Baltic Sea

Local environment

Definition and basic facts

Figure 1:Baltic Sea and its Drainage area

The Baltic Sea – a shallow, epicontinental sea of volume as 21,700 km³ , with a drainage area of ~1.7 million km² - is one of the largest brackish seas in the world. It is situated between 10⁰ E ~54^oN and ~31⁰E to 66⁰N (close to Arctic Circle) being under influence of mild Atlantic climate in south-west end to harsh continental – boreal climate in Bothnian Bay area. It is connected with Atlantic Ocean through system of very narrow and shallow straits (Great Baelt, Øresund and Little Baelt). Drainage runoff (660 km³ per year) exceeds ten times precipitation (if exclude evaporation) and is 2% of sea volume.

Table 1. Basic data of the Baltic Sea not included in the text (after Bonsdorff).

Parameter	Measure
Area	415 000km2
Length	1300 km
Width	1200km
Maximum depth	459m
Sill depth	17m
Residence time of water	25yr

Primary production

Characteristic feature of primary production in Baltic Sea is its seasonality and spatial variability. Spring bloom – main pulse of new organic matter in higher latitudes starts in February March in Westernmost while in Northern part, in May. Annual primary production vary from 500 [gC*y^-1 *m^-2] in Danish fjords to [50 gC*y^-1 *m^-2] in open waters of Western part of Baltic Proper (Rydberget al. 2006 ) in Gulf of Gdańsk annual primary production is as high as ~200[gC*m^-2y^-1] (Lorentz et al. 1991) and well below 100[gC*m^-2y^-1] in Northern part of the Sea (Kangas et al. 1993,). This decreasing trend reflects both salinity and climatic gradients.

Specific biodiversity issues

The flora and fauna of the Baltic is unusual in that there are areas in which freshwater, brackish water and marine species co-exist. For example, the freshwater plant Phragmites spp. and the marine wrack Fucus spp. can be found side by side. The Baltic Sea has existed for a relatively short time period and has undergone major changes; subsequently it contains a very limited brackish-water flora and fauna. The area is characterised by low species diversity, but many individuals of each species.

Threats

View of Baltic Sea from Dierhagen. Photo D Schiedek

Many of the marine species present are at the limit of their biogeographical distribution. The highest biodiversity is found in the southwest of the Baltic Sea. The major threats to marine biodiversity in the region are unsustainable exploitation of fisheries resources, eutrophication (enrichment from plant nutrient, reducing oxygen levels), pollution from contaminants and oil and the introduction of alien species.

See also

• Baltic Marine Environment Protection Commission (Helsinki Convention)
• An exercise in comparing the pelagic and benthic macrofauna species diversity in Arctic, Antarctic and Baltic sites using the taxonomic distinctiveness index [1]
  
• Values of, and threats to, marine and coastal habitats in the southern Baltic [2]
  
• Shallow sandy sublittoral: the ecological treasure of the southern Baltic Sea [3]
  
• Daily sea surface temperatures rom the late 1800s to the early 2000s implications for biodiversity in the Baltic Sea [4]
  
• Application of benthic indices to assess biodiversity in the southern Baltic Sea [5]
  

The main author of this article is Wiktor, Józef Please note that others may also have edited the contents of this article. Citation: Wiktor, Józef (2009): Baltic Sea. Available from http://www.coastalwiki.org/wiki/Baltic_Sea [accessed on 22-11-2024] For other articles by this author see Category:Articles by Wiktor, Józef For an overview of contributions by this author see Special:Contributions/Józef