Temperature and Concentration of Nutrients
Temperature like salinity remains almost constant in the oceans in contrast to the land or terrestrial ecosystems ranging from about 2°C in the polar seas to 32°C or more in the tropics. The annual variation in any part of the sea is usually not more than 6°C.
Concentration of Nutrients
The marine environment is low in concentrations of dissolved nutrients, which since they occur in very little amount are measured in parts per billion (ppb) in contrast to salts, such as sodium chloride which is measured in parts per thousand (ppt). This low quantity of nutrients acts as a major limiting factor in determining the size of marine populations.