MEPS 543:163-171 (2016)  -  DOI:

Reversal of intraspecific interactions by an ecosystem engineer leads to variable seedling success along a stress gradient

S. Yang1,2,*, J. HilleRisLambers1, J. L. Ruesink1

1Department of Biology, University of Washington, Box 351800, Seattle, WA 98195-1800, USA
2Present address: Shannon Point Marine Center, Western Washington University, 1900 Shannon Point Road, Anacortes, WA 98221, USA
*Corresponding author:

ABSTRACT: By definition, ecosystem engineers can have large effects on resource flows and habitat structure, with impacts on other organisms ranging from facilitative to inhibitory. The stress gradient hypothesis posits that facilitative interactions predominate in conditions of environmental stress and switch to competitive interactions in benign environments. We conducted an empirical test of the stress gradient hypothesis for a marine ecosystem engineer, eelgrass Zostera marina L., across a hydrodynamic gradient. Eelgrass meadows perform important functions in coastal ecosystems and have experienced contemporary declines worldwide with variable recruitment success. In this study, we first determine whether eelgrass modified the local hydrodynamic conditions and then how the presence of an adult eelgrass canopy affected the plants’ own relative seedling success over the hydrodynamic gradient. Eelgrass reduced water motion significantly, which provided a positive feedback on survival and growth for conspecific seedlings, but only at the stressful end of the hydrodynamic gradient. By contrast, adult conspecifics negatively impacted seedling recruitment and growth in calmer environments, presumably due to intraspecific competition. Thus, eelgrass ecosystem engineering does not always facilitate the plant’s own performance, and our results support the stress gradient hypothesis as an explanation for this context dependence. The balance of these complex interactions may provide a mechanism for delayed or failed recovery of eelgrass in habitats exposed to high hydrodynamic exposure.

KEY WORDS: Context dependence · Density dependence · Habitat modification · Seagrass · Stress gradient hypothesis

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Cite this article as: Yang S, HilleRisLambers J, Ruesink JL (2016) Reversal of intraspecific interactions by an ecosystem engineer leads to variable seedling success along a stress gradient. Mar Ecol Prog Ser 543:163-171.

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