The behavior of lobsters in response to reduced salinity

Two experiments were conducted to measure the behavioral responses of lobsters, Homarus americanus (Milne-Edwards), to reductions in salinity. In the first experiment animals were placed in a 3 ft diameter tank that was divided in half by plastic mesh. Spontaneously active lobsters were able to move between the two halves of the tank by passing through either of two conduits. The conduits were equipped with optical sensors to monitor the passage of animals, and a perfusion system to control the salinity of the area in, and around, the conduit. When the salinity in the vicinity of both conduits was the same (28–32 ppt), lobsters exhibited no preference for either conduit. However, when the salinity in one of the conduits was lowered, lobsters preferred to pass through the high salinity (20–25 ppt) conduit rather than the one with low salinity (10–15 ppt). In addition, females appeared to be more selective in their preference and exhibited higher overall activity than males when exposed to reduced salinity. In the second experiment, individual lobsters were placed in a shelter at one end of a long seawater table and exposed to seawater of gradually decreasing salinity. The salinity required to cause a movement out of a shelter, i.e. an avoidance response, was recorded. On average, lobsters first ventured small distances (\u3c one body length) out of their shelter when the salinity reached a level of 18.4 ppt ± 1.42 (SEM), and definitively moved away from their shelter (\u3e one body length) when levels approached 12.62 ppt ± 1.59. Although it was not statistically significant, females again seemed to be either more sensitive to salinity or found it more aversive, because they tended to initiate movements at salinities greater than those required to influence males. These behavioral data indicate that: (1) adult lobsters are capable of detecting changes in salinity which are comparable to the levels found during natural fluctuations in coastal bays and estuaries; (2) when exposed to low salinity of sufficient magnitude, they attempt to avoid it, and; (3) females appear to be more sensitive to drops in salinity and/or they find it more aversive. Previous studies have demonstrated that estuarine lobster populations are dominated by males and that there are seasonal migrations of lobsters into, and out of, estuaries. We conclude that the behavioral responses of male and female lobsters to low salinity may determine, in part, the distribution and movements of lobsters in estuarine habitats