A marine habitat is a habitat that supports marine life. Marine life depends in some way on the saltwater that is in the sea (the term marine comes from the Latin mare, meaning sea or ocean). A habitat is an ecological or environmental area inhabited by one or more living species.Abercrombie, M., Hickman, C.J. and Johnson, M.L. 1966.A Dictionary of Biology. Penguin Reference Books, London The marine environment supports many kinds of these habitats.
Marine habitats can be divided into coastal and open ocean habitats. Coastal habitats are found in the area that extends from as far as the tide comes in on the shoreline out to the edge of the continental shelf. Most marine life is found in coastal habitats, even though the shelf area occupies only seven percent of the total ocean area. Open ocean habitats are found in the deep ocean beyond the edge of the continental shelf.
Alternatively, marine habitats can be divided into pelagic and demersal zones. Pelagic habitats are found near the surface or in the open water column, away from the bottom of the ocean. Demersal habitats are near or on the bottom of the ocean. An organism living in a pelagic habitat is said to be a pelagic organism, as in pelagic fish. Similarly, an organism living in a demersal habitat is said to be a demersal organism, as in demersal fish. Pelagic habitats are intrinsically shifting and ephemeral, depending on what ocean currents are doing.
Marine habitats can be modified by their inhabitants. Some marine organisms, like corals, kelp, mangroves and seagrasses, are ecosystem engineers which reshape the marine environment to the point where they create further habitat for other organisms. By volume the ocean provides most of the habitable space on the planet.Living Ocean NASA Science. Retrieved 17 December 2016.
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Overview
In contrast to terrestrial habitats, marine habitats are shifting and ephemeral. Swimming organisms find areas by the edge of a continental shelf a good habitat, but only while upwellings bring nutrient rich water to the surface. Shellfish find habitat on sandy beaches, but storms, tides and currents mean their habitat continually reinvents itself.
The presence of seawater is common to all marine habitats. Beyond that many other things determine whether a marine area makes a good habitat and the type of habitat it makes. For example: temperature – is affected by geographical latitude, ocean currents, weather, the discharge of rivers, and by the presence of hydrothermal vents or cold seeps sunlight – photosynthetic processes depend on how deep and turbid the water is nutrients – are transported by ocean currents to different marine habitats from land runoff, or by upwellings from the deep sea, or they sink through the sea as marine snow salinity – varies, particularly in estuaries or near river deltas, or by hydrothermal vents dissolved gases – oxygen levels in particular, can be increased by wave actions and decreased during algal blooms acidity – this is partly to do with dissolved gases above, since the acidity of the ocean is largely controlled by how much carbon dioxide is in the water. turbulence – ocean waves, fast currents and the agitation of water affect the nature of habitats cover – the availability of cover such as the adjacency of the sea bottom, or the presence of floating objects substrate – The slope, orientation, profile and rugosity of hard substrates, and particle size, sorting and density of unconsolidated sediment bottoms can make a big difference to the life forms that can settle on it. the occupying organisms themselves – since organisms modify their habitats by the act of occupying them, and some, like corals, kelp, mangroves and seagrasses, create further habitats for other organisms.
There are five major oceans, of which the Pacific Ocean is nearly as large as the rest put together. Coastlines fringe the land for nearly 380,000 kilometres.
Ocean Areamillion km2 % VolumeThe World's Oceans and Seas. Encarta. Retrieved 19 April 2008.million cu km % Mean depthkm Max depthkm Coastlinekm % Ref Pacific Ocean 155.6 46.4 679.6 49.6 4.37 10.924 135,663 CIA Factbook: Pacific ocean. Atlantic Ocean 76.8 22.9 313.4 22.5 4.08 8.605 111,866 CIA Factbook: Atlantic ocean. Indian Ocean 68.6 20.4 269.3 19.6 3.93 7.258 66,526 CIA Factbook: Indian ocean. Southern Ocean 20.3 6.1 91.5 6.7 4.51 7.235 17,968 CIA Factbook: Southern ocean. Arctic Ocean 14.1 4.2 17.0 1.2 1.21 4.665 45,389 CIA Factbook: Arctic ocean. Overall 335.3 1370.8Elert, Glenn Volume of Earth's Oceans. The Physics Factbook. Retrieved 19 April 2008. 4.09 10.924 377,412
Altogether, the ocean occupies 71 percent of the world surface, averaging nearly four kilometres in depth. By volume, the ocean contains more than 99 percent of the Earth's liquid water.Where is Earth's water?, United States Geological Survey.Eakins, B.W. and G.F. Sharman, Volumes of the World's Oceans from ETOPO1, NOAA National Geophysical Data Center, Boulder, CO, 2010.Water in Crisis: Chapter 2, Peter H. Gleick, Oxford University Press, 1993. The science fiction writer Arthur C. Clarke has pointed out it would be more appropriate to refer to the planet Earth as the planet Sea or the planet Ocean.Planet "Earth": We Should Have Called It "Sea" Quote Invertigator, 25 January 2017.Unveiling Planet Ocean NASA Science, 14 March 2002.
Marine habitats can be broadly divided into pelagic and demersal habitats. Pelagic habitats are the habitats of the open water column, away from the bottom of the ocean. Demersal habitats are the habitats that are near or on the bottom of the ocean. An organism living in a pelagic habitat is said to be a pelagic organism, as in pelagic fish. Similarly, an organism living in a demersal habitat is said to be a demersal organism, as in demersal fish. Pelagic habitats are intrinsically ephemeral, depending on what ocean currents are doing.
The land-based ecosystem depends on topsoil and fresh water, while the marine ecosystem depends on dissolved nutrients washed down from the land.
Ocean deoxygenation poses a threat to marine habitats, due to the growth of low oxygen zones.
Ocean currents
In marine systems, ocean currents have a key role determining which areas are effective as habitats, since ocean currents transport the basic nutrients needed to support marine life.Ocean Habitats Marietta College. Retrieved 17 April 2011. Plankton are the life forms that inhabit the ocean that are so small (less than 2 mm) that they cannot effectively propel themselves through the water, but must drift instead with the currents. If the current carries the right nutrients, and if it also flows at a suitably shallow depth where there is plenty of sunlight, then such a current itself can become a suitable habitat for photosynthesizing tiny algae called phytoplankton. These tiny plants are the primary producers in the ocean, at the start of the food chain. In turn, as the population of drifting phytoplankton grows, the water becomes a suitable habitat for zooplankton, which feed on the phytoplankton. While phytoplankton are tiny drifting plants, zooplankton are tiny drifting animals, such as the larvae of fish and marine invertebrates. If sufficient zooplankton establish themselves, the current becomes a candidate habitat for the forage fish that feed on them. And then if sufficient forage fish move to the area, it becomes a candidate habitat for larger predatory fish and other marine animals that feed on the forage fish. In this dynamic way, the current itself can, over time, become a moving habitat for multiple types of marine life.
Ocean currents can be generated by differences in the density of the water. How dense water is depends on how saline or warm it is. If water contains differences in salt content or temperature, then the different densities will initiate a current. Water that is saltier or cooler will be denser, and will sink in relation to the surrounding water. Conversely, warmer and less salty water will float to the surface. Atmospheric winds and pressure differences also produces surface currents, waves and seiches. Ocean currents are also generated by the gravitational pull of the sun and moon (tides), and seismic activity (tsunami).
The rotation of the Earth affects the direction ocean currents take, and explains which way the large circular ocean gyres rotate in the image above left. Suppose a current at the equator is heading north. The Earth rotates eastward, so the water possesses that rotational momentum. But the further the water moves north, the slower the earth moves eastward. If the current could get to the North Pole, the earth would not be moving eastward at all. To conserve its rotational momentum, the further the current travels north the faster it must move eastward. So the effect is that the current curves to the right. This is the Coriolis effect. It is weakest at the equator and strongest at the poles. The effect is opposite south of the equator, where currents curve left.
Topography
Biomass
One measure of the relative importance of different marine habitats is the rate at which they produce biomass. Producer Biomass productivity(gC/m2/yr) Ref Total area(million km2) Ref Total production(billion tonnes C/yr) Comment swamps and marshes 2,500 Includes freshwater coral reefs 2,000 0.28 Spalding, Mark, Corinna Ravilious, and Edmund Green. 2001. World Atlas of Coral Reefs. Berkeley, CA: University of California Press and UNEP/WCMC. 0.56 algal beds 2,000 river estuaries 1,800 open ocean 125 311 39
Coastal
Marine coasts are dynamic environments which constantly change, like the ocean which partially shape them. The Earth's natural processes, including weather and sea level change, result in the erosion, accretion and resculpturing of coasts as well as the flooding and creation of continental shelves and drowned river valleys.
The main agents responsible for deposition and erosion along coastlines are waves, tides and currents. The formation of coasts also depends on the nature of the rocks they are made of – the harder the rocks the less likely they are to erode, so variations in rock hardness result in coastlines with different shapes.
Tides often determine the range over which sediment is deposited or eroded. Areas with high tidal ranges allow waves to reach farther up the shore, and areas with lower tidal ranges produce deposition at a smaller elevation interval. The tidal range is influenced by the size and shape of the coastline. Tides do not typically cause erosion by themselves; however, tidal bores can erode as the waves surge up river estuaries from the ocean.Davidson (2002), p.421.
Waves erode coastline as they break on shore releasing their energy; the larger the wave the more energy it releases and the more sediment it moves. Sediment deposited by waves comes from eroded cliff faces and is moved along the coastline by the waves. Sediment deposited by rivers is the dominant influence on the amount of sediment located on a coastline.Easterbrook (1999).
The sedimentologist Francis Shepard classified coasts as primary or secondary.Shepard FP (1937) Revised "Classification of Marine Shorelines" The Journal of Geology, 45(6): 602–624.