What’s happening? The recent record-breaking heatwave in British Columbia, Canada may have killed over one billion seashore animals along the coast of the Salish Sea, according to Professor Chris Harley of the University of British Columbia. Infrared cameras deployed by Harley’s team recorded temperatures above 50C on shorelines during the heatwave, which saw temperatures top 40C in Vancouver. Although intertidal species such as mussels can endure temperatures in the high 30s for limited periods, the recent heat combined with low tides proved fatal for the creatures.
Why does this matter? A topical subject on both sides of the Atlantic, heatwaves have steadily become more frequent as the world’s average temperature has risen, and their frequency is expected to increase further under future climate change scenarios. As indicated above, their impacts are widespread and can extend to marine life.
Harley speculates the current level of shoreline filter feeders will not be able to be sustained as these events become more frequent. His team later suggested the ultimate number of animals that perished as a result of this particular incident (which has been scientifically attributed to human-caused climate change) could be significantly larger than a billion, with one million dead mussels counted in one site in an area the size of a tennis court. In addition, this loss of mussels can have knock-on destabilising effects for other local species, as they provide an important ecosystem service by filtering water.
It’s not just mussels that made headlines in the heatwave. Further south in California, reports indicated juvenile chinook salmon in the Sacramento River were under threat due to the heating of the waterway affecting the fishes’ ability to live beyond their egg stage.
Although it’s difficult to estimate the true extent of the damage to coastlines and rivers across western North America, in British Columbia sensors are being deployed around Vancouver Island to examine the effects there.
Gathering such data will be increasingly important to understand the effects of such events, and the state of the ocean more generally. Monitoring and sensor-based approaches can be utilised to track ocean biodiversity, as is the case with the UK government’s Global Ocean Wildlife Analysis Network targeting UK Overseas Territories. On a broader scale, effective monitoring is an important part of the High Level Panel for a Sustainable Ocean Economy’s goals to improve ocean health. Both local and satellite data can play a role.
It’s important to note heatwaves can occur underwater. Marine heatwaves are also increasing in frequency, and this should come as no surprise considering the ocean acts as a fundamental “heat sink” in our warming world – with one study suggesting it has absorbed 90% of the planet’s heat from 1971 to 2010.
Between 2014 and 2016, a northeast Pacific marine heatwave – known as “the blob”– caused a record number of whale entanglements in crab fishers’ nets as a result of ecosystem shifts and habitat compression. It also killed a million North Pacific seabirds. Changes to species’ tolerable geographical ranges as a result of these events could continue to have significant implications, particularly when it comes to breeding.
For species physically fixed to their habitat, the problem is yet more serious, which is why research is being conductedto train corals to become more resilient to rising temperatures. Investment is also being made into marine heatwave warning systems to alert ocean-dependent industries. Promoting biodiversity levels more broadly also can play a role – a recent study has indicated the presence of local shark species was critical to restoring seagrass meadows off the coast of Western Australia that were damaged in a marine heatwave.