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Life in Freshwater

Animal Communities

The plants form a distinct series of zones through the littoral region. The animals may fit this zonation as well but the variety of microhabitats is enormous.

The main habitat regions for animals:

  1. Epineuston - on the surface film

  2. Hyponeuston - beneath the surface film

  3. Pelagic Region - open water within the light

  4. Profundal Region - below the photic zone so no light

  5. Benthos - the bottom. This may be the fringe benthic region (within photic) or profundal benthic region

Lake Zones by depth
Zones for Animals at the Edge of a large Pond or Lake

The profundal region may not be present as this will depend on the depth. Two groups of animals exist in the pelagic or profundal region: plankton if they drift at the whim of the wind and turbulence; larger animals that have the power to determine their movement between the regions, e.g. fish, are called the nekton.

Nektonic creatures are often dominated by the fish that move freely between the microhabitats to feed.

Pond skaters are a good example of animals living on the surface (epineuston), using surface tension to support themselves. Many of these are predatory bugs but may be eaten by those living beneath the surface like fish and greater water boatmen ( Notonecta sp). Whirligig beetles are associated with the surface and can see both above and below as they have two pairs of eyes. However, like many species that living just below the surface they can leave the surface and dive considerable distances. Most invertebrates live either in the fringe weeds or benthos.

Fringe Weed: The various shapes and sizes of the weed leaves provide ideal shelter for a huge variety of invertebrates. Hydra and sponges are sedentary creatures that wait for the food to go to them. Mayflies, pond snails and many others remove material like the periphyton from the surface of the macrophyte, often waiting for nightfall before moving around the plants. Predators like damselflies and dragonflies lurk on the plant material waiting for the prey to come within grabbing distance. The larvae of diving beetles are another good example of lurking predators.

Benthos: in ponds and the edge of lakes the benthic region can be covered by leaf debris providing huge amounts of nutrient for benthic animals. The water hoglouse ( Asellus ) is a good example of a detritivore consuming the leaf litter. Others like the worms and flatworms can be found in abundance under the dead leaves. Snails and some bivalves may be here although the larger ones like the swan mussel may be in deeper water. Profundal mud is dominated by sediment and can be more difficult to study with a net because of it. Potentially messy!

There may be bivalve molluscs living in the bethos, e.g. swan mussels

 


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