Research

Effects of Hypoxia on Fish Communities and Fisheries

Nutrient inputs to coastal ecosystems provide an external subsidy at the base of marine and estuarine food webs that enhances the productivity of fish and other upper trophic levels. However, nutrient over-enrichment, or the stimulation of primary productivity to harmful levels by the anthropogenic addition of nutrients, can lead to low dissolved oxygen, also known as hypoxia, that can have negative effects on growth, survival, and reproduction. Because the world's major fisheries often occur in regions with high nutrient levels, the balance between nutrient-enhanced productivity and hypoxia-induced habitat degradation can have important ecological, economic, and social implications.

There has been a decadal doubling in the reported frequency of hypoxic zones around the world since the 1960s, indicating that many coastal ecosystems are experiencing nutrient over-enrichment. While it is well-documented that direct exposure to low oxygen leads to decreased growth and survival, particularly in sessile species, most fishes and mobile invertebrates are able to behaviorally avoid hypoxia by moving to alternative habitats. This behavioral avoidance alters spatial distributions, however, and may have indirect effects on vital rates such as growth, survival, and reproduction. Though such indirect effects have been hypothesized as a primary means by which hypoxia influences population and community dynamics, the linkages among behavioral avoidance, associated shifts in spatial distribution, and attendant consequences for population vital rates are not well known. We are currently involved in multiple projects addressing various aspects of how hypoxia influences fish and fisheries via both direct and indirect mechanisms. Understanding and quantifying these effects is important for efforts to development nutrient reduction strategies in coastal watersheds.

CURRENT PROJECTS

The Ecological and economic effects of hypoxia on harvested ecosystems (NOAA Center for Sponsored Coastal Ocean Research). This project is investigating how nutrient enrichment and hypoxia in estuarine and nearshore shelf ecosystems influence commercial fisheries, particular shrimp trawl fisheries, in southeast US estuaries and on the northern Gulf of Mexico continental shelf (Collaborators: L. Crowder, M. Smith, Duke University; J. Nance NOAA National Marine Fisheries Service).

Reproductive effects of hypoxia in the northern Gulf of Mexico (NOAA Center for Sponsored Coastal Ocean Research). This project is investigating the reproductive effects of hypoxia on the population dynamics of Atlantic croaker in the Gulf of Mexico using a combination of field surveys, laboratory experiments, and simulation modeling. Collaborators: P. Thomas, University of Texas; K. Rose, Louisiana State University).