Some aspects of the respiratory physiology of Cancer pagurus L. (crustacea : decapoda) in Scottish west coast waters

Abstract

For the largely immature population of crabs studied no difference in length weight relationships could be detected between males and females unless fresh weight was used for comparison. Females and immature males showed isometric growth throughout their life while mature males showed allometric growth. The use of length, fresh weight, dry weight and ash-free dry weight for the basis of comparative metabolic studies is discussed. Oxygen consumption rate was found to be related to the 0.799 power of body dry weight or ash-free dry weight for both males and females and resting and active rates. Scope for activity was constant at 3.7 across the entire body weight range. A marked diurnal rhythm of oxygen consumption rate was found, the exact form of which depended on season being bi-modal in short day length and uni-modal in long day length. The beat rates of heart and scaphognathite were found to show a high degree of correlation throughout all phases of the daily cycle. A typical short period rhythm of beat rates is shown during the resting phase. Ventilation volume showed a linear relationship with scaphognathite beat rate up to active rates of pumping. Above this ventilation efficiency was impaired. The short period rhythm had a period of almost exactly twenty minutes, and was divided into three phases, the high-rate, the low-rate and the changing phase. In order to conserve metabolic stores, the duration of the low-rate phase is increased, at the expense of the level and duration of the high-rate phase, with increasing starvation. Percentage utilisation of oxygen was at its highest during the high-rate phase (40 - 42%) and it appears that efficient oxygen exchange is limited to the rates of pumping of the active phase. Possible functions for the short period rhythm are discussed in the light of this observation. Haemocyanin was more or less absent from the local population of Cancer but not Carcinus and Portunus. Reasons for this are discussed. A new method for measurement of haemocyanin oxygen capacity was used. Effectiveness of oxygen uptake by the blood was low due to the lack of haemocyanin, but effectiveness of oxygen removal from the ventilatory water was high due to a decrease in ventilation:perfusion ratio. Ventilation:perfusion ratio did not change greatly with increased starvation. The physiological significance of these measurements is discussed.