Armchair rockpooling

Felt a sudden urge to do a bit of rock-pooling at the weekend so called in at Marsden bay near South Shields, to see it there was anything interesting on the shore. This is an exposed coast and it's early in the season so were weren't expecting to find much.

There were plenty of common limpets on top of the rocks and ...

..... lots of chitons aka polyplacophorans aka coat-of-mail shells underneath rocks. But not a lot else. 

It was freezing cold and blowing a gale, which dimmed my enthusiasm when my hands began to turn blue. So I collected a small tuft of red seaweed that I found growing in a rock crevice and carried it home in a vial of seawater (about an egg cup-full) for a closer look under the microscope, in the comfort of an armchair.

Spring comes to the coastal waters just like anywhere else, but it's not immediately obvious until you look really closely. As the spring plankton bloom progresses numerous small animals settle out of the plankton onto the shore, especially amongst the fronds of small red seaweeds that begin to grow now.

To go rockpooling in comfort, all you need is one of these - a binocular microscope with a zoom range between x7 and x45. It costs about as much as an entry level digital SLR camera and can provide hours of amusement.

Almost immediately I found these attached to the seaweed - tiny hydroids, waving their tentacles in the air, until the slightest tremor .....

... sent them into contractions

Then there were these minute mussels, translucent but beginning to acquire their darker pigment at their base, that were anchored to the seaweed after the mussel larvae had settled out of the plankton.

This little animal is an isopod crustacean, hard to spot amongst the seaweed fronds, but best of all there were ...

... loads of these little gammarid shrimps, beautifully pigmented to match the seaweed forest.

Their compound eyes are particularly striking, as are the highly reflected patches embedded in their exoskeleton

This tiny seaweed microcosm was home to about 20 of these gammarids, some of which had highly reflective, sparkly eyes. 

The exoskeleton is this one contained small reflective patches that looked like interior lighting and it had eyes that glowed.

Aside from the mussels, gammarids, hydroids and isopods I also saw a minute sea slug and a flatworm, as well as copepods. 

The photos aren't very good (they were taken by holding a pocket compact camera up against the eyepiece of the microscope) but they do illustrate the wealth of microscopic marine life that's present even on exposed shores, down at the bottom of the inshore marine food chain. And at this time of year it's the most comfortable way to go rock-pooling.

Pond Life

 A quick sampling of the tadpoles in our garden pond showed that many of them were still some way off developing limbs, which I guess is a sign of the late spring - the frogs spawned very late this year. (Double-click for a larger image).

This tadpole is a sharing the trough that I photographed it in with a flatworm.

A water log-louse Asellus aquaticus. There are vast numbers of these scavengers down at the bottom of the pond, where there's  thick layer of decaying leaves.

Underside of a water hog-louse. These crustaceans are isopods - all their legs are more or less the same length. For more isopods, click here and here.

Possibly the least lovable animal in the pond - a leech. I suspect that these parasitize the pond snails. The dark patterning is its digestive system, visible through the body wall.

Britain's Largest Woodlouse and a dozy seal

Today's Guardian Country Diary describes encounters with two very interesting animals during a stroll on Roker Pier at Sunderland. Here's the pier, below, on a calm, sunny day.

This sea slater Ligia oceanica had crawled out of a crack between the stone blocks on the pier. They usually do most of their feeding at dusk, grazing on algae, and you don't often see them in the open in broad daylight. This is Britain's largest woodlouse species and it's confined to areas just above the high water mark on the seashore. The coin is a 10 pence piece, 25mm. in diameter, so you can get an idea of the animal's size - about four times larger than a garden woodlouse.

These little animals are very well camouflaged, especially when they hunker down so that the skirts of their armour plates are pressed close to the ground and they cast no shadow. It matched the stone so well that it was very lucky that I didn't tread on it.

The most remarkable thing about sea slaters is the ease and speed with which they change colour, due to being able to expand and contract pigment spots in their cuticle, so that they match their background. This is the same animal as the one on the grey stone, after it had been kept on a white background in bright sunlight for a few minutes. The pigment spots have contracted and it's almost translucent.

Sea slaters have large eyes for a woodlouse, perhaps because they do most of their feeding at dusk.

The sea slaters that live between the granite blocks here are often pummelled by waves that break over the pier (see picture below) but can maintain a tenacious grip on the stone with those needle-sharp bristles on the tip of their legs. Their flattened shape is perfect for squeezing into the gaps between the stone blocks.

You can see the jaws quite nicely here, and also the pigment spots in the body armour, fully contracted so they are just small brown dots.

We might have missed this character too if it hadn't raised a flipper to have a scratch. It was sunbathing on Roker beach below the pier and its smooth outline and mottled colouring made it surprisingly inconspicuous against the sand and rocks at low tide. I wonder if seals dream when they are asleep? If so, then it's probably having a very satisfying fantasy about pursuing fat, succulent salmon.

I'd guess that this grey seal must have been born on the Farne Islands last autumn. It had been left high up on Roker beach by an extremely high equinoctial spring tide. It didn't seem to be at all concerned and was content to bask in the sun and wait for the tide to return.  

Lovely animal, isn't it?

This is Roker pier a week later. Somewhere between the granite blocks, under the waves, there'll be sea slaters hunkered down. As for the seal, that'll be somewhere out to sea.

Water Hog-louse

Our small garden pond (the same one that's home to the newts mentioned in a previous post) is also home to a thriving water hog-louse (aka water slater) Asellus aquaticus population - and this is their breeding season. This is a mating pair and eventually the female will carry her fertilised eggs around with her under the front of her flattened body. These are crustaceans which exhibit a considerable level of maternal care of their offspring and when the eggs have hatched the female will continue to carry her young under her body, between the front two pairs of legs until they're old enough to fend for themselves. Water hog-lice aren't too fussy about water quality and so will thrive in small aquaria, where it's easy to watch their reproductive cycle. 

The brown pigmentation of their exoskeleton takes time to develop and in the youngsters it's transparent, which makes it easy to watch the workings of their internal organs under a microscope. This one is a juvenile that is only just beginning to develop the vestiges of pigmentation .....

..... and this one is a little further along the road to adulthood.


Asellus is an isopod crustacean, meaning that all of its legs are of similar length, unlike the amphipods that have a combination of long and short legs.