Effects of salinity and temperature on survival and behavior of two sympatric species of grass shrimp, Palaemonetes pugio and Palaemonetes vulgaris, and implications of these effects on their distribution of Point Lookout State Park, Maryland

Effects of salinity and temperature on survival and behavior were studied in two sympatric species of grass shrimp, Palaemonetes pugio and P. vulgaris, to determine if differences exist that explain their coexistence. Both species were similarly euryhaline and eurythermic, exhibiting no significant differences that would result in niche differentiation. Winter temperatures at the study site, Point Lookout, Maryland, fell below levels at which significantly more deaths of both species occurred in laboratory experiments, suggesting low temperature may limit distribution there. Upper temperatures, and upper and lower salinities, at which significantly more deaths occurred, were beyond levels encountered at the site, and are not believed to delimit distribution of either species there.; Behavioral experiments in which initiating and response acts, resembling aggression and avoidance behaviors, respectively, described in decapod behavioral studies, were conducted by monitoring intraspecific and interspecific encounters under different conditions of salinity and temperature. Palaemonetes vulgaris exhibited more initiating acts than P. pugio. Salinity had no effect on numbers of behaviors. Higher temperatures resulted in more behaviors in P. vulgaris but not P. pugio . If initiating behaviors are interpreted as aggressive, P. vulgaris is more aggressive than P. pugio and more sensitive to temperature. These results are consistent with reports of displacement of P. pugio by P. vulgaris and observed differences in seasonal distribution between species.; Results of this study indicate that interaction of temperature and behavior is more important in explaining niche separation than either factor alone. It is necessary to consider not only the role of multiple factors in niche determination, but how they affect each other.; Differences in behavior are linked to differences in morphology. Palaemonetes vulgaris possesses longer second pereiopods and larger chelae than P. pugio. These appendages, used in initiating acts, provide a morphological basis for the hypothesis that P. vulgaris aggressively displaces P. pugio.; It is suggested that differences between the distribution of the two species are indirectly due to low salinity and temperature. At these levels, the fouling community, upon which P. vulgaris is more dependent, is less developed, limiting its available habitat.