Cross-Hemisphere Study Reveals Geographically Ubiquitous, Plastic-Specific Bacteria Emerging from the Rare and Unexplored Biosphere

While it is now appreciated that the millions of tons of plastic pollution travelling through marine systems carry complex communities of microorganisms, it is still unknown to what extent these biofilm communities are specific to the plastic or selected by the surrounding ecosystem. To address this, we characterized and compared the microbial communities of microplastic particles, nonplastic (natural and wax) particles, and the surrounding waters from three marine ecosystems (the Baltic, Sargasso and Mediterranean seas) using high-throughput 16S rRNA gene sequencing. We found that biofilm communities on microplastic and nonplastic particles were highly similar to one another across this broad geographical range. The similar temperature and salinity profiles of the Sargasso and Mediterranean seas, compared to the Baltic Sea, were reflected in the biofilm communities. We identified plastic-specific operational taxonomic units (OTUs) that were not detected on nonplastic particles or in the surrounding waters. Twenty-six of the plastic-specific OTUs were geographically ubiquitous across all sampled locations. These geographically ubiquitous plastic-specific OTUs were mostly low-abundance members of their biofilm communities and often represented uncultured members of marine ecosystems. These results demonstrate the potential for plastics to be a reservoir of rare and understudied microbes, thus warranting further investigations into the dynamics and role of these microbes in marine ecosystems

The Seasonal and Inter-Annual Fluctuations of Plankton Abundance and Community Structure in a North Atlantic Marine Protected Area

Marine Protected Areas have become a major tool for the conservation of marine biodiversity and resources. Yet our understanding of their efficacy is often limited because it is measured for a few biological components, typically top predators or species of commercial interest. To achieve conservation targets, marine protected areas can benefit from ecosystem-based approaches. Within such an approach, documenting the variation of plankton indicators and their covariation with climate is crucial as plankton represent the base of the food webs. With this perspective, we sought to document the variations in the emerging properties of the plankton to better understand the dynamics of the pelagic fishes, mammals and seabirds that inhabit the region. For the first time, we analyze the temporal variations of the entire plankton community of one of the widest European protected areas, the Parc Naturel Marin de la Mer d’Iroise. We used data from several sampling transects carried out in the Iroise Sea from 2011 to 2015 to explore the seasonal and inter-annual variations of phytoplankton and mesozooplankton abundance, composition and size, as well as their covariation with abiotic variables, through multiple multivariate analyses. Overall, our observations are coherent with the plankton dynamics that have been observed in other regions of the North-East Atlantic. We found that both phytoplankton and zooplankton show consistent seasonal patterns in taxonomic composition and size structure but also display inter-annual variations. The spring bloom was associated with a higher contribution of large chain-forming diatoms compared to nanoflagellates, the latter dominating in fall and summer. Dinoflagellates show marked inter-annual variations in their relative contribution. The community composition of phytoplankton has a large impact on the mesozooplankton together with the distance to the coast. The size structure of the mesozooplankton community, examined through the ratio of small to large copepods, also displays marked seasonal patterns. We found that larger copepods (members of the Calanidae) are more abundant in spring than in summer and fall. We propose several hypotheses to explain the observed temporal patterns and we underline their importance for understanding the dynamics of other components of the food-web (such as sardines). Our study is a first step toward the inclusion of the planktonic compartment into the planning of the resources and diversity conservation within the Marine Protected Area

Morphological diversity increases with oligotrophy along a zooplankton time series

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Individual shrinking to enhance population survival: quantifying the reproductive and metabolic expenditures of a starving jellyfish, Pelagia noctiluca

The holoplanktonic jellyfish Pelagia noctiluca is renowned for periods of high abundance, causing considerable problems to tourism and aquaculture. Little is understood about the drivers of its periodic presence and absence or how it survives unfavourable periods. Studying the effect of starvation, we evaluated the main metabolic expenses (reproduction, respiration and excretion) during those periods. P. noctiluca could shrink in size, losing up to 85% of their mass (6.6-7.1% loss day(-1)), while continuing to release eggs quasi-daily over a 28-day period. Egg production was proportional to size (mean 759 eggs day(-1) at 6 cm bell diameter), with up to 19 526 eggs released in a single spawn, thereby providing huge potential for population growth despite undergoing starvation. Small food rations decreased the rate of shrinking to 3.1% day(-1), prolonging life (49 days), potentially enhancing the chances of encountering more prey and regrowing. Metabolism increased with wet mass (allometric exponent: 0.93 for respiration, 0.82 for ammonium), however reproduction was the greatest carbon expenditure for individuals larger than 9 cm bell diameter. Temperature (9-29 degrees C) also significantly increased both respiration and, to a greater extent, excretion (Q(10) = 2.25 and 4.76). Consequentially a warming ocean may negatively affect survival rates unless prey abundance balances the increased metabolic demands

Morphological diversity increases with oligotrophy along a zooplankton time series

International audienceBiological diversity encompasses all the variations of life, from genes to ecosystems, and is typically described from a taxonomic, genetic, phylogenetic, or functional point of view. Here we describe the changes in morphological diversity of zooplankton along a coastal time series. Morphology is of course characteristic of taxa but also has functional consequences; size, for example, is often considered as a dominant functional trait for zooplankton. Using high-throughput imaging of weekly plankton samples, collected from 2009 to 2017 in the Mediterranean Sea, we automatically measured ~40 morphological traits on ~542,000 individuals. A reduced morphological space was defined through Principal Component Analysis and individuals were regrouped in 200 "morphs" through clustering in that space. In this morphological space, time series of indices of morphological richness, divergence, and evenness were computed using the same metrics as the ones usually defined for functional diversity. Size, circularity, and opacity were the characteristics of the organisms that varied the most along the series. The morphs were homogeneous in appearance and recognisable, but often comprised more than one taxon. All morphological diversity indices were lower in the spring. This seemed related to the dominance of copepods during this season, which are quite homogeneous in appearance. But this could also be caused by selective disadvantages of extreme (and specialised) morphological types in this relatively eutrophic time of the year. Over the nine years, morphological divergence increased significantly while overall plankton concentrations decreased; since 2001, surface waters became significantly warmer and more oligotrophic. Overall, this fits the theory that oligotrophy leads to niche specialisation which, here, translates into morphological divergence

Statistical Methodology for Identifying Microplastic Samples Collected During TARA Mediterranean Campaign

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Morphological diversity increases with decreasing resources along a zooplankton time series

International audienceBiodiversity is studied notably because of its reciprocal relationship with ecosystem functions such as production. Diversity is traditionally described from a taxonomic, genetic or functional point of view but the diversity in organism morphology is seldom explicitly considered, except for body size. We describe morphological diversity of marine zooplankton seasonally and over 12 years using quantitative imaging of weekly plankton samples, in the northwestern Mediterranean Sea. We extract 45 morphological features on greater than 800 000 individuals, which we summarize into four main morphological traits (size, transparency, circularity and shape complexity). In this morphological space, we define objective morphological groups and, from those, compute morphological diversity indices (richness, evenness and divergence) using metrics originally defined for functional diversity. On both time scales, morphological diversity increased when nutritive resources and plankton concentrations were low, thus matching the theoretical reciprocal relationship. Over the long term at least, this diversity increase was not fully attributable to taxonomic diversity changes. The decline in the most common plankton forms and the increase in morphological variance and in extreme morphologies suggest a mechanism akin to specialization under low production, with likely consequences for trophic structure and carbon flux

Changes in the Floating Plastic Pollution of the Mediterranean Sea in Relation to the Distance to Land.

The composition, size distribution, and abundance of floating plastic debris in surface waters of the Mediterranean Sea were analyzed in relation to distance to land. We combined data from previously published reports with an intensive sampling in inshore waters of the Northwestern Mediterranean. The highest plastic concentrations were found in regions distant from from land as well as in the first kilometer adjacent to the coastline. In this nearshore water strip, plastic concentrations were significantly correlated with the nearness to a coastal human population, with local areas close to large human settlements showing hundreds of thousands of plastic pieces per km2. The ratio of plastic to plankton abundance reached particularly high values for the coastal surface waters. Polyethylene, polypropylene and polyamides were the predominant plastic polymers at all distances from coast (86 to 97% of total items), although the diversity of polymers was higher in the 1-km coastal water strip due to a higher frequency of polystyrene or polyacrylic fibers. The plastic size distributions showed a gradual increase in abundance toward small sizes indicating an efficient removal of small plastics from the surface. Nevertheless, the relative abundance of small fragments (< 2 mm) was higher within the 1-km coastal water strip, suggesting a rapid fragmentation down along the shoreline, likely related with the washing ashore on the beaches. This study constitutes a first attempt to determine the impact of plastic debris in areas closest to Mediterranean coast. The presence of a high concentration of plastic including tiny plastic items could have significant environmental, health and economic impacts

Culture and growth of the jellyfish Pelagia noctiluca in the laboratory

International audienceFour cohorts of the scyphozoan jellyfish Pelagia noctiluca were grown in the laboratory. For the first time, P. noctiluca was grown from eggs through to reproductive adults. The maximum life span in the laboratory was 17 mo. Pelagia noctiluca were first observed to release gametes at an umbrella diameter of 2.4 cm. Laboratory growth under steady feeding conditions showed initial growth followed by stagnation until dietary conditions were altered. A mismatch between the availability of optimal food and the presence of developmental stages may significantly increase the mortality rates of the young stages. Non-motile prey improved survival of ephyrae stages compared with zooplankton, but good survival and ephyrae growth were only obtained with a high-energy sea urchin egg diet. Maximal growth rates were up to 30% d(-1) for young ephyrae and 1.5-4% d(-1) for adults. Maximal growth rates were comparable between laboratory and in situ growth observations in the Ligurian Sea during 1969 and 2013. Combining observations would suggest that 230 d of continuous growth are required to reach the largest mean size observed in the wild (June 2013, mean +/- SD = 15.6 +/- 2.8 cm, range = 12-21 cm). We suggest that 90-120 d of continuous growth from planula larvae would yield reproductive individuals under ideal growing conditions. We discuss the daily prey abundances required by each individual to sustain basal metabolism and the observed growth rates