Alexandrium monilatum

Dinoflagellates- Alexandrium Karlodinium Pfiesteria Prorocentrum

The chain-forming dinoflagellate, Alexandrium monilatum, has been reported to produce a bioactive substance with hemolytic properties (causes destruction of red blood cells and release of hemoglobin). A. monilatum most commonly blooms in warm coastal waters along the U.S. Gulf Coast, although it has also been reported from the tropical Pacific Ocean off Ecuador and as far north as Chesapeake Bay along the U.S. mid-Altantic Coast. A. monilatum blooms have been associated with massive fish mortalities off the Gulf Coast and Venezuela (Figure 1). A. monilatum typically occurs as motile cells in long chains, and less commonly as single cells. Long chains tend to predominate when cultures are in log phase growth, and as cultures age shorter chains (<4 cells) or single cell morphologies become more common. Like other dinoflagellate species, A. monilatum forms resting cysts under nutrient-deficient conditions.

We have been examining environmental controls (e.g. salinity, temperature, nutrient concentrations) on development of A. monilatum blooms. We are using bioassays coupled with various analytical techniques to assess potential impacts of A. monilatum on higher trophic levels (finfish, shellfish). Although not fully characterized, the toxins produced by A. monilatum appear to be constrained within the cell membrane during log-phase growth but, as noted for certain other Alexandrium species, the cells can leach toxins into the surrounding medium during senescence. Previous research by other laboratories supports the premise that A. monilatum toxin(s) can adversely affect a range of finfish and shellfish species, as well as other fauna such as polycheates. We have found that exposure to A. monilatum culture filtrate can significantly alter the behavior of juvenile sheepshead minnoes (Cyprinodon variegatus; see below).

a. b.

a. Movie clip of Sheepshead minnow (Cyprinodon variegatus) exposed to A.monilatum filtrate
b. Movie clip of C. variegatus exposed to filtered seawater control

 

In addition to the short-term effects (within less than 1 hour) observed above, we have found that juvenile C. variegatus exposed to both whole-cell culture material and culture filtrate generally die within 24 hours of exposure. Impacts of A. monilatum on commercially important shellfish species is the subject of a graduate thesis project nearing completion.