Since early September of this year, the Monterey Bay has been experiencing greater and lesser degrees of a red tide. A red tide is essentially a large algal bloom that occurs when environmental conditions allow for explosive growth of phytoplankton (a single-celled organism often called algae). Very dense blooms can change the color of ocean water and lead to red (or brown or orange) tides, depending on the type of phytoplankton.

Many red tides are harmless, but others might contain toxins or be detrimental in other ways, so they are called harmful algal blooms (HABs). Discoloration of the water alone is not an accurate way to determine whether harmful conditions exist. HABs can occur during red tides or they can be colorless and difficult to detect.

In California, strong winds and an influx of cold, nutrient-dense waters at the coast lead to blooms of diatoms in the spring, but dinoflagellates are more likely to bloom in the warmer, stratified conditions of the fall. Dinoflagellates are responsible for most red tides, although both dinoflagellates and diatoms can cause HABs.

The Recent Red Tide: Not A HAB

The recent red tide is a classic fall event in that the phytoplankton culprit (Akashiwo) is a dinoflagellate that has probably bloomed because of warmer-than-average waters in the bay — around 56 to 58 degrees. Akashiwo is not toxic to humans.

However, an Akashiwo bloom can cause a considerable amount of foam when the phytoplankton die and breakdown, especially if it’s stormy. The foam can then act as a surfactant and strip seabird feathers of their waterproof coating. On October 15th and 16th, high winds and rain, combined with a large concentration of Akashiwo, produced a lot of foam. So far though, there have been no confirmed bird deaths as a result.

Have you seen “The Birds” movie? Modern research suggests that a HAB was the cause of the strange behavior that Alfred Hitchcock observed in seabirds, which inspired the story. A bloom of Pseudo-nitzschia, which can produce the potent neurotoxin called domoic acid, is thought to be the cause of the birds’ behavior.

Researchers who monitor the environment can identify many types of HABs and their effects on organisms. However, new and unusual HAB occurrences can still stump scientists. In 2007, hundreds of seabirds were found stranded or dead in Monterey Bay in California. They were coated with a mysterious greenish substance that was stripping the protective oils off their feathers. The cause was eventually traced to the decay of an ongoing bloom of a nontoxic phytoplankton species, which turned out to be Akashiwo. The decaying cells, coupled with turbid water conditions, led to a thick foamy substance with properties similar to detergent. So during this fall’s Akashiwo bloom, wildlife experts knew to look for birds in trouble. Wildlife Emergency Services of Moss Landing led patrols along Del Monte Beach and Asilomar State Beach on October 15, 2016 and did not find any birds in distress.

For more information and images of red tides and HABs, visit the Ocean Data Center website. You can also see the results of weekly phytoplankton sampling by the Raphael Kudela Lab at the Santa Cruz and Monterey wharves.

More Information about Phytoplankton

This post is part of the Mobile Ranger “Phytoplankton Guide” created by the Kudela Laboratory at the University of California, Santa Cruz. Download our free Mobile Ranger Guides app to read the “Phytoplankton Guide” and take several of the self-guided mobile tours of the Santa Cruz area that are included in the free app.