Prioritization or Summation of Events? Cardiovascular Physiology of Postprandial Dungeness Crabs in Low Salinity

Abstract

Decapod crustaceans commonly forage in estuarine environments. The osmoregulatory mechanisms that allow them to cope with periodic episodes of low salinity have been well documented. There is less information on how ventilatory and cardiovascular mechanisms aid survival in low salinity. Prior experiments have shown that most species exhibit a tachycardia coupled with an increase in ventilation rate and oxygen uptake. However, these previous experiments were conducted on animals that were starved before experimentation in order to avoid increases in metabolism associated with digestive processes. This study investigated how the Dungeness crab Cancer magister balances the demands of physiological systems during feeding and digestion in low salinity. Cardiac and ventilatory parameters increased during feeding. When the crabs were subjected to low salinity after feeding, heart rate increased in 25% seawater (SW) but decreased in 50% SW. Instead of an expected increase in ventilation rate during low-salinity exposure, there was a decrease. Feeding was associated with an increase in sternal artery flow, with subsequent decreases in flows through the sternal and anterolateral arteries in low salinity. When low salinity was administered first, a tachycardia occurred, coupled with decreased stroke volume and cardiac output. There was also an increase in ventilation rate. When crabs were fed in low salinity, heart rate decreased in 50% SW but was maintained in 25% SW. Ventilation rate decreased when crabs fed in 50% and 25% SW. Flow through the sternal artery and anterolateral arteries decreased in low salinity, and except for transient increases while feeding, there were further decreases during digestion. Cardiac and ventilatory parameters were rapidly regained when control conditions were restored. The results suggest that events during low salinity are prioritized. Nevertheless, these alterations in physiological parameters may not be beneficial; although digestive processes did not affect osmoregulatory ability, postprandial crabs did not survive as long as starved crabs in 25% SW. The results show that the digestive state of an animal is important in modulating its physiological responses to environmental perturbations, underscoring the importance of an integrative approach to studying physiological responses at the organismal level.