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Forecasts Regarding the Future of Shallow Coastal Ecosystems for 2100

According to a recent study on shallow-water ecosystems, by 2100, mangroves, tidal marshes, and coral habitats could all significantly diminish due to climate change and coastal land usage, whereas seagrass meadows could expand and macroalgal beds might remain steady. The results of this study are published in the open-access journal PLOS Climate by Hirotada Moki and colleagues from the Port and Airport Research Institute in Japan.

Image Credit: Oliver Osvald/

Since shallow-water ecosystems take up a large quantity of carbon dioxide, they should be able to slow down global warming. In the meantime, climate change—which includes warmer seawater—will probably have an impact on these ecosystems. It is not evident, yet, precisely how climate change might affect the extent of shallow-water ecosystems in the future.

Moki and associates projected future changes in the total area inhabited by the five shallow-water ecosystems considered to be most significant—seagrass meadows, macroalgal beds, tidal marshes, mangroves, and coral habitats—to help shed light on their future.

They employed a global climate model to forecast possible changes through 2100, combining topographic data with information on the existing sizes and distributions of the ecosystems. They took into account two conventional hypothetical scenarios, one of which (RCP2.6) represented the lowest and the other (RCP8.5) highest projections for future greenhouse gas emissions.

According to the study, global coral habitat might collapse by up to 74% by 2100. Meanwhile, due to an anticipated rise in the depth to which photosynthesis-powering sunlight can enter these environments, seagrass meadows could extend by up to 11%. For macroalgal beds, that depth is not expected to change significantly, implying that the current area will be maintained until 2100.

According to the predictions, tidal marshes and mangroves will remain the same size because shrinking caused by rising sea levels will be countered by development into new places. After accounting for coastal development and land use, the analysis predicts that tidal marshes will reduce by 91.9% and mangroves will shrink by 74.3%.

Based on their findings, the researchers propose using an ideal combination of shallow-water ecosystems and man-made infrastructure to combat coral habitat decline. Meanwhile, appropriate coastal management might harness the other four ecosystems’ climate-change-mitigating effects.

The study authors noted, “Although global coral habitat considerably can considerably shrink (as much as 75%), other shallow water ecosystems (macroalgal beds, mangroves, tidal marshes and seagrass meadows) can remain or increase in the future.If appropriate coastal management (e.g., to consider the effect of hard infrastructure for landward shift of ecosystems) is achieved, the four shallow water ecosystems can help mitigate the climate change influences.

This research was funded in part by the Environmental Restoration and Conservation Agency of Japan’s Environmental Research and Technology Development Fund (S-14: JPMEERF15S11408 to TK) and the Japan Society for the Promotion of Science's Grants-in-Aid for Scientific Research (KAKENHI) (no. 18H04156 and 26630251 to TK).

Journal Reference:

Moki, H., et al. (2023) Projections of changes in the global distribution of shallow water ecosystems through 2100 due to climate change. PLOS Climate. doi:10.1371/journal.pclm.0000298.

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