The fish kill mechanism of the harmful raphidophyte Chattonella subsalsa.

摘要

Harmful algae blooms (HABs) and toxins associated with HAB species are a significant threat to the health of marine species and coastal environments. In the South Carolina coastal zone, HABs have proliferated with intensified anthropogenic eutrophication in coastal waters. The raphidophyte species Chattonella subsalsa is a prominent cause of algal blooms resulting in fish kills in South Carolina. Though C. subsalsa is a known ichthyotoxic alga, the fish kill mechanism of this species remains unidentified. C. subsalsa is likely to elicit fish mortality via one of two mechanisms: (1) gill damage induced by cell contact irritation or (2) the production of a bioactive compound or toxin. We hypothesized physical damage and subsequent mortality was caused by direct contact with C. subsalsa cells and that the lethality of C. subsalsa is related to the algal growth phase, with the maximum harmful effect occurring during the exponential growth phase. Larvae of Fundulus heteroclitus were exposed to cultures of C. subsalsa at various phases of growth both directly and indirectly (through a 0.2 mum mesh) for 48 hours. Fish mortality and gill tissue damage were used to measure the effects of C. subsalsa exposures. The greatest mortalities and gill damage were observed via indirect exposure to C. subsalsa cultures in the exponential growth phase. These results suggest C. subsalsa produces a bioactive compound that induces gill damage and subsequent mortalities without the necessity of contact with algal cells and that C. subsalsa is most lethal during the exponential growth phase.