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Marine Ecosystems in Danger From Climate Change

Marine Ecosystems in Danger From Climate Change

In the News

October 28, 2012

Climate change is projected to shrink the body weight of marine fishes by 14 to 24% globally by 2050, according to a recent study from The University of British Columbia. The results of the study provide a new understanding of climate change’s impact on marine ecosystems.

Prior studies looked at the implications of thermal tolerance and limitations of other environmental factors – i.e. increasing the metabolic rate of terrestrial ectotherms globally across taxonomic groups, but this study was one of the few to assess the integrated responses of changes in ecophysiology, distribution and their effects on key characteristics, such as body size. 

Indeed, changes in temperature and oxygen content directly affect the ecophysiology (the adaptation of an organism’s functions to environmental conditions) of marine water-breathing organisms and lead to a reduction in both individual and assemblage-level body size. A fish assemblage is the sum total of fish collected at a single sampling location, and understanding how these assemblages work is an important component of fisheries management.

Researchers say that the ocean is projected to become warmer over the next 50 years, with some regions also becoming less oxygenated. This is important because oxygen is one of the key ingredients for body growth in aquatic water-breathing animals.

Interestingly, although the projected rate of change in temp and oxygen seems relatively small, the resulting projected changes in fish body size are surprisingly large. Results show that size was smallest in the tropics, and approximately five to two times larger in the northern and southern temperate regions. Projected decrease in size is largest in the Indian Ocean (24%), followed by the Atlantic (20%) and Pacific (14%). 

In other words, the amount by which fish size decreases is larger in areas with higher rates of warming and reduction in oxygen content. And as more fish move poleward, as predicted as a result of these various temperature and oxygen changes, fish size continues to decrease.

Researchers say that failing to cut back on greenhouse-gas emissions will have a larger impact in marine ecosystems than previously expected. While other human impacts, like overfishing and pollution, will further exacerbate the situation, the effects of climate change could have large implications on ecosystem functions, fisheries and global protein supply.

Fish provide nearly three billion people with 15% of their annual protein needs, and marine fisheries support 8% of the world’s population (about 520 million people). Worldwide, fisheries revenue is estimated at between $80 billion and $85 billion annually.

"We were surprised to see such a large decrease in fish size," says the study's lead author Dr. William Cheung, an assistant professor at the UBC Fisheries Centre. "Marine fish are generally known to respond to climate change through changing distribution and seasonality. But the unexpectedly big effect that climate change could have on body size suggests that we may be missing a big piece of the puzzle of understanding climate change effects in the ocean."