My trip to the River Coquet included a brief diversion to the Northumberland coast to help a colleague from the Royal Botanic Garden in Edinburgh collect some samples for a different study. Her interest was in the coastal diatom flora and, alongside sampling sand and mud, she also used a Pasteur pipetted to hoover up samples of the foam that accumulated around the low tide mark.
Diatom-bearing foam accumulating around a rock at low tide at Alnmouth, Northumberland, May 2014. Note the “selfie” of my thumb in the top left hand corner.
This foam proved to be rich in a diatom called Asterionellopsis glacialis, which we have met before in this blog (see “Back to Druridge Bay”). On this trip, I had found A. glacialis in brown-diatom rich patterns growing close to the low water level. We don’t know much about the ecology of Asterionellopsis glacialis, but there is a good study of another surf-zone diatom, Anaulus, which appears to move between the sand patches, foam and the inshore water over the course of a day. This is linked to a cycle of cell-division and mucus production – the latter occurring as the cells move back from the water to the sand and, it is suggested, the mucus may help the diatom cells to stick to the sand, and so helps them to maintain a population in one place rather than being washed away with the tide. As so often with diatoms, something as unprepossessing and easily-overlooked as foam on a beach proves to hide a complicated ecological story.
Asterionellopsis glacialis from the surf at Alnmouth, May 2014. The helical arrangement of cells can just be discerned, though it is hard to capture this crisply with the limited depth of field available under a high power microscope.
One other find on the Alnmouth sand were a few cells of Druridgea compressa, another constituent of the sand flora. I looked for this species last year (“In the footsteps of a Victorian microscopist …”) but without any luck. This, too, has been studied and shows a similar pattern, exuding sticky mucilage as they settle out from the sea water at low tide. The wave action then acts as a “whisk”, whipping these organic compounds into the froth that we saw at Alnmouth.
Life for a microscopic organism on a sandy beach is tough, with regular inundations from the tide and the constant movement of the substrata to add to the challenges faced by other organisms. Consequently the density of cells of all these organisms is very low, making it harder to find and study them. There are a few papers on the taxonomy and morphology of Druridgea compressa but, apart from the paper referenced below, we really do not know much about its ecology at all. Ironically, much the same can be said for Arthur Scott Donkin, the Victorian microscopist who first described Druridgea back in 1861. We have gleaned a few more details of his life since I wrote my post in May last year, but not much. Donkin, like Druridgea, remains elusive.
Two cells of Druridgea compressa from the sand at Alnmouth, May 2014.
Berryman, J. (2010). A contribution to the ecology of Druridgea compressa on Porthmeor Beach, Cornwall. Quekett Journal of Microscopy 41: 193-202.
McLachlan, A. and Brown, A.C., (2006). The Ecology of Sandy Shores (2nd edition). Elsevier, Burlington MS.