Plant Cuttings

Toxin-tainted submarine snow

Human pollution of the seas is turning a gentle rain of food in the marine abyss into something nastier.

Terrestrial ecology is reasonably straightforward [Ed. – Careful, Mr C., there’ll be letters…]: Plants do their productivity thing via photosynthesis and get bigger, etc. and are eaten by grazing animals (which, in their turn, are preyed upon by carnivores…). When plants – and other organisms – die their carbon-/energy-rich bodies and ‘bits-and-pieces’ provide sustenance for the decomposing community, whose inorganic outputs are then available to be taken up by plants to be incorporated anew into organic materials. Notwithstanding the fact that some trees can reach heights of 100 metres plus, all of that land-based activity takes place from a few metres above the ground to a few feet below the soil surface. Basically, terrestrial ecology takes place in one rather small space. Marine ecology is rather different (!)

One major distinction is that photosynthesis takes place within a thin veneer of sunlit water at the top of the oceans, yet biodiverse communities – many of which depend ultimately for their energy from the products of this near-surface photosynthesis – are found many thousands of metres below on the ocean floor, where photosynthesis is not possible. How do such seafloor-occupying organisms survive? What is the connection between the photosynthetic/producing part of the oceans and those consumers in the abyss?

For many at depth it is a gift from above – not light itself, but organic material that is produced one way or another from the efforts of photosynthetic organisms – that gives them energy-rich organic inputs. This constant ‘rain’ – ‘a shower of organic material’ – is termed marine snow because it looks a little like that terrestrial precipitation. Now, if the only lifeline to support yourself and your community is provided from action far above, it would be nice to think that gift wasn’t going to cause you harm. Well, that assumption might be unwarranted according to work by Astrid Schnetzera et al..

Studying marine snow derived from the toxic diatom Pseudo-nitschia australis, they show that a significant amount of domoic acid survives the descent to the depths. Domoic acid is a potent neurotoxin, which causes Amnesic Shellfish Poisoning (ASP) in humans who might unwittingly consume it via tainted shellfish that have in turn fed – and equally unknowingly – upon a diet rich in domoic acid-producing diatoms when present in large populations, so-called harmful algal blooms (HABs). Although the impacts upon marine organisms that feed upon such domoic acid-enriched marine snow is not yet known, any potential ‘interactions with aggregate-associated microbes and zooplankton consumers warrant further consideration.’

If Miss Smila was a denizen of the deep, one wonders what her feeling for marine snow might be. Might this tainted snow be considered a marine equivalent of acid rain that so bedevils parts of the terrestrial environment …?


Schnetzer, A., Lampe, R. H., Benitez-Nelson, C. R., Marchetti, A., Osburn, C. L., & Tatters, A. O. (2017). Marine snow formation by the toxin-producing diatom, Pseudo-nitzschia australis. Harmful Algae, 61, 23–30.

Schnetzer, A., Jones, B. H., Schaffner, R. A., Cetinic, I., Fitzpatrick, E., Miller, P. E., … Caron, D. A. (2013). Coastal upwelling linked to toxic Pseudo-nitzschia australis blooms in Los Angeles coastal waters, 2005-2007. Journal of Plankton Research, 35(5), 1080–1092.

About the author

Nigel Chaffey

Nigel is a botanist and full-time academic at Bath Spa University (Bath, near Bristol, UK). As News Editor for the Annals of Botany he contributes the monthly Plant Cuttings column to that august international botanical organ. His main goal is to inform (hopefully, in an educational, and entertaining way...) about plants and plant-people interactions.