Chesapeake Ecotox Research Program: Research

This research project is guided by four major hypotheses:

Sub-lethal levels of contaminants alter the size-structure in estuarine populations.
Sub-lethal levels of contaminants reduce the reproductive fitness of organisms by altering (a) time to first reproduction, (b) fecundity or (c) offspring quality of estuarine organisms.
Sub-lethal levels of contaminants reduce the population growth rate of estuarine organisms.
Sub-lethal levels of contaminants alter the distribution or behavior of estuarine organisms.

Because commercially important species of fish and shellfish are rarely amenable to experimental approaches on the chronic effects of heavy metals and organic compounds, surrogate species that have been widely studied will serve to represent different ecological types. Experiments will be run in mesocosms – containerized habitats designed to simulate particular aquatic habitats – while contaminated sediments for these experiments will come from Baltimore Harbor, the Elizabeth River and the Anacostia River, all identified by the Chesapeake Bay Program as "regions of concern." Sediments in the three regions exhibit high levels of contaminants and give evidence of impacts on fish and bottom-dwelling organisms.

A fundamental management question is whether contaminants in sediments are permanently removed from the ecosystem or whether they are reinjected into the aquatic food web. Reinjection can occur through natural processes (e.g., storm-induced resuspension, bioturbation) or human activities such as dredging and prop wash. In determining organism exposure and bioaccumulation, the study will quantify the factors that control the rates of contaminant transport from historically-contaminated sediments into bottom-dwelling (benthic) organisms.

: Figure 1. Nested view of biological organization at individual level with emergent factors affecting organism/population coupling.

A key feature of CERP will be in linking the effects of contaminant exposure across several levels of biological organization, for instance, from the subcellular to the organism to the population. Figure 1 is a schematic diagram in which effects at one biological level are related to the next higher level. In principle, molecular and cellular alterations resulting from contaminant exposure are diagnostic and can be used to predict the effect on organisms.

Toxicological effects at the organism level can have ecological significance. To establish such relationships, researchers will focus on the effects of contaminants at the molecular and cellular level as well as at the whole organism - these effects should have ecological relevance, such as mortality, growth and reproduction. Researchers will conduct experiments using biomarkers from Leptocheirus plumulosis and Fundulus species and will assess physiological and behavioral responses. The outcome of these experiments will be important in developing models that account for effects of contaminants at the population level.