On my recent walks at the Marin Headlands, I’ve been seeing a lot of sea foam washing up along the shore. Are these large amounts of foam normal for this time of year? Is the foam toxic to marine life? — Katy Yeh, Bay Nature staffer
Sea foam is a common feature in coastal regions, and can be caused by several factors. There are very dramatic foam events in some parts of the world, including the Netherlands and Australia, caused by an algae called Phaeocystis. It produces a lot of organic material that gets churned by the waves into very thick foam. We tend not to have that organism at high abundance in California so it would be unusual to get that type of foam. What we do get is foam from kelp, and foam from a dinoflagellate called Akashiwo sanguinea. The dinoflagellate foam is the one that caused bird mortalities in both 2007 and 2009.
All of these foams are similar, in that they are composed of organic material that has properties similar to whipped cream or egg whites—when beaten, the organics form long chains of proteins that become stiff and trap air bubbles (that’s how whipped egg whites also form). It’s the wave action from the ocean that provides the energy to “beat” the organics into a foam. As far as we know, only the foam from Akashiwo causes problems, because it has another unusual property—the foam< strips the waterproofing from bird feathers. None of the foams (from the algae or kelp) are toxic, and are generally harmless to touch, smell, or even taste. At this time of year the foam along the Marin headlands could be either from kelp, or from a dinoflagellate bloom. We tend to get blooms of Akashiwo in late summer or autumn. If that were the source of foam, then there will likely also be “red tides”, or discoloration of the water, because Akashiwo forms dense blooms with a reddish-mahogany color. An easy way to tell the difference is to pick up some foam in your hand. Kelp foam is very delicate, and will usually collapse shortly after you touch it. Akashiwo foam is more dense, and can last for hours, even when you handle it. The Akashiwo foam also feels soapy or slippery, while the kelp foam does not.
So, the foam is normal for this time of year, probably coming from kelp or the dinoflagellates (it is more obvious at this time of the year because of the bigger waves that churn it up). It is not toxic, and does not become toxic, but if it’s foam from Akashiwo, then it could cause problems for marine birds. Other than being kind of fun to play with, there are absolutely no issues with humans (or pets) interacting with the foam.
Raphael Kudela, Ph.D. is a phytoplankton ecologist at UC Santa Cruz whose Biological Oceanography Lab studies phytoplankton growth and distribution in the Eastern Pacific Ocean. Learn about his lab’s research on harmful algal blooms on UCSC’s website.