Land Use and Salinity Drive Changes in SAV Abundance and Community Composition

Abstract

Conserving and restoring submerged aquatic vegetation (SAV) are key management goals for estuaries worldwide because SAV integrates many aspects of water quality and provides a wide range of ecosystem services. Management strategies are typically focused on aggregated abundance of several SAV species, because species cannot be easily distinguished in remotely sensed data. Human land use and shoreline alteration have been shown to negatively impact SAV abundance, but the effects have varied with study, spatial scale, and location. The differences in reported effects may be partly due to the focus on abundance, which overlooks within-community and amongcommunity dynamics that generate total SAV abundance. We analyzed long-term SAV aerial survey data ) and ground observations of community composition in subestuaries of Chesapeake Bay to integrate variations in abundance with differences in community composition. We identified five communities (mixed freshwater, milfoil-Zannichellia, mixed mesohaline, Zannichellia, and Ruppia-Zostera). Temporal variations in SAV abundance were more strongly related to community identity than to terrestrial stressors, and responses to stressors differed among communities and among species. In one fifth of the subestuaries, the community identity changed during the study, and the probability of such a change was positively related to the prevalence of riprapped shoreline in the subestuary. Mixed freshwater communities had the highest rates of recovery, and this may have been driven by Hydrilla verticillata, which was the single best predictor of SAV recovery rate. Additional species-specific and community-specific research will likely yield better understanding of the factors affecting community identity and SAV abundance, more accurate predictive models, and more effective management strategies.

Salinity and water clarity dictate seasonal variability in coastal submerged aquatic vegetation in subtropical estuarine environments

“…Salinity was the dominant factor driving species assemblages, biomass and species number, matching findings from past studies along the Gulf coast and in other regions (i.e. Carter et al 2009, Borgnis & Boyer 2016, Cho & Biber 2016, Patrick et al 2018. Overall, SAV biomass and species number were consistently higher in the fresh and intermediate assemblages throughout the year.…”

“…These gradients vary across and between estuaries, and inter-and intra-annually in response to landscape variation, climatic cycles, disturbance and management. Along estuarine environmental gradients, SAV distribution and biomass vary spatially and temporally, responding rapidly to changing water salinity, light and nutrient conditions resulting from precipitation, storm events and human activities (Frankovich et al 2011, Correia et al 2012, DeMarco et al 2018, Patrick et al 2018. The resulting temporal and spatial variation in the environment determine the composition of SAV assemblages through direct and indirect impacts on species survival, reproduction and growth rates, ultimately defining the distribution, abundance and composition of the community (Fourqurean et al 2001, Patrick et al 2018.…”

Impacts of Coastal Land Use and Shoreline Armoring on Estuarine Ecosystems: an Introduction to a Special Issue

“…Two papers in this special issue explored the complex relationships between land use, shoreline armoring, and SAV abundance. Building on previous work (Patrick et al 2014, Patrick and Weller 2015, Patrick et al (2017) (Land use and salinity drive changes in SAV abundance and community composition) analyzed long-term SAV data to better understand how watershed land use, shoreline alteration, salinity, and SAV community composition affect trends and inter-annual variation in SAV abundance. An ordination identified five SAV community types throughout Chesapeake Bay subestuaries.…”

Integrating Regional Management Needs into a Mid-Atlantic Shorelines Research Project

“…The comparisons spanned a range of spatial scales. At the broadest scale, there were comparisons of more than 100 Chesapeake Bay sub-estuaries and Delmarva coastal bay systems to relate SAV distribution to shoreline type, sediment characteristics, geomorphology, wave energy, watershed land-use, and other factors (e.g., Patrick et al 2017). Field studies compared selected subestuary and bay systems with watersheds dominated by forest, agriculture, or developed land.…”