Tolerances to hypo-osmotic and temperature stresses in native and invasive species of Gracilaria (Rhodophyta)

Physiological responses to the hypo-osmotic and temperature stresses of an invasive species, Gracilaria vermiculophylla, were compared to those of the native Atlantic species, G. tikvahiae and G. cervicornis. For the hypoosmotic and lower lethal temperature experiment, a Connecticut (CT) strain of the invasive G. vermiculophylla and a Rhode Island (RI) strain of the native G. tikvahiae were cultivated at combinations of five different salinities (S = 5, 15, 20, 25 and 30) and at five different temperatures (5 degrees C, 10 degrees C, 15 degrees C, 20 degrees C and 25 degrees C) for 3 weeks. For the upper lethal temperature experiment, two strains of G. vermiculophylla from CT and Portugal, two strains of G. tikvahiae from CT and RI and one Florida strain of G. cervicornis were cultivated at temperatures ranged from 22 degrees C to 39 degrees C in 2 degrees C or 3 degrees C increments for 14 days. Gracilaria vermiculophylla showed a wide range of temperature (5 degrees C-34 degrees C) and salinity (5 - 30 S) tolerance; whereas, G. tikvahiae cannot withstand harsher environmental stresses, such as prolonged exposures to salinities of <= 20 S and temperatures of <= 10 degrees C or >= 34 degrees C. Gracilaria vermiculophylla also grew faster and had higher survival rates than G. tikvahiae or G. cervicornis. These results suggest that the high tolerance and growth capacity of G. vermiculophylla may be responsible for the successful invasion of this alga into Long Island Sound and elsewhere along the east coast of North America.