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Inhibitory effects of the brown macroalga Turbinaria ornata on cyst germination and progeny cells of five harmful dinoflagellate species

Mohamed Zakaria, Alamri Saad, Hashem Mohamed

Oceanologia

2022

No. 64 (1)

63--74

This study investigates the inhibitory effects of thalli and their extracts of the macroalga Turbinaria ornata on the germination of dinoflagellate cysts, previously isolated from Red Sea surface sediments. The experiments were conducted on cysts of five harmful dinoflagellate species including Alexandrium catenella, Cochlodinium polykrikos, Dinophysis accuminata, Prorocentrum cordatum and Scrippsiella trochoidea. The results showed neither macroalgal thalli nor their extracts had direct impact on the cyst germination of all species. Instead, these macroalgal materials remarkably affected the germling viability and culturability of progeny cells of these cysts. Dry macroalgal thalli exhibited stronger inhibitory effects on germling viability and cell culturability (IC50= 0.235–0.543, 0.385–1.43 mg mL−1, respectively) than fresh thalli (IC50=2.201–4.716, 2.17–7.18 mg mL−1, respectively). The macroalgal ethanol extract was approximately 2-5 times more effective (IC50 = 0.012–0.047 and 0.024–0.089 mg mL−1, respectively) than aqueous extract (IC50 = 0.04–0.1 and 0.054–0.207 mg mL−1, respectively) against the germling viability and vegetative progeny cells of all cyst species. Among different species, A. catenella and C. polykrikos germlings were more sensitive to macroalgal thalli and their extracts than those of S. trochoidea, P. cordatum and D. acuminata. Meanwhile, progeny cells of A. catenella exhibited the highest sensitivity to all macroalgal materials. Our results suggest that the use of T. ornata may be a promising strategy for inhibiting the division of progeny cells of dinoflagellate cysts and impairing the recurrence of HABs in confined coastal areas.

Do toxic cyanobacteria blooms pose a threat to the Baltic ecosystem?

Mazur-Marzec H., Pliński M.

Oceanologia

2009

No. 51 (3)

293-319

Cyanobacteria, otherwise known as blue-green algae, are oxygenic, photosynthetic prokaryotes. They occur naturally in many fresh, marine and brackish waters worldwide and play an important role in global carbon and nitrogen cycles. In their long history, cyanobacteria have developed structures and mechanisms that enable them to survive and proliferate under different environmental conditions. In the Baltic Sea, the mass development of cyanobacteria is compounded by a high level of eutrophication. The dominant species in the Baltic, the filamentous Aphanizomenon flos-aquae and Nodularia spumigena, can fix dissolved atmospheric N2, as a result of which they can outcompete other phytoplankton organisms. Heterocystous, filamentous cyanobacteria also make a significant contribution to the internal nutrient loading in the Baltic. The blooms of N. spumigena are of particular concern, as this cyanobacterium produces nodularin (NOD), a hepatotoxic peptide. The concentration of the toxin in the sea is regulated mainly by dilution with uncontaminated water, photolysis, sorption to sediments and microbial degradation. The transfer of the toxin in the Baltic trophic chain through zooplankton, mussels, fish and birds has been reported, but biodilution rather than bioconcentration has been observed. Cyanobacterial blooms are thought to pose a serious threat to the ecosystem. Their harmful effects are related to the occurrence of a high biomass, oxygen depletion, a reduction in biodiversity, and the production of toxic metabolites.