Baltic Sea - Biology

Biology

Approximately 100,000 km2 (38,610 sq mi) of the Baltic's seafloor (a quarter of its total area) is a variable dead zone. The more saline (and therefore denser) water remains on the bottom, isolating it from surface waters and the atmosphere. This leads to decreased oxygen concentrations within the zone. It is mainly bacteria that grow in it, digesting organic material and releasing hydrogen sulfide. Because of this large anaerobic zone, the seafloor ecology differs from that of the neighbouring Atlantic.

Plans to artificially oxygenate areas of the Baltic that have experienced eutrophication have been proposed by the University of Gothenburg and Inocean AB. The proposal intends to use wind-driven pumps to inject oxygen (air) into waters at, or around, 130m below sea level

Since the Baltic Sea is so young there are only a few endemic species, such as the small cockle Parvicardium hauniense and the asexually reproducing alga Fucus radicans. However, several marine species have populations in the Baltic Sea adapted to the low salinity, such as the Baltic Sea herring which is smaller than the Atlantic herring. The benthic fauna consists mainly of Monoporeia affinis, which is originally a freshwater species. The lack of tides has affected the marine species as compared with the Atlantic.

The fish fauna of the Baltic sea is a mixture of marine species such as cod, herring, hake, plaice, flounder, shorthorn sculpin and turbot, and freshwater species such as perch, pike, whitefish and roach.

A peculiar feature of the fauna is that it contains a number of glacial relict species, isolated populations of arctic species which have remained in the Baltic Sea since the last glaciation, such as the large isopod Saduria entomon, the Baltic subspecies of ringed seal, and the fourhorn sculpin.

There is a decrease in faunal species from the Belts to the Gulf of Bothnia. The decreasing salinity along this path causes restrictions in both physiology and habitats.

Satellite images taken in July 2010 revealed a massive algal bloom covering 377,000 square kilometres (146,000 sq mi) in the Baltic Sea. The area of the bloom extends from Germany and Poland to Finland. Researchers of the phenomenon have indicated that algal blooms have occurred every summer for decades. Fertilizer runoff from surrounding agricultural land has exacerbated the problem and led to increased eutrophication.