Prokaryotic Diversity and Dynamics during Dinoflagellate Bloom Decays in Coastal Tunisian Waters

(1) Background: Harmful algal blooms (HABs) can negatively impact marine ecosystems, but few studies have evaluated the microbial diversity associated with HABs and its potential role in fates of these proliferations. (2) Methods: Marine prokaryotic was investigated using high-throughput sequencing 16S rRNA gene during bloom declines two dinoflagellates detected summer 2019 along northern southern Tunisian coasts (South Mediterranean Sea). The species Gymnodinium impudicum (Carthage, Tunis Gulf) Alexandrium minutum (Sfax, Gabes were identified microscopy molecular methods related to physicochemical factors compositions. (3) Results: abundance G. decreased over time decreasing phosphate concentrations. During decay, prokaryotes predominated by archaeal MGII group (Thalassarchaeaceae), Pelagibacterales (SAR11), Rhodobacterales, Flavobacteriales. At Sfax, A. declined concentrations increasing pH. peak, communities largely dominated anoxygenic phototrophic sulfur-oxidizing Chromatiaceae (Gammaproteobacteria) before at end survey. Both ubiquitous found low proportions decay. Contrary photosynthetic Cyanobacteria, photo-autotrophic -heterotrophic Rhodobacterales Flavobacteriales contents remained stable dinoflagellate decays. (4) Conclusions: These results indicated changes community decays, suggesting different bacterial adaptations environmental conditions, core populations that potentially able degrade HABs.