USGS Aquatic GAP Program

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[Copyright: USGS GAP Analysis Program]

The goal of the GAP Analysis Program is to keep common species common by identifying those species and plant communities that are not adequately represented in existing conservation lands. Common species are those not currently threatened with extinction. By identifying their habitats, GAP Analysis gives land managers and policy makers the information they need to make better-informed decisions when identifying priority areas for conservation.

Regional Projects:


Featured Marine Resource

[Image: NBII]
[Image: NBII]

The NBII Marine Habitats Node provides access to information about marine habitats, including general information, coral reefs, federal management agencies, invasive species, plants and animals, and data. Key projects of the Marine Habitat Node include the Coral Reefs Project, which integrates coral reef datasets, maps, publications, fact sheets, images, and other information from a variety of partner organizations; and OBIS-USA, a one-stop source for biogeographic data collected from U.S. waters and oceanic regions which is part of the global Ocean Biogeographic Information System (OBIS).



Fishbase is a searchable global database of fish species information.

FishBase on the web contains practically all fish species known to science. Search over 28,000 fish species by common name, scientific name, ecosystem, or country. Or, use the search feature to find tools, maps, or references.

Learn more about FishBase.

Aquatic Habitats

Ganges River Delta [Photo: NASA]
Ganges River Delta [Photo: NASA]

The Earth's hydrosphere contains almost 1.4 billion km 3 of water, which is the combined mass of water on the planet including its surface, atmospheric, and subsurface sources. There are many different types of aquatic habitats on Earth, of which the major types are estuaries, lakes, oceans, rivers and wetlands. Water, the context for all of these habitats, has unique chemical and physical properties which in turn affect the species and communities that live in these aquatic habitats.

Unique properties of water and aquatic habitats
The molecular structure of water is the reason for many of its unique attributes, such as its density, specific heat, high surface tension, and versatility as a solvent, all of which are critical to life. Water is a polar molecule that consists of one oxygen and two hydrogen atoms. When water molecules are in contact with each other, they form strong bonds between the positive and negative poles. Frozen water is less dense than liquid water because of these bonds, which when frozen create a lattice-like structure that spreads the molecules out, enabling ice to float. This surface ice in turn allows organisms in lakes and streams to survive cold winter temperatures, because the surface of ice acts as an insulator, preventing the water beneath from freezing. Water has a high specific heat, meaning it takes much more heat to raise the temperature of water than the surrounding air and soil. This enables water to buffer changes in temperature in the natural world, allowing for a relatively stable environment for aquatic life. Water has the second highest surface tension of any liquid on Earth, also due to its strong molecular bonds. This creates a special environment at the air-water interface, giving some aquatic insects the option to skate on the surface of water. Another of water's important characteristics is its capability as a nearly universal solvent. This property allows the waters of the world to have mixtures of dissolved gases, salts, and organic compounds, which are used by aquatic organisms to sustain life as they know it.

Adaptations to life in water
Aquatic animals have evolved adaptations to deal with the issue of respiration under water. Many use gills to breathe, which are areas of high surface area that allow the animal to take up dissolved oxygen from water through gas exchange with their circulatory system. Some small animals, such as invertebrates, may use their entire bodies to respire. In addition to animals that live under water, other animals such as shorebirds and wetland birds have life history adaptations and behaviors to utilize aquatic habitats.

Adaptations to salinity
Marine and freshwater environments are very different in part due to the different properties of salt and fresh water. Adaptations to these differences are most notable in fish. Freshwater fish do not drink water, but instead absorb it through their gills by osmosis. They solve the issue of living in water less saline than themselves by having very efficient kidneys to aid in excretion of excess water. In contrast, marine fish must drink large amounts of water in order to replace what has been lost by osmosis to their more saline surroundings.

Closs, G., B. Downes, and A. Boulton. 2004. Freshwater Ecology. Blackwell Publishing. Victoria, Australia.
Hornberger, G.M., J.P. Raffensperger, P.L. Wiberg, and K.N. Eshleman. 1998. Elements of Physical Hydrology. Johns Hopkins University Press. Baltimore, MD.
Moyle, P. and J. Cech. 2004. Fishes: An Introduction to Ichthyology. Fifth Edition. Prentice Hall. Upper Saddle River, NJ.

Find out more about the major types of aquatic habitats, including classification, subhabitats, and human impacts:

Read about the diversity of estuaries, where rivers meet the ocean.
Learn about lakes, inland reservoirs of water.
Find out about the habitat that covers 71% of the Earth.
Learn about the rivers, flowing freshwater habitats.
Discover the saturated world of wetlands.

Discover the National Fish Habitat Action Plan and Data

NFHAP logo [Image: National Fish Habitat Action Plan]
[Image: National Fish Habitat Action Plan]

The National Fish Habitat Action Plan (NFHAP) is an unprecedented attempt to address a nationwide fish crisis by focusing on the loss and degradation of their habitat. The Plan was born in 2001 by an ad hoc group supported by the Sport Fishing and Boating Partnership Council. This group was inspired to develop a partnership effort for fish conservation in the image of the successful and strategic North American Waterfowl Management Plan.

As a federal-level partner, the USGS-NBII was designated by the National Fish Habitat Board to house the data delivery system supporting the National Fish Habitat Action Plan. Find out more about NBII's role in the NFHAP and the data associated with the Plan.

Featured Habitat: Edwards Aquifer

Texas Blind Salamander [Photo: Texas Parks and Wildlife]
Texas Blind Salamander [Photo: Texas Parks and Wildlife]

The Edwards Aquifer is a hydrogeologically sensitive Karst aquifer in central Texas that is home to fourteen threatened and endangered species. The aquifer is comprised mainly of limestone, with many caves and natural springs honeycombed throughout the aquifer to provide small habitats that are ecologically unique. These habitats are home to approximately 45 troglobotic (obligate cave-dwelling) species and many other species that can live in both surface and subsurface environments (troglophiles). Monitoring and managing changes in surface and ground water quantity and quality is critical to the stewardship of species that reside in the Edwards Aquifer, especially those that are threatened and endangered.

The Edwards Aquifer portal, developed by the NBII Central Southwest/Gulf Coast Information Node, gives users information describing surface water and groundwater quality, water quantity, precipitation trends, species information, and critical habitat areas of the threatened and endangered species of the Edwards Aquifer.

Aquatic Food Webs

Aquatic Food Webs [Image: US EPA]
Aquatic Food Webs [Image: US EPA]

Aquatic food webs are conceptual diagrams that demonstrate the flow of energy and nutrients in aquatic systems. Although the species that make up aquatic food webs will greatly vary depending on habitat type, the basic trophic levels or feeding levels of food webs are similar. Producers such as phytoplankton, aquatic plants, and algae use photosynthesis to convert sunlight and nutrients into living tissue. Primary consumers such as zooplankton and plant grazers eat producers. Secondary and tertiary consumers such as invertebrate predators, birds, fish, mammals, and humans eat lower-level prey items. Decomposers consume dead plants and animals, breaking organic matter down into nutrients. Since organisms seldom feed exclusively on another, several food chains are often woven together to form a "food web," a complex cycle of interconnected organisms and organic matter.

Explore the NBII Fisheries and Aquatic Resources Node's Aquatic Organisms section for more information about the wide variety of organisms that use the aquatic environment, ranging from endangered species to aquaculture.

Discover the NBII Bird Conservation Node's U.S. Fish and Wildlife Service Focal Bird Species, many of which are shorebirds, seabirds, and waterfowl that are important components of aquatic food webs.

The NBII Program is administered by the Biological Informatics Program of the U.S. Geological Survey
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