Ecological Impacts of Open-Ocean Aquaculture: Evaluating Bottom-Up Disturbances on Food Webs Using Stable Isotope Analyses

EPA Grant Number: F07E20875
Title: Ecological Impacts of Open-Ocean Aquaculture: Evaluating Bottom-Up Disturbances on Food Webs Using Stable Isotope Analyses
Investigators: Lin, David T.
Institution: University of Hawaii at Manoa
EPA Project Officer: Packard, Benjamin H
Project Period: January 1, 2007 through January 1, 2010
RFA: STAR Graduate Fellowships (2007) RFA Text |  Recipients Lists
Research Category: Fellowship - Aquatic Ecology and Ecosystems , Academic Fellowships , Fellowship - Marine Community Ecology


The relative role of bottom-up effects in controlling food web structure is a central question in community ecology. This question is also particularly pertinent in assessing the ecological impacts of recent open-ocean aquaculture ventures. The objective of this research project is two-fold: (1) to determine how marine benthic food webs change in response to bottom-up disturbances such as nutrient enrichment, and (2) to evaluate any ecological impacts from open-ocean aquaculture. The findings of this research would not only be important for advancing ecological theory, but also in immediate and direct applications in developing sustainable aquaculture and effective environmental regulations.


The focus of this research project will be a marine soft-sediment community situated below an open-ocean aquaculture farm off the south shore of O‘ahu, Hawai‘i. This infaunal food web is largely detritus-based and is expected to respond to any nutrient additions from the overlying fish cages (presumably fish feces and feed pellets). Food web structure and food chain length will be characterized through stable isotope methods. Abundances of the natural, non-radioactive isotopes 13C and 15N can be quantified in different species and used to trace biogeochemical pathways and trophic interactions within food webs. Marine fish aquaculture provides a specific source of nutrient enrichment in the form of fish feces and feed wastes, creating a situation ideal for isotopic tracing studies. A stable isotope approach also allows for identification of the dominant nutrient source to the benthic food web. This finding could help fish farmers improve their operations and minimize any ecological impacts to promote sustainability in the aquaculture industry.

Expected Results:

It is expected that impacted communities will display shifts in food web structure and changes in specific trophic interactions relative to communities at control sites. For example, these impacted sites may develop nutrient-enriched seagrasses and epiphytic macroalgae (lower C:N ratio and elevated δ15N) resulting in increased plant palatability and herbivory within the food web. A similar effect is expected with benthic detritus enriched with biodeposited fish farm wastes.

Project Synopsis

The relative importance of resources (bottom-up) and predators (top-down) to a given food web is a controversial question in ecology. Open-ocean aquaculture (fish farming) is also a controversial topic as a potential economic boon and as possible source of bottom-up nutrient pollution to the ocean floor. This project will study the role of bottom-up effects on food webs and evaluate any ecological impacts of open-ocean aquaculture. Findings from this project may not only advance ecological theory, but also progress aquaculture towards economic and environmental sustainability.

Supplemental Keywords:

bottom-up, top-down, benthic ecology, open-ocean aquaculture, nutrient enrichment, stable isotopes, food web, polychaete, soft-sediment, detritus, seagrass,

Progress and Final Reports:

  • 2007
  • 2008
  • Final