The toxic benthic dinoflagellates of the genus Ostreopsis in temperate areas: a review

The toxic benthic dinoflagellates of the genus Ostreopsis in temperate areas: a review

Stefano Accoroni, Cecilia Totti

Advances in Oceanography and Limnology, 2016; 7(1): 1-15

DOI: 10.4081/aiol.2016.5591

Key Points:

• Correct ID of Ostreopsis species in the field (distinguishing between them) is “highly problematic” requiring a comparison of precise anatomical measurements and experience comparing strains from different regions.  Even genetic ID has been complicated.  They are now referring to some Ostreopsis as species-complexes and clades.
• Either P- or N-depletion has been shown to lower Ostreopsis ovata toxicity.  (Strain, growth phase and salinity all figure it too.)
• Turbulence affects growth rate/cell-size.
• Cell counts were consistently lower in exposed sites vs sheltered ones.
• Dino’s are easy to dislodge, which is why they show a preference for calm areas
• Turbulence is most effective against them at the peak population levels when they are mat-forming.
• While it appears there is a general preference for higher temperatures during the peak bloom (77ºF+) they tend to range widely and some strains appear to have multiple optimal ranges.
• N:P around the Redfield ratio and temperatures of at least 77ºF seems necessary to allow cell proliferation.
• Temperatures to stop a bloom were much lower, however – around or under 60ºF.
• Blooms appear to be initiated under low-N/low-P conditions and then spike with a flush of nutrients.
• It’s also suggested that Ostreopsis toxins might be intended for survival under low-N/low-P conditions while waiting for conditions to become ideal.  (Which seems to be an elevation in temperature along with a spike in nutrients.)
• At least one strain of Ostreopsis showed a very strong demand for P in depletion tests, which was remarkable among dinoflagellates.
• It’s suggested that Ostreopsis may share the habit known of other dinoflagellates for resorting bacterivory/mixotrophy under low-P/low-nutrient conditions.
• Most Ostreopsis species exhibited lowered growth rates at light intensities around 250 PAR and higher….sometimes only slightly lowered, sometimes significantly.
• Higher light levels may also be related to mucus formation (for photodamage protection) and settling from their planktonic stage.
• However, being motile, they are also capable of migrating from brighter to shadier areas.
• Although recorded in the wild on a variety of substrates, there are many reports that they prefer to be epiphytic on macroalgae, which as an environment is known to have low light availability.
• Interestingly, living substrates like macroalgae support the lowest cell densities of all sampled substrates.
• All investigated seaweed types exhibited a negative effect on Ostreopsis counts: brown, red and green algae.  The brown algae Dictyota dichotoma had the strongest effect….a red algae the weakest.