Energy metabolism of eggs during embryogenesis inBalanus balanoides

Abstract

The partitioning and utilization of energy reserves during embryogenesis were followed in the cirripedeBalanus balanoidesand related to the described sequence of developmental stages. Egg volume and dry weights were measured. Between the recently fertilized egg and eggs containing well-developed embryos at the end of natural incubation there is a doubling of egg volume.The biochemical composition of the newly fertilized egg is dominated by TCA-insoluble protein (55 %). Neutral lipid accounts for 17 % of the dry weight, while phospholipid and polysaccharide contribute 3–5% and 5–7% respectively. About 36% of the TCA-insoluble protein is utilized duringin vivodevelopment, accounting for about three-quarters of the energy expenditure. During this time 40% of the carbohydrate and 20% of the neutral lipid reserves are also utilised. However, when starved adults retain their mature egg masses beyond the normal term, egg metabolism occurs largely at the expense of the remaining lipid reserves. These would be exhausted in a further 6–7 weeks and the embryos unable to survive. The ability of adults to postpone hatching may therefore have important implications for the energy reserves and viability of the newly hatched nauplii. Protein supplies most of the energy during embryogenesis, with neutral lipid assuming increased importance after development has been completed.Oxygen consumption of the egg masses measuredin vitrowas converted through aerobic oxycalorific equivalent into biochemical loss. This showed good agreement with direct measurement of summed energy losses of the biochemical components. It was apparent that oxygen uptake rate in the later stages was restricted by diffusion resistance due to egg packing, since eggs freed from the egg mass matrix showed a 30% increase in oxygen uptake and a reduction in development time.