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Landscape Ecology

, Volume 33, Issue 12, pp 2253–2272 | Cite as

Physical drivers of seagrass spatial configuration: the role of thresholds

  • Amy V. UhrinEmail author
  • Monica G. Turner
Research Article

Abstract

Context

Seagrass landscapes vary substantially in extent and pattern, resulting from depth zonation and hydrodynamic stress gradients and may exhibit threshold behavior in response to changes in physical drivers. Seagrass landscapes persist in a delicate balance between processes of disturbance and recovery and therefore may exhibit behavior typical of classic critical systems.

Objectives

Examine how hydrodynamic drivers and physical setting influence seagrass landscape composition and configuration. Determine if seagrass patch size distributions typify patterns observed for critical systems.

Methods

We used landscape metrics to quantify the spatial configuration of seagrass and then modeled the response of these metrics to wave energy, tidal current speed, and water depth at 62 estuarine sites in North Carolina, USA. Seagrass landscapes were representative of cover types observed in the estuary generated by wave energy.

Results

Percent cover, patch size, and number of patches all declined with increasing wave energy. Threshold behavior occurred at wave energy change points between 675–774 J m−1. Seagrass landscapes differed in spatial configuration and physical setting, above and below change points. There was moderate support for a power law relationship for patch size distribution across a wide range of seagrass landscape cover and wave energy.

Conclusions

With weather extremes on the rise, much of this estuarine seagrass will be exposed to increased wave energy. Where seagrass exists just below the wave energy change points, increases in wave energy could tip those habitats into a new stable state of lower cover resulting in less cover overall in the estuary.

Keywords

Seagrass Spatial configuration Hydrodynamics Ecological thresholds Alternate state North Carolina 

Notes

Acknowledgements

Funding was provided to AVU by the NOAA National Ocean Service Coastal Science Board with indirect support from the NOAA National Centers for Coastal Ocean Science, the NOAA Office of Response and Restoration, and the University of Wisconsin-Madison. MGT acknowledges support from the University of Wisconsin Vilas Trust and UW2020 initiative. We are immensely grateful to M. Fonseca for invaluable insights regarding hydrodynamic properties of seagrass beds and historical knowledge of the seagrass ecosystem in the Albemarle-Pamlico Sound Estuary System, and for critical review of earlier versions of the manuscript. We appreciate statistical consultation and R code provided by J. Qiu. Aerial imagery was generously provided by the Albemarle-Pamlico National Estuary Partnership. We thank W. Rogers for organizing the current speed measurements in the field. We benefited from discussion with S. Carpenter, E. Damschen, P. Townsend and J. Zedler. We appreciated and incorporated suggestions from the anonymous reviewers assigned by the journal. The views expressed here do not necessarily reflect those of NOAA.

Supplementary material

10980_2018_739_MOESM1_ESM.pdf (560 kb)
Supplementary material 1 (PDF 559 kb)

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Authors and Affiliations

  1. 1.Marine Debris Division, Department of Commerce, National Oceanic and Atmospheric Administration, National Ocean ServiceOffice of Response and RestorationSilver SpringUSA
  2. 2.Department of Integrative BiologyUniversity of WisconsinMadisonUSA

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