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Net global losses of seagrasses have accelerated efforts to understand recovery from disturbances. Stressors causing disturbances (e.g., storms, heatwaves, boating) vary temporally and spatially within meadows potentially affecting recovery. To test differential recovery, we conducted a removal experiment at sites that differed in thermal stress for a temperate seagrass (Zostera marina). We also synthesized prior studies of seagrass recovery to assess general patterns. Seagrass shoots were removed from 28.3 m2 plots at edge and central sites of a meadow in South Bay, Virginia, USA. We hypothesized faster recovery for edge plots where greater oceanic exchange reduces thermal stress. Contrary to our hypothesis recovery was most rapid in the central meadow matching control site shoot density in 24 months. Recovery was incomplete at the meadow edge and estimated to require 158 months. Differences in recovery were likely due to storm‐driven sediment erosion at the edge sites. Based on data from prior recovery studies, which were primarily on monospecific meadows of Zostera, seagrasses recover across a broad range of conditions with a positive, nonlinear relationship between disturbance area and recovery time. Our experiment indicates position within a seagrass meadow affects disturbance susceptibility and length of recovery. Linking this finding to our literature synthesis suggests increased attention to spatial context will contribute to better understanding variation in recovery rates. [ABSTRACT FROM AUTHOR]

In shallow coastal bays where nutrient loading and riverine inputs are low, turbidity, and the consequent light environment are controlled by resuspension of bed sediments due to wind-waves and tidal currents. High sediment resuspension and low light environments can limit benthic primary productivity; however, both currents and waves are affected by the presence of benthic plants such as seagrass. This feedback between the presence of benthic primary producers such as seagrass and the consequent light environment has been predicted to induce bistable dynamics locally. However, these vegetated areas influence a larger area than they footprint, including a barren adjacent downstream area which exhibits reduced shear stresses. Here we explore through modeling how the patchy structure of seagrass meadows on a landscape may affect sediment resuspension and the consequent light environment due to the presence of this sheltered region. Heterogeneous vegetation covers comprising a mosaic of randomly distributed patches were generated to investigate the effect of patch modified hydrodynamics. Actual cover of vegetation on the landscape was used to facilitate comparisons across landscape realizations. Hourly wave and current shear stresses on the landscape along with suspended sediment concentration and light attenuation characteristics were then calculated and spatially averaged to examine how actual cover and mean water depth affect the bulk sediment and light environment. The results indicate that an effective cover, which incorporates the sheltering area, has important controls on the distributions of shear stress, suspended sediment, light environment, and consequent seagrass habitat suitability. Interestingly, an optimal habitat occurs within a depth range where, if actual cover is reduced past some threshold, the bulk light environment would no longer favor seagrass growth.

Macroalgae structure coastal ecosystems affecting metabolism, nutrient dynamics, and food webs. Spatially explicit prediction of macroalgal abundance is critical for understanding coastal ecosystems and trajectories. However, models of macroalgal distribution tend to be mechanistic and generalize poorly, or biogeographic and too coarse to use over spatial scales most appropriate to ecosystem research and management (1–100 km2). Our objective was to develop spatial distribution models for benthic macroalgae in soft‐sediment environments. We compared macroalgal abundance quantified as percent cover, with environmental drivers on 1 ha intertidal flats in a > 900 km2 lagoon system along the Atlantic Coast of Virginia, U.S.A. Physical drivers of macroalgae (e.g., depth‐mediated light availability, exposure to waves) are related to bed morphology. We developed a novel topographic index (τ) to determine whether bed morphology predicts macroalgal abundance. This topographic index described variation in elevation occurring over spatial scales relevant to macroalgae, ranging from smooth to hummocky (τ = 0.01–1.07). Models tested τ along with mean elevation, fetch, and water residence time as predictors of macroalgal abundance. τ, and the interaction with water residence time, were most strongly related to macroalgal abundance. Hummocky flats accumulated less macroalgae than smoother flats, but exceptions occurred with short residence times. Model error (root mean square error) was low, varying between 8% and 18% across models. These models, based on readily measured physical features, are a useful approach for assessing macroalgal abundance in relation to shoreline hardening, species invasions, sea‐level rise, and changing sedimentation affecting coastal ecosystems. [ABSTRACT FROM AUTHOR]

Seagrass meadows play an important role in "blue carbon" sequestration and storage, but their dynamic metabolism is not fully understood. In a dense Zostera marina meadow, we measured benthic O2 fluxes by aquatic eddy covariance, water column concentrations of O2, and partial pressures of CO2 (pCO2) over 21 full days during peak growing season in April and June. Seagrass metabolism, derived from the O2 flux, varied markedly between the 2 months as biomass accumulated and water temperature increased from 16°C to 28°C, triggering a twofold increase in respiration and a trophic shift of the seagrass meadow from being a carbon sink to a carbon source. Seagrass metabolism was the major driver of diurnal fluctuations in water column O2 concentration and pCO2, ranging from 173 to 377 μmol L−1 and 193 to 859 ppmv, respectively. This 4.5‐fold variation in pCO2 was observed despite buffering by the carbonate system. Hysteresis in diurnal water column pCO2 vs. O2 concentration was attributed to storage of O2 and CO2 in seagrass tissue, air–water exchange of O2 and CO2, and CO2 storage in surface sediment. There was a ~ 1:1 mol‐to‐mol stoichiometric relationship between diurnal fluctuations in concentrations of O2 and dissolved inorganic carbon. Our measurements showed no stimulation of photosynthesis at high CO2 and low O2 concentrations, even though CO2 reached levels used in IPCC ocean acidification scenarios. This field study does not support the notion that seagrass meadows may be "winners" in future oceans with elevated CO2 concentrations and more frequent temperature extremes. [ABSTRACT FROM AUTHOR]