Warming Oceans Leading to Extinction of Some Plankton, A Vital Marine Food Source

Raising ocean temperatures are leading toward the extinction of a tiny creature that plays a key role in the food chain, according to research scheduled for publication in the journal Global Change Biology.

Numerous tiny plankton species dwell in the cold waters of the North Atlantic Ocean, a favorite food of cod and hake -- two fish widely grown in fisheries in the region.

According to researchers from Deakin University in Australia and Swansea University in the UK, warming ocean temperatures are causing the plankton to die off, which may go on to threaten the food supply of cod and hake, and place new pressures on local fisheries.

"There is overwhelming evidence that the oceans are warming and 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," said Graeme Hays, a professor of marine science at Deakin University.

"We know that warm water species are expanding their ranges as warming occurs, and vice versa," Hays said. "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."

For their study, the researchers examined the distribution of two types of common but contrasting types of North Atlantic plankton over the course of 50 years.

They focused on Calanus helgolandicus, a plankton that lives in warmer water and Calanus finmarchicus, which lives in cold water. Both species act as a vital food for fish and a key component for North Atlantic fisheries.

C. finmarchicus continuously contracted its range over 50 years of warming, according to the researchers. 

"In other words, even over 50 generations (each plankton lives for one year or less) there is no evidence of adaptation to the warmer water," Hays said in a statement.

"The consequences of this study are profound. It suggests that cold water plankton will continue to become scarcer as their ranges contract to the poles, and ultimately disappear. So certainly for these animals, thermal adaptation appears unlikely to limit the impact of climate change."

Hays continued: "C. finmarchicus is a key food source for fish such as cod and hake. So continued declines in abundance will have a negative impact on the long-term viability of cold water fisheries in the North Sea and other areas in the southern part of their range. At the same time the continued increase in abundance of the warm water plankton, C. helgolandicus, will likely play a role in the emergence of new fisheries for warm water species."

Hays also noted that because oceans are warming on a global scale, it is likely a similar phenomenon is happening to plankton on other parts of the world.

"Ocean warming is occurring globally and so these findings are likely to apply to other areas around the world including southern hemisphere locations such as Australia, South Africa and South America that support important fisheries dependent on plankton," Hays said.