Physiological Effects of an Ectocommensal Gill Barnacle, Octolasmis Muelleri, on Gas Exchange in the Blue Crab Callinectes Sapidus

Abstract

ABSTRACT The effect of infestation by an ectocommensal gill barnacle, Octolasmis muelleri, on gas exchange in the blue crab Callinectes sapidus was assessed by comparing respiratory parameters of infested crabs with those of uninfested controls. Infested crabs maintained their oxygen uptake (MO2) at the same level as controls (28 µmol O2 kg-1 min-1); however, heart rate (Fh) and scaphognathite rate (Fsc) increased 1.4 × and 1.8 ×, respectively. Heavily infested crabs did not differ from uninfested crabs with respect to prebranchial hemolymph pH (7.5), CO2 concentration (6.6 mmol 1-1), PO2 (1.9 kPa), or to postbranchial pH (7.4), PO2 (4.1 kPa), and O2 concentration (0.1 mmol 1-1). This suggests that these crabs can compensate for the presence of the barnacle in their ventilatory stream. However, moderately infested crabs exhibited lower prebranchial hemolymph pH (7.2) and CO2 concentration (4.5 mmol 1-1) and an elevated PO2 (3.23 kPa). These values are similar to those of blue crabs during exercise. Compensation is achieved by increasing ventilation volume (1.7 x) and cardiac output (1.4 x). Concomitant facilitation of oxygen delivery at the tissues would be necessary for complete compensation. Circulating lactate levels were similar for all crabs, indicating that an increase in anaerobic metabolism is not necessary for compensation. Although heavily infested crabs (>20 ectocommensals) appeared to compensate for barnacle presence, extremely heavily infested crabs (> 50 ectocommensals) did not survive the experimental stress. Because median natural infestation levels are low, the barnacle probably does not pose a serious threat to the blue crab population.