Searching sediment shores

Species found on a sediment shore are almost invariably buried to some extent. Most species tend to be found in wetter areas on the lower shore. Often there will be tell-tale signs on the surface which are most easily detected just as the tide begins to rise. These signs include holes (where the siphons have been protruding) or trails left in the sand. For example Polinices species leave winding trails often terminating in a bump where the animal may be found. Bivalves such as Donax may also leave short trails. Some species are very shallow burrowers and can often be spotted sitting proud of the surface. Examples include Cerastoderma edule or Circomphalus casina.

Coarse gravel and pebble shores can be dug with a garden fork for bivalves such as Mya and venerids while a spade or trowel is more appropriate for fine gravel, sand and mud. Where the sediment is very wet the sediment may simply be turned over and left to drain back into the hole - species of mollusc may be left on the surface. A good sieve with a mesh of 1-2 mm can also be invaluable for picking out smaller species. If conditions are relatively calm, wading out into the shallow water can also reveal species which do not tolerate emersion at all.

On the upper shore, particularly where the conditions are muddy and slightly brackish, there are also some species that occur on the surface of the sediment such as Hydrobia ulvae and Retusa obtusa. In addition mats of weed such as Vaucheria should be carefully examined as species such as Limapontia depressa and Alderia modesta are often found underneath.

One important point to bear in mind when exploring sandy shores is that some species of mollusc tend to be associated with other non-molluscan species, particularly echinoderms. The so-called 'Sea potato' (Echinocardium cordatum) often has Tellimya ferruginosa or Gari species living either adjacent to it or, in exceptional cases actually attached to it (see for example Jessica's Nature Blog). When burrows of this species are encountered, in addition to extracting and examining the specimen of Echinocardium itself a sample of the surrounding sediment shoud be sieved (e.g. over a 1mm sieve) to pick up any species that are living adjacent to the area.

Similarly any species of holothurian encountered should be very carefuly examined for commensals such as Devonia perrieri and also eulimid species such as Melanella alba.