Hepatotoxic Cyanobacterial Blooms in Louisiana's Estuaries: Analysis of Risk to Blue Crab (Callinectes sapidus) Following Exposure to Microcystins

Abstract

The most common toxins detected following freshwater harmful algal blooms are microcystins, a group of hepatotoxins produced by cyanobacteria (e.g., Microcystis and Anabaena spp.). Preference for filter-feeding prey, including bivalves, makes the blue crab, Callinectes sapidus, vulnerable to microcystin contamination and makes the commercially important crab a potential vector of microcystins. I used a combination of field and laboratory studies to determine blue crab vulnerability to microcystin contamination and consequent impacts on crab physiology. Samples collected from a hyper-eutrophic freshwater lake, Lac des Allemands, Louisiana, were analyzed for cyanobacterial abundances and microcystins in surface water and blue crabs using light-microscopy and enzyme-linked immunosorbent assay (ELISA). Alternating blooms of Microcystis and Anabaena spp. occurred throughout the sampling period. Highest microcystins concentration in surface water (1.42 &181;g/l) was above tolerable daily intake (TDI) guidelines set by the World Health Organization (WHO). Highest microcystin concentrations in crab tissue were 820, 65, and 105 &181;g microcystins/ kg in hepatopancreas, viscera, and muscle, respectively, which were close to or exceeding the WHO-TDI guidelines. The study demonstrated the ability of Microcystis and Anabaena blooms to produce toxins that accumulate in blue crab tissues and are possibly transferred to higher level consumers, including humans. Laboratory studies were aimed at understanding distributions and physiological effects of two microcystin congeners, microcystin-LR and -RR, in orally exposed blue crabs. Crabs administered 0, 10, 100, 500, or 1000 &181;g microcystin/kg of crab body weight of either congener were sacrificed 48-hours following exposure. Using ELISA, microcystins were detected in hepatopancreas and viscera, but not in muscle or hypodermis for both microcystin-LR and -RR exposed crabs. There was significant correlation between microcystin-LR uptake in hepatopancreas and crab weight loss after 48-hours (P<0.050). In crabs administered daily doses of 50 &181;g microcystin-RR/kg of crab body weight for 7-days, significant (P<0.050) accumulation was seen in hepatopancreas and viscera, but not in muscle, hypodermis, or gills. Lipid hydroperoxides in hepatopancreas were significantly (P<0.050) altered following exposure, indicating oxidative stress. These studies indicate that natural populations of blue crabs may be subjected to physiological stress following microcystin accumulation.