Temporal variability in potential connectivity of Vallisneria americana in the Chesapeake Bay

Abstract

Context Submersed aquatic vegetation (SAV) performs water quality enhancing functions that are critical to the overall health of estuaries such as the Chesapeake Bay. However, eutrophication and sedimentation have decimated the Bay's SAV population to a fraction of its historical coverage. Understanding the spatial distribution of and connectedness among patches is important for assessing the dynamics and health of the remaining SAV population.Objectives We seek to explore the distribution of SAV patches and patterns of potential connectivity in the Chesapeake Bay through time. Methods We assess critical distances, from complete patch isolation to connection of all patches, in a merged composite coverage map that represents the sum of all probable Vallisneria americana containing patches between 1984 and 2010 and in coverage maps for individual years within that timeframe for which complete survey data are available. Results We have three key findings: First, the amount of SAV coverage in any given year is much smaller than the total recently occupied acreage. Second, the vast majority of patches of SAV that are within the tolerances of V. americana are ephemeral, being observed in only 1 or 2 years out of 26 years. Third, this high patch turnover results in highly variable connectivity from year to year, dependent on dispersal distance and patch arrangement. Conclusions Most of the connectivity thresholds are beyond reasonable dispersal distances for V. americana. If the high turnover in habitat occupancy is due to marginal water quality, relatively small improvements could greatly increase V. americana growth and persistence.

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

“…Some subestuaries always remain the same community, while other subestuaries switch communities one or more times (Kendrick et al 2012;Lloyd et al 2016). Z. palustris does well in freshwater streams worldwide (Wilby et al 1998;Stegen et al 2000), so reservoir populations in the streams flowing into a subestuary could support subestuary Z. palustris.…”

Calm after the storm? Similar patterns of genetic variation in a riverine foundation species before and after severe disturbance

“…If losses at 2015 sites, for which we have no pre‐storm data, were of similar magnitude to losses at Croton, their similarity in genotypic and genetic diversity to levels found at extirpated sites may signal a downward trend of diversity and increased vulnerability. When compared to other western Atlantic estuaries (Lloyd et al., 2011 , 2016 ; Marsden et al., 2022 ), lower Hudson River Vallisneria beds were genetically depauperate even before the storms. Signatures of recent genetic bottlenecks in 6 out of 13 sites, N e values that were far lower than is considered viable (Franklin, 1980 ), and low GD at most sites (Table 1 ) may reflect recurring disturbance even before the 2011 storms and cause concern.…”

Sediment–vegetation interactions determine the fate of fluvial sediment in the upper reaches of a large estuary

“…Most previous research has focused on the main bed, but it is fairly unique in its width ($ 5 km across) and perpendicular orientation immediately in front of a large sediment source. The western patches ($ 1-10 m across) are more similar in size to SAV beds in the Chesapeake and elsewhere (e.g., Lloyd et al 2016) and tend to be oriented parallel to the flow. Thus, dynamics in the patches are more relevant to restoration and nutrient management strategies but likely differ from dynamics in larger SAV beds due to the distance over which flow decelerates as it enters the vegetation.…”