Crabs Mediate Interactions between Native and Invasive Salt Marsh Plants: A Mesocosm Study

Abstract

Soil disturbance has been widely recognized as an important factor influencing the structure and dynamics of plant communities. Although soil reworkers were shown to increase habitat complexity and raise the risk of plant invasion, their role in regulating the interactions between native and invasive species remains unclear. We proposed that crab activities, via improving soil nitrogen availability, may indirectly affect the interactions between invasive Spartina alterniflora and native Phragmites australis and Scirpus mariqueter in salt marsh ecosystems. We conducted a two-year mesocosm experiment consisting of five species combinations, i.e., monocultures of three species and pair-wise mixtures of invasive and native species, with crabs being either present or absent for each combination. We found that crabs could mitigate soil nitrogen depletion in the mesocosm over the two years. Plant performance of all species, at both the ramet-level (height and biomass per ramet) and plot-level (density, total above- and belowground biomass), were promoted by crab activities. These plants responded to crab disturbance primarily by clonal propagation, as plot-level performance was more sensitive to crabs than ramet-level. Moreover, crab activities altered the competition between Spartina and native plants in favor of the former, since Spartina was more promoted than native plants by crab activities. Our results suggested that crab activities may increase the competition ability of Spartina over native Phragmites and Scirpus through alleviating soil nitrogen limitation.

Temperature impact on the influence of penguin‐derived nutrients and mosses on non‐native grass in a simulated polar ecosystem

“…The overall aim of this study was to better understand how mosses affect the success of non‐native plants in polar regions. The data obtained clearly support the hypothesis that penguins may potentially act as invasion engineers through their manuring activity on land which can benefit the growth of non‐native plants, similar to animal‐activity effects on plant growth reported at lower latitudes (Farji‐Brener et al, 2010 ; Zhang et al, 2013 ). However, this nitrogen effect was limited by temperature and there were large differences between moss species on grass seed germination, growth and nitrogen pathways.…”

“…However, the current study used Antarctic substrate with nitrogen content that is naturally present in the field. Penguins and other marine vertebrates, such as seals, that transfer large amounts of nutrients from the ocean to land in Antarctica (Bokhorst et al, 2019;Lindeboom, 1984) may act as invasion engineers in synergy with climate warming for non-native plants, similar to ant and crab activity reported elsewhere (Farji-Brener et al, 2010;Zhang et al, 2013). Sites of animal activity that affect soil nutrient availability may therefore present some of the best opportunities for non-native plants to establish and require particular attention with respect to environmental protection and biosecurity measures.…”

Harnessing Positive Species Interactions to Enhance Coastal Wetland Restoration

“…For example, sponges on mangrove roots provide nitrogen to and receive carbon from mangroves, which promotes the growth of both species (Ellison et al, 1996). Similarly, mutualistic mussels can augment Spartina success and resilience after disturbance by reducing sulfide and nutrient stress (Derksen-Hooijberg et al, 2018) and marsh crabs can slow soil nitrogen depletion, promoting the growth of marsh plants (Zhang et al, 2013). Although less visually apparent, FIGURE 1 | Examples of positive interactions in salt-marsh ecosystems.…”

Can a Single Species Challenge Paradigms of Salt Marsh Functioning?

“…Then, the study of SW Atlantic salt marshes could provide valuable information to better incorporate herbivory and bioturbation into current models or paradigms about how salt marshes work. This is essential because SW Atlantic salt marshes are likely not unique, given that several marshes along East Asia and Oceania, as well as Northeast USA, are inhabited by similar burrowing crabs (see for example, Holdredge et al 2009;Wang et al 2010;Needham et al 2010;Zhang et al 2013).…”