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.

Mid-winter Pond Dipping

Thursday's Guardian Country Diary is about freshwater invertebrates that remain active all through the winter. There may be no bees or butterflies about at the moment, but there are plenty of aquatic animals to look at - the only problem is that the water is bone-numbingly cold, so collecting them can be a bit of an ordeal! 

All the animals below (except the bottom one) were found in a single jam jar of water, dredged along the edge of our garden pond which had been frozen over on the previous night.

This is a freshwater orb-cockle Sphaerium sp. There must the hundreds of these little bivalves (the largest was about 8mm. across) in our pond. The two pink protruding tubes on the left are the inhalent and exhalent siphons that circulate water over the gills. You can just see the muscular foot protruding through the shell valves in the 5 o'clock position. 

Orb-cockles are surprisingly mobile, especially when they are small. This one, whcih was about 4mm. long, is using its muscular foot (which you can see protruding from the back of the shells) to scoot across the bottom of the container.

There are scores of these red ramshorn snails in our pond but it's providing difficult to identify it precisely. I posted the pictures on the excellent iSpot web site and there are varying opinions as to its identify. It might be Planorbis corneus rubrum or it could be Planorbella duryi which is the American ramshorn snail. Either way it's an introduced species that probably came in with pond weed bought from a garden centre.

If there are scores of ramshorn snails, then there must be many thousands of these flatworms (Polycelis nigra?) in our garden pond - there were over 50 in a single jam jar sample. They glide along like magic carpets, propelled by a covering of beating cilia which you can see on a marine species by clicking here.

Our pond has a thick layer of decomposing leaves at the bottom - perfect conditions for water slaters (aka water hog-lice), so there are large numbers present.

Gammarid shrimps like these prefer well oxygenated flowing water so our somewhat stagnant pond is far from ideal, but there are still plenty present in the shallows and they are very active swimmers, making them difficult to photograph.  Mostly they swim on their sides, or sometimes upside down, curling up when they are alarmed. These have an interesting history - I introduced them from a population that I rescued from the bottom of Wearmouth Colliery before it closed; you can read the details here.

The young gammarids are almost transparent - I think this must be a male, judging from those prominent claws on the front pair of legs.

And finally, this animal (below) is not from our pond. I collected it a few days ago from the gravelly bottom of a ditch, with snow melt water flowing over it, on the edge of the moors at St. John's near Wolsingham in Weardale, and it's ........

...... an exquisite little caddisfly larva, with a tube constructed mostly from quartz grit. They can be coaxed to build their tubes from more exotic materials - for a stunning example, click here

Condemned to life in total darkness beneath the Stadium of Light

I found these two photos amongst colour transparencies that I took back in 1994. They are of a little gammarid shrimp, similar to the species that live in ponds and streams everywhere, but this one has a very unusual story attached to it.

One day in late spring 1994, just before Monkwearmouth colliery, also known as Wearmouth colliery (see photos here), was due to close, I had a telephone call from a journalist on the Northern Echo who had been talking to some of the miners who were about to be made redundant. This was more than just another pit closure: Monkwearmouth was the last deep mine to close in the Durham coalfield and had been there for 178 years. It had once been the deepest coal mine in the world.

The miners told a story about shrimps that lived in pools of water at the bottom of the mine. The crustaceans had most likely been taken down there in water for the pit ponies and were well known to miners who had worked the seams in  the oldest shafts. 

At that time the deepest hole in the ground I've ever been down was at Cheddar caves, so the offer of a trip down to the bottom of the mine to collect some shrimps was too good to miss. At the bottom of the old shaft that had been abandoned for many years we found the shrimps living in the coal dust in pools of water, where they most probably fed on bacteria that lived on sulphur and fungi that lived on rotting wood. If you look at the photos above you can see grey coal dust in their digestive tracts. They had an aversion to light and when the beam of our helmet lamps fell on them they scuttled down into coal dust slurry. If you look at the enlargement of the eye (below) you can see that it had only a few, rather disorganised lenses, compared with a crustacean that lives in daylight like this one - these troglodyte shrimps may have been on their way to losing their redundant power of sight. 

We brought a couple of buckets of them up to the surface and kept them in a tank in my laboratory at Durham University. We had hoped to go back for more but British Coal demolished the winding tower with indecent haste before we could mount another expedition.

 This is the piece about the collecting trip that I wrote at the time for the Guardian Country Diary:

We entered the rusty cage of B Pit at Monkwearmouth colliery on a rescue mission, in search of an underground colony of shrimps that has persisted there since the shaft was opened in 1841. After a 12-minute descent we jerked to a halt 1080 feet underground, stepping out into caverns lined with crystals that glistened in our lamp beams. 

We found the colony, in a small black lagoon at a tunnel entrance littered with rusty picks and blocked by a collapsed roof. The half-inch-long shrimps dashed across the surface, thrashing through pools of light from our helmets and disappearing into the black ooze. These tiny crustaceans, familiar to generations of miners, live in a seasonless world of perpetual darkness and constant temperature, probably feeding on bacteria that grow on sulphur in the coal. Kenny Drysdale, the shaftsman who led us to them, told us that miners once supplemented the shrimp' diet with bread crusts. Within a few minutes we had scooped up as many animals as we could catch. The only other sign of life was a spider's web. Its builder, long since gone, must have been drawn down by the shaft ventilation system. 

In the tunnels we passed massive, rusty iron grates where controlled fires had once burned, to draw in cold air from above in the wake of their rising column of heat. Then, this pit must have resembled a scene from the underworld. The names of generations of miners were chalked or scratched on walls and beams in silent tunnels strewn with rusty pulleys and rails, thick with dust, shored up by props and baulks and boards and sealed with doors that hung from creaking hinges. 

Back on the surface, the rescued shrimps now live in my laboratory, thriving in an aquarium. Soon the unlucky ones will be sealed underground for ever, when the life of the colliery finally expires. Yesterday, I dropped a crust of bread in the tank. The shrimps swarmed around, tore crumbs off and retreated to their corners, just as Kenny said they would.

June 1994.

There's a rather sad postscript, which leaves me with an abiding sense of guilt. Soon after we brought the shrimps up our new laboratories at Durham University were completed and we had to move out of the old ones in a tearing hurry so that builders could move in. The shrimp tanks were due to be the last items to be moved but somehow someone mistook the tanks of grey water and coal slurry for rubbish to be disposed of, and tipped the water down the drain and threw the old tanks in the skip. So all that remains are a few specimens preserved in alcohol and, perhaps, the descendants of some that I had released into our garden pond.

Almost as soon as the pit was demolished and the site was cleared work began on  Sunderland Football Club's new Stadium of Light on the surface, immediately above. The population of shrimps is still down there, 1000 feet underground, nibbling away at fungi growing on rotting pit props and feeding on the sulphur bacteria, and will now remain there, in total darkness, for all eternity.