Caulerpa taxifolia responses to hyposalinity stress

An investigation into salinity responses of Caulerpa taxifolia was undertaken in a series of laboratory trials to evaluate the use of hyposalinity stress as an eradication strategy. The effect of instantaneous (or shock) exposure to reduced salinity (10 ppt) on the effective quantum yield (EQY) of C taxifolia for different incubation periods (15, 30, 45, 60, 90, 180, 360, 720 and 1440 min) indicated that 180 min or more at this salinity was required to kill the alga. Average EQY declined by 88.2 +/- 14.6% (mean SE.) of the pre-treatment level for the 180 min treatment but were as much as 96.6 +/- 2.5% lower than pre-treatment EQY for the 1440 min exposure. Exposure for 90 min or less resulted in an intermediate response, whereas lesser exposures (60, 30 and 15 min) bad no lasting effect on C. taxifolia health. The effect of gradual changes in salinity, as might be anticipated in an eradication scenario, on EQY of C. taxifolia was investigated through the dilution of seawater (35 ppt) over different time scales (5 h, 2, 4, 7 and 27 days). In all trials > 5 h, the response to hyposalinity was the same regardless of the rate of change in salinity with all treatments resulting in a marked loss in EQY below similar to 15 ppt. Declines in the average ratio of EQY after to EQY before for 4, 7 and 27 days treatments (85.2 +/- 8.2%, 78.8 +/- 9.05% and 77.3 +/- 18.2% of pre-treatment levels, respectively), were significantly larger than the 5 h treatment (2.6 +/- 4.4% of pre-treatment levels). The 2 days salinity reduction (48.5 +/- 17.1%) resulted in an intermediate response. In the 5 h treatment, the exposure to salinities below 15 ppt was less than 3 h, which given the result of the preceding trial explains the lack of substantial EQY response as the minimum exposure period required to kill the alga at 10 ppt is >= 180 min. There is thus no evidence that C. taxifolia is capable of acclimation to gradual reductions in salinity. Consequently, hyposalinity is an effective means of killing the algae and may prove highly effective for populations in relatively small, contained water bodies. Crown Copyright (c) 2007 Published by Elsevier B.V. All rights reserved.