Reproductive Effort And Value In Different Populations Of The Marine Mussel Mytilus-Edulis-L

Fecundity, reproductive effort (estimated both from production measurements and from physiological data), the energetic costs of reproduction and the reproductive value of different size classes were measured for mussels at different sites and related to age and to tissue weight. Variability between sites was considerable and differences as great as 10 x were recorded between minimum and maximum values for egg production, reproductive effort and reproductive value. However, similarities between mussels from different sites were also apparent, as regards egg size, the estimated metabolic costs of egg production (based on measurements of oxygen consumption), the relationship (isometric) between egg production and body size, the fact of an increase in reproductive effort with increase in size, and the age at which maximum residual reproductive values was expressed. These relationships are discussed in terms of the fundamental reproductive strategy of the species and the degree of environmental stress imposed on the mussels at the different sites.

Seasonal-Changes In The Physiology Reproductive Condition And Carbohydrate Content Of The Cockle Cardium (=Cerastoderma) Edule (Bivalvia Cardiidae)

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.