Aspects of the biology,ecology and seasonal fluctuations in biochemical composition of Donax Serra in the East Cape

Donax serra ROding (Pelecypoda) isalargesand mussel which forms vast populations on some East Cape shores. It is most abundant on exposed beaches where the sand is not too coarse and phytoplankton production is high. Adultsoccupy ¹ zonejust above the mean level of spring tide. Spat settle subtidally and move upshore as they grow. Growth is initially rapid, to about 32 mmatoneyearand48 mmattwoyears. Thereafter growth is very slow and most adult productions goesinto reproduction, with a small summerspawning and a large winterspawning each year. Somatic production is low, as large adults totally dominate the population and have low growth and low mortality. Reproductive production is relatively high and P/B values of 0,2 and 0,5 are suggested for growth and reproduction. D. serra was found to be very tolerant of fluctuating salinitiesforupto four days and should be able to penetrate river mouths, but is limited by restricted swash action. Total dry-tissue mass, energy and biochemical constituents showed some seasonal fluctuations related mainly to the reproductive cycle. Carbohydrate appears to be a moreimportant energy reserve than lipids.