How marine heatwaves are reshaping ocean ecosystems

Research from the University of Victoria has gone to new lengths to highlight how marine heatwaves can not only dramatically impact marine ecosystems but reshape ocean life as we know it, by offering a stark preview into the future of ocean warming.

From 2014 to 2016, the pacific coast of North America experienced the longest marine heatwave ever recorded, with temperatures reaching two to six degrees above historical averages over a prolonged period of time.

It’s according to researchers from the University of Victoria’s Baum Lab that this marine heatwave alone resulted in the ‘unprecedented ecological disturbance’ of some thousands of kilometres of North American west coast. 

By reviewing the findings from 331 primary studies and governmental reports, the researchers believe they are now gaining a better understanding of the ecological impacts of marine heatwaves, including its effect on marine life.

According to the study, around 240 different species were found outside of their typical geographic range during the heatwave, with many of them found further north than ever before. Several species, such as the northern right whale dolphin and the sea slug Placida cremoniana were found over 1,000 kilometres north of their typical habitat.

The heatwave caused widespread kelp and seagrass decline and many kelp forests collapsed. Species from sea stars to seabirds died on unprecedented scales and unusual mortality events were observed in several species of marine mammal. Meanwhile, a key rocky shore predator, Pycnopodia helianthoides, came close to extinction.

Researchers found that many of the impacts of the heatwave were cascading, with direct impacts on some species driving complex dynamics that affected everything from plankton to whales. Temperature-linked diseases – such as sea star wasting disease – also contributed to ecosystem collapse, while the reduced abundance and nutritional quality of forage fish cased issues for predators. Meanwhile, plankton communities reorganised and offshore oceanographic productivity was found to be altered.