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GCE IV - Key Finding in 2020

    The role of megafauna in salt marsh ecosystems

    Feral hogs are known to cause disturbances in salt marshes, negatively affecting Spartina growth and recovery via activities such as rooting, trampling and wallowing (Sharp and Angelini 2019). In a new study, Hensel et al. (in revision) documented that they also consume mussels, based on the presence of mussel shells in hog fecal material. Previously, Angelini et al. (2016) had demonstrated that there is a mutualism between Spartina and mussels in which Spartina patches associated with mussels are more resilient to drought because mussels enhance water storage and reduce soil stress. In order to understand how hogs affected this relationship, Hensel et al. (in review A) did an experimental manipulation that crossed hog exclusion with mussel additions in patchy areas that were recovering from drought. In treatments where hogs were excluded, Spartina patches recovered 40% faster than in controls over three years. As expected, plant densities increased even more when mussels were added due to their positive effect on Spartina. When hogs were present, however, the effect of adding the mussels switched, such that plants in these treatments did worse than those affected by the hogs alone (Fig. 3). This was likely due to foraging activities, as the hogs destroy both plants and crab burrows while consuming mussels. In a separate study, Hensel et al. (in review B) found that the presence of hogs in a brackish marsh increased plant diversity, decreased plant cover, and changed the identity of the spatially dominant plant to a species that was competitively inferior. Both of these studies show that the presence of wild hogs can change the outcome of interactions among important marsh species. In addition to improving our understanding of the ecological role of megafauna in coastal marshes, this work is relevant to management because densities of exotic hogs in the southeastern US have approximately doubled since the 1980s (Hensel et al, in review A). These papers, along with ongoing research by GCE scientists and colleagues on the impacts of horse grazing in coastal marshes, build on our previous studies of alligators as megafaunal predators in salt marshes. As a group, they illustrate that the GCE study area supports a suite of large-bodied consumers that can have strong effects on marsh structure and function. In general, however, both the historical and current role of megafauna in salt marshes is poorly understood, as highlighted in a recent meta-analysis (Gaskins et al. 2020).


    Fig. 3 Interactions between Spartina and mussels are positive when hogs are excluded (A), and negative when they are present (B). Photo in (C) depicts feral hogs in the salt marsh. Photo credit: Brandon Messick. Adapted from Hensel et al., in review A.


This material is based upon work supported by the National Science Foundation under grants OCE-9982133, OCE-0620959, OCE-1237140 and OCE-1832178. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.