Organisms in the Mud

Corophium - a crustacean amphipod (shrimp-like with legs on both sides of body). Lives in upper 5cm of mud in U-shaped burrow, emerging to collect fragments of detritus. Can only utilise bacteria adsorbed onto clay and silt 4 - 63microns in diameter. Often co-exists with Hydrobia but feeds on smaller sized particles. During summer up to 28,000 per square metre. Prefers salinity above 5% but can tolerate 2%.

Hydrobia - A Gastropod snail. Commonly three species (H.ulvae (4-6 whorls, 3-4.5 mm high and yellow-brown), H. ventrosa (5-6 whorls, 2-3mm high and grey) and H. neglecta (5-6 whorls, 2-3mm high and grey or brown)) Feeds on detritus and algae from the surface of mudflats at high tide. Retreats under surface when tide recedes. A selective deposit feeder. Concentrations of 9,000 to 42,000 per square metre depending on the abundance of algal mats. Can survive in salinities from 8 to 60% and up to 35°C. Optimum conditions are 37.6% salinity and 19.9°C. H. ulvae maintains its blood hyperosmotic to surroundings being able to retreat into its shell in very low salinity to avoid osmotic stress. The three species are usually found in different ranges of salinity: H.ulvae from 10% to full sea water, H. neglecta from 10-24% and H. ventrosa from 6-20%. All three avoid strong currents and generally prefer still conditions.

Macoma - A tellin e.g. Macoma balthica (the Baltic tellin). Lies buried in mud with input and output syphons protruding. Indulges in suspension feeding (takes in water and particles from water column) or deposit feeding ("vacuuming" mud surface). Typically grows to 14mm in 6 years. Up to 3,500 per square metre.

Mytilus - A mussel. e.g. Mytilus edulis (the common edible mussel). Filter feeder on phytoplankton. Found commonly in the mouths of estuaries where salinity is high. Survival in low salinity is achieved by shutting the bivalved shell but this limits their feeding ability and reduces growth rate. Death will occur at salinities below 4%. Selectively eaten by oystercatcher (33mm), gulls (2-10mm) and eider (18mm)

Cardium - A cockle. e.g. Cardium edule (the edible cockle). Lives buried in sand and filter feeds on phytoplankton using syphons which only protrude when covered by water. C. edule is found above 18% salinity and C. lamarki down to 5%. (Although growth is poor at low salinities)

Arenicola - Polychaetes worm e.g. lugworm (A. marina). Can only maintain its burrow in mud/sand with particles larger than 80 microns. Water and sand is sucked into one end of its U-shaped burrow and faeces expelled out of other end as a worm cast. Concentrations of lugworm are directly proportional to the amount of organic matter in the sediment. Maintains body fluids iso-osmotic to surroundings (unlike Nereis) and will die at salinities below 8%.

Nereis - A bristle worm (or annelid - a segmented worm) e.g. ragworm (N. diversicolor). Feeds on Corophium, small Macoma, detritus, algae and chironomid larvae. Tend to live buried in the mud to be in a stable saline conditions, however they can exist in a wide range of salinities and can regulate the salt and fluid concentration to counteract osmotic stress. Body fluids are generally hyperosmotic with respect to surrounding water. The range of salinity of body fluids is narrower than range of sourrounding salinities that it can tolerate. Up to 960 per square metre.

Nematodes - Round worms between 0.5 and 2 mm in size. Found in large numbers (2,800,000 per square metre in Blyth, Northumberland) in top 1cm of mud.

Nephthys - Polychaetes worm e.g. catworm (N. hombergi). Invertebrate predator.

Carcinus - C. maenus - the common shore crab. An invertebrate predator, feeds on annelids. Eaten by eider, gulls, turnstones, curlews.

Crangon - Shrimps and prawns. C. crangon - the edible brown shrimp.

Littorina - Winkle L. saxatilis. primarily an animal of the rocky shore, is only found in estuaries in strong currents and salinities above 14%. L. littorea can be found down to 10% salinity.

Zostera - Eel grass. Important source of detritus growing in inter-tidal area down to 11m.

Flounder - Feeds on invertebrates. Mainly a Summer visitor - up to 0.05 per square metre in Winter and 0.24 per square metre in Summer (Ythan)

Plaice - Eats syphons of tellins, arenicola and macoma.

Sand Goby - Feeds on Corophium. Mainly an autumn/winter visitor - up to 0.6 per square metre (Ythan in Sept)