Toxicity and availability of copper and zinc to queen conch: Implications for larval recruitment in the Florida Keys

The presence of heavy metals and other pollutants is detrimental to marine ecosystems. The queen conch, once an important fisheries species in the Florida Keys, has not sufficiently recovered after a 25-year fishery closure. Research has shown high levels of copper and zinc in the gonads and digestive glands of adult conch found in the nearshore waters. Four sites relevant to queen conch larval recruitment were tested in 2010 for the presence of copper and zinc in the water, phytoplankton, sediment, and seagrass epiphytes over seven months. Both metals were detected in all sample types and no seasonal or geographical differences were detected. Surface water concentrations from the field were used to conduct acute and chronic toxicity tests on various ages of queen conch larvae and their phytoplankton food source. When zinc concentrations (0--40 microg/L) similar to those measured in situ were used, there was no significant impact on conch larval survival although some velar lobe development was impaired. However, field concentrations of copper (0--15 microg/L), which often surpassed water quality standards, negatively impacted growth, survival, and development of the larvae. Chronic exposure to copper, through the water and food, disrupted the metamorphic success of competent larvae and decreased post-metamorphosis survival. Exposure to copper at later life stages increased mortality, suggesting that heavy metals have a negative effect on larval recruitment in localized areas of the Florida Keys. Structural equation modeling revealed that copper and zinc are moving through the systems differently and are best represented by two different models. The Florida Keys National Marine Sanctuary, NOAA's Office of National Marine Sanctuaries, and the Environmental Protection Agency will be able to use this data to better understand the extent of copper and zinc contamination in the Florida Keys and its effect on an important invertebrate species. It is suggested that long-term sampling of metals be incorporated into the already established water quality monitoring programs. Further research on the synergistic behavior of heavy metals with other marine pollutants should be examined to determine the long term effect on juvenile conch growth and development.