A team of seaweed experts and specialist survey divers have found entirely unknown areas of maerl beds just off the Roseland Peninsula and St Austell Bay.

Using scant knowledge from a few previous surveys, the skills of dive boat skipper Mike Anselmi from Porthkerris Divers and Natural England’s underwater drone, the team were able to find and survey the maerl beds which are crucial in supporting other marine species.

Very little maerl is thought to exist outside Cornwall, where it particularly thrives in clear waters, estuaries and tide swept bays. The beautiful and ancient maerl beds of the Fal and Helford Estuaries have long been known about and were duly designated within a Marine Protected Area in 2005.

But far less is known about the maerl that exists outside the estuaries in the bays along Cornwall’s south coast, but Natural England’s expedition to find out more has payed off. 

The rose pink, slow growing, fragile maerl beds of rare pink calcified seaweeds form the basis of marine food chains in the area, and as well as being breathtakingly beautiful, are hugely important for the local ecosystem. 

Maerl beds act a little like coral reefs, slowly growing to provide three-dimensional structure which is a habitat for many other seaweeds and small organisms. This has led maerl to be recognised for its crucial role in supporting fish populations and underpinning healthy fisheries.

It is classed as an “irreplaceable habitat”, because of its almost complete inability to recover from damage and if the maerl is lost the species it supports will also be lost.

Natural England’s marine senior officer, Angela Gall, who led the survey said: ”It’s incredible to think, that in Britain, within sight of the shore, there are still completely undiscovered sites. We will use this new evidence on the maerl bed sites to seek better protection for these ‘ancient woodlands of the sea.” 

The divers surveyed the sites in detail, recording 110 different seaweed species and 79 different types of animals living on the maerl. They assessed the health of the beds and collected photographic evidence.

Small samples were collected for genetic work by the University of Exeter, which will help with understanding the genetic uniqueness of maerl beds in this area. The work was intensive, with detailed microscopic examination of many seaweeds, small snails and worms back at base camp following the dives. 

The new information about maerl sites will be used to help target mapping efforts this autumn, adding to understanding of where these precious beds can be found. It is hoped that by knowing where these sensitive habitats occur it will be possible to better protect them as the foundations of healthy ocean ecosystems.