Balancing the demands of physiological processes: Decapod crustacean feeding and digestion in hypoxia

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Dissolved oxygen levels in coastal areas have changed more than any other environmental variable during the past few decades, leading to widespread hypoxia. Crustaceans are among the most sensitive organisms to hypoxia and could therefore act as important indicator species of a healthy environment. Knowledge of their behavioural and physiological responses will be invaluable when predicting long-term effects of hypoxia on benthic communities. In general crustaceans respond to a decline in oxygen tension by increasing ventilation rate in an attempt to maintain a stable oxygen (O2) uptake, at a certain level they are unable to maintain O2 uptake and thereafter it drops in line with that of the environment. All organisms must feed in order to survive and the subsequent digestion of a meal leads to a general increase in metabolism termed the specific dynamic action (SDA). Thus current trends in hypoxia will reduce the available dissolved O2 at a time when organisms need to uptake more O2 for digestive processes.**** This research will investigate how several species of decapod crustaceans (rock crab, green crab, lobster, Dungeness crab) with differing ability to deal with hypoxia balance cardiorespiratory variables (respiration, cardiac function, blood chemistry) when they feed and digest in hypoxia. If animals are unable to maintain O2 uptake during hypoxia we will determine if they can slow or halt digestive processes (mechanical costly” physiological mechanisms. A Loligo shuttlebox® will be used to determine if feeding status alters O2 preference. The apparatus allows animals to choose between two O2 regimes while a computer tracks movement. By monitoring speed of movement, O2 choice and feeding activity we will be able to determine if fed and starved animals have different O2 preferences, or if trade-off occurs whereby with increasing starvation time an animal will be more likely expend energy entering into low O2 in order to obtain a food reward.**** Ecophysiology has had a renaissance in the last decade and this integrative approach studying the connections between whole animal physiology and behaviour is important when investigating interactions between the animal and its environment. Historically scientists carried out experiments under controlled conditions where feeding was carefully regimented, the results of this research will show how multiple stressors may interact in more natural conditions. In light of climate change and the exponential increase in hypoxia the results of this research will not only be of interest to the scientific community, but will also be important for environmental resource managers in understanding potential responses of communties to environmental change.****