it is estimated that of the world s major marine ecosystems have been degraded or are being used unsustainably many fisheries are overexploited with some stocks on the verge of collapse and coral reefs are bleaching due to exposure to high temperatures and other pressures concurrently pollution from landbased sources including marine litter is threatening species and marine habitats and climate change compounds these effects and alters both the thermal and chemical characteristics of the ocean as well as its dynamics and nutrient availability since the s for example an estimated of global mangroves have been lost and of coral reefs have disappeared