Rockpools waiting to be explored
W inter, and a cloudless blue sky as Tigga bounded along the track beside the ‘donkey paddock’ near Scalby Manor Hotel, and onto the cliff-top.
The rocks lay in natural shallow terraces, with interesting pools inviting exploration. Purple laver seaweed, used in the making of laver bread, cling limply onto sand-strewn rocks, glistening like films of black oil.
Looking at rock surfaces, one noticed they were encrusted with clusters of tiny acorn barnacles. They appear so lifeless at low tide, one would believe they constituted the rock itself. Look closer, and their shells are like greyish-white, ridged cones with an inner trapdoor of four minute plates. These remain tightly closed to resist desiccation at low tide.
As the tide rises, they open and extend legs like feathery tentacles. Fanning the water, they grasp microorganisms from the sea. The numerous dog whelks in the vicinity will in turn feed on the barnacles.
Large limpets abounded, especially on the sheltered side of rocks away from severe wave action. Each conical shell was like a small stone tent, or maybe a Chinese hat! It clung tenaciously to its hollow depression. If we tried to take it by surprise, and thump it with a clenched fist, it moved only fractionally, and clung more tightly. Its strong, rounded foot acts as an effective suction pad, and provides resistance to rough wave action.
Try and dislodge a limpet using a strong penknife. Turn it over to reveal its broad, muscular foot on which it crawls during damp weather, or when submerged. At one end you’ll see the tiny head, and mouth from which a finely-toothed tongue or radula, is able to rasp away seaweeds and germinating spores on the rocks. As they browse, they may each graze almost a meter in radius from their home base.
Look closely, and you may just discern zig-zag lines which limpets have scratched on patches of green algae.
Limpets leave scars on the rocks, caused by the abrasive action of the shell which gradually wears down the rock to fit its contours perfectly. It returns to its original base before the falling tide exposes it again. By trapping a small quantity of water inside its shell, the delicate gills that surround its foot can breathe until the tide returns. Clamping its shell to fit the outline of the scar prevents water evaporating even on the hottest days. By the time they have a shell base of 5cm, they may be in their teens, but predators reduce their numbers.
Six oyster-catchers magnificent in their black and snowy-white plumage and glowing red bills - scoured the beach for unwary prey. Their strong, chisel-like bills can dislodge any unsuspecting limpet and remove the snail-like contents. Amazing how each creature is uniquely adapted to its environment.