Loss of Coastline Habitat with Rising Global Temperature
Global warming is estimated to change coastal ecosystems.
Background
Coastal ecosystems have long been recognized as essential to the wellbeing of millions of people as well as aquatic species. Marine vegetation protects coastlines by acting as a buffer to reduce the force of ocean waves, which helps to protect people from hurricanes. It also provides suitable habitat to many different kinds of species. Vegetated coastal ecosystems, such as mangroves and tidal marshes, are important to coastal fisheries because they provide a habitat for fish. They also store carbon dioxide that would otherwise be emitted into the atmosphere, which helps to keep global warming below 2°C.
Climate change is creating an uncertain future for the survival of these ecosystems. Scientists have observed higher growth rates and resilience in coastal ecosystems despite the current relative sea-level rise (RSLR) rates, prompting a reassessment of their vulnerability. RSLR reflects changes in local levels over time and are often the most critical trend for habitat restoration or coastal management.
The potential for high rates of sedimentation, productivity, and organic matter preservation in mangroves and tidal marshes and the productivity of coral reefs allow them to grow vertically with relative sea-level rise. This process is referred to as vertical adjustment. Vertical adjustment can maintain a wetland above a drowning threshold and encourage growth and survival of reef island systems. However, if the rate of vertical adjustment falls behind the rate of RSLR for an extended period of time, serious consequences can result. Long-term submersion of coastal habitats and increased wave exposure can cause coastlines to degrade and recede.
Summary
Habitat change under current sea-level rise of tidal marshes in low-to-moderate tidal range settings found that coastline habitat retreats about four to six millimeters per year. This amount of marsh loss can be associated with greater damage from hurricanes and reduced marine vegetation diversity. Conversely, mangrove and tidal marsh growth can also increase with the rate of RSLR because submergence can encourage higher plant productivity and root growth.
Current studies show that tidal marsh sites were more likely to advance once RSLR exceeded 2.3 millimeters per year. However, if RSLR increased above 5.4 millimeters per year, tidal marshes were observed to be more likely to retreat than to expand. This study has revealed a tendency for these ecosystems to be more likely to shrink as RSLR increases.
There is less data on the change of coastal reef habitats, but based on present findings, size reduction is likely at RSLR above 6.2 millimeters per year. This is startling because there are multiple locations well above this threshold. The Solomon Islands have averaged between 7 and 10 millimeters per year since 1994, and many reef islands in the Isabel Province are completely eroded. Observations of coastal reef habitats show a continuous decline in size and quality.
Researchers have modeled possible responses of coastal ecosystems to future sea-level rise and increasing global temperatures. Global temperatures have increased by nearly 1.5 °C with models suggesting that one third of global mangroves will be subjected to RSLR rates of over 7 millimeters per year. Nearly all will be exposed to over 4 millimeters per year if global temperature reaches 2 degrees Celsius. For reef islands, increasing island instability occurring at an RSLR of 7 millimeters per year is likely.
In conclusion, researchers have concluded that widespread retreat of coastline habitat is likely at warming levels above 1.5 degrees Celsius. This loss proves that preservation and restoration efforts are a necessity. A few ways this can be done is by creating a safe operating space for coastal ecosystems, cleaning up pollution in coastal reefs, or to restore degraded wetlands.
