Animals in the marine environment

Temperatures at sea are less variable than those on land. The daily and seasonal temperature ranges (differences between the minimum and maximum temperatures reached) are actually shorter there. Salinity, even if very different in different seas, does not normally change too much in one sea. This is why marine organisms, especially those of deeper and offshore waters, did not have to adapt to sudden changes in temperature and salinity, and generally do not tolerate dramatic changes in these two factors. Animals that live in the sea can be divided into:

  • benthos: organisms that live on the bottom, can be stationary (such as corals and sponges) or move (such as worms, some types of fish, many molluscs, etc.);
  • plankton: it is an extremely important water biocenosis. Biocenosis is the whole of the populations of animal and vegetal species that live together in space and time, in a mutual relationship.

Plankton is composed of animals (zooplankton) and plants (phytoplankton) that live suspended in the mass of water and are carried by the sea currents.
These organisms are small in size, some of them are part of the plankton only when they are larvae (for instance larvae of molluscs, Anellida, etc.), then, when adult, they live on the bottom and become part of the benthos. Plankton is eaten by some organisms that are at the higher levels of the ecological pyramid, such as fish. Plankton is however an extremely delicate biocenosis, which is directly related to the chemical and physical conditions of the water: small changes in these conditions can therefore affect its development, by dramatically disrupting the balance of the entire food chain.

  • nekton: this biocenosis includes all the animals that can move smoothly enough to overcome currents and actively swim in water (nekton actually means “to swim”). The most common animals that belong to it are, among vertebrates, many types of fish, reptiles (tortoises and water snakes), sea mammals (whales, dolphins, sperm whales, etc.). They are generally predators, i.e. consumers placed at the end of the food chain, at the top of the ecological pyramid.

Special reports

From the Multimedia section

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Facts