Meeting Abstract

P3.52  Sunday, Jan. 6  Hydrostatic pressure is unequally distributed in the branchial chambers of lobsters, Homarus americanus, and Atlantic blue crabs, Callinectes sapidus JORGENSEN, D.*; BRYANT, M.; HINLICKY, A.; Roanoke College; Roanoke College; Roanoke College jorgensen@roanoke.edu

Lobsters and crabs have two sets of gills each enclosed in a branchial chamber (BC) located on either side of the thoracic body region. Each BC contains a scaphognathite (scaph), a muscularly-driven pump, which moves cyclically, generating a Negative (suction) pressure in the BC to pull water unidirectionally past its gill set, bringing hemolymph and ventilatory water into close apposition. It has been assumed previously that pressure resulting from scaph movement is equally distributed in the BC. We wished to determine the validity of this assumption. We measured hydrostatic pressure at different locations along the longitudinal axis of the BC in American lobsters and Atlantic blue crabs using catheters attached to strain gauge transducers. Our data indicate that pressure is unevenly distributed in the BC in resting animals, being 2-3X more negative in the anterior and posterior regions of the BC as compared to that in the mid-longitudinal region. Previous work has shown that BC pressure decreases (i.e., increased BC suction) during periods of exertion when increased scaph activity is invoked to drive increased BC ventilation. We found that pressure decreased below resting levels by 2-3X in all regions of the BC of exercising lobsters and crabs (steady state walking on a submerged treadmill), but to a greater extent in the anterior and posterior BC regions. This unequal pressure distribution may affect a range of gill functions that relate to transmural hydrostatic pressure, including the movement of hemolymph through individual gill vascular circuits.