042619 Vertical plankton net tow

Steve Pengilley, project scientist with Tenera Environmental, performs a vertical plankton net tow Friday aboard the Pacific Gas and Electric Co. marine research vessel off the coast from Diablo Canyon Power Plant.

A saying that I heard growing up is that you should only harvest shellfish, like 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 that axiom 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 ocean upwelling.

That, in turn, brought frigid, clear, 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.

That 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 more than 7,000 feet and eventually dissipate, leaving behind clear skies with plenty of sunshine.

If there’s enough sunlight, enormous phytoplankton blooms may occur due to photosynthesis.

During periods of warmer and calmer seas, a group of phytoplankton species called dinoflagellates can explode in numbers and produce “red tides” and even flashes of electric-blue bioluminescence when agitated.

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 brick-red or brown in color.

Unfortunately, red tides can also create toxins.

You see, mussels, clams, scallops and oysters are bivalve mollusks that filter vast amounts of water through their gills to obtain food. That allows their tissues to accumulate toxins from red tides that can cause diarrhetic shellfish poisoning.

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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 that can accumulate not only in bivalves but also in Dungeness and rock crabs as well as baitfish, like anchovies and sardines.

If you consume enough of that neurotoxin, you can develop amnesic shellfish poisoning, as the toxin kills neurons in your brain responsible for short-term memory.

Many of us who live along the Central Coast may have seen seabirds or marine mammals like sea lions that feed on baitfish suffering from domoic poisoning.

The months more likely to see red tides occur during summer — the months without an “R.”

However, red tides can occur in other months of the year, like September.

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In full disclosure, I love seafood, and I’ve personally never gotten sick eating shellfish or anything else from the sea.

I feel fortunate to live near a pristine marine environment with so many wholesome seafood restaurants to enjoy.

Helping to keep us safe, the California Department of Public Health (www.cdph.ca.gov) closely monitors our coast for the presence of toxin-producing phytoplankton in the bivalves, crabs and fish we enjoy.

The Phytoplankton Monitoring Program coordinates and analyzes weekly plankton samples from numerous vertical net tows along the California coast, like the one from the Center for Coastal Marine Sciences on the Cal Poly Pier and the Morro Bay National Estuary Program.

Most of the monitoring stations are along the immediate shoreline or in bays or estuaries.

However, one station Pacific Gas and Electric Co. and Tenera Environmental marine biologists have sampled over many years is located about a half-mile offshore from Diablo Canyon Power Plant along the Pecho Coast.

Due to its offshore location, it can often detect algae blooms earlier than the nearshore stations.

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John Lindsey is Pacific Gas and Electric Co.’s Diablo Canyon Power Plant marine meteorologist and a media relations representative. Email him at pgeweather@pge.com or follow him on Twitter @PGE_John.