Warming also reduces nutrient levels in the mesopelagic zone (about 200 to 1000 m deep). This in turn limits the growth of diatoms in favour of smaller phytoplankton that are poorer biological pumps of carbon. This inhibits the ability of the ocean ecosystems to sequester carbon as the oceans warm.[3] What is clear, is that healthy ocean and coastal ecosystems are necessary to continue the vital role of the ocean carbon sinks, as indicated, for example, by the Blue Carbon[4] assessment prepared by UNEP and the coastal carbon sinks report[5] of IUCN and growing evidence of the role of fish biomass[6] in the transport of carbon from surface waters to the deep ocean.