ECO-PHYSIOLOGY, BIO-OPTICS AND TOXICITY OF THE ICHTHYOTOXIC CHRYSOCHROMULINA LEADBEATERI (PRYMNESIOPHYCEAE)

A toxic phytoplankton bloom, dominated by the prymnesiophyte Chrysochromulina leadbeateri Estep, developed in the Ofotfjord–Tysfjord area (North Norway) in mid‐May and ended in late June 1991 in Vestfjorden and the adjacent fjord areas. Chrysochromulina leadbeateri dominated at total cell densities of >2 × 106 cells·L−1; at lower total cell densities, C. leadbeateri was accompanied by other Chrysochromulina species, peridinin‐containing dinoflagellates, and diatoms. Bio‐optical characteristics and pigmentation in laboratory and field strains of C. leadbeateri allowed for the interpretation of the optical signatures within the bloom. The bio‐optical data suggested healthy and actively growing cells during the bloom. About 600 metric tons of pen‐raised Atlantic salmon were killed by the C. leadbeateri bloom. A laboratory study was conducted to assess the potential impact of finfish on C. leadbeateri growth. It was found that the polyamine putrescine enhanced cell biomass and hemolytic activity. Given this, a possible scenario for the development of this bloom and the level of toxicity is hypothesized: (1) The nutrient loading in the Ofotfjord area was enhanced during the winter of 1990–1991 due to the overwintering of 1.5 × 106 metric tons of herring from a depth of 0–250 m. This may have sustained a large stock of the mixotrophic C. leadbeateri in early spring before light regime (irradiance, spectral irradiance, and day length) made net photosynthesis possible. (2) The release of polyamines during the decay of dead fish (e.g. putrescine, cadaverine, and histamine) may have acted as cofactors with ichthyotoxins making “hypertoxic complexes” with the polyamines enhancing growth in the mixotrophic C. leadbeateri.