Distribution of picophytoplankton and nanophytoplankton along an anthropogenic eutrophication gradient in French Mediterranean coastal lagoons

Abstract

We explored the role of natural and anthropogenic environmental perturbations in shaping the community structure and dynamics of pico-and nanophytoplankton in coastal waters. The distribution patterns of phycoerythrin-rich picocyanobacteria (PE-CYAN) and phycocyanin-rich picocyanobacteria (PC-CYAN), autotrophic picoeukaryotes (PEUK) and nanophytoplankton (NANO) were examined over a period of 3 yr in 24 Mediterranean coastal lagoons displaying wide trophic gradients (from 0.2 to 630 µg chlorophyll a [chl a] l -1 ) and salinity gradients (from fresh to marine waters). In summer, picoplanktonic abundances reached 3 × 10 8 cells l -1, 5 × 10 9 cells l -1 and 6 × 10 10 cells l -1 for PE-CYAN, PC-CYAN and PEUK, respectively. PE-CYAN and PC-CYAN showed opposing responses to environmental gradients, resulting in a restricted dominance of PE-CYAN in oligotrophic marine lagoons and a dominance of PC-CYAN in some eutrophic brackish lagoons. Most lagoons exhibited steady-state nutrient conditions, giving competitive advantages to small eukaryotic algae, even in eutrophic and hypertrophic waters. Among the picophytoplankton, picoeukaryotes (ca. 2 to 3 µm) are the most competitive with increasing nutrient availability; in terms of abundance and biomass, their relative and absolute importance tended to increase with increasing total chl a biomass. Freshwater discharges resulted in large pulses of nutrient and more turbulent systems that altered the structure of the phytoplankton community and stimulated fast-growing NANO composed of phytoflagellates and diatoms (ca. 3 to 6 µm, up to 1.6 × 10 9 cells l -1). Members of the microphytoplankton (ca. 20 to 200 µm) were rarely observed in eutrophic and hypertrophic lagoons and were composed of harmful dinoflagellates in oligotrophic lagoons. These results show that anthropogenic and meteorological changes are highly influential on the composition and size structure of phytoplankton communities.

Candidate gene variation in gilthead sea bream reveals complex spatiotemporal selection patterns between marine and lagoon habitats

“…Since these marinelike nurseries have almost identical fish species composition (Pérez-Ruzafa et al 2011) and similar physico-chemical characteristics (e.g. Bec et al 2011), temporal changes in allele frequency observed between TH and SL may suggest convergence to equilibrium frequencies while fish were genetically distinct at the 2 candidate gene markers in spring. TH and SL individuals were also different for the average size in spring but were not in autumn, indicating that both genotypic and phenotypic convergence occurred in TH and SL.…”

“…In this study, we first specifically assessed the temporal stability of habitat-based genetic differentia-tion at the GH and Prl loci, extending our spatial coverage to another large coastal lagoon, Salses-Leucate (SL), which is a marinelike habitat ecologically similar to the TH lagoon (Bec et al 2011, Mercier et al 2012, Tournois et al 2013. Twenty-one putatively neutral microsatellite loci were analysed together with GH and Prl markers to partition the relative influence of drift and selection in patterns of genetic variation.…”

Unique picoeukaryotic algal community under multiple environmental stress conditions in a shallow, alkaline pan

“…While in situ measurements and focused experimental efforts have provided a substantial amount of information on their ecology, their phylogenetic identification requires the use of molecular biological methods, since their small size mostly hinders microscopic identification on lower taxonomic levels (Callieri 2008). In several cases, the major picoplanktonic groups, picocyanobacteria and picoeukaryotes have been found to show characteristic temporal dynamics with their relative abundance highly depending on various physicochemical factors, such as light intensity, nutrient availability (Bec et al 2011, Winder 2009 or temperature .…”

Multi-element otolith fingerprints unravel sea−lagoon lifetime migrations of gilthead sea bream Sparus aurata

“…1). These 3 lagoons are the largest in the study area (Table 1) Bec et al (2011) and IFREMER (2002, 2008, 2009 (Lasserre 1976, Quignard et al 1984 and, because of their differences in marine influence, main freshwater source, depth, and productivity, are good representatives of the contrasts in lagoon environmental conditions existing within the Languedoc-Roussillon region (Table 1). Seasonal variations in the signature for the marine habitat were assessed mainly from detailed analysis of the otoliths of 3 aquaculture fish (total length [TL]: 30.4 to 32.4 cm) collected at a local offshore farm (Pro vence Aquaculture, Frioul Island, 43°16' N, 5°18' E; Fig.…”