Monoporeia affinis, (syn. Pontoporeia affinis) (, ' = Pontus / Black Sea; , ' = to travel), is a small, yellowish benthic amphipod living in the Baltic Sea, the Arctic Sea and the lakes of the Nordic countries.
Description
Monoporeia affinis measures up to long when fully grown, with two pairs of antennae and one pair of black eyes.
Ecology
M. affinis is one of the Baltic glacial relicts. Originally a freshwater species, it also exists in lakes. M. affinis lives on soft bottoms down to 80 metres; usually hundreds to thousands of individuals per square metre, but can get up to 10,000 to 20,000 per square metre. The increasing loss of oxygen in the Baltic Sea bottoms – especially in the Gulf of Finland – has lately been affecting the M. affinis population, since its eggs and embryos are very sensitive to lack of oxygen. Thus M. affinis is often used as an indicator species of the state of bodies of water.
Life cycle
After mating in the autumn and bearing over the winter, the female M. affinis gives birth to 20–30 offspring, which only happens once during its 2–4 year lifespan. M. affinis has a recurring population cycle, with abundance oscillating every 6 to 7 years.