Grantee Research Project Results

Shifting Baselines? The Ecological Implications of Simultaneous Eutrophication and Overfishing

EPA Grant Number: FP917087
Title: Shifting Baselines? The Ecological Implications of Simultaneous Eutrophication and Overfishing
Investigators: Allgeier, Jacob Edward
Institution: University of Georgia
EPA Project Officer: Packard, Benjamin H
Project Period: August 1, 2010 through July 31, 2013
Project Amount: $111,000
RFA: STAR Graduate Fellowships (2010) RFA Text |  Recipients Lists
Research Category: Fellowship - Ecosystem Services: Aquatic Systems Ecology , Academic Fellowships

Objective:

Overfishing and human-derived nutrient pollution affect the supply of growth-limiting nutrients (nitrogen and phosphorus) for algae and seagrasses, the base of most marine ecosystems. Human inputs increase the supply of nutrients, which are largely sewage-derived, while overfishing has been shown to reduce nutrient supply because fish provide substantial inputs of nutrients via excretion. These contrasting inputs present the paradox that human-derived nutrients may supplant fish-derived nutrients. However, human-derived nutrients are higher in phosphorus relative to fish-derived nutrients, shifting the baseline at which nutrients are supplied and potentially altering the diversity and growth rates of algae and seagrass species.

Synopsis:

Overfishing and nutrient pollution affect the supply of growth-limiting nutrients for algae and seagrasses, the base of most marine ecosystems. Human inputs increase the supply of nutrients, while overfishing can reduce nutrient supply because fish provide inputs of nutrients via excretion. We test the hypothesis that human-derived nutrients can supplant fish-derived nutrients by simulating both of these scenarios independently and simultaneously using artificial patch reef habitats.

Approach:

Overfishing and nutrient enrichment will be simulated independently and simultaneously on experimental patch-reef ecosystems in the Bahamas by manipulating the community structure of fishes on the reef, and through the use of commercial fertilizing compounds, respectively. The implications for changes in diversity, growth, and nutrient limitation of algae and seagrass species will be measured through the use of benthic surveys, examination of seagrass nutrient content, and nutrient limitation assays for benthic algae.

Expected Results:

We predict that changes in nutrient supply rates will alter the seagrass community by favoring species that are typically less dominant but have a greater affinity for these baseline nutrient conditions. We also predict substantial shifts in benthic algae nutrient limitation, whereby nutrient limitation will decrease with increased perturbation (i.e., simultaneous overfishing and nutrient enrichment).

Potential to Further Environmental/Human Health Protection:

Subtropical and tropical marine ecosystems have evolved to function under extremely low nutrient conditions, making them particularly susceptible to even minor alterations in nutrient dynamics. The enormous services provided by these ecosystems appear to critically hinge on the amount and relative supply of nitrogen and phosphorus, yet understanding of the effects of simultaneous overfishing and eutrophication for these services is lacking, particularly in the Caribbean. Increased understanding of nutrient effects is critical to the management and conservation of marine ecosystems globally.

Supplemental Keywords:

coastal ecosystems, enrichment, interaction, nitrogen, nutrient, phosphorus, patch reefs,

Progress and Final Reports:

2011

2012

Final