Seagrass (Ruppia maritima L.) Life History Transitions in Response to Salinity Dynamics Along the Everglades-Florida Bay Ecotone

Abstract

Coastal estuaries receiving low and fluctuating freshwater flows are creating more variable salinity environments for submerged aquatic vegetation (SAV), including seagrasses. Some SAV species, such as Ruppia maritima L. (wigeongrass), are adapted to variable salinity, but rapid salinity changes can limit population persistence. For example, R. maritima historically dominated at the Everglades-Florida Bay ecotone under greater freshwater flows, but has a more limited distribution in recent decades with greater salinity variability. While R. maritima is an indicator species for Everglades restoration, little is known about how ecotone salinity patterns drive its current limited distribution in southern Everglades estuaries. Seed production is important for population maintenance in this disturbance-tolerant species. Thus, we examined R. maritima life history transitions, including seed germination, seedling and adult survival, and sexual reproduction under site-specific salinity variability across the Everglades ecotone. Seedlings were most susceptible to fluctuating salinity with only 13 % survival at the lower more marine ecotone site under conditions of relatively large-amplitude fluctuations. Adult survival also decreased from upper (93 %) to lower (25 %) sites, resulting in a significant decline in per capita clonal reproduction rates. The markedly low survival rate at the lower ecotone was associated with rapid salinity fluctuations (2.5–20 psu) with short periodicities (<24 h). In addition, no sexual reproduction occurred at any of our ecotone sites, indicating that seed production may be limiting. Thus, hydrologic restoration targets should consider optimization of salinity levels and dynamics that promote SAV early life stage survival and sexual reproduction to restore critical coastal habitats in the Everglades and other highly dynamic estuarine systems.