Aegean Baselines is the first community-powered marine biodiversity monitoring program in Salamina Island, Saronic Gulf, Greece. We aim to establish the first baseline and long-term observation (3-5 years; 3 coastal sites, 3-4 surveys/year) of sea urchin population density (as keystone species and environmental stress indicators) and help understand: 1. How our ecosystem responds to environmental stressors, 2. Provide input to local and national authorities 3. Inspire the next generation of marine scientists and citizen science volunteers We will conduct underwater sea urchin population density and environmental data surveys in accessible shallow waters using belt transects, quadrats and roving visual censuses.