Plenty more fish in the (North) Sea

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There are now more species of fishes in the North Sea, due to global warming, according to a study published in the journal Global Change Biology.

The study by Jan Hiddink of Bangor University and Remment ter Hofstede of the Wageningen Institute for Marine Resources and Ecosystem Studies examined the relationship between winter bottom temperature of the North Sea between the latitudes of 51 and 62N and the annual fish distribution data for the area.

The authors found a positive link between the number of species and the temperature for the area of the North Sea studied.

The average winter bottom temperature of the North Sea has increased at the rate of 0.7C per decade between 1977 and 2003 (this is more than 10 times the global average temperature increase of 0.06C).

At about the same time (1985"2006), 34 species of fishes displayed significant increases in distribution ranges to include the North Sea: the five species whose ranges had expanded the most are the Anchovy Engraulis encrasicolus, Red mullet Mullus surmuletus, Scaldfish Arnoglossus laterna, Solenette Buglossidium luteum and Lesser weever Echiichthys vipera).

Scaldfish, Arnoglossus laterna by Hans Hillewaert (Creative Commons)

Why the increase?The authors believe that the increase in species richness is due to the rise in temperature, and have recorded a positive link between average bottom temperature and increase in species richness over the past five years.

The study also showed that southerly species, which had a northern latitude boundary near the north sea had expanded their ranges further north as sea temperatures increased. Only a handful of northerly fish species had declined, as the northern latitude boundary of these species is typically much further north than the north sea.

The authors said: All four observations confirm the prediction from macroecological patterns of fish species richness that increasing temperature results in to a northward shift of latitudinal patterns and lead to an increase of local fish species richness at temperate latitudes, because the number of species lost is lower than the number of species gained.

Solenette, Buglossidium luteum by Hans Hillewaert (Creative Commons)

Negative effectsThe authors conclude by emphasizing that ...an increase in species richness due to climate change may have negative ecological and socio-economic effects.

The observed replacement of large species by small species will have an effect on energy flow through the food web and, therefore, change the dynamics of the ecosystem.

Socio-economically, all three species that decreased their range in the North Sea are commercial important species, while only one of the five most increasing species (M. surmuletus) and less than half of all 34 species that expanded their range are of commercial value in the North Sea.

For more information, see the paper: Hiddink, JG and R ter Hofstede (2008) Climate induced increases in species richness of marine fishes. Global Change Biology 14, pp. 453"460.