Picoplankton diversity in the South-East Pacific Ocean from cultures

International audienceIn late 2004, the BIOSOPE cruise sailed between the equatorial influenced waters off Marquesas islands and the nutrient enriched waters of the Chilean upwelling. Along the way, it explored the Southeast Pacific gyre centred around Easter Island, which is probably the most oligotrophic oceanic region on earth. During this cruise, we undertook a vigorous effort to isolate novel photosynthetic picoplanktonic eukaryotes. Two strategies were attempted on board: enrichment of samples with culture medium and sorting of specific populations by flow cytometry based on chlorophyll fluorescence. Over 1900 pre-cultures were started and then further purified by flow cytometry, serial dilution or pipette isolation to yield a total of 212 strains. These strains were characterized morphologically and for more than 50% of them, genetically, through partial sequencing of the 18 S rRNA gene. Among the characterized strains, the largest number are stramenopiles (Heterokontophyta) with a record of 38 strains belonging to the species Pelagomonas calceolata (Pelagophyceae). Strains from the recently described genera Bolidomonas and Florenciella have been re-isolated for the first time since their description. Two other abundant groups are the Chlorophyta, especially Prasinophyceae, and the Haptophyta, especially the genera Phaeocystis and Emiliania. A limited number of heterotrophic flagellates have also been isolated, all of them closely related to known species. Finally over a dozen of unicellular cyanobacteria strains have been obtained, some forming unusual short chains. Overall our strategy was quite successful since it allowed us to isolate a large number of picoplankton strains but failed in two respects. First, apparently very few novel taxa have been obtained. One set of strains is related to Prasinoderma coloniale (Prasinococcales, Prasinophyceae) but their sequences are sufficiently different from the latter to probably belong to a new genus or species. The sequences of two other strains are phylogenetically affiliated to stramenopile environmental sequences, probably corresponding a new algal class. Second, very few strains have been obtained from the very oligotrophic central gyre itself. Future work should probably combine flow cytometry sorting with culture media and cultivation approaches specifically developed for oligotrophic water species

Changes in marine phytoplankton diversity: Assessment under the Marine Strategy Framework Directive

Publisher’s embargo period: Embargo set on 11.03.2019 by SR (TIS)

Citizen participation in monitoring phytoplankton seawater discolorations

International audienceA citizen monitoring program (Phenomer) of marine water discolorations caused by high biomass phytoplankton development (Harmful Algal Blooms, HABs) was conducted in 2013, 2014 and 2015 in the coastal waters of Brittany (France). This project aimed to explore the feasibility of acquiring scientifically valuable data on water discolorations phenomena through a citizen science approach, extending the surface area of monitored coastal waters by means of citizen observations. During the three years of the project implementation, respectively 14, 32 and 28 warnings were sampled and recognized as phytoplankton water discolorations. Respectively, 7, 24 and 14 phenomena were observed outside of routine monitoring points. Citizen observations contributed towards evaluating the extension of red discolorations caused by Noctiluca scintillans and the duration and impact on marine fauna of green discolorations of Lepidodinium chlorophorum. A bivalve mortality event coincided with a dark-brown phytoplankton bloom characterized by the dominance of the toxic raphidophytes Heterosigma akashiwo and Pseudochattonella verruculosa, whose presence indicate a new potential hazard in Brittany. Interview analysis of citizen observations showed that the contributors to Phenomer are generally well-informed on environmental issues and concerned about the status of the marine environment. Phenomer demonstrates the complementary value of citizen science programs to routine phytoplankton monitoring, as well as providing scientific information on water discolorations phenomena, whose observations over a large territory have rarely been structured. The advantages and limits shown by the Phenomer project will help to optimize future applications of citizen science approaches for phytoplankton and HAB studies

Consistent patterns of spatial variability between NE Atlantic and Mediterranean rocky shores

In the frame of the COST ACTION ‘EMBOS’ (Development and implementation of a pan-European Marine Biodiversity Observatory System), coverage of intertidal macroalgae was estimated at a range of marine stations along the European coastline (Subarctic, Baltic, Atlantic, Mediterranean). Based on these data, we tested whether patterns in macroalgal diversity and distribution along European intertidal rocky shores could be explained by a set of meteo-oceanographic variables. The variables considered were salinity, sea surface temperature, photosynthetically active radiation, significant wave height and tidal range and were compiled from three different sources: remote sensing, reanalysis technique and in situ measurement. These variables were parameterized to represent average conditions (mean values), variability (standard deviation) and extreme events (minimum and maximum values). The results obtained in this study contribute to reinforce the EMBOS network approach and highlight the necessity of considering meteo-oceanographic variables in long-term assessments. The broad spatial distribution of pilot sites has allowed identification of latitudinal and longitudinal gradients manifested through species composition, diversity and dominance structure of intertidal macroalgae. These patterns follow a latitudinal gradient mainly explained by sea surface temperature, but also by photosynthetically active radiation, salinity and tidal range. Additionally, a longitudinal gradient was also detected and could be linked to wave height

Geographic patterns of biodiversity in European coastal marine benthos

Within the COST action EMBOS (European Marine Biodiversity Observatory System) the degree and variation of the diversity and densities of soft-bottom communities from the lower intertidal or the shallow subtidal was measured at 28 marine sites along the European coastline (Baltic, Atlantic, Mediterranean) using jointly agreed and harmonized protocols, tools and indicators. The hypothesis tested was that the diversity for all taxonomic groups would decrease with increasing latitude. The EMBOS system delivered accurate and comparable data on the diversity and densities of the soft sediment macrozoobenthic community over a large-scale gradient along the European coastline. In contrast to general biogeographic theory, species diversity showed no linear relationship with latitude, yet a bell-shaped relation was found. The diversity and densities of benthos were mostly positively correlated with environmental factors such as temperature, salinity, mud and organic matter content in sediment, or wave height, and related with location characteristics such as system type (lagoons, estuaries, open coast) or stratum (intertidal, subtidal). For some relationships, a maximum (e.g. temperature from 15–20°C; mud content of sediment around 40%) or bimodal curve (e.g. salinity) was found. In lagoons the densities were twice higher than in other locations, and at open coasts the diversity was much lower than in other locations. We conclude that latitudinal trends and regional differences in diversity and densities are strongly influenced by, i.e. merely the result of, particular sets and ranges of environmental factors and location characteristics specific to certain areas, such as the Baltic, with typical salinity clines (favouring insects) and the Mediterranean, with higher temperatures (favouring crustaceans). Therefore, eventual trends with latitude are primarily indirect and so can be overcome by local variation of environmental factors

Temperature is a key factor in Micromonas-virus interactions

International audienceThe genus Micromonas comprises phytoplankton that show among the widest latitudinal distributions on Earth, and members of this genus are recurrently infected by prasinoviruses in contrasted thermal ecosystems. In this study, we assessed how temperature influences the interplay between the main genetic clades of this prominent microalga and their viruses. The growth of three Micromonas strains (Mic-A, Mic-B, Mic-C) and the stability of their respective lytic viruses (MicV-A, MicV-B, MicV-C) were measured over a thermal range of 4–32.5 °C. Similar growth temperature optima (Topt) were predicted for all three hosts but Mic-B exhibited a broader thermal tolerance than Mic-A and Mic-C, suggesting distinct thermoacclimation strategies. Similarly, the MicV-C virus displayed a remarkable thermal stability compared with MicV-A and MicV-B. Despite these divergences, infection dynamics showed that temperatures below Topt lengthened lytic cycle kinetics and reduced viral yield and, notably, that infection at temperatures above Topt did not usually result in cell lysis. Two mechanisms operated depending on the temperature and the biological system. Hosts either prevented the production of viral progeny or maintained their ability to produce virions with no apparent cell lysis, pointing to a possible switch in the viral life strategy. Hence, temperature changes critically affect the outcome of Micromonas infection and have implications for ocean biogeochemistry and evolution