Science

Marine forests are a patchwork of life and opportunity

Seagrasses can capture carbon up to 35 times faster than tropical rainforests

Seagrass (Zostera marina) beds

Alex McMaster
Thu Feb 10 2022 - 06:00

Ireland’s coasts can be harsh and foreboding. But a coarse perception of bleak rocky shores is inconsistent with the abundance that sways just a few feet beyond them.

In the immediate depths grows a patchwork of meadows and forests. Two distinct groups of plants – seagrasses and seaweeds – form vibrant habitats supporting a spectrum of undersea life.

Their richness extends opportunities for coastal economies and climate change mitigation. Seagrasses in particular are effective carbon sinks, and the life thriving within them provides a base for modern livelihoods.

Cuvie (Laminaria hyperborea) is one of more than 500 seaweed species skirting the shores of Ireland and Britain. It is our most common native kelp, a group of seaweeds that fix themselves to the rocky bottom and grow up to three metres in length. Its dark blades can often be seen hanging in the tide.

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"They [kelp forests] are incredibly diverse habitats," says Dr Kathryn Schoenrock, a researcher at NUI Galway. They host different seaweeds, huge sponges, cup corals, jewel anemones, invertebrates that are eating and colonising what's living on the kelp itself. "So it's almost like an apartment building with an apartment building on top of it!"

The variety fostered by kelp forests is important, Schoenrock adds, since diversity is the basis of resilience in ecology: “Ireland is going to see more frequent storm events with climate change, and that is likely to take out whole swathes of kelp forest. So if we can ensure that diversity is maintained, that will help them keep recovering.”

Coastal communities

Resilience is a survival trait needed not only in coastal ecosystems but the livelihoods built upon them. The richness of seaweed is something that has been transferred to the land for generations, nourishing coastal communities.

John Bhaba Jack Ó Conghaola is a traditional seaweed harvester from Leitir Mealláin in Connemara. He describes how kelp and other seaweeds, such as feamainn bhuí (Ascophylum nodosum), were used in the past as a fertiliser and food source: “People were given bogs to heat the house and seaweed rights to manure their gardens. They’d put seaweed out on the hay; seaweed on the potatoes, carrots, parsnips.”

For generations, seaweed rights have been allowing households to exploit a portion of the foreshore associated with their land. Harvesting was so extensive in the 1960s that there was an export market, with crops shipped to England and Scotland.

In the 2010s Ó Conghaola was part of a movement to protest against the use of heavy machinery, seen by some traditional harvesters as threatening coastal ecosystems. But modernising seaweed livelihoods can be sustainable, says Dr Liam Carr of NUI Galway.

Carr outlines how seaweed farming – a form of mariculture – can have benefits for both coastal ecosystems and the communities who rely on them. It is different from wild harvesting in that seaweed is cultivated specifically for human use.

“Mariculture can reside at the scale of the community. There’s no reason that it has to turn into large industry,” he says.

“It could be something [for] a rural community that is looking for diversification and maybe some retention of population, with stable, secure, well-paying jobs that people are proud to be a part of.”

Sustainable, community-scale seaweed enterprises do exist in Ireland. Oilean Glas Teoranta, in Donegal, contracts local harvesters in the production of fertilisers and animal feed supplements; and Bláth na Mara is a family business in the Aran Islands processing seaweed into food and cosmetics.

Carr emphasises the need for a foundation of location-specific knowledge, since the complexity of ecosystems and communities contravenes a one-size-fits-all approach. Both scientific data and traditional knowledge are a part of constructing an idea of what will work in the long term.

"Making decisions with as complete a knowledge base as one can, and making decisions and implementing plans that are reflective of what the community is looking for. So what might work on the south coast of the Aran Islands would be different from what you might do in Waterville or Westport. "

When it comes to our scientific understanding of Ireland’s kelp forests in particular, Schoenrock notes information is sorely lacking. These forests extend from the shore to a depth of about 40m, making them difficult to access without diving equipment.

“We have a basic understanding of kelp in Ireland . . . you have this swathe of the coastline that we can’t really get to. So we’re missing that data,” she says. A solid base of knowledge is needed for the successful management of coastal resources such as seaweed.

In some cases, seaside communities – the long-standing custodians of coastal knowledge – are setting out to gather that missing information themselves. Seasearch Ireland is a group of volunteer divers who have conducted some of the first detailed research on kelp forests in the country.

Another organisation of citizen scientists is Coastwatch. With volunteers combing the foreshore all around Ireland, much of their research is focused on seagrasses, a group of species distinct from seaweeds. While seaweeds grip rock by means of a structure called a holdfast, seagrasses have a system of roots stitched directly into the seabed.

Carbon sinks

It is this root system that makes seagrasses an excellent carbon sink. Karin Dubsky, the coastal ecologist who co-ordinates Coastwatch, explains carbon is sequestered in the ground by the roots, much in the same way that trees draw it down on land. She describes this storage of carbon as a package held within the fingers of the roots: "[Seagrass] on the top might come and go, but as long as the package underneath is solid and healthy, you're okay."

In fact, seagrasses are capable of capturing carbon up to 35 times more quickly than tropical rainforests. So although these habitats represent an area smaller than that of terrestrial woodland, their contribution to carbon storage is significant. The term “blue carbon” has been coined in association with such habitats, which also include salt marshes and mangrove swamps in the tropics.

Karin Dubsky of Coastwatch out surveying the Dublin coastline with volunteer surveyor Roslyn Nicholson. File image

Ireland’s climate action plan, launched in October 2021, calls for the nation to recognise the mitigation and adaption potential of its seas. A better understanding of seagrass ecosystems would take a step in this direction, according to Dubsky.

Coastwatch has launched a nationwide campaign to find and identify seagrass. Based on the premise that local people are best placed to find and protect these habitats, it is also a way for communities to learn more about the value of their coastal ecology. Like seaweed, seagrass can be an anchor in small-scale economies.

“Most of our traditional estuarine fishermen are in trouble, but they benefit from what’s living in the seagrass,” Dubsky adds. “There are quite a number of small-scale fishermen who are supporting [our work], who are telling us where they’re finding seagrass, and who are interested in looking after it . . . fishermen in some estuaries like Lough Swilly knew these meadows by name and told us of their loss.”

Dubsky describes seagrass as part of a wider opportunity for coastal ecosystems to drive sustainable economies based on fishing and ecotourism. She reiterates that communities must be equipped to manage their coasts for their own benefit: “If you look ahead, what kind of management should we have? If we have management with local people trained up, facilitated to manage, it is much stronger than parachuting in a scientist.”

Mottled green and brown seascapes have the capacity to seed resilience in coastal waters. In fact, the aggregation of marine flora takes their benefits to a new level, Dubsky says: “You’ve got a higher biodiversity where you have that habitat mosaic of kelp and seagrass, and other seaweeds.”

Reflected in their diversity are the many ways of knowing marine forests. They can capture the imagination, Carr says, and this has value in itself. “We need to have an attachment to the sea. If we can bring it in to ourselves, to our imaginations, then we have a better chance of understanding it.”

Yet again, that multiplicity of understanding is of great importance. Through a blend of tradition and science, innovation and creativity, a strong base can be cultivated for the future.

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