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.

Source: www.cbc.ca/news/canada/british-columbia/intertidal-animals-ubc-research-1.6090774

Why does this matter? This “habitat compression” phenomenon is another significant event attributed to the 2014-2016 marine heatwave, otherwise known as “the blob”, with a separate recent study also linking it to the death of a million North Pacific seabirds – the largest avian mass mortality event ever recorded.

The blob (which has recently shown signs of re-emergence) was the result of a confluence of atmospheric activity, enhanced by the El Nino ocean-atmospheric phenomenon. Its effects were widespread and continue today. These types of marine heatwaves are expected to increase in both frequency and intensity, as climate change continues to raise the amount of heat absorbed by the world’s oceans.

The humpback whale entanglements, which remained prevalent over subsequent years, are one element of a series of environmental problems facing California’s commercial crab and other fisheries. Frequent algal blooms led a coalition of commercial fishers to bring a lawsuit against fossil fuel firms in 2018. And a study last year found California waters are acidifying at twice the rate of the global average, which has its own recently reported significant impacts on crabs’ and other species’ ability to form shells.

Aside from taking widespread action on climate change to protect the world’s oceans – without which events like the blob are set to become the new normal – for the time being the crab industry and humpback whales may have to learn to be bedfellows.

The start of the crab fishing season was delayed last year to help protect the animals. The multidisciplinary California Dungeness Crab Fishing Gear Working Group has also been established to work on effective crab fishery management. And the researchers behind the Nature study are developing a website which will use oceanographic data to forecast where whales are most likely to feed off the West Coast, so fishermen can react accordingly.

Sources: Nature Communications

The Independent

https://www.independent.co.uk/environment/climate-crisis-humpback-whale-entanglements-ocean-heatwave-california-a9304571.html