Abstract
Restoration projects provide a valuable opportunity to experimentally establish foundational habitats in different combinations to test relative effects on community assembly. We evaluated the development of macroinvertebrate communities in response to planting of eelgrass (Zostera marina) and construction of reefs intended to support the Olympia oyster (Ostrea lurida) in the San Francisco Estuary. Plots of each type, alone or interspersed, were established in 2012 in a pilot living shorelines project, and quarterly invertebrate monitoring was conducted for one year prior to restoration, and three years post-restoration using suction sampling and eelgrass shoot collection. Suction sampling revealed that within one year, oyster reefs supported unique invertebrate assemblages as compared to pre-restoration conditions and controls (unmanipulated mudflat). The eelgrass invertebrate assemblage also shifted, becoming intermediate between reefs and controls. Interspersing both types of habitat structure led eelgrass invertebrate communities to more closely resemble those of oyster reefs alone, though the eelgrass assemblage maintained some distinction (primarily by supporting gammarid and caprellid amphipods). Eelgrass shoot collection documented some additional taxa known to benefit eelgrass growth through consumption of epiphytic algae; however, even after three years, restored eelgrass did not establish an assemblage equivalent to natural beds, as the eelgrass sea hare (Phyllaplysia taylori) and eelgrass isopod (Pentidotea resecata) remained absent or very rare. We conclude that the restoration of two structurally complex habitat types within tens of meters maximized the variety of invertebrate assemblages supported, but that close interspersion dampened the separately contributed distinctiveness. In addition, management intervention may be needed to overcome the recruitment limitation of species with important roles in maintaining eelgrass habitat.
Highlights
The study of habitat structure includes assessing the impacts of biotic and abiotic arrangements on ecological patterns and processes [1,2]
The degree of habitat complexity is often determined by foundation species, which provide the physical structure on which other species depend
We hypothesized that oyster reefs and eelgrass would attract different assemblages of taxa and that restoring the two together would maximize invertebrate taxa diversity due to the additive design
Summary
The study of habitat structure includes assessing the impacts of biotic and abiotic arrangements on ecological patterns and processes [1,2]. The degree of habitat complexity is often determined by foundation species, which provide the physical structure on which other species depend. Foundation species engineer their environment by strongly influencing the availability of resources to other organisms through habitat creation, modification, or maintenance [7]. The loss of these organisms can, have heavy consequences for entire ecosystems, including associated biota [8]
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