How freshwater trees respond to salt stress:implications for management

Estuarine wetlands are increasingly being affected by saltwater intrusion, caused mainly by climate change and human alteration of estuaries. As saltwater reaches these areas, it can lead to vegetation mortality with cascading negative effects on the whole system. To help mangers safeguard estuarine wetlands we need to understand how saltwater (and its interaction with other factors) impacts vegetation. We tested the response of three common wetland trees (willow Salix alba, alder Alnus glutinosa, and elderberry Sambucus nigra) to temporary and continuous saltwater stress under different tidal regimes. These freshwater species were remarkably resistant to saltwater: two months were required to see the effects of salinity and only continuous high salinity were detrimental for the plants. Rather than completely exclude saltwater from wetlands, increasing species diversity and reducing the time plants are exposed to saltwater might provide a cost-effective method to improve wetland resilience in a saline future

Patterning in mussel beds explained by the interplay of multi-level selection and spatial self-organization

Cooperation, ubiquitous in nature, is difficult to explain from an evolutionary perspective. Many modeling studies strive to resolve this challenge, but their simplifying assumptions on population and interaction structure are rarely met in ecological settings. Here we use a modeling approach that includes more ecological detail to investigate evolution of cooperation in spatially self-organized mussel beds. Mussels cooperate with each other through aggregative movement and attachment using byssal threads. These cooperative behaviors shape the spatial structure of the mussel bed, which can range from scattered distributions to labyrinth-like patterns and dense mussel clumps. The spatial pattern in turn impacts an individual’s fitness at two levels: (i) proper attachment to neighboring individuals decreases predation risk, and (ii) attachment to a sufficiently large group prevents dislodgement by wave stress. Without this second level of selection, our simulations do typically not result in evolutionary attractors that lead to the labyrinth-like spatial patterns that are characteristic for natural mussel beds. Yet, when group-level selection is included, labyrinth-like patterns emerge under a wide range of conditions. Our model demonstrates that multiple selection factors working at different spatial scales – predation of individuals and dislodgement of entire mussel clumps – combinedly determine evolution of cooperative traits in mussels and thereby result in emergence of the labyrinth-like spatial patterns that we observe in natural mussel beds

Algal-Induced Biogeomorphic Feedbacks Lay the Groundwork for Coastal Wetland Development

Ecosystem establishment under adverse geophysical conditions is often studied within the “windows of opportunity” framework, identifying disturbance-free periods (e.g., calm wave climate) where species can overcome establishment thresholds. However, the role of biogeophysical interactions in this framework is less well understood. The establishment of saltmarsh vegetation on tidal flats, for example, is limited by abiotic factors such as hydrodynamics, sediment stability and drainage. On tidal flats, raised sediment ridges colonized by algal mats (Vaucheria sp.) appear to accomodate high densities of plant seedlings. Such ridges were previously found to have higher sediment strength than substratum without algae. Here, we investigate whether these measurements can be explained by geophysical factors only, or that biological (Vaucheria-induced) processes influence tidal marsh establishment by forming stabilized bedforms. We performed two experiments under controlled mesocosm conditions, to test the hypotheses that (a) Vaucheria grows better on elevated topographic relief, that (b) the binding force of their algal filaments increases sediment strength, and that (c) Vaucheria consequently creates elevated topographic relief that further facilitates algal growth. Our experimental results confirm the existence of this algal-induced biogeomorphic feedback cycle. These findings imply that benthic algae like Vaucheria may contribute significantly to tidal marsh formation by creating elevated and stabilized substratum. This suggests biogeophysical feedbacks can “widen” the windows of opportunity for further ecosystem establishment. Our results could be useful for the design of managed realignment projects aimed at restoring the unique ecosystem services of coastal wetlands, such as habitat biodiversity, carbon sequestration potential and nature-based flood defense

Spatial self-organization as a new perspective on cold-water coral mound development

Cold-water corals build extensive reefs on the seafloor that are oases of biodiversity, biomass, and organic matter processing rates. The reefs baffle sediments, and when coral growth and sedimentation outweigh ambient sedimentation, carbonate mounds of tens to hundreds of meters high and several kilometers wide can form. Because coral mounds form over ten-thousands of years, their development process remains elusive. While several environmental factors influence mound development, the mounds also have a major impact on their environment. This feedback between environment and mounds, and how this drives mound development is the focus of this paper. Based on the similarity of spatial coral mound patterns and patterns in self-organized ecosystems, we provide a new perspective on coral mound development. In accordance with the theory of self-organization through scale-dependent feedbacks, we first elicit the processes that are known to affect mound development, and might cause scale-dependent feedbacks. Then we demonstrate this concept with model output from a study on the Logachev area, SW Rockall Trough margin. Spatial patterns in mound provinces are the result of a complex set of interacting processes. Spatial self-organization provides a framework in which to place and compare these processes, so as to assess if and how they contribute to pattern formation in coral mounds

Evasion of tipping in complex systems through spatial pattern formation

The concept of tipping points and critical transitions helps inform our understanding of the catastrophic effects that global change may have on ecosystems, Earth system components, and the whole Earth system. The search for early warning indicators is ongoing, and spatial self-organization has been interpreted as one such signal. Here, we review how spatial self-organization can aid complex systems to evade tipping points and can therefore be a signal of resilience instead. Evading tipping points through various pathways of spatial pattern formation may be relevant for many ecosystems and Earth system components that hitherto have been identified as tipping prone, including for the entire Earth system. We propose a systematic analysis that may reveal the broad range of conditions under which tipping is evaded and resilience emerges

Ecosystem engineering by large grazers enhances carbon stocks in a tidal salt marsh

Grazers can have a large impact on ecosystem processes and are known to change vegetation composition. However, knowledge of how the long-term presence of grazers affects soil carbon sequestration is limited. In this study, we estimated total accumulated organic carbon in soils of a back-barrier salt marsh and determined how this is affected by long-term grazing by both small and large grazers in relation to age of the ecosystem. In young marshes, where small grazers predominate, hare and geese have a limited effect on total accumulated organic carbon. In older, mature marshes, where large grazers predominate, cattle substantially enhanced carbon content in the marsh soil. We ascribe this to a shift in biomass distribution in the local vegetation towards the roots in combination with trampling effects on the soil chemistry. These large grazers thus act as ecosystem engineers: their known effect on soil compaction (based on a previous study) enhances anoxic conditions in the marsh soil, thereby reducing the oxygen available for organic carbon decomposition by the local microbial community. This study showed that the indirect effects of grazing can significantly enhance soil carbon storage through changing soil abiotic conditions. This process should be taken into account when estimating the role of ecosystems in reducing carbon dioxide concentration in the atmosphere. Ultimately, we propose a testable conceptual framework that includes 3 pathways by which grazers can alter carbon storage: (1) through above-ground biomass removal, (2) through alteration of biomass distribution towards the roots and/or (3) by changing soil abiotic conditions that affect decomposition.</p

Mussel seed is highly plastic to settling conditions:The influence of waves versus tidal emergence

Phenotypic plasticity is important for organisms to adjust to a new environment.Therefore, the transplantation success of an organism to a new environment can be increased with knowledge of its capacity for phenotypic plasticity in different life stages, and the phenotypic adjustments it needs to make in specific environmental situations. Both the capacity for phenotypic plasticity and the necessary phenotypic adjustments for transplantation were tested in a mesocosm experiment using blue mussels Mytilus edulis as a model organism. This study tested (1) to what extent mussel seed coming from collectors in the water column are still capable of adjusting their phenotype, and (2) whether exposure to air or wave action is more important as a driver of phenotypic adjustments for mussels living in intertidal conditions. We found that musselseed had a high capacity for phenotypic plasticity, and were capable of adjusting their morphology to accommodate different intertidal hydrodynamic conditions. Exposure to air influenced the shell shape, condition, byssal attachment strength and aggregation behaviour, but exposure to waves played the most important role in determining the phenotype of mussels. Wave-exposedmussels grew bigger, rounder, had thicker shells and a stronger byssal attachment strength than mussels exposed to either calm tidal or calm submerged environments. This knowledge is important for selecting a suitable source population and transplantation location