The Marin Post

The Voice of the Community

Blog Post < Previous | Next >

California Department of Public Health

Red tides, dead zones, and other reasons for concern about climate change

When I was a kid, I used to love to get up in the morning and go down to the beach in the summer, on the North Shore of Long Island, and with nothing more than a seining net, a spear gun, and a wire basket I could bring home a feast of smelts, small rock fish, flounders, and mussels for my mother to make for dinner.

But, that’s all gone now.

There is no longer any serious debate among credible scientists that the climate and just about everything else is changing because of our collective, seemingly, insatiable need to extract, transform, and consume everything in our planet's fragile ecosystems. As such, there have been many articles in the mainstream media about global heating and climate change. But, much of that coverage has focused on severe weather events, sea level rise, and occasionally on endangered species.

What gets less attention is what is happening in our oceans, other than the occasional report about the amount of plastic in the Pacific Garbage Patch. However, ocean warming, acidification, salinity, and pollution have been increasing for decades. And although the impacts are not evenly distributed around the world, in combination, these are probably more important than what’s happening on land.

The increased magnitude of hurricanes and flooding from torrential rainfall are the most widely reported examples of the serious consequences of warming ocean waters. But there are other issues we might want to pay more attention to. Because, while mainstream media’s stories about plastics in the bellies of sea life are certainly important, it may be the least of our worries.

Red Tides

Red tides are the result of hyper-growth of microscopic algae that produce powerful neurotoxins that can cause massive die-offs of fish, marine mammals, sea turtles, and seabirds and make shellfish dangerous to eat. It gets the name “red tide” because these algae blooms can turn the water a brownish-red color.

Red tides are increasing around the world because of increased nutrient runoff from chemical fertilizers, sewage treatment, and urbanization. But, it’s equally important to note that warming ocean waters and high levels of atmospheric CO2 are major enablers of red tides.

A study published in Nature found that ocean algal blooms increased in size by about 13% (1.5 million additional square miles) and in frequency, by 59%, between 2003 and 2020. And the frequency is speeding up. At this rate, the socioeconomic consequences are potentially catastrophic.

Dead Zones

When algal blooms die and decompose, they consume so much oxygen that it creates “hypoxic” (oxygen-depleted) "dead zones" in the oceans, where fish and other marine life can no longer survive. And, the death of zooplankton and bottom-dwelling organisms that we never see impacts the entire aquatic and terrestrial food web and normally functioning ecosystems, with highly unpredictable results.

Meanwhile, warming surface waters are unable to hold as much dissolved oxygen as cooler waters, which increases ocean stratification (the warmest water stays at the top while colder waters stays at the bottom) and limits oxygen replenishment in bottom waters.

Acidification of ocean waters makes fish and other organisms more susceptible to hypoxic conditions, while increased rainfall from climate change can increase harmful chemical and nutrient runoff, change global wind patterns, and disrupt normal ocean up-welling patterns, causing secondary , negative, weather-related ecosystem impacts on land and in the sea.

All this exacerbates dead zone formation until these areas become underwater biological deserts. Worse still, the death and decay of marine life killed by red tides release nutrients back into the water, which fuels further algal growth, creating a vicious cycle.

In this way, global heating, red tides, and dead zones are self-reinforcing phenomena.

The second largest dead zone in the world extends from the mouth of the Mississippi River into the Gulf of Mexico, covering an area the size of New Jersey. The Chesapeake Bay and coastal areas in the Pacific Northwest, including parts of Oregon and Washington, also experience significant hypoxic conditions, particularly during the summer months.

In the San Francisco Bay area, the last major red tide occurred in the summer of 2022 when thousands of fish, crabs, and other marine organisms, including sturgeon, leopard sharks, striped bass, bat rays, and anchovies died. Even in Lake Merritt, in Oakland, which is connected to San Francisco Bay, as many as 10,000 fish died. The economic losses to the fishing, recreation, and tourism industries were significant.

Unfortunately, there are no simple ways to fix this. There are no magic bullets. Technology will not save us. But, we need to resist the urge to react with our innate “out of sight, out of mind” tendencies and start to think about how we can reverse these trends... before we no longer can.