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  Geography
Lake eutrophication causes loss of fish species
17/02/2012   |   11:21 AM | World News
تصغير الخطالشكل الأساسيتكبير الخط

By Tamer Aboalenin

GENEVA, Feb 17 (KUNA) -- Eutrophication has led to a reduction of almost 40 percent in the number of endemic whitefish species in Swiss lakes, within a relatively short period of time.
Only in deep perialpine lakes least exposed to high nutrient inputs, such as Lakes Thun, Brienz and Lucerne, has the original diversity of endemic species been able to survive, a study by the Swiss Federal Institute of Aquatic Science and Technology (EAWAG) and the Swiss University of Bern said on Friday.
The study said that the decline in the diversity of whitefish species is not merely due to a loss of habitats but also due to the disappearance of species caused by the hybridization of formerly distinctive species.
In 1950 to 1980, the study explained that the eutrophication of Swiss lakes, where the bottom and deep waters were severely oxygen-depleted, deprived many species of their ecological niche.
The species, which had evolved since the last ice age, had to move to shallower waters. Here, they interbred with related species, thus losing their genetic and functional distinctiveness within a few generations, in a process known as speciation reversal.
The study demonstrates that eutrophication levels not only account for the loss of species but are also responsible for the loss of differentiation among the surviving species.
Evolutionary biologist Ole Seehausen, the lead author of the study, comments "Speciation reversal appears to be more widespread than has previously been supposed; this process involves the rapid disappearance of species which evolved over thousands of years by adaptation to specific ecological conditions.
"This means that the protection of biodiversity requires not only the conservation of existing species, but the protection of ecological and evolutionary processes which assure the maintenance of specialists and promote the generation of new species.
Whitefish are regarded as a model organism by the scientists involved in the study. Seehausen, who is affiliated with both Bern University and Eawag, said "We must assume that lake eutrophication has caused similar losses of diversity among other fish, and perhaps also among their invertebrate prey species." He also interprets this study as a warning to those in the fishing community who have recently called for the restriction of phosphorus elimination measures at wastewater treatment plants in the hope that fishing yields would be increased as a result of nutrient enrichment. (end) ta.nfm KUNA 171121 Feb 12NNNN

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