Why is kelp declining?

Could you please enlighten me as to why kelp, a marine plant renowned for its nutritional benefits, is currently experiencing a decline? I'm particularly interested in understanding the potential causes behind this trend, whether it's due to environmental changes, overfishing, or perhaps a lack of conservation efforts. Could you also elaborate on the potential impact of this decline on the marine ecosystem and the human communities that rely on kelp for various purposes? Thank you for your insights.