2002 Progress Report: Fisheries-induced changes in the structure and function of shallow water "nursery habitats": an experimental assessment

EPA Grant Number: R827072C009
Subproject: this is subproject number 009 , 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: Fisheries-induced changes in the structure and function of shallow water "nursery habitats": an experimental assessment
Investigators: Heck, Kenneth L. , Cowan, James H. , DeVries, Dennis R , Valentine, John F.
Institution: University of South Alabama
EPA Project Officer: Packard, Benjamin H
Project Period: October 1, 1999 through September 30, 2000
Project Period Covered by this Report: October 1, 2001 through September 30, 2002
RFA: Alabama Center For Estuarine Studies (ACES) (1999) RFA Text |  Recipients Lists
Research Category: Ecological Restoration , Targeted Research


Nutrient enrichment and overfishing are two of the most common man-induced perturbations of coastal systems. Eutrophication can produce many undesirable effects in coastal systems, including: (1) a decline in submerged aquatic vegetation (SAV) through increased light attenuation and algal overgrowth; and (2) a reduction in primary and secondary production (including commercially important finfish and shellfish that rely on SAV as a "nursery" ground) in near-coastal waters. Losses of top predators in SAV-dominated systems in both freshwater and marine ecosystems could indirectly lead to the disappearance of SAV, similar to the decline associated with eutrophication. Overfishing can reduce the population of large predators, allowing for an increase in the number of smaller predators. Increasing the number of smaller predators can lead to a decrease in the number of mesograzers, which in turn, may cause an increase in the number of epiphytes. Shading by an increased epiphyte population may ultimately cause a loss in seagrass biomass. Consideration of the degree of top-down susceptibility to cascading trophic effects for both freshwater and marine ecosystems is necessary to understand the consequences of overfishing. Important differences in ecosystem responses are to be expected among riverine, estuarine, marine, and freshwater ponds and lakes, because cumulative effects likely are to be more profound in small, "closed" systems and less important in large, "open" systems.

It also has been suggested that marine communities, with many omnivorous taxa and high levels of food-web redundancy, may be less susceptible than simpler fresh water communities. This "top-down" alternative to the "bottom-up" nutrient enrichment hypothesis may explain reductions in SAV biomass in heavily fished areas, but to date remains inadequately tested. We sought to remedy this by conducting field experiments over a multiyear period. The objectives of this research project are to: (1) develop a mechanistic understanding of the indirect effects resulting from overharvesting large predators in two different but common types of SAV-dominated aquatic ecosystems; (2) evaluate the degree to which “openness” influences the susceptibility to top-down effects; and (3) evaluate the degree to which “omnivory” influences the susceptibility to top-down effects.

Progress Summary:

We completed the final year of our 3-year study that examined how the degree of openness and the degree of omnivory affected our study systems’ susceptibility to trophic cascades caused by overfishing. We studied two systems: (1) a freshwater/oligohaline environment in the Mobile Bay Delta; and (2) a mesohaline environment at Big Lagoon in the Perdido Bay system. Preliminary results from both study systems provided little evidence supporting the proposed trophic cascade. Having increased the density of small predators within our enclosures to simulate the effects of overfishing, we expected a decrease in mesograzer abundance; however, we detected no significant changes or consistent trends in mesograzer abundance. We also did not see any significant changes or consistent trends in epiphyte abundance or seagrass biomass within our enclosures. Therefore, the degree of openness and the degree of omnivory did not seem to play a significant role in systems, such as these, which contain complex food webs and many alternative prey items. These results suggest that systems with reticulate food webs might not be susceptible to trophic cascades caused by overfishing.

Future Activities:

Future activities are to complete data analysis and synthesis. In addition, the project's final report will be written and submitted along with the raw data and metadata.

Supplemental Keywords:

top-down control, trophic cascades, submerged aquatic vegetation, SAV, eutrophication, mesograzers, Gulf Coast, finfish, shellfish, primary and secondary production, light attenuation, algal overgrowth, overharvesting large predators, top-down effects ecosystem, ecosystem protection, ecology, ecological effects, ecological indicators, water, 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, Water, ECOSYSTEMS, Ecosystem Protection/Environmental Exposure & Risk, Ecology, Aquatic Ecosystems & Estuarine Research, estuarine research, Ecosystem/Assessment/Indicators, Ecosystem Protection, Restoration, Aquatic Ecosystem, Ecological Effects - Environmental Exposure & Risk, Aquatic Ecosystems, Ecological Monitoring, Ecology and Ecosystems, Ecological Risk Assessment, Aquatic Ecosystem Restoration, Ecological Indicators, coastal ecosystem, eutrophication, nursery habitats, water use, estuaries, watersheds, fish, nutrients, biomass, fisheries, aquatic plants, algal blooms, submerged aquatic vegetation, ecosystem, environmental indicators, estuarine waters, water quality, human modifications

Relevant Websites:

http://www.southalabama.edu/aces/ Exit
http://www.disl.org/~faculty/kheck.html Exit
http://www.disl.org/~faculty/jvalentine.html Exit
http://www.auburn.edu/~devridr/index.html Exit

Progress and Final Reports:

Original Abstract
  • 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