No one can miss the inevitable shells on the beach, we walk the strandline hunting for the biggest or most colourful, yet often fail to register the vast army of living ones in the mud or on the rocks.
Molluscs are snails, basic creatures with a hard secreted outer shell, a foot for locomotion, muscles to grip the shell, tentacles for touch sensors and eye spots for very limited vision. A basic primitive creature that does not really do much. Wrong, molluscs include Chitons, gastropods including beautiful sea slugs and the classic snail-like creatures, bivalves such as mussels, scallops and cockles, tusk shells and squid, cuttlefish and the extremely intelligent octopus. This is a group that goes from a grazing machine like a limpet to a creature that can change body shape and colour to blend in with anything, squeeze through impossibly small spaces and even walk on land between rockpools and has incredible eyesight. Unfortunately, although they are out there the squid, cuttlefish and octopus are rare (alive) on the shore. So we are left with the boring snails.
A limpet can live for over 15 years, it has a tongue (radula) of supreme hardness that is fortified by silica and iron, can find a single location on a rock by chemical sensing, uses chemicals and physical activity to create a perfect shell impression in rock and so reduce water loss between tides. Significantly controls the growth of seaweed and of course is a protandrous hermaphrodite. It has been observed to live life as a male breed at 2 years old then change to a female at 4 yrs. Not so boring after all and we think menopause is problematic!
Sea slugs are one of the most colourful animals of the sea, unlike their terrestrial cousins they seem to positively welcome being seen. This is due to their fantastic weapons, Onchidoris bilamellata can release acid if disturbed, the grey sea slug uses the stinging cells from anemonies that it eats and moves these undigested into cerata (projections on the body) many marine slugs do this. Others though do not have any defence but the bright colours hint that they do. If garden slugs were this effective we would not so lightly pick them up and throw them over the neighbour's fence.
Last we need to consider the phenomenal numbers of these creatures. Hydrobia (tiny snails found on mud) have a population density of 20,000 per square meter in the top 25 mm of the mud, this biomass is clearly a rich energy source for globally migrating birds. Tiny and insignificant easily overlooked because they are boring. Yet who does not love to watch the thousands of winter waders and ducks on an estuary feeding on them?