National Biodiversity Week: Quilty Bay displays marine riches

A "discovery fieldtrip" to Quilty Bay in Co Clare organised by Coastwatch to coincide with National Biodiversity Week, which runs up to May 22nd, was an opportunity to experience the remarkable richness of the Irish shoreline. But it also illustrated its vulnerability to climate disruption and an immediate threat to newly discovered seagrass beds.

The value of seagrass beds as a habitat for marine creatures, including fish and bird species, such as migratory Brent Geese, is well-known. But their value for carbon storage is increasingly recognised, especially in mapping and preserving them. While seagrass only covers about 0.1 per cent of the ocean floor, it is responsible for 13 per cent of the carbon stored in the ocean.

Quilty Bay's dune-rimmed sandy beach slopes gently into a sheltered intertidal reef. At low tide reef ridges form "paddocks", separating the open sea from sandy mud, pools, seagrass meadows and seaweed patches, explains Coastwatch co-ordinator Karin Dubsky.

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Beware the presence of Sargassum, the invasive species.

She describes the scene: “The shore was heaving with life. Apart from acres of lugworm casts, winkles of different species held onto seaweeds waiting for the tide to turn with limpets and dogwhelks resting on rocks.

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“Netted whelks just finished gluing disc-shaped eggs neatly onto blades of seagrass under water, while sea hares were swimming and crawling about with only one thing on their mind judging by the pink and orange spaghetti egg strings tied around seagrass and seaweeds.”

A seagrass check was a key task as the location’s seagrass meadow growing on flat sandy mud in the reef ridge shelter was only discovered last summer. It was extensive, stretching from shallow water out along the reef with up to 1.73m-tall plants measured at the deep end.

Seagrass meadow

The survey teams this month, however, saw a different picture as they waded to the short blade grass in shallowest waters, while swimmers and paddle boarders explored the deeper seagrass meadow.

Storm waves must have topped reef ridges and scoured the sandy sediment out right down to boulders and stones, Clare Coastwatch co-ordinators Frances Galloway and Jane Kellegher explained. Where the sandflats had been colonised by seagrass, the network of roots and rhizomes offered resistance, so the deeper water seagrass remained intact.

But in shallow water waves managed to break in, get under the seagrass roots and rhizomes, and roll it all up like carpets, then dump these seagrass carpet rolls, scouring the sand below it on the next wave. This has created a highly unusual uneven seafloor landscape with scoured pools beside seagrass humps and rolls.

Locals say the sea filled sand back into scoured ground after previous storms. However there is a problem in the form of “wire weed” Sargassum muticum; an invasive alien seaweed from the Pacific first noticed attached to small stones as isolated fronds and the odd cluster in summer 2021. It is now abundant in several reef paddocks. Some Sargassum on light stones seem to have already rafted into the scoured pools before the sea has had time to refill them with sandy mud.

As Coastwatchers have observed in Co Wexford, once established this tough brown seaweed can withstand sediment burial at the base. "As it grows much faster than seagrass, it would outcompete it in the race for space. Indeed, it can become several metres long and form a matt over the adjacent seagrass and block sunlight to it," she notes.

Deceased molluscs

Apart from the seagrass issue, Quilty Bay provides an invaluable insight on Irish marine diversity. Empty seashells of deceased molluscs high on the beach are a fingerprint of what lived in the sea. In Quilty, it’s diverse and includes some less common species like cowries and painted top shells. Repurposed for hermit crabs habitation, from mid-shore down, empty shells become a rarity as hermit crabs occupy them – from the smallest flat winkle starter pad, right up to significant dog whelk homes and even a common whelk mansion.

Hermit crabs could be seen in little huddles whether to mate or just wait for a bigger home. Once one large shell becomes available, others can shift one up; the remarkable order of nature. “There appears to be a housing crisis here too,” remarked a participant. Children were fascinated, especially when it was explained they must be carefully lifted and put back into the correct spot in “the shell house queue”.

Recent strong waves had ripped out seaweeds from the sublittoral and swept up an amazing diversity and sizes range. One sugar kelp measured 3.42m from holdfast to tip. It was repurposed as skipping rope to warm up. There were oyster thieves (a brown round seaweed), Irish moss and lots of red seaweeds.

A common sight was cuvie, a type of kelp. The big rough stiped cuvie or mayweed kelp Laminaria hyperborea grows a new frond every year. As this grows from the blade base, it pushes the old frond up until finally the old frond breaks loose and floats away “like a brown worn hand” as Dubsky describes it.

Various molluscs, sand hoppers and microbes munch and mulch these “hands”. It’s all part of the marine food web. In Quilty this breaking loose process had just happened with old hands strewn across the shore.

Invasive alien

As the tide turned, participants headed to the Armada Hotel for teams to discuss their findings. Oddities were identified and issues discussed. It was agreed that posters, signage and well-managed ecotours were needed to highlight Quilty Bay’s key features and designation status as a Natura 2000 site. Efforts to monitor seagrass recovery or otherwise was another. Most urgent in that regard is removal of the invasive alien Sargassum and the local citizen science community could be the way to do it.

By mid-summer, sargassum spores could be ripe and spread even more. The removal method developed by Coastwatch in the southeast can be adapted to local conditions, according to Dubsky. “It is a labour-intensive removal, requires volunteer training, but one which causes least collateral damage. Over 100 volunteers have now be trained up in three pilot counties. An official removal permit is needed and will hopefully be granted along with support.”

Another possible action with big benefit would be to close off an area of “splashzone beach”, where a storm had cast up a huge seaweed and sand load – right in front of a severely eroded dune face. “Here nature is fixing itself – if we let it. But if trampled and flattened by cars this summer, dune plants cannot grow to form a new front dune natural sea defence,” Dubsky adds.

Coastwatch and the community in Fenit, Co Kerry, have done this successfully. "With climate change, sea level is rising, storms are becoming more frequent and precious sites like Quilty are so vulnerable. Tread softly, lift only what is gently liftable and put it back as you found it," she advises.

To volunteer as a Coastwatch surveyor contact: Survey@coastwatch.org

Details of NBW events over coming days are available at https://biodiversityweek.ie/