Researchers have known for some years that the Atlantic cod beats the retreat in the direction of the Arctic when the waters in its traditional habitat become too warm. In summer, shoals from the Atlantic Ocean, for example, are now moving up as far as Spitsbergen into the waters the Arctic cod calls its own.
Until recently, Flemming Dahlke, fishery biologist at the Alfred Wegener Institute (AWI), could not have imagined that he would one day have to resort to the fishing rod to pursue his doctorate. But after several fruitless attempts at getting hold of an Atlantic cod ready to spawn, a fishing trip proved to be the most profitable method. Flemming Dahlke stripped off the eggs from his catch, fertilised these with Atlantic cod sperm and was finally able to start on his actual research work.
“As for all other organisms, the Atlantic cod and Arctic cod feel the most comfortable in a specific temperature range. During the spawning season, for example, the Atlantic cod prefers temperatures of between three and seven degrees Celsius. By contrast, the Arctic cod breeds at temperatures of between zero to four degrees Celsius. If the temperature of the sea now increases due to climate change, the animals become stressed, a condition which is greatly exacerbated by the increasing ocean acidification. We suspect that these new environmental conditions will lead to the comfort ranges of both species becoming smaller and that the habitat of the fish will increasingly overlap. This means that the Atlantic cod can be expected to seriously compete with the Arctic cod “, says Dr. Daniela Storch, biologist at the Alfred Wegener Institute.
Just which fish species has the best chances of survival will be investigated by the project members in complex behavioural experiments and during a four-week expedition. “From mid August to mid September this year we will be fishing the fjords of the north, west and south coasts of Spitsbergen on the research vessel Heincke. We firstly wish to document where we find which species at this time of year. Secondly, we are interested in catching a great deal of fish which we will bring back alive to Bremerhaven and can then study in the over 100 new basins of our aquarium facility”, explains Felix Mark.
The planned experiments include performance analyses in the ultra-modern flow channel and the two MRI scanners of the Alfred Wegener Institute in Bremerhaven. “Using this apparatus we can not only look into the brain of the fish but even into its individual cells. We are able to recognise, for example, how its metabolism alters within the cells, how heart and blood circulation of the fish react to the rise in water temperature, at which pH value of the water the fish reaches its performance limits or in which way temperature and degree of acidification affect its senses”, explains Felix Mark.The researchers know from investigations of tropical fish, for example, that their offspring have a reduced sense of smell as ocean acidification rises. The consequence: the young fish find it more difficult to return home and are more likely to fall prey to others. So are heat-shy Atlantic cod and its Arctic cousin facing a similar fate in view of climate change? Flemming Dahlke’s first results are at least interesting: “There are many signs that the water temperature plays an important role in the breeding of the cod. There was as virtually no life in those eggs fertilised in sea water at a temperature of twelve degrees”, reports the phd student.
Ralf Röchert | idw
Further reports about: > AWI > Agriculture Organization > Antarctic Predators > Arctic Ocean > Atlantic mollies > BIOACID > Baltic Sea > Helmholtz > MRI scanner > Marine science > Pacific Ocean > Spitsbergen > agriculture > coastal water > fish species > marine biologist > ocean acidification > research project > water temperature
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