Abstract
Restoration is increasingly utilized as a strategy to stymie the loss of coastal habitats. Coastal habitat restoration has predominantly emphasized designs that minimize physical stress and competition. As evidence of the pervasiveness of this approach, we conducted a global survey of seagrass restorationers and found a strong affinity for stress-avoidant designs with adult shoots in dispersed rather than aggregated configurations. To test the alternative hypothesis that including positive interactions can enhance restoration success, we experimentally incorporated: (i) interspecific facilitation (clam additions) into seed sowing, and (ii) both intra- and interspecific facilitation (planting a single-large versus multiple-small patches and adding clams) into shoot planting. Clam additions to seeds significantly enhanced plant biomass and patch size; and nutrient analysis suggested the causative mechanism was clam enhancement of available nitrogen. In contrast, adult outplant growth was enhanced by intra- but not inter-specific facilitation. Dispersed configurations consistently declined, whereas large-intact patches, which had the same initial biomass as dispersed plots, increased in patch area and doubled in shoot density. These results demonstrate that expanding restoration strategies to include positive interactions with respect to seagrass ontogeny has the capability to switch the trajectory of restoration from failure to success.
Highlights
Climate change, pollution, habitat destruction, overharvest of predators, among others, have contributed to the global loss or conversion of roughly 29% of seagrasses (Waycott et al, 2009), 85% of oyster reefs (Beck et al, 2011), and 42% of North American salt marshes (Gedan and Silliman, 2009a)
The list of potential respondents was compiled from known seagrass restoration practitioners and researchers, state agencies tasked with coastal environmental conservation and management, and organizations or companies frequently contracted for coastal environmental remediation and mitigation
Our study adds to the growing amount of literature that calls for a new coastal restoration paradigm that systematically includes positive interactions and facilitation theory into designs
Summary
Pollution, habitat destruction, overharvest of predators, among others, have contributed to the global loss or conversion of roughly 29% of seagrasses (Waycott et al, 2009), 85% of oyster reefs (Beck et al, 2011), and 42% of North American salt marshes (Gedan and Silliman, 2009a). Facilitation Enhances Seagrass Restoration promoted as a primary strategy by nations, corporations, and non-profit organizations to bolster shoreline ecosystems and communities, combat habitat losses, compensate for urban development, and create jobs (CWA, 1972; ERA, 2000; RESTORE Act, 2012; Edwards et al, 2013; Sutton-Grier et al, 2015, 2018). To meet this increasing demand, marine restoration approaches must quickly become more affordable and effective, as the failure rate and costs of marine ecosystem restoration are often high (Bayraktarov et al, 2016; Saunders et al, 2020). Key to determining if inclusion of positive species interactions can maximize restoration productivity and resilience across diverse ecosystems are tests that examine the utility of incorporating multiple types of facilitation in different marine habitats and at multiple stages of outplant maturity (e.g., seeds vs. adults) during restoration
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