What happens when millions – or billions – of marine animals one day die? | Emily carrington

AAs a marine biologist who has studied the effects of extreme weather events for decades, I expected it to be bad. The “heat dome” brought record air temperatures to the Pacific Northwest, and for the plants and animals living along our vast coasts, the timing of late June could not have been. worse. The scorching heat wave coincided with some of the lowest daytime tides of the year, leaving the tidal lands exposed to hot air and sun for hours during the hottest part of the day, several days of following.

And it was wrong. In the days immediately following the historic heatwave, I visited shores that looked and smelled of death. Mussel, oyster and clam shells open wide with exposed decaying tissue, snails and chitons are no longer able to cling to rock, kelp and surfgrass turn white and peel away from tissue dead. Similar scenes have been reported in the Washington and British Columbia Salish Seas by scientists, shellfish farmers and the general public, with mortality estimates ranging from millions to billions of individuals. We’ve never seen anything like it before.

What happens next? In a few weeks, the dead tissue will be scavenged and the empty shells will be washed away, leaving bare spaces on the shore. Gone are all the ecosystem services provided by these organisms, such as filtering water (a single mussel or oyster can clean up to 10 gallons of seawater per day), building a wetland habitat for an assemblage diversified from other species and the provision of food to species. at higher levels of the food chain, such as crabs, birds and humans.

In the following months, areas with high mortality may have poorer water quality, less biodiversity, and fruitless foraging predators. Populations that were not directly affected by the heatwave may experience the spillover effects of the extensive disruption of ecosystem function. Shellfish farmers, already struggling with reduced demand during the Covid-19 pandemic, will struggle to maintain the supply chain. As a result, the central role of aquaculture in many rural coastal economies will diminish.

Affected shorelines will likely repopulate over time. How quickly this will happen, if at all, depends on a number of factors. On the positive side, many killed species are known to have population growth strategies that promote rapid recolonization. Mussels and oysters produce lots of offspring that spread widely and reach reproductive maturity quickly, so recovery could be achieved in just a few years. On the negative side, there may not be enough survivors to provide the offspring. Additionally, species with such a “live fast, die young” strategy tend to be physiologically weak and will struggle to establish a viable population if extreme heat waves become the norm. They will simply move to cooler places, joining the pole march of so many other aquatic and terrestrial species around the world.

Shellfish growers can work around these limitations by growing ‘seeds’ in hatcheries and culture to promote stress tolerance, but the trade-offs – slower growth, longer time to market, and increased hatchery costs – will significantly reduce profit margins.

It is important to note that many species have survived the extreme heat. These were generally larger, longer-lived species that have more robust physiological tolerances, special behaviors, and growth strategies. For example, some species of clams can burrow deeper into cooler sand, large California mussels can store enough water to cool by evaporation below the lethal temperature, and many bleached algae can grow back from them. tissues that remain attached to the rock. This does not necessarily mean that they were not affected by the extreme heat, because recovering from physiological stress takes a lot of energy. These species are likely to have less energy available for growth, reproduction and disease control, which could affect the ability of populations to persist in the longer term.

What can we do about it? We can hope that the next extreme heat wave will occur at low tide and that coastal species will be protected by a cool blanket of seawater. But, given the increased rate of global warming over the past decade, Extreme heat waves are expected to be more frequent and more severe, and the odds of catastrophic death will also increase.

As a marine biologist who lives near the shore, I can see that this massive coastal mortality is a climate crisis happening in my own backyard. I understand that the imagery of decaying seashells may not resonate with most people in the United States, who don’t live near the ocean. Hope there will be more conversations about what is going on in your garden. No more flooding? Increase in hurricane activity? Prolonged drought? The effects of climate change are manifold and the face you see depends on where you live. These local conversations can spur action to tackle the root cause of all of these problems – the increase in atmospheric carbon dioxide resulting from more than a century of burning ever increasing amounts of fossil fuels. Of the many helpful actions that individuals can take, focusing your efforts on those that make sense for your personal situation is a great place to start. As activist David Suzuki says, “In a world of over seven billion people, each of us is a drop in the bucket. But with enough drops we can fill any bucket.


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