Benthic zone (habitat)
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Benthic zone (habitat)
International Common Names
- English: abyssal zone; bathyal zone; benthal zone; benthonic zone; deep sea; hadal zone; ocean bottom; ocean floor; sea bottom; sea floor
- Russian: bental'
OverviewTop of page
Benthic habitats cover about 70% of the earth surface. Of the marine species, 98% live on or in the ocean floor. The benthic zone maintains a substantial part of the world’s biodiversity. However not all of the benthic habitats are equally susceptible to alien species invasion. The so-called ‘hot spots’ for the introduction of benthic invasive species are first of all the nearshore or estuarine zones, since these areas are extensively exploited and disturbed by humans. The majority of established benthic invasives tend to occur in the coastal inlets, lagoons and gulfs. Almost no invasions are known to have occurred in the mid-ocean benthic habitats. Most likely this is due to the very specific physical, geochemical and biological characteristics of those environments.
DescriptionTop of page
Summary of common/typical species
Of all marine species, 98% live on or in the ocean floor. These organisms are called benthos, or bottom dwellers. There are those called infauna that live buried in the sand, shells or mud. Those that live attached to rocks or move over the surface of the ocean bottom are the epifauna. Benthos such as some shrimp and demersal flounder that live in the bottom but move with relative ease through the water above the ocean floor are the nektobenthos (Thurman, 1991).
Benthic organisms are different from those elsewhere in the water column. Many are adapted to live on the substrate (bottom). In their habitats they can be considered as dominant creatures. Many organisms adapted to deep-water pressure cannot survive in the upper parts of the water column as the pressure difference can be very significant.
Because light does not penetrate very deep ocean-water, the energy source for the benthic ecosystem is often organic matter from higher up in the water column which drifts down to the depths. This dead and decaying matter sustains the benthic food chain; most organisms in the benthic zone are scavengers or detritovores.
Main ecological processes
Benthic habitats are important for a variety of reasons. Estuarine and nearshore benthic habitats support a wide diversity of marine life by providing spawning, nursery, refuge, and foraging grounds for fisheries species. They function in nutrient cycling, and contribute to the removal of contaminants from the water column. Benthic organisms are also important members of the lower food web, consuming organic matter and phytoplankton and serving as food sources for higher-level consumers.
Many benthic habitats (for example, coral reefs, eelgrass beds, and kelp forests) have three-dimensional structures that serve as shelter and provide storm protection by buffering wave action along coastlines. Benthic habitats can play an important role in maintaining water quality. Many benthic organisms, including filter feeders like hard clams, bay scallops, and mussels, obtain their food by taking in seawater. As the water flows through their bodies, sediments, organic matter, and pollutants are filtered out and ingested. This role makes these benthic communities good indicators of health in estuarine ecosystems. Benthic habitats play a critical role in the breakdown of organic matter, through the actions of scavengers, deposit-feeders, and bacteria.
Succession and change
Most of the benthic habitats are in deep, pressured areas of the ocean. Because of the high pressure and seclusion neither tidal changes nor human interference has had much of an effect on these areas, and the habitats have not changed much over the years. Many benthic organisms have retained their historic evolutionary characteristics; some organisms have significantly changed size.
Human mediated history
Most of the human mediated changes in benthic habitats occur in response to major disturbances of the substrate. These include natural conditions, such as reworking of sediments and till, turbidity flow and icescouring, and cultural factors, such as industrial pollution, dredging and deposition of mud. Benthic plants and animals will respond by re-colonizing the substrate. Submerged structures, such as shipwrecks, also provide substrate for the colonization of species.
Commercial fishing is one of the most important human impacts on the benthic environment. One such impact is through disturbance to benthic habitats as fishing gear (trawls and dredges) are dragged across the seafloor. As the result, the bottom landscape, structure and characteristics of sediments and, finally, benthic communities are strongly affected and sometimes destroyed (Thrush et al., 1998).
DistributionTop of page
Benthic habitats cover about 70% of the Earth (Leontyev, 1982). The abyssal zone accounts for 75% of the benthic habitat area of the oceans, and the bathyal and subtidal zones 16% and 8% of the area, respectively. Finally, the hadal zone accounts only for 1 % of the total benthic area (Kennish, 2001).
The benthic sub-habitats are not evenly distributed over the world. The subneritic (continental shelf) zone is extended along the continental margins and its width may vary from 0 to 1500 km (average about 80 km). In some regions the continental shelf is extremely wide or narrow: e.g. in the Arctic ocean, from the southern coast of the Hudson Bay towards the Baffin Bay, it is almost 2000 km wide. While along some African coasts, the width of the continental shelf does not exceed 2 km (Duxbury, 1971).
The bathyal zone is a substantial part of the ocean, being larger than the shallow shelf zone, including the sublittoral. However this zone does not form a continuous belt. In some places it is interrupted by steep continental rises or deep-sea trenches on the edge of the continental slope.
The largest area of the ocean floor is occupied by the abyssal zone. It includes the abyssal hills and abyssal plains. Abyssal hills or mid-ocean ridges are present in all the oceans. They cover an area of about 55 million square kilometers of the ocean floor. Abyssal plains are separated from each other by deep-sea trenches or seamount ridges. These landscape forms are poorly pronounced in the Pacific Ocean, where the most deep-sea troughs and longest island chains are situated.
The hadal zone is a restricted environment, found only in the trenches along the margins of continents (Thurman, 1991).
ImpactTop of page
The impact of benthic invasive species on native biodiversity and ecosystem processes may assert itself as competition for food and/or space, habitat change, food-prey for native species, predation on native species, herbivory, hybridisation with native populations, parasitism, community dominance – changes in community structure, benthic-pelagic interaction – introducing new linkages between benthic and pelagic environment, bioaccumulation – storage of toxic substances. However not all of these possible impacts are equally typical for benthic invaders. The most abundant are habitat change, benthic-pelagic coupling and community dominance. Among these, habitat change or habitat engineering should be emphasized as one of the most important, as it may be relevant to many ecosystem functions and elements. As reported by Vitousek (1990), invasive habitat engineer species have much larger effects on their new community than non-engineer species, since both biological and physical characteristics of the environment will be altered. On the other hand, the combination of invasive species and habitat modification is often considered as a presage for new invasions (Cuddington and Hastings, 2004).
Impacts on biodiversity are revealed mostly through aggressive predation and grazing mechanisms. This is particularly important for benthic ecosystems that are not able to adjust as fast to alien species, as alien species can do.
Economic and social impacts
It is easier to assess and evaluate the economic impact of an invasive species than its impact on ecosystem functioning. Yet these impacts are closely related to each other. The possible impacts on uses/resources include impacts on aquaculture, aquatic transport, fisheries, etc. Among the benthic invasive species, the biggest economical losses are caused by fouling organisms, e.g. Balanus improvisus [Amphibalanus improvisus], Dreissena polymorpha, Dreissena bugensis, some seaweed species. Their ability to settle down on almost every substrate together with rapid growth may cause clogging of water abstraction pipes, fouling of ship hulls and underwater harbour constructions, and deterioration of recreational areas (Eno et al., 1997). Another side of the problem is a lack of management mechanisms for an established nuisance species. Most of the techniques applied are not efficient and are rather expensive.
The predatory benthic species, like Asterias amurensis (northern Pacific seastar) eating almost anything it can find, including dead fish and fish waste, is considered a serious aquaculture pest. In Japan seastar outbreaks cost the mariculture industry millions of dollars (NIMPIS, 2002a).
Habitat ImpactsTop of page
|Amphibalanus improvisus||Present, no further details|
|Asterias amurensis||Present, no further details|
|Carcinus maenas||Present, no further details|
|Caulerpa taxifolia||Present, no further details|
|Crassostrea gigas||Present, no further details|
|Dreissena polymorpha||Present, no further details|
|Dreissena rostriformis bugensis||Present, no further details|
|Eriocheir sinensis||Present, no further details|
|Undaria pinnatifida||Present, no further details|
Habitat Management: ProtectionTop of page
Risk assessment for marine bioinvasions provides a tool to aid managers in controlling and reducing the rate of current invasions. It can provide a mechanism to better understand the invasion problem and determine better operating procedures, high-risk routes or system failures, or can aid in the process of management strategy evaluation to determine what components of the invasion process are more susceptible to control, or more apt to fail under specific management regimes (Hewitt and Hayes 2002).
The principal ways to avoid potential problems caused by benthic invasive species include:
strict control of import of all live specimens
use of native instead introduced species
adoption of regulations on a regional basis
- attempt eradication before species establishes (Eno and Hamer, 2002).
The main prevention measures of bioinvasions occur as a barrier control or quarantine response. Concerning the benthic invasive organisms, the control of ballast water introductions is likely the most abundant and popular preventive approach, since a majority of benthic aliens are being transported via extensive world-wide shipping and, particularly, in ballast water tanks. One reason for this arises from three different ‘habitats’ inside ballast water tanks: tank walls, ballast water, and the sediment – where benthic organisms or their larvae may be transported. Because of the diversity in ship design and improved technology (e.g. double hulls, higher economical cruising speeds), the survival rates of some species carried in ballast tanks have increased, and consequently, many introductions of non- indigenous organisms in new locations have occurred in recent years highlighting the need for effective ballast water management. This quarantine approach does not intend to provide an absolute barrier to prevent the introduction of unwanted species but rather aims for a significant reduction in risk. It has become clear that that no single treatment process is likely to universally achieve the required inactivation, kill or total removal of all unwanted organisms in ballast water. Two-stage treatment may comprise some form of mechanical removal of organisms (e.g. filtration, cyclonic separation, sedimentation/floatation, etc.) followed by a physical or chemical treatment method (heating, cooling, UV irradiation, ultrasonic, electrical inactivation, hypochlorite, ozone, peracetic acid use, etc.) (Taylor et al., 2002).
To date, international guidelines have been adopted as the IMO Assembly Resolution. The IMO has not generally promoted regionally different systems, emphasising that a universal global approach is preferred to solve the ballast water problem. The guidelines are not concerned only with the exchange of ballast water at sea but include also reference to ballast water management practices that would reduce the risk of introducing non-native benthic species, such as precautionary procedures when taking on ballast water in shallow areas; discharging ballast sediments to on-shore facilities (if available) (Taylor et al., 2002).
ReferencesTop of page
Carlton JT, 2002. Bioinvasion ecology: assessing invasion impact and scale. In: Invasive aquatic species of Europe. Distribution, impacts and management [ed. by Leppäkoski E, Gollasch S, Olenin S] Netherlands: Kluwer Academic Publishers, 7-19.
Eno C; Hamer JP, 2002. Nature conservation implications of invasions. In: Invasive aquatic species of Europe. Distribution, impacts and management [ed. by Leppäkoski E, Gollasch S, Olenin S] Netherlands: Kluwer Academic Publishers, 477-483.
Hewitt CL; Hayes KR, 2002. Risk assessment of marine bioinvasions. In: Invasive aquatic species of Europe. Distribution, impacts and management [ed. by Leppäkoski E, Gollasch S, Olenin S] Netherlands: Kluwer Academic Publishers, 456-466.
Kuzmin SA; Olsen S; Gerasimova OV, 1996. Barents Sea king crab (Paralithodes camttschatica): the transplantation experiments were successful. In: Proceedings of the International Symposium on Biology, Management, and Economics of Crabs from High Latitude Habitats, Alaska Sea Grant College Program, Anchorage, Alaska, USA USA, 649-663.
Minchin D; Gollasch S, 2002. Vectors - how exotics get around. In: Invasive aquatic species of Europe. Distribution, impacts and management [ed. by Leppäkoski E, Gollasch S, Olenin S] Netherlands: Kluwer Academic Publishers, 183-192.
NIMPIS, 2002. Asterias amurensis species summary. In: National Introduced Marine Pest Information System [ed. by Hewitt CL, Martin RB, Sliwa C, McEnnulty FR, Murphy NE, Jones T, Cooper S] Australia: CSIRO. http://crimp.marine.csiro.au/nimpis
NIMPIS, 2002. Carcinus maenas species summary. In: National Introduced Marine Pest Information System [ed. by Hewitt CL, Martin RB, Sliwa C, McEnnulty FR, Murphy NE, Jones T, Cooper S] Australia: CSIRO. http://crimp.marine.csiro.au/nimpis
NIMPIS, 2002. Caulerpa taxifolia species summary. In: National Introduced Marine Pest Information System [ed. by Hewitt CL, Martin RB, Sliwa C, McEnnulty FR, Murphy NE, Jones T, Cooper S] Australia: CSIRO. http://crimp.marine.csiro.au/nimpis
Olenin S; Daunys D, 2003. Invaders in suspension-feeder systems: variations along the regional environmental gradient and similarities between large basins. In: The comparative role of suspension-feeders in ecosystems [ed. by Dame RF, Olenin S] Netherlands: Springer, 221-237.
Taylor A; Rigby G; Gollasch S; Voigt M; Hallegraeff G; McCollin T; Jelmert A, 2002. Preventive treatment and control techniques for ballast waters. In: Invasive aquatic species of Europe. Distribution, impacts and management [ed. by Leppäkoski E, Gollasch S, Olenin S] Netherlands: Kluwer Academic Publishers, 484-507.
Thrush SF; Hewitt JE; Cummings VJ; Dayton PK; Cryer M; Turner SJ; Funnell GA; Budd RG; Milburn CJ; Wilkinson MR, 1998. Disturbance of the marine benthic habitat by commercial fishing: impacts at the scale of the fishery. Ecological Applications, 8(3):866-879.
Zaiko A; Olenin S; Daunys D; Nalepa T, 2007. Vulnerability of benthic habitats to the aquatic invasive species. Biological Invasions, 9(6):703-714. http://www.springerlink.com/content/h43436712300l235/?p=b9b42fa49fca49f8b09b0dc2cdae5406&pi=7
OrganizationsTop of page
Lithuania: Coastal Research and Planning Institute (Lithuania), Klaipeda University, H. Manto 84, Klaipeda, LT92294, http://www.corpi.ku.lt/
Russian Federation: Zoological Institute of the Russian Academy of Sciences, St. Petersburg, http://www.zin.ru/
USA: NOAA: Great Lakes Environmental Research Laboratory, 2205 Commonwealth Blvd., Ann Arbor, MI, http://www.glerl.noaa.gov/
New Zealand: National Institute of Water and Atmosphere, Private Bag 14901, Wellington, New Zealand, http://www.niwa.com.nz
ContributorsTop of page
6/26/2008 Original text by:
Anastasija Zaiko, Klaipeda University, Coastal Research and Planning Institute, H. Manto 84, Klaipeda, LT-92294, Lithuania