An estuary is where the river meets the sea, and plays an important role in the life of many animals. Throughout the day, week or year the physical and chemical variation can change dramatically. The major source of this variation is the tidal fluctuations. This means that the animals that live in these environments must be able to cope with these drastic changes in salinity, temperature and water level, making them very unique and special creatures.
Many juvenile fish migrate into the estuaries during late winter, spring and early summer. This is when the water temperatures are high and the food supply is abundant. The juvenile fish are better protected from most marine predators in the estuaries and therefore rely on these habitats in order to survive into adolescence. They return to the open ocean when they are big enough. (Wallace JH, “South African Estuaries and their importance to fishes”, South African Journal of Science 80, 203-207 (1984).
Human activities can have severe effects on estuaries resulting in the loss of biological diversity. Some of the most common problems include dredging, pollution and accelerated sedimentation due to erosion. If we want the estuaries and the species that thrive there to survive we must limit these destructive activities as much as possible.
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