Limnology. The freshwater fauna

CRUSTACEA

A swarm of water fleas (<i>Daphnia</i>) in a pond at Kapp Linné.<i>Lepidurus arcticus</i>, tadpole shrimp. Typical of the clean freshwaters on Svalbard that do not contain char.

There are some 34 species of freshwater crustacean known from freshwater lakes and ponds on Svalbard. Perhaps the most obvious are Daphnia, water fleas, common in many ponds. This species is clonal, that is the population only consists of egg laying females. The species of Svalbard have a high melanin content and so appear darker than individuals from more southerly locations such as the Norwegian mainland. This is considered an adaptation to help protect against high ultraviolet light levels.

In some of the freshwaters you can find the tadpole shrimp, Lepidurus arcticus. This animal may be up to 3cm long as an adult and can be seen scuttling around on the mud at the bottom of the pond. In fact, only a small proportion of the population are visible since most will be hidden within the mud. This animal is considered a living fossil being unchanged for around 200 million years. They feed on dead organic matter but may predate the Daphnia and are cannibalistic, eating each other. 

Tadpole shrimps overwinter as an egg and develop rapidly into adults each year. They are typical of clean and cold freshwaters, especially those without fish. If fish are present then few tadpole shrimps can avoid being eaten unless there are shallow margins to the pond, areas to shallow for the fish to enter. In these shallows the tadpole shrimp may survive. Otherwise present the presence of tadpole shrimps is a good indicator that fish, charr on Svalbard, are absent. They also provide food for arctic terns. 

A chief enemy of the freshwater invertebrate fauna, the Arctic charr. Linnevatn Studying invertebrate drift in a stream, Midtre Lovénbre, Kongsfjord.Examining the catch of the drift nets, left to right, Malu, Fredrik, Lena, Hanna-Kaisa, Martin.After only a short trapping period large numbers of fly larvae (the small worm-like shapes) were caught indicating a substantial drift of these larvae out into the fjord.