Climate change will bring a combination of rising temperatures and increased predation that will result in biodiversity loss – and it may be worse than currently predicted, claims a study by University of British Columbia (UBC) zoologist Christopher Harley.
“Global warming is already having significant ecological impacts and it’s only going to get more dramatic,” Harley warned.
Published in the current issue of the journal Science, the study examines how rocky shore barnacles and mussels react to the combined effects of warming and predation by sea stars.
Harley looked at the upper and lower temperature limits of barnacles and mussels from the cool west coast of Vancouver Island to the warm shores of the San Juan Islands, where water temperature rose from relatively cool in the 1950s to the much warmer years of 2009 and 2010.
He found that in cooler locations, mussels and rocky shore barnacles could live high on the shore and be shielded from their predators. But as temperatures rose, barnacles and mussels had to move to lower shore levels — and be exposed to predatory sea stars, whose location has not shifted.
“Sea stars are the terrors of the intertidal zone,” said Harley, Vancouver Sun reports. “As it gets hotter you would expect [species] to just move down to lower positions on the shore where they wouldn’t be out of the water for so long. But things aren’t shifting in unison.”
As daily high temperatures during the summer have jumped by almost 3.5 degrees Celsius in the last 60 years, barnacle and mussels have moved 50 cm lower on the shore. However, the effects of predators, and therefore the position of the lower limit, have thus far remained unchanged.
“That loss represents 51% of the mussel bed. Some mussels have even gone extinct locally at three of the sites I surveyed,” said Harley.
He then found that when stress from sea star predation was reduced by using exclusion cages, mussels and other species were able to live in hotter sites where they usually can’t — and their populations there more than doubled.
“A mussel bed is kind of like an apartment complex – it provides critical habitat for a lot of little plants and animals,” said Harley. “The mussels make the habitat cooler and wetter, providing an environment for crabs and other small crustaceans, snails, worms and seaweed.”
In contrast with many previous studies on how species ranges will change due to global warming, this analysis does not assume that species will simply relocate to remain in their current temperature range.
As animals or plants are unable to change their habitat ranges, Harley told, the findings show that warming and predation together could spawn more widespread extinction than scientists currently anticipate.
“Warming is not just having direct effects on individual species,” Harley added. “This study shows that climate change can also alter interactions between species, and produce unexpected changes in where species can live, their community structure, and their diversity.”
The effect on fishers
Relatedly, UBC researchers have also determined how climate change can impact the economic viability of current fisheries practices. Fish stocks are already yielding fewer fish due to overfishing and environmental factors such as pollution.
“Climate change is likely to cause more losses unless we choose to act,” said Rashid Sumaila, principal investigator of the Fisheries Economics Research Unit at UBC and lead author of the study.
A collaboration between economists, biologists and climate-change scientists, the study gives a broad outlook of the effect of climate change on fisheries and their profitability; it was published online in the journal Nature Climate Change. It received the support of the Pew Charitable Trusts, National Geographic, the World Bank and the U.S. National Oceanic and Atmospheric Administration (NOAA).
As waters warm, species move to cooler waters
Warming ocean temperatures have led many species to move farther towards the poles and into deeper and cooler waters. This means that while fishers in a few regions, such as Scandinavia in the far north, may benefit because they will now have more fish to catch, many others, and particularly fishers in the tropics, will lose an important food source along with their livelihoods. (Many fishers in tropical regions are poor and fish to feed themselves and their families.)
Researchers examined regional phenomena to help them find out what could happen on a global scale. For instance, lower catches of pelagic fish (such as sardines and anchovies) in Peru resulting from warmer waters during the 1997-1998 El Niño event caused more than USD 26 million in losses.
“For example, if you think about sardines on the Pacific Coast here: Whenever the temperatures are a bit higher, we see more sardines moving from Mexico through the US to Canada,” Sumaila noted, CBC News reports.
Fish survival is compromised
William Cheung, a biologist at the UBC Fisheries Center, said changes in temperature and ocean chemistry directly and adversely affect the physiology, growth, reproduction and distribution of marine life.
“Fish in warmer waters will probably have a smaller body size, be smaller at first maturity, with higher mortality rates and be caught in different areas,” he explained.
NOAA scientist and co-author Sam Herrick is calling for ongoing studies on how climate change and related factors will shape marine ecosystems and the productivity of fish populations.
Richer fish stocks = better adaptation to change
It was found that the bigger populations are, the better fish can adjust to environmental shifts such as warming temperatures. Minimizing the combined strains from overfishing, habitat degradation, pollution runoff, land-use transformation, competing aquatic resource uses and other anthropogenic factors will also contribute to helping stocks cope with climate change.
“We have to remember that the effect of climate change on the marine environment will occur alongside the impacts on land,” said Daniel Pauly, a UBC fisheries biologist and co-author. “It will not be easy to divert resources from one sector to help another sector. This is why a strong governance system is needed – to temper the losses on the sectors that are worst hit.”
In other words, government officials need to step up and work harder to stop overfishing and illegal fishing, reduce runoff from agriculture and other polluting sources, and fight habitat destruction, among taking other measures.
Take a small step to make a difference
In the meantime, if you eat fish, something you can do is commit to purchasing only sustainably caught seafood. Read more about how to do this here:
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- Marine experts spell doom for world’s oceans, Pt. 2
- Marine experts spell doom for world’s oceans, Pt. 1