Farm Findings: Seaweed farms can integrate with natural seabed ecology

Over the years, marine infrastructure has become more present in U.K. waters. Aquaculture operations have increased as we pursue a sustainable, blue economy, and researchers have been hard at work trying to understand how the cages, anchors and chains affect the ecosystems in which they are placed. 

Fig. 1. Reference diagram for the block and chain mooring of the seaweed farm's infrastructure.

In a seaweed farm, crop kelp is often grown from ropes suspended at the sea surface between buoys. However, the farms also have their own seabed installations. Câr-Y-Môr, for example, uses a set up of two metal chains and a concrete block to anchor the floating buoys (Fig. 1). 

In 2022, a diver examined Câr-Y-Môr’s block-and-chain moorings at the St. Justinian farm eight months apart, mainly inspecting them for security and safety, but also recording a video at one of the sites. The difference was striking and we thought it worth sharing. Less than a year later, organisms such as seaweeds and shellfish were observed to be growing densely on the surfaces of the surrounding rocks as well as the chains and anchor itself. 

Fig. 2. Photos of the riser chain element of the seaweed farm infrastructure after initial deployment (Top row of photos taken Aug’22) and after 8 months (bottom row of photos taken April’23).  All images taken at St. Justinian's farm.

There are potential negative side-effects to any kind of seabed infrastructure. For example, at St. Justinian, the diver observed some light scouring on adjacent boulders. “Scouring” occurs when a chain rubs repeatedly against the sea bed or nearby rocks. This can displace sediment and prevent organisms from attaching themselves to the said rocks. 

Fig. 3. Photo of riser chain running along seabed near to where it leaves the seabed and rises to the surface. The two black circles indicate areas where chafing from the chain is likely to have occurred.

Simultaneously, the chain and block themselves offer new surfaces on which organisms can anchor, as shown here, with even the joint between chain and block being heavily colonised. Studies have also shown that pieces of farm infrastructure can serve as fish aggregation devices (FADs), attracting species in open water (1).

Infrastructure is by no means a substitute for natural “hardscape," – rocks and stony coral – in U.K. waters, but what we suggest here is that the metal and concrete associated with seaweed farms integrates with the natural seabed flora and fauna while deployed.

As always, more research is necessary to document the potential benefits of this infrastructure. Regular inspections, such as the one discussed here at Câr-Y-Môr, are key to continued environmental safety. 

Thank you to Martin from Pembrokeshire Marine Services for conducting these monitoring divers!

References

1. Barrett, L.T., Swearer, S.E., Dempster, T., 2019. Impacts of marine and freshwater aquaculture on wildlife: a global meta-analysis. Reviews in Aquaculture 11, 1022–1044. https://doi.org/10.1111/raq.12277