2002 Progress Report: Food Web Interactions, Spatial Subsidies and the Flow of Energy Between the Mobile Bay Delta and Offshore Waters: A SGER Proposal to the Alabama Center for Estuarine Studies

EPA Grant Number: R827072C036
Subproject: this is subproject number 036 , established and managed by the Center Director under grant R827072
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: Alabama Center For Estuarine Studies (ACES)
Center Director: Shipp, Robert L.
Title: Food Web Interactions, Spatial Subsidies and the Flow of Energy Between the Mobile Bay Delta and Offshore Waters: A SGER Proposal to the Alabama Center for Estuarine Studies
Investigators: Valentine, John F. , Cowan, James H. , Sherman, Timothy
Institution: University of South Alabama
EPA Project Officer: Packard, Benjamin H
Project Period: April 1, 2001 through March 31, 2003
Project Period Covered by this Report: April 1, 2001 through March 31, 2002
RFA: Alabama Center For Estuarine Studies (ACES) (1999) RFA Text |  Recipients Lists
Research Category: Targeted Research

Objective:

The goal of the project is to develop a new proposal designed to assess the importance of cross-habitat linkages and spatial subsidies in determining the productivity of coastal food webs in the northern Gulf of Mexico.

In the review of our initial proposal, the Scientific Advisory Committee (SAC) identified two key issues that must be addressed before a larger proposal could be funded. The issues involved the need to: (1) identify a control site(s) that could be used to assess the impacts of the causeway on food web linkages between Alabama's offshore waters and higher order consumers found in the Mobile Bay Delta (MBD); and (2) provide evidence that stable isotope analyses could identify the sources of energy at the base of the MBD food web. Through this Small Grant for Exploratory Research, we sought to address the SAC concerns and collect the preliminary data required to more fully develop our initial proposal.

The specific objectives of this research project are to: (1) determine if estuarine-dependent prey were subsidizing the diets of higher order freshwater consumers, and show that isotopes would be useful tools to assess the strength of this linkage; and (2) demonstrate that isotopic signatures within the tissues of freshwater consumers would vary with estuarine-dependent prey density.

Progress Summary:

Objective 1

The first objective was to determine if estuarine-dependent prey were subsidizing the diets of higher order freshwater consumers, and to show the SAC that isotopes would be useful tools to assess the strength of this linkage. We concluded that an ideal control site would have a hydrological barricade that would prevent higher order freshwater consumers from encountering estuarine-dependent prey. As such, we hypothesized that the City of Mobile's water reservoir (Big Creek Lake) might serve as an appropriate control site for a future study. Big Creek Lake is located within Mobile County. This freshwater impoundment supports the same consumer species found within the MBD. To document this, we collected multiple consumer and prey species.

Objective 2

To demonstrate that isotopic signatures within the tissues of freshwater consumers would vary with estuarine-dependent prey density, some 44 higher order consumers (including largemouth bass, hybrid striped bass, gars, pike, and bluegill) were collected at our control site in April 2001. An additional 154 fishes were collected throughout the lower MBD. Of these, some 24 individuals from Big Creek Lake and 77 from MBD were processed for carbon and nitrogen isotopes. These data have been received and are in the process of analysis (see below for two examples of our findings to date). Published reports of fish diets, plus our previous field observations, indicated that there might be important seasonal shifts in the significance of marine prey subsidies. As a result, a second sampling was conducted in September 2001. In this effort, more than 200 fishes were collected and processed for analyses. The carbon data have been received from the September collections and we anticipate that the nitrogen analyses will be completed by the end of May 2002. Now, we have all of the nitrogen analyses on hand and are completing the stomach content analyses from these fishes. We are comparing and contrasting the isotopic signatures of these fishes with those of likely sources of energy at the base of each food web. We have identified a number of new basal sources that we will need to collect this coming summer.

Expected Results and Our Findings to Date

We hypothesized that there would be important differences in the isotopic signatures of the same species of consumers collected from MBD Big Creek Lake. Also, we hypothesized that there would be important seasonal shifts in the significance of estuarine-dependent prey in freshwater consumer diets. Based on our initial analyses, we find support for both hypotheses. We have found, using two-way ANOVA, that there were highly significant differences (p<0.003) in the carbon signatures, between seasons and locations, of large mouth bass (Micropterus salmoides). Post-hoc, pairwise comparisons of sites found that carbon signatures of fishes collected from our control site (Big Creek Lake) varied significantly from all other sites. There were no differences among signatures at collection sites throughout the Delta. This indicates that the carbon signatures of this higher order consumer shift with season and that these differences are probably related to increasing abundances of estuarine-dependent prey in the diets of these fishes in the MBD in September.

Omnivores seem to be similarly affected by the degree of openness in their surrounding environment. Similar analyses of bluegills (Lepomis macrochirus) found no significant effect of season on the carbon signature. Location, however, did have a highly significant effect on their carbon signatures. As with the findings from the largemouth bass comparison, bluegill signatures varied greatly between the control site and the MBD, further indicating an important role for cross habitat exchange of production in open ecosystems in the MBD.

Future Activities:

We plan to complete the analyses of these data by the end of August. Based on the information we currently have on hand, we believe that our new and improved experimental design will allow us to produce a scientifically justifiable, expanded ACES proposal for the 2003 funding cycle.

Supplemental Keywords:

cross-habitat linkages, productivity, coastal food webs, food web linkages, Mobile Bay Delta, MBD, estuarine-dependent prey, carbon isotopes, nitrogen isotopes, large mouth bass, Micropterus salmoides, bluegills, Lepomis macrochirus, hybrid striped bass, gars, pike, ecosystem, ecosystem protection, ecology, ecological effects, ecological indicators, environmental exposure, geographic area, water, water use, aquatic ecosystem, coastal ecosystem, coastal environments, estuary, estuaries, estuarine research, estuarine waters, environmental chemistry, chemistry, risk, assessment, indicators, Alabama, AL, Region 4, human modifications, fishery sampling., RFA, Scientific Discipline, Geographic Area, Water, Ecosystem Protection/Environmental Exposure & Risk, Ecology, Aquatic Ecosystems & Estuarine Research, estuarine research, Restoration, Aquatic Ecosystem, Ecology and Ecosystems, Aquatic Ecosystem Restoration, Gulf of Mexico, coastal ecosystem, river discharge, trophic levels, Mobile Bay, estuaries, watersheds, nutrients, biomass, food web interactions, aquatic ecosystems, environmental indicators, estuarine waters

Relevant Websites:

http://www.southalabama.edu/aces/ Exit

Progress and Final Reports:

Original Abstract
  • 2001
  • Final

  • Main Center Abstract and Reports:

    R827072    Alabama Center For Estuarine Studies (ACES)

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R827072C001 Fluorescent Whitening Agents As Facile Pollution Markers In Shellfishing Waters
    R827072C002 Red Snapper Demographics on Artificial Reefs: The Effect of Nearest-Neighbor Dynamics
    R827072C003 Stabilization of Eroding Shorelines in Estuarine Wave Eliminates with Constructed Fringe Wetlands Incorporating Offshore Breakwaters
    R827072C004 Interaction Between Water Column Structure and Reproduction in Jellyfish Populations Of Mobile Bay (SGER)
    R827072C005 Effects of Variation in River Discharge and Wind-Driven Resuspension on Higher Trophic Levels in the Mobile Bay Ecosystem
    R827072C006 Results of Zooplankton Component
    R827072C007 Benthic Study Component
    R827072C008 A Preliminary Survey of Macroalgal and Aquatic Plant Distribution in the Mobile Tensaw Delta
    R827072C009 Fisheries-induced changes in the structure and function of shallow water "nursery habitats": an experimental assessment
    R827072C010 Effects Of Variation in River Discharge and Wind-Driven Resuspension on Lower Trophic Levels of the Mobile Bay Ecosystem
    R827072C011 Evaluation of Alabama Estuaries as Developmental Habitat for Juvenile Sea Turtles
    R827072C012 Effects of Salinity Stress on Natural and Anthropogenically-Derived Bacteria in Estuarine Environments
    R827072C013 The Role of Land-Use/Land-Cover and Sub-estuarine Ecosystem Nitrogen Cycling in the Regulation of Nitrogen Delivery to a River Dominated Estuary; Mobile Bay, Alabama
    R827072C014 Environmental Attitudes of Alabama Coastal Residents: Public Opinion Polls and Environmental Policy
    R827072C015 Synthesis and Characterization of an Electrochemical Peptide Nucleic Acid Probe
    R827072C016 Determinants of Small-Scale Variation in the Abundance of the Blue Crab Callinectes Sapidus
    R827072C017 Effects of Estrogen Pollution on the Reproductive Fitness of the Gulf Pipefish, Syngnathus scovelli
    R827072C019 A Model for Genetic Diversity Aquatic Insects of the Mobile/Tensaw River Delta
    R827072C020 Evaluating Trophic Processes as Indicators of Anthropogenic Eutrophication in Coastal Ecosystems: An Exploratory Analysis
    R827072C021 Effects of Anthropogenic Eutrophication on the Magnitude and Trophic Fate of Microphytobenthic Production in Estuaries
    R827072C022 Characteristics of Ship Waves and Wind Waves in Mobile Bay
    R827072C023 Methods Comparison Between Stripping Voltammetry and Plasma Emission Spectroscopy for Metals in Mobile Bay
    R827072C024 Changes in Water Conditions and Sedimentation Rates Associated With Construction of the Mobile Bay Causeway
    R827072C025 Cold-Induced Hibernation of Marine Vibrios in the Gulf of Mexico: A Study of Cell-Cell Communication and Dormancy in Vibrio vulnificus
    R827072C026 Holocene Sedimentary History of Weeks Bay, AL: Human and Natural Impacts on Deposition in a Gulf Coast Estuary
    R827072C027 Shelter Bottlenecks and Self-Regulation in Blue Crab Populations: Assessing the Roles of Nursery Habitats and Juvenile Interactions for Shelter Dependent Organisms
    R827072C028 Predicting Seagrass Survival in Nutrient Enriched Waters: Toward a New View of an Existing Paradigm
    R827072C029 DMSP and its Role as an Antioxidant in the Salt Marsh Macrophyte Spartina alterniflora
    R827072C030 A Preliminary Survey of Aerial and Ground-Dwelling Insects of the Mobile/Tensaw Delta
    R827072C031 Natural Biogeochemical Tags of Striped Mullet, Mugil cephalus, Estuarine Nursery Areas in the North Central Gulf of Mexico
    R827072C032 Resolution of Sedimentation Rates in Impacted Coastal Environments Using 137Cs and 210Pb Markers: Dog River and Fowl River Embayments
    R827072C033 Investigation of the Use of Pulse Amplitude Modulated (PAM) Fluorometry as an Indicator of Submerged Aquatic Vegetation Health in Mobile Bay
    R827072C034 Influence of Invasive Plant Species in Determining Diversity of Aquatic Vegetation in the Mobile-Tensaw Delta
    R827072C035 The Influence of Shallow Water Hydrodynamics on the Importance of Seagrass Detritus in Estuarine Food Webs
    R827072C036 Food Web Interactions, Spatial Subsidies and the Flow of Energy Between the Mobile Bay Delta and Offshore Waters: A SGER Proposal to the Alabama Center for Estuarine Studies
    R830651C001 Meteorological Modeling of Hurricanes and Coastal Interactions: A Stability Study For Vertical Pressure Levels
    R830651C002 Characterization of Glycoprotein Cues Used by the Parasitic Rhizocephalan Barnacle Loxothylacus texanus To Identify Its Blue Crab Host, Callinectes sapidus
    R830651C003 Survey of Diamondback Terrapin Populations in Alabama Estuaries
    R830651C004 An Assessment of Environmental Contaminant Levels in Water and Dragonfly Larvae Tissues from the Mobile/Tensaw Delta