The effect of boat propeller scarring intensity on genetic variation in a subtropical seagrass species

We report here the effect of one form of disturbance, boat propeller scarring, on genetic variation in the subtropical seagrass Halodule wrightii. We developed an amplified fragment length polymorphism assay to measure genetic var-aition in plots representing four levels of scarring intensity: reference (0% scarring), low (1–5%), moderate (5–15%) and severe (>15%). Although we found severely scarred plots to have the lowest, and moderately scarred plots to have the highest, mean genetic diversity estimates (He,P), differences among scarring levels were found to be non-significant(as0.05). Analysis of molecular variance also showed no significant effect of scarring intensity. While propeller scar-ring can cause significant habitat loss, scarring intensities of up to 20% may not yet have seriously affected those factors (population size, flowering density, recruitment, gene flow)that strongly influence population genetic variation. The relatively recent occurrence of this type of disturbance, how-ever, could mean that any long-term effects have yet to detected