The narrow zones of the world where the land meets the sea hosts some of the most diverse ecosystems in the world. Coastal wetlands, estuaries, backwaters, deltas, lagoons, reefs, bays all come under a broad term called coastal ecosystems. Together, they add up to 1.6 million kilometers. of coastline. Each one is unique, but has certain common factors:
- These ecosystems are very, very beneficial to all forms of life, including humans.
- These ecosystems are very, very sensitive to environmental changes.
- Thus, they are very, very vulnerable to external stresses.
The coastal ecosystems today are threatened by two main forces; climate change and human activities. In this post, I’m going to take a look at the major influences that climate change has/will have on these fragile and massively important parts of the world.
What are these ecosystems sensitive to?
Mainly, coastal ecosystems comprise of organisms ranging from microbes like phytoplankton, to primitive organisms like corals, mussels, sea urchins, star fishes, to higher organisms like fishes, birds, amphibians, reptiles and mammals. They also host a variety of plant life, including mangroves.
All of these organisms live out a part or all of their lives in coastal zones. The complex interaction of sea and fresh water provides a unique habitat for these organisms. Many of the fishes and birds migrate to coastal ecosystems specially, in order to breed or escape harsh weather in their other habitats.
The specific environmental conditions, which includes salinity, temperature ranges, climatic factors and presence of prey is what attracts these organisms here. Unfortunately, climate change affects these very features of that environment.
Sea level rise
This is the most famous consequence of climate change in the world. Images of flooding cities, especially the famous ones like New York City, Chennai and Sydney are enough to cause some form of action against climate change. However, sea level rise can do much more…
Over the last century, sea level has risen by 8 inches all over the world. The rise may be more or less than this in specific areas; this depends on local features like subsidence and extraction of water. But the fact is: the sea is rising. It is expected to continue this rise over the 21st century. It could be anywhere between 1-3 feet (0.1-0.9 meters).
Apart from flooding the vast human settlements, this is going to cause acute changes in the coastal ecosystems.
For one, inundation of land close to the shore will completely flood habitats like mangroves, wetlands, lagoons and estuaries. These habitats, ideally, would migrate inland to maintain the form and integrity of the ecosystem, but is met with human land use. They are caught between humans and sea level rise, and will end up dying.
The increasing sea level will result in salt water intrusion into inland water systems like river mouths and groundwater aquifers. First of all, this will make this water unfit for consumption. Second, it will alter the physiological pathways of many organisms, that have adapted to a specific concentration of salt water in their habitat. Saltwater fishes that need to spawn will have to swim further upstream, where they may not find ideal locations to breed. This will directly impact their populations. Altered groundwater regimes will affect the plant life in the area, as well as the humans living there.
The increase in sea level is likely to affect the sedimentation process of the rivers. Increasing sea level leads to an increase in elevation of the base level (much like how a dam affects the river upstream). It will lead to extension of deltas and its growth upstream. In another scenario, the increasing sea level could cause erosion of sediments by the sea water.
Coastal water temperatures
The temperature regimes of the coasts are very unique. Consequently, even the smallest change is likely to cause massive changes in the ecosystems present there. This has already been observed all over the world in the case of corals. As recent as last year, a global bleaching event took place in response to higher ocean water temperatures.
In general, we are likely to see a migration of fish species into deeper waters in search of a cooler environment. This has already been seen in the case of corals and associated fish species in the Arabian Sea region.
Unpredictable weather and severe storms
Climate change is most likely to cause more severe rainfall in coastal regions, along with stronger hurricanes hitting the hurricane-prone regions. This has been observed even as recently as last year, with massive hurricanes hitting the coasts of India and the American continent.
Heavy rainfall will increase surface run-off in the low lying areas. This could cause flooding, as well as changing flow dynamics in the coastal waters. The added danger with this is the fact that the run-off will carry many pollutants from human sources into the coastal waters. This will cause eutrophication, eventually killing aquatic plants and animals. Such “dead zones” are already present in the Gulf of Mexico and Chesapeake Bay.
If climate change results in droughts, it will massively affect the salinity of these ecosystems. The salinity in these regions is maintained by the controlled addition of freshwater into the system. With droughts, less freshwater will be present for run-off into the sea and will increase the salinity of the entire region. This is potentially disastrous for most organisms there.
We have to bother, because coastal ecosystems contribute to our economies in the form of fisheries, tourism, oil and construction. 1/3 of the world population lives in the coast, with 40% living within 100 km of the coast. Socially, it supports some of the poorest communities in the world.
All of this will come crashing down if we do not protect the coasts from the effects of climate change. A lot of work is already underway. More on this in the upcoming posts…
- World Bank report for the Latin America/Caribbean region.
- Paice, R., and Chambers, J., 2016: Climate change adaptation planning for protection of coastal ecosystems. CoastAdapt Information Manual 10, National Climate Change Adaptation Research Facility, Gold Coast.