A habitat is defined as a place where a plant or animal lives, receiving sufficient food, water, and shelter to survive and reproduce. Several factors control the distribution and diversity of organisms in a habitat. These factors may include the amount of light present, the salinity and temperature of the water, food and nutrient availability, and the stability and type of substrate associated with the habitat.

In marine and aquatic ecosystems, there are many varied habitats. However, these habitats may be divided into three general categories: benthic, open water, and shorelines and wetlands. The organisms that inhabit these areas have adapted to avoid predation; to compete for resources; and to survive daily and seasonal stresses occuring from changes in temperature, salinity, and exposure.

The benthic habitat is found at the bottom of a water column. A benthic community may exist in water that is shallow or deep, warm or cold, or dark or illuminated. Benthic habitats include rocky intertidal zones, kelp forests, coral reefs, oyster reefs, deep ocean environments, salt marshes, estuaries, mangrove swamps, and hydrothermal vent communities. The benthos, or bottom dwelling organisms, who live in these habitats have developed certain adaptations to allow them to survive in their respective habitats. For instance, clams, tubeworms, and mussels found in the deep ocean environments have developed a symbiotic relationship with chemosynthetic bacteria. These symbiotic bacteria live inside the host organism and provide it with abundant food in the form of simple sugars in exchange for abundant oxygen, carbon dioxide, hydrogen sulfide, and protection from predators.

Open water is the second general habitat category. Organisms that live suspended in the water column encounter difficulties in maintaining their vertical position in the water, obtaining food and oxygen, and surviving long enough to reproduce. Phytoplankton, tiny one-celled plants, drift near the surface and can lift themselves higher in the water column. This elevated position enables them to maximize the amount of sunlight obtained for use in photosynthesis. Phytoplankton form the base for all aquatic and marine food chains. Through photosynthesis, phytoplankton provide 60-70% of the oxygen in the atmosphere, as well as the vast majority of oxygen in the water. Zooplankton feed almost exclusively on phytoplankton and, in turn, are preyed upon by small fish and some large whales and sharks. Fish are the most numerous and diverse of the major vertebrate groups, consisting of more than 22,000 species. Whether bony fish such as salmon or flounder, or cartilaginous fish such as sharks or rays, these vertebrates all depend on plankton to turn sunlight into energy for use in their metabolism.

Shorelines and wetlands compose the third habitat category. Rocky shores, sandy beaches or banks along rivers, lakes and oceans, estuaries, mangrove swamps, and salt marshes are all examples of habitats within this category.

The rocky shore proves to be a very harsh environment in which to live. Wave action can dislodge plants and animals clinging to the rocks. Freshwater input from rain, increasing water temperatures, and the effects of desiccation (drying out) in the upper tidepool can result in death or shock to many tidepool inhabitants. However, rocky shores represent one of the most diversely populated habitats, since they receive nutrients from both the land and the sea. Abundant food and shelter may be obtained in the rocky shore habitat, making it a desirable place to live for many organisms.

Salt marshes, with their abundant grasses, are among the world’s most productive areas. Seventy to eighty percent of all coastal organisms, including many commercially important species, rely upon the salt marsh for some part of their life cycle. Marshes serve as nursery areas for juvenile organisms, as buffers against storms for inland areas, as natural filters for the marine environment, and as resting places for many species of migratory birds.

Mangrove swamps represent the tropical equivalent of temperate salt marshes in that they provide abundant nutrients for resident plants and animals. The root systems trap sediments, provide shelter to many organisms, and build barriers to protect coastal communities.

Freshwater wetlands are dominated by grasses and herbaceous, woody vegetation. Standing surface water or saturated soils are generally present in a wetland, year-round. The wildlife indigenous to a freshwater wetland is quite diverse. For instance, red-winged blackbirds breed and nest in cattail marshes. Wading birds such as bitterns, herrings, rails, and snipes enjoy feeding in freshwater wetlands. Beaver, muskrat, and other small mammals, as well as large numbers of aquatic insects, reside in freshwater wetlands. Snakes, fish, and amphibians live in swamps and bayous, feeding on the abundant insects and small mammals.

Habitat loss is a primary concern of scientists, environmental organizations, and many federal and state agencies. Constant encroachment by humans has resulted in the loss of a large percentage of freshwater wetlands and salt marshes. One hundred and five million acres of wetlands exist in the United States today, which represents only one half of the acreage present during the Revolutionary War. By the year 2000, it is estimated that at least 70 percent of the human population will live close to a body of water.

In order to curb the high rate of habitat loss and degradation, Congress passed the Coastal Zone Management Act (CZMA) in 1972. This Act establishes a national policy to “preserve, protect, develop, and where possible, to restore or enhance the resources of the Nation’s Coastal Zone for this and succeeding generations” and to “encourage and assist the states to exercise effectively their responsibilities in the Coastal Zone through the development and implementation of management programs to achieve wise use of the land and water resources of the Coastal Zone...” [16 U.S. C.1452, sec. 303 (1) and (2)].

Also, in 1972, Congress passed the Clean Water Act (CWA). This act was designed to restore and maintain the quality of United States’ waters. The CWA regulates the discharge of pollutants into United States’ waters from any point source that includes stormwater drainage systems, industrial facilities, and sewage treatment plants. The CWA requires states to develop water quality management plans that regulate nonpoint source pollution. Within the Act are provisions that require oil and hazardous substance spills in or near waterways be reported and cleaned. Permits for activities that might adversely affect wetlands are required under the CWA.

National Parks, wildlife refuges, marine sanctuaries, wilderness areas, nature preserves, and national seashores are designed to protect environmental and natural resources. These areas also set aside and protect important habitats for many organisms.

It is imperative habitat research continue and data be collected and interpreted, thereby enabling managers to develop effective strategies for preserving and protecting these fragile areas. It is also essential that our children learn about the important role these habitats play in the environment and the subsequent effects of the loss of these habitats on ecosystems and their inhabitants.