Predation
Variations in density are the result of predation and subsequent recovery of Corophium volutator. Corophium volutator is an important food source for dunlin (Calidris alpina) (Jensen & Kristensen, 1990), redshank (Tringa totanus) (Hughes, 1988; Raffaelli et al., 1991), shelduck (Tadorna tadorna) and flounder (Platichthys flesus) and these predators can consume 55% of annual Corophium volutator production (Raffaelli et al., 1991). Corophium volutator is also fed upon by the brown shrimp (Crangon crangon) and the green shore crab (Carcinus maenas) which can consume 57% and 19% of Corophium volutator production respectively (Flach & de Bruin, 1994). In the summer months, as the tide recedes, male Corophium volutator crawl on the surface of the mud, searching for females (Fish & Mills, 1979; Hughes, 1988; Forbes et al., 1996), making them more vulnerable to predation. In North American estuaries, the semipalmated sandpiper (Calidris pusilla) can consume 50 males per minute as they follow the ebbing tide (Brown et al., 1999).

There is no dispersive larval phase in the life history of Corophium volutator, instead, the embryos develop in a ventral thoracic brood pouch and emerge as miniature replicas of their parents and build a burrow off that of the parent (Hughes, 1988). Reproduction ceases below 7°C (McLusky, 1968) so, in the winter, predation significantly decreases the density of Corophium volutator.

Corophium volutator has the habit of swimming when immersed, which makes them available as prey for the common goby (Pomatoschistus microps) (Flach & de Bruin, 1994), herring (Clupea harengus), sprat (Sprattus sprattus) and smelt (Osmerus eperlanus) (Essink et al., 1989). The swimming behaviour of Corophium volutator has been reported by several authors. In the Ems Estuary, Wadden Sea, it was estimated that 0.06% of the population (3 x 10⁸ individuals) swim on the flood of each tide, leading to a net landward movement of the population (Essink et al. 1989). In the Stour Estuary, southeast England, Corophium volutator was found to swim only at night, on or around spring tides and only between May and August. It was estimated that on any one tide 6-19% of the population swam and that it was mainly immature animals that swam (Hughes, 1988). Holmström & Morgan (1983a) also found this species swimming at spring tide, mainly on the ebb just after high tide. Corophium volutator is a poor swimmer and is vulnerable to predation whilst in the water column, so there must be a benefit to swimming that outweighs the risk of predation. Hughes (1988) proposed several theories as to why Corophium volutator would elect to swim:

1. as a means of dispersal to prevent inbreeding;
2. to prevent intrasibling competition;
3. in response to diminishing food supplies in high density areas, or
4. females may swim to release their young.

1. Suspension feeding from a current generated by the pleopods (Hughes, 1988). In this way an individual can irrigate its burrow at a rate of 25-100 ml per hour (Limia & Rafaelli, 1997).
2. Deposit feeding by leaving the burrow and scraping surface detritus and microorganisms into the burrow with the second antennae, the current generated by the pleoplods then passes this material over the mouth parts(Hughes, 1988).
3. Epipsammic browsing, where the microbial biofilm is scraped off individual sediment grains (Gerdol & Hughes, 1994a, 1994b).