Mystery of the Brown Beach Foam

Just a few weeks ago, I was in St Andrews for a meeting on the progress of our ocean acidification research group. Hard to believe it’ll all be coming to an end next year! St Andrews makes a fitting venue for a marine science meeting not only as the home of the Scottish Oceans Institute, but as a settlement perched neatly on the eastern Scottish coastline. With both rocky cliffs and sandy beaches sitting right next to each other, it boasts quite diverse wildlife. It’s a haven for seabirds and seals, and other marine mammals are seen regularly off shore. I made sure to give myself some time to walk along the West Sands (did not have time to recreate my own Chariots of Fire), and came across some rather neat things.

st andrews 1

I was surprised to find a fair few songbirds around, including song thrushes and pipits. They’re not the first birds I think of when I picture a sandy beach, but they seemed to be enjoying themselves alongside the gulls.

A chubby song thrush (Turdus philomelos) poking through seaweed on the strand line

A chubby song thrush (Turdus philomelos) poking through seaweed on the strand line.

A common gull (Larus canus) strutting his stuff.

A common gull (Larus canus) strutting his stuff.

I also came across a lot of washed up jellyfish. Only the one species, Aurelia aurita, also known as the moon jellyfish. Even in this semi decomposed state, it’s easy to ID. Just look for those 4 purple rings! They’re actually the jelly’s gonads. Just like plankton, jellies can form blooms where they appear in dense numbers. A jellyfish bloom is usually indicative of poor water quality though, so it’s probably not a great sign that these were everywhere.

Moon jellyfish, Aurelia aurita, slightly degraded but still recognisable with those purple gonads

Moon jellyfish, Aurelia aurita, slightly degraded but still recognisable with those purple gonads.

The gonad close up, complete with photo-bombing tiny insect.

The gonad close up, complete with photo-bombing tiny insect.

Of course, I can’t write a blog entry about the sea shore without mentioning algae. There was plenty around in the form of macroalgae, the seaweeds. Particularly abundant along this stretch of the West Sands was egg-wrack, Ascophyllum nodosum. This is a really common brown seaweed found throughout the north Atlantic, and actually the only species in the Ascophyllum genus. Those “eggs” are gas vesicles, filled with air to help keep the algae afloat when it’s underwater.

Seaweed eggs. I mean, gas vesicles of Ascophyllum nodosum.

Seaweed eggs. I mean, gas vesicles of Ascophyllum nodosum.

Frond of Ascophyllum nodosum

Frond of Ascophyllum nodosum.

There was a curious find distributed all along the beach that I overheard many holiday makers talking about. Along the strand line, sticking to piles of desiccating seaweed, were clusters of this weird, brownish foam. I saw a several folks poking the congealing stuff with sticks, trying to figure out what the heck it was.

Congealed foamy goodness

Congealed foamy goodness

Brown sea foam is a common phenomenon of coastlines in the North Sea shelf area, in particular around the UK, Germany, Denmark and the Netherlands. It can be a little disconcerting when you don’t know what it is. Local environment officers often get called out to the scene to test the waters, but they can usually tell what it is without having to take samples. The cause of the foam is not that much of a mystery – it’s in fact the doings of our old friends, the phytoplankton.

Phytoplankton foam!

Phytoplankton foam!

Well, one particular species of phytoplankton to be exact, Phaeocystis pouchetii. Another brown algae, and a globally distributed one at that. It’s abundant in the North Sea, but we encountered Phaeocystis in the Arctic and Antarctic too (though it may have been another equally well distributed species, P. globosa). P. pouchetii, like most Phaeocystis species, has two forms; a free-swimming, unicellular form that sports not one but two flagella, and a gelatinous colonial form. The plankton blooms in its colonial state, often forming aggregates that are so large, you can see them with your own eyes in the water. This is why we hated sampling a Phaeocystis station – they clogged up EVERYTHING.

In the North Sea, P. pouchetii blooms between March and September, and during these blooms, the cells churn out various kinds of organic compounds. While it’s still not fully understood why, we do know that the main compound produced, acrylic acid, is antibiotic, so it could be to ward off any harmful bacteria, or kill the competition. It might also make the cells unpalatable to grazers, though there is less evidence to support that hypothesis. At any rate, this organic material coalesces together through wave movement into these foamy masses, and eventually get washed up on the beach. When the bloom is particularly big, much larger clumps of foam make it to land. In the early 1980s, such a large Phaeocystis bloom occurred in the German Bight that the foam stacked 2m high in some areas of the German and Danish coast.

Not quite 2m high... but getting there...

Not quite 2m high… but getting there…

So, is it harmful? Well, no. It sure looks gross, and when the algae have a good year, it can be annoying for the people that own the beaches it ends up on as it does certainly turn people away from going to the seaside. I mean, I’m not advocating that you touch/jump around in/eat it, but it’s not deadly.

I personally think it’s really cool that an organism that is unable to be seen without a microscope can exude so much junk that it shuts down a beach.

But then again, I might be a little biased.


4 thoughts on “Mystery of the Brown Beach Foam

  1. Thank you! We have foam similar to that wash up in the Great Lakes on the Michigan shore from time to time, and I wondered what it was. It may not be the exact same species since it’s fresh water, but probably a similar species.

    • Yes, it’s actually far more common to get this kind of foam on lakes because they contain organic matter in much higher concentrations. Often it’s not even a plankton bloom at all, simply the decomposition of dead matter in the lake! The same sorts of things are released, and get clumped together by the wind. In smaller lakes, you can actually end up with the whole surface covered in the stuff, but I’d imagine in a lake as big as one of the Great Lakes it’d be more like finding it on a beach, just washed up on the shore like you said.

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