What is in the Sea foam?

Everyone has seen this white foam while walking along the seashore, but what is it made of? Why does it foam?

Sea foam is a foam formed by wind and agitation of seawater that can be found all over the planet. It forms as waves break when the concentration of dissolved organic matter (including proteins, lignins, and lipids mainly from the decomposition of organisms) is sufficiently high. This organic matter behaves like a biofilm of mucilaginous substances and acts as a surfactant (foaming agent), trapping air bubbles and forming a foam that persists for varying lengths of time. The composition of sea foam is generally a mixture of algae, phytoplankton, zooplankton (including, in some cases, the larvae of certain organisms), fungi, protozoa, plant debris and bacteria2. New species are still regularly discovered in it3. Some studies have even found cosmic dust in it⁴! Human activities and coastal pollution (e.g. petroleum derivatives, detergents, pesticides and herbicides) can also cause sea foam to form⁵. The exact composition of sea foam varies depending on the location in the ocean, and each occurrence of sea foam has a specific composition. It has also been shown that the presence of phytoplankton blooms promotes the formation of sea foam and seasonal variations in its composition.

Sea foam is not toxic by nature, but it can be if it contains pollutants or certain harmful microorganisms (e.g. certain dinoflagellates)1.

When waves break on the coast and rocks, air from the atmosphere is incorporated into the water column, leading to the formation of bubbles. Through this mechanism, these bubbles play an important role in gas exchange between the ocean and the atmosphere7. These bubbles are transported to the top few metres of the ocean surface, where the smallest ones dissolve completely and contribute to an increase in the concentration of dissolved gases at the surface. Those that do not dissolve completely rise to the surface and accumulate, stabilised by the presence of organic matter, and form sea foam1.

Sea foam also plays an ecological role. It helps transport nutrients for certain organisms that find food there, as well as transporting the organisms themselves2. It is also home to many microorganisms, which are sometimes found in greater numbers there than elsewhere in the ocean8,9. It occasionally acts as an exchange zone between marine and terrestrial environments, influencing both environments in the process. Current climatic and environmental changes are likely to influence and be influenced by changes in the presence and composition of sea foam6,7,10.

Bibliography

1. Schilling, K. & Zessner, M. Foam in the aquatic environment. Water Research 45, 4355–4366 (2011). DOI: 10.1016/j.watres.2011.06.004.

2. Craig, D., Ireland, R. J. & Bärlocher, F. Seasonal variation in the organic composition of seafoam. Journal of Experimental Marine Biology and Ecology 130, 71–80 (1989). DOI: 10.1016/0022-0981(89)90019-1.

3. Wright, L. et al. Nocardia australiensis sp. nov. and Nocardia spumae sp. nov., isolated from sea foam in Queensland, Australia. International Journal of Systematic and Evolutionary Microbiology 73, (2023). DOI: 10.1099/ijsem.0.005952.

4. McGeoch, J. E. M. & McGeoch, M. W. Sea foam contains hemoglycin from cosmic dust. RSC Adv. 14, 36919–36929 (2024). DOI: 10.1039/D4RA06881E.

5. Naik, S. et al. Anthropogenic impact influences the episodic events in the coastal waters of Chennai metropolitan city. in OCEANS 2022 - Chennai 1–7 (IEEE, Chennai, India, 2022). DOI:10.1109/OCEANSChennai45887.2022.9775355.

6. O’Dowd, C. et al. Connecting marine productivity to sea-spray via nanoscale biological processes: Phytoplankton Dance or Death Disco? Sci Rep 5, 14883 (2015). DOI: 10.1038/srep14883.

7. Jenkinson, I. R., Seuront, L., Ding, H. & Elias, F. Biological modification of mechanical properties of the sea surface microlayer, influencing waves, ripples, foam and air-sea fluxes. Elementa: Science of the Anthropocene 6, 26 (2018). DOI: 10.1525/elementa.283.

8. Porri, F., Puccinelli, E., Weidberg, N. & Pattrick, P. Lack of match between nutrient-enriched marine seafoam and intertidal abundance of long-lived invertebrate larvae. Journal of Sea Research 170, 102009 (2021). DOI: 10.1016/j.seares.2021.102009.

9. Rahlff, J. et al. Sea foams are ephemeral hotspots for distinctive bacterial communities contrasting sea-surface microlayer and underlying surface water. FEMS Microbiology Ecology 97, fiab035 (2021). DOI: 10.1093/femsec/fiab035.

10. Jenkinson, I. R. et al. Harmful or beneficial algae? How organic matter secreted by plankton and neuston algae, including that in the surface microlayer and in sea foam, may be participating in climate regulation: a review. (2022). DOI:10.5281/ZENODO.7033151.

January 2026

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