Edition 5, June 2010
Mediterranean Siege A Glimpse Of The Future
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June 18th, 2010
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| Two-banded seabream. Image source |
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The Mediterranean Sea qualifies as a biodiversity hotspot and one of the most climate change impacted seas in the world due to synergies with invasive species and disease.
In a paper reviewing impacts of climate, disease and invasive species, Christophe Lejeusne and co-researchers call the Mediterranean a “sea under siege” and a potential model of global patterns that will occur in the world’s marine environment under climate change.
Although the Mediterranean consists of only 0.3% of the volume of the world’s oceans, it hosts 4-18% of the world’s marine species, many of them endemic, in part because of the co-occurrence of cold, temperate and sub-tropical organisms.
However, as sea temperatures steadily increase, “extreme climatic events and related disease outbreaks are becoming more frequent, faunas are shifting, and invasive species are spreading”.
The number of invasive species in the Mediterranean has more or less doubled every 20 years since the early 1900s, and there are now about 600 introduced species.
While the increase in species does not seem to be related to climate change, the warming of the Mediterranean has been favouring their spread.
Most of the introduced species are from tropical areas, and were mostly confined to the easternmost Levantine shores.
“They are now rapidly progressing westwards and northwards, through the whole eastern basin, with some now reaching the Adriatic and the western basin.”
The rate of spread seems to have accelerated in the past 20 years, although natural range expansion cannot be distinguished from climate-induced effects.
There have also been increasing reports of toxic dinobionts (algae) in coastal areas, with possible consequences for human disease. Some are exotic species favoured by environmental changes occurring in the Mediterranean.
The authors expect massive alterations in the ecosystem, but these will be difficult to predict because of the numerous biotic and abiotic factors interacting:
“Newcomers (whether natural or introduced) can trigger major changes in ecosystem functioning. But the same ecosystems are increasingly exposed to pollution, overfishing, and to alterations in the normal patterns of temperature and several other physical–chemical factors associated with temperature, such as sea level changes and acidification.”
References
Lejeusne C, Chevaldonne P, Pergent-Martini C, Boudouresque CF and Perez T. 2010. Climate change effects on a miniature ocean: the highly diverse, highly impacted Mediterranean Sea. Trends in Ecology & Evolution 25(4): 250-260.