THE EFFECTS OF REDUCED SALINITY ON LOBSTER (HOMARUS-AMERICANUS MILNE-EDWARDS) METABOLISM - IMPLICATIONS FOR ESTUARINE POPULATIONS

During periods of substantial freshwater runoff, lobsters that inhabit estuaries, such as the Great Bay Estuary in NH, are exposed for sever al days to weeks to seawater that is diluted as low as 10 ppt. To asse ss the physiological stress imposed by these conditions, we measured t he oxygen consumption, heart rate, ventilation rate and hemolymph osmo larity of lobsters while sequentially exposing them, for 24-h periods, to seawater of 20, 15, and 10 ppt. Measurements of hemolymph osmolari ty confirmed previous results which demonstrated that at salinties bel ow 20 ppt lobsters are limited osmoregulators; allowing their hemolymp h osmolarity to drop as the environmental salinity is reduced, but alw ays maintaining it higher than the ambient osmolarity. All animals exp osed to 10 ppt, at 15-degrees-C, were capable of surviving for at leas t 72 h. There was a nearly linear increase in oxygen consumption, hear t and scaphognathite rates in animals exposed to dilute seawater, with almost a twofold increase in metabolic rate when animals were moved f rom 20 to 15 to 10 ppt. At the lowest salinity tested (10 ppt) the ave rage oxygen consumption was higher for females than for males. We conc lude that at low salinities the energetic demands of osmoregulation ar e greater for females than males, and for both sexes the physiological stress imposed may determine, in part, their distribution and/or move ments in estuarine habitats.