NATURE NOTES: Plunging into an alien world on the rocky shore

I have left behind the quiet land to become an explorer of other, more vibrant, worlds; surveyor of the inbetween places.

By Ceris Aston
Friday, 22 February, 2019, 13:00
Rocky shore surveying. Picture by Catherine Scott

As the tide ebbs and flows, the rocky shore transforms – sometimes land, sometimes sea, home to creatures both beautiful and bizarre.

You have to be tough to survive here, where the tide pushes and pulls and throws everything it has at you, where you must adapt to extremes – from seabed to shallow pool.

Beadlet anemone. Picture by Katherine Dunsford

Animals here are different, the laws of the world up above unheeded.

Why have two legs when you can have five? Or pump blood, when sea water will do just as well?

It is a new world to me, but I have guides. I follow the two Katherines, both marine biologists, and try not to slip on the wet rocks.

We are many-layered and pink-cheeked. The day is bitingly cold.

Limpet, by Katherine Dunsford.

We are conducting an invasive species survey of the rock pools on Holy Island; examining the undersides of rocks for orange-tipped sea squirts, small invertebrates resembling Werther’s Originals.

Creatures of the southern hemisphere, they are believed to have come north attached to ships – thumbless hitchhikers whose spread around the UK has been rapid.

These aliens have landed on the shores of Lindisfarne National Nature Reserve, effective colonisers who threaten to displace native species.

Of Holy Island’s rocky shore, all but the harbour is encompassed within the Reserve’s protection.

Star ascidian, by Katherine Dunsford.

Space is at a premium on the rocky shore, where many animals are sessile filter feeders – staying put for all of their days on one spot on one rock, and filtering fragments of food from the water.

The rocky shore is rich in biodiversity. Rocks encrusted with barnacles lie half in and half out of the pools. Beneath reflections of the sky, eyes adjust to movement in the water.

There, a hermit crab scuttling fast in its borrowed shell, then the flitting of a fish too fast to identify.

It might be a goby, sand-coloured with comical bulbous eyes or a slim butterfish, who have the unusual ability to breathe air through their gills.

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In a large crevice, we find dog whelks – predatory sea snails who bore holes in the shells of other species, releasing a chemical from their foot to soften shells.

Beadlet anemones, attached by suction to the rocks, resemble blobs of rich, red jelly when the tide is out, but unfurl into flower-like blossoms in the pools.

The ‘petals’ are tentacles; nearly 200 of them arranged in six circles. These sense the movement of prey, trap it, and draw it into the anemone’s central mouth.

It’s life, Jim, but not as we know it…

There are whole galaxies beneath the water. Star Ascidian, another filter feeder, forms patterned constellations on the underside of rocks, while single stars hunt in dark pools – common starfish, brittle stars, bloody Henrys ... good cocktail names, I think briefly – add a dash of rum, a sprinkling of salt.

Starfish are voracious predators. When hunting molluscs, common starfish attach their feet and gradually prise the shells apart.

They need only the smallest fraction – a millimetre is enough for the starfish to insert part of its stomach and begin the process of digesting the body of its unfortunate prey.

The starfish don’t have it all their own way though, for limpets have evolved a method to escape the inexorable pull towards annihilation.

As the starfish uses its hundreds of tiny tube feet to prise shell from rock, the limpet stomps – bringing their shell down sharply upon the starfish’s arm.

Imagine a well-deployed stilettoed heel on a dancefloor.

The starfish slink off in search of easier prey.

The tide incoming, we place the rocks gently back in place, wince to hear them scraping.

We emerge into the world above – this strange world of only two arms and two feet and stomachs that stay inside bodies. We have been aliens in another realm and it takes a moment to adjust.

When we do, we become aware of the cold – the gloves that were not waterproof – the wave that engulfed one boot, leaving hands and foot numb.

First rule of fieldwork: Bring spare socks. Katherine hands me a pair.

We return to land.

Ceris Aston is an apprentice at Lindisfarne National Nature Reserve and author of thewordsandthebees.blog