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Kevin McLean - Marine Invasions

Stanford University, California

Salinity Tolerance and Reproductive Output in Two Atlantic Coast Amphipods

The success of non-native aquatic species is heavily influenced by their competitive ability with respect to environmental tolerance and reproductive capacity in an introduced habitat.  This competitive ability was examined experimentally by comparing salinity tolerance and reproductive output of two gammarid amphipod species, Gammarus tigrinus and Gammarus mucronatus.  Collected from Canning House Bay on the Rhode River, 61 mating pairs of G. tigrinus and 23 mating pairs of G. mucronatus were placed in salinity treatments of freshwater, 5 ppt, ambient (10-12 ppt), 24 ppt, and 34 ppt.  The number of offspring released from each pair across salinity levels was compared.  G. tigrinus showed a strong negative correlation (r = -0.989) between salinity and reproductive output, while G. mucronatus showed a weak positive correlation (r = 0.195).  Variance across salinity levels was insignificant for both G. tigrinus and G. mucronatus (p = 0.16 and 0.34, respectively), however more important is the fact that both species were capable of successful reproduction at all salinity levels.  While reproductive output is certainly not the only means of predicting of successful introductions, this study provides valuable insight into the invasive potential of these species.  Extending comparisons of environmental tolerances to a wider range of species may provide valuable information for management and prevention of future and current invasions.