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Reestablishment of trophic interactions in restored coastal wetlands: the relative importance of top-down and bottom-up forces in structuring Cerithidea californica (Gastropoda) abundance

  • Author(s): Armitage, Anna R
  • et al.
Abstract

The few remaining coastal wetlands in California are heavily impacted by development, pollution, and eutrophication. Habitat restoration is an increasingly important method for preserving wetland species, but whether reestablishment of plant infrastructure results in recovery of habitat functions remains unknown. I propose to use an experimental approach to investigate the functional recovery of wetlands. Specifically, I will examine the effects of top-down (predation) and bottom-up (food availability) forces on a common gastropod (Cerithidea californica) in southern California coastal wetlands.

This study will consist of three series of experiments performed in natural and restored wetland sites. First, I will investigate the effects of bottom up forces on C. californica abundance, growth, and reproductive output. In caged mudflat enclosures I will alter food availability (by increasing benthic microalgal density through nutrient addition) and snail abundance. I will repeat this experiment seasonally, as the nature of the snail microalgae interaction is likely to change through the year. Second, I will use exclosure cages to examine the top down effects of predation by shorebirds and crabs on lower trophic levels, particularly on C. californica juveniles. These experiments will be timed to correspond with seasonal peaks in predator abundance. Third, based on the results of the previous studies, I will manipulate both food availability and predation to evaluate the combined effects of top down and bottom up forces on C. californica. This synthesis study will simulate trophic interactions that occur in a wetland community, and will enable functional comparisons between natural and restored wetlands.

This unique experimental field approach will allow direct comparison between natural and restored sites, providing valuable insight into whether restoration projects that nominally fill mitigation criteria are truly functioning wetlands. This understanding will contribute to the development of mitigation goals that include functional criteria and will allow functional assessment of restoration success.

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