Farm Findings: Seaweed farms can comfortably coexist with locally important species.

The U.K.’s coastal waters are teeming with life, from the tiniest crustaceans to large mammals like seals, and everything in between. Seaweed farms share these waters, playing neighbour to some of the country's most recognizable and commercial species: sardines, cod, haddock, flounder, the list goes on. It is well known that natural seaweed forests support these creatures, providing food and shelter, but does this relationship hold true with farmed seaweed? How does growing seaweed change how many species – “diversity” – and how many of each – “abundance” – there are in an area? 

Figure 1. Left: Underwater camera used to record species underwater. Remaining images: Subset of species detected during our Baited Remote Underwater Video (BRUV) surveys.

In this study we compared sites at Câr-y-Môr’s sea farms off the Pembrokeshire coast before and during the seaweed growing season. We sunk our SubCams at 3 sites, and attached bait bags to the rig, encouraging local species to swim into the camera’s field of view for identification. We monitored the sites monthly, collecting data at Porthlysgi and Carn ar Wig from April 2022 to July 2023, and at St. Justinian in September 2022, as well as April and June 2023.

What we found?

At all three monitored sites species diversity and abundance remained consistent during and after farming operations, demonstrating that local species and seaweed farms can coexist in harmony.

We identified 21 different species at Câr-y-Môr’s sea farms, and counted how many of each we saw every month in the pre- and during-farming periods. When we ran the numbers, we found no significant differences between the two periods for any of these species. Essentially, the farm’s underwater neighbours remained unchanged throughout the year. 

Table 1. The abundance per month (columns headed “2022” and “2023”) and average abundance (column headed “N max (mean)”) of each species detected using Baited Remote Underwater Video (BRUV) surveys at two seaweed farms: Porthlysgi and Carn ar Wig. Species denoted with a * are commercially important in the UK.

This is a strong first piece of evidence showing that seaweed farming doesn’t detract from species diversity and abundance. Furthermore, 10 of the species we identified are considered to be commercially important in the U.K., suggesting that seaweed farming and local fisheries can, and do, exist in harmony.

It is always important to present the limitations of any scientific study, and, as mentioned above, this is first evidence. The farm sites we monitored at are relatively small, and we had only 15 months of data to work with. We also were not able to include comparisons to sites completely unaffected by seaweed farming. Lastly, we used bait on our camera rigs, which is standard practice for this kind of underwater video survey, but can skew which species show up to the camera – some like the bait more than others!

In our next study, which is taking place at Câr-y-Môr and other U.K. seaweed farms, we (1) are monitoring for a longer period of time, (2) including comparisons to unaffected sites, and (3) not baiting our camera rigs. We are excited to expand on these initial findings, and look forward to sharing data with you in the future!