Toxin-producing algae are a significant impact IN freshwater and marine aquaculture

The EPA and USGS have identified over 50% of all US waterbodies as being impaired by nitrification, with many having harmful algal blooms.  Recently mysid mortality in marine aquaculture systems was related to occurrence of a new to science benthic cyanobacterium Toxifilum mysidocida. Recent developments in harmful algal blooms will be discussed.

Microcystin is one of 48 toxin classes produced by cyanobacteria.  In the early 2000s, fish-killing concentrations of microcystin were identified in catfish production ponds.  Zimba and Grimm conducted a synoptic survey of 486 ponds for off-flavor and microcystin occurrence and found <1% had levels above USEPA/WHO levels of concern. In a recent survey of 149 cyanobacterial cultures (originally isolated from terrestrial, freshwater, and marine systems) toxin production was widespread averaging six toxin classes per species (Figure 1).  Protease inhibitors such as aeruginosins and micropeptins accounted for ~45% of observed toxins (Figure 2).  Co-occurrence of protease inhibitors (preventing peptide degradation) and protein toxins would mean that toxicity would be greater than if the single protein toxin was ingested.

Other toxin producing divisions of microalgae include the Euglenophyceae and Dinophyceae, producing euglenophycin and saxitoxin(-like) compounds.  Euglenophycin was first identified from aquaculture systems and is currently known from 17 US States and four continents.  In a divisional survey of the euglenoids (Figure 3), 6 of the 22 species tested produced toxins. Algal toxin advancements will be discussed.