Kennedy, C. G., M. E. Mather, J. M. Smith, J. T. Finn, L. A. Deegan. 2015. Discontinuities concentrate mobile predators: Quantifying organism-environment interactions at a seascape scale. Ecosphere 7(2):e01226. 10.1002/ecs2.1226.
ABSTRACT Understanding environmental drivers of spatial patterns is an enduring ecological problem critical to successful environmental conservation. Spatial discontinuities, both naturally occurring (e.g., river confluence, forest edge, drop-off) and anthropogenic (e.g., dams, roads), can strongly influence the distribution of highly mobile organisms that have land or seascape scale home ranges. Critical information about drivers of spatial patterns may be missed if only regularly-occurring environmental variables (e.g., depth, substrate, current velocity) are considered. A geomorphic discontinuity framework, expanded to include ecological patterns, provides a different way of examining organism-environment relationships that can capture the influence of these important but irregularly-distributed environmental conditions. Here, we test if highly mobile striped bass (Morone saxatilis) on a coastal feeding migration are consistently and predictably concentrated by spatial discontinuities. Specifically, we quantified the distribution of 50 acoustically-tagged striped bass relative to six types of physical features (sand bars, confluences, drop-offs, depth, channel proximity, region) during four monthly surveys at 40 sites within Plum Island Estuary (PIE). All striped bass survived tagging, were coastal migrants, displayed seasonal residency within PIE, and moved frequently within the estuary ecosystem. Striped bass were predictably and consistently clustered in the middle region of PIE at sites with high sandbar area, close to channel networks, adjacent to complex confluences, and at intermediate levels of bottom unevenness. In addition, the highest striped bass counts occurred at sites with the greatest additive heterogeneity (i.e., where multiple discontinuities co-occurred). Thus, the ecological discontinuity framework provided new insights about how mobile predators were distributed at the seascape scale that did not emerge from traditional habitat use perspectives. Consequently, our approach provides a fundamentally different way of looking at interactions among mobile animals and seascape-scale natural and anthropogenic physical features.