Marine habitats are habitats that support marine life. An ecosystem is a system of living organisms which interact with one another and their surrounding habitat.
A balance in the various ecosystems around the world is what is vital for a sustainable and healthy planet.
Marine life depends in some way on the saltwater that is in the sea. A habitat is an area inhabited by one or more living species. The marine environment supports many kinds of these habitats.
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.
The marine environment has several different habitats with a set of specific physical factors: ocean tides, wave action, sea temperature, ocean currents, levels of light, wind, type of topography, climate.
Sandy beaches may at first seem barren and devoid of life but that is because most animals are hiding in the sand and they are only becoming active at high tide or at night.
Characterised by instability, sandy beaches are constantly changing as sand is continually lifted and shifted by the action of waves and wind. Flora and fauna have had to adapt to this incessant instability and constant change in order to survive. Most seaweed cannot grow in beachy areas as there is nothing to attach themselves to. However, beyond the beach, in the dunes, a huge number of plants thrive. Animal life on the sandy shore is restricted to birds and small species such as worms and crustaceans, which live in the spaces between the sand grains. Some bigger species such as plough snails and crabs burrow into the sand following the rhythms of the rising and falling tide. The food web is extremely dependent upon plankton, seaweed and other edible food items which are deposited on the beach by wave action.
Shrimps, crabs and fishes living on the bottom of the sea such as flatfish, cuttlefish or gobies, cruise over the sand feeding on snails, mussels, worms and prawns.
A variety of bird species such as plovers, terns and gulls probe the exposed beach for crustaceans, bivalves, molluscs and other animals and organic matter.
Rocky shores are characterised by the flora and fauna living in the intertidal zone – the area between the high tide and low tide water mark. Exposure to surf and sun differs considerably, relative to the rise and fall of the tide. Marine life occupying the rocky shores need to be extremely hardy and easily adaptable to be able to survive.
Plants and animals need to deal with very strong wave action, avoid predation and adapt to changing currents. Filter feeding organisms such as black mussels, oysters and barnacles thrive during high tide as the wave action brings nutrient rich water.
Adaptations are vital for the survival of plants and animals which find themselves exposed and in direct sunlight during low tide. Certain seaweeds such as sea lettuce (Ulva spp.) can tolerate very harsh conditions by surrounding themselves with a mucous layer. Crabs, snails and bivalves have thick shells which help them to slow down evaporation.
Mangroves (Rhizophora sp., Avicennia sp., Laguncularia sp.) are clusters of small, shrub-like trees which are found in tropical to subtropical tidal areas. Mangroves dangle their roots in saline or brackish water and are able to withstand high salinity levels.
Forests of these plants provide a safe shelter for a variety of marine life and are important nursery areas for young marine animals. These ecosystems are usually found in warmer areas between the latitudes of 32 degrees north and 38 degrees south.
Estuaries are dynamic systems or bodies of water found where a river meets the sea. They are home to unique plant and animal communities which have adapted to the constantly changing salinity levels.
Estuaries provide calm nursery grounds for many fish species and support a large number of wading birds. Estuaries are delicate, vital and one of the most productive ecosystems in the world. They provide a source of food, shelter, migration stopovers and a breeding ground for a variety of species.
Bacteria, microscopic diatoms, small bivalves, prawns and burrowing worms thrive in estuaries – feeding on detritus (decaying plant matter).
In tropical regions, estuaries are often lined with mangrove swamps, creating an entirely different ecosystem within itself.
Coral reefs are found in tropical regions where ocean temperatures are warmer than 26 degrees Celsius. The coral reefs of South Africa are found along the east coast. In such environments, the diversity of life is high even if nutrient levels are low, creating a very competitive living space for most species. Corals are colonial anemone-like animals which cluster to develop extensive reefs by slowly depositing skeletons made of calcium carbonate.
The living corals capture food particles by using their tentacles. They also house microscopic algae in their cell walls which make use of the corals waste products to photosynthesise, ultimately providing the coral with food. Healthy coral reef ecosystems provide a shelter for many species which have developed symbiotic relationships to help ensure their survival in such a predatory environment. An example of an effective symbiosis is the clown fish and sea anemone who offer each other protection from predators in the potentially dangerous reefs.
Who calls coral reefs home?
Invertebrates such as species of coral, sponges, crabs, shrimp, lobsters, anemones, worms, bryozoans, sea stars, urchins, nudibranchs, octopuses, squid, and snails all call coral reefs home.
The resident vertebrates may include a wide variety of fish, sea turtles and marine mammals such as seals and dolphins.
The word “pelagic” is derived from Ancient Greek and means “open sea”. The pelagic zone is the upper layers of the open ocean waters.
The open ocean consists of an infinite amount of plankton which spend their lifespan in a drifting state. Plankton which is derived from the word “planktos”, meaning wandering, refers to the organisms which form the very basis of the food web.
Phytoplankton is a microscopic plant-like organism and form the basis of the food web in this ecosystem. Phytoplankton provides a source of food for zooplankton (microscopic animals) and other larger animals which feed on the zooplankton.
Life in the pelagic zone consists of significantly different forms. Planktonic species have adapted to floating, drifting and minimal swimming whilst some of the fastest predatory fish such as sail fish and short-fin mako sharks are also found here. Areas where productivity of phytoplankton is high, large shoals of fish such as sardines will occur.. Predatory marine animals feed in this high ecological zone as there is an abundance of food. Many zooplankton species move to the surface at night and sink during the day, often followed by fish and squid.