Human‐caused shifts in carbon (C) cycling and biotic exchange are defining characteristics of the Anthropocene. In marine systems, saltmarsh, seagrass, and mangrove habitats—collectively known as “blue carbon” and coastal vegetated habitats (CVHs)—are a leading sequester of global C and increasingly impacted by exotic species invasions. There is growing interest in the effect of invasion by a diverse pool of exotic species on C storage and the implications for ecosystem‐based management of these systems. In a global meta‐analysis, we synthesized data from 104 papers that provided 345 comparisons of habitat‐level response (plant and soil C storage) from paired invaded and uninvaded sites. We found an overall net effect of significantly higher C pools in invaded CVHs amounting to 40% (±16%) higher C storage than uninvaded habitat, but effects differed among types of invaders. Elevated C storage was driven by blue C‐forming plant invaders (saltmarsh grasses, seagrasses, and mangrove trees) that intensify biomass per unit area, extend and elevate coastal wetlands, and convert coastal mudflats into C‐rich vegetated habitat. Introduced animal and structurally distinct primary producers had significant negative effects on C pools, driven by herbivory, trampling, and native species displacement. The role of invasion manifested differently among habitat types, with significant C storage increases in saltmarshes, decreases in seagrass, and no significant effect in mangroves. There were also counter‐directional effects by the same species in different systems or locations, which underscores the importance of combining data mining with analyses of mean effect sizes in meta‐analyses. Our study provides a quantitative basis for understanding differential effects of invasion on blue C habitats and will inform conservation strategies that need to balance management decisions involving invasion, C storage, and a range of other marine biodiversity and habitat functions in these coastal systems.

Abstract. Recent climate warming has led to asynchronous species migrations, with major consequences for ecosystems worldwide. In woody communities, localized microclimates have the potential to create feedback mechanisms that can alter the rate of species range shifts attributed to macroclimate drivers alone. Mangrove encroachment into saltmarsh in many areas is driven by a reduction in freeze events, and this encroachment can further modify local climate, but the subsequent impacts on mangrove seedling dynamics are unknown. We monitored microclimate conditions beneath mangrove canopies and adjacent open saltmarsh at a freeze-sensitive mangrove-saltmarsh ecotone and assessed survival of experimentally transplanted mangrove seedlings. Mangrove canopies buffered night time cooling during the winter, leading to interspecific differences in freeze damage on mangrove seedlings. However, mangrove canopies also altered biotic interactions. Herbivore damage was higher under canopies, leading to greater mangrove seedling mortality beneath canopies relative to saltmarsh. While warming-induced expansion of mangroves can lead to positive microclimate feedbacks, simultaneous fluctuations in biotic drivers can also alter seedling dynamics. Thus, climate change can drive divergent feedback mechanisms through both abiotic and biotic channels, highlighting the importance of vegetation-microclimate interactions as important moderators of climate driven range shifts.

1. Climate change alters freshwater availability in many ecosystems leading to shifts in distributions for many plants. Despite living exclusively in intertidal, saline environments, mangroves rely on non-saline water to maintain plant productivity. However, several mangrove species persist in arid environments where non-saline water from rain and groundwater sources are limited. Under these conditions, foliar water uptake from fog and mist may be an important water acquisition strategy. 2. We conducted a field experiment in arid Baja California Sur, Mexico along with a controlled mist chamber experiment (using seedlings sourced from humid subtropical region, Florida, USA) to show that three co-occurring, neotropical mangrove species, Avicennia germinans, Laguncularia racemosa and Rhizophora mangle, growing in both arid and humid environments can access water condensed on their leaves. 3. Foliar water uptake was greatest in A. germinans and lowest in R. mangle, possibly reflecting leaf traits associated with species-specific water balance strategies. In our field misting experiment, the contribution of foliar water uptake was higher in A. germinans (32 ± 2%) than L. racemosa (26 ± 2%) and R. mangle (16 ± 1%). Foliar water uptake also varied across locations for L. racemosa and R. mangle, with declining uptake towards both species' northern range limits in Baja California Sur, suggesting the distribution patterns of arid-zone mangroves may be affected by species-specific spatial variation in foliar water use. Within species, foliar water use was comparable across field and controlled experiments irrespective of source population (Baja California Sur vs. Florida), suggesting foliar water uptake is not an arid-zone adaptation, and is instead used as a supplemental water balance strategy in arid and humid neotropical mangroves. 4. Synthesis. Our findings indicate mangroves have the potential to access atmospheric water, such as rain, dew and sea fog, through their leaves to offset soil water deficits. Variation in foliar water use across these three neotropical mangrove species may influence mangrove species distributions across arid-zone and pseudo-drought (highly saline) environments, with implications for mangrove response to climate change.