Another Life: Anemones, urchins and, in Lough Hyne, the richest rock pool in Ireland

The Mayo sea in November can be tamed by a wind from the east, sidling in to the strand in little lappets of frilly waves. A whole day of sun can come with it, bouncing from sand under water in a turquoise, stained-glass glow. It still looks bloody cold, even in the shallows, but the ocean is slow to give up its summer warming. On a fine, calm Saturday morning earlier this month, with an air temperature of 3 degrees, the reading in the water was close to 10 degrees.

That was actually a lot farther north, in Mulroy Bay, Co Donegal, where a party of the Sheephaven Diving Club spent up to 40 minutes submerged, watching squadrons of thornback rays gliding peacefully over the seabed. As their joyful blog recorded, “there was easily 10 metres of horizontal visibility in the upper reaches of the water column”. Next morning the snorkellers were out at Port na Blagh pier, riding a great swell that was roaring into the bay ahead of the next Atlantic depression.

Things have greatly changed in amateur exploration of the sea. It's 50 years since a group of young Waterford men, fired by the films of Jacques Cousteau, jumped into the sea off Tramore with air tanks and home-made rubber suits, and survived as pioneer Irish adventurers. Today 80 clubs, all over the country, are affiliated to the Irish Underwater Council. Its own glossy magazine, Subsea, is full of scuba-gear advertising and exotic underwater scenes from tropical holidays: Red Sea, Lanzarote, Sardinia, Trinidad.

Stubbing my toe on a heavy lead buckle, a diving weight, now a doorstop in my workroom, I remember my own youthful forays in black rubber and being put off, weakly, by the chill of the Dingle Peninsula. So much kinder, as one of multitudes inspired by Cousteau’s documentaries, were my snorkelling holidays in the Aegean islands.

It was there that I plunged for an exquisite souvenir, the empty, pearl-white shell of a paper nautilus, a cornucopia whorl of fluted, translucent folds and one of the most beautiful of molluscs. I brought it home in cotton wool and had it for years until it shattered. “Take only pictures, leave only bubbles” is the diving clubs’ motto now.

There are comparably lovely creatures in the Irish ocean: the anemones, urchins and nudibranchs are just the beginning. A special sight is the huge and spectacular fireworks anemone, Pachycerianthus multiplicatus, featured among An Post's international airmail stamps. This burrowing anemone, waving white tentacles like a fountain of sparklers from the mud of sheltered bays, was known from only two western Irish bays, Kilkieran and Kenmare, until a new population was found in Bantry Bay in August by divers from the Cork Sub Aqua Club. They included divers trained by Seasearch Ireland, the research programme established in the UK and now making headway among diving clubs here.

Led by Dr Tim Butter, a scientific officer for the Irish Underwater Council, Seasearch Ireland brings the rigour of scientific identification and recording to the hitherto casual sightings of the amateur diving world. It will help find and conserve the richer hot spots of marine species and track new arrivals brought by climate change and the spread of invasive aliens (go to facebook.com/seasearchireland). This recording will enrich the fine digital maps of marine life at the National Biodiversity Data Centre at Waterford.

Where do divers go in the wintertime? To sea, regardless of temperature, when the weather allows, but also to lakes, flooded quarries and even swimming pools to improve underwater skills. For fully trained divers, Seasearch education in species and habitats will add to the options from now until the ocean season opens, next March. Winter, too, is when the clubs offer introductory dives for beginners, training in scuba diving, and snorkelling courses for children (go to diving.ie, website of the Irish Underwater Council).

Meanwhile, readers have reported on some of the puzzling creatures washed up at this time of the year. Drifts of the southern jellyfish Pelagia noctiluca (the "purple stinger", but often a marmalade orange on the shore) have even penetrated Lough Hyne, in west Cork, where they were found by Dr Butter and his fellow divers.

Lough Hyne is the curious and wonderful lagoon invaded by the ocean through a narrow tidal channel as levels rose after the Ice Age. It became Europe's first marine nature reserve, in 1981, after a century of study by marine biologists. Among them are Dr Colin Little and Dr Cynthia Trowbridge, who write on its ecology, with glorious species photographs, in Lough Hyne: From Prehistory to the Present (Macalla Publishing, €30), an uncommonly fine local history by Terri Kearney of Skibbereen Heritage Centre.

Marine life in the warmth and shelter of Lough Hyne includes 73 kinds of sea slug, more than 100 sponges, 24 kinds of crab and 18 species of anemone – the richest rock pool on our island.