Climate change is generating extreme climate events, affecting ecosystem integrity and function directly through increases in abiotic stress and disturbance and indirectly through changes in the ...strength of biotic interactions. As consumers play an essential role in ecosystem functioning and have been shown to be highly sensitive to climate conditions, improved understanding of their role under changing environmental conditions is necessary to accurately anticipate climate change impacts on ecosystem integrity.
We evaluated if prolonged periods of extreme rain, a climatic event increasing in severity in many places around the world, and coincident increases in coastal flooding duration intensify consumer control of foundational salt marsh grass structure and quantify the consequences of flooding–consumer interactions on salt marsh range extent. To achieve this, we analysed: historic trends in crab grazing; crab numbers and activity in and out of rainy years on the low marsh edge; vegetation retreat from the low marsh edge at a plot scale in a manipulative exclosure experiment; vegetation retreat at a landscape‐scale from drone image analyses; and the vertical erosion in the lowest edge of an Argentinean salt marsh.
During flooded periods, crabs congregated in the low marsh, resulting in localized overgrazing of salt marsh grass and the rapid horizontal retreat of the marsh edge (98.5 cm on average). Salt marsh edge retreat resulted in a loss of ~4.5% of the total marsh area at the landscape scale. Inside crab exclusion plots, although grass cover declined slightly during the study period, the marsh edge did not retreat.
Synthesis. This study provides experimental evidence that an extreme climate event can destabilize a local consumer–prey interaction, indirectly triggering the range contraction of a critical coastal habitat. This work contributes to a growing body of research demonstrating that consumers can be unleashed, rather than suppressed, by extreme climatic events. Moreover, in cases where consumer fronts form during such events, the result can be not only local (along habitat edges) but also landscape‐scale extinction of foundation species and the habitats they biogenically create. Together, this supports the general idea that models of future climate scenarios integrate the indirect effects on ecosystem‐regulating food web interactions.
Resumen
El cambio climático está generando fenómenos climáticos extremos que afectan a la integridad y el funcionamiento de los ecosistemas directamente a través del aumento del estrés abiótico y los disturbios, e indirectamente a través de los cambios en la fuerza de las interacciones bióticas. Dado que los consumidores desempeñan un papel esencial en el funcionamiento de los ecosistemas, y se ha demostrado que son muy sensibles a las condiciones climáticas, es necesario mejorar la comprensión de su papel en condiciones ambientales cambiantes para anticipar con precisión los impactos del cambio climático en la integridad de los ecosistemas.
Aquí evaluamos si inundaciones más prolongadas provocadas por precipitaciones extremas, un fenómeno que se está dando en muchos lugares del mundo, intensifican el control de los consumidores sobre las plantas fundacionales de marismas afectando al funcionamiento de estos sistemas. Para ello, analizamos: (i) las tendencias históricas de precipitaciones y herbivoría de cangrejos; (ii) el número y la actividad de los cangrejos antes y durante años lluviosos en el borde de la marisma baja; (iii) el retroceso de la vegetación en el límite inferior de la marisma baja a escala de parcela en un experimento de exclusión de cangrejos; (iv) el retroceso de la vegetación a escala de paisaje a partir del análisis de imágenes tomadas con drones; y (v) la erosión vertical en el límite inferior de una marisma argentina.
Durante los periodos de inundación asociados a precipitaciones extremas, los cangrejos se congregaron en la marisma baja, lo que provocó un sobreconsumo de la vegetación y una rápida retracción de su límite inferior de distribución (98,5 cm en promedio). Este retroceso resultó en una pérdida de ~4,5% de la superficie total de la marisma a escala del paisaje. Dentro de las parcelas de exclusión de cangrejos, aunque la cobertura de plantas disminuyó ligeramente durante el periodo de estudio, el límite de distribución no se vio afectado.
Síntesis. Este estudio proporciona pruebas experimentales de que un evento climático extremo puede desestabilizar una interacción consumidor‐presa, desencadenando indirectamente la retracción del rango de un hábitat costero crítico. Este trabajo contribuye a un creciente cuerpo de investigación que demuestra que los consumidores pueden ser liberados, en lugar de suprimidos, por eventos climáticos extremos. Además, en los casos en los que se forman frentes de consumo durante esos fenómenos, el resultado puede ser no sólo locales (a escala de parche), sino también a escala de paisaje. En conjunto, esto apoya la idea más general de que los modelos de escenarios climáticos futuros necesitan incorporar los efectos directos e indirectos de las interacciones tróficas que regulan los ecosistemas.
Extremely atypical rainfall promotes longer flooding periods in salt marshes. This concentrates crab feeding activity in the low salt marsh edge, and propagates upwards, leading to die‐off vegetation zones and the retreat of the lower edge of salt marsh vegetation. Vegetation loss potentially accelerates shoreline vertical erosion, ultimately affecting the delivery of ecosystem services (i.e. shoreline protection and C accumulation).
It has recently been proposed that many communities are structured by a hierarchy of interactions in which facilitation by foundation species is of primary importance. We conducted the first explicit ...experimental test of this hypothesis by investigating the organization of positive interactions on New England cobblestone beaches. In this midintertidal community, wave‐generated substrate instability and solar stress largely limit marine organisms to the shelter of cordgrass beds. Cordgrass, which can establish and persist without the aid of other foundation species, facilitates a dense assemblage of inhabitants (e.g., mussels, snails, seaweeds) with roots/rhizomes that stabilize substrate and a dense canopy that baffles waves and provides shade. Within the cordgrass bed community, ribbed mussels further enhance physical conditions and densities of other species (e.g., amphipods, barnacles) by providing crevice space and hard substrate. We conclude that cordgrass bed communities are hierarchically organized: secondary interactions (e.g., facilitation by ribbed mussels) play a key role within an assemblage dependent on primary facilitation by the independently successful foundation species cordgrass. Our results identify emergent indirect positive interactions in the form of facilitation cascades, have broad implications for conservation, and help unify existing models of community organization that were developed without considering the fundamental role of positive interactions.
Aim: Given its catastrophic consequences, the extinction of apex predators has long been of interest to modern ecology. Despite major declines, no presentday species of marine apex predator has yet ...become extinct. Because of their vulnerability, understanding the mechanisms leading to their extinction in the past could provide insight into the natural factors that interact with human threats to drive their loss. We studied the geographical distribution patterns of the extinct macro-predatory shark Carcharocles megalodon in order to elucidate its pathway to extinction. Location: World-wide from the Miocene to the Pliocene (c. 23-2.6 Ma). Methods: A meta-analysis of C. megalodon occurrence records was performed using the Paleobiology Database as a platform. The data were binned into geological time slices, and the circular home range around each data point was mapped in reconstructions made in GPlates. We then quantitatively assessed the species' geographical range and global abundance over time, and the relationship between distribution and climate. Results: The pathway to extinction of C. megalodon probably started in the late Miocene with a decrease in its global abundance. This decrease was then followed by a decline in its geographical range during the Pliocene. Although the extinction of C. megalodon has been attributed to climate change, we found no evidence of direct effects of global temperature. Instead, we found that the collapse in geographical distribution coincided mainly with a drop in the diversity of filter-feeding whales and the appearance of new competitors (large predatory whales and the great white shark). Main conclusions: This research represents the first study of the distributional trends of an extinct, cosmopolitan apex predator in deep-time. Our results suggest that biotic factors, and not direct temperature limitations, were probably the primary drivers of the extinction of the largest marine apex predators that ever lived.
Coral disease is becoming increasingly problematic on reefs worldwide. However, most coral disease research has focused on the abiotic drivers of disease, potentially overlooking the role of species ...interactions in disease dynamics. Coral predators in particular can influence disease by breaking through protective tissues and exposing corals to infections, vectoring diseases among corals, or serving as reservoirs for pathogens. Numerous studies have demonstrated the relationship between corallivores and disease in certain contexts, but to date there has been no comprehensive synthesis of the relationships between corallivores and disease, which hinders our understanding of coral disease dynamics. To address this void, we identified 65 studies from 26 different ecoregions that examine this predator–prey-disease relationship. Observational studies found over 20 positive correlations between disease prevalence and corallivore abundance, with just four instances documenting a negative correlation between corallivores and disease. Studies found putative pathogens in corallivore guts and experiments demonstrated the ability of corallivores to vector pathogens. Corallivores were also frequently found infesting disease margins or targeting diseased tissues, but the ecological ramifications of this behavior remains unknown. We found that the impact of corallivores was taxon-dependent, with most invertebrates increasing disease incidence, prevalence, or progression; fish showing highly context-dependent effects; and xanthid crabs decreasing disease progression. Simulated wounding caused disease in many cases, but experimental wound debridement slowed disease progression in others, which could explain contrasting findings from different taxa. The negative effects of corallivores are likely to worsen as storms intensify, macroalgal cover increases, more nutrients are added to marine systems, and water temperatures increase. As diseases continue to impact coral reefs globally, a more complete understanding of the ecological dynamics of disease—including those involving coral predators—is of paramount importance to coral reef conservation and management.
Restoration has been increasingly adopted to halt trends in coastal wetland loss globally. Existing restoration often assumes that once abiotic stress is relieved, disturbances are prevented, and ...invasive species are eradicated, coastal wetlands will recover if propagules of native species are supplied either through natural dispersal or planting. Whether other factors including consumers can help explain the often suboptimal performance of existing restoration remains poorly understood. In a series of field experiments in the Yangtze estuary, we examined the relative importance of abiotic stress and crab grazing in regulating the recovery of the native foundation plant species Scirpus mariqueter in salt marsh areas where exotic cordgrass was successfully eradicated. We found that grazing by herbivorous crabs, rather than abiotic stress, was the primary obstacle restricting the recovery of planted Scirpus. This negative effect of crab grazing varied predictably across elevation and was strongest at low elevations where abiotic conditions were positive for Scirpus. These findings highlight that i) measures to control crab grazing are needed to enhance the success of Scirpus restoration, even in areas where abiotic conditions are set to be optimal, and ii) restoration measures purely focused on reducing abiotic stress could be ineffective or suboptimal in field conditions, likely jeopardizing restoration investment and success. Since top-down control of foundation plant species is common in many coastal wetlands and can be especially important in degraded systems where herbivores are abundant, we urge that future coastal wetland restoration assesses for the impacts of grazers and, when present, apply intervention measures.
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•We investigated the recovery of native Scirpus marshes in the Yangtze estuary.•Scirpus recovery was regulated primarily by crab grazing, not abiotic stress.•The impact of crab grazing on Scirpus recovery varied with elevation.•Coastal wetland restoration needs to manage top-down factors to amplify success.
Self-organized spatial patterns occur in many terrestrial, aquatic, and marine ecosystems. Theoretical models and observational studies suggest self-organization, the formation of patterns due to ...ecological interactions, is critical for enhanced ecosystem resilience. However, experimental tests of this cross-ecosystem theory are lacking. In this study, we experimentally test the hypothesis that self-organized pattern formation improves the persistence of mussel beds (Mytilus edulis) on intertidal flats. In natural beds, mussels generate self-organized patterns at two different spatial scales: regularly spaced clusters of mussels at centimeter scale driven by behavioral aggregation and large-scale, regularly spaced bands at meter scale driven by ecological feedback mechanisms. To test for the relative importance of these two spatial scales of self-organization on mussel bed persistence, we conducted field manipulations in which we factorially constructed small-scale and/or large-scale patterns. Our results revealed that both forms of self-organization enhanced the persistence of the constructed mussel beds in comparison to nonorganized beds. Small-scale, behaviorally driven cluster patterns were found to be crucial for persistence, and thus resistance to wave disturbance, whereas large-scale, self-organized patterns facilitated reformation of small-scale patterns if mussels were dislodged. This study provides experimental evidence that self-organization can be paramount to enhancing ecosystem persistence. We conclude that ecosystems with self-organized spatial patterns are likely to benefit greatly from conservation and restoration actions that use the emergent effects of self-organization to increase ecosystem resistance to disturbance.
The global biodiversity crisis impairs the valuable benefits ecosystems provide humans. These nature-generated benefits are defined by a multitude of different ecosystem functions that operate ...simultaneously. Although several studies have simulated species loss in communities and tracked the response of single functions such as productivity or nutrient cycling, these studies have involved relatively similar taxa, and seldom are strikingly different functions examined. With the exception of highly managed ecosystems such as agricultural fields, rarely are we interested in only one function being performed well. Instead, we rely on ecosystems to deliver several different functions at the same time. Here, we experimentally investigated the extinction impacts of dominant consumers in a salt marsh. These consumers are remarkably phylogenetically diverse, spanning two kingdoms (i.e., Animalia and Fungi). Our field studies reveal that a diverse consumer assemblage significantly enhances simultaneous functioning of disparate ecosystem processes (i.e., productivity, decomposition, and infiltration). Extreme functional and phylogenetic differences among consumers underlie this relationship. Each marsh consumer affected at least one different ecosystem function, and each individual function was affected by no more than two consumers. The implications of these findings are profound: If we want ecosystems to perform many different functions well, it is not just number of species that matter. Rather, the presence of species representing markedly different ecologies and biology is also essential to maximizing multiple functions. Moreover, this work emphasizes the need to incorporate both microcomponents and macrocomponents of food webs to accurately predict biodiversity declines on integrated-ecosystem functioning.
The pervasive impact of invasive species has motivated considerable research to understand how characteristics of invaded communities, such as native species diversity, affect the establishment of ...invasive species. Efforts to identify general mechanisms that limit invasion success, however, have been frustrated by disagreement between landscape-scale observations that generally find a positive relationship between native diversity and invasibility and smaller-scale experiments that consistently reveal competitive interactions that generate the opposite relationship. Here we experimentally elucidate the mechanism explaining the large-scale positive associations between invasion success and native intertidal diversity revealed in our landscape-scale surveys of New England shorelines. Experimental manipulations revealed this large-scale pattern is driven by a facilitation cascade where ecosystem-engineering species interact nonlinearly to enhance native diversity and invasion success by alleviating thermal stress and substrate instability. Our findings reveal that large-scale diversity-invasion relationships can be explained by small-scale positive interactions that commonly occur across multiple trophic levels and functional groups. We argue that facilitation has played an important but unrecognized role in the invasion of other well studied systems, and will be of increasing importance with anticipated climate change.
The Deepwater Horizon oil spill led to the severe contamination of coastal environments in the Gulf of Mexico. A previous study detailed coastal saltmarsh erosion and recovery in a number of ...oil-impacted and nonimpacted reference sites in Barataria Bay, Louisiana over the first 18 months after the spill. Concentrations of alkanes and polyaromatic hydrocarbons (PAHs) at oil-impacted sites significantly decreased over this time period. Here, a combination of DNA, lipid, and isotopic approaches confirm that microbial biodegradation was contributing to the observed petroleum mass loss. Natural abundance 14C analysis of microbial phospholipid fatty acids (PLFA) reveals that petroleum-derived carbon was a primary carbon source for microbial communities at impacted sites several months following oil intrusion when the highest concentrations of oil were present. Also at this time, microbial community analysis suggests that community structure of all three domains has shifted with the intrusion of oil. These results suggest that Gulf of Mexico marsh sediments have considerable biodegradation potential and that natural attenuation is playing a role in impacted sites.
Although it has long been recognized that marsh plant community composition shifts across estuarine salinity gradients, the mechanisms responsible for this species zonation have never been ...experimentally examined. In southern New England marshes of the United States, we investigated the relative importance of physical and biotic factors in generating estuarine species distribution patterns. Greenhouse studies revealed that all of the common plants in this system grow better in fresh water than in full-strength salt water. To test the hypothesis that the spatial segregation of these plants is driven by differential tolerance to salt stress and plant competition, we performed transplant experiments with 10 common plants in the system. When freshwater marsh plants were transplanted to salt marshes, they did poorly and generally died with or without neighbors present. In contrast, when saltmarsh plants were transplanted to freshwater marshes, they thrived in the absence of neighbors, growing better than they did in salt marshes, but when neighbors were present, they were strongly suppressed. These results suggest that the spatial segregation of plants across estuarine salinity gradients is driven by competitively superior freshwater marsh plants displacing salt-tolerant plants to physically harsh saltmarsh habitats, whereas fresh-water marsh plants are limited from living in salt marshes by physical factors (e.g., high salinities). These results contribute to our understanding of the organization and assembly of tidal marsh plant communities and have important implications for understanding how marsh plant communities will respond to human modification of estuarine hydrology and climate change.
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