Warming may force fish menu switch

THE world’s tiniest creatures are heading for extinction and could take south-west fisheries with them.

According to new research led by Warrnambool’s Deakin University and the UK’s Swansea University, a species of cold water plankton is struggling to adapt to changes in sea temperature as the oceans warm.

As a vital food source for many common types of fish, the extinction would put pressure on the fisheries relying on abundant catches and potentially force consumers to eat different species of fish.

Deakin’s professor of marine science, Graeme Hays, said overwhelming evidence showed oceans were warming and changing marine life.

“It will be the response of animals and plants to this warming that will shape how the oceans look in future years and the nature of global fisheries,” Professor Hays said.

“We know that warm water species are expanding their ranges as warming occurs and vice versa. 

“What is not known is whether species are able to adapt to new temperatures. 

“Will, for example, cold water species gradually adapt so they can withstand warming seas and not continually contract their ranges? From the results of our study, it is looking like the answer is no.”

The question of adaptation was not easy to answer, requiring long-term observations spanning multiple generations.

Deakin and Swansea’s research team has examined a 50-year time series from the North Atlantic on the distribution and abundance of two very common but contrasting species of ocean plankton — the warm water Calanus helgolandicus and the cold water Calanus finmarchicus.

These crustaceans are vital food for fish and underpin many commercial fisheries in the North Atlantic region.

The researchers were surprised to find that the cold water Calanus finmarchicus had continued to contract its range over 50 years of warming.

Professor Hays said the impact of ocean warming was not confined to the North Atlantic region.  It also impactedAustralia, South Africa and South American regions with fisheries reliant on plankton.

“Around the world, including the coast here, the same warming is occurring,”he said. “It may be that existing fish stocks switch their diets ... and warm water fish species may start to occupy the coast.

“Human preferences for what sort of fish we eat may have to change as well.”

The results of the study were published online in the Global Change Biology journal last week.

j.pech@fairfaxmedia.com.au

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