Effects of storm-induced salinity changes on submersed aquatic vegetation in Kings Bay, Florida

Hurricanes and other major storms cause acute changes in salinity within Florida's streams and rivers. Wind-driven tidal surges that increase salinities may have long-lasting effects on submersed aquatic vegetation (SAV) and the associated fauna. We investigated potential effects of salinity pulses on SAV in Kings Bay, Florida, by subjecting the three most common macrophytes, Vallisneria ammicana, Myriophyllum spicatum, and Hydyilla verticillata, to simulated salinity pulses. In Kings Bay, we documented changes in salinity during three storms in September 2004 and measured biomass and percent cover before and after these storms. During experiments, macrophytes were exposed to salinities of 5 parts per thousand, 15 parts per thousand, or 25 parts per thousand for 1, 2, or 7 d, with a 28-d recovery period in freshwater. Relative to controls, plants subjected to salinities of 5%o exhibited few significant decreases in growth and no increase in mortality. All three species exhibited decreased growth in salinities of 15 parts per thousand or 25 parts per thousand. H. verticillata exhibited 100% mortality at 15 parts per thousand and 25 parts per thousand, irrespective of the duration of exposure. M. spicatum and V. americana exhibited increased mortality after 7-d exposures to 15 parts per thousand or any exposure to 25 parts per thousand. Maximum daily salinities in Kings Bay approached or exceeded 15 parts per thousand after each of the three storms, with pulses generally lasting less than 2 d. Total aboveground biomass and percent cover of vascular plants were reduced following the storms. M. spicatum exhibited an 83% decrease in aboveground biomass and an 80% decrease in percent cover. H. verticillata exhibited a 47% and 15% decline in biomass and percent cover, respectively. V. americana exhibited an 18% increase in aboveground biomass and a 37% increase in percent cover, which suggests greater tolerance of salinity pulses and release from competition with the invasive H. verticillata and M. spicatum. Our results indicate that rapid, storm-induced pulses of high salinity can have important consequences for submersed aquatic vegetation, restoration efforts, and management of invasive species.