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Larval dispersal enables demographic and genetic connectivity among marine populations. For many sessile species, it is the only natural mechanism for resilience after major population disturbances, as those that have been affecting Mediterranean gorgonian species inside and outside Marine Protected Areas (MPAs). Larval dispersal simulation is a powerful tool to anticipate connectivity among populations which might be altered by modelling choices. We assessed how flow representation (resolution and vertical turbulence) and larval traits (pelagic larval duration, release timing and duration, larval vertical behaviour) influenced populations connectivity among five coastal rocky locations in the northwestern Mediterranean, four of them being designated as MPAs. We used a finer (0.3 km) and coarser (1.5 km) flow resolution in two years to assess, using a hierarchical simulation approach, the sensitivity of connectivity patterns to the above parameters. Larval traits corresponded to two gorgonian species, the neutrally buoyant Eunicella singularis and the passive sinker Paramuricea clavata. Ocean model resolution was the most influential factor on resulting connectivity patterns. When using the finer flow model resolution, connectivity patterns were equally influenced by all larval traits while vertical turbulence could be neglected. Hence, advising the design of coastal MPAs with regional connectivity estimates requires adequate flow simulation resolution. [ABSTRACT FROM AUTHOR]

Ocean circulation is the engine of dispersal and population connectivity in marine ecosystems, knowledge of which is essential for conservation planning. Understanding connectivity patterns at a large scale can help define the spatial extent of metapopulations. In this study, we built connectivity networks from Lagrangian transport simulations of neutrally buoyant particles released along the Indian coastline, a significant region in the Indian Ocean. We assessed the variation in connectivity networks across release periods for the major drivers of oceanography including the two monsoonal seasons, El Niño–Southern Oscillation (ENSO) years and for the entire range of region‐specific pelagic larval durations (PLDs) for marine invertebrates. We detected well‐connected communities, mapped frequent connectivity breaks, and assessed the functional role of coastal areas within the connectivity network using node metrics. Network characteristics did not differ based on the ENSO year, but varied with season and PLD. Connectance for the Indian coastline was relatively low, ranging from 0.5% to 3.4%, and increased significantly for PLD larger than 20 d. The number of cohesive coastal communities decreased gradually from 60 (PLD < 4 d) to 30 (PLD > 20 d) with increasing PLD. Despite variation in the location of connectivity breaks with the time of particle release within a monsoonal season, four disconnected provinces were consistently identified across the entire PLD range, which partially overlapped with observed genetic and biogeographic breaks reported along the Indian coastline. Our results support the adoption of a coordinated management framework within each of the four provinces delineated in the present study. [ABSTRACT FROM AUTHOR]

Accurately predicting the flow speed is crucial for applications of coastal ocean circulation simulations such as sediment, larval or contaminant dispersal. This study aims to assess the accuracy of simulated flow speed in a coastal circulation model in comparison with field observations. Deviation between simulated and observed flow speed was assessed in four shallow, coastal locations and four deep, offshore locations in the Gulf of Lion (NW Mediterranean Sea) using six indicators (bias, relative bias, root mean square error, Hanna & Heinold index, correlation and scatter index). Statistical distributions of indicators were calculated during reference periods with low wind, no waves and no stratification. During these periods, relative bias indicated the model displayed a higher performance in predicting transport at shallow stations than at deep stations probably due to grid refinement at these stations. However, there was a low correlation between simulated and observed flow speed, indicating short term time/space mismatches, at all stations during reference periods. Indicators were then calculated during three types of events (wind, waves and stratification) when model assumptions were expected to be violated and their corresponding probability during reference periods indicated that neither wind, wave nor stratification events worsens model's performance. • First statistical description of simulated flow speed accuracy in the Gulf of Lion. • The model performs better at shallow depths than deep depths. • The SYMPHONIE model did not perform worse during wind, wave or stratification events. [ABSTRACT FROM AUTHOR]

Accounting for connectivity is essential in marine spatial planning and the proper design and management of marine protected areas, given that their effectiveness depends on the patterns of dispersal and colonization between protected and non-protected areas. The genetic structure of populations is commonly used to infer connectivity among distant populations. Here, we explore how population genetic structure is affected by pre- and settlement limitations with a spatially explicit coupled metapopulation-gene flow model that simulates the effect of demographic fluctuations on the allele frequencies of a set of populations. We show that in closed populations, regardless of population growth rate, the maintenance of genetic diversity at saturating initial population density increases with species life expectancy as a result of density-dependent recruitment control. Correlatively, at low initial population density, the time at which a population begins to lose its genetic diversity is driven larval and post-settlement mortality (comprised in the recruitment success parameter) —the larger the recruitment success, the stronger the genetic drift. Different spatial structures of connectivity established for soft bottom benthic invertebrates in the Gulf of Lions (NW Mediterranean, France) lead to very different results in the spatial patterns of genetic structuration of the metapopulation, with high genetic drift in sites where the local retention rate was larger than 2%. The effect of recruitment failure and the loss of key source populations on heterozygosity confirm that transient demographic fluctuations help maintain genetic diversity in a metapopulation. This study highlights the role of intraspecific settlement limitations due to lack of space when the effective number of breeders approaches saturating capacity, causing a strong reduction in effective reproduction. The present model allows to: (i) disentangle the relative contribution of local demography and environmental connectivity in shaping seascape genetics, and (ii) perform in silico evaluations of different scenarios for marine spatial planning. [ABSTRACT FROM AUTHOR]

Abstract: Resuspension of microphytobenthic biomass that builds up during low tide has been acknowledged as a major driver of the highly productive food web of intertidal mudflats. Yet, little is known about the contribution to pelagic food web of the resuspension of other microorganisms such as viruses, picoeukaryotes, cyanobacteria, bacteria, nanoflagellates, and ciliates, living in biofilms associated with microphytobenthos and surficial sediment. In the present study, a novel approach that involves simultaneous Lagrangian and Eulerian surveys enabled to disentangle the effects of resuspension and mixing with offshore waters on the dynamics of water column microorganisms during a rising tide in the presence of waves. Temporal changes in the concentration of microorganisms present in the water column were recorded along a 3km cross-shore transect and at a fixed subtidal location. In both surveys, physical and biological processes were separated by comparing the time-evolution of sedimentary particles and microorganism concentrations. During a rising tide, sediment erosion under wave action occurred over the lower and upper parts of the mudflat, where erodibility was highest. Although erosion was expected to enrich the water column with the most abundant benthic microorganisms, such as diatoms, bacteria and viruses, enrichment was only observed for nanoflagellates and ciliates. Grazing probably overwhelmed erosion transfer for diatoms and bacteria, while adsorption on clayed particles may have masked the expected water column enrichment in free viruses due to resuspension. Ciliate enrichment could not be attributed to resuspension as those organisms were absent from the sediment. Wave agitation during the water flow on the mudflat likely dispersed gregarious ciliates over the entire water column. During the rising tide, offshore waters imported more autotrophic, mainly cyanobacteria genus Synechococcus sp. than heterotrophic microorganisms, but this import was also heavily grazed. Finally, the water column became a less heterotrophic structure in the subtidal part of the semi-enclosed bay, where mixing with offshore waters occurs (50% decrease), compared to the intertidal mudflat, when resuspension occurs. The present study suggests that this differential evolution resulted predominantly from dilution with offshore waters less rich in heterotrophic microorganisms. Indeed, any input of microorganisms accompanying physical transfers due to bed erosion or offshore water mixing was immediately buffered, probably to the benefit of grazers. [Copyright &y& Elsevier]

The average bed shear stress and bed friction factor of samples with any roughness was derived from the head loss between upstream and downstream of a test section in an erosion tunnel. The method was validated in both hydraulically smooth (plexiglass; Reynolds number less than 25,000) and rough regimes (calibrated particles with known roughness). As a first step toward using this method on natural sediment, this method was tested with experimental mesocosms assembled from field collected materials (sieved sediments; diatoms). Bed shear stress measurement precision was high enough in the experiments to detect a positive significant relationship between bed friction factor and core roughness. The observed bed friction factor increase could be related to diatom growth but not to diatoms biomass. [ABSTRACT FROM AUTHOR]

Abstract: A one-dimensional vertical unsteady numerical model for diffusion-consumption of dissolved oxygen (DO) above and below the sediment–water interface was developed to investigate DO profile dynamics under wind waves and sea swell (high-frequency oscillatory flows with periods ranging from 2 to 30s). We tested a new approach to modelling DO profiles that coupled an oscillatory turbulent bottom boundary layer model with a Michaelis–Menten based consumption model. The flow regime controls both the mean value and the fluctuations of the oxygen mass transfer efficiency during a wave cycle, as expressed by the non-dimensional Sherwood number defined with the maximum shear velocity (Sh). The Sherwood number was found to be non-dependent on the sediment biogeochemical activity (μ). In the laminar regime, both cycle-averaged and variance of the Sherwood number are very low . In the turbulent regime, the cycle-averaged Sherwood number is larger . The Sherwood number also has intra-wave cycle fluctuations that increase with the wave Reynolds number (VAR(Sh) up to 30%). Our computations show that DO mass transfer efficiency under high-frequency oscillatory flows in the turbulent regime are water-side controlled by: (a) the diffusion time across the diffusive boundary layer and (b) diffusive boundary layer dynamics during a wave cycle. As a result of these two processes, when the wave period decreases, the Sh minimum increases and the Sh maximum decreases. values vary little, ranging from 0.17 to 0.23. For periods up to 30s, oxygen penetration depth into the sediment did not show any intra-wave fluctuations. Values for the laminar regime are small (≤1mm for μ =2000gm−3 d−1) and decrease when the flow period increases. In the turbulent regime, the oxygen penetration depth reaches values up to five times larger than those in the laminar regime, becoming asymptotic as the maximum shear velocity increases. [Copyright &y& Elsevier]

Abstract: Experimental and field studies were carried out to quantify the hydrodynamic mobility under swells of a circalittoral epifauna species. The spatial distribution and structure of one population (NW Mediterranean) of the serpulid polychaete Ditrupa arietina was assessed before and after a moderate swell event in late winter 2006 with the two readings separated by a seven-week interval. The overall density in the bay did not change significantly. However, in certain locations, significant but heterogeneous changes occurred: at some stations, D. arietina disappeared, at others it appeared with high densities while at others, densities remained fairly constant, although in this third case, the population size structure was different. In addition, no trend was observed along a cross-shore gradient. Experimental studies were conducted to determine bed friction velocity thresholds for incipient motion, bed load transport and suspension transport for different sizes of D. arietina. The minimum friction velocity required to transport D. arietina as bed load over a smooth rigid bed ranged from 1.5 to for tube lengths ranging from 6 to 25mm. Thus, calcified worms (more than 6mm long) cannot be destabilized by ordinary currents. Conversely, during the moderate swell event, the maximum bed friction was large enough to mobilize D. arietina, making probably all sizes available for bed load transport, while only worms with a tube length of less than 12mm were transported in suspension at 27m water depth. Wave statistics in Banyuls Bay indicate that D. arietina transport under moderate swell events should not be a rare phenomenon (28 days per year at 20m water depth). Thus, the spatial scale for population dynamics studies should account for the extent of D. arietina spatial redistribution by the hydrodynamics. It is also recommended D. arietina be discarded from biotic quality index computations as this species is sensitive to natural hydrodynamic conditions. [Copyright &y& Elsevier]

In this paper, we compare experiments on short gravity wave phase shifting by surface solitary waves to a Wentzel–Kramers–Brillouin–Jeffreys (WKBJ) refraction theory. Both weak interactions (head-on interaction) and strong interactions (overtaking interaction) are examined. We derive a dispersion relation and wave action conservation relation which are similar to the ones obtained for short waves refraction on slowly varying media. The model requires an exact solitary wave solution. To this end, a steady wave solution is numerically computed using the algorithm devised by Byatt-Smith [Proc. R. Soc. London, Ser. A 315, 405 (1970)]. However, two other solitary wave solutions are incorporated in the model, namely the classical Korteweg and De Vries (KdV) [Phil. Mag. 39, 422 (1895)] solution (weakly nonlinear/small amplitude solitary wave) and the Rayleigh [Phil. Mag. 1, 257 (1876)] solution (strongly nonlinear/large amplitude solitary wave). Measurements of the short wave phase shift show better agreement with the theoretical predictions based on the Byatt-Smith numerical solution and the Rayleigh solution rather than the Korteweg and De Vries one for large amplitude solitary waves. Theoretical phase shifts predictions based on Rayleigh and Byatt-Smith numerical solutions agree with the experiments for A/h[sub 0]≼0.5. A new heuristic formula for the phase shift allowing for large amplitude solitary waves is proposed as a limiting case when the short wave wave number increases. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Representing data as networks cuts across all sub-disciplines in ecology and evolutionary biology. Besides providing a compact representation of the interconnections between agents, network analysis allows the identification of especially important nodes, according to various metrics that often rely on the calculation of the shortest paths connecting any two nodes. While the interpretation of a shortest paths is straightforward in binary, unweighted networks, whenever weights are reported, the calculation could yield unexpected results. We analyzed 129 studies of ecological networks published in the last decade that use shortest paths, and discovered a methodological inaccuracy related to the edge weights used to calculate shortest paths (and related centrality measures), particularly in interaction networks. Specifically, 49% of the studies do not report sufficient information on the calculation to allow their replication, and 61% of the studies on weighted networks may contain errors in how shortest paths are calculated. Using toy models and empirical ecological data, we show how to transform the data prior to calculation and illustrate the pitfalls that need to be avoided. We conclude by proposing a five-point check-list to foster best-practices in the calculation and reporting of centrality measures in ecology and evolution studies. [ABSTRACT FROM AUTHOR]

Betweenness has been used in a number of marine studies to identify portions of sea that sustain the connectivity of whole marine networks. Herein we highlight the need of methodological exactness in the calculation of betweenness when graph theory is applied to marine connectivity studies based on transfer probabilities. We show the inconsistency in calculating betweeness directly from transfer probabilities and propose a new metric for the node-to-node distance that solves it. Our argumentation is illustrated by both simple theoretical examples and the analysis of a literature data set. [ABSTRACT FROM AUTHOR]

Habitat-forming species sustain biodiversity and ecosystem functioning in harsh environments through the amelioration of physical stress. Nonetheless, their role in shaping patterns of species distribution under future climate scenarios is generally overlooked. Focusing on coastal systems, we assess how habitat-forming species can influence the ability of stress-sensitive species to exhibit plastic responses, adapt to novel environmental conditions, or track suitable climates. Here, we argue that habitat-former populations could be managed as a nature-based solution against climate-driven loss of biodiversity. Drawing from different ecological and biological disciplines, we identify a series of actions to sustain the resilience of marine habitat-forming species to climate change, as well as their effectiveness and reliability in rescuing stress-sensitive species from increasingly adverse environmental conditions. [ABSTRACT FROM AUTHOR]

Abstract: Reproductive cycles of marine invertebrates with complex life histories are considered to be synchronized by water temperature and feeding conditions, which vary with season and latitude. This study analyses seasonal variation in the occurrence of oyster (Crassostrea gigas) and mussel (Mytilus edulis/galloprovincialis) larvae across European coastal waters at a synoptic scale (1000s of km) using standardised methods for sampling and molecular analyses. We tested a series of hypotheses to explain the observed seasonal patterns of occurrence of bivalve larvae at 12 European stations (located between 37°N and 60°N and 27°W and 18°E). These hypotheses included a model that stated that there was no synchronisation in seasonality of larval presence at all between the locations (null hypothesis), a model that assumed that there was one common seasonality pattern for all stations within Europe, and various models that supposed that the variation in seasonality could be grouped according to specific spatial scales (i.e., latitude, large marine ecosystems and ecoregions), taxonomic groups, or several combinations of these factors. For oysters, the best models explaining the presence/absence of larvae in European coastal waters were (1) the model that assumed one common seasonal pattern, and (2) the one that, in addition to this common pattern, assumed an enhanced probability of occurrence from south to north. The third best model for oysters, with less empirical support than the first two, stated that oysters reproduced later in the south than in the north. For mussels, the best models explaining the seasonality in occurrence of larvae were (1) the model that assumed four underlying trends related to large marine ecosystems, and (2) the one that assumed one common seasonal pattern for larvae occurrence throughout Europe. Such synchronies in larval occurrences suggest that environmental conditions relevant to bivalve larval survival are more or less similar at large spatial scales from 100s to 1000s of km. To unravel the underlying mechanisms for this synchronisation is of particular interest in the light of changing environmental conditions as the result of global climate change and the possible consequences for marine food webs and ecosystem services. [Copyright &y& Elsevier]

The Mediterranean Sea hosts 5.6% of the world benthic invertebrate species on 0.82% of the ocean surface. Mediterranean ecosystems are also characterized by low densities (and biomasses) compared to other oceanic ecosystems, a feature often attributed to their oligotrophic environment. Oligotrophic conditions can induce lower growth rates and higher mortality rates, and a stronger competition for food between individuals. A theoretical model was developed in order to study the diversity vs. density patterns in coastal benthic invertebrate species. This model describes their minimal population dynamics including basic processes (growth, mortality, reproduction and effects of competitive interactions between individuals) and incorporating fluxes of larvae (finally recruited as juveniles) between a mosaic of local habitats. Populations are therefore structured in a metacommunity. The connectivity between local communities is ensured by passive pelagic larval dispersal. In the Mediterranean Sea, because of the microtidal regime, the connectivity between coastal habitats is lower and more variable than in macrotidal basins. Mathematical properties of the model revealed that competitive interactions (intra- and interspecific competitions) have a stabilizing effect on interacting organisms when gains by recruitment are higher than losses by mortality. In addition, low mortality rates and low connectivity which decreases negative local interactions maintains high regional species diversity with low local densities. This property suggested that oligotrophy cannot be the only factor leading to the high diversity–low density pattern observed in the Mediterranean Sea. [Copyright &y& Elsevier]

The Corsica Channel, a strait between Italy and Corsica, connects the Tyrrhenian and Ligurian seas. The dynamics within the Channel has been historically explored with long term mooring observations and targeted field campaign. At present, however, little work has been done in modeling the Corsica Channel at high-resolution. In this study, we investigate with a realistic, high-resolution (∼1.5 km) numerical setup flow reversals within the Corsica Channel.The simulations compare well with available water mass transport estimates, with hydrographic observations in the area, and current velocity measurements showing a flow in the Corsica Channel predominantly directed northward from the Tyrrhenian to the Ligurian Sea. On top of the well-documented Corsica Channel seasonal variability, a higher-frequency variability can be found throughout the year but more frequently during the summer season. This temporal variability, highest close to the western flank of the Channel, is of the order of a few days to a week and associated with reversals of the currents. We find that this variability is ascribed to periodic intrusions of the West Corsica Current on the Eastern side of the Island. Moreover, our findings suggest the importance, of a so-far neglected, across-channel variability of the meridional velocity. Lagrangian particles are released into the hydrodynamical simulations and show that the exchanges between the Tyrrhenian and Ligurian seas are crucial for biological processes, like the spreading of propagules or larvae. For example, we find that the red gorgonian populations in the basin are connected through a stepping-stone strategy among different colonies. [ABSTRACT FROM AUTHOR]

The migratory shorebirds of the East Atlantic flyway land in huge numbers during a migratory stopover or wintering on the French Atlantic coast. The Brouage bare mudflat (Marennes-Oléron Bay, NE Atlantic) is one of the major stopover sites in France. The particular structure and function of a food web affects the efficiency of carbon transfer. The structure and functioning of the Brouage food web is crucial for the conservation of species landing within this area because it provides sufficient food, which allows shorebirds to reach the north of Europe where they nest. The aim of this study was to describe and understand which food web characteristics support nutritional needs of birds. Two food-web models were constructed, based on in situ measurements that were made in February 2008 (the presence of birds) and July 2008 (absence of birds). To complete the models, allometric relationships and additional data from the literature were used. The missing flow values of the food web models were estimated by Monte Carlo Markov Chain – Linear Inverse Modelling. The flow solutions obtained were used to calculate the ecological network analysis indices, which estimate the emergent properties of the functioning of a food-web. The total activities of the Brouage ecosystem in February and July are significantly different. The specialisation of the trophic links within the ecosystem does not appear to differ between the two models. In spite of a large export of carbon from the primary producer and detritus in winter, the higher recycling leads to a similar retention of carbon for the two seasons. It can be concluded that in February, the higher activity of the ecosystem coupled with a higher cycling and a mean internal organization, ensure the sufficient feeding of the migratory shorebirds. [ABSTRACT FROM AUTHOR]