My final year dissertation investigated the effect of emersion on the heart rate of the Velvet swimming crab, Necora puber. This was done via a small piece of electronic equipment that I designed and created from a series of wires and components. This equipment is currently being used further by my lecturers at both Hull and Scarborough University campuses and may find new information on crab behaviour; which before were unknown.
The velvet swimming crab, Necora puber, is a commercially fished crustacean in the UK. Transportation of Necora puber to distant markets such as Spain exposes the organisms to emersion, which is known to cause many problems and eventual death of Necora puber. The aim of this investigation is to find what effect emersion has on the heart rate of Necora puber; by recording heart rates of different sized subjects in immersed and emersed conditions over 24 h periods. It was found that emersed conditions caused a lack of oxygen to the cardiac ganglion, resulting in metabolic problems leading to bradycardia. This hypoxia in the cardiac ganglion explains why heart rate voltage reduced over the emersed period and why the heart rate became more irregular. The size difference of the branchial chamber between the larger subjects and the smaller ones explains why bradycardia occurred quicker and to a greater extent in the smaller subjects than the larger ones. Death of subjects in emersed conditions was due to the branchial chamber losing water, and the gills collapsing or due to the accumulation of ammonia in the branchial chamber. This also affected the acid–base balance resulting in reduced activity levels. Diel patterns were observed in immersed conditions; caused by the automated aquarium lights. This was because Necora puber remain inactive during the day to survive at temperatures and humidities that defeat their physiological adaptations and are nocturnal foragers.
