Decline in seagrasses are due to a number of factors including drought, water quality issues, agricultural practices, invasive species, pathogens, fishing and climate change. Over 35% of global mangrove habitat remains. Decreases in habitat is due to damming of rivers, clearing for aquaculture, development etc., overfishing, and climate change, according to the World Wildlife Fund. Nearly 16% of mangroves assessed by the IUCN are on the IUCN Red List; due to development and other causes 1 in 6 worldwide mangroves are in threat of extinction. Dams threaten habitats by slowing the amount of freshwater reaching mangroves.
Quantifying rates of decrease are difficult to calculate, however measurements have been estimated by researchers indicating that if blue carbon ecosystems continue to decline, for any number of reasons, 30-40% of tidal marshes and seagrasses and approximately 100% of mangroves could be gone in the next century.