Estuaries’ Two-Front Battle Against Climate Change

By Naomi Hill

Our estuaries are on the frontlines of climate change.

Estuarine systems sit at the intersection of marine and terrestrial environments, making them vulnerable to the subtlest of changes on both fronts.

Most of the impacts we are experiencing today as a result of climate change are far from subtle, though. Seas are rising and devastating storms threaten coastlines and their communities more each year.

An equal, but maybe less spoken about, threat to estuaries comes from our inland ecosystems in the form of drought.

When a region experiences low levels of precipitation for an extended period of time, there is a reduction of freshwater and nutrient inflow to estuaries which increases their salinity levels.

With heightened salinity, salt water from the ocean is able to encroach further inland upsetting the delicate balance of estuarine ecosystems, threatening their health, and potentially infiltrating drinking water supplies.

Around the country estuaries and keystone species are at heightened risk due to drought conditions (among other impacts of climate change).


The U.S. Caribbean and other tropical regions of the world are home to a variety of species of mangroves. These aquatic forests are vital for the stability of shorelines and help provide habitat and shelter for other estuarine species thanks to their interwoven root system.

Additionally, mangroves act as a powerful filter for both the atmosphere and the ocean. They help maintain coastal water clarity by filtering out harmful pollutants and act as a blue carbon ecosystem storing over 6 billion tons of carbon in their soils globally.

While their root structures can help them withstand changing sea levels and hurricanes (to an extent), they are less prepared for conditions of drought. Black mangroves in particular are highly sensitive to shifts in hydrological conditions. This means that both flooding and drought can cause excessive mortality for the species.

If conditions of drought persist over long periods of time mangrove ecosystems may be lost and replaced by salt marshes or mud flats, drastically altering the habitat of the coast and reducing biodiversity.

One of the most extreme and devastating cases of mangrove dieback occurred in 2015 in Australia. A concoction of extreme high temperatures and prolonged drought conditions associated with a severe El Niño event led to the loss of almost 40 million mangrove trees in the Gulf of Carpentaria. 

It was estimated that over 800,000 tons of carbon was released into the atmosphere as a result of the dieback, and around 30 square miles of mangrove ecosystem was lost.

This was one of the more severe cases of mangrove death in recent history, but drought and other climate change impacts continue to threaten these important trees around the globe.


Another keystone species impacted by drought is Pacific Salmon. Pacific Salmon rely on cooler water to absorb oxygen and conserve energy and need higher water levels in order to reach their spawning grounds. Without these conditions the fish are placed under stress and risk “predation, disease, and death”.

Over the course of their lifetime salmon fulfill a variety of different roles, all of which are vital to health of the coastal ecosystems in the Pacific Northwest and California.

As young salmon, they help keep the insect population in check while traveling downstream to the ocean. Their diet during this time consists of over 50% insects.

Salmon populations also feed a large swath of species native to the Pacific Coast including eagles, bears, killer whales, and even wolves. After death, they help return many nutrients back into the watershed supporting growth and productivity.

 In Vancouver, British Columbia, recent drought conditions have negatively impacted Pacific Salmon populations. The summer heatwave was especially devastating with numerous die offs being reported by local organizations.

Now that spawning season has arrived, salmon are faced with higher water temperatures and low river flows due to the extreme drought threatening their survival and the entire ecosystem that rely on them.

While estuaries and their inhabitants can be adaptable and resilient, drought is a serious threat, especially while marine threats are occurring simultaneously. Prioritizing restoration and protection on a watershed scale gives us the best hope to protect estuaries from the impacts of climate change, and in-turn, protects the keystone species that are integral to their health and survival.



Naomi Hill is a senior at Chapman University, studying political science and environmental studies. This semester she is participating in the Washington Semester Program through American University in Washington, DC and is a Northern Virginia native. She joined RAE this fall as our Communications Intern.