Identifying impacts of current temperature elevation on sea fauna and flora populations is difficult because natural changes, fishery and eutrophication are also taking place. There are signs, however, that the distribution of some species is moving to the north. It appears that catches of common shrimps in the southern part of the North Sea (in the vicinity of Belgium) has decreased in recent years. This cannot be explained by the pressure of fishing activity, which did not increase. Instead it seems that the lower limit of the range of shrimps is moving to the north (1).
In a recent study for the North-Sea, U.K scientists estimated that two thirds of the most common bottom dwelling fishes have moved to cooler waters, going north or to deeper waters. Fishery is currently the most important pressure on commercial species. The researchers concluded, however, that further temperature rises are likely to have profound impacts on commercial fisheries through continued shifts in range and alterations in interactions between species (predation, etc.) (2).
In parallel, southern species such as sardine and anchovy are increasingly being observed in the North Sea. Species which had their northern range limit in the English Channel or extreme south of the North Sea are more regularly found near Belgium. Sea warming has probably contributed to the development of local communities of exotic species brought on by human activities (shipping). An example is the Pacific oyster which is reproducing in Belgian waters, while it was believed that temperatures would be too cold for its larvae. Land species are competing with local species: pacific oysters are taking the place of mussels (3).
Future warming is expected to increase biodiversity in the North Sea, mainly because warmer waters tend to suit more species. New species will arrive either as vagrants from more southern European waters or in the form of non-indigenous species from warm marine regions elsewhere in the world. Fishes from warm waters, however, are often commercially less valued than cold water species. Climate change will also add to existing pressures, in particular from fishery, and may have a significant adverse impact on this commercial activity in the future (4).
The spatial distribution and/or recruitment of species important for the Belgian fisheries like sole, plaice, and cod were already negatively affected by climate change (9). More southern commercial species, like red mullet and John Dory, which are currently not important for Belgian fisheries but have a high economic value, are likely to increase their northerly presence in response to climatic warming. Further rises in temperature are likely to have profound impacts on commercial fisheries through continued shifts in distribution and alterations in community interaction (10).
Many species of plankton and fish have shifted their distribution northward and sub‑tropical species are occurring with increasing frequency in European waters, changing the composition of local and regional marine ecosystems in a major way (4). Recent studies have shown that the northward movement of southerly species has caused species richness in the North Sea to increase (5). This may have negative ecological and socio‑economic effects: the three large species that have decreased their range the most in the North Sea are all commercially relevant, while only one of the five most increasing species and less than half of the all the species that expanded their range are of commercial value. A climate change-induced shift from large to smaller species is thus likely to reduce the value of North Sea fisheries (5).
During the past 40 years there has been a northerly movement of warmer‑water plankton by 10° latitude (1100 km) in the north‑east Atlantic and a similar retreat of colder‑water plankton to the north. This northerly movement has continued over the past few years and appears to have accelerated since 2000. Sole and other warm‑water species have become relatively more abundant in northerly areas, while plaice and other cold‑water species have become rare in southerly areas (8). Climate is only one of many factors which affect distribution and abundance, but the consistency of the response of this particular index to temperature, both within particular areas (i.e. time trend) and across all areas (i.e. geographic trend) suggest that the causal relationship is quite strong. Scenario projections of future movements of marine species have not yet been made (6).
The kinds of fish which are available for human consumption are not necessarily affected by the distribution changes shown above, because fish are often transported long distances from where they are caught to where they are marketed, but the prices of fish may change if certain species that are common today become less common. People eating locally caught fish may notice changes in the species they catch or buy. Changes in distribution may affect the management of fisheries. Fisheries regulations in the EU include allocations of quotas based on historic catch patterns, and these may need to be revised (6). In general it is not possible to predict whether northward shifts in distribution will have a positive or a negative effect on total fisheries production (7).
The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Belgium.
- Kerkhof (2004), in: Ministry for Social Affairs, Health and Environment (2009)
- Perry et al. (2005), in: Ministry for Social Affairs, Health and Environment (2009)
- Ministry for Social Affairs, Health and Environment (2009)
- Brander et al. (2003); Beare et al. (2004); Beare et al. (2005); Perry et al. (2005); Stebbing et al. (2002), in: EEA, JRC and WHO (2008)
- Hiddink and Hofstede (2008), in: EEA, JRC and WHO (2008)
- EEA, JRC and WHO (2008)
- Brander (2007), in: EEA, JRC and WHO (2008)
- Brander et al., 2003, in: EEA, JRC and WHO (2008)
- Rijnsdorp et al. (2010), in: National Climate Commission Belgium (2010)
- Van den Eynde et al. (2009), in: National Climate Commission Belgium (2010)