Sowing the success of the seaweed industryWhy site selection is the foundation of seaweed farming

Before a single seedling is deployed, the most fundamental decision for any aspiring seaweed farmer is where to put their farm. Get this wrong, and even the most rigorous cultivation efforts may struggle to bear fruit. 

In property, it’s a mantra that everyone knows: the three most important factors are "location, location, location". Seaweed farming is no different. A seaweed farm's success – its yield, its quality, and ultimately its profitability – is fundamentally tied to the patch of sea it occupies. Yet, finding that perfect spot is one of the biggest challenges a farmer faces.

For a seaweed farm to succeed, it requires three equally strong pillars and the removal or weakness of any one will jeopardise the success of the farm. These pillars are equally vital for commercial success and must be evaluated in parallel when assessing the suitability of a farm’s location. 

I suggest that we think of these three interdependent pillars as:

1) Survival factors – the physiological core requirements for the seaweed to survive. 

2) Growth factors – the environmental conditions that determine whether the seaweed will grow well, influencing yield and quality. 

3) Logistical factors – the practical, social and economic considerations that allow a farm to operate profitably and sustainably.

The logistics-first approach

Currently, many farm sites are chosen primarily for logistical reasons. Is the area available? Is it permitted for aquaculture use? Is it sheltered from the worst storms? How close is it to the nearest harbour and land-based processing facilities? These are all critical, practical questions. Nobody wants to farm in a location that is inaccessible or where equipment is constantly being destroyed by the weather. However, prioritising convenience over biology is a risky strategy. A site that is easy to access might be too sheltered and therefore have low nutrient levels, or it might be close to a river outflow which kills the seaweed by exposing it to freshwater. While logistics are undeniably important for a farm's business model, the initial assessment must also be grounded in the environmental and biological requirements of the seaweed crop. After all, a perfectly accessible farm that produces a low yield is not a sustainable business. To truly succeed, all three pillars must be robust. However, all sites usually end up being a compromise between the three pillars; avoiding “bad sites”  is as important as finding the perfect one.

Pillar 1: survival factors – fundamental requirements

The foundational pillar is survival. On the seaweed’s journey from small vulnerable seedling to mature adult, the fundamental physiological requirements of the chosen seaweed species must be met. 

For kelp species common in the West, this means water temperatures that stay roughly between 5 and 20°C and salinity levels that don’t drop below 15-25 practical salinity units (PSU) due to freshwater runoff. . Prolonged darkness, at higher latitudes during winter or if the farm is too deep, can also be an issue as algae need to produce sugars from photosynthesis to survive.

Other seaweeds, such as sea lettuce (Ulva) are generally more tolerant of lower salinity and higher temperatures, illustrating how the same site may be suitable for some local species but not others. Environmental pollutants that threaten the survival of the seaweed must also be kept to a minimum and there must be an adequate supply of oxygen and carbon dioxide dissolved in the seawater to keep the seaweed alive. This may not be the case in eutrophic regions for example, where microbial respiration creates regions of low oxygen concentration during the breakdown of large quantities of organic matter.

Pillar 2: growth factors – optimising for yield and quality

Once the ability to survive is confirmed, the focus should be on the environmental conditions that allow the seaweed to thrive, directly influencing biomass yield and quality, and thereby ensuring the farm produces a commercially viable crop.

Optimal light conditions are paramount, varying seasonally with sun angle and day length (latitude dependent), cloud cover, sea surface state (choppy waters scatter and reflect more light) and water clarity (dependent on particles in the water). Seaweed also requires a consistent supply of macronutrients, especially nitrogen, which often becomes a limiting factor at temperate latitudes during late spring and summer as the water column becomes less well mixed and phytoplankton blooms. Adequate water movement is also critical, constantly replenishing the nutrients around the seaweed. In addition to these “bottom up” growth factors, we also need to consider “top down” factors that hinder growth and quality, such as biofouling pressure (e.g. from bryozoans and snails) and predation risk from grazers,, such as snails and sea urchins. 

A potential strategy for enhancing the growth potential of a site could be implementation of integrated multi-trophic aquaculture (IMTA).The IMTA approach often involves the strategic co-location of seaweed farms with other aquaculture sites, such as salmon farms. The finfish pens release a steady stream of dissolved nutrients, particularly nitrogen (mainly in the form of ammonium), which can significantly boost seaweed growth rates, especially during periods when ambient nutrient levels are low (e.g. summer months). This is something being addressed by an ongoing large research project here in Norway, named Aurora IMTA.  Similarly, co-location with shellfish such as mussels can also be beneficial; their filter-feeding can improve water clarity, thereby increasing light availability for the seaweed.

Whether a site is "good" or "bad" for growth can depend on the species being farmed, as different species often have different physiological preferences for temperature, salinity, nutrients and light.  Cultivation strategy also plays a role. A location with a higher biofouling risk, for example, might be a poor choice for direct seeding, as microscopic seedlings are highly vulnerable to being outcompeted by other organisms on the rope. That same site, however, could still be productive if the farmer uses larger, more robust seedlings from a nursery. The success of the site will also be affected by the farmer’s understanding of how to optimise the farm design (e.g. cultivation depth and orientation relative to currents), as well as the timing of both deployment and harvesting operations, which will in turn depend on the environmental characteristics of their site, including nutrient concentrations, temperature, light availability and biofouling risk. This shows how site selection and cultivation strategies are deeply interconnected and that sea cultivation needs to be tightly integrated with the vital hatchery stage of seaweed production. 

Another consideration is that, in contrast to fields on land, the sea is dynamic. From hour to hour, even minute to minute, there are different “parcels” of water moving through a sea farm, and the water characteristics at any moment in time can change a lot – depending on the tides, sea conditions, weather,  season and activities/processes on land. This is why site evaluation can be difficult and why it’s essential to obtain measurements frequently throughout the year. It is also why we use sophisticated ocean models to make predictions about how the oceans will behave, using past observations together with oceanographic knowledge and mathematical reasoning. 

One such model is Sintef Ocean’s SINMOD, which connects and simulates physical and biological processes in the ocean down to farm-level resolution  and links them with a dynamic seaweed growth model to make accurate predictions about growth potential. The model might also provide information on how the cultivated seaweed interacts with the marine environment, including nutrient uptake, oxygen (and CO2)  production/utilisation and organic matter dispersal.

Pillar 3: logistical factors – enabling commercial success

Even with perfect survival and growth conditions, a farm cannot be commercially successful if the logistical hurdles are insurmountable. This final pillar encompasses the practical, economic and social factors that transform biological potential into a profitable operation. 

One primary consideration, assuming a site is available and that permits for cultivation of seaweed can be obtained, is proximity to port and processing facilities, which minimises transportation costs, reduces spoilage of fresh biomass, and supports efficient processing. Closely related is ease of access to the farm site itself (including favourable sea-state), as this directly reduces operational costs, saves time and enhances safety for deploying and maintaining infrastructure, as well as for all harvesting activities. Furthermore, access to skilled labour and existing infrastructure, such as a local workforce with maritime experience and accessible land-based facilities like electricity, roads, cold storage, or workshops, can lead to significant operational cost savings. 

As an example, Atlantic Sea Farms in the USA has benefited enormously from the skills and boats of the Maine lobster fishermen who farm their seaweed, which is critical to their “buy-back” business model. It is also vital to consider the potential for conflict with other ocean users, as minimising competition for sea space with established industries like fishing, shipping, or tourism reduces operational hurdles and potential disputes. Beyond legalities, social acceptance is crucial; a site where the local community is supportive or at least neutral towards the farm reduces friction and leads to a positive operating environment, which is vital for long-term operations. In large parts of Norway, for example, there is a broadly high level of acceptance for aquaculture installations due to the salmon industry’s prevalence here. In England, however, there was a recent controversy about proposed plans by Biome Algae to install a seaweed farm off the Cornish coast, where both tourism and fishing are the dominant industries. All these interwoven logistical elements must be considered for the farm to achieve true commercial success. .

From guesswork to a data-driven strategy

So, how can a farmer apply this framework to find a great site? I suggest a three-step process that moves from a broad overview to a highly specific site confirmation.

1. The bird's-eye view: The first step is to use freely-available historical ocean data (including from nearby observation stations), including remote sensing data from satellites. These can be free services, such as the EU’s Copernicus Marine Service. Some of these data sources provide years of historical data on key parameters like sea surface temperature and salinity, but they can have limitations in terms of spatial resolution and poor data quality close to land or at high latitudes. Additionally, there are more sophisticated tools such as ocean models, as previously discussed with Sintef Ocean’s SINMOD. The farmer can then cross reference these data sources with the known growth requirements for the seaweed they wish to cultivate, and compare this to available sites that meet their logistical requirements for a seaweed farm.
2. Getting your feet wet: Once a few promising regions have been identified, the next step is to gather in-situ data. This involves deploying sensors at the potential sites to measure the actual conditions below the surface. This is critical for understanding water temperature and water clarity (light penetration) at the cultivation depth, nutrient dynamics and salinity. Choosing the right sensors and using them correctly is not easy though, even for experienced professionals. If you do not have this expertise then it is a good idea to collaborate with reputable organisations that know what they are doing when it comes to oceanographic measurements.
3. The ultimate test: The final and most important step is to conduct small-scale growth trials, before fully building out your farm. By deploying test lines at the most promising locations, farmers can directly measure growth rates and monitor for biofouling. This provides definitive proof of a site's potential. This may sound like a lot of effort, but the costs of building a farm on the wrong site can be enormous. Some seedling suppliers, such as Seaweed Solutions and Hortimare, offer farmers assistance with preparing these tests.

The offshore frontier: a case for moving further out

As coastal areas become more crowded with different stakeholders competing for space, many people are looking further offshore for the future of seaweed farming. Moving into more exposed, offshore locations presents significant engineering and logistical challenges, but the potential rewards could be worth it. In addition to reducing conflict with other coastal activities, these sites often feature more stable growing conditions, improved water flow, reduced biofouling and a more consistent supply of deep, nutrient-rich water. 

However, there is also a potential trade-off between logistical factors and growth factors. To move offshore successfully the industry must ensure that the latter compensates for the former, otherwise the extra costs won’t justify the improved yield. To unlock this potential for the wider industry, we need dedicated infrastructure and projects to develop and test the necessary methods and technology to improve the logistics of offshore farming. At Sintef Ocean, our offshore test site, Storflua – which is also part of the Norwegian Seaweed Centre – is designed for exactly this purpose: to build the knowledge base required for building a robust and profitable offshore seaweed farming industry. 

Conclusions

Ultimately, the sustained success and global scaling of the seaweed industry hinge on improving our methods for site selection. We cannot afford to view farm placement as an afterthought or a simple logistical exercise. Instead, it must be seen as a strategic imperative where survival, growth and logistical factors are recognised as three equally vital pillars supporting commercial viability. 

A weakness in any one of these pillars – whether it's suboptimal growth conditions, persistent biofouling, or a lack of social acceptance – will lead to ineffective capital allocation into expensive and inefficient infrastructure. By embracing a data-driven, systematic strategy that thoroughly assesses each pillar, and integrates it with cultivation practices, we can move beyond guesswork. 

This integrated approach, bolstered by dedicated research efforts to explore the effective use of offshore environments and IMTA, will be part of the blueprint for unlocking high, predictable yields and ensuring a stable, profitable future for seaweed aquaculture in the West.