A tiny sea creature that plays a big role in the ocean food chain faces the threat of extinction as it struggles to adapt to changes in sea temperature, a new study found. 

A species of cold-water plankton in the North Atlantic, that is a vital food source for fish such as cod and hake, is in decline as the waters warm, according to research led by Deakin University in Australia and Swansea University in the UK. The decline puts pressure on the fisheries that rely on abundant supplies of these fish.

The cold-water plankton lives for one year or less. Researchers examined a 50-year dataset from the North Atlantic to determine how the creature and other species of plankton that thrive in warmer water fared over half a century.

"Lots of people speculated that animals with short generation times will simply adapt to change," Graeme Hays, a marine scientist at Deakin University told NBC News. "We show that is not the case."

The study shows that the range and abundance of the cold-water plankton, Calanus finmarchicus, declined while the warm-water species, C. helgolandicus, expanded its range and increased in abundance.

"In other words, even over 50 generations ... there is no evidence of adaptation to the warmer water," Hays said of the cold-water plankton.

That shift may have profound ramifications for fish that eat the cold-water plankton, as well as, for the livelihoods of people who catch and sell these fish, Hays noted.

Warm-water species of the plankton is filling the niche vacated by the cold-water plankton "is abundant at the wrong time of year" for cod and hake, Hays said.

"So, it is not available as food for the developing fish larvae," Hays said.

While the study was based on available data from the North Atlantic, the findings may be applicable to oceans all over the world as ocean temperatures are warming everywhere and closely-related species of Plankton are distributed globally.

Over time, Hays said, the surging abundance of warm-water plankton "will likely play a role in the emergence of new fisheries for warm-water species."