La Nane 1* , Alfi Sahri R Baruadi 2 , Herinda Mardin 3 1,2 Department of Aquatic Resources Management, Universitas Negeri Gorontalo; 3 Department of Biology, Universitas Negeri Gorontalo. * Email Correspondence: lanane@ung.ac.id Abstract The blue-black urchin has been widely known and utilized as food in the world, including Indonesia because sea urchin gonad can be consumed. However, the utilization of sea urchins in Gorontalo has not been performed. On the other hand, natural resources information is needed as the database for natural resources management in Tomini Bay. The aim of this study is to document the blue-black urchin Echinotrix diadema. This study conducted at Blue Marlin Beach, South Leato, Gorontalo, from November 2019 to December 2020. Sea urchin density was calculated with a 1 m × 1 m transect quadrate that positioned at interval 5 m in distance along 15 m of the transect line at the coral reef ecosystem. In parallel with the measurement of the density, sea urch