Search

Phytoplankton composition, abundance and carbon biomass were investigated at monthly intervals during 2006–2007 at a coastal site, “Acqua Alta” an oceanographic tower, in the northern Adriatic Sea. Results were compared with chlorophyll a concentrations of phytoplankton classes attributed by HPLC-CHEMTAX analysis. Changes in the taxonomic structure were associated with environmental parameters. The total carbon biomass of phytoplankton was positively correlated with the temperature and negatively correlated with silicate concentrations. Nutrient concentrations were higher in the winter–spring period than in the summer-autumn period. The highest carbon biomass and abundance of phytoplankton were observed during summer–autumn months. Diatoms were the group that had the highest contribution to the total carbon biomass during the sampling period. Small flagellates, which were the major contributors to the total cell counts were dominant during the summer period. There was a significant correlation between carbon biomass and CHEMTAX-derived Chl a values of diatoms and dinoflagellates. However, the total carbon biomass of phytoplankton was not correlated with Chl a, which seemed to be related to seasonal changes in the ratios of C:Chl a of all taxonomic classes. This ratio was higher during the summer-autumn period (73 ± 33) than during the winter–spring period (17 ± 20).

The coccolithophorid Ochrosphaera neapolitana was reported for the first time from samples obtained during a large-scale mucilage event in the Sea of Marmara in May 2022 in a previous study. We also found this species in our samples obtained about a year ago (i.e., in June 2021). In our study, O. neapolitana was further isolated and produced in the laboratory as a monoculture for further investigations using electron microscopy and molecular methods. Ochrosphaera neapolitana was identified using a small sub-unit (SSU) rRNA sequence and subsequent phylogenetic analysis. During the laboratory experiments, O. neapolitana was surprisingly observed to produce conspicuous levels of mucilage as a skim layer in mono- or multi-species cultures, mainly comprising other diatom species. This observation could be a significant milestone in understanding the reasons and mechanisms of mucilage events that occur in the Sea of Marmara.

Harvesting impacts the costs of microalgae production and affects the characteristics of the final product. Therefore, this study evaluated Moringa oleifera seed powder (MP) as a bioflocculant compared to two chemicals (Aluminium Sulphate—AS and Iron Chloride—IC) to harvest a mixed microalgae culture (Chlorella vulgaris and Desmodesmus sp.) grown on digestate. MP was the most stable flocculant but resulted in the lowest harvesting efficiency of 75%, compared to 94% for AS and 100% for IC. Process parameters such as pH, duration of mixing, grinding method for obtaining the powder, and granulometry had no significant effect on the harvesting efficiency of MP, reinforcing that this is a robust flocculant. The use of a water extraction step increased the harvesting efficiency of MP to 91%, albeit with the need for a higher dosage of flocculant. The algae harvested with MP complied with maximum tolerable levels for swine, cattle, and poultry regarding most trace elements. Nevertheless, all algae samples had Fe and Al contents above the recommended levels, possibly due to the entrapment of metal-rich digestate particles. Therefore, more attention should be paid to the final composition of algae when proposing flocculation as a harvesting method for feed production.