity Importance

Rank

Contributors

Regulators

Interaction

Species Functional Habitat

Habitat Maintenance Services

Landscape linkage & structure/habitat/refugia

1

deep sea corals, methane seeps

oxygen, temperature, depth, substrate

carbon flux, larval stages

2

2 2

Aesthetic Services

Spiritual/cultural

1

0

0 0

Aesthetic

1

3

1 2

Recreation

1

0

0 0

Scientific understanding

3

new life forms, microbes, symbioses

depth, sulfide, methane

3

3 3

anemones, and bryozoans capture, ingest, and deposit organic matter or small plankton onto the sea floor in quiescent regions. Passive suspension feeders such as corals, crinoids, selected polychaetes, ophiuroids, and brisingid starfish do the same in higher energy settings. Epibenthic holothurians consume massive deposits of phytodetritus that carpet deep-sea sediments following phytoplankton blooms (Billet 1991), while other surface-deposit feeders are often the first to ingest and transform incoming organic matter into tissue. Nearly all metazoans participate in deep-sea food chains, although diets of most species are unknown (Fauchald & Jumars 1979; Sokolova 2000).

Areas at a depth of greater than 1,000 meters are thought to have reduced biological activity and therefore to be relatively stable compared with shallower ecosystems, and thus they have been a repository for many different kinds of wastes over the last half century (see Snelgrove et al., Chapter 7). However, recent studies show that labile organic matter reaching the deep sea is processed rapidly by benthic macrofauna such as sipun-culans and maldanid polychaetes (Graf 1989; Levin et al. 1997), despite low overall fau-nal biomass (Rowe 1983).

Microbes account for a significant proportion of sediment community oxygen consumption (e.g., 80 percent, Heip et al. 2001), contributing to nutrient cycling through transformation, degradation, and sequestration of organic matter. They control redox conditions within sediments, provide food for protozoan and metazoan consumers (via heterotrophy and symbioses), and their role in nutrient cycling relates strongly to sediment oxygenation (Fenchel & Finlay 1995). Microbes form unusual natural products, enzymes, and detoxification functions (Bunge et al. 2003) that may be exploited commercially. Living microbes have been discovered much deeper in the Earth's crust than any other life form (Parkes et al. 1994).

Key benefits from sediment-based nutrient cycling and carbon burial may include removal of carbon over extended periods of centuries or longer (Heip et al. 2001). The deep sea is currently being considered for more rapid removal of CO2 in liquid form through direct injection (Ozaki 1997; and see Snelgrove et al., Chapter 7).

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