Cerastoderma

Abstract: Pronounced seasonal cycles in the rates of oxygen consumption and feeding were found for Cardium (=Cerastoderma) edule L. measured in the field under ambient conditions. The cockles had a maximum rate of oxygen consumption (0.89 ml O2 g-1 h-1) in April which declined to a minimum of 0.35 ml O2 g-1 h-1 in March. Their feeding rate was variable but had a maximum value (3.91 l g-1 h-1) in April and a minimum value (0.73 l g-1 h-1) in October. There was no apparent seasonal variation in absorption efficiency, with a mean value of 67.6%. Gametogenesis was initiated in January and the population reached a peak in reproductive condition in April/May, followed by a 3 month spawning period. Carbohydrate reserves were synthesised during spawning, and were then utilised during the winter and early spring. An adaptive function for a reduction in time spent feeding is postulated, and correlations between the rates of certain physiological processes and some exogenous and endogenous variables are discussed.

Abstract: SUMMARY (1) This study examines the growth of two marine bivalves, Modiolus modiolus (L.) and Cerastoderma edule (L.) in Strangford Lough, N. Ireland, the former from the relatively stable conditions of subtidal reefs, the latter from midtidal sand flats where environmental conditions are less predictable. (2) Cerastoderma grows rapidly in its first year after settlement. It first reproduces during its second year and the resumption of rapid growth is thus generally delayed until spawning has been completed. In subsequent years, growth becomes progressively slower. (3) In Modiolus reproduction is delayed and rapid growth can thus continue for a period of several years. (4) The growth strategies exhibited by these bivalves may reflect the essentially different patterns of mortality experienced by these two populations. In Cerastoderma, mortality is heavy in all age classes and relatively few cockles survive beyond their third year. Early reproduction following a period of very rapid growth is therefore probably the optimal strategy for this species. Modiolus, by contrast, experiences intense predation early in life but can escape further predation by growing too large to be eaten; only then is energy redirected towards reproductive development. These large but slower growing mussels then enjoy enhanced longevity.

Abstract: Aspects of the physiology of the two cockles Cerastoderma edule (L.) and C. glaucum (Poiret) in air have been investigated. Both cockles exhibit bradycardia during exposure and are similarly tolerant of anoxic conditions, but C. edule survives longer in air than C. glaucum. This is accounted for by the fact that C. edule displays a behaviour pattern of valve movements upon emersion which allows air-breathing. Oxygen uptake rates of this cockle measured in air lie close to the lowest rates recorded in water, and are considered to approximate to a basal or quiescent level. C. glaucum does not air-breathe and is restricted to lowest shore levels. Values for ‘maximal’ levels of oxygen uptake in water have also been obtained together with estimates of metabolic scope for the cockle.