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Population dynamics of marine species that are sessile as adults are driven by oceanographic dispersal of larvae from spawning to nursery grounds. This is mediated by life-history traits such as the timing and frequency of spawning, larval behaviour and duration, and settlement success. Here, we use 1725 single nucleotide polymorphisms (SNPs) to study the fine scale spatial genetic structure in the commercially important cockle species Cerastoderma edule and compare it to environmental variables and current-mediated larval dispersal within a modelling framework. Hydrodynamic modelling employing the NEMO Atlantic Margin Model (AMM15) was used to simulate larval transport and estimate connectivity between populations during spawning months (April - September), factoring in larval duration and seasonal variability of ocean currents. Results at neutral loci reveal the existence of three separate genetic clusters (mean FST=0.021) within a relatively fine spatial scale in the northwest Atlantic. Environmental association (EA) analysis indicates that oceanographic currents and geographical distance between the populations explain over 20% of the variance observed at neutral loci, while genetic variance (71%) at outlier loci was explained by sea surface temperatures extremes. These results fill an important knowledge gap in the management of a commercially important, overexploited species, and bring us closer to understanding the role of larval dispersal in connecting populations at a fine geographical scale.

Access to high performance computing has made 3-D modelling de rigueur for tidal energy resource assessments. Advances in computing resources and numerical model codes have enabled high resolution 3-D ocean models to be applied at basin scales, albeit at a much higher computational cost than the traditional 2-D modelling approach. Here, a comparison between 2-D and 3-D tidal energy extraction modelling techniques is undertaken within a 3-D modelling framework, and differences between the methods are examined from both resource and impact assessment perspectives. Through a series of numerical experiments using the Regional Ocean Modeling System (ROMS), it is shown that 3-D tidal energy extraction can be successfully incorporated in a regional ocean model of the Pentland Firth - one of the top regions in the world for tidal stream energy development. We demonstrate that resolving 3-D flow is important for reducing uncertainty in environmental resource assessments. Further, our results show that 2-D tidal energy extraction methods lead to a misrepresentation of the velocity profile when applied to 3-D models, demonstrating the importance of resolving 3-D flows in the vicinity of tidal arrays.

As the marine renewable energy industry evolves, in parallel with an increase in the quantity of available data and improvements in validated numerical simulations, it is occasionally appropriate to re-assess the wave and tidal resource of a region. This is particularly true for Scotland - a leading nation that the international community monitors for developments in the marine renewable energy industry, and which has witnessed much progress in the sector over the last decade. With 7 leased wave and 17 leased tidal sites, Scotland is well poised to generate significant levels of electricity from its abundant natural marine resources. In this state-of-the-art review of Scotland's wave and tidal resource, we examine the theoretical and technical resource, and provide an overview of commercial progress. We also discuss issues that affect future development of the marine energy seascape in Scotland, applicable to other regions of the world, including the potential for developing lower energy sites, and grid connectivity.

Temporal variability in renewable energy presents a major challenge for electrical grid systems. Tides are considered predictable due to their regular periodicity; however, the persistence and quality of tidal-stream generated electricity is unknown. This paper is the first study that attempts to address this knowledge gap through direct measurements of rotor-shaft power and shore-side voltage from a 1 MW, rated at grid-connection, tidal turbine (Orkney Islands, UK). Tidal asymmetry in turbulence parameters, flow speed and power variability were observed. Variability in the power at 0.5 Hz, associated with the 10-min running mean, was low (standard deviation 10–12% of rated power), with lower variability associated with higher flow speed and reduced turbulence intensity. Variability of shore-side measured voltage was well within acceptable levels (∼0.3% at 0.5 Hz). Variability in turbine power had 2 = 85% and ∼14% error). Therefore, the predictability and quality of tidal-stream energy was high and may be undervalued in a future, high-penetration renewable energy, electricity grid.

Population dynamics of marine species that are sessile as adults are driven by oceanographic dispersal of larvae from spawning to nursery grounds. This is mediated by life‐history traits such as the timing and frequency of spawning, larval behaviour and duration, and settlement success. Here, we use 1725 single nucleotide polymorphisms (SNPs) to study the fine‐scale spatial genetic structure in the commercially important cockle species Cerastoderma edule and compare it to environmental variables and current‐mediated larval dispersal within a modelling framework. Hydrodynamic modelling employing the NEMO Atlantic Margin Model (AMM15) was used to simulate larval transport and estimate connectivity between populations during spawning months (April–September), factoring in larval duration and interannual variability of ocean currents. Results at neutral loci reveal the existence of three separate genetic clusters (mean F ST = 0.021) within a relatively fine spatial scale in the north‐west Atlantic. Environmental association analysis indicates that oceanographic currents and geographic proximity explain over 20% of the variance observed at neutral loci, while genetic variance (71%) at outlier loci was explained by sea surface temperature extremes. These results fill an important knowledge gap in the management of a commercially important and overexploited species, bringing us closer to understanding the role of larval dispersal in connecting populations at a fine geographic scale.

International audience; One of the biggest uncertainties in tidal stream energy resource assessment is how tidal energy conversion, particularly at large scale, will interact with the resource. As few arrays are currently operational, data collected from these developments tends to be commercially sensitive. Therefore, array interaction with the resource is generally assessed using numerical models. A fully three-dimensional numerical approach based on Actuator Disk theory was implemented into the Regional Ocean Modelling System (ROMS) to simulate the energy extraction by tidal stream turbines. Emphasis was placed on wake interactions and cumulative effects of individual devices on energy extraction at array scale. This model was applied at the tidal stream energy site of the Fromveur Strait (western Brittany, France) considering an array of horizontal-axis turbines of 10-m diameter, matching the device technology currently operating in the Strait. Two tidal energy metrics were considered to describe asymmetries in tidal current magnitude and direction. The area with reduced asymmetry in current magnitude was selected to implement the turbine array. A nested grid technique was adopted to cascade processes from the regional scale to the high-resolution local farm domain. The computation was conducted over the inner-nested array domain covering the tidal farm with horizontal and vertical resolutions of 1 m, matching the 1/10th turbine diameter (D) recommended to resolve velocity and turbulence intensity along device wakes. The array layout initially followed recommended staggered configurations with longitudinal and lateral spacings of 10D and 5D, respectively. However, during mean spring tidal conditions, the misalignment of peak flood currents induced significant wake interactions that reduced the array output by about 15% in comparison to peak ebb. These interactions were investigated to adapt array layouts, minimise wake interactions, and optimise the energy conversion. By reducing the lateral spacing between devices to 3D (measured centre to centre rather than tip to tip), the flood ebb asymmetry in energy extraction was lowered from 15% to 2%.

There are many uncertainties associated with the wave models used to generate regional wave energy resource assessments. One of these sources of uncertainty is the temporal resolution of the wind input. Wave models are typically forced with 3-hourly synoptic wind fields. In reality, winds are highly turbulent and exhibit high spatial and temporal variability. Therefore, by using 3-hourly wind fields to force wave models, much of the high frequency nature of the wind climate is not captured, and this could lead to substantial errors when estimating the wave energy resource of a region. Until now, research has focused on the importance of spatial model resolution, with little attention given to the importance of temporal resolution. Here, we use the SWAN wave model to simulate an idealised storm event within an idealised model domain characteristic of the North Sea. The extent to which fluctuating wind affects wave power is examined, with a test case where wind, in the absence of gustiness, was input as the control. Wave power is a function of the wave period and the square of wave height, both of which are altered as a result of high frequency wind input. Our results indicate that, for this idealised study, the inclusion of wind variability at sub-hourly time-scales can lead to a difference in wave height of up to 35%, which corresponds to a difference of up to 56% in simulated wave power. Consequently, understanding and accurately simulating the high frequency nature of winds can improve the accuracy of regional wave energy resource assessments.

International audience; Reynolds-Averaged Navier Stokes (RANS) models have, in the past, primarily been implemented to assess the available tidal kinetic energy resource, neglecting the influence of turbines on tidal hydrodynamics. However, evaluating environmental impacts, as well as array layouts, requires integration of the turbine wakes with the ambient flow field (Goward Brown et al., 2017). The widely used method, commonly integrated in depth-averaged models, consists of integrating an additional bed friction term related to array scale turbine effects. Such approach permits to simulate the global effect of a tidal array. However, the flow interactions between turbines are neglected. A fully three-dimensional (3-D) approach is here developed to account for cumulative effects of individual interacting turbine wakes. The actuator disc sub-model, that represents the turbine as a non-rotating porous disc, is implemented and incorporated into the Regional Ocean Modelling System (ROMS), following the method initially developed by Roc et al. (2013). A nested grid technique is adopted to cascade processes from the regional scale to the high resolution local farm domain. This method was first implemented in the steady-state laboratory experiment of Myers and Bahaj (2010). Numerical predictions match measurements of velocity and turbulent intensity profiles along the disc wakes for minimum spatial resolutions of 1/5th the turbine diameter. This is also confirmed at ocean scale. The modelling methodology is finally applied to the tidal stream energy site of the Fromveur Strait (western Brittany), where an array of 20 m-diameter turbines is considered. The computation is conducted over an inner-nested array domain that is 700 m in length and 200 m in width, at a spatial resolution of 4 m, embedded in two nested regional grids with resolutions of 100 m (intermediate) and 500 m (outer). Different configurations varying in scale from one to 14 devices are investigated in terms of wake interactions and power output from individual turbines to the whole array.