Effects of climate change on seagrasses and seagrass habitats relevant to the Pacific Islands

TLDR: In this article, a lack of knowledge on the extent and area cover of seagrass resources in Pacific Island Countries and Territories (PICTs) does not allow accurate assessments of resource status, or losses and gains in SEGrass cover to be made.

Abstract: Due to anthropogenic pressure, seagrass habitats are declining by over 7% annually worldwide, with approximately 29% of the world seagrass stock having already been destroyed. Losses in seagrass habitats for the tropical Pacific by the year 2100 are estimated to be between 5 to 35%, but a lack of knowledge on the extent and area cover of seagrass resources in Pacific Island Countries and Territories (PICTs) does not allow accurate assessments of resource status, or losses and gains in seagrass cover to be made. Low human resource capacity and little awareness by the general public and business community of the economic value and importance of seagrass ecosystem services, including a lack of inclusion of seagrass habitats at a regional policy level, is severely hampering conservation efforts. Seagrasses and seagrass habitats provide at least 24 different service benefits in the Indo-Pacific region. These include coastal protection, provision of food, cultural value and exceptional carbon storage ability beyond terrestrial forests. If properly managed, seagrass habitats could provide a highly significant carbon mitigation service in a high-CO2 world through a net influx of organic carbon both above and belowground. Massive seagrass carbon storage losses have recently been recorded in Australia after a period of elevated seawater temperature, and increased oceanic temperature will be one of the most important environmental stressors on seagrass habitats. Different tropical seagrass species show different tolerances to increased seawater temperatures, but thermal tolerance has not been well studied in seagrass in PICTs. Increases in seawater temperature also translate into stronger extreme weather events such as heavy rainfall and tropical cyclones and storms, which put additional stress on seagrass habitats through direct physical damage, increase in turbidity causing reductions in photosynthetic rates and growth, and a general loss of ecosystem resilience and productivity. Both gains and losses to seagrass resources will result from climate change, with increases in productivity due to higher CO2 levels being buffered by the negative consequences of higher seawater temperatures and most importantly additional anthropogenic factors such as “polluted” land runoff. These factors are very likely to be currently resulting in increasing losses of vital ecosystem services in the Pacific islands.