Intraspecific variation in resilience traits of eelgrass across intertidal stress gradients and oyster aquaculture methods

Authors: RUESINK, JENNIFER - University Of Washington; HOULE, KATIE - Pacific Shellfish Institute; KROEKER, KRISTY - University Of California Santa Cruz; Dumbauld, Brett; BOARDMAN, FIONA - University Of Washington; LEWIS, NATHANIEL - Oregon State University; Mc Intyre, Brooke; SUHRBIER, ANDREW - Pacific Shellfish Institute; HUDSON, BOBBI - Pacific Shellfish Institute

Submitted to: Frontiers in Marine Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2024
Publication Date: 11/1/2024
Citation: Ruesink, J., Houle, K., Kroeker, K., Dumbauld, B.R., Boardman, F., Lewis, N., Mc Intyre, B.A., Suhrbier, A., Hudson, B. 2024. Intraspecific variation in resilience traits of eelgrass across intertidal stress gradients and oyster aquaculture methods. Frontiers in Marine Science. 11. Article 1427595. https://doi.org/10.3389/fmars.2024.1427595.
DOI: https://doi.org/10.3389/fmars.2024.1427595

Interpretive Summary: Eelgrass (Zostera marina) is a flowering plant that grows and creates structured habitat in US West Coast estuaries. Eelgrass responds to both natural stressors like emersion at low tide and human activities like shellfish aquaculture which affect its abundance, persistence and distribution and therefore quantifying its response to these stressors is of particular management importance. In this study, eelgrass traits were measured across a vertical tidal range of 1 m at 12 intertidal sites where shellfish aquaculture occurs in estuaries along the US west coast. Traits were divided into those related to resistance to stressors (above-ground size, below-ground storage) and recovery after disturbance (flowering, branching, and rhizome extension). Eelgrass density and cover responded additively to intertidal stress and oyster aquaculture. Shoot length, above-ground shoot mass, and below-ground mass per rhizome length declined at higher elevations, whereas in oyster culture declines occurred only in above-ground traits, not below-ground, suggesting that resistance to stress was maintained in aquaculture. Eelgrass flowering increased but branching declined at higher tidal elevations and ground culture of oysters moderated these recovery traits lessening the negative effect on branching and enhancing flowering and rhizome extension. Eelgrass recovery traits differed by tidal elevation in off-bottom culture, with flowering reduced at higher elevation and rhizome extension reduced at lower elevation. Resistance and recovery have been essential for eelgrass to persist in spatio-temporally variable intertidal conditions and these traits were also responsive to oyster aquaculture. Ground culture promoted resilience and off-bottom culture had less effect relative to intertidal emersion.

Technical Abstract: Species persist through resistance and recovery traits induced by natural stressors. Whether human activities exacerbate or moderate the effects of natural stressors is an open question. Because eelgrass (Zostera marina) creates coastal habitat, its response to natural stressors and human activities is of particular management importance. In this study, emersion was considered a natural stressor for eelgrass. And eelgrass traits that are hypothesized to provide resilience to emersion were measured seasonally in intertidal eelgrass meadows spanning 10 degrees of latitude in the California Current Ecosystem. We then measured how these traits were affected by oyster aquaculture. At 12 intertidal sites on the US west coast, eelgrass density and cover declined additively in response to intertidal stress and oyster aquaculture, confirming their roles as natural and anthropogenic stressors. Traits were divided into those related to increased resistance to emersion (smaller above-ground size, greater below-ground storage) and enhanced recovery (increased flowering, branching, and rhizome extension). Shoot length, above-ground shoot mass, and below-ground mass per rhizome length declined at higher elevations, whereas, in oyster culture, declines occurred only in above-ground traits, rarely below-ground, suggesting eelgrass in oyster culture maintained resistance traits overall. Since flowering increased but branching declined at higher tidal elevations, these recovery traits responded in opposite directions along an intertidal stress gradient. Ground culture moderated the negative effect of tidal elevation on branching, and flowering and rhizome extension of eelgrass increased in ground culture, suggesting ground culture of oysters increased recovery traits. In off-bottom culture, eelgrass recovery traits differed by elevation, with flowering reduced at higher elevation and rhizome extension reduced at lower elevation. Resistance and recovery have been essential for eelgrass to persist in spatio-temporally variable intertidal conditions, and these traits are also responsive to the anthropogenic stressor of oyster aquaculture. The enhancement of resilience traits of eelgrass in ground culture, while some resilience traits declined in off-bottom culture, aligns with the different intertidal environmental conditions generated by each culture type.