Small rocks were seeded with kelp propagules (Saccharina latissima) and reared in the laboratory until 2–3cm (2.5 months), before out-planting to the field. The gravel was dispersed in three ways; by throwing it off the boat, placing it on the substrate or placing it in trays on the substrate. A second experiment was carried out where green gravel was deployed in habitats dominated by bare rock and turf, to compare success.
Green gravel successfully grew kelps, and growth, length and survival were similar amongst deployment methods.
Out-planted kelp had high survival and growth over 9 months, even when dropped from the surface. At 85 days after out-planting, 60% of the gravel in trays and 53% of the gravel in open plots retained kelp, and between 85 and 203 days 100% of the gravel retained kelp. Kelp growth and length was similar between treatments. In the turf/bare rock experiment, after 4 months, 18.5% (± 7.1 SD) of gravel held a kelp plant that was attached to the underlying rock or turf. There was no difference in attachment success on turf or bare rock.