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.

Wandering Limpet

I noticed this limpet's conspicuous feeding tracks when I visited the North Yorkshire coast earlier this week. 


When the tide turns and begins to go out limpets return to their resting place on the rocks, where they fidget with their shells to grind a groove that their shell will fit into with a water-tight seal, trapping water inside the shell between tides. 


When the tide comes in again they wander around to feed in a very efficient way, zig-zagging from side to side so they can rasp as much alga as possible from the rocks without straying too far from home. The length of the feeding trails depends on the state of the tides; during spring tides when they're covered with sea water for longer they have time to stray further from home before they need to retreat to their resting niche.  


The most recent feeding trail here runs from top left to bottom right, while older ones have faded because the covering of algae on the rocks has had a chance to regrow.


You can find some impressive scanning electron microscope images of a limpet's file like radula by clicking here and read more about the biology of limpets here.


Here there's a time lapse movie showing 6 hours of limpet feeding compressed into 5 seconds.