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large carrying capacity , meaning that they are very fertile and can
support large populations of organisms.
Phytoplankton species in estuaries have growth , reproduction , and
survival requirements similar to those of
other marine-plant
communities. They need both macronutrients and micronutrients ,
adequate sunlight , and suitable water quality (temperature, salinity,
oxygen , PH , water clarity). Because these factors vary considerably
from season to season and from spot to spot , plankton blooms are
irregular .
Zooplankton , like the phytoplankton , are hampered by the turbid water
common in estuaries. Their distribution tends to be regulated by salinity
gradients , with freshwater species in the headwaters , brackish water
species in the middle reaches, and marine species near the mouth of the
estuary.
Temperature also plays a role in their distribution and behaviour over
time.
As is true for the plankton and benthos , estuarine fishes are typically
abundant , but represent very few species , largely because of the
stressful nature of their environment . Fish species with high
physiological tolerances to environmental changes favor estuaries for
their reproductive , spawning and feeding activities .Many estuaries are
considered « nursery » grounds because the vast majority of fish
in
estuaries are juveniles.These young , immature fish feed voraciously and
grow rapidly under the relatively low predation pressures there.
Lagoons :
Unlike estuaries , which are greatly affected by river inflow , lagoons
are isolated or semi-isolated bodies of shallow coastal water that do not
receive an appreciable input of freshwater . In other words, dilution of
salt water in a lagoon is negligible. As a consequence, lagoons tend to
have much simpler water-circulation patterns and salinity distributions
than do estuaries.
A lagoon that is cut off from the ocean is basically a body of standing
water.