Summary

Climate change impacts coastal ecosystems and the humans who live and work in these regions. The coastal ecosystem, or the coastal zone, is defined as the margin between land, air, and ocean where complex interactions occur between living and nonliving parts of the system. This interconnectivity generally gives rise to areas of high productivity, that is, areas where life flourishes. These systems are also some of the most dynamic (but also fragile) regions on the planet, supporting tremendous ecological, biological, and human diversity. Climate change, however, can alter sea temperature, raise sea level, and modify weather patterns, ultimately impacting the ecosystem services provided by the system. All these changes can have varying (positive, negative, or neutral) outcomes depending on the type of coastal ecosystem experiencing the impacts.

Some coastal ecosystems, like rocky coasts, will experience tropicalization leading to many species shifting further toward the poles. This process may lead to the expansion of oyster reefs and mangroves into salt marshes. Species distributions will also be affected by marine heat waves, which are periods of high temperature anomalies in the ocean. Prolonged periods of elevated sea surface temperatures can cause coral reefs and kelp forests to collapse. Ocean acidification, caused by increased CO₂ uptake by the ocean, is likely to further limit coral reef and oyster larvae growth but may also lead to increases in some kelp species’ abundance and distribution.

Sea level rise will affect sediment dynamics and light availability for kelps, seagrasses, and submerged aquatic vegetation. This phenomenon will also pose a direct threat to coastal marshlands and vulnerable low-lying island nations. Other ecosystems, like oyster reefs and mangrove forests, may have some level of resistance to sea level rise, as their three-dimensional structure allows them to cope with rising water levels.

In conjunction with rising sea levels, modified weather patterns will greatly affect coastal ecosystems. Many coastlines, especially sandy beaches and barrier islands, will be impacted by more frequent and intense storms that disrupt the cycle of sediment erosion and accretion. These events may result in rapid changes to the shape and location of the coast or even complete loss of landmasses. Changes in storm intensities can also significantly damage coral reefs, cause kelp to be detached from the seafloor, erode marshland, and prevent seagrass establishment. However, storms may also potentially expand mangrove distributions, because the storm currents and waves may enable the transport of their seeds longer distances. Combined with increased air temperatures, mangroves will continue to expand into regions where they were previously not found.

Climate change impacts on coastal systems will be varied in degree and may even help some ecosystems flourish, rather than degrade. Given the many types of ecosystems that occur in the coastal zone, coupled with synergistic impacts of climate change and human disturbances, a collective effort will be needed to mitigate against the varied changes to these fragile ecosystems.