Have you ever noticed how some days there is a lot of sea foam on the beach, but other days not much? On those “foamy days” I often get questions about it: Where does it come from? What causes it? This almost always happens on windy days when the wind is blowing onto the beach from offshore. These are the kind of days you are more likely to see accumulations of sea foam.
First of all though, what it isn’t. Sea foam, as we see it, is not due to water pollution or poor water quality. You’ve probably seen pictures of polluted waters where detergents or foam-producing substances have spilled into an area and caused suds, bubbles, and foam. But that is not the case or cause of our beach seafoam.
Our beach sea foam is due to oil in the seawater. But wait! It’s not petroleum or pollution-type oil. Instead, it is more like vegetable oil. Many of the tiny, microscopic algae, or phytoplankton, that live in the coastal water manufacture oil as their food and energy reserve and store it inside their cells. There are benefits to making this oil. Oil contains lots of chemical energy in a small space, so tiny oil droplets are a great way to store excess energy that the algal cells make when doing photosynthesis. Additionally, the tiny oil droplets inside help the algal cells to float, or keep from sinking. And as a water-dwelling organism that depends on sunlight to make its own energy for survival, algae need to be able to stay near the surface. So anything that helps it from sinking is a beneficial adaptation.
Our coastal water has lots of phytoplankton in it. In fact, the main reason our water is green and slightly cloudy rather than crystal clear is because we have so much plankton in it. These tiny living particles make the water cloudy, but they also provide the start of the food chain that so many of our bigger animals depend on.
As the phytoplankton manufacture oil, they also leak it. When they die, they leak it, along with proteins. When they are eaten and their consumers die, they also leak it into the water. So this sort of “vegetable” oil is a natural component of seawater, especially in places like ours where the water is rich with these tiny algae.
On days when the wind is blowing, stirring up the ocean, and the waves are white-capping, the oils get worked toward the surface. If the wind is blowing from offshore toward the beach, this imperceptible film of oil and protein gets constantly blown onto shore. As the film catches the blowing air, that oily film forms bubbles. And as the wind continues to blow, all those bubbles result in piles of foam that accumulates on the shoreline.
So, on days when the wind is right, you might see seafoam. But remember, it’s not due to pollution, but rather is due to our plankton-rich, healthy seawater.
Dr. Joe Richardson is a retired marine science professor with 35+ years of research and teaching experience along GA and the southeastern coast and Bahamas. Besides research, he conducts Tybee Beach Ecology Trips year-round (www.TybeeBeachEcology.com) and frequently posts pictures of what they are finding on his Tybee Beach Ecology Trips Facebook page.