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Accelerated sea-level rise poses a significant threat to coastal habitats, such as salt marshes, which provide critical ecosystem services. Persistence of salt marshes with rising sea levels relies, in part, on vertical accretion. Ecogeomorphic models emphasize the role of plant production in vertical accretion via sediment trapping and belowground organic matter contribution. Thus, changes in plant production can influence saltmarsh persistence with sea-level rise. However, models of marsh accretion do not consider animal-mediated changes in plant production. We tested how 2 marsh crabs, Minuca pugnax and Sesarma reticulatum , which have contrasting effects (facilitation vs. herbivory) on Spartina alterniflora production, may indirectly influence sediment deposition and belowground production, through observational surveys and field manipulation. Minuca facilitated Spartina biomass in some marshes, but not sediment deposition, and had no effect on belowground organic matter contribution, suggesting that in isolation, Minuca has little indirect impact on saltmarsh geomorphic processes. Sesarma reduced Spartina biomass; however, sediment deposition increased, contrary to ecogeomorphic models, likely due to sediment resuspension by Minuca . When Minuca and Sesarma co-occur, the effect on Spartina production and sediment deposition depended on the amount of grazing. When Sesarma grazing is low, Minuca facilitates Spartina growth and mitigates the effect of grazing. However, when Sesarma grazing is high and vegetation is removed, Minuca can resuspend sediment through bioturbation, suggesting the net effect of these species may depend on their relative abundance. This study demonstrates that the effects of plant-animal interactions on marsh resilience against sea-level rise are context dependent. 

When a species colonizes a new range, it can escape enemies found in its original range. Examples of enemy escape abound for invasive species, but are rare for climate migrants, which are populations of a species that colonize a new range due to climate-driven range shifts or expansions. The fiddler crab Minuca (= Uca ) pugnax is found in the intertidal salt marshes of the US east coast. It recently expanded its range north into the Gulf of Maine as a result of ocean warming. We tested the hypothesis that M. pugnax had escaped its parasite enemies. Parasite richness and trematode intensity were lower in populations in the expanded range than in populations in the historical range, but infection prevalence did not differ. Although M. pugnax escaped most of its historical parasites when it migrated northward, it was infected with black-gill lamellae (indicative of Synophrya hypertrophica ), which was found in the historical range, and with the trematode Odhneria cf. odhneri , which was not found in the historical range. To our knowledge, this is the first time that O. cf. odhneri has been reported in fiddler crabs. These results demonstrate that although M. pugnax escaped some of its historical parasites when it expanded its range, it appears to have gained a new parasite ( O. cf. odhneri ) in the expanded range. Overall, our results demonstrate that climate migrants can escape their enemies despite colonizing habitats adjacent to their enemy-filled historical range. 

Ecosystems across the United States are changing in complex and surprising ways. Ongoing demand for critical ecosystem services requires an understanding of the populations and communities in these ecosystems in the future. This paper represents a synthesis effort of the U.S. National Science Foundation-funded Long-Term Ecological Research (LTER) network addressing the core research area of “populations and communities.” The objective of this effort was to show the importance of long-term data collection and experiments for addressing the hardest questions in scientific ecology that have significant implications for environmental policy and management. Each LTER site developed at least one compelling case study about what their site could look like in 50–100 yr as human and environmental drivers influencing specific ecosystems change. As the case studies were prepared, five themes emerged, and the studies were grouped into papers in this LTER Futures Special Feature addressing state change, connectivity, resilience, time lags, and cascading effects. This paper addresses the “connectivity” theme and has examples from the Phoenix (urban), Niwot Ridge (alpine tundra), McMurdo Dry Valleys (polar desert), Plum Island (coastal), Santa Barbara Coastal (coastal), and Jornada (arid grassland and shrubland) sites. Connectivity has multiple dimensions, ranging from multi-scalar interactions in space to complex interactions over time that govern the transport of materials and the distribution and movement of organisms. The case studies presented here range widely, showing how land-use legacies interact with climate to alter the structure and function of arid ecosystems and flows of resources and organisms in Antarctic polar desert, alpine, urban, and coastal marine ecosystems. Long-term ecological research demonstrates that connectivity can, in some circumstances, sustain valuable ecosystem functions, such as the persistence of foundation species and their associated biodiversity or, it can be an agent of state change, as when it increases wind and water erosion. Increased connectivity due to warming can also lead to species range expansions or contractions and the introduction of undesirable species. Continued long-term studies are essential for addressing the complexities of connectivity. The diversity of ecosystems within the LTER network is a strong platform for these studies.