We Must Remember Our Estuaries When Conserving Our Oceans

Often when we lend our oceans a helping hand, many of us focus on collecting plastic debris from the tideline or supporting those who help remove ghost fishing nets from the wider ocean and rescue entangled animals from the waves. Very few of us consider the importance of protecting our estuaries when it comes to conservation, despite their waters being constantly interlinked with the ocean waves.

If we want to enjoy healthy oceans once more, then healthy estuaries are an essential requisite. Their nickname ‘nurseries of the sea’ can give you a good idea of one reason why they are so important. Multiple marine animals head into our tidal estuaries to reproduce and spend time raising their young in waters which are calm, free from larger predators and abundant in food. For example, in the UK, Atlantic salmon and trout make the long and arduous journey back upstream to their familiar spawning grounds where they lay their eggs in the loose gravel and pebbles which lie the bottom of riverbeds. Once the young salmon hatch in the spring, they start their voyage towards the sea, growing in size in the estuary where they feed, rest and slowly adapt from freshwater to saltwater.

Estuaries are rapidly changing environments with the tides sweeping in and out each day unveiling or hiding a plethora of habitats. With water depth, salinity and the strength of the current constantly changing, habitats found along these coastal stretches can include mudflats, saltmarshes, rockpools, sandy banks, kelp forests, oyster reefs and mangroves, depending on where you are in the world. In fact, our overlooked estuaries are one of the most productive ecosystems on Earth! When the tide retreats out towards the horizon, large muddy plains are often exposed and within hide thousands of insects and crustaceans who survive on the rich nutrients contained in the mud. Anything from brittlestars to anemones, cockles to worms can be found at low tide and it is often then that an overwhelming amount of bird life can be seen too as they descend from the sky to feast on the exposed critters. In the UK, species such as heron, curlews, oystercatchers and plovers are often seen in clusters on the mud flats as their beaks search for tasty grubs. Estuaries are also incredibly important for migratory birds who often use them as a rest spot and refuelling station.

Aside from housing a fantastic abundance of wildlife, why else are our tidal waterways important? Sandwiched between our rivers, oceans and terrestrial spaces, estuaries have the power to influence a large proportion of our environment. Rushing rivers carry with them muddy silty sediment and pollutants from upstream, such as sewage particles or agricultural fertilisers, and the marshes and plants growing in the intertidal area do an excellent job of slowing down the water, allowing these particles to sink to the estuary floor where they are stored. This prevents harmful pollutants reaching our oceans where they can be carried vast distances with the currents. Estuaries also protect our rivers from storm surges, flooding and big tides by absorbing large amounts of water. This often benefits us as a high number of communities are built on the banks of rivers. Finally, our estuaries are simply yet another beautiful environment in which we can relax, take part in exercise and catch a glimpse of the wildlife the world has to offer.

Sadly though, like many of our ecosystems, estuaries are under threat from a range of human actions. If the health of our estuaries continues to decline, our efforts for protecting the ocean could be undermined. Let’s start with the greatest issue, pollution. Over the last century, the number of pollutants we pour into the environment has risen dramatically, whether that be untreated sewage, toxic chemical fertilisers and pesticides or oil from our roads. When it rains, the water runs across the land and picks up all of these pollutants along the way and because the land backing onto estuaries is now increasingly covered in concrete, the water has nowhere to go except straight down into our aquatic habitats, rather than be absorbed into grassland or woodland. In particularly built-up areas, this is causing ‘toxic hotspots’. In these areas, a high number of nutrients, which come from chemicals running off the land, can cause algal blooms and low oxygen levels. The algae can also block sunlight which prevents plants, such as seagrass, from growing and results in a barren environment where animals and plants fail to thrive. Not only is this a great loss to the natural world but it also costs fisheries a large amount of money as stocks plummet whilst this cocktail of chemicals can be carried out to the ocean on the next tide where it will affect an even larger number of species.

The banks of the estuaries are suffering too as erosion is wearing them away and changing the shape of many water courses. This can be caused by direct human activity, such as building work, or less direct impacts such as an increase in boat traffic causing larger waves which eat away at the soft, muddy banks. As the effects of climate change become more apparent, rising sea levels and a high number of storm surges will also speed up erosion, causing the waterline to head closer towards our homes and towns.

For years, many countries felt that draining wetlands was the best course of action and it is only now, several decades later, that we are trying to refill these areas with water to coax back the wildlife we have lost. In other countries, water has been directed away from rivers and estuaries and towards farm fields which has changed the whole shape of the local landscape. Today, our estuaries are still facing threats as we try to bend and manipulate their natural flow in order to benefit society. The Severn Estuary flows into the Atlantic Ocean and laps at the banks of Bristol and Cardiff. The area is considered to be of international importance due to the 74,000 birds which stop off on its muddy banks each winter as they migrate along the ‘North Atlantic Flyway’ which stretches from Siberia across Europe to Africa. Alongside feeding waterfowl are over 100 fish species and millions of insects and crustaceans. This estuary is unique in that it has the second largest tides in the world, with 14 metres between high and low tide and this means that enormous amounts of nutrients are carried along its length. However, there have been talks about generating energy from the Severn’s massive tides for decades and it is only now that climate change is pressuring us to find renewable energy sources that the plans are being seriously considered, despite the area’s protected status. Multiple projects are being considered but the largest is a barrage which would stretch 16 kilometres across the estuary. It is thought that this would massively influence the natural tides and in consequence, up to 76% of intertidal habitat could be lost, causing a decline in species whilst a possible local extinction of salmon and twaite shad as migrations are interrupted.

It seems that our estuaries are just as much in need of some TLC as our oceans and with their waters being so closely connected, it seems illogical to try and conserve one without also protecting the other. So whilst you’re next collecting litter, opting for sustainable seafood or ditching the use of a plastic item, why not also consider what you could do for our rivers and estuaries which feed into our seas. Can you do a cleanup further upstream? If you live near a waterway, can you eliminate the use of any chemicals in your garden? Can you support a local conservation project or environmental charity? Do you have a way of sharing your concerns with the local community and council?

By Neve McCracken-Heywood