By Matthew Lee ‘21

Algal blooms are known for their ability to turn an entire body of water a different color. These periodic blooms harm humans, marine species, and aquatic ecosystems. One such species is the benthic dinoflagellate Ostreopsis ovata, most prevalent in the Mediterranean Sea. It has been observed that Ostreopsis may be vulnerable to allelopathic,  or germination- inhibiting, chemicals produced by diatoms, single-celled organisms with silica cell walls. A team of researchers led by Salvatore Pichierri from Università Politecnica delle Marche recently decided to examine the allelopathic effect of diatoms on Ostreopsis populations.

The researchers used Thalassiosira and Skeletonema marinoi plankton to assess diatom impact on Ostreopsis growth, while Tabularia affinis, Proschkinia complanatoides, and Navicula sp. (benthic) were used to assess diatom impact on Ostreopsis cell health. The Ostreopsis was grown in flasks containing cell-free filtrates derived from diatom growth.

The results showed that  Ostreopsis grown in the planktonic filtrates experienced 57% and 78% growth inhibition compared to their control groups. All three benthic diatoms had clear negative impacts on Ostreopsis cell growth – most notably Proschkinia – decreasing growth almost 7000 cells/mL compared to the control group. In addition, Ostreopsis sustained heavy cellular damage from the Proschkinia and Navicula filtrates. The damage is evident in the resultant lack of motility, abnormal vesicle structures, contraction of cytoplasm, chromatin damage, nucleus enlargement, and lack of red autofluorescence.

Although the researchers could not carry out a chemical analysis of the filtrates, the results suggest the diatom filtrates were able to have an allelopathic effect on the Ostreopsis. This study as well as related studies are significant in demonstrating that allelopathy is likely an important factor – in addition to abiotic factors – when studying algal bloom dynamics.

References:

1. S. Pichierri, et. al., Allelopathic effects of diatom filtrates on the toxic benthic dinoflagellate Ostreopsis cf. ovata. Marine Environmental Research xxx, 1-7 (2017). doi: https://doi.org/10.1016/j.marenvres.2017.09.016
2. Image retrieved from: https://commons.wikimedia.org/wiki/File:Blooms_in_the_Sea_of_Marmara_(18162220028).jpg