Comparison of zooplankton community structure between impacted and non-impacted areas of Paranagua Bay Estuarine Complex, south Brazil

We analysed the seasonal distribution of the zooplankton community in an anthropogenically impacted area (Paranagua Bay) and a non-impacted area (Laranjeiras Bay) of the Paranagua Bay Estuarine Complex. Large phytoplankton (>50 mu m) and zooplankton were collected every two months, between August 2003 and June 2004. The phytoplankton community was numerically dominated by diatoms (78%) and dinoflagellates (19%). Zooplankton abundance varied between 670 and 100,716 individuals m(-3), with a dominance of copepods, mainly the calanoids Acartia lilljeborgii, Acartia tonsa and Pseudodiaptomus acutus. A clear seasonal pattern was observed: copepods were significantly more abundant during the rainy than in the dry season. Significant differences in abundance between the two bays were detected only for cirripede larvae, which were more abundant in Paranagua Bay. This lack of difference between the two areas was probably a consequence of the water circulation along the estuary, which may have diluted and dispersed the pollutants from Paranagua Bay to other areas of the estuary.

INTERSPECIFIC VARIATION OF THE BACTERIAL COMMUNITY STRUCTURE IN THE PHYLLOSPHERE OF THE THREE MAJOR PLANT COMPONENTS OF MANGROVE FORESTS

Mangrove forests encompass a group of trees species that inhabit the intertidal zones, where soil is characterized by the high salinity and low availability of oxygen. The phyllosphere of these trees represent the habitat provided on the aboveground parts of plants, supporting in a global scale, a large and complex microbial community. The structure of phyllosphere communities reflects immigration, survival and growth of microbial colonizers, which is influenced by numerous environmental factors in addition to leaf physical and chemical properties. Here, a combination of culture-base methods with PCR-DGGE was applied to test whether local or plant specific factors shape the bacterial community of the phyllosphere from three plant species (Avicenia shaueriana, Laguncularia racemosa and Rhizophora mangle), found in two mangroves. The number of bacteria in the phyllosphere of these plants varied between 3.62 x 10(4) in A. schaeriana and 6.26 x 10(3) in R. mangle. The results obtained by PCR-DGGE and isolation approaches were congruent and demonstrated that each plant species harbor specific bacterial communities in their leaves surfaces. Moreover, the ordination of environmental factors (mangrove and plant species), by redundancy analysis (RDA), also indicated that the selection exerted by plant species is higher than mangrove location on bacterial communities at phyllosphere.

Interspecific variation of the bacterial community structure in the phyllosphere of the three major plant components of mangrove forests

Mangrove forests encompass a group of trees species that inhabit the intertidal zones, where soil is characterized by the high salinity and low availability of oxygen. The phyllosphere of these trees represent the habitat provided on the aboveground parts of plants, supporting in a global scale, a large and complex microbial community. The structure of phyllosphere communities reflects immigration, survival and growth of microbial colonizers, which is influenced by numerous environmental factors in addition to leaf physical and chemical properties. Here, a combination of culture-base methods with PCR-DGGE was applied to test whether local or plant specific factors shape the bacterial community of the phyllosphere from three plant species (Avicenia shaueriana, Laguncularia racemosa and Rhizophora mangle), found in two mangroves. The number of bacteria in the phyllosphere of these plants varied between 3.62 x 10(4) in A. schaeriana and 6.26 x 10³ in R. mangle. The results obtained by PCR-DGGE and isolation approaches were congruent and demonstrated that each plant species harbor specific bacterial communities in their leaves surfaces. Moreover, the ordination of environmental factors (mangrove and plant species), by redundancy analysis (RDA), also indicated that the selection exerted by plant species is higher than mangrove location on bacterial communities at phyllosphere.

Planktonic community structure and variability in the Canary Islands waters: the role of microplankton

[ES] En este trabajo hemos contribuido al estudio de la estructura de la comunidad planctónica y a su variabilidad temporal, utilizando un enfoque de end-to-end , desde las bacterias hasta el mesozooplancton haciendo especial énfasis en el microplancton. Nuestro trabajo muestra la importancia de los efectos bottom-up y top-down que regulan la estructura de las comunidades planctónicas.

Ichthyofauna associated with Cymodocea nodosa meadows in the Canarian Archipelago (central eastern Atlantic): Community structure and nursery role

We carried out 84 trawls in 41 seagrass meadows composed of the phanerogam Cymodocea nodosa at three islands of the Canarian Archipelago, during June to September 2003, in order to describe the associated ichthyofauna (composition, richness, and abundance), to analyze the role that this habitat can play in fish recruitment, and to determine the potential relationship between the spatial structure of the seagrass meadow and the patterns of richness and abundance of the fish assemblage. A total of 8298 individuals were captured. The five most relevant species, in terms of abundance and frequency, were Spondyliosoma cantharus, Diplodus annularis, Syngnathus typhle, Mullus surmuletus, and Pagellus erythrinus. Gran Canaria had the largest species richness (36 species) and mean number of species per sample (8.69 ± 0.49; mean ± SE). Lanzarote had the largest number of individuals (64.83% of the total registered) and mean total abundance per sample (168.39 ± 30.91). High densities of individuals were registered (95.86 ± 13.5) and 92.91% of fishes were juveniles. Our data showed that the physical configuration of the seagrass meadows did not significantly affect the patterns of richness and abundance of the associated fish assemblage. In conclusion, the C. nodosa meadows exhibited a singular ichthyofauna and they contribute to the maintenance of the diversity of the coastal fish assemblages in the Canarian Archipelago. This habitat constitutes, during spring and summer, a nursery habitat for juvenile fishes of many species, several of them commercially targeted.

Mesoscale eddies: Hotspots of prokaryotic activity and differential community structure in the ocean

[EN] To investigate the effects of mesoscale eddies on prokaryotic assemblage structure and activity, we sampled two cyclonic eddies (CEs) and two anticyclonic eddies (AEs) in the permanent eddy-field downstream the Canary Islands. The eddy stations were compared with two far-field (FF) stations located also in the Canary Current, but outside the influence of the eddy field. The distribution of prokaryotic abundance (PA), bulk prokaryotic heterotrophic activity (PHA), various indicators of single-cell activity (such as nucleic acid content, proportion of live cells, and fraction of cells actively incorporating leucine), as well as bacterial and archaeal community structure were determined from the surface to 2000m depth. In the upper epipelagic layer (0?200 m), the effect of eddies on the prokaryotic community was more apparent, as indicated by the higher PA, PHA, fraction of living cells, and percentage of active cells incorporating leucine within eddies than at FF stations. Prokaryotic community composition differed also between eddy and FF stations in the epipelagic layer. In the mesopelagic layer (200?1000 m), there were also significant differences in PA and PHA between eddy and FF stations, although in general, there were no clear differences in community composition or single-cell activity. The effects on prokaryotic activity and community structure were stronger in AE than CE, decreasing with depth in both types of eddies. Overall, both types of eddies show distinct community compositions (as compared with FF in the epipelagic), and represent oceanic ?hotspots? of prokaryotic activity (in the epi- and mesopelagic realms).

Mesozooplankton community structure during summer months in the Bay of Cádiz

[EN] Mesozooplankton organisms (>250 μm) were sampled at two stations (inner and outer Bay) in the Bay of Cádiz between May and July 2008. Samples were analysed by means of a semi-automated technique in order to give a preliminary view of the mesoozooplankton community structure in the Bay, based on taxonomic diversity and biomass distribution among size classes. The abundance of organisms increased from May to July in accordance with the increase in temperature and Chlorophyll a (Chla) concentrations. Abundances were higher in the outer Bay station, where Chla concentrations are greater and the water column is more stable. The community changed from being meroplankton- to holoplankton-based due to an increase of Calanoida and especially Cladocera individuals (mainly Peniliaavirostris), which are known to peak acutely in the summer. The analysis of Normalised Biomass-Size spectra revealed fairly steep slopes (average -1.3) and relatively high departures from steady state (r2 = 0.8 – 0.94), expectable in a coastal system such as the Bay of Cádiz were disturbance factors are introduced from benthic and tidal processes, together with anthropogenic pressure.

Is there a seamount effect on microbial community structure and biomass?: the case study of Seine and Sedlo seamounts (Northeast Atlantic)

[EN] Seamounts are considered to be ??hotspots?? of marine life but, their role in oceans primary productivity is still under discussion. We have studied the microbial community structure and biomass of the epipelagic zone (0?150 m) at two northeast Atlantic seamounts (Seine and Sedlo) and compared those with the surrounding ocean. Results from two cruises to Sedlo and three to Seine are presented. Main results show large temporal and spatial microbial community variability on both seamounts. Both Seine and Sedlo heterotrophic community (abundance and biomass) dominate during winter and summer months, representing 75% (Sedlo, July) to 86% (Seine, November) of the total plankton biomass. In Seine, during springtime the contribution to total plankton biomass is similar (47% autotrophic and 53% heterotrophic). Both seamounts present an autotrophic community structure dominated by small cells (nano and picophytoplankton). It is also during spring that a relatively important contribution (26%) of large cells to total autotrophic biomass is found. In some cases, a ??seamount effect?? is observed on Seine and Sedlo microbial community structure and biomass. In Seine this is only observed during spring through enhancement of large autotrophic cells at the summit and seamount stations. In Sedlo, and despite the observed low biomasses, some clear peaks of picoplankton at the summit or at stations within the seamount area are also observed during summer. Our results suggest that the dominance of heterotrophs is presumably related to the trapping effect of organic matter by seamounts. Nevertheless, the complex circulation around both seamounts with the presence of different sources of mesoscale variability (e.g. presence of meddies, intrusion of African upwelling water) may have contributed to the different patterns of distribution, abundances and also changes observed in the microbial community.

Patterns in marine microbial community structure

Programa en Oceanografía

Prokaryotic community structure in ultra-slow spreading Southwest Indian Ridge.

The Southwest Indian Ridge segment that extends between 10° and 16° E has the slowest spreading rate of any other oceanic ridge (about 8.4 mm/year). In 2013 during the expedition ANTXXIX/8 seismology, geology, microbiology, heat flow analyses were carried out. Here, no hydrothermal plumes or black smoker systems were found but the results of the survey allowed to identify areas with peculiar characteristics: Area 1 with higher heat flux bsf; Area 2 where in 2002 the presence of hydrothermal emissions was hypothesized (Bach et al., 2002); Area 3 with anomalies of methane, ammonium, sulphide and dissolved inorganic carbon in pore water sediment profiles, and recovery of fauna vents. All these aspects suggest the presence of a hydrothermal circulation. Using Illumina 16S gene tag, statistical tools and phylogenetic trees, I provided a biological proof of the presence of hydrothermal circulation in this ridge segment. At Area 3, alpha and beta diversity indexes showed similarities with those described for venting microbial communities and about 40-70% of the dominant microbial community was found phylogenetically related to clones isolated hydrothermal-driven environments. Although the majority of chemosynthetic environment related taxa were not classified like autotrophic prokaryotes, some of them are key taxa in support of the presence of hydrothermal circulation, since they are partners of consortia or mediate specific reaction typically described for hydrothermal and seep environments, or are specialized organisms in exploiting labile organic substrates. Concluding, these results are remarkable because support the importance of ultra slow spreading ridge systems in contributing to global geochemical cycles and larval dispersion of vent fauna.

Diatoms community structure in superficial sediments of eight Andean lakes of central Chile

In this research the taxonomic structure of diatoms in sediments of high mountain lakes was studied. These lakes are located in Chile between 32°49' and 38°48' S in the Andean Cordillera. A total of 99 diatom taxa distributed in 48 genera were identified and all this taxa are cosmopolitan excepting a Eunotia andinofrequens, Gomphonema punae, Pinnularia araucanensis and Pinnularia acidicola, which are know only for the Southern Hemisphere. The assemblages of diatoms were different in the studied lakes. So the high mountain lakes Ocho, Huifa, Ensueño and Negra, dominated benthic diatoms which are typical of oligotrophic and acid waters as Achnanthidium exiguum, Achnanthidium minutissimum, Encyonema minutum, Pinnularia acidicola and Planothidium lanceolatum. In the assemblages from lakes Galletué, Icalma and Laja planktonic diatoms were more abundant, which are common in alkaline and mesotrophic waters, e.g., Asterionella formosa, Aulacoseira distans, Aulacoseira granulata, Cyclotella stelligera and Rhopalodia gibba.