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ABSTRACT Species conservation and management benefit from precise understanding of natural patterns of dispersal and genetic variation. Using recent advances in indirect genetic methods applied to both adult plants and dispersed seeds, we find that the mean seed dispersal in a threatened marine foundation plant (the eelgrassZostera marina) is approximately 100–200 m. This distance is surprisingly more similar to that of wind‐dispersed terrestrial seeds (~10s to 100s of meters) than the passive dispersal of marine propagules via currents (~10s to 100s of kilometres). Because nearshore marine plants likeZosteraare commonly distributed across strong selective gradients driven by bathymetry (depth) even within these restricted spatial scales, seeds are capable of dispersing to novel water depths and experiencing profound shifts in light availability, temperature and wave exposure. We documented strong phenotypic variation and genome‐wide differentiation among plants separated by approximately the spatial scale of mean realised dispersal. This result suggests genetic isolation by environment in response to depth‐related environmental gradients as one plausible explanation for this pattern. The ratio of effective to census size (or Ne/Nc) approximated 0.1%, indicating that a fraction of existing plants provides the genetic variation to allow adaptation to environmental change. Our results suggest that successful conservation of seagrass meadows that can adapt to microspatial and temporal variation in environmental conditions will be low without direct and persistent intervention using large numbers of individuals or a targeted selection of genotypes. 

Intraspecific variation in host susceptibility to individual parasite species is common, yet how these effects scale to mediate the structure of diverse parasite communities in nature is less well understood. To address this knowledge gap, we tested how host genetic identity affects parasite communities on restored reefs seeded with juvenile oysters from different sources—a regional commercial hatchery or one of two wild progenitor lines. We assessed prevalence and intensity of three micro- and two macroparasite species for 4 years following restoration. Despite the spatial proximity of restored reefs, oyster source identity strongly predicted parasite community prevalence across all years, with sources varying in their relative susceptibility to different parasites. Oyster seed source also predicted reef-level parasite intensities across space and through time. Our results highlight that host intraspecific variation can shape parasite community structure in natural systems, and reinforce the importance of considering source identity and diversity in restoration design. 

Abstract Nutrient enrichment impacts ecosystems globally. Population history, especially past resource environments, of numerically dominant plant species may affect their responses to subsequent changes in nutrient availability. Eutrophication can also alter plant–microbe interactions via direct effects on associated microbial communities or indirect effects on dominant species’ biomass production/allocation as a result of modified plant–soil interactions.We combined a greenhouse common garden and a field reciprocal transplant of a salt marsh foundation species (Spartina alterniflora) within a long‐term, whole‐ecosystem, nutrient‐enrichment study to determine whether enrichment affects plant production and microbial community structure differently depending on plant population history. For the greenhouse portion, we collected 20S. alternifloragenotypes—10 from an enriched creek that had received elevated nutrient inputs for 10 years and 10 from an unenriched reference creek—and reared them in a common garden for 1 year. For the field portion, we conducted a 2‐year, fully crossed reciprocal transplant experiment with two gardens each at the enriched and unenriched sites; we examined the effects of source site (i.e. population history), garden site and plant genotype.After 2 years, plants in enriched gardens had higher above‐ground biomass and altered below‐ground allocation compared to plants in unenriched gardens. However, performance also depended on plant population history: plants from the enriched site had decreased above‐ground and rhizome production compared to plants from the unenriched site, most notably in unenriched gardens. In addition, almost all above‐ and below‐ground traits varied depending on plant genotypic identity.Effects of nutrient enrichment on the associated microbial community were also pronounced. Following 1 year in common garden, microbial community structure varied by plant population history andS. alternifloragenotypic identity. However, at the end of the reciprocal transplant, microbial communities differed primarily between enriched and unenriched gardens.Synthesis. Nutrient enrichment can impact plant foundation species and associated soil microbes in the short term. Most importantly, nutrient enrichment can also have long‐lasting effects on plant populations and associated microbial communities that potentially compromise their ability to respond to changing resource conditions in the future. 

The global distribution of primary production and consumption by humans (fisheries) is well-documented, but we have no map linking the central ecological process of consumption within food webs to temperature and other ecological drivers. Using standardized assays that span 105° of latitude on four continents, we show that rates of bait consumption by generalist predators in shallow marine ecosystems are tightly linked to both temperature and the composition of consumer assemblages. Unexpectedly, rates of consumption peaked at midlatitudes (25 to 35°) in both Northern and Southern Hemispheres across both seagrass and unvegetated sediment habitats. This pattern contrasts with terrestrial systems, where biotic interactions reportedly weaken away from the equator, but it parallels an emerging pattern of a subtropical peak in marine biodiversity. The higher consumption at midlatitudes was closely related to the type of consumers present, which explained rates of consumption better than consumer density, biomass, species diversity, or habitat. Indeed, the apparent effect of temperature on consumption was mostly driven by temperature-associated turnover in consumer community composition. Our findings reinforce the key influence of climate warming on altered species composition and highlight its implications for the functioning of Earth’s ecosystems.