Golden Alga Workshop Summary Report - Texas Parks & Wildlife ...

A Review of Fish-killing Microalgae: Causes, Impacts, and Management with Emphasis on
Prymnesium
Jan H. Landsberg
Florida Marine Research Institute, Florida Fish and Wildlife Conservation Commission, 100
Eighth Avenue Southeast, St. Petersburg, Florida 33712 USA
Abstract.--Harmful algal blooms (HABs) cause mass animal mortalities, shellfish and tropical
fish poisonings, respiratory irritation, and neurocognitive disease in humans. Globally, HABs
have been directly or indirectly associated with fish kills in a variety of aquatic systems. At least 60
species are ichthyotoxic, and more than 30 species are harmful to fish. The sudden appearance of
toxic planktonic blooms, such as red tides that lead to acute, mass fish mortalities, has been
historically documented since the mid 1800s. Increased reports of HAB-associated fish kills
signify their expanding effects in aquatic systems. Microalgae can affect fish in a number of ways:
the production of lethal or sublethal toxins can cause neurological impairment, behavioral change,
or neurointoxication; the production of bioactive compounds (e.g., hemolysins) can cause cellular
damage, or impair respiration and other physiological functions; toxins can be transferred up the
food chain via predation, bioaccumulation, and lethal bioconcentration; microalgal anatomical
structures can cause mechanical damage and pathology; microalgae can act as vectors for disease
pathogens; they can cause immunosuppression and increase the susceptibility of fish to disease;
and they can negatively influence water quality (e.g., low dissolved oxygen, increased
ammonia). Historically, many fish kills have been associated with the low dissolved oxygen levels
produced by nontoxic algal blooms. At all trophic levels, fish chronically exposed to microalgal
toxins can experience lethal or sublethal effects such as impaired feeding, avoidance behavior,
physiological dysfunction, impaired immune function, reduced growth and reproduction,
pathological effects, and mortality. The wide variety of life strategies adopted by many HAB
species suggests that fish in numerous trophic niches can be affected. Traditionally, only
planktonic HABs have been recognized as having acute effects, but benthic and predatory HAB
species can also kill or harm fish. The majority of fish kills are caused by dinoflagellates such as
Karenia, Karlodinium, Gymnodinium, Gyrodinium, and Pfiesteria and others are caused by the
raphidophytes Chattonella, Fibrocapsa, and Heterocapsa and the prymnesiophytes
Chrysochromulina and Prymnesium. At least four Prymnesium species have been reported to be
ichthyotoxic, with the majority of fish kill reports involving P. parvum. Prymnesium produce
bioactive glycosides known as prymnesins. Prymnesins are released into the water naturally
during Prymnesium blooms with even higher concentrations released during stressful conditions,
or after the cells die. Fish are affected directly because prymnesins are absorbed across the gills.
Other gill-breathing organisms such as amphibian larvae and shellfish can also be susceptible to
prymnesins. Unlike many other toxic microalgae, the toxins from Prymnesium do not affect
mammals, so less attention has been drawn to their effects because they are not a public health
risk. However, Prymnesium blooms have caused significant ecological and economical impacts.
Primarily responsible for high-density blooms and fish kills in aquaculture systems and fish
farms, Prymnesium species have also been responsible for significant natural kills in brackish
waters. Strategies for management include chemical and biological controls, and predictive
monitoring that uses a combination of sensitive bioassays, traditional monitoring methods, and
innovative technologies.
View the presentation
PWD RP T3200-1203