Spatial and Temporal Environmental Variation in a Eutrophic Coastal River: Impacts on Fish and Marine Mammals

EPA Grant Number: R826100
Title: Spatial and Temporal Environmental Variation in a Eutrophic Coastal River: Impacts on Fish and Marine Mammals
Investigators: Crowder, Larry B. , Read, Andrew J.
Institution: Duke University
EPA Project Officer: Hahn, Intaek
Project Period: October 20, 1997 through October 19, 2000
Project Amount: $357,262
RFA: Exploratory Research - Environmental Biology (1997) RFA Text |  Recipients Lists
Research Category: Biology/Life Sciences , Ecosystems


Human activities in estuarine watersheds have contributed to an alarming increase in nutrient loading and associated water quality declines, habitat loss and declining fisheries. Recent increases in algal blooms in the Neuse River estuary, NC have led to its designation as one of the top 20 most threatened river systems in the U.S. We will examine the distribution of fish and marine mammals in the Neuse in relation to spatial and temporal dynamics of water quality. In particular, we seek to understand the effects of episodic hypoxic or anoxic events. These events, increasing in both frequency and magnitude, impact these highly visible and economically valuable components of the estuarine food web. Mobile fish likely move out of hypoxic areas, but may become trapped if these zones expand into oxygenated refuges. Bottlenose dolphins can tolerate a wider range of water quality than fish, but their distribution is likely closely tied to that of their prey. We hypothesize that: (1) the distribution and composition of fish communities will respond to spatial and temporal changes in temperature, salinity, and the extent of hypoxia in estuarine systems; and (2) the distribution of bottlenose dolphins will respond to changes in the distribution of their prey caused by changes in water quality.


Our approach involves spatially-explicit, synoptic field sampling of water quality, fish and marine mammal distribution. Few prior studies have examined temporal and spatial dynamics of hypoxia and its relation to fish and marine mammals in estuarine systems. The extent of hypoxia in time and space are critical, however, in determining whether such perturbations have a detrimental effect on these economically important resources. We will use spatial statistics developed in landscape ecology to examine relationships between environmental variability and habitat use by fish and marine mammals. Knowledge of the physiology and behavior of individual species is insufficient to predict the impact of hypoxia on communities of fish and marine mammals. Instead, it is necessary to take a spatially explicit approach and work within the context of the entire community.

Expected Results:

We expect to observe changes in the distribution of demersal fish with the development of hypoxic zones in the Neuse River estuary. Fish will move out of hypoxic and anoxic areas, decreasing the total amount of useable habitat and possibly increasing overlap between predators and prey. The degree to which the fish community is impacted will depend on the physiological tolerances of individual species, life history characteristics, and the extent and duration of hypoxia. The decrease in available habitat for demersal fish may result in aggregations of prey patches for bottlenose dolphins. This change in prey distribution may result either in increased food availability in oxygenated refuges or in a decrease in the extent of critical summer feeding areas if the hypoxic areas are large and of long duration. Overall, we believe that this research will help us to gain a better understanding of how meso-scale environmental perturbations influence the distribution and ecology of populations of fish and marine mammals.

Publications and Presentations:

Publications have been submitted on this project: View all 3 publications for this project

Supplemental Keywords:

anoxia/hypoxia, ecological effects, estuary, habitat, fisheries, indicators, landscape ecology, nutrient loading., RFA, Scientific Discipline, Water, Ecosystem Protection/Environmental Exposure & Risk, Nutrients, Water & Watershed, Ecosystem/Assessment/Indicators, Ecosystem Protection, exploratory research environmental biology, Oceanography, Ecological Effects - Environmental Exposure & Risk, Environmental Monitoring, Ecological Risk Assessment, Ecology and Ecosystems, Ecological Indicators, Watersheds, coastal ecosystem, ecological effects, marine ecosystem, eutrophication, nutrient supply, nutrient transport, ecological exposure, food web, landscape indicator, watershed management, mammal, algal growth, fisheries, ecological assessment, anoxia/hypoxia, aquatic ecosystems, bottlenose dolphin, water quality, fish , nutrient fluxes, land use

Progress and Final Reports:

  • 1998 Progress Report
  • 1999
  • Final