Morphology, molecular phylogeny and okadaic acid production of epibenthic Prorocentrum (Dinophyceae) species from the northern South China Sea

Around 30 epibenthic Prorocentrum species have been described, but information about their biogeography is limited. Some species are able to produce okadaic acid (OA) and its derivatives, which are responsible for diarrheic shellfish poisoning (DSP). In the present study, we examined the diversity of epibenthic Prorocentrum in the northern South China Sea by isolating single cells from sand, coral, and macroalgal samples collected from 2012 to 2015. Their morphology was examined using light microscopy and scanning electron microscopy. Among 47 Prorocentrum strains, seven morphospecies were identified as P. lima, P. rhathymum, P. concavum, P. cf. emarginatum, P. fukuyoi, P. cf. maculosum and P. panamense. The latter five species have not been previously reported in Chinese waters, and this is the first record of P. panamense outside its type locality. Partial large subunit (LSU) ribosomal DNA and internal transcribed spacer region sequences were obtained and molecular phylogenetic analysis was carried out using maximum likelihood and Bayesian inference. Chinese P. cf. maculosum strains share 99.5% similarity of LSU sequences with the strain from Cuba (close to the type locality), but Chinese P. lima strains share only 96.7% similarity of LSU sequences with the strain from the type locality. P. cf. emarginatum differs from P. fukuyoi mainly in the presence/absence of marginal pores and they form a well-resolved clade together with P. sculptile. OA was detected in all Chinese strains of P. lima and P. cf. maculosum based on liquid chromatography-mass spectrometry analysis, but dinophysistoxin was produced only by two P. lima strains. Chinese strains of P. concavum, P. rhathymum, and P. panamense do not produce detectable level of OA. Our results support the wide distribution of epibenthic Prorocentrum species and highlight the potential risk of DSP in the northern South China Sea

(E)-Methyl 3-(3,5-dibromo-2-hydroxybenzylidene)carbazate

The title compound, C9H8Br2N2O3, crystallizes with two very similar independent molecules in the asymmetric unit, each of which adopts a trans configuration with respect to the C=N bond. Intramolecular O—H...N hydrogen bonds are observed in each independent molecule. In the crystal structure, molecules are linked into chains propagating along [010] by N—H...O and C—H...O hydrogen bonds. In addition, C—H...π interactions stabilize the structure

Ecological studies of phytoplankton and harmful algal blooms in Junk Bay, Hong Kong

published_or_final_versionEcology and BiodiversityDoctoralDoctor of Philosoph

Spatial-Temporal Distribution of Prorocentrum concavum Population in Relation to Environmental Factors in Xincun Bay, a Tropical Coastal Lagoon in China

A harmful benthic Prorocentrum concavum bloom was recorded in August 2018 in Xincun Bay, China, which is the location of a national seagrass nature reserve. Annual ecological surveys have been conducted to study the population dynamics of P. concavum in the benthic community and water column. Seasonal variations in benthic P. concavum abundance were found and the abundances on seagrass and macroalgae in the wet season were 2.5 and 2.82 times higher, respectively, than those in the dry season, although the differences were not statistically significant. The abundance of P. concavum in the water column differed significantly between seasons. The maximum abundances of benthic and planktonic P. concavum were (1.7 ± 0.59) × 106 cells (100 cm2)−1 on Thalassia hemperichii in July and 2.0 × 104 ± 4.7 × 103 cells L−1 in June, respectively. High spatial heterogeneity in P. concavum abundance was observed among five sampling sites. Abundances were significantly higher in seagrass beds than those in macroalgae beds, mangroves, and coral reefs. The abundance of P. concavum at site A (in a seagrass bed and close to a cage-culture area) was 5.6 times higher than that at site D (seagrass bed and distant from the cage-culture area). Planktonic P. concavum showed a similar spatial distribution and presented a maximum density at site A. Moreover, the abundance of benthic P. concavum also showed heterogeneity on host substrates, and the abundance on T. hemperichii was significantly higher than that on sediment. Based on a Spearman’s test, temperature, dissolved organic phosphorus, and dissolved organic nitrogen were the three important factors driving the spatiotemporal distribution of benthic P. concavum in Xincun Bay. Planktonic P. concavum were derived from cells on the substrates and were influenced by concentrations of dissolved oxygen. In conclusion, seagrass beds may be a reservoir of harmful benthic algal blooms in Xincun Bay and the dense cage-culture area provides sufficient organic nutrients for the growth and reproduction of benthic dinoflagellates.</jats:p

The effect of riverine dissolved organic matter and other nitrogen forms on the growth and physiology of the dinoflagellate Prorocentrum minimum (Pavillard) Schiller

The effect of various nitrogen (N) sources, including riverine dissolved organic matter (DOM), nitrate, ammonium, and urea, on the growth and physiology of the dinoflagellate Prorocentrum minimum was compared in a batch culture experiment. P. minimum grew equally well in the presence of identical amounts of nitrate, ammonium, and urea. Approximately 18 to 20% of organic N bound to the DOM was bioavailable. Although the available N added in the DOM treatment was only 1/3 of the amount of any other N sources, the cell densities of P. minimum in the DOM treatment increased to 61 similar to 65% of those in the nitrate, ammonium or urea treatment. The maximum specific growth rates did not differ significantly between the treatments with the highest in the ammonium treatment (0.55 +/- 0.13 d(-1)) and the lowest in the urea treatment (0.39 +/- 0.04 d(-1)). P. minimum assimilated the available DOM-bound N in a short period (fewer than 5 days), which was faster than utilizing urea. The increase in the cellular N:P ratios of P. minimum showed the alleviation of N stress in all the treatments after the addition of various N forms. The densities and cellular compositions of P. minimum stabilizing in all the treatments for the whole stationary phase indicated that P. minimum has adaptive physiology under sub-optimal conditions and is a competitive bloom species. We suggest that P. minimum cells utilize DOM-bound N for their growth, and the efficiency in utilizing the available DOM-bound N for growth is comparable to when P. minimum utilizes nitrate, ammonium or urea