Glossary

Glossary

adaptation -Any genetically determined feature which conveys selective advantage and so increases an organism's evolutionary fitness. This word may have other meanings in ordinary usage, and is often misused in the biological context. However, the key feature of "adaptation" in the evolutionary context is that the feature must be genetically inherited, and organisms possessing the feature must possess some advantage over organisms lacking it.

centrifugal force -a force directed away from the centre of a revolving body.

coastal high pressure system -the occurrence of atmospheric high pressure system over a coastal region. The high atmospheric pressure displaces the water seaward, and results in lower than expected tides.

coastal low pressure system -the occurrence of atmospheric low pressure system over a coastal region.Water is usually displaced towards the coast, resulting in higher than expected tides.

equinox -the time at which the sun crosses the plane of the equator, approximately March 21 and September 22. Day and night are equal in duration. Important in understanding tides is the fact that this coincides with the times when the earth and sun are closest together.

gravity -the mutual force of attraction between two bodies. The gravitational force is proportional to mass.

intertidal zone - the region of the seashore between the highest high water of spring tides and the lowest low water of spring tides (see littoral zone).

littoral zone -in the context of the seashore, this is approximately synonymous with intertidal zone> (see intertidal zone).

lunar cycle -the approximately 28 days it takes for the moon to revolve around the earth.

neap tides -condition of the tides resulting from the earth and sun being arranged at right angles to one another. As a result of the gravitational and centrifugal effects of the sun and moon cancelling one another, the tidal range is minimal.

offshore winds -winds which blow from the land, out towards the sea. Offshore winds displace water away from the coast and cause lower than expected tides.

onshore winds -winds which blow in from the sea, towards the land. Onshore winds displace water towards the coast and cause higher than expected tides.

salinity -the total concentration of all dissolved inorganic solutes in seawater; roughly equivalent to saltiness.

semidiurnal tides -condition in which two high, and two low tides occur every day.

solstice -either of two points in the sun's path at which the sun is furthest north or south of the equator, about June 21 and December 22 respectively. Important in understanding tides is the fact that this coincides with the times when the earth and sun are furthest apart in their orbit.

spring tide -condition of the tides resulting from the alignment of the earth and sun. As a results of the gravitational and centrifugal effects of the sun and moon reinforcing one another, the tidal range is maximal.

stress -any external factor which limits the rate at which a plant or animal grows, reproduces or stores energy.

tidal cycle -the 14 days from one spring tide to the next spring tide, or from one neap tide to the next neap tide.

tidal range -the vertical distance between low and high water.

wave action -the forceable movement of water caused by waves breaking on the seashore.

zonation -tthe horizontal banding of the seashore caused by the dominance of different organisms at different levels on the shore.