Leaf growth rates (Thalassia testudinum, Banks ex Koning) as an indicator of seagrass responses to regulated freshwater discharges
Milbrandt, E.C., and J. Siwicke
Published In 2016
Gulf of Mexico Science 2016(1):38–46
In southwest Florida, changes in hydrology have fundamentally changed the timing and amount of freshwater delivered to the estuarine ecosystem. Biological indicators such as oyster and submerged aquatic vegetation distribution and abundance have been used to establish minimum and maximum discharges to the estuary. These indicators are robust long-term indicators for comparing interannual and climatological changes; however, they lack sensitivity to variable freshwater flows that occur over the course of months or seasons. Seagrass leaf growth rates could provide an integrated biological response for evaluating events caused by climatological shifts (e.g., El Niño) or to evaluate the biological responses to management actions (e.g., flood control releases of freshwater from Lake Okeechobee). Leaf growth rates for Thalassia testudinum were determined monthly across a gradient of increasing distance from the mouth of the Caloosahatchee estuary. Leaf growth at sites near the Caloosahatchee (within 5 km) had significantly lower growth rates during the April–June period. Salinity was also significantly lower, while light attenuation and temperature were not significantly different. High discharges for flood control caused lower salinities and significantly slowed leaf growth rates. Leaf growth can be a sensitive indicator to water management and climatological events and can show an integrated biological response to high flows.