Fine‐scale genetic structure and flowering output of the seagrass Enhalus acoroides undergoing disturbance

Abstract

Seagrass are under great stress in the tropical coast of Asia, where Enhalus acoroides is frequently the dominant species with a large food web. Here, we investigate the question of the fine‐scale genetic structure of this ecologically important foundation species, subject to severe anthropogenic disturbance in China. The genetic structure will illuminate potential mechanisms for population dynamics and sustainability, which are critical for preservation of biodiversity and for decision‐making in management and restoration. We evaluated the fine‐scale spatial genetic structure (SGS) and flowering output of E. acoroides , and indirectly estimated the relative importance of sexual versus asexual reproduction for population persistence using spatial autocorrelation analysis. Results reveal high clonal diversity for this species, as predicted from its high sexual reproduction output. The stronger Sp statistic at the ramet‐level compared with genet‐level indicates that clonality increases the SGS pattern for E. acoroides . Significant SGS at the genet‐level may be explained by the aggregated dispersal of seed/pollen cohorts. The estimated gene dispersal variance suggests that dispersal mediated by sexual reproduction is more important than clonal growth in this study area. The ongoing anthropogenic disturbance will negatively affect the mating pattern and the SGS patterns in the future due to massive death of shoots, and less frequency of sexual reproduction.

Persistent Clones and Local Seed Recruitment Contribute to the Resilience of Enhalus acoroides Populations Under Disturbance

“…Populations of E. acoroides in our study are sustained by clonal growth and local seed recruitment which confirms the mixed reproduction strategy in populations of Hainan Island affected by physical disturbance and catchment effluents ( Yu et al, 2019 ). Becheler et al (2014) studied temporal dynamics of clonal structure for Zostera marina and identified similar patterns of clonal richness and structure whereas populations persisted by both initial recruitment, with a stable core of clones which dominance increased over time, and repeated (annual) recruitment of seedlings.…”

“…A higher relatedness of individuals over small distances within meadows (5–10 m) was found in more disturbed sites on both ramet level, due to the aggregation of clones over several meters, and genet level. The aggregated distribution of pollen in male floating flowers and of seeds that are released simultaneously from the floating fruit could explain the fine-scale genetic structure found for E. acoroides among genets rather than pollen and seed dispersal restriction ( Yu et al, 2019 ). The effect of the aggregated dispersal of propagules on the fine-scale structure may be elevated in disturbed sites when population density is low as a result of high mortality and decreased reproductive output.…”

“…Fruits can disperse up to 63.5 km ( Lacap et al, 2002 ) and contain 8–14 non-dormant seeds which are released in the water column ( Ackerman, 2006 ), hence E. acoroides does not rely on seed banks for recruitment. Sexual reproduction appears to be more important for the maintenance and persistence of E. acoroides populations compared to clonal growth ( Rollón et al, 2003 ; McMahon et al, 2017 ; Yu et al, 2018 , 2019 ; Nguyen and Jutta, 2019 ) although a variety of sampling methods (e.g., spacious distance between sampled shoots) could underestimate the role of asexual reproduction. Quiros et al (2017) studied the effect of human-induced disturbance on seagrass communities and showed that sites characterized by large areas of coastal human development and farmland had lower species richness but increased E. acoroides cover.…”

The characteristics of the complete chloroplast genome of Enhalus acoroides

“…In China, E. acoroides is the dominant species along the east coastline of Hainan Island, of which the distribution area has been declining dramatically (Chen et al 2015). This dioecious seagrass displays the capacity for both sexual and clonal reproduction (den Hartog 1970;Yu et al 2019). Most of the seagrasses pollinate underwater mediated by water currents (Ackerman 2006).…”

Sequential disturbances alter the outcome of inter‐genotypic interactions in a clonal plant

“…Observational surveys of clonal plants provide mixed evidence regarding the correlation between genotypic diversity and disturbance (e.g. McMahon et al., 2017; Reisch & Scheitler, 2009; Reynolds et al., 2019; Rusterholz et al., 2009; Yu et al., 2019), and disentangling the underlying mechanisms driving variance in this relationship remains an important avenue of research (Banks et al., 2013). Manipulative field experiments can assess the effects of varying disturbance regimes on the recruitment of new individuals (Herrera & Bazaga, 2016; Hidding et al., 2014; Macreadie et al., 2014; Peng et al., 2015; Reusch, 2006; Veeneklaas et al., 2011) but sampling at a fine enough scale to capture the effects of disturbance on altering the outcome of inter‐genotypic interactions is challenging.…”