Toxic crab signals the ‘new normal’ in a warming world

Dungeness crab is more than just seafood to many San Franciscans — it’s a tradition, and, like a display of festive lights, a signal that the holidays have arrived.

But today, Thanksgiving, will be the first when fresh, local crab won’t be available for the feast. The delay and possible cancellation of this year’s crab season offers another troubling signal — that the dynamics and chemistry of the ocean are changing in ways that may forever alter life as we know it. Along with coral reefs in tropical waters, our toxic crabs are the ocean’s canaries in the coal mine.

The unusually warm water, massive algae bloom and resulting neurotoxin in our coastal waters are natural occurrences. But we’re changing nature. Numerous studies show human activities make this situation worse and more frequent. The domoic acid outbreak now infecting crabs, clams, sardines, marine mammals and even whales is the worst on record — a record likely to be broken again and again in the future.

Massive algae blooms along the West Coast have occurred for centuries at the end of the summers, but the magnitude, duration and geographical range of such events have increased in recent years. During normal conditions in spring and summer off the Pacific Northwest, northerly winds drive coastal upwelling along the West Coast, bringing cold, salty and nutrient-rich waters from the deep. This is the main reason for why our region is so productive. Nutrients fuel the entire marine ecosystem, phytoplankton flourish, zooplankton explode, small fish like sardines and anchovies become abundant, and countless species, from sharks and birds to dolphins and whales, feast on this abundance of food.

But if this balance is disrupted, everything changes. Weak northerly winds shorten the upwelling season, keeping coastal water warm, and opportunistic microalgae species such as Pseudo-nitzschia bloom and thrive, producing toxins like domoic acid. Compounding the problem, coastal pollution and ocean acidification can increase the toxicity levels of these algae, with destructive results in vulnerable areas.

Most people accept that carbon emissions from our excessive burning of fossil fuels are changing our climate and making the ocean warmer and more corrosive. More than 90 percent of the heat trapped in the atmosphere is absorbed and retained by the oceans, warming them by 1.5 degrees Fahrenheit over the past century, with more rapid increases predicted by 2050.
The resulting changes to our world have unfolded slowly, but in recent years they’ve accelerated, fueling extreme weather events, massive coral bleaching and harmful algal blooms. Toxic waters may be more common in the near future, drastically affecting not only marine ecosystems but also coastal economies that depend on healthy oceans.

This year’s algae bloom shut down the clamming in Washington, crabbing in California, and poisoned marine mammals from Mexico to Alaska. This is a wake-up call — a glimpse of the new normal if we don’t get serious about curbing our carbon emissions and taking care of our ocean.

Dr. Abel Valdivia is an ocean scientist with the Center for Biological Diversity, based in Oakland.

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