Spatial Variation in Mercury Accumulation in Bottlenose Dolphins (Tursiops spp.) in Southeastern U.S.A

Abstract

Bottlenose dolphins (Tursiops spp.) inhabit bays, sounds, and estuaries (BSEs) throughout the southeast region of the U.S.A. and are sentinel species for human and ecosystem-level health. Dolphins are vulnerable to the bioaccumulation of contaminants through the coastal food chain because they are high-level predators. Currently, there is limited information on the spatial dynamics of mercury accumulation in these dolphins. Total mercury (THg) was measured in dolphin skin from multiple populations across the U.S. Southeast Atlantic and Gulf of Mexico coasts, and the influence of geographic origin, sex, and age class was investigated. Mercury varied significantly among sampling sites and was greatest in dolphins in St. Joseph Bay, Florida Everglades, and Choctawhatchee Bay (14,193 ng/g ± 2196 ng/g, 10,916 ng/g ± 1532 ng/g, and 7333 ng/g ± 1405 ng/g wet mass (wm), respectively) and lowest in dolphins in Charleston and Skidaway River Estuary (509 ng/g ± 32.1 ng/g and 530 ng/g ± 58.4 ng/g wm, respectively). Spatial mercury patterns were consistent regardless of sex or age class. Bottlenose dolphin mercury exposure can effectively represent regional trends and reflect large-scale atmospheric mercury input and local biogeochemical processes. As a sentinel species, the bottlenose dolphin data presented here can direct future studies to evaluate mercury exposure to human residents in St. Joseph Bay, Choctawhatchee Bay, and Florida Coastal Everglades, as well as additional sites with similar geographical, oceanographic, or anthropogenic parameters. These data may also inform state and federal authorities that establish fish consumption advisories to determine if residents in these locales are at heightened risk for mercury toxicity.

Keywords: bottlenose dolphin; cetacean; marine mammal; sentinel species; total mercury (THg).

Figure 1

Mean mercury (ng/g, wet mass) in skin from bottlenose dolphins (Tursiops spp.) sampled along the U.S. Southeast Atlantic and Gulf of Mexico coasts. Sampling sites included Charleston (CHS) [29], Skidaway River Estuary (SRE), Sapelo Island (SAP), Brunswick (BRU), Indian River Lagoon (IRL) [29], Biscayne Bay (BBF), Florida Coastal Everglades (FCE) [28], Lower Florida Keys (LFK) [28], Sarasota Bay (SAR) [7,30], St. Joseph Bay (SJB), and Choctawhatchee Bay (CBF) The number of dolphins sampled within each site is represented as n.

Figure 2

Mean mercury ± SE (ng/g, wet mass) in skin from bottlenose dolphins (Tursiops spp.) sampled along the U.S. Southeast Atlantic and Gulf of Mexico coasts. Sampling sites included Charleston (CHS), Skidaway River Estuary (SRE), Sapelo Island (SAP), Brunswick (BRU), Indian River Lagoon (IRL), Biscayne Bay (BBF), Florida Coastal Everglades (FCE), Lower Florida Keys (LFK), Sarasota Bay (SAR), St. Joseph Bay (SJB), and Choctawhatchee Bay (CBF). The mean mercury of all dolphin individuals at each site is displayed in the top graph. Sites with different letters above the error bars are significantly different (p < 0.05) from each other.