title: Evidence for a novel marine harmful algal bloom: cyanotoxin (microcystin) transfer from land to sea otters.
abstract: "Super-blooms" of cyanobacteria that produce potent and environmentally persistent biotoxins (microcystins) are an emerging global health issue in freshwater habitats. Monitoring of the marine environment for secondary impacts has been minimal, although microcystin-contaminated freshwater is known to be entering marine ecosystems. Here we confirm deaths of marine mammals from microcystin intoxication and provide evidence implicating land-sea flow with trophic transfer through marine invertebrates as the most likely route of exposure. This hypothesis was evaluated through environmental detection of potential freshwater and marine microcystin sources, sea otter necropsy with biochemical analysis of tissues and evaluation of bioaccumulation of freshwater microcystins by marine invertebrates. Ocean discharge of freshwater microcystins was confirmed for three nutrient-impaired rivers flowing into the Monterey Bay National Marine Sanctuary, and microcystin concentrations up to 2,900 ppm (2.9 million ppb) were detected in a freshwater lake and downstream tributaries to within 1 km of the ocean. Deaths of 21 southern sea otters, a federally listed threatened species, were linked to microcystin intoxication. Finally, farmed and free-living marine clams, mussels and oysters of species that are often consumed by sea otters and humans exhibited significant biomagnification (to 107 times ambient water levels) and slow depuration of freshwater cyanotoxins, suggesting a potentially serious environmental and public health threat that extends from the lowest trophic levels of nutrient-impaired freshwater habitat to apex marine predators. Microcystin-poisoned sea otters were commonly recovered near river mouths and harbors and contaminated marine bivalves were implicated as the most likely source of this potent hepatotoxin for wild otters. This is the first report of deaths of marine mammals due to cyanotoxins and confirms the existence of a novel class of marine "harmful algal bloom" in the Pacific coastal environment; that of hepatotoxic shellfish poisoning (HSP), suggesting that animals and humans are at risk from microcystin poisoning when consuming shellfish harvested at the land-sea interface.
authors.affiliation: Marine Wildlife Veterinary Care and Research Center, California Department of Fish and Game, Office of Spill Prevention and Response, Santa Cruz, California, United States of America. mmiller@ospr.dfg.ca.gov
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Miller
authors.forename: Raphael M
authors.initials: RM
authors.lastname: Kudela
authors.forename: Abdu
authors.initials: A
authors.lastname: Mekebri
authors.forename: Dave
authors.initials: D
authors.lastname: Crane
authors.forename: Stori C
authors.initials: SC
authors.lastname: Oates
authors.forename: M Timothy
authors.initials: MT
authors.lastname: Tinker
authors.forename: Michelle
authors.initials: M
authors.lastname: Staedler
authors.forename: Woutrina A
authors.initials: WA
authors.lastname: Miller
authors.forename: Sharon
authors.initials: S
authors.lastname: Toy-Choutka
authors.forename: Clare
authors.initials: C
authors.lastname: Dominik
authors.forename: Dane
authors.initials: D
authors.lastname: Hardin
authors.forename: Gregg
authors.initials: G
authors.lastname: Langlois
authors.forename: Michael
authors.initials: M
authors.lastname: Murray
authors.forename: Kim
authors.initials: K
authors.lastname: Ward
authors.forename: David A
authors.initials: DA
authors.lastname: Jessup
mesh_terms: D000818:Animals; D001427:Bacterial Toxins / Q000032:analysis / Q000378:metabolism / Q000633:toxicity*; D000458:Cyanobacteria / Q000378:metabolism; D004784:Environmental Monitoring; D005618:Fresh Water / Q000032:analysis; D057097:Harmful Algal Bloom; D052998:Microcystins / Q000032:analysis / Q000378:metabolism / Q000633:toxicity*; D010041:Otters / Q000002:abnormalities / Q000378:metabolism*; D012623:Seawater / Q000032:analysis; D014873:Water Pollutants / Q000378:metabolism / Q000633:toxicity*
chemical_list: D001427:Bacterial Toxins; D052998:Microcystins; D014873:Water Pollutants; C078588:microcystin