A general framework for propagule dispersal in mangroves

Abstract

Dispersal allows species to shift their distributions in response to changing climate conditions. As a result, dispersal is considered a key process contributing to a species' long-term persistence. For many passive dispersers, fluid dynamics of wind and water fuel these movements and different species have developed remarkable adaptations for utilizing this energy to reach and colonize suitable habitats. The seafaring propagules (fruits and seeds) of mangroves represent an excellent example of such passive dispersal. Mangroves are halophytic woody plants that grow in the intertidal zones along tropical and subtropical shorelines and produce hydrochorous propagules with high dispersal potential. This results in exceptionally large coastal ranges across vast expanses of ocean and allows species to shift geographically and track the conditions to which they are adapted. This is particularly relevant given the challenges presented by rapid sea-level rise, higher frequency and intensity of storms, and changes in regional precipitation and temperature regimes. However, despite its importance, the underlying drivers of mangrove dispersal have typically been studied in isolation, and a conceptual synthesis of mangrove oceanic dispersal across spatial scales is lacking. Here, we review current knowledge on mangrove propagule dispersal across the various stages of the dispersal process. Using a general framework, we outline the mechanisms and ecological processes that are known to modulate the spatial patterns of mangrove dispersal. We show that important dispersal factors remain understudied and that adequate empirical data on the determinants of dispersal are missing for most mangrove species. This review particularly aims to provide a baseline for developing future research agendas and field campaigns, filling current knowledge gaps and increasing our understanding of the processes that shape global mangrove distributions.

Temperature thresholds for black mangrove (Avicennia germinans) freeze damage, mortality and recovery in North America: Refining tipping points for range expansion in a warming climate

“…In response to warming winter temperature extremes (USGCRP, ), mangroves and other tropical organisms are expected to move northward into more temperate biomes in eastern and central North America (Carter et al, ; Cavanaugh et al, ; Osland et al, ; Osland & Feher, ). In combination with temperature projections and models of mangrove propagule dispersal (Van der Stocken, Carroll, Menemenlis, Simard, & Koedam, ; Van der Stocken, Wee, et al, ), establishment (Krauss et al, ), and growth (Berger et al, ), the temperature thresholds identified for A. germinans leaf damage, mortality and biomass recovery can be used to help scientists and natural resource managers better anticipate mangrove range dynamics in a warming world.…”

Channel network structure determines genetic connectivity of landward–seaward Avicennia marina populations in a tropical bay

“…Reported flotation and viability times for A. marina propagules are relatively short, spanning a couple of days to weeks (Clarke et al, 2001;Clarke & Myerscough, 1991;Steinke, 1986). However, it should be mentioned that the duration of the experimental trials on which these findings are based may be too short to obtain meaningful frequency distributions of these propagule traits, and should ideally extend beyond maximum values (Van der Stocken et al, 2019).…”

“…Estimates of gene flow and knowledge on the factors that determine the distribution of genetic diversity is not only of theoretical interest, but can be useful to inform management and conservation of these coastal ecosystems (Balbar & Metaxas, 2019;Carr et al, 2017;Nakajima et al, 2017;Pujolar et al, 2013;Schwarzbach & Ricklefs, 2001). as propagule buoyancy and viability period, species-specific propagule morphological traits (size and shape), landscape complexity, and the position of the parent tree in the tidal frame (Van der Stocken et al, 2019). Rabinowitz (1978) proposed that the interacting effects of water depth with species-specific propagule traits ("tidal sorting") might explain the differential distribution (zonation) of mangrove species along the tidal gradient.…”

“…Mangrove propagules are transported by the hydrokinetic energy from waves, rivers, tides, near‐shore and open‐ocean currents, as well as wind energy, over short (near the parent tree) to transoceanic distances. Dispersal potential and the patterns of gene flow depend on the cumulative effect of a wide range of factors, such as propagule buoyancy and viability period, species‐specific propagule morphological traits (size and shape), landscape complexity, and the position of the parent tree in the tidal frame (Van der Stocken et al., 2019). Rabinowitz (1978) proposed that the interacting effects of water depth with species‐specific propagule traits (“tidal sorting”) might explain the differential distribution (zonation) of mangrove species along the tidal gradient.…”

Geographical and environmental contributions to genomic divergence in mangrove forests

“…This model appears to be common in studies of plants (Sexton et al, 2014;Segarra-Moragues et al, 2016;Cruz-Nicolás et al, 2019) and mangroves (Cerón-Souza et al, 2010;Sandoval-Castro et al, 2014;Kennedy et al, 2016;Binks et al, 2019;Ochoa-Zavala et al, 2019). Although evidence of water dispersion over long distances exists for mangrove species (Nettel & Dodd, 2007;Takayama et al, 2013;Mori et al, 2015;Van der Stocken et al, 2019b), our results indicate that the large geographic extension and major oceanic currents of the Brazilian coast physically limit the dispersal of Avicennia species. Although these correlations were significant for the total set of sampling locations, they were not significant when considering only the set of A. schaueriana and A. germinans sampling locations north of the SEC.…”