Salinity is defined as the amount of solid material contained in each kilogram of seawater, assuming all carbonate is converted into oxide form, bromine and iodine replaced by chloride and units of salinity expressed in grams per kilogram, or as thousandths, commonly called “ppt”. Sea water also contains fine droplets in suspension. Most of these substances will be dissolved and some will settle to the bottom of the sea and the rest are described by marine bacteria. All solutes is what causes the saltiness of the sea water.
To measure the salinity of sea water which is then used term salinity. Salinity can also be used in any waters, but it is most striking is in the sea. Salinity can be defined as the total amount in grams of substances dissolved in one kilogram of water. In a steady state at sea salinity levels ranging between 34% up to 35%. Each region has a different salinity levels in the tropics is different as salinity ranges between 30-35%, but there is no increase salinity.
Salinity is fixed and does not change throughout time. Then why salinity levels in each of the different waters, whereas the salt content remains? This disebakan because of the distribution of salinity in the ocean. This distribution occurs vertically and horizontally. Salinity distribution is influenced by several key factors, namely:
a) The pattern of water circulation: help the spread of salinity
b) Evaporation (evaporation): the higher the rate of evaporation in the area, the salinity was increased or vice versa because the salts are left behind in the water for example in the Red Sea salinity levels reach 40%.
c) Curan rain (precipitation): the higher the level of rainfall in the area, the salinity is reduced or otherwise this is due to the dilution by rainwater.
d) The flow of the river around (run off): the more the flow of rivers that flow into the sea, the salinity decreases and vice versa.
Based on the difference in water salinity can be divided into 4 groups, among others:
a) fresh waters (fresh water) that waters having salinity ranging between 0-5 ppt. for example in drinking water, river water, wells, etc.
b) brackish waters (brakish water) that waters having salinity ranging between 5-30 ppt, for example in mangrove areas, estuaries and ponds area.
c) sea waters (saline water), the waters have a salinity ranging between 30-50 ppt. for example the high seas
d) Water hipersaline (brine water), the waters have a salinity> 50 ppt. for example sea near the poles
Variations in salinity in sea water will affect the bodies of aquatic life through the control of density and diversity of osmotic pressure. The types of aquatic biota is destined to have almost all the soft tissues that its density approaching normal seawater specific gravity, while the types of organisms that live on the seabed (benthic) has a higher density than the water above it. Salinity cause osmotic pressures.
In general, the salt content in the cells of marine life tend to approach most of the salt content in seawater. If the cells are in an environment with other salinity osmoregulation then a mechanism is needed to maintain the balance between cell density and the environment. In most animals a decrease in the salinity of estuaries starters usually accompanied by a decrease in salinity in the cell, a new osmoregulation mechanism occurs after a real decrease in salinity (Romimohtarto, 1985).
Ways osmoregulation outer protective covering of the surrounding waters, the protection of the cell membrane, a mechanism to remove excess excretion of fresh water and the cells of the body. The ability to deal with fluctuations stemming from the salinity found in groups of diverse stars of protozoa to fish. Biota estuaries usually have tolerance to salinity variations are large (euryhalin). Examples of milkfish (Chanos Chanos), mullet (Mugil sp.) And fish tilapia (Oreochromis mossambicus).