The goal of this research was to determine the contaminant loads in the strictly-piscivorous black skimmer (Rynchops niger) in the South San Diego Bay Unit of the San Diego Bay National Wildlife Refuge. Specifically, we tested for a broader range and number of contaminants to determine if traditional targeted analyses had gaps in their detection of potent species and ecosystem threats.
The San Diego Bay hosts the largest western colony of black skimmers, with approximately 350 breeding pairs. Yet, while colony size has held steady and even increased over the years, reproductive output has remained relatively low. Initial studies both locally and nationally have provided evidence that black skimmers accumulate contaminants in higher amounts than conspecifics. Furthermore, as fish specialists, skimmers may be at an increased risk of bioaccumulative effects.
Increased anthropogenic disturbance in and around the San Diego Bay has led to large accumulations of contaminated urban runoff. Persistent organic pollutants—including organohalogen compounds, DDT, and flame-retardants—are known to bioaccumulate, causing reproductive impairments and detrimental effects to birds and other wildlife.
Working in collaboration with Dr. Eunha Hoh at SDSU’s Graduate School of Public Health, this study combined contaminant analysis with stable isotope analysis to link contaminant concentrations with diet composition. We also analyzed non-targeted compounds, which are compounds that are not typically monitored. Our purpose was to determine if any other substances, either naturally-occurring HNPs (halogenated natural products) or man-made, represent a potential threat to skimmers and other wildlife dependent on the bay.
Our findings and recommendations
Through a nontargeted analytical approach, we were able to identify 27 novel contaminants that were previously unreported or unknown. We recommend the use of the nontargeted analytical approach that we employed to improve our knowledge of contaminant occurrence and of environmental risk for species and ecosystems.
Why this research matters
With only ten percent of historical marshes in California remaining, the functional integrity of these areas is essential in supporting resident species. San Diego Bay’s coastline is extensively developed with only the southern portion of the Bay retaining remnants of natural estuarine habitat.
One of the biggest concerns for the preservation of the Bay and natural resources more broadly is the ability to determine whether an ecosystem is healthy and functioning properly. Using seabirds as indicators of ecosystem health by evaluating heavy metal pollutants in black skimmer eggs, we were able to identify novel contaminants and recommend the use of a novel nontargeted analytical approach that we developed to improve our knowledge of contaminant occurrence and of environmental risk for species and ecosystems.
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