For a tourist, nothing quite ruins a picturesque sandy beach like the sight and smell of rotting seaweed - which is why the owners and managers of beaches in many a seaside town spend time and money dragging large rakes attached to tractors through the intertidal. Mechanical beach cleaning takes away all the seaweed that is brought to shore by the ebb and flow of the tide, but it also destroys the habitat of the life that relies on it.
“It might look like nothing more than dead and rotting seaweed, but the ‘strandline’ is an important food source and habitat for much of our coastal wildlife” Dr Lissa Batey, Senior Living Seas Officer at UK based NGO The Wildlife Trusts explains. Under and in the strandline lies myriad lifeforms, like the shimmering golden-brown dune chafer beetle which travels from nearby dunes to eat rotting seaweed, and the aptly named seaweed fly who lay their eggs in amongst the decaying plants so that their young can feast on the seaweed’s bacteria when they hatch. Remove the seaweed and you hurt the whole food web, from microscopic bacteria and humble marine isopods to the shorebirds and small mammals that feed on them.
Yet the beach is covered at high tide, bringing varying amounts of seaweed to shore. Surely seaweed-reliant communities have plenty of opportunities to recover? Not quite, says new research by Caroline Griffin, an ecologist who spent several months studying strandline macroinvertebrate communities on cleaned and uncleaned beaches across eastern Scotland and western Sweden during her time at Scotland’s University of Stirling.
Griffin found that the thicker the layer of seaweed, the greater diversity of macroinvertebrate life the strandline held. Unsurprisingly ungroomed beaches had, on average, deeper strandlines and greater diversity of macroinvertebrates than groomed beaches. But even when comparing groomed with ungroomed beaches with similar strandline depth, she found that that diversity on ungroomed beaches was higher. Griffin also found that even when grooming is put on hold — say, for the tourist-light winter season — seaweed-dependent communities do not always fully recover. Winter storms will rebuild much of the seaweed cover, but because that build-up takes time, macroinvertebrate communities do not necessarily have the chance to bounce back before grooming starts again following summer.
In the UK at least Batey notes that managers are becoming increasingly aware of the importance of leaving seaweed on the beach, but there are still challenges; “Work is still needed to raise public awareness of the importance of strandlines, as public attitudes towards leaving seaweed on the beach are often negative”, she explained. “The removal of all surface debris creates a sterile, artificial environment and further exacerbates the disconnection between society and our natural environment”.
This article was originally written for (and appears as a shortened version in) Hakai Magazine.