Real-time polymerase chain reaction assays for rapid detection and quantification of Noctiluca scintillans zoospore

Ingestion rate estimated from food concentration and predatory role of copepod nauplii in the microbial food web of temperate embayment waters

To quantitatively evaluate the role of copepod nauplii as predators in the microbial food web, the ingestion rate (IR) of copepod nauplii and the food requirement (FR) of microzooplankton were estimated monthly for 3 consecutive years in temperate embayment waters. The IR of dominant copepod nauplii (Acartia spp. nauplii) was estimated from water temperature, individual carbon weight and food concentration and peaked (>0.50 μgC ind^-1 d^-1) with relatively high food concentration (>57.5 μgC L^-1). This result suggests that food concentration should be considered to estimate copepod naupliar IR in marine environments, especially where biological conditions fluctuate largely. The comparison of copepod naupliar and microprotozoan FR showed the dominance of naked ciliate FR (77.0-90.2%) during the study period except in spring when comparable values were observed between the FR of naked ciliates (41.6%) and copepod nauplii (33.6%). During spring, transfer efficiency (10.5%) from primary production (PP) to microzooplankton production was lower than in other seasons (16.2-17.1%). This study indicates that copepod nauplii are seasonally important micro-sized predators in the microbial food web of temperate embayment waters and that carbon flow through copepod nauplii is a pathway which inefficiently transfers PP to higher trophic levels.

Isolation and characterization of a high-efficiency algicidal bacterium Pseudoalteromonas sp. LD-B6 against the harmful dinoflagellate Noctiluca scintillans

The dinoflagellate Noctiluca scintillans is a harmful algal species that is globally distributed and poses a certain threat to marine ecosystems. Recent research has shown that the application of algicidal bacteria is a promising method to prevent and control such harmful algal blooms (HABs), given its advantages of safety and efficiency. In this study, a strain of algicidal bacterium LD-B6 with high efficiency against N. scintillans was isolated from the coastal waters of Lianyungang, China. 16S rDNA sequence analysis showed that the strain LD-B6 belongs to the genus Pseudoalteromonas. Furthermore, the algicidal effect of LD-B6 on N. scintillans was investigated. The results showed that strain LD-B6 exerted strong algicidal activity against N. scintillans. After 12 h of bacterial culture addition to algal cultures at a 2% final volume rate, the algicidal activity reached 90.5%, and the algicidal activity of LD-B6 was influenced by the density of N. scintillans. In addition, the algicidal bacterium LD-B6 was found to indirectly lyse algal cells by secreting extracellular compounds. These algicidal compounds were stable, indicating that they are not proteins. Importantly, strain LD-B6 was broadly general, showing varying degrees of lysing effects against five of the six algal species tested. On the basis of the described studies above, the algicidal powder was also initially developed. In summary, the isolated bacterial strain LD-B6 shows the potent algicidal capability to serve as a candidate algicidal bacterium against N. scintillans blooms.

Population dynamics and interactions of Noctiluca scintillans and Mesodinium rubrum during their successive blooms in a subtropical coastal water

A time series field survey were conducted in Port Shelter, a subtropical coastal water in NW Pacific, beginning before the onset of a chain of Noctiluca scintillans and/or Mesodinium rubrum blooms, and ending after the blooms had declined. At the first mixed bloom stage, seed of N. scintillans and the consequent outbreak of both N. scintillans and M. rubrum were largely due to the physical forcing. Plenty food supply and their different feeding habits supported N. scintillans and M. rubrum to bloom massively and concomitantly. Following that, there was a small N. scintillans bloom followed by a small crest of M. rubrum. Their initiation and scale were mainly affected by limited food supply and/or the inferior food source. Sudden change of wind from mild northeast wind to strong southeast wind might contribute to the termination of N. scintillans bloom. Finally, physical accumulation was the most important driving factors of the formation and dispersal of the third and largest bloom of N. scintillans. Formation of these bloom events may involve vertical migration and/or the concentrating mechanism of M. rubrum and N. scintillans. Meanwhile, biotic interactions such as mutual supportive relationship between N. scintillans and M. rubrum, and O. hongkongense fed on the progametes of N. scintillans, as well as other abiotic factors like seawater temperature and rainfall, also play important roles in this series of bloom events. Our findings have important implications for coastal zones worldwide, which are affected recurrently by these two ubiquitous red tide-forming species.

A Cryptic Marine Ciliate Feeds on Progametes of Noctiluca scintillans

The dinoflagellate Noctiluca scintillans (Noctiluca) has the ability to reproduce sexually, which may help to increase or restore its population size during periods of blooms or environmental stress. Here, we documented for the first time a marine ciliate Strombidium sp. that feeds on Noctiluca's progametes undergoing stages 5 to 9 of nuclear division. This ciliate frequently swam on or around gametogenic and some vegetative Noctiluca cells. The ciliates associated with gametogenic cells had significantly lower swimming speed and changed direction more frequently than those associated with vegetative cells, which overall increased their time spent around the food patches (progametes). This trophic interaction constitutes an upside-down predator-prey link, in which ciliates within the typical size range of Noctiluca prey, become the predators. Based on the phylogenetic tree (maximum-likelihood), there are 14 environmental clones similar to Strombidium sp. found in other coastal waters, where Noctiluca presence or blooms have been reported. This novel predator-prey relationship could therefore be common in other Noctiluca habitats. Additional studies are needed to assess the magnitude of its impacts on Noctiluca population dynamics and plankton bloom succession.