Scientists say climate change is making fish hungrier

By Mark Waghorn via SWNS

Climate change is making fish hungrier - which could rob humans of our favorite seafood, warns new research.

As the ocean heats up, apex predators will take control - reshaping ocean communities, scientists say.

Impacts in the Atlantic and Pacific were found to peak at higher temperatures - with effects cascading down to transform life under the waves.

It threatens to disrupt the balances that have existed for millennia, the international team explained.

Lead author Dr. Gail Ashton, a marine biologist at the Smithsonian Environmental Research Center (SERC), Maryland, said: "It has taken thousands of years to get to this state, and then suddenly we are ramping up the temperature at a much higher rate.

"And we don't really know the implications of that temperature increase."

The biggest project of its kind coordinated partners at 36 locations running along the coasts of the Americas.

Sites spanned from Alaska in the north to Tierra de Fuego at the tip of South America.
The same three experiments were performed at each.

In the first, overall predator activity was tracked using 'squid pops' - resembling cake treats at coffee shops.

A piece of dried squid attached to a stake acted as standard bait and was left underwater to attract fish.

After an hour, it was checked to see how many had been devoured. Results confirmed their suspicions.

At warmer sites, predation was more intense. In colder waters, below 68 degrees F, predation dropped to near zero.

Co-author Professor Amy Freestone, of Temple University, Philadelphia, said: "This temperature threshold represents an ecological tipping point in these coastal marine ecosystems, above which predation intensity increases.

"With climate change, more coastal waters will exceed this tipping point, or warm even further, fundamentally changing how these ecosystems function."

In further tests, they looked at stationary invertebrates fish like to feast upon - like tunicates and bryozoan - to see how predators would impact growth and abundance.

Prey colonize and spread on underwater plastic panels for three months. Some had protective cages that kept predators out. Others were left open and vulnerable.

In the final trial, protective cages were put around all the underwater prey for 10 weeks, and then half the communities were uncaged for two more weeks.

In hotter waters, predators' more voracious appetites left outsized marks. Total biomass plunged in the tropics when prey were left unprotected.

But in the coldest zones, leaving prey exposed or protected made almost no difference - suggesting predators did not pose much of a threat.

Co-author Dr. Mark Torchin, of the Smithsonian Tropical Research Institute, Panama, said: "We knew from previous work in Panama that predation in the neotropics can be intense.

"However, working with our colleagues across the Americas allowed us to test the generality of this and to evaluate how the effects of predation change in colder environments."

The kinds of organisms changed with predator access as well. They liked eating solitary, bottle-shaped 'sea squirts' or tunicates.

They suffered major losses in the tropics when left unprotected. Meanwhile, encrusting 'moss animals' or bryozoans flourished in the newly free space. Fish left them alone.

Solitary tunicates filter the water and offer nooks and crannies for other organisms to settle - two important functions bryozoans do not do quite as well.

They offer just one example of how a rise in predator activity could alter ecosystems as cooler ecosystems heat up.

Co-author Dr. Greg Ruiz, head of SERC's Marine Invasions Research Lab, said: "As predation changes, some species will be winners and some will be losers.

"Some will be defended, others will be vulnerable. But we don't know exactly how that will play out."

What will happen at the equator - where temperatures may rise even higher than what scientists can see today - remains even more of a mystery.

Dr. Ashton said: "We don’t really know what might happen in the tropics, because we don't have data from those warmer temperatures."

The findings in the journal Science support previous research that hinted predators are more active in the tropics.

Animals' metabolism increases in hot weather. But empirical evidence had been conflicting.

Co-author Dr. Emmett Duffy, director of Smithsonian's Marine Global Earth Observatory network (MarineGEO), added: "Warmer waters tend to favor animals high in the food chain, which become more active and need more food - and it is their prey who pay for that increased activity.

"This suggests warming seas could see big shifts in the life of sensitive seabed habitats.”