chapter 6

salinity

The concentration of dissolved salts in a body of water, affecting the kinds of organisms that are present.

Marine Snow

Most organisms of the oceanic province depend on this organic debris which drifts down from the upper, lighted regions.

Zooxanthellae

Symbiotic algae that live and photosynthesize in the tissues of some coral animals and aid in the growth of reefs.

Estuary

A coastal body of water, partly surrounded by land, with access to the open ocean and a large supply of fresh water provided by rivers.

Plankton

Small or microscopic organisms that are poor swimmers and are carried about by waves and currents.

Phytoplankton

These free-floating photosynthetic cyanobacteria and algae form the base of most aquatic food webs.

Nekton

Large strong swimmers such as fishes, whales, and turtles.

Littoral zone

A shallow-water area along the shore of a lake or pond that is the most productive section.

Limnetic zone

The open area away from the shore of a lake, extending down as far as sunlight penetrates; the main organisms are phytoplankton, zooplankton, and larger fishes.

Thermal stratification

The marked layering of large temperate lakes caused by the depth into which light penetrates.

Interdial Zone

A biologically productive habitat located in the shoreline area between low and high tides.

Mangrove forest

The tropical equivalent of a salt marsh, covering approximately 70% of tropical coastlines.

Atoll

A circular coral reef surrounding a central lagoon that forms as a volcano submerges below the water level.

Freshwater wetlands

Also called marshes and swamps, these areas are usually covered by shallow water for at least part of the year.An aquatic biome that is submerged or saturated by water for at least part of each year, but shallow enough to support emergent vegetation.

Thermocline

An abrupt temperature transition separating the cool and warm water in a lake.

Fall turnover

A mixing that occurs in a lake as a result of the cooling and sinking of surface water, eventually resulting in a uniform temperature throughout the lake.

Spring turnover

When ice melts in a lake and sinks to the bottom, causing bottom water to return to the surface.

Benthos

Bottom-dwelling organisms that fix themselves to one spot, burrow into the sand, or walk on the bottom of aquatic ecosystems

Profundal zone 

The deepest zone of a lake where no light penetrates; is mineral-rich and anaerobic.

Salt marsh

A shallow, swampy area dominated by grasses, where the salinity fluctuates between that of sea water and that of fresh water.