Inclusion of Intra- and Interspecific Facilitation Expands the Theoretical Framework for Seagrass Restoration

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.

Greater Consideration of Animals Will Enhance Coastal Restoration Outcomes

“…Zhang and colleagues ( 2021 ) planted seagrass seeds within experimental plots (20 × 20 centimeter plots of Zostera marina ) and added juvenile quahog clams ( Mercenaria mercenaria ; figure 3 a). The addition of ten clams per plot led to significantly increased seagrass shoot length, a 500% expansion in patch size (versus no change in patches without clams), and ten times greater belowground biomass.…”

“…The most likely casual mechanism was clams enhancing nitrogen availability. Zhang and colleagues ( 2021 ) also added harvest-size clams to 50 × 50 centimeter plots with transplanted adult seagrass ( Zostera marina and Halodule wrightii ), but clam addition had no effect.…”

“… 2020 ), and only a small proportion of seagrass restoration efforts explicitly manipulate animals (Zhang et al. 2021 ). In the present article, habitat-forming animals are those that form the structural habitat being restored, such as reef building corals and oysters, whereas non-habitat-forming animals are all other animals.…”

Multi-habitat seascape restoration: optimising marine restoration for coastal repair and social benefit

“…The co-produced functions and complexity created by interacting foundation species can help enhance the recovery (Lang'at et al, 2013), stability (Angelini et al, 2015) and resilience of multi-habitat ecosystems (Zabin et al, 2022), with productivity that far exceeds single-species habitats (Thomsen et al, 2018;Thomsen et al, 2022). Consequently, calls are increasing for restoration practice to utilise positive species interactions to restore seagrass meadows (Gagnon et al, 2020;Zhang et al, 2021), kelp forests (Eger et al, 2020), oyster reefs (Reeves et al, 2020, McAfee et al, 2021b, mangroves (Gedan and Silliman, 2009;Renzi et al, 2019) and saltmarsh (Derksen-Hooijberg et al, 2018).…”

Nested interactions between chemosynthetic lucinid bivalves and seagrass promote ecosystem functioning in contaminated sediments

“…However, over the years, many seagrass restoration and/or transplantation programs have been costly and unsuccessful (Cunha et al, 2012;van Katwijk et al, 2016). Possibly, this is because these programs did not take into account factors such as the genetic features of donor populations (Pazzaglia et al, 2021) or the important role of positive species interactions in effectively contributing to ecosystem functioning (Cardinale et al, 2002;Bulleri et al, 2018;Valdez et al, 2020;Gagnon et al, 2021;Malkin and Cardini, 2021;Zhang et al, 2021).…”