The Site, lying off the Western Cape Province, is the second-largest coastal island on the South African continental shelf. It is within the Benguela upwelling ecosystem, which lifts cold, nutrient-rich water to the surface. Sandy inner shelf, rocky mid-shelf mosaic, island shore and kelp forest are the main habitat types. Dassen Island is covered by Cape seashore vegetation and a number of cetacean species are found in the surrounding seas. The Site is an Important Bird Area providing habitat for significant numbers of seabird and shorebird species, including 10 of the 15 seabirds endemic to southern Africa, and numerous Palearctic and sub-Antarctic migrants. It provides safe breeding refuge for threatened species such as the African penguin (Spheniscus demersus) and Cape cormorant (Phalacrocorax capensis) and other coastal birds: it is one of only two breeding sites of the great white pelican in South Africa. The nature reserve supports more than 1% of the population of African penguin and bank cormorant (Phalacrocorax neglectus), and more than 1% of the South African coastal breeding population of white-breasted cormorant (Phalacrocorax lucidus). Historical guano harvesting and African penguin egg collecting mark the Site, and it features shipwrecks, a lighthouse, and a penguin exclusion wall. A management plan is implemented, as well as conservation measures and monitoring of birds and plant communities including invasive plant species.