Quantifying Site-Specific Physical Heterogeneity Within an Estuarine Seascape
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Quantifying physical heterogeneity is essential for meaningful ecological research and effective resource management. Spatial patterns of multiple, co-occurring physical features are rarely quantified across a seascape because of methodological challenges. Here, we identified approaches that measured total site-specific heterogeneity, an often overlooked aspect of estuarine ecosystems. Specifically, we examined 23 metrics that quantified four types of common physical features: (1) river and creek confluences, (2) bathymetric variation including underwater drop-offs, (3) land features such as islands/sandbars, and (4) major underwater channel networks. Our research at 40 sites throughout Plum Island Estuary (PIE) provided solutions to two problems. The first problem was that individual metrics that measured heterogeneity of a single physical feature showed different regional patterns. We solved this first problem by combining multiple metrics for a single feature using a within-physical feature cluster analysis. With this approach, we identified sites with four different types of confluences and three different types of underwater drop-offs. The second problem was that when multiple physical features co-occurred, new patterns of total site-specific heterogeneity were created across the seascape. This pattern of total heterogeneity has potential ecological relevance to structure-oriented predators. To address this second problem, we identified sites with similar types of total physical heterogeneity using an across-physical feature cluster analysis. Then, we calculated an additive heterogeneity index, which integrated all physical features at a site. Finally, we tested if site-specific additive heterogeneity index values differed for across-physical feature clusters. In PIE, the sites with the highest additive heterogeneity index values were clustered together and corresponded to sites where a fish predator, adult striped bass (Morone saxatilis), aggregated in a related acoustic tracking study. In summary, we have shown general approaches to quantifying site-specific heterogeneity.
KeywordsPhysical heterogeneity Estuarine seascape
The Kansas Cooperative Fish and Wildlife Research Unit (Kansas State University, the US Geological Survey, US Fish and Wildlife Service, the Kansas Department of Wildlife, Parks, and Tourism, and the Wildlife Management Institute) provided support during manuscript preparation. The University of Massachusetts at Amherst and the University of Massachusetts School of Marine Sciences, especially Robert Gamache, provided financial support. The Plum Island Ecosystems LTER program (OCE-0423565, OCE-1058747, OCE-1238212) provided lodging and field assistance. Invaluable field, laboratory, and other assistance were provided by members of the University of Massachusetts and Kansas State University fish ecology groups. D. Beauchamp and two anonymous reviewers provided useful comments. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the US Government. This research was conducted under the auspices of University of Massachusetts IACUC Protocol no. 28-02-15; 2012-0023.
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