Ecological structure and function of restored habitats across a range of coastal environments
Rezek, Ryan Joseph
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Coastal habitat loss represents a major threat to biodiversity and ecosystem services worldwide. Habitat restoration plays a key role in efforts to mitigate this loss by supporting the recovery of ecological communities (i.e., structure) and important ecosystem processes (i.e., functions). The objective of this dissertation was to evaluate the ability of constructed habitat restorations to support equivalent ecological communities and functions to reference habitats across a range of coastal environments. This was accomplished through an analytical framework combining community structure analysis with stable isotope based food web analysis. In Chapter I, the scale and implications of coastal degradation, the use of constructed habitats for coastal restoration, and the use of stable isotope analysis to study food webs and function are outlined. In Chapter II, the development of a constructed subtidal oyster reef in the Mission-Aransas estuary was surveyed alongside a natural oyster reef over a 5- to 29-month post-restoration timeframe to evaluate recovery. The results demonstrated structural and functional recovery occurring between 12-15 months post-restoration, as oysters and predatory consumers increasingly colonized the developing reef. In Chapter III, a constructed salt marsh was monitored alongside a natural reference marsh in Nueces Bay over a 4- to 6-year post-restoration timeframe. The results of this study demonstrated the ability of the restored marsh to support communities with similar composition as the natural marsh, however, stable isotope mixing models demonstrated that dominant macrofauna in the restored marsh consumed less organic matter originating from macrophyte production than their natural counterparts. This functional variation was attributed to the relatively low amounts of organic matter and detritus contained in the recently constructed salt marsh sediments. In Chapter IV, I examined the epibenthic community and food web structure of subsurface “Rigs-to-Reefs” artificial reefs in comparison to standing operational platforms in the Texas offshore Gulf of Mexico shelf region. Reefed platforms were found to support similar communities as standing platform habitats at similar depths (30-m), however shallow standing platform sites (5-m) were found to support communities that were distinct from deeper standing platform and clearance-limited reefed platform sites. Reefed platform and standing platforms at 5- and 30-m depths were found to support similar food web structure, indicating that reefed platforms replicate the fundamental ecological functions associated with standing platforms. Although, the loss of shallow water substrate, associated with platform reefing, could be expected to reduce the biodiversity associated with these structures. In Chapter V, I conclude with a summary of the findings in this dissertation and outline general patterns of functional recovery between different coastal habitat types that can be inferred from these results and established theory. This study provides strong evidence for the ability of constructed habitats to support similar communities as natural/pre-existing habitats across a range of coastal environments. The results suggest that constructed habitats in systems driven by microalgal producers are likely to functionally recover as community structure develops. However, functional recovery in systems driven by vascular plant production are limited by the recovery of detrital food web intermediaries. The insights obtained from this study have broad implications for coastal restoration practitioners and resource managers.