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57-528: The Virginia Marine Resources Commission is a state agency charged with overseeing Virginia's marine and aquatic resources, and its tidal waters and homelands. One of the primary functions of the Commission is to zone water areas for outdoor swimming , for oyster and clamming grounds, and for fishing use. This United States law enforcement agency article is a stub . You can help Misplaced Pages by expanding it . This Virginia -related article

114-411: A benthopelagic species, 17% of the bodyweight is liver of which 70% are lipids. Benthic rays and skates have smaller livers with lower concentrations of lipids; they are therefore denser than water and they do not swim continuously, intermittently resting on the seabed. Some fish have no buoyancy aids but use their pectoral fins which are so angled as to give lift as they swim. The disadvantage of this

171-518: A large number of organisms and support very high productivity. Estuaries provide habitats for salmon and sea trout nurseries, as well as migratory bird populations. Two of the main characteristics of estuarine life are the variability in salinity and sedimentation . Many species of fish and invertebrates have various methods to control or conform to the shifts in salt concentrations and are termed osmoconformers and osmoregulators . Many animals also burrow to avoid predation and to live in

228-411: A mutually beneficial relationship with mangrove forests at high tide level and sea grass meadows in between: the reefs protect the mangroves and seagrass from strong currents and waves that would damage them or erode the sediments in which they are rooted, while the mangroves and seagrass protect the coral from large influxes of silt , fresh water and pollutants . This additional level of variety in

285-476: A result, estuaries are suffering degradation by many factors, including sedimentation from soil erosion from deforestation; overgrazing and other poor farming practices; overfishing; drainage and filling of wetlands; eutrophication due to excessive nutrients from sewage and animal wastes; pollutants including heavy metals, PCBs, radionuclides and hydrocarbons from sewage inputs; and diking or damming for flood control or water diversion. Estuaries provide habitats for

342-516: A unique three-dimensional habitat for marine organisms and are a source for understanding many ecological processes. Over the last century, they have been the focus of extensive research, particularly in trophic ecology, and continue to provoke important ideas that are relevant beyond this unique ecosystem. For example, kelp forests can influence coastal oceanographic patterns and provide many ecosystem services . However, humans have contributed to kelp forest degradation . Of particular concern are

399-460: Is 3.6 cu km of ocean space available somewhere for marine habitats. Intertidal zones , those areas close to shore, are constantly being exposed and covered by the ocean's tides . A huge array of life lives within this zone. Shore habitats range from the upper intertidal zones to the area where land vegetation takes prominence. It can be underwater anywhere from daily to very infrequently. Many species here are scavengers, living off of sea life that

456-604: Is a stub . You can help Misplaced Pages by expanding it . Marine habitats 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 . 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

513-401: Is a highly important link in the food chain, with hundreds of species feeding on seagrasses worldwide, including green turtles , dugongs , manatees , fish , geese , swans , sea urchins and crabs . Demersal Being just above the ocean floor, the demersal zone is variable in depth and can be part of the photic zone where light can penetrate, and photosynthetic organisms grow, or

570-481: Is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea . Estuaries form a transition zone between river environments and ocean environments and are subject to both marine influences, such as tides, waves, and the influx of saline water; and riverine influences, such as flows of fresh water and sediment. The inflow of both seawater and freshwater provide high levels of nutrients in both

627-508: 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: 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. Altogether, the ocean occupies 71 percent of the world surface, averaging nearly four kilometres in depth. By volume,

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684-408: 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. 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

741-406: 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. The sedimentologist Francis Shepard classified coasts as primary or secondary . Continental coastlines usually have a continental shelf , a shelf of relatively shallow water, less than 200 metres deep, which extends 68 km on average beyond

798-428: Is nearby, there are large discharges of nutrient rich land runoff into coastal waters. Further, periodic upwellings from the deep ocean can provide cool and nutrient rich currents along the edge of the continental shelf. As a result, coastal marine life is the most abundant in the world. It is found in tidal pools , fjords and estuaries , near sandy shores and rocky coastlines, around coral reefs and on or above

855-432: Is not easily shifted by waves and currents, and when it dries out, cakes into a solid. By contrast, sand is easily shifted by waves and currents, and when sand dries out it can be blown in the wind, accumulating into shifting sand dunes . Beyond the high tide mark, if the beach is low-lying, the wind can form rolling hills of sand dunes. Small dunes shift and reshape under the influence of the wind while larger dunes stabilise

912-422: Is predominantly a pelagic species but forms large aggregations near the seabed when it spawns on banks of gravel. Two types of fish inhabit the demersal zone: those that are heavier than water and rest on the seabed, and those that have neutral buoyancy and remain just above the substrate . In many species of fish, neutral buoyancy is maintained by a gas-filled swim bladder which can be expanded or contracted as

969-514: Is that, if they stop swimming, the fish sink, and they cannot hover, or swim backwards. Demersal fish have various feeding strategies; many feed on zooplankton or organisms or algae on the seabed; some of these feed on epifauna ( invertebrates on top of the seafloor), while others specialise on infauna (invertebrates that burrow beneath the seafloor). Others are scavengers , eating the dead remains of plants or animals, while still others are predators . Zooplankton are animals that drift with

1026-417: Is washed up on the shore. Many land animals also make much use of the shore and intertidal habitats. A subgroup of organisms in this habitat bores and grinds exposed rock through the process of bioerosion . Sandy shores, also called beaches , are coastal shorelines where sand accumulates. Waves and currents shift the sand, continually building and eroding the shoreline. Longshore currents flow parallel to

1083-480: The aphotic zone , which begins between depths of roughly 200 and 1,000 m (700 and 3,300 ft) and extends to the ocean depths, where no light penetrates. The distinction between demersal species of fish and pelagic species is not always clear cut. The Atlantic cod ( Gadus morhua ) is a typical demersal fish , but can also be found in the open water column , and the Atlantic herring ( Clupea harengus )

1140-411: 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. 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. Plankton are the life forms that inhabit

1197-431: 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

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1254-414: 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,

1311-492: The tides . Their productivity is largely dependent on the turbidity of the water. The main phytoplankton present are diatoms and dinoflagellates which are abundant in the sediment. Kelp forests are underwater areas with a high density of kelp . They form some of the most productive and dynamic ecosystems on Earth. Smaller areas of anchored kelp are called kelp beds . Kelp forests occur worldwide throughout temperate and polar coastal oceans. Kelp forests provide

1368-451: 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

1425-461: The beaches, making waves break obliquely on the sand. These currents transport large amounts of sand along coasts, forming spits , barrier islands and tombolos . Longshore currents also commonly create offshore bars , which give beaches some stability by reducing erosion. Sandy shores are full of life, The grains of sand host diatoms , bacteria and other microscopic creatures. Some fish and turtles return to certain beaches and spawn eggs in

1482-419: The body of an individual organism is known as a thallus rather than as a plant (Kingdom: Plantae ). The morphological structure of a kelp thallus is defined by three basic structural units: In addition, many kelp species have pneumatocysts , or gas-filled bladders, usually located at the base of fronds near the stipe. These structures provide the necessary buoyancy for kelp to maintain an upright position in

1539-411: The circumstances require. A disadvantage of this method is that adjustments need to be made constantly as the water pressure varies when the fish swims higher and lower in the water column. An alternative buoyancy aid is the use of lipids, which are less dense than water— squalene , commonly found in shark livers, has a specific gravity of just 0.86. In the velvet belly lanternshark ( Etmopterus spinax ),

1596-493: The coast. Worldwide, continental shelves occupy a total area of about 24 million km (9 million sq mi), 8% of the ocean's total area and nearly 5% of the world's total area. Since the continental shelf is usually less than 200 metres deep, it follows that coastal habitats are generally photic , situated in the sunlit epipelagic zone . This means the conditions for photosynthetic processes so important for primary production , are available to coastal marine habitats. Because land

1653-514: The continental shelf. Coastal fish include small forage fish as well as the larger predator fish that feed on them. Forage fish thrive in inshore waters where high productivity results from upwelling and shoreline run off of nutrients. Some are partial residents that spawn in streams, estuaries and bays, but most complete their life cycle in the zone. There can also be a mutualism between species that occupy adjacent marine habitats. For example, fringing reefs just below low tide level have

1710-414: 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

1767-422: The current, but many have some limited means of locomotion and have some control over the depths at which they drift. They use gas-filled sacs or accumulations of substances with low densities to provide buoyancy, or they may have structures that slow down any passive descent. Where the adult, benthic organism is limited to life in a certain range of depths, their larvae need to optimise their chances of settling on

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1824-501: 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

1881-435: The effects of overfishing nearshore ecosystems, which can release herbivores from their normal population regulation and result in the over-grazing of kelp and other algae. This can rapidly result in transitions to barren landscapes where relatively few species persist. Frequently considered an ecosystem engineer , kelp provides a physical substrate and habitat for kelp forest communities. In algae (Kingdom: Protista ),

1938-411: The environment is beneficial to many types of coral reef animals, which for example may feed in the sea grass and use the reefs for protection or breeding. Coastal habitats are the most visible marine habitats, but they are not the only important marine habitats. Coastlines run for 380,000 kilometres, and the total volume of the ocean is 1,370 million cu km. This means that for each metre of coast, there

1995-420: The equator, where currents curve left. Seabed topography (ocean topography or marine topography) refers to the shape of the land ( topography ) when it interfaces with the ocean. These shapes are obvious along coastlines, but they occur also in significant ways underwater. The effectiveness of marine habitats is partially defined by these shapes, including the way they interact with and shape ocean currents , and

2052-467: 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,

2109-409: The humans live by the coast, putting pressure on coastal habitats. Mudflats are coastal wetlands that form when mud is deposited by tides or rivers. They are found in sheltered areas such as bays , bayous , lagoons , and estuaries . Mudflats may be viewed geologically as exposed layers of bay mud , resulting from deposition of estuarine silts , clays and marine animal detritus . Most of

2166-975: The leaves are long and narrow and are very often green, and because the plants often grow in large meadows which look like grassland. Since seagrasses photosynthesize and are submerged, they must grow submerged in the photic zone , where there is enough sunlight. For this reason, most occur in shallow and sheltered coastal waters anchored in sand or mud bottoms. Seagrasses form extensive beds or meadows , which can be either monospecific (made up of one species) or multispecific (where more than one species co-exist). Seagrass beds make highly diverse and productive ecosystems . They are home to phyla such as juvenile and adult fish, epiphytic and free-living macroalgae and microalgae , mollusks , bristle worms , and nematodes . Few species were originally considered to feed directly on seagrass leaves (partly because of their low nutritional content), but scientific reviews and improved working methods have shown that seagrass herbivory

2223-550: 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. 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

2280-425: The more stable sedimental environment. However, large numbers of bacteria are found within the sediment which have a very high oxygen demand. This reduces the levels of oxygen within the sediment often resulting in partially anoxic conditions, which can be further exacerbated by limited water flux. Phytoplankton are key primary producers in estuaries. They move with the water bodies and can be flushed in and out with

2337-402: The ocean contains more than 99 percent of the Earth's liquid water. 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. 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

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2394-421: 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

2451-421: 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

2508-459: 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

2565-505: The open ocean, they include underwater and deep sea features such as ocean rises and seamounts . The submerged surface has mountainous features, including a globe-spanning mid-ocean ridge system, as well as undersea volcanoes , oceanic trenches , submarine canyons , oceanic plateaus and abyssal plains . One measure of the relative importance of different marine habitats is the rate at which they produce biomass . Marine coasts are dynamic environments which constantly change, like

2622-566: The rocks. Competition can develop for the rocky spaces. For example, barnacles can compete successfully on open intertidal rock faces to the point where the rock surface is covered with them. Barnacles resist desiccation and grip well to exposed rock faces. However, in the crevices of the same rocks, the inhabitants are different. Here mussels can be the successful species, secured to the rock with their byssal threads . Rocky and sandy coasts are vulnerable because humans find them attractive and want to live near them. An increasing proportion of

2679-648: The salinity of ocean seawater (up to 90 ppt). There are many mangrove species, not all closely related. The term "mangrove" is used generally to cover all of these species, and it can be used narrowly to cover just mangrove trees of the genus Rhizophora . Mangroves form a distinct characteristic saline woodland or shrubland habitat, called a mangrove swamp or mangrove forest . Mangrove swamps are found in depositional coastal environments, where fine sediments (often with high organic content) collect in areas protected from high-energy wave action. Mangroves dominate three quarters of tropical coastlines. An estuary

2736-410: The sand with vegetation. Ocean processes grade loose sediments to particle sizes other than sand, such as gravel or cobbles . Waves breaking on a beach can leave a berm , which is a raised ridge of coarser pebbles or sand, at the high tide mark. Shingle beaches are made of particles larger than sand, such as cobbles, or small stones. These beaches make poor habitats. Little life survives because

2793-552: The sand. Birds habitat beaches, like gulls , loons , sandpipers , terns and pelicans . Aquatic mammals , such sea lions, recuperate on them. Clams , periwinkles , crabs , shrimp , starfish and sea urchins are found on most beaches. Sand is a sediment made from small grains or particles with diameters between about 60 μm and 2 mm. Mud (see mudflats below) is a sediment made from particles finer than sand. This small particle size means that mud particles tend to stick together, whereas sand particles do not. Mud

2850-614: The sediment within a mudflat is within the intertidal zone , and thus the flat is submerged and exposed approximately twice daily. Mangrove swamps and salt marshes form important coastal habitats in tropical and temperate areas respectively. Mangroves are species of shrubs and medium size trees that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes 25° N and 25° S. The saline conditions tolerated by various species range from brackish water , through pure seawater (30 to 40 ppt ), to water concentrated by evaporation to over twice

2907-525: 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

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2964-403: The stones are churned and pounded together by waves and currents. The relative solidity of rocky shores seems to give them a permanence compared to the shifting nature of sandy shores. This apparent stability is not real over even quite short geological time scales, but it is real enough over the short life of an organism. In contrast to sandy shores, plants and animals can anchor themselves to

3021-620: 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

3078-410: The water column and sediment, making estuaries among the most productive natural habitats in the world. Most estuaries were formed by the flooding of river-eroded or glacially scoured valleys when sea level began to rise about 10,000-12,000 years ago. They are amongst the most heavily populated areas throughout the world, with about 60% of the world's population living along estuaries and the coast. As

3135-517: The water column. The environmental factors necessary for kelp to survive include hard substrate (usually rock), high nutrients (e.g., nitrogen, phosphorus), and light (minimum annual irradiance dose > 50 E m ). Especially productive kelp forests tend to be associated with areas of significant oceanographic upwelling , a process that delivers cool nutrient-rich water from depth to the ocean's mixed surface layer . Water flow and turbulence facilitate nutrient assimilation across kelp fronds throughout

3192-694: The water column. Water clarity affects the depth to which sufficient light can be transmitted. In ideal conditions, giant kelp ( Macrocystis spp. ) can grow as much as 30-60 centimetres vertically per day. Some species such as Nereocystis are annual while others like Eisenia are perennial , living for more than 20 years. In perennial kelp forests, maximum growth rates occur during upwelling months (typically spring and summer) and die-backs correspond to reduced nutrient availability, shorter photoperiods and increased storm frequency. Seagrasses are flowering plants from one of four plant families which grow in marine environments. They are called seagrasses because

3249-426: The way sunlight diminishes when these landforms occupy increasing depths. Tidal networks depend on the balance between sedimentary processes and hydrodynamics however, anthropogenic influences can impact the natural system more than any physical driver. Marine topographies include coastal and oceanic landforms ranging from coastal estuaries and shorelines to continental shelves and coral reefs . Further out in

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