Aquatic creatures ranging from fish to phytoplankton become smaller as their watery environments warm, scientists report. In rivers and oceans, dwindling body sizes may be as common a response to climate change as migration to higher latitudes and shifting seasonal life cycles.
Martin Daufresne and colleagues at Cemagref in France analyzed reports of fish body size in French rivers and northern oceans for the past three decades. Not only were fish communities increasingly made up of smaller species, but in the French rivers, fish of the same species were about 50 per cent smaller than twenty years ago. The team ruled out commercial fishing as the sole cause of the shrinking trend, noting that the freshwater areas studied have not been heavily fished. They also found that warming affects the size of even the tiniest aquatic denizens, the zooplankton, phytoplankton and bacteria that form the base of the food web. After being kept at higher temperatures in lab experiments, these organisms tended to be smaller than their counterparts living in cooler waters.
The researchers have not been able to pinpoint the link between warming and smaller body size, but they suggest that temperature may be affecting organisms' size by influencing their metabolism.