Effects of nutrients, salinity, pH and light:dark cycle on the production of reactive oxygen species in the alga Chattonella marina

Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Journal of Experimental Marine Biology and Ecology 346 (2007): 76-86, doi:10.1016/j.jembe.2007.03.007.Experiments were carried out to investigate the effects of nutrients, salinity, pH and light:dark cycle on growth rate and production of reactive oxygen species (ROS) by Chattonella marina, a harmful algal bloom (HAB) species that often causes fish kills. Different nitrogen forms (organic-N and inorganic-N), N:P ratios, light:dark cycles and salinity significantly influenced algal growth, but not ROS production. However, iron concentration and pH significantly affected both growth and ROS production in C. marina. KCN (an inhibitor of mitochondrial respiration) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (an inhibitor of photosynthesis) had no significant effects on ROS production. Vitamin K3 (a plasma membrane electron shuttle) enhanced ROS production while its antagonist, dicumarol, decreased ROS production. Taken together, our results suggest that ROS production by C. marina is related to a plasma membrane enzyme system regulated by iron availability but is independent of growth, photosynthesis, availability of macronutrients, salinity and irradiance.The work described in this paper was supported by a CERG grant from the University Grants Committee of the Hong Kong Special Administrative Region, China to RSSW (Project No. 9040864). Support for DMA is provided by U.S. National Science Foundation grant # OCE-0136861

Release of available nitrogen from river-discharged dissolved organic matter by heterotrophic bacteria associated with the cyanobacterium Microcystis aeruginosa

The use of riverine dissolved organic matter by the heterotrophic bacteria associated with a culture of the cyanobacterium Microcystis aeruginosa and release of simple nitrogen compounds were studied in an experimental series. Bacteria reduced the bulk of dissolved organic nitrogen (DON) by half, but when associated with M. aeruginosa, DON was excreted and its concentration rose by 13%. During the stationary growth phase bacteria released ammonium, doubling the concentration of ammonia as well as of nitrates. Bacteria associated with M. aeruginosa consumed riverine DON and joined the ammonification and nitrification process, supplying cyanobacteria with simple nitrogen compounds

Phytoplankton allelochemical interactions change microbial food web dynamics

This study investigates the effect of filtrates from an allelopathic dinoflagellate, Alexandrium tamarense, on four microbial food webs that have been manipulated experimentally from natural seawater by modifying the availability of resources in the form of dissolved organic carbon with additions of peptone, and by altering the grazing pressure with size fractionation. Bacterial production was generally not affected by allelochemicals, but bacteria showed higher net growth in all food webs when allelochemicals were added, whereas heterotrophic nanoflagellates . 7 mm and ciliates were constrained in all food webs. Allelochemicals had the largest negative effects on microbial communities with low grazing pressure. In food webs with high grazing pressure and additional resources, phytoplankton and small nanoflagellates were positively affected by the addition of allelochemicals, suggesting that those were interfering with trophic interactions in the microbial communities. By the lysis of organisms sensitive towards allelochemicals, resources are made available and grazing pressure on certain microorganisms is reduced. However, the intensity of these interactions is modulated by both the availability of resources and the biomass of grazers in the initial food web

Experimental infection of Mytilus edulis by two Vibrio splendidus ‐related strains: Determination of pathogenicity level of strains and influence of the origin and annual cycle of mussels on their sensitivity

International audienceThis study aimed at assessing the pathogenicity of two Vibrio splendidus‐related species and evaluating the influence of the origin and annual life cycle of mussels on their sensitivity during a bacterial challenge. Thus, in vivo infection assays were made with Vibrio crassostreae 7T4_12 and Vibrio splendidus 3G1_6, over, respectively, thirteen and 9 months, on adult blue mussels from five recruitment areas in France. Two bacterial concentrations were tested: one consistent with the loads of Vibrio spp. in environment and mussel tissues (~105 CFU/ml) and another one much higher (~108 CFU/ml). The tested environmental concentration has no pathogenic effect whatever the time of year, the strain used and the origin of mussels. However, at the highest concentration, a pathogenic effect was observed only at specific moments, and one of the origins appeared to be more resistant. The physiological state of mussels—depending on the time of year—seemed significant in mussels’ sensitivity, as their recruitment origin. This study is the first to test the pathogenicity of V. splendidus‐related strains at concentrations close to what is found in the wild, over the annual cycle of mussels, and considering their origin

Phytoplankton allelochemical interactions change microbial food web dynamics

This study investigates the effect of filtrates from an allelopathic dinoflagellate, Alexandrium tamarense, on four microbial food webs that have been manipulated experimentally from natural seawater by modifying the availability of resources in the form of dissolved organic carbon with additions of peptone, and by altering the grazing pressure with size fractionation. Bacterial production was generally not affected by allelochemicals, but bacteria showed higher net growth in all food webs when allelochemicals were added, whereas heterotrophic nanoflagellates . 7 mm and ciliates were constrained in all food webs. Allelochemicals had the largest negative effects on microbial communities with low grazing pressure. In food webs with high grazing pressure and additional resources, phytoplankton and small nanoflagellates were positively affected by the addition of allelochemicals, suggesting that those were interfering with trophic interactions in the microbial communities. By the lysis of organisms sensitive towards allelochemicals, resources are made available and grazing pressure on certain microorganisms is reduced. However, the intensity of these interactions is modulated by both the availability of resources and the biomass of grazers in the initial food web

Mortality of marine mussels Mytilus edulis and M. galloprovincialis: systematic literature review of risk factors and recommendations for future research

The aim of this study was to summarise the literature reporting the risk factors for mortality in the mussel species Mytilus edulis and Mytilus galloprovincialis in order to identify potential science‐based solutions to prevent or mitigate mussel mortality outbreaks. We followed the PRISMA methodology: Preferred Reporting Items for Systematic Reviews and Meta‐Analyses. The studied corpus of 91 publications (114 studies) was highly heterogeneous with respect to the methodological approaches used to define or estimate mussel mortality and the related putative risk factors. Results showed that the mortality risk of both mussel species M. edulis and M. galloprovincialis varied across the seasons, increased with an elevated seawater temperature above a thermal threshold of 20 and 24°C, respectively, decreased by protecting mussels from predation, and was associated with the presence of pathogens in M. edulis. For M. galloprovincialis, using mussel spat from the same area where the farming is carried out and farming them together with another mussel species appears to reduce the mortality risk. However, for M. edulis, this could be achieved by using pure crosses and in particular mussel spat having a selected genotype. For wild bed conservation, sand accumulation and anthropogenic sedimentation should be minimised. Our analysis showed that current approaches to this research topic are limited and are unlikely to yield actionable evidence to identify mussel mortality prevention or mitigation strategies. Therefore, recommendations are offered to increase the ability of future eco‐epidemiological research to identify multiple exposures associated with mussel mortality, underpinned by standardised efforts and cooperative initiatives