Open ocean aquaculture: the future of seaweed farming Researchers at TU Braunschweig test new infrastructure for the open ocean

Aquaculture is the fastest growing food sector in the world. More than half of the fish, seafood and algae consumed worldwide already come from this type of farming. In order to meet the growing demand, solutions are needed outside of coastal waters, which are heavily polluted by shipping, tourism and the expansion of coastal structures. The international joint project “Ngā Punga o te Moana – Anchoring Our Open Ocean Future”, in which Technische Universität Braunschweig is involved, addresses precisely this issue. It aims to shift aquaculture from congested coastal regions to  exposed ocean areas, some of which are relatively near to shore, but high energy, and others which are further offshore. Experts from the fields of hydraulic engineering, structural engineering and marine biology are working together to develop innovative, production efficient technologies that can withstand high energy environments.

Cooperation partners of the international joint project ‘Ngā Punga o te Moana – Anchoring Our Open Ocean Future’ (from left): Prof. Nils Goseberg (Leichtweiß Institute for Hydraulic Engineering and Water Resources), Prof. Arndt Hildebrandt (Blue C GmbH), Prof. Bela Buck (Alfred Wegener Institute), Henrik Neufeldt (Leichtweiß Institute for Hydraulic Engineering and Water Resources) and Dr Kevin Heasman (Cawthron Institute, New Zealand). Picture credits: Kristina Rottig/TU Braunschweig

Producing technology that enables sustainable marine farming in exposed ocean areas has tangible benefits. Many exposed ocean locations are not currently utilised, offering new space for expansion, cleaner and cooler water, less marine animal fouling of farmed structures and an abundant food supply for the farmed species. In addition, aquaculture here has less negative impact on the seabed habitat. “This means that the agricultural potential of the open sea could be tapped,” says Professor Nils Goseberg, Head of the Leichtweiß Institute for Hydraulic Engineering and Water Resources at TU Braunschweig.

However, these areas are also associated with significantly greater challenges: Deeper waters, stronger currents and higher waves place high demands on the stability and resilience of aquaculture facilities. A crucial aspect is therefore the precise determination of the forces acting on the infrastructure in order to avoid oversizing, which leads to high costs for the anchors and their components, as well as undersizing, which would result in the system failing during storms. Greater distances from the coast also have an impact on the costs of travelling to and maintaining the system, which requires low-maintenance systems.

Innovative seaweed farm off the coast of New Zealand

One aim of the international project “Ngā Punga o te Moana – Anchoring Our Open Ocean Future” is therefore to develop a new type of seaweed farm, which is to be installed as a prototype off the coast of New Zealand. Seaweed is extremely flexible and moves with the waves, which means that its surface area is constantly changing. “This additional dynamic makes it difficult to calculate the forces acting on the seaweed and the entire farm – an aspect that has not yet been sufficiently researched scientifically,” explains project team member Henrik Neufeldt from the Leichtweiß Institute for Hydraulic Engineering and Water Resources and iTUBS, the innovation company of TU Braunschweig.

The research work of the scientists at the Leichtweiß Institute for Hydraulic Engineering and Water Resources includes experiments in the wave flume and wave pool as well as computer modelling to analyse the behaviour of seaweed and farm structure under real conditions. In the first series of experiments, the researchers investigated the forces and movement of seaweed on longlines in the 2-metre wave flume. These are synthetic ropes on which the seaweed grows, which are held to the water surface by floats and whose ends are anchored to the bottom. Substitute bodies with the same rigidity and thickness were created to realistically reproduce the deformations of the seaweed. “The shape was also modelled on seaweed,” says Henrik Neufeldt. Special sensor systems, such as the particle tracking velocimetry (PTV) system, record the flow field around the structure, while the forces acting on the plants are determined by so-called load cells.

The aim of the series of experiments is to find out how the forces and movements of the kelp change under different wave conditions and how neighbouring cultivation lines influence each other. These findings are incorporated into computer models in order to check and further optimise the load determination for the overall system.

In the wave basin, the Braunschweig scientists recreated the kelp farm on a scale of 1:20. Picture credits: Kristina Rottig/TU Braunschweig

Realistic offshore conditions in the wave pool

In a second series of tests in the wave basin, the Braunschweig scientists recreated the kelp farm on a scale of 1:20. The focus here was on determining the usability of the system under realistic exposed ocean conditions. Different materials for the head lines, which connect the cultivation lines and thus serve as connection points between the anchor and the farm, as well as different types of anchoring systems were tested to ensure optimal conditions for kelp growth. “The tension and stability of the lines are particularly crucial to ensure consistent growth conditions in terms of light and nutrients,” says Henrik Neufeldt. By combining force sensors, wave levels, speed sensors and motion tracking cameras, the researchers were able to record and analyse the deformations and movements of the system in detail.

The overarching aim of the research is to make exposed ocean aquaculture sustainable and efficient in order to meet the growing demand for marine resources – always with a view to ecological responsibility. By developing new technologies, the future of aquaculture should not only open up enormous production opportunities beyond pure food production, but also help to protect the marine environment.

Project data

The open ocean aquaculture project led by the Cawthron Institute in New Zealand, “Ngā Punga o te Moana”, is a five-year (2021-2026) national research programme. The project is funded by the New Zealand Government’s Endeavour Fund with around 11 million New Zealand dollars and aims to overcome the challenges to enable the expansion of the aquaculture industry into exposed ocean areas. Researchers from New Zealand, USA, Ireland, Chile, Norway and Germany are involved in the international project. TU Braunschweig is involved with the Leichtweiß Institute for Hydraulic Engineering and Water Resources in cooperation with iTUBS, the innovation company of TU Braunschweig.

Further information:
https://openocean.cawthron.org.nz