Green Gravel Update

May 2024

The kelp we deployed did not survive the winter

Last year we deployed more green gravel than ever before in Portugal. The goal was to move beyond the small scale pilot trials that showed good survival rates and actually deploy in large enough numbers to establish self-sustaining kelp forests. As we showed in the most recent video update, the kelp did really well at sea initially. Subsequent monitoring showed that some of the kelp survived for over 200 days and grew up to 30cm.

The challenge

Unfortunately, more recent monitoring suggests that the kelp failed to attach to the rocky reef at the bottom of the ocean and so probably did not survive the winter storms (upcoming dives will confirm if this is what happened). This seems to be a common challenge for green gravel projects done in high-energy coastlines. This has also been discussed in a recently published scientific article to which our partners at contributed. The technique, which was originally developed and tested in calm Norwegian Fjords, may need additional adaptations to deal with the fierce Atlantic coast in Portugal.

The site in Cascais where we carried out the deployments also had some peculiar features, namely that the rock formed shallow depressions where the gravel tended to accumulate. This in itself would not be a problem and it actually has the advantage of preventing the gravel from moving around too much. However, because these depressions also accumulated sand they were not a good place for the kelp to attach through their holdfast (the holdfast is the ‚Äúroot‚ÄĚ of the kelp and it requires exposed rock to attach).

What next?

These are all important lessons which we can now use to improve the process for the next deployments. The goal now is to tweak variables such as deployment time, stone size, and site selection to maximize the chances of long term survival of the kelp. We currently have another batch in production to be deployed around July-August which we suspect is the time of year that will maximize the probability of survival and holdfast attachment.

Although we were disappointed that last year's kelp has failed to establish as we would hope, we still think this is a very worthwhile investment. Given that the kelp are surviving and growing after deployment, it seems that we are at a critical stage where small improvements may be enough to start getting consistent results. If that's the case, the investment we are making now (despite the inherent uncertainties) is what will open the doors for large scale restoration in the future.

We will keep you updated on the details of the next deployments as our kelp restoration journey continues.