Climate Change Affects Marine Fish Species
In the January 5 issue of Science, Dr. Hans-Otto Portner and his colleague published their findings on their study of climate influences on ecosystems, specifically addressing thermal limits of member species and their ability to deal with changing temperatures. Dr. Portner answers our questions.
How is this significant in relation to other areas of the ocean?
For that species there is no data in any other ocean areas, but we know for other fish stocks that they have experienced similar phenomena, not just in the North Sea, but also along the Pacific coast, the California coast, and further north. There are recent examples about a shift in species composition in an ecosystem in the Japanese sea; the ecological data there combined with the data on growth performance indicates to us that the same principles are operative in those effects as they have been operative in our example.
You and your colleague suggest something about it being difficult to determine direct causal relationships and indirect causal relationships. Could you comment on that?
Yes, you see for many of the species that are relevant commercially there is fishing activity. This has on the one hand contributed to compiling long term data sets about the well-being of the species in its natural environment, while on the other hand, certainly if thereís fishing pressure on a species then there are influences that disturb the natural signal and its influence on the population. This is not true for the eelpout which is of no commercial interest, because itís not being fished for, and itís a non-migratory species staying in the area where it is. It has a low rate of reproduction, a low number of offspring, meaning that itíll react quite readily to disturbancesómore readily than other species which have a very high number of offspring, so this makes it ideal as a bioindicator species. I think this is one reason why we could really elaborate the climate signal in the change of the population. I would like to add that this was the first example where we could relate a physiological disturbance observed in the fish with ecological processes seen in the field, so itís a step forward to a cause-and-effect understanding of how climate acts on marine fishes in their ecosystem.
Portner, Hans O. and Knust, Rainer. Climate Change Affects Marine Fishes Through the Oxygen Limitation of Thermal Tolerance. Science. 5 January 2007: Vol. 315. no. 5808, pp. 95 - 97. DOI: 10.1126/science.1135471
Dr. Portner is a researcher studying animal ecophysiology at the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany.
Interview by: Thanh-Tam Candice Vu