Effects of the algicide, thiazolidinedione derivative TD49, on microbial communities in a mesocosm experiment.

We investigated the effects of the algicide thiazolidinedione derivative TD49 on microbial community in mesocosm experiments. The TD49 concentration exponentially decreased over time, with half-life of 3.5 h, following addition in the seawater (R2=0.98, P<0.001). Among microbial communities, heterotrophic bacteria and heterotrophic nanoflagellates (HNFs) grew well in all treatments following the addition of TD49. The abundance of HNFs lagged behind the increase in heterotrophic bacteria by 24 h in the 0.2 and 0.4 µM TD49 concentrations (R2=0.28, P<0.05), and by 48 h in the 0.6 and 1.0 µM TD49 concentrations (R2=0.30, P<0.05). This implies a strong concentration-dependent top-down effect of TD49 on microbial communities, with indications that the degradation of planktonic organisms, including the target alga, led to high heterotrophic bacteria concentrations, which in turn stimulated the population growth of predatory HNF. However, total ciliate numbers remained relatively low in the TD49 treatments relative to the control and blank groups, suggesting limited carbon flow from bacteria to these grazers even though the abundance of aloricate ciliates gradually increased toward the end of the experimental period, particularly at the high TD49 concentrations. TD49 appears to provide an environmentally safe approach to the control of harmful algal blooms (HABs) in aquatic ecosystems.

Epiphytic Bacterial Community Analysis of Ulva prolifera in Garorim and Muan Bays, Republic of Korea.

The bacterial communities related to seaweed can vary considerably across different locations, and these variations influence the seaweed's nutrition, growth, and development. To study this further, we evaluated the bacteria found on the green marine seaweed Ulva prolifera from Garorim Bay and Muan Bay, two key locations on Republic of Korea's west coast. Our analysis found notable differences in the bacterial communities between the two locations. Garorim Bay hosted a more diverse bacterial population, with the highest number of ASVs (871) compared to Muan Bay's 156 ASVs. In Muan Bay, more than 50% of the bacterial community was dominated by Pseudomonadota. On the other hand, Garorim Bay had a more balanced distribution between Bacteroidota and Pseudomonadota (37% and 35.5%, respectively). Additionally, Cyanobacteria, particularly Cyanothece aeruginosa, were found in significant numbers in Garorim Bay, making up 8% of the community. Mineral analysis indicated that Garorim Bay had higher levels of S, Na, Mg, Ca, and Fe. Function-wise, both locations exhibited bacterial enrichment in amino acid production, nucleosides, and nucleotide pathways. In conclusion, this study broadens our understanding of the bacterial communities associated with Ulva prolifera in Korean waters and provides a foundation for future research on the relationships between U. prolifera and its bacteria.

Effects of harmful microalgae on the behavior and morphology of ephyrae of the moon jellyfish Aurelia aurita.

Although microalgae typically serve as prey for jellyfish ephyrae in marine food webs, this study investigated the potential of harmful microalgae to produce detrimental effects on the moon jellyfish Aurelia aurita. Understanding the biological interactions between Aurelia and microalgal species is crucial, particularly considering their common co-occurrence in coastal waters worldwide. We examined the effects of 11 protist strains, comprising seven species of harmful microalgae and two non-toxic microalgae, on A. aurita ephyrae. The rhythmic pulsation behavior of A. aurita was significantly suppressed when exposed to the raphidophytes Heterosigma akashiwo and Chattonella marina var. ovata and the dinoflagellates Amphidinium carterae, Coolia canariensis, and Pfiesteria piscicida. Notably, the media filtrates of all H. akashiwo strains and C. marina var. ovata killed ephyrae, implying a possible extracellular release of chemicals. This study discovered novel interactions between microalgae and jellyfish ephyrae, implying that harmful algal blooms may suppress mass occurrences of Aurelia medusae.

The impact of adding organic carbon on the concentrations of total residual oxidants and disinfection by-products in approval tests for ballast water management systems.

In the G8 and G9 approval tests for ballast water management systems, organic carbon additives are frequently supplemented into test water to satisfy the water quality requirements. Because organic additives can affect the approval test, the additive selected, and its use and validation should be included in the test report. This study assessed the effects of organic carbon additives on the concentration of total residual oxidants (TROs) and the formation of disinfection by-products (DBPs). The concentration of dissolved organic carbon (DOC) in test water containing additives varied depending on the type of additive, but all additives, except for methylcellulose, had concentrations similar to or higher than the theoretical values. There was a low concentration of particulate organic carbon (POC) compared to the amount of corn starch added. Over the course of the five-day holding time, TRO concentrations tended to decrease. In general, substances with a large molecular size had a higher DBP concentration than their counterparts with a smaller molecular size, some of which, however produced the highest DBP concentrations due to their molecular structure. The results suggest that the formation of DBPs is affected by the reaction with TROs, molecular size, and molecular structure in a complex manner.

Enhancing the efficacy of electrolytic chlorination for ballast water treatment by adding carbon dioxide.

We examined the synergistic effects of CO2 injection on electro-chlorination in disinfection of plankton and bacteria in simulated ballast water. Chlorination was performed at dosages of 4 and 6ppm with and without CO2 injection on electro-chlorination. Testing was performed in both seawater and brackish water quality as defined by IMO G8 guidelines. CO2 injection notably decreased from the control the number of Artemia franciscana, a brine shrimp, surviving during a 5-day post-treatment incubation (1.8 and 2.3 log10 reduction in seawater and brackish water, respectively at 6ppm TRO+CO2) compared with water electro-chlorinated only (1.2 and 1.3 log10 reduction in seawater and brackish water, respectively at 6ppm TRO). The phytoplankton Tetraselmis suecica, was completely disinfected with no live cell found at >4ppm TRO with and without CO2 addition. The effects of CO2 addition on heterotrophic bacterial growth was not different from electro-chlorination only. Total residual oxidant concentration (TRO) more rapidly declined in electro-chlorination of both marine and brackish waters compared to chlorine+CO2 treated waters, with significantly higher amount of TRO being left in waters treated with the CO2 addition. Total concentration of trihalomethanes (THMs) and haloacetic acids (HAAs) measured at day 0 in brackish water test were found to be 2- to 3-fold higher in 6ppm TRO+CO2-treated water than in 6ppm TRO treated water. The addition of CO2 to electro-chlorination may improve the efficiency of this sterilizing treatment of ballast water, yet the increased production of some disinfection byproducts needs further study.