Cerastoderma edule

• Cerastoderma edule grow rapidly in their first 1 -2 years after which growth rate declines with increasing size (Seed & Brown, 1977).
• Growth rates decrease with increasing tidal height, probably due to decreased immersion times and hence reduced food availability at higher shore heights (Richardson et al., 1980; Jensen, 1993; Montaudouin & Bachelet, 1996; Montaudouin, 1996). The highest growth rates in Cerastoderma edule were reported in continuously immersed populations (Guevara & Niell 1989).
• Local variability in growth rate occurs in areas separated by relatively short distances within sites, e.g. Llanrhidian Sands, Wales (Hancock, 1967).
• Growth rates were reported to vary between years and geographical locations (Hancock, 1967; Ducrotoy et al., 1991).
• Growth rates decrease as population density increases probably due to increased competition for food, and direct interference or disturbance due to burrowing and direct contact between individuals (Orton, 1926; Hancock, 1967; Jensen, 1993; Montaudouin & Bachelet, 1996). Montaudouin & Bachelet (1995) reported highest juvenile growth rates at low density (160-200 adults /m²) whereas adult growth rates were only depressed at the highest density examined (2000 adults/m²).
• Cerastoderma edule is unable to acclimatise to low temperatures, resulting in reduced metabolic rate and oxygen consumption during winter months. However, reduced food availability in the winter months results in low or negligible growth (Smaal et al. 1997).

Predation
Predation has been show to influence recruitment and population dynamics in Cerastoderma edule. (Sanchez-Salazar et al., 1987a; Masski & Guillou, 1999;. Sanchez-Salazar et al. (1987a) reported that low shore cockles had high mortalities when small which decreased with size due to predation by shore crab (Carcinus maenas) in the summer months that preferred cockles <15mm in length. Higher on the shore cockle mortality was moderately in the first year (47%) but increased with size, due to predation by oystercatchers (Haematopus ostralegus) in the winter months, which prefer cockles of at least 20mm in length. As a result, the lower shore populations studied were composed of spat and fewer large individuals whereas higher shore populations contained smaller cockles.

• Geographical location (Ducrotoy et al. 1991; Olaffsson et al., 1994).
• Annual variation in climate. Ducrotoy et al. (1991) reported the variation in annual recruitment between years for several sites in Europe, and noted a correlation between good recruitment and a previous severe winter (presumably due to high adult mortality, reduced population density of adults and reduced numbers of infaunal predators), in many but not all cases.
• Good recruitment was also observed after heavy storm surges reduced the adult population (Ducrotoy et al. 1991).
• Post-settlement erosion and surface sediment erosion by currents and storms. Juveniles may be transported by currents until 2mm in size and high densities of juveniles may be swept away by winter storms resulting in subsequent patterns of adult distribution (Olaffsson et al., 1994).
• Post-settlement mortalities of 60-96% have been reported, resulting from intra and interspecific mortality and predation (Sanchez-Salazar et al., 1987a; Montaudouin & Bachelet, 1996; André et al.,1993; Guillou & Tartu, 1994).
• Adult suspension feeders, including adult cockles, may reduce settlement by ingestion of settling larvae and juveniles or smothering by sediment displaced in burrowing and feeding (Montaudouin & Bachelet, 1996). Therefore, recruitment may be dependant on adult population density (André et al.,1993). André et al. (1993) observed that adults inhaled 75% of larvae at 380 adults/m², which were also ingested. However, Montaudouin & Bachelet, (1996) noted that adults that inhaled juveniles, rejected them and closed their siphons but that rejected juveniles usually died.
• Predation (see distribution) (Dame, 1996; Sanchez-Salazar et al. 1987a).
• Guillou & Tartu (194) noted that spat also suffered from mortality in their first year in the spring following their settlement, even through food was available, probably due to exhausted energy reserves (after winter) and spring predation from shore crabs.

• 'Crisis': a few age classes and successive spawnings and maximal growth due to low density;
• 'Recovery': single high density recruitment to first year class (breeding stocks may be synchronised by severe temperatures);
• 'Upholding': several age classes, higher densities of older age classes, seasonal recruitment, and low growth rate;
• 'Decline': reducing abundance, adult mortality or unsuccessful recruitment due to climatic factors, lower food levels, competition or parasitic infection.