Copepod‐associated microbial biogeography in the epipelagic ocean

Distribution of artificial radionuclides in deep sediments of the Mediterranean Sea

In oceanic ecosystems, the nature of barriers to gene flow and the processes by which populations may become isolated are different from the terrestrial environment, and less well understood. In this study we investigate a highly mobile species (the sperm whale, Physeter macrocephalus) that is genetically differentiated between an open North Atlantic population and the populations in the Mediterranean Sea. We apply high-resolution single nucleotide polymorphism (SNP) analysis to study the nature of barriers to gene flow in this system, assessing the putative boundary into the Mediterranean (Strait of Gibraltar and Alboran Sea region), and including novel analyses on structuring among sperm whale populations within the Mediterranean basin. Our data support a recent founding of the Mediterranean population, around the time of the last glacial maximum, and show concerted historical demographic profiles in both the Atlantic and the Mediterranean. In each region there is evidence for a population decline around the time of the founder event. The largest decline was seen within the Mediterranean Sea where effective population size is substantially lower (especially in the eastern basin). While differentiation is strongest at the Atlantic/Mediterranean boundary, there is also weaker but significant differentiation between the eastern and western basins of the Mediterranean Sea. We propose, however, that the mechanisms are different. While post-founding gene flow was reduced between the Mediterranean and Atlantic populations, within the Mediterranean an important factor differentiating the basins is probably a greater degree of admixture between the western basin and the North Atlantic and some level of isolation between the western and eastern Mediterranean basins. Subdivision within the Mediterranean Sea exacerbates conservation concerns and will require consideration of what distinct impacts may affect populations in the two basins.

Primary and bacterial production in the Mediterranean Sea: a modelling study

Abstract. The Mediterranean Sea is one of the most oligotrophic regions of the oceans, and nutrients have been shown to limit both phytoplankton and bacterial activities, resulting in a potential major role of dissolved organic carbon (DOC) export in the biological pump. Strong DOC accumulation in surface waters is already well documented, though measurements of DOC stocks and export flux are still sparse and associated with major uncertainties. This study provides the first basin-scale overview and analysis of organic carbon stocks and export fluxes in the Mediterranean Sea through a modeling approach based on a coupled model combining a mechanistic biogeochemical model (Eco3M-MED) and a high-resolution (eddy-resolving) hydrodynamic simulation (NEMO-MED12). The model is shown to reproduce the main spatial and seasonal biogeochemical characteristics of the Mediterranean Sea. Model estimations of carbon export are also of the same order of magnitude as estimations from in situ observations, and their respective spatial patterns are mutually consistent. Strong differences between the western and eastern basins are evidenced by the model for organic carbon export. Though less oligotrophic than the eastern basin, the western basin only supports 39 % of organic carbon (particulate and dissolved) export. Another major result is that except for the Alboran Sea, the DOC contribution to organic carbon export is higher than that of particulate organic carbon (POC) throughout the Mediterranean Sea, especially in the eastern basin. This paper also investigates the seasonality of DOC and POC exports as well as the differences in the processes involved in DOC and POC exports in light of intracellular quotas. Finally, according to the model, strong phosphate limitation of both bacteria and phytoplankton growth is one of the main drivers of DOC accumulation and therefore of export.

Recruitment of Yellow Perch ( Perca flavescens) Affected by Stock Size and Water Temperature in Lakes Erie and St. Clair, 1965–85

By analyzing in situ observations and conducting a series of ocean general circulation model experiments, this study investigates the physical processes controlling intraseasonal variability (ISV) of the Equatorial Undercurrent (EUC) of the Indian Ocean. ISV of the EUC leads to time-varying water exchanges between the western and eastern equatorial Indian Ocean. For the 2001–14 period, standard deviations of the EUC transport variability are 1.92 and 1.77 Sv (1 Sv ≡ 106 m3 s−1) in the eastern and western basins, respectively. The ISV of the EUC is predominantly caused by the wind forcing effect of atmospheric intraseasonal oscillations (ISOs) but through dramatically different ocean dynamical processes in the eastern and western basins. The stronger ISV in the eastern basin is dominated by the reflected Rossby waves associated with intraseasonal equatorial zonal wind forcing. It takes 20–30 days to set up an intraseasonal EUC anomaly through the Kelvin and Rossby waves associated with the first and second baroclinic modes. In the western basin, the peak intraseasonal EUC anomaly is generated by the zonal pressure gradient force, which is set up by radiating equatorial Kelvin and Rossby waves induced by the equatorial wind stress. Directly forced and reflected Rossby waves from the eastern basin propagate westward, contributing to intraseasonal zonal current near the surface but having weak impact on the peak ISV of the EUC.

Of 2427 walleyes (Stizostedion vitreum vitreum (Mitchill)) examined from Lake Erie in 1964–66, no females were mature at ages below III and all were mature at age V. All male walleyes from the eastern basin were mature at age II, and those from the western basin at age III. Females from the western basin matured at a shorter length and a younger age than those from the eastern basin. Males from the western basin, on the other hand, matured at a longer length and greater age than those from the eastern basin.Egg production, which was estimated for 60 walleyes from the eastern basin and 78 from the western basin, ranged from 48,000 to 614,000. The number of eggs increased rapidly with increase in total length, but the relation between fecundity and weight was almost linear. Walleyes from the western basin were much more fecund for any given length, weight, or age than those from the eastern basin. Weight was the most accurate indicator of fecundity. The mean diameter of eggs from 32 ripe walleyes was 1.72 mm. Little relation existed between egg diameter and length or age of fish.

Estimating climatological age from a model-derived oxygen–age relationship in the Mediterranean

Seventeen years (1998–2014) of satellite-derived chlorophyll concentration (Chl) are used to analyse the seasonal and non-seasonal patterns of Chl variability and the long-term trends in phytoplankton phenology in the Mediterranean Sea. With marked regional variations, we observe that seasonality dominates variability representing up to 80% of total Chl variance in oceanic areas, whereas in shelf-sea regions high frequency variations may be dominant representing up to 49% of total Chl variance. Seasonal variations are typically characterized by a phytoplankton growing period occurring in spring and spanning on average 170 days in the western basin and 150 days in the eastern basin. The variations in peak Chl concentrations are higher in the western basin (0.88 ± 1.01 mg m−3) compared to the eastern basin (0.35 ± 1.36 mg m−3). Differences in the seasonal cycle of Chl are also observed between open ocean and coastal waters where more than one phytoplankton growing period are frequent (>0.8 probability). During the study period, on average in the western Mediterranean basin (based on significant trends observed over ~95% of the basin), we show a positive trend in Chl of +0.015 ± 0.016 mg m−3 decade−1, and an increase in the amplitude and duration of the phytoplankton growing period by +0.27 ± 0.29 mg m−3 decade−1 and +11 ± 7 days decade−1 respectively. Changes in Chl concentration in the eastern (and more oligotrophic) basin are generally low, with a trend of −0.004 ± 0.024 mg m−3 decade−1 on average (based on observed significant trends over ~70% of the basin). In this basin, the Chl peak has declined by −0.03 ± 0.08 mg m−3 decade−1 and the growing period duration has decreased by −12 ± 7 days decade−1. The trends in phytoplankton Chl and phenology, estimated in this study over the period 1998–2014, do not reveal significant overall decline/increase in Chl concentration or earlier/delayed timings of the seasonal peak on average over the entire Mediterranean Sea basin. However, we observed large regional variations, suggesting that the response of phytoplankton to environmental and climate forcing may be complex and regionally driven.

The Caribbean basins, surrounded by lands and islands marked by a history of tectonic and volcanic activity, have remained remarkably stable throughout the Cenozoic. Sedimentation has been characterized by pelagic biogenic material and volcanic ash typical of a deep marine environment. Acoustic basement, reached at 5 sites by the Deep Sea Drilling Project, is composed of Late Cretaceous dolerites and basalts considerably younger than the surrounding lands. The Mediterranean Sea may be divided into eastern and western basins. The eastern basin is dominated by the Hellenic arc, an island-arc structure, and the Mediterranean Ridge, a low ridge characterized by thick folded and faulted sediments. The western basin has more features in common with the Gulf of Mexico, such as thick terrigenous sediments and salt diapirs. Drilling has revealed buried evaporites in association with shallow water sediment and fossil indicators that led the scientific team to the conclusion that the Mediterranean desiccated during the late Miocene. End_of_Article - Last_Page 616------------

Oxygen consumption, new production, vertical advection and environmental evolution in the Mediterranean Sea

One of the main challenges in soil science lies in the passage from heterogeneous soil structure to a quantified multi-scale 3D model. Here a new approach to quantify the microbial distribution relating to soil pore structure is presented. Characterising 3D microbial soil structural in digital porous media is not found and most soil process models tend to assume a homogenous spatial distribution of microbes. We measured the in situ spatial distribution of bacteria in arable soils across scales from sub-micrometers to metres and here we describe further progress to quantify and explicitly model the 3D microbial distributions, based on a stochastic Bayesian approach to predict spatial variation in the underlying bacterial intensity measure. A 3D higher order Multi-Markov chain model is introduced to model complex geometry of real soil structure and associated microbial distribution. In this study, Markov random fields are used to construct multiscale 3D Pore Architecture Models (PAM). The binary structure of PAM has been successfully used to predict multiphase flow behaviour in porous media such as hydrocarbon bearing reservoir rocks, we explore further to use such a new multi-components scheme in modelling pore structure incorporating with microbial spatial distribution, the multicomponent Markov chain model, which is a stationary multiple higher order Markov chain. The models parameterisation is based on high resolution SEM images of soil that have been prepared in a manner that preserves the microbial community information in situ. Based on the quantified 3D multiscale soil structure associated with microbial distribution components, the accurate reactive flow of microbial degradation can be simulated to predict environmental impact of microbial activates in the field. A variety of examples of structures and bacterial distribution created by the models are presented.

Surface samples of phytoplankton were collected from April to December 1970 at approximately 4-wk intervals from 25 stations distributed over the entire lake. Taxonomic identification and enumeration was done by the Utermöhl technique. About 125–150 species were identified in each basin. "Less common" or rare species contributed significantly to the total phytoplankton biomass. The species comparison among the three basins indicated that species like Rhodomonas minuta and Cryptomonas erosa were perennial in all the basins. Aphanizomenon flos-aquae, Anabaena spiroides var. contracta, Coscinodiscus rothii, Actinastrum hantzschii, and Ceratium hirundinella were typical for the Western basin. Ochromonas spp. and Peridinium aciculiferum were common in the Central basin whereas Gymnodinium helveticum and G. uberrimum were characteristic for the Eastern basin.The diatoms contributed least in the Eastern basin (36%) but showed high percentage in both Central (55%) and Western (58%) basins. The phytoflagellates made important contributions in the three basins; highest percentage (41%) was in the Eastern basin. Phytoflagellate abundance increased from west to east and appeared to have a wide range of adaptability to different nutrient conditions. During July and August high biomass concentration but uneven horizontal distribution was observed. Phytoplankton biomass ranged between 0.8 and 13.2, 0.6 and 6.0, and 1.0 and 4.2 g/m3 in the Western, Central, and Eastern basins, respectively. The highest biomass of 13.2 g/m3 was in the Western basin during April. Inshore–offshore differentiation was observed in the Central and Eastern basins with many peaks in the inshore region. Size analysis of phytoplankton on a few stations showed that the nannoplankton [Formula: see text] comprised a major portion of phytoplankton biomass during spring and fall periods. Based on maximum biomass concentration the Lake Erie Western basin was classified as highly eutrophic, the Eastern basin as mesotrophic, and the Central basin between the mesotrophic and eutrophic conditions.

Zinc budget in the Mediterranean Sea: a hypothesis for non-steady-state behavior

AimThe Mediterranean Sea is a biodiversity hotspot, hosting a wide variety of habitats and organisms resulting from its complex past history and present‐day processes. Although several biogeographical areas are defined within the Mediterranean Sea, a comprehensive description of the main connectivity patterns among these areas is still lacking. In the present work, we describe the main features structuring the past and present genetic diversity and connectivity in a shallow subtidal limpet across the Mediterranean Sea.LocationMediterranean Sea.MethodsThe genetic diversity and structure of the common and widespread limpet Patella caerulea were analysed in 32 locations across the Mediterranean Sea using two mitochondrial markers (COI and 16S) and five nuclear microsatellite loci. Demographic history and phylogenetic analyses were carried out using mitochondrial markers, and assignment tests were performed on nuclear markers.ResultsTwo main evolutionary units were detected according to both mitochondrial markers. The most significant genetic differentiation was located between the southern tip of Sicily and the Calabria Peninsula. However, the full transition between the Western and Eastern basins is broadly located in the area between the Siculo–Tunisian Strait and the eastern Ionian Sea. Highly variable nuclear markers revealed further complexity related to current connectivity patterns, showing a genetic structure in the Sicily Channel and the Tyrrhenian–Ligurian transition and gene flow across the Messina Strait. The three markers showed a consistent pattern of isolation by distance only in the Eastern basin.Main conclusionsComplex connectivity patterns in the central Mediterranean confirm that this area represents a genetic diversity hotspot for limpets, reflecting the interplay of the past and present processes. For this crucial area, we propose to use the term “transition area,” which may better reflect its complexity and so avoid further debate on the location of a single “genetic barrier.”