Weather Watch

It’s ‘red tide’ season on the Central Coast. That’s not good if you’re a seafood lover

A saying that I heard growing up is that you should only harvest shellfish, such as mussels, clams, scallops and oysters, in the months with the letter “R.”

In other words, from September through April, but not in May, June, July or August. So where did this theory come from, and is it true? In early April, the northwesterly “spring” winds kicked in along the Northern and Central Coast, which produced a lot of fog-free days and huge amounts of upwelling.

This, in turn, brought frigid, clear and nutrient-rich water from the ocean’s depths to the surface along the immediate shoreline to replace the shallow water that was pushed out to sea. Last week, seawater temperatures at the Diablo Canyon Marina dropped to a bone-chilling 49 degrees.

Well, a significant change in the weather pattern occurred this week as a trough of low pressure developed along the California coast while a Catalina Eddy (not someone you don’t want to meet in a dark alley) formed in the Southern California Bight, the coast from Point Conception to just south of San Diego.

This condition quickly put an end to the relentless northwesterly winds and allowed extensive marine low clouds to develop over the coastal regions, which allowed seawater temperatures to increase as upwelling diminished and warmer water from the south moved north along the shoreline.

Next week, the marine layer could rise to over 7,000 feet and eventually dissipate, leaving behind clear skies with plenty of sunshine. If there’s enough sunlight, enormous phytoplankton blooms due to photosynthesis may occur. During periods of warmer and calm seas, a group of phytoplankton species called dinoflagellates can explode in numbers.

This group of phytoplankton can produce red tides and even flashes of electric-blue bioluminescence when agitated. Unfortunately, red tides can also create toxins. These red tides have nothing to do with the gravitational forces of the sun or moon but can turn vast expanses of the near-shore ocean environment to brick red or brown in color.

You see, mussels, clams, scallops and oysters are bivalve mollusks that filter vast amounts of water for their food through their gills. This allows their tissues to accumulate toxins from red tides that can cause diarrhetic shellfish poisoning. According to the Woods Hole Oceanographic Institution website, “Diarrhetic Shellfish Poisoning produces gastrointestinal symptoms, usually beginning within 30 minutes to a few hours after consumption of toxic shellfish. Although not fatal, the illness is characterized by incapacitating diarrhea, nausea, vomiting and abdominal pain. Recovery usually occurs within three days, with or without medical treatment.”

Worse, is domoic acid from diatoms, another type of phytoplankton/algae/red tide that can accumulate not only in bivalves but also in Dungeness and rock crabs and baitfish, such as anchovies and sardines. If you consume enough of this neurotoxin, you can develop amnesic shellfish poisoning.

This toxin kills neurons in your brain responsible for short-term memory. Many of us who have lived along the Central Coast may have seen seabirds or marine mammals, such as sea lions that feed on these baitfish, suffering from domoic poisoning. The months more likely to see red tides occurr during summer, hence months without an “R.” However, red tides can occur in other months of the year, like September.

In full disclosure, I love seafood, and I’ve personally never gotten sick eating shellfish or anything from the sea. I feel fortunate to live near a pristine marine environment with so many wholesome seafood restaurants to enjoy. Helping us to keep safe, is the California Department of Public Health, which closely monitors our coast for the presence of toxin-producing phytoplankton and the bivalves, crabs and fish we enjoy.

The Phytoplankton Monitoring Program coordinates and analyzes weekly the plankton samples from numerous vertical net tows along the California coast, such as the from the Cal Poly Center for Coastal Marine Sciences and Morro Bay National Estuary Program. Most of these monitoring stations are along the immediate shoreline or in bays or estuaries.

One station, however, that PG&E and Tenera Environmental marine biologists have sampled over many years is located about a half-mile offshore of Diablo Canyon Power Plant along the Pecho Coast. Due to its offshore location, it can often detect algae blooms earlier than the near-shore stations.

Practice caution on rivers and streams

With the exceptional California snowpack melting as temperatures rise, rivers and streams are full of dangerously cold and swift moving water this spring. PG&E encourages water enthusiasts to take extra precautions when in or near waterways, especially around hydroelectric facilities and dams, where water flows can change rapidly.

Anglers are also encouraged to take precautions as trout season opened Saturday for most California rivers. California’s snowpack measured 175 percent of normal in early April, ensuring cold runoff well into summer. “Public safety is our highest priority. We encourage everyone recreating in or near water to know at all times how they can quickly get out or away. Put safety first, especially while outdoors,” said Debbie Powell, PG&E’s vice president of power generation.

John Lindsey’s column is special to The Tribune. He is PG&E’s Diablo Canyon marine meteorologist and a media relations representative. Email him at or follow him on Twitter: @PGE_John.
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