Final answer:
Mangrove ecosystems and estuaries are destroyed mainly due to coastal development, dredging, and agricultural expansion. These activities lead to loss of biodiversity, economic impacts, and reduced coastline protection from storms and tsunamis.
Step-by-step explanation:
Mangrove ecosystems and estuaries are often destroyed to make way for land development necessitated by the increasing demands for land, water, food, and energy due to a growing population.
Factors such as coastal development, dredging of beaches for property protection, and agricultural expansion are significant threats to these ecosystems. For example, dredging attempts to prevent coastal erosion can cause serious harm by increasing storm impact, damaging reefs, sea grass beds, and killing marine life, leading to economic impacts on fisheries, tourism, and local economies.
Furthermore, mangrove forests, which play a critical role in protecting coastlines and supporting marine biodiversity, have diminished; over one-third of these forests were lost in the final decades of the 20th century, particularly in Southeast Asia.