In recent years, the concept of co-location of multiple species in aquaculture has gained interest among the scientific community and the industry. The integration of pellet-fed finfish with inorganic extractive algae and organic extractive shellfish is seen as a potential approach for sustainable aquaculture. In this context, a deeper understanding of the hydrodynamic forces and wave dissipation properties of macroalgae become relevant, especially in exposed environments such as offshore aquaculture locations where macroalgae could increase the forces on existing structures and moorings by attaching to them or, alternatively, could be used to shelter those systems.

Currently, there is very limited knowledge about the drag forces of real M. pyrifera specimens. In the current project, a detailed hydrodynamic characterisation of the giant kelp Macrocystis pyrifera is proposed. This kelp species can be found along a large percentage of the coasts of the Pacific Ocean, including North America, South America and Australia, and can play a relevant role for aquaculture, as well as a mean to dissipate waves acting on marine structures.

To achieve this, the proposal is based on physical modelling using real macroalgae individuals (scale 1:1) and artificial samples of fields (scale ~1:10) to characterize the hydrodynamic fluid-structure interaction in the wave tank at Universidad Austral de Chile.

In a first stage of the physical modelling of wave-algae interaction, a geometrical, hydrostatic, and hydrodynamic characterisation will be conducted on selected samples. The geometrical characterisation will provide measures of stipe, blade, pneumatocyst and holdfast geometry, as well as weight ratios (pneumatocyst, blade and stipe weight to total weight). For the hydrostatic characterisation, the buoyant force of selected individuals will be measured as in, followed by the separated measurement for stipes, blades and pneumatocysts. For the hydrodynamic characterization, a set of individuals will be towed to obtain drag coefficients and deflection under a steady current.

In a second stage, preliminary ~1:10 artificial models will be created, searching for adequate materials and geometries to attain similar geometric, hydrostatic, and hydrodynamic characteristics under a steady current, considering similitude laws. For these models, validation tests for individuals will be carried out, obtaining drag coefficients and deflections for the scaled model. Based on several tests, minor adjustments will be made to the geometry until the obtained results match the deflections from full-scale individuals. From these results, a more detailed characterization of the drag forces on M.pyrifera specimens will be gained, which can be used for future tests in waves under different configuration and to improve numerical models.