Demographic and genetic connectivity: the role and consequences of reproduction, dispersal and recruitment in seagrasses

Abstract

Accurate estimation of connectivity among populations is fundamental for determining the drivers of population resilience, genetic diversity, adaptation and speciation. However the separation and quantification of contemporary versus historical connectivity remains a major challenge. This review focuses on marine angiosperms, seagrasses, that are fundamental to the health and productivity of temperate and tropical coastal marine environments globally. Our objective is to understand better the role of sexual reproduction and recruitment in influencing demographic and genetic connectivity among seagrass populations through an integrated multidisciplinary assessment of our present ecological, genetic, and demographic understanding, with hydrodynamic modelling of transport. We investigate (i) the demographic consequences of sexual reproduction, dispersal and recruitment in seagrasses, (ii) contemporary transport of seagrass pollen, fruits and seed, and vegetative fragments with a focus on hydrodynamic and particle transport models, and (iii) contemporary genetic connectivity among seagrass meadows as inferred through the application of genetic markers. New approaches are reviewed, followed by a summary outlining future directions for research: integrating seascape genetic approaches; incorporating hydrodynamic modelling for dispersal of pollen, seeds and vegetative fragments; integrating studies across broader geographic ranges; and incorporating non-equilibrium modelling. These approaches will lead to a more integrated understanding of the role of contemporary dispersal and recruitment in the persistence and evolution of seagrasses.

Predicting the cumulative effect of multiple disturbances on seagrass connectivity

“…Studies examining both sexual and asexual reproduction have found that while some seagrass populations rely largely on clonal growth for population maintenance (Rasheed, , ), in the case of large scale meadow loss (Rasheed, McKenna, Carter, & Coles, ), or for annual or ephemeral populations (Hovey et al., ; York et al., ), sexual reproduction is of critical importance. Seagrass fruits and propagules of most species are capable of dispersing long distances via the convective forces of ocean waves and currents (Kendrick et al., ; McMahon et al., ). Long distance dispersal supports meadow connectivity and the natural recolonisation of sites after disturbance events (Kendrick et al., ); however, very few studies have attempted to quantify seagrass dispersal and connectivity at broad spatial scales (Jahnke et al., ; Ruiz‐Montoya, Lowe, & Kendrick, ).…”

“…Seagrass fruits and propagules of most species are capable of dispersing long distances via the convective forces of ocean waves and currents (Kendrick et al., ; McMahon et al., ). Long distance dispersal supports meadow connectivity and the natural recolonisation of sites after disturbance events (Kendrick et al., ); however, very few studies have attempted to quantify seagrass dispersal and connectivity at broad spatial scales (Jahnke et al., ; Ruiz‐Montoya, Lowe, & Kendrick, ). Tropical seagrasses occur in some of the world's most threatened coastal regions (Orth et al., ; Waycott et al., ), and there is a critical need to assess the role of connectivity in seagrass replenishment and recovery after disturbance events, the effect of disturbance events on seagrass connectivity and its implications for the conservation of coastal habitats (York et al., ).…”

Recruitment and Patch Establishment by Seed in the Seagrass Posidonia oceanica: Importance and Conservation Implications

“…This is mainly because of the historical paradigm that sexual reproduction contributes only marginally to the maintenance and growth of populations. However, there is growing recognition that the long-term persistence of species depends to some extent on sexual reproduction, as even low rates of recruitment may provide evolutionary potential and increased resistance/resilience to environmental alterations (Reusch et al, 2005; Ehlers et al, 2008; Reynolds et al, 2012; Kendrick et al, 2016). Recruitment by seed also plays a role in colonizing new habitats or recolonizing following local extinction, and contributes to patch expansion in some species (Orth et al, 2006; van Dijk et al, 2009; Kendrick et al, 2012; McMahon et al, 2014; Furman et al, 2015; Sherman et al, 2016; Smith et al, 2016).…”

Genetic signatures of Bassian glacial refugia and contemporary connectivity in a marine foundation species

“…Distinguishing the historical effects of gene migration and vicariance on contemporary genetic structure is problematic without testable biogeographical hypotheses based on pre‐existing geological and environmental evidence (Nason et al ., ). A capacity for long‐distance dispersal (LDD) and demographic connectivity over multiple climatic epochs is a feature in the movement ecology of seagrasses, with significant evolutionary and ecological consequences associated with the different life‐history stages (Kendrick et al ., , ). The effective dispersal of sexually derived propagules by water plays an important role in range expansion into new habitats, range shifts under changing environmental conditions, and population turnover (Triest, ; Johnson et al ., ).…”