Properties of seawater
Seawater is a dynamic element whose properties change in space and time. Its movements, its physical properties (temperature, salinity, density), the dissolved gases and solids create a variety of environmental conditions significantly affecting the composition of each biological community that inhabits it. Temperature Seawater is heated mainly by solar energy, though some smaller scale contributions are also made by geothermy and underwater volcanic activity etc. The impact of solar radiation on seawater temperature is regulated by factors such as:
Water temperature affects the life of marine organisms to a very great extent: at
high temperatures,metabolism is faster and results in a greater demand for food
and oxygen. Development and genetic maturation are also faster at higher
temperatures. Organisms able to live in a wide temperature range are called
eurothermic in contrast to stenotherms, organisms which have very specific and
narrow temperature demands. The thermophilics prefer high and the psychrophilics
low temperatures. SalinitySea water includes dissolved salts and ions in different quantities, the ions of Chlorine and Potassium being dominant. Salinity (S) is the total quantity (in g) of inorganic salts dissolved in 1000g of sea water. In the open ocean, salinity values at the surface are determined by the equilibrium precipitation - evaporation (see Figure 5) which shows only latitudinal variation with an average value of approximately 35˜. However, in closed seas and mainly in the coastal system, salinity variations can be quite important because of river and fresh water inputs.
Osmoregulation Most marine organisms (except for bony fish,
mammals, birds
and reptiles) have
body fluids whose osmotic pressure equals that of sea water. |