March 10th, 2011 by Richard Lord
If you walk down a Guernsey beach in early March to the edge of the sea on a low spring tide you may see lots of balls of jelly attached to the sand. These marble-sized blobs of jelly are the egg cocoons of a polychaete worm, Scoloplos armiger.
The worms synchronise the laying of gelatinous egg cocoons with the large spring tides. The male fertilises the eggs as they leave the female and the eggs are encapsuled in a protective cocoon. Gulls and oyster catchers show no interest in them.
Each pear-shaped cocoon can hold up to 5000 eggs. The cocoons are attached by a hollow stalk which can penetrate up to 10 cm below the surface of the beach. The larvae that hatch from the eggs after two to three weeks descend down the stalk into the beach to avoid predators.
The cocoons can be either brown or green and are about 15 mm long.
Scoloplos armiger feed on organic detritus. They are eaten by flatfishes. There is also a sub-tidal species of Scoloplos that releases larvae into the water column.
The green paddleworm, another polychaete or ‘many bristled’ worm, also produces large numbers of eggs encased in a protective gelatinous cocoon. These green balls of jelly are often attached to seaweed in rock pools or below the low water mark.
Ribbon worms spawn in early March. Ribbon worms, which are predators of polychaete worms, lay their eggs in strings of jelly under boulders and cobbles usually on the upper shore.
Turn a boulder or a cobble over on the upper shore of Havelet Bay or Belle Greve Bay and at this time of year you will frequently see on the base of the stone a tube of jelly housing numerous tiny eggs.
If you miss the gelatinous cocoons of Scoloplos armiger and various ribbon worms, you can still see the spawning of rag worms during big spring tides in April. Rag worms spawn in the lower reaches of streams running down the shore at L’Eree. The males come out of the sand and swim actively in the stream. They undulate the posterior portion of their body vigorously to release copious quantities of sperm into the flowering water for the females waiting in the burrows downstream. Both male and female rag worms die after reproducing.