You could speak with Siobhan Vye or others involved in the Capturing Our Coast nationwide citizen science programme for experience and lessons learned https://www.capturingourcoast.co.uk/ .

Our Ecostructure colleagues in Ireland have also set up a public engagement platform https://observatory.ecostructureproject.eu/ to seek input from coastal communities. I'm not sure how much engagement they've had to date but it could be a useful platform to be adopted by organisations into the future.