Grantee Research Project Results

Nutrients & Benthic Invasion Dynamics

EPA Grant Number: F07E21150
Title: Nutrients & Benthic Invasion Dynamics
Investigators: Weiskel, Heidi W.
Institution: University of California - Davis
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 - Ecology , Fellowship - Aquatic Ecology and Ecosystems , Academic Fellowships

Objective:

Nutrients and invasive species represent two of the most significant threats to estuarine systems worldwide. This project is designed to investigate how these threats interact, by examining the effects of nutrients on invasion success and competitive interactions. Specifically, it asks whether nutrient additions confer an advantage on an invasive snail species in a benthic soft sediment west coast estuary (San Francisco Bay) and how species interactions change over time. The project addresses the following questions: 1) Do nutrients influence invasion success in a benthic marine habitat?, and 2) How do competitive interactions between native and invasive species shift over time and in the presence of nutrients?

Approach:

NUTRIENTS & AQUATIC INVASION SUCCESS. This experiment employs a factorial design to quantify the impact of elevated nutrients on resource utilization and determine whether the addition of nutrients changes growth rates or reproductive activity for either the native mud snail Cerithidea californica or the native mud snail Ilyanassa obsoleta. Factors for the experiment include 2 nutrient levels, 2 snail species, and 6 snail densities, plus appropriate controls. Response variables include a suite of sediment characteristics, as well as snail growth and fecundity. Specifically, measures will include infaunal community composition, oxygen levels in the sediment (REDOX potential), carbon-nitrogen ratios, and changes in the benthic microalgal community. Growth of individually marked snails, egg cases, and size-specific snail mortality will also be recorded. Results will be analyzed using appropriate statistical methods.

SHIFTS IN COMPETITIVE INTERACTIONS OVER TIME. This study is composed of a series of behavioral trials between I. obsoleta and C. californica from multiple populations under simulated low- and high-tide conditions. Isolated containers that allow snails to interact in a constant light-temperature environment that is similar to summer conditions—when both species are most actively grazing and interacting—are used. First, an inventory for typical behavioral responses will be developed. Second, different populations of each species (both naïve and sympatric) will be tested for these responses under differing nutrient conditions. This experiment will lend insight into whether prior exposure confers an advantage to either species in historically negative native-invasive interactions, and whether nutrients change these interactions.

Expected Results:

Results from this collection of experiments will serve to inform how pollution impacts ecosystems and how marine species can be affected by excessive nutrient levels. Nutrient loading and invasive species are unlikely to disappear as threats to estuarine systems but a greater understanding of their interactions and effects on native species can facilitate better protection for native species and the habitats on which they depend. As human development pressure mounts along the coast, studies that connect pollution and ecosystem health are increasingly important, as are studies that deepen our understanding of the relationship between pollution and species interactions. This dissertation aims to do both.

Supplemental Keywords:

Invasive species, nutrients, marine gastropods, competitive interactions, benthic invertebrates, estuarine habitats, eutrophication,

Progress and Final Reports:

2007

2008

Final