Mrs Nahlah Alsuwaiyan1,2, Dr Karen Filbee-Dexter1,3, Sofie Vranken1, Celina Burkholz1, Dr Marion Cambridge1, Dr Melinda A Coleman1,4,5, Prof Thomas Wernberg1,3,6
1School of Biological Sciences and UWA Oceans Institute, University of Western Australia, Crawley, Australia, 2Department of Biology, Unaizah College of Sciences and Arts, Qassim University, Unaizah, Kingdom of Saudi Arabia , 3Institute of Marine Research, His, Norway , 4National Marine Science Centre, Southern Cross University, Coffs Harbour, Australia , 5Department of Primary Industries, National Marine Science Centre, Coffs Harbour, Australia, 6Department of Science and Environment, Roskilde University, Roskilde, Denmark
Kelp forests are experiencing substantial declines due to climate change and active interventions are necessary to halt this decline. A new restoration tool “green gravel” has shown promise for upscaling kelp restoration. Here, we tested the feasibility of cultivating the kelp Ecklonia radiata on green gravel. We seeded substrata with E. radiata gametophytes at two average seeding densities: high density of ~230 and low density of ~115 fragments mL-¹. The tested substrata were small basalt, large basalt, crushed laterite and limestone. Gametophytes successfully adhered to all four substrata, however, gametophytes that adhered to the limestone (the natural reef type off Western Australia) suffered extreme tissue bleaching. Gametophytes that adhered to the other substrata were healthy, fertilised following seeding and microscopic sporophytes were observed attaching to the gravel. Substrata and seeding density did not affect sporophyte growth after three months of rearing in incubators but over time substrata showed a significant effect with larger sporophytes observed on both basalt gravel than on the crushed laterite after 12 months. Gametophytes were also found to not only survive on the gravel itself but also detach from the gravel, settle successfully, fertilise and develop into healthy sporophytes ex situ on surrounding substratum through lateral transfer. Substrata had a significant effect on density of detached gametophytes with rougher and larger gravel showing higher densities of detachment. Our results show the potential for green gravel to be a vector of dispersal for restoration in Western Australia where natural recovery of kelp forests has not occurred.
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