Ecosystem structure in disturbed and restored subtropical seagrass meadows

Authors

Amanda Bourque, Florida International UniversityFollow

Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Biology

First Advisor's Name

James Fourqurean

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

Judson Kenworthy

Third Advisor's Name

Rebecca Vega-Thurber

Fourth Advisor's Name

Craig Layman

Fifth Advisor's Name

Jennifer Rehage

Keywords

disturbance, restoration, recovery, sediments, macroalgae, infauna, microbial diversity, herbivory, blue carbon, Biscayne National Park

Date of Defense

11-7-2012

Abstract

Shallow seagrass ecosystems frequently experience physical disturbance from vessel groundings. Specific restoration methods that modify physical, chemical, and biological aspects of disturbances are used to accelerate recovery. This study evaluated loss and recovery of ecosystem structure in disturbed seagrass meadows through plant and soil properties used as proxies for primary and secondary production, habitat quality, benthic metabolism, remineralization, and nutrient storage and exchange. The efficacy of common seagrass restoration techniques in accelerating recovery was also assessed.

Beyond removal of macrophyte biomass, disturbance to seagrass sediments resulted in loss of organic matter and stored nutrients, and altered microbial and infaunal communities. Evidence of the effectiveness of restoration actions was variable. Fill placement prevented additional erosion, but the resulting sediment matrix had different physical properties, low organic matter content and nutrient pools, reduced benthic metabolism, and less primary and secondary production relative to the undisturbed ecosystem. Fertilization was effective in increasing nitrogen and phosphorus availability in the sediments, but concurrent enhancement of seagrass production was not detected. Seagrass herbivores removed substantial seagrass biomass via direct grazing, suggesting that leaf loss to seagrass herbivores is a spatially variable but critically important determinant of seagrass transplanting success.

Convergence of plant and sediment response variables with levels in undisturbed seagrass meadows was not detected via natural recovery of disturbed sites, or through filling and fertilizing restoration sites. However, several indicators of ecosystem development related to primary production and nutrient accumulation suggest that early stages of ecosystem development have begun at these sites. This research suggests that vessel grounding disturbances in seagrass ecosystems create more complex and persistent resource losses than previously understood by resource managers. While the mechanics of implementing common seagrass restoration actions have been successfully developed by the restoration community, expectations of consistent or rapid recovery trajectories following restoration remain elusive.

Identifier

FI12120601

Recommended Citation

Bourque, Amanda, "Ecosystem structure in disturbed and restored subtropical seagrass meadows" (2012). FIU Electronic Theses and Dissertations. 792.
https://digitalcommons.fiu.edu/etd/792