Predicting Seagrass Survival in Nutrient Enriched Waters: Toward a New View of an Existing Paradigm

EPA Grant Number: R827072C028
Subproject: this is subproject number 028 , 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: Predicting Seagrass Survival in Nutrient Enriched Waters: Toward a New View of an Existing Paradigm
Investigators: Heck, Kenneth L. , Valentine, John F. , Spitzer, Patricia
Institution: University of South Alabama
EPA Project Officer: Packard, Benjamin H
Project Period: April 1, 2002 through March 31, 2005
RFA: Alabama Center For Estuarine Studies (ACES) (1999) RFA Text |  Recipients Lists
Research Category: Targeted Research


The objective of this research project is to test the generality of previous experimental studies, including our own, that found that consumption by small herbivores could greatly reduce the incidence of algal overgrowth in eutrophic coastal waters. We are focusing on seagrass-dominated ecosystems because they are well documented to serve as nursery habitats for a broad variety of economically valuable finfish and shellfish, and because eutrophication is strongly implicated in the disappearance of these critically important habitats in the Gulf of Mexico and the nation as a whole. We are testing the ability of different types of small grazers (both individually and collectively) to buffer the effects of eutrophication by conducting field studies at small spatial scales that will allow us to sustain elevated nutrient concentrations at levels that will mimic those of up to the most highly eutrophic of coastal waters. Therefore, we will test the degree to which different types and abundances of herbivores can explain the observed variation in algal responses to eutrophication.

Global riverine discharges of nitrogen may have as much as doubled over the past 2 centuries due in large part to the two- to threefold increase in human fixation of nitrogen since 1960. This increasing input of nutrients to the coastal ocean has been linked closely to a variety of negative impacts on biological resources. In fact, eutrophication is arguably the most serious of humankind’s impact on nearshore waters, and a variety of recent summaries document the extent of this problem. The most obvious consequences of eutrophication of the coastal ocean include: increasing occurrences of hypoxic and anoxic events; elevated frequencies and extents of harmful algal blooms, both of which are often associated with extensive fishkills; and the overgrowth of extraordinarily productive seagrass meadows and coral reefs by rapidly growing algae.

In contrast to freshwater lakes, where phosphorus is primarily responsible for the negative consequences of nutrient overenrichment, nitrogen is the nutrient that appears to cause most of the harmful effects of nutrient over-enrichment in coastal waters. This conclusion has been reached in the last 10 years, after a variety of studies in different estuaries demonstrated that nitrogen most often was the nutrient whose availability limited algal growth.

An important recent finding is that different types of herbivores can differentially affect algal abundance and species composition because of preferential feeding by different herbivore species on different algal types. The important implication of these studies is that different suites of herbivores (e.g., gastropods versus amphipods, caridean shrimp, or small herbivorous fishes) may have very different effects on the accumulation of algae in areas receiving nutrient enrichment, and that these herbivores may be primary determinants of the degree to which algal overgrowth occurs in the presence of eutrophication. Currently, however, we have inadequate knowledge to predict how adding or subtracting different types of herbivores will influence algal species composition or abundance.

To date, the few existing studies that have simultaneously evaluated the effects of nutrient enrichment and herbivory in the field (most of them referenced above) have all been restricted to intermediate-sized (1 to several square meters) field enclosures. Although one can load nutrients at high rates in such experimental plots, it is difficult to sustain water-column nutrient concentrations above the micromolar levels that are characteristic of highly eutrophic coastal waters. In addition, an important limitation of these studies, which greatly restricts their predictive power, is that none of them has tested the effects of herbivore species composition on algal responses to nutrient addition. Therefore, there is reason to question the generality of these few studies, especially because their conclusions are in conflict with the conventional wisdom that eutrophication usually results in algal overgrowth of both the water column and the benthos.

Supplemental Keywords:

eutrophication, grazer diversity, submerged aquatic vegetation, SAV, Gulf Coast, consumption, small herbivores, algal overgrowth, eutrophic coastal waters, seagrass-dominated ecosystems, nitrogen, human fixation of nitrogen, fishkill, harmful algal blooms, phosphorus, polyvinyl chloride, PVC, ecosystem, ecosystem protection, ecology, ecological effects, ecological indicators, environmental exposure, geographic area, water, aquatic ecosystem, coastal ecosystem, coastal environments, estuary, estuaries, estuarine research, estuarine waters, environmental chemistry, chemistry, risk assessment, indicators, Alabama, AL, human modifications., RFA, Scientific Discipline, Water, ECOSYSTEMS, Ecosystem Protection/Environmental Exposure & Risk, estuarine research, Aquatic Ecosystems & Estuarine Research, Ecosystem/Assessment/Indicators, Ecosystem Protection, Restoration, Aquatic Ecosystem, Aquatic Ecosystems, Terrestrial Ecosystems, Ecological Monitoring, Ecology and Ecosystems, Aquatic Ecosystem Restoration, Ecological Indicators, coastal ecosystem, eutrophication, water use, nursery habitats, estuaries, fish, watersheds, nutrients, biomass, fisheries, aquatic plants, algal blooms, submerged aquatic vegetation, ecosystem, environmental indicators, water quality, estuarine waters, human modifications, seagrass

Progress and Final Reports:

  • 2002 Progress Report
  • 2003
  • 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