Seasonal changes in the biochemical composition of the adult barnacle,Balanus balanoides,and the possible relationships between biochemical composition and cold-tolerance

Abstract

Seasonal changes in cold-tolerance ofBalanusbalanoidesare correlated with the seasonal changes in free glycerol level in the body parts of adult barnacles and with the degree of unsaturation (iodine number) of the body lipids. Glycerol levels and iodine values were highest in the winter when the barnacles were most cold-tolerant and lowest in the summer when they were least tolerant. There was no correlation between the seasonal changes in cold-tolerance and seasonal changes in free amino acid level or triglyceride: total lipid ratio.Under laboratory conditions barnacles kept without food at 5 °C over the summer to winter period became cold-tolerant and had high, winter levels of glycerol and high iodine values. Winter barnacles kept at shore temperatures and fedAnemianauplii until mid-summer lost their cold-tolerance and had low, summer levels of glycerol and low iodine values. In contrast, winter barnacles kept for the same period without food at 5 °C remained cold-tolerant and had high glycerol levels and high iodine values.The maximum level of free glycerol in the winter corresponded to a concentration in the body tissues of 1 ·06 mM. This is 1000—fold lower than the concentration of glycerol in the pupal haemolymph of glycerol-forming insects and is far below the level necessary to promote general supercooling of the body water. Itis suggested that the mechanism of cold-tolerance inB. balanoidesis one oftolerance to freezing, or frost resistance, rather than avoiding ice formation.Triglycerides and phospholipids are the main lipid components inB. balanoides.