BAFFIN BAY PESTICIDE LOADING
Texas’s Coastal Bend bays are treasured ecosystems, vital to wildlife and the regional economy. Unfortunately, water quality in the upper Laguna Madre (ULM), particularly Baffin Bay, has declined in recent years resulting in algal blooms, dead zones and fish kills. Several drivers of these ecosystem problems are under study by Drs. Mike Wetz (water quality monitoring) and Jennifer Pollack (surveys of benthic organisms) at Texas A&M Corpus Christi. However, local stakeholders are increasingly concerned about an important yet unaddressed parameter in these efforts: agricultural pesticide loading and accumulation in Baffin Bay sediments, where the main food source for black drum (Pogonias cromis), the dwarf surf clam (Mulinia lateralis), lives.
The ULM black drum fishery has struggled in recent years. Historically, the ULM accounted for 64% of all annual black drum landings in Texas, but these numbers dropped to 44% in 2012.1 This decline is tied to black drum catches in Baffin Bay, which once supplied 63 to 75% of black drum landings in the ULM, but these catch rates dropped to 55 and 46% in 2011 and 2012. Black drum production by body weight also dropped 33% in the bay, and the fish caught looked emaciated and produced “jelly-like fillets,” forcing fishermen to discard ~40% of their catch. Additionally, Texas Parks and Wildlife found that 15% of fish were underweight and linked these issues to declines in their main food source, the dwarf surf clam.
The dwarf surf clam is found at salinities ranging from 5 to 80 ppt, allowing it to thrive in the highly variable salinities of Baffin Bay (mean 36.5). However, salinities sometimes reach 90 ppt in Baffin Bay, exceeding the upper limit for the dwarf surf clam and inducing stress and/or mortality. A second and potentially compounding stressor facing the dwarf surf clam in Baffin Bay is the accumulation of pesticides in its sedimentary habitat.
Concentrations of pesticides in Baffin Bay sediments were last analyzed in the early 2000’s, but only for legacy compounds banned several decades ago. Unknown are the sediment concentrations of current-use compounds, which can be toxic to benthic organisms. The lone survey of “modern” pesticides (USGS 1996-1998) only examined aqueous concentrations. In that survey, 21 compounds were detected in runoff from a small area of the watershed, with loadings >300 lbs for atrazine and diuron in 1997. These two compounds are soluble, but many pesticides are hydrophobic and rapidly partition to sediment, evading detection in water. Thus, previously measured aqueous samples likely underestimated pesticide loading, particularly to bay sediment. Hence, Baffin Bay dwarf surf clams are routinely exposed to unknown pesticides at potentially toxic levels. Pesticide exposure, coupled with stress caused by poor water quality, may have adverse synergistic effects on dwarf surf clam survival. A recent study found that poor water quality increased pesticide toxicity resulting in higher mortality for larval clams. The combination of pesticides, salinity stress and excess nutrients may decrease dwarf surf clam survival as well as that of higher trophic level organisms that depend on them as a staple food source.
While Drs. Wetz and Pollack are addressing many water quality and food resource issues in Baffin Bay, pesticide loading is still a missing key component. The PI will collaborate with Wetz, Pollack and volunteers to integrate pesticide sampling into their existing routines. Samples collected will be analyzed for concentrations of legacy and current-use pesticides in Baffin Bay water, sediment and dwarf surf clam tissues. This research will quantify loading and accumulation of pesticides in Baffin Bay and assess their impacts on the dwarf surf clam and subsequently the economically important black drum. Ultimately, this research will provide a critical parameter needed to fully assess water pollution impacts on the ecosystem health of Baffin Bay.