OFFSHORE FLOATING MULTI-USE-PLATFORMS IN A HIGHLY ENERGETIC UPWELLING REGION

Abstract

The availability of wild mussel seed and nutrients are key factors for a successful multi-use scenario in offshore sites. While there is great potential, the transition to high-energy environments introduces challenges, as the hydrodynamic intensity and the consistency of nutrient availability required for commercial feasibility remain insufficiently characterized. Therefore, this study explores the connectivity between the coast of Galicia (Spain), the North of Portugal and the offshore floating wind farms Nor1 (Spain) and Viano do Castelo (Portugal), both in the early planning phase (Fig. 1). The goal is to better understand the role of coastal dynamics in shaping the conditions at the wind farm sites through the export of water masses, nutrients and larvae. The NW Iberian Peninsula is considered as the study site, with its high-energy environment, complex coastal dynamics and established aquaculture sector in the Galician Rías, Spain (Padin et al., 2024).

Fig.1: Bathymetry of the study site on a high resolution grid (300 m), demonstrating the wind farm (WF) locations of Nor1 (red), Viana do Castelo (magenta) and main rivers included in this domain.

Introduction

The potential of multi-use wind farms to combine wind energy production and low-trophic aquaculture has been widely explored in the Baltic-North Sea in Europe. By combining various stakeholders' interests, it is possible to create more sustainable and cost-effective commercial solutions. Current research on the co-location of wind energy and aquaculture is largely restricted to bottom-fixed foundations in semi-exposed waters, leaving the technical and economic feasibility of systems in high-energy offshore environments as a critical area for future investigation (Mascorda Cabre et al., 2021). In addition, the long-term viability of offshore aquaculture depends on consistent larval recruitment and sufficient trophic support to ensure survival and optimal growth rates. Therefore, this study explores the connectivity between coast and offshore floating wind farms using numerical modelling tools.

Materials and methods

The three-dimensional state-of-the-art Coastal and Regional Ocean COmmunity modelling system (CROCO, v1.3.1) together with the biogeochemical model PISCES were implemented to assess the coastal-offshore connectivity. In addition, the oceanographic model was coupled offline to a Lagrangian Individual Base model Roms OFfline Floats (IBM ROFF) to study the availability of wild mussel seed (Mytilus gallopprovincialis) in wind farm areas during the peaks of the reproductive cycles. The modelling system uses a two-way nested grid setup. The study area is represented using a high-resolution grid, of approximately 300 m, allowing to simultaneously resolve the oceanic, coastal and estuarine dynamics. These configurations are based on previously well-established modelling systems (Nolasco et al., 2013; Viitak et al., 2026).

Results and Discussion

Modelling results indicated that coastal dynamics significantly influence the biogeochemical conditions within the wind farm sites under specific oceanographic regimes. Intense upwelling events promoted the vertical transport of nutrient-rich waters to the surface layers and their offshore export through the surface layers. Galician Rías, as a highly productive region, acted as a source of chlorophyll onto the adjacent ocean, including the wind farm areas. Moreover, during the spring spawning peak of the mussel reproductive cycle, upwelling events promoted the southward and offshore dispersal of larvae. These transport patterns highlight the coast-offshore connectivity, making the wind farm sites as potential settlement habitats for mussel populations.

Acknowledgment

This research has received funding from Grant Agreement No. 101094065 Olamur (https://olamur.eu/).

References

Nolasco, R., Dubert, J., Domingues, C.P., Pires, A.C. and Queiroga, H., 2013. Model-derived connectivity patterns along the western Iberian Peninsula: asymmetrical larval flow and source-sink cell. Marine Ecology Progress Series, 485, pp.123-142.

Viitak, M., Nolasco, R., Villacieros-Robineau, N., Silva, P.A., Castro, C.G. and Dubert, J., 2026.

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Mascorda Cabre, L., Hosegood, P., Attrill, M.J., Bridger, D. and Sheehan, E.V., 2021. Offshore longline mussel farms: a review of oceanographic and ecological interactions to inform future research needs, policy and management. Reviews in Aquaculture, 13(4), pp.1864-1887.

Padin, X.A., Babarro, J.M., Otero, P., Gilcoto, M., Rellan, T., Suárez, L., Velo, A. and Peteiro, L.G., 2024.

The declining availability of wild mussel seed for aquaculture in a coastal upwelling system. Frontiers in Marine Science, 11, p.1375269.