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Coastal Habitats. The term coast has a much broader meaning than shoreline and includes many other habitats and ecosystems associated with terrestrial and marine processes. The six major coastal settings are: estuary, lagoon, salt marsh, mangrove swamp and coral reef.
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The term coast has a much broader meaning than shoreline and includes many other habitats and ecosystems associated with terrestrial and marine processes. • The six major coastal settings are: estuary, lagoon, salt marsh, mangrove swamp and coral reef. • Shorelines are one of the most productive ecosystems and because they are shallow, they strongly respond to the effects of waves, tides and weather.
12-1 Estuaries Estuaries are semi-enclosed bodies of water where fresh water from the land mixes with sea water. • Estuaries originate as: drowned river valleys, fjords, bar-built estuaries, and tectonic estuaries. • Salinity typically grades from normal marine salinity at the tidal inlet to fresh water at the mouth of the river.
12-1 Estuaries Estuaries can be subdivided into three types based upon the relative importance of river inflow and tidal mixing. • Salt-wedge estuaries are dominated by the outflow from rivers. • Partially-mixed estuaries are dominated by neither river inflow nor tidal mixing. • In well-mixed estuaries tidal turbulence destroys the halocline and water stratification. • Because river discharge and tidal flow vary, conditions within an estuary can also change, being well-mixed when river flow decreases relative to tidal mixing, to becoming a salt-wedge estuary at times of maximum river discharge.
12-1 Estuaries The widely fluctuating environmental conditions in estuaries make life stressful for organisms. • Estuaries are extremely fertile because nutrients are brought in by rivers and recycled from the bottom because of the turbulence. • Stressful conditions and abundant nutrients result in low species diversity, but great abundance of the species present. • Despite abundance of nutrients, phytoplankton blooms are irregular and the base of the food chain is detritus washed in from adjacent salt marshes. • The benthonic fauna strongly reflects the nature of the substrate and most fishes are juvenile forms living within the estuary until they mature and migrate to the ocean.
12-2 Lagoons Lagoons are isolated to semi-enclosed, shallow, coastal bodies of water that receive little if any fresh water inflow. • Lagoons can occur at any latitude and their salinities vary from brackish to hypersaline depending upon climate and local hydrology. • Bottom sediments are usually sand or mud eroded which was from the shoreline or swept in through the tidal inlet. • In the tropics, the water column is typically isothermal. • In the subtropics, salinity generally increases away from the inlet and the lagoon may display inverse flow.
12-3 Salt Marshes Salt marshes are intertidal flats covered by grassy vegetation. • Marshes are most commonly found in protected areas with a moderate tidal range, such as the landward side of barrier islands. • Marshes flood daily at high tide and then drain through a series of channels with the ebb tide. • They are one of the most productive environments. • Marshes can be divided into two parts: Low salt marshes and High salt marshes. • Distribution and density of organisms in salt marshes strongly reflects availability of food, need for protection, and frequency of flooding.
12-4 Mangrove Swamps Mangroves are large woody trees with a dense, complex root system that grows downward from the branches. • Mangroves are the dominant plant of the tropical and subtropical intertidal area. • Distribution of the trees is largely controlled by air temperature, exposure to wave and current attack, tidal range, substrate and sea water chemistry. • Detritus from the mangrove forms the base of the food chain.
12-5 Coral Reefs A coral reef is an organically constructed, wave-resistant, rock-like structure created by carbonate-secreting organisms. • Most of the reef is composed of loose to well-cemented organic debris of carbonate shells and skeletons. • The living part of the reef is just a thin veneer on the surface. • Corals belong to the Cnidara. • The animal is the coral polyp. • The corallite is the exoskeleton formed by the polyp. • Corals share a mutualistic relationship (mutually beneficial) with the algae zooxanthallae which lives within the skin of the polyp and can comprise up to 75% of the polyp’s body weight.
12-5 Coral Reefs • Corals can be either solitary or colonial. • Corals can not survive in fresh, brackish water or highly turbid water. • Corals do best in nutrient poor water because they are easily out-competed by benthonic filter feeders in nutrient-rich water where phytoplankton are abundant.
12-5 Coral Reefs Coral reefs consist of several distinct parts developed in response to their exposure to waves. • The algal ridge occurs on the windward side of the reef and endures the pounding waves. • The butress zone is the reef slope extending down from the algal ridge. • The reef face extends downward from the butress zone and usually is devoid of living colonial corals because insufficient light reaches this depth. • The reef terrace is landward of the algal ridge and lies at mean water level. • The shape of the colonial coral masses reflects the environment in which they live.
12-5 Coral Reefs As a result of corals growing continuously upward towards the sunlight as sea level rises and/or land subsides and, coral reefs pass through three stages of development. • Fringe reefs form limestone shorelines around islands or along continents and are the earliest stage of reef development. • As the land is progressively submerged and the coral grows upward, an expanding shallow lagoon begins to separate the fringe reef from the shoreline and the reef is called a barrier reef. • In the final stage the land vanishes below the sea and the reef forms a ring of islands, called an atoll, around a shallow lagoon.
