Tag Archives: intertidal

Team Rock Pooling Near Falmouth

It is going to be hard to top our last, sea slug filled rock pooling session at this beach, but we can’t resist popping back for another look. This time, we have reinforcements!

I have the best friends in the world. Not only do they obsess about rock pool creatures but Sarah has picked up pasties for Other Half and me, and Charlotte arrives bearing a gift of homemade cake. As this is the fourth day in a row of rockpooling in the biting cold, comfort food is going to be essential. Sarah’s partner is gallantly entertaining the kids for the day and we’re joined by our film maker friend, Greg who is looking for sea slugs – it’s the sort of mission we can all buy into.

Returning to a beach we visited only a few days before is a bit like a memory game: if we can just find the right pools and rocks, we should be able to rediscover some favourite creatures. Sure enough, Greg is rewarded for his enthusiasm by coming across what is probably the same fabulously colourful Facelina auriculata slug we found before.

Meanwhile, Sarah, Charlotte, Other Half and I are on a mission to record the incredible diversity of species at this site.

Anthopleura ballii anemone

There is so much here, it is hard to know where to start. I make the most of my waders and explore the pools and overhangs which would otherwise overtop my wellies. Some species are unusually common here, like the Anthopleura ballii anemone. Its brown and white speckled pattern gives it something of the look of a 1970s pub carpet. The distinctive lines of crimson spots on its column make it instantly recognisable.

Among the sand are occasional pieces of maerl, a red encrusting seaweed with a calcareous skeleton which forms bright pink living sculptures. Offshore in this area, these slow-growing structures can cover the seabed, building up in layers to provide shelter for many small creatures and young fish. Nationally and internationally such maerl beds are scarce.

The new spring growth of the rainbow wrack is everywhere, sprouting into great bushes of turquoise and iridescent greens and blues that seem to change constantly. Around their thick, branching forms, dense colonies of encrusting animals form and I spend a long time staring into their tiny worlds of densely packed sponges, starry sea squirts, feathery hydroids and busy crustaceans.

Rainbow wrack

Sarah finds our little Palio nothus slug, still powering through the same giant goby eggs. I spot another, larger one nearby and Charlotte discovers yet another near the end of our session. None of us had seen this species before this week and now they are everywhere.

Palio nothus among the goby eggs
Another Palio nothus

We seemed destined to find slugs this week. All of us keep spotting more and I can hardly keep up. The largest is this great grey sea slug, Aeolidia filomenae, which is hunting for anemones under a rock. Judging by its size and pink colour, it has been feeding well.

Great grey sea slug, Aeolidia filomena, hanging upside down under a rock.

Among the thick, velvety branches of the codium seaweed there are a few solar powered sea slugs, Elysia viridis. These remarkable little slugs feed on the seaweed and retain the plant’s chloroplasts in their bodies. The chloroplasts carry on photosynthesising and provide the slug with energy.

Codium seaweed
Elysia viridis – the solar powered sea slug.

While I am exploring the seaweed, an isopod swims over and rests for a moment on my finger. These little crustaceans are relatives of woodlice and come in all sorts of shapes and sizes. This one is a Dynamene bidentata, so-called because of the two little prongs on its back (bidentata means two-toothed).

Dynamene bidentata, an isopod.

The slugfest continues apace, with one of my favourites. Limacia clavigera, the orange-clubbed sea slug, is a species I often find, but it’s always a delight. Like many sea slugs, it looks like it has been let loose in a dressing up box. Its slender white body is splendidly adorned with long yellow and orange appendages, sticking out in every direction. Greg finds one so large that it looks like two slugs.

Limacia clavigera, the orange-clubbed sea slug.

The tide is turning. I am so cold I should probably have left a while ago. I have to shake my hands and windmill my arms around my head to try to restore feeling in my frozen fingers, but I can’t bear to miss a thing.

We see plenty of sea hares and their spawn, and count around a dozen Geitodoris planata slugs, but some tiny finds are the most exciting of all.

A tangle of sea hare spawn.

Sarah calls me over. She has located some possible slugs on a rock, but they are so small she is doubting herself. Bracing myself, I put my hands in the water once again.

It’s hard to operate the buttons on my camera and hold it steady enough, but I’m sure she is right that there is something here. There is a faint pale mark on the rock that could be spawn and something alongside it that is just a speck.

The image takes shape on my screen. There are two slugs and it looks as though they are busy spawning. Their chunky cerata are prettily speckled with white and they have red lines on their heads. There are lots of similar species, but I’m fairly sure these are Trinchesia foliata (a name I remember as the ‘three-cheese foliage slug’).

The two Trinchesia foliata slugs with their white spawn in the background.
You need to look carefully to spot slugs! The Trinchesia foliata slugs with a finger in shot for scale.

I have only found this species once before in Looe, so it’s fantastic to see two spawning like this.

Trinchesia foliata

Charlotte calls me to look at a slug she has found and doesn’t recognise. It’s another tiny one with a colour pattern I have never seen before. The tide is coming in fast now and the wind is picking up, making it hard to find a sheltered patch of water to observe. I kneel in a pool and place the slug on a small stone to view it better.

Favorinus branchialis juvenile slug.

Each long cerata on the slug’s back is decorated with a red spot at the tip, like a cherry on the cake. It has a wide moustache-like pair of oral tentacles on its head as well as tall browny-orange rhinophores with white tips. It is these that make me think it might be a Favorinus branchialis, but it seems to lack the distinctive onion-dome bulges that I associate with that species.

It is only when I get the photos home and onto a large screen that I can see all the features, including the the slight curve in the rhinophores and decide that it is F. branchialis after all. The bulges are less pronounced in juveniles than in the adult slugs. This species is often found feeding on the eggs of other sea slugs.

Favorinus branchialis

While Charlotte returns the slug to where she found it, I take a look at a stalked jellyfish that Other Half has spotted on some sea grass. The jellyfish and the frond of seagrass are swaying in the current, making it hard to take a photo.

Haliclystus octoradiatus stalked jellyfish on seagrass.

Back in Sarah’s pool I discover even more slugs. A ‘feathered Bertha’, Berthella plumula, is under one rock, while another Limacia clavigera is feeding near the pair of Trinchesia foliata. Charlotte finds another little Palio nothus slug.

The tide is gushing into the lagoon, flowing around the spot where Other Half is still trying to photograph the stalked jellyfish. After a couple more minute he gives up and wades out, sitting on the rocks to take off his boots and wring out his socks.

Greg spots a yellow blob, which I find almost impossible to focus on, probably because my fingers now have no feeling at all. The sandy-looking spots on this sea slug show that it is a Doris ocelligera. This is a species that was very rarely recorded around our coasts in the past, but which I have found frequently in recent years, possibly due to warming waters.

Doris ocelligera slug near Falmouth.

With the sea lapping at our heels, we finally admit defeat. I’m not a great fan of tea, but I have never been more grateful to the inventor of the thermos flask than now, sitting at the top of the beach, cradling my hot drink and feeling my fingers gradually become reacquainted with the rest of my body.

As always, I have seen new things today and learned more about the creatures on the shore from glimpsing their world. It is incredible to me that anything can survive here and yet there is enormous richness in this ecosystem. Charlotte and I will make sure that everything we have found is recorded with our local records centre.

Recording the species we have seen helps to monitor changes in the wildlife over time and to inform conservation projects and policies. Online systems such as ORKS and i-Naturalist make it easy for anyone to submit their finds.

It will be another month before the tides are this good again – time that I will use wisely warming up and eating cake!

Pheasant shell on codium seaweed.
Yellow star ascidian with patches of the non-native red-ripple bryozoan Watersipora subatra.
Velvet swimming crab hiding in the sand.