MARINE ECOSYSTEMS
Marine ecosystems are the largest of Earth's aquatic ecosystems, distinguishable by their high sodium chloride (NaCL) content. Conversely, Freshwater ecosystems contain trace amounts of NaCL content. Marine waters cover more than 70% of the surface of the Earth and account for more than 97% of Earth's water supply and 90% of habitable space on Earth.
Marine ecosystems include nearshore systems, such as the salt marshes, mudflats, sea grass meadows, mangroves, rocky intertidal systems and coral reefs. Extending outwards from the coast are offshore systems which include, pelagic ocean waters, the deep sea, hydrothermal vents, and the sea floor.
Marine ecosystems are characterised by their unique combination of community of organisms, adapted around unique physical environment. The variety of abiotic (Non-Living) and biotic (Living) factors are what essentially facilitate the diversity of ecosystems found throughout our blue planet.
Diversity of life throughout all ecosystems, both terrestrial and aquatic depends of the divergence of ecosystems. Each ecosystem has its own set of pressures, and within each one of these ecosystems are smaller systems. For example, some of the marine ecosystems such as coral reefs contain hundreds of different species of coral, all creating different structures, thereby creating further unique subsystems to support their own unique network of species.
“Some marine ecosystems are so highly diverse, they exceed tropical rain forests for the sheer number of species! ”
Salt Marshes
Salt marshes are a transition from the ocean to the land, where fresh and saltwater mix. The soil in these marshes is often made up of mud and a layer of organic material called peat. Peat is characterised as waterlogged and root-filled decomposing plant matter that often causes low oxygen levels (hypoxia). These hypoxic conditions are caused the growth of bacteria that also give salt marshes the sulphurous smell they are often known for.
Salt marshes exist around the world and are needed for healthy ecosystems and a healthy economy. They are extremely productive ecosystems and they provide essential services for more than 75 percent of fishery species and protect shorelines from erosion and flooding. Salt marshes can be generally divided into the high marsh, low marsh, and the upland border.
The low marsh is closer to the ocean, with it being flooded at nearly every tide except low tide. The high marsh is located between the low marsh and the upland border and it usually only flooded when higher than usual tides are present. The upland border is the freshwater edge of the marsh and is usually located at elevations slightly higher than the high marsh. This region is usually only flooded under extreme weather conditions and experiences much less waterlogged conditions and salt stress than other areas of the marsh.
Mangroves
Mangroves are trees or shrubs that grow in low-oxygen soil near coastlines in tropical or subtropical latitudes. They are an extremely productive and complex ecosystem that connects the land and sea.
Mangroves consist of species that are not necessarily related to each other and are often grouped for the characteristics they share rather than genetic similarity. Because of their proximity to the coast, they have all developed adaptions such as salt excretion and root aeration to live in salty, oxygen-depleted water.
Mangroves can often be recognised by their dense tangle of roots that act to protect the coast by reducing erosion from storm surges, currents, wave, and tides.6 The mangrove ecosystem is also an important source of food for many species as well as excellent at sequestering carbon dioxide from the atmosphere with global mangrove carbon storage is estimated at 34 million metric tons per year.
Estuaries
Estuaries occur where there is a noticeable change in salinity between saltwater and freshwater sources. This is typically found where rivers meet the ocean or sea.
The wildlife found within estuaries is unique as the water in these areas is brackish - a mix of freshwater flowing to the ocean and salty seawater.
Estuaries are extremely productive ecosystems that many humans and animal species rely on for various activities. This can be seen as, of the 32 largest cities in the world, are located on estuaries as they provide many environmental and economic benefits such as crucial habitat for many species and being economic hubs for many coastal communities.
Estuaries also provide essential ecosystem services such as water filtration, habitat protection, erosion control, gas regulation nutrient cycling, and it even gives education and tourism opportunities to people.
Lagoons
Lagoons are areas that are separated from larger water by natural barriers such as coral reefs or sandbars. There are two types of lagoons, coastal and oceanic/atoll lagoons. A coastal lagoon is, as the definition above, simply a body of water that is separated from the ocean by a barrier. An atoll lagoon is a circular coral reef or several coral islands that surround a lagoon. Atoll lagoons are often much deeper than coastal lagoons.
Most lagoons are very shallow meaning that they are greatly affected by changed in precipitation, evaporation, and wind. This means that salinity and temperature are widely varied in lagoons and that they can have water that ranges from fresh to hypersaline.
Lagoons can be found in on coasts all over the world, on every continent except Antarctica and is an extremely diverse habitat being home to a wide array of species including birds, fish, crabs, plankton and more.
Lagoons are also important to the economy as they provide a wide array of ecosystem services in addition to being the home of so many different species. Some of these services include fisheries, nutrient cycling, flood protection, water filtration, and even human tradition.
Coral Reefs
Coral reefs are large underwater structures composed of the skeletons of colonial marine invertebrates called coral. The coral species that build reefs are known as hermatypic, or "hard," corals because they extract calcium carbonate from seawater to create a hard, durable exoskeleton that protects their soft, sac-like bodies. Other species of corals that are not involved in reef building are known as “soft” corals. These types of corals are flexible organisms often resembling plants and trees and include species such as sea fans and sea whips.
Each individual coral is referred to as a polyp. Coral polyps live on the calcium carbonate exoskeletons of their ancestors, adding their own exoskeleton to the existing coral structure. As the centuries pass, the coral reef gradually grows, one tiny exoskeleton at a time, until they become massive features of the marine environment.
Corals are found all over the world's oceans, from the Aleutian Islands off the coast of Alaska to the warm tropical waters of the Caribbean Sea. The biggest coral reefs are found in the clear, shallow waters of the tropics and subtropics. The largest of these coral reef systems, the Great Barrier Reef in Australia, is more than 1,500 miles long (2,400 kilometers).
The Deep Sea
The deep sea contains up to 95% of the space occupied by living organisms. Combined with the sea floor (or benthic zone), these two areas have yet to be fully explored and have their organisms documented.