Long-term Changes in Community of Planktonic Algae of the Northeastern Black Sea (2005-2011)

Phytoplankton dynamics in bays and open waters of the northeastern Black Sea was studied in 2005-2011. Species composition comprised 11 classes and 210 species including 19 potentially toxic species and 5 new records for the study area. The maximum species richness was found among dinoflagellates (96 species) and diatoms (78); other major taxonomic groups were represented by a small number of species (2 to 10). The highest abundance of planktonic algae was observed in the Novorossiysk port waters (5.1x105 cells/ L; 1.08 g/m3). Algal abundance and biomass in the bays of Anapa, Gelendzhik and Tuapse were 2 to 5 times less than in the bay of Novorossiysk. Smallcelled mesosaprobic species of diatoms (Skeletonema, Leptocylindrus, Thalassionema and Chaetoceros), euglenophyceans (Eutreptia lanowii), cyanobacteria (Lyngbya and Oscillatoria) and mixotrophic dinoflagellates (Gymnodinium, Heterocapsa, Gyrodinium and Prorocentrum) were found in the bays. Abundance and biomass in the open sea in front of the bays were 1.5-2 times higher than those observed within the bays. The minimum abundance and biomass were observed in the open sea (5.4x104 cells/L, 0.28 g/m3) and the Kerch Strait (9.8x104 cells/L, 0.186 g/m3). In these areas the most significant part of the population (34-40% of phytoplankton abundance) was composed of the nanoplanktonic prymnesiophycean Emiliania huxleyi, the large-celled diatoms Proboscia alata and Pseudosolenia calcar-avis and dinoflagellates of the genus Protoperidinium (up to 45% of phytoplankton biomass)

Associated Bacteria and Their Effects on Growth and Toxigenicity of the Dinoflagellate Prorocentrum lima Species Complex From Epibenthic Substrates Along Mexican Coasts

The dinoflagellate genus Prorocentrum is globally represented by a wide variety of species found upon benthic and/or epiphytic substrates. Many epibenthic Prorocentrum species produce lipophilic polyether toxins, some of which act as potent protein phosphatase inhibitors and tumor-promoters associated with Diarrheic Shellfish Poisoning (DSP). Most members of the Prorocentrum lima species complex (PLSC) commonly found in the tropics and sub-tropics are toxigenic. Epiphytic and planktonic bacteria co-occur with toxigenic Prorocentrum but reciprocal allelochemical interactions are under-investigated. The aim of the present study was to identify the culturable bacteria collected together with isolates of the PLSC from seagrass (Thalassia testudinum) and macroalgae along tropical Atlantic coasts of Mexico, and to explore potential species interactions with selected isolates. Twenty-one bacterial genera belonging to Proteobacteria, Actinobacteria, and Bacteroidetes were identified by amplification of the 16S rRNA gene marker from nine clonal Prorocentrum cultures, with gamma-proteobacteria comprising the dominant class. A positive correlation was found between the bacterial genera associated with two Prorocentrum clones and the esterified toxin analog DTX1a-D8, but there was no apparent correlation between the other PLSC clones and their associated bacteria with the other five DSP toxins detected. No bacteriostatic or allelochemical response was found for cell-and culture medium extracts of five Prorocentrum isolates assayed for bioactivity against Staphylococcus sp. DMBS2 and Vibrio sp. HEL66. Bulk cell-washing of Prorocentrum PA1, followed by growth with antibiotics, was only effective in reducing bacterial load in the initial growth stages, but did not yield axenic cultures or lower bacterial cell densities throughout the culture cycle. Antibiotic treatment did not impair growth or survival of the dinoflagellate, or apparently affect DSP toxin production. There was no significant correlation between Prorocentrum cell volume, growth rate, bacterial cell counts, or cellular toxin concentration over the entire time-series culture cycle. Benthic Prorocentrum and associated bacterial communities comprise highly diverse and characteristic microbiomes upon substrates, and among compartments in culture, but this study provides little evidence that allelochemical interactions among Prorocentrum cells and associated bacteria originating from epibenthic substrates play a definable role in growth and toxigenicity