Fiddler crabs facilitate Spartina alterniflora growth, mitigating periwinkle overgrazing of marsh habitat

Abstract

Ecologists have long been interested in identifying and testing factors that drive top-down or bottom-up regulation of communities. Most studies have focused on factors that directly exert top-down (e.g., grazing) or bottom-up (e.g., nutrient availability) control on primary production. For example, recent studies in salt marshes have demonstrated that fronts of Littoraria irrorata periwinkles can overgraze Spartina alterniflora and convert marsh to mudflat. The importance of indirect, bottom-up effects, particularly facilitation, in enhancing primary production has also recently been explored. Previous field studies separately revealed that fiddler crabs, which burrow to depths of more than 30 cm, can oxygenate marsh sediments and redistribute nutrients, thereby relieving the stress of anoxia and enhancing S. alterniflora growth. However, to our knowledge, no studies to date have explored how nontrophic facilitators can mediate top-down effects (i.e., grazing) on primary-producer biomass. We conducted a field study testing whether fiddler crabs can facilitate S. alterniflora growth sufficiently to mitigate overgrazing by periwinkles and thus sustain S. alterniflora marsh. As inferred from contrasts to experimental plots lacking periwinkles and fiddler crabs, periwinkles alone exerted top-down control of total aboveground biomass and net growth of S. alterniflora. When fiddler crabs were included, they counteracted the effects of periwinkles on net S. alterniflora growth. Sediment oxygen levels were greater and S. alterniflora belowground biomass was lower where fiddler crabs were present, implying that fiddler crab burrowing enhanced S. alterniflora growth. Consequently, in the stressful interior S. alterniflora marsh, where subsurface soil anoxia is widespread, fiddler crab facilitation can mitigate top-down control by periwinkles and can limit and possibly prevent loss of biogenically structured marsh habitat and its ecosystem services.

Classic paradigms in a novel environment: inserting food web and productivity lessons from rocky shores and saltmarshes into biogenic reef restoration

“…Top‐down effects also profoundly affect rocky intertidal food webs and can interact with abiotic stressors to impact saltmarsh communities (Paine ; Gittman & Keller ). Our observational data lead us to hypothesize that predation by crustaceans and gastropods likely played a significant role in generating differences among depth treatments (Johnson & Smee ; Fig.…”

The Importance and Benefits of Species

“…In 1985, research showed that burrows created by fiddler crabs (Uca pugnax) increased soil drainage, soil oxidation-reduction potential (that Helps promote beverage sales and to raise awareness for the conservation of tiger quolls [72] is, tendency to acquire electrons; a common measure of water quality), and belowground decomposition of plant debris, which in turn led to significant increases to the primary productivity of the saltmarshes (Figure 1) [27]. Recently, fiddler crabs have proven to be so effective at promoting saltmarsh growth that they alone can compensate for herbivory from marsh periwinkles (Littoraria irrorata) that would otherwise demolish the habitat [28]. Fiddler crabs are also now known to dramatically increase leaf production, trunk diameter and height of mangrove trees, providing a substantial boost to their ecosystem services [29,30].…”

Microplastic Distribution at Different Sediment Depths in an Urban Estuary

“…Benthos is an important feeding environment for many marine species (Anderson and Lovvorn, 2008;MacDonald et al, 2012;Gittman and Keller, 2013) and a recent study has shown marine benthic species ingest microplastics (Courtene-Jones et al, 2017). Knowledge of the harmful effects of microplastics on benthic marine species and communities is growing (Green, 2016;Galloway et al, 2017), however, little is known of past microplastic accumulation in benthic environments.…”