Integrating genetics, biophysical, and demographic insights identifies critical sites for seagrass conservation

Abstract

The eelgrass Zostera marina is an important foundation species of coastal areas in the Northern Hemisphere, but is continuing to decline, despite management actions. The development of new management tools is therefore urgent in order to prioritize limited resources for protecting meadows most vulnerable to local extinctions and identifying most valuable present and historic meadows to protect and restore, respectively. We assessed 377 eelgrass meadows along the complex coastlines of two fjord regions on the Swedish west coast—one is currently healthy and the other is substantially degraded. Shoot dispersal for all meadows was assessed with Lagrangian biophysical modeling (scale: 100–1,000 m) and used for barrier analysis and clustering; a subset (n = 22) was also assessed with population genetic methods (20 microsatellites) including diversity, structure, and network connectivity. Both approaches were in very good agreement, resulting in seven subpopulation groupings or management units (MUs). The MUs correspond to a spatial scale appropriate for coastal management of “waterbodies” used in the European Water Framework Directive. Adding demographic modeling based on the genetic and biophysical data as a third approach, we are able to assess past, present, and future metapopulation dynamics to identify especially vulnerable and valuable meadows. In a further application, we show how the biophysical approach, using eigenvalue perturbation theory (EPT) and distribution records from the 1980s, can be used to identify lost meadows where restoration would best benefit the present metapopulation. The combination of methods, presented here as a toolbox, allows the assessment of different temporal and spatial scales at the same time, as well as ranking of specific meadows according to key genetic, demographic and ecological metrics. It could be applied to any species or region, and we exemplify its versatility as a management guide for eelgrass along the Swedish west coast.

Major impacts and societal costs of seagrass loss on sediment carbon and nitrogen stocks

“…Recent studies have identified the most valuable and vulnerable eelgrass meadows along the Swedish west coast based on connectivity and genetic diversity (Jahnke et al. 2018, 2020). The present study may provide complementary information to the seascape management of eelgrass by identifying meadows that provide important ecosystem services by mitigating climate changes and eutrophication.…”

Biophysical models of dispersal contribute to seascape genetic analyses

“…Demographic modelling is a very powerful tool to understand (i) historical causes of differentiation and (ii) project the genetic structure of the metapopulation into the future that also includes modelled dispersal, particularly also range evolution within species or metapopulations. Only four of the 87 assessed papers used demographic modelling of the past [13,29,41,42], and only two modelled future persistence and evolution of populations [10,11]. This approach using the tool SLiM [43] is especially appealing in seascape genetics/ genomics, as it is possible to construct models including many populations.…”

“…A few studies used an unstructured grid for the computation of the circulation model (e.g. [10]), which may offer a suitable compromise between extent and resolution. There was no clear relationship between model spatial resolution and the match between genetic and biophysical predictions, but the category ‘structure–no barrier’ had on average lower resolution of the biophysical modelling, indicating that important barriers to dispersal were not resolved.…”

“…For instance, Jahnke et al . [10] used a seascape genetic approach for seagrass in a fjord-scale study in Sweden to define management units, provided a list of particularly valuable meadows (based on genetic and biophysical connectivity) that require protection and even suggested ideal restoration candidate sites to improve dispersal probabilities within the metapopulation [10]. Similarly, Matz et al .…”

Charting a course for genetic diversity in the UN Decade of Ocean Science

“…As an example, the maintenance of genetic diversity in seagrass restoration efforts has been shown to support successful long‐term re‐establishment through increased environmental resilience and complementarity effects (Evans et al, 2018; Reynolds et al, 2012) (Box 1). Genetic approaches also represent important management tools for the identification of key locations for restoration, as well as suitable donor populations, by providing estimates of genetic diversity, connectivity, and demographic parameters (Jahnke et al, 2020). Advances in genomic techniques are also allowing the identification of resilient “climate‐ready” genotypes or functional markers from donor populations for enhancing the resilience of restored populations (Carvalho et al, 2021; Coleman, Minne, et al, 2020; Coleman, Wood, et al, 2020; Coleman & Wernberg, 2020; Connolly et al, 2018; Wood, Marzinelli, et al, 2021).…”