Coastal urbanisation

In this section we’ll talk about one of the key human impacts affecting our coastlines. Urbanisation. Hi there. My name is Dr. Ben Gilby. I’m a coastal ecologist at the University of the Sunshine Coast Australia. People like to live by the sea. Coastal areas provide us with places to live, recreation and food. According to the UN, 40% of people throughout the world live within 100 kilometres of the coast. In some parts of the world, this number is even greater. In Australia, over 85% of people live within 50 kilometres of coastlines, and this number continues to rise each year. The sea is also crucial to the economics of the world.

The ocean economy, which includes employment ecosystem services provided by the ocean and cultural services is estimated to be worth between three to 6 trillion US dollars per year. Fisheries and Aquaculture contribute 100 billion US dollars per year, and about 260 million jobs to the global economy. Shipping is responsible for up to 90% of trade between countries. Not only do people like to live near the sea, we need to live near the sea. But of course this presents significant problems for coastal landscapes. People need homes to live in places to work food to eat. centralising human populations along coastlines results in several key impacts to these environments.

Urbanisation fragments remnant coastal vegetation, agricultural areas surrounding urban areas lead to degraded coastal water quality through processes like fertiliser and insecticide release and stream bank erosion. Urban areas are significant sources for plastic debris and other marine pollutants. Fishing is centralised around major ports in the coastal zone, leading to local fisheries declines in many parts of the world. This has led all across the world to severe declines in coastal biodiversity. Coastal biodiversity is in crisis, and much of the blame can be placed on coastal urbanisation. Perhaps the most obvious effects of urbanisation in the coastal zone is the replacement of coastal habitats with human structures like buildings, sea walls, jetties, and ports.

This has resulted in substantial decline of some ecosystems at global scales. For example, globally, over 20% of mangroves have been destroyed since the mid 80s. Urban ecosystems like sea walls and jetties, are fundamentally different to the natural ecosystems that they replace. First and foremost, sea walls and urban infrastructure is hard. It is made of steel, concrete and plastic. Natural ecosystems are softer. They are built on muds and sands and comprised of plants like marshes and mangroves. This represents a fundamental change to coastal ecology. Life that thrives in sandy or muddy environments is completely replaced with life that thrives on Rocky and hard environments. Beyond this, urban ecosystems are flat and relatively lifeless.

Compare a straight and vertical Jetty pylon or seawall to the complexity of nooks and crannies that you might see on a natural rocky shore or along a shellfish bank. This is what we call the simplification of coastal ecosystems. And such simplification in response to urbanisation is one of the key threats to biodiversity in urbanised coastal seascapes. Many parts of the world have protections for coastal ecosystems like these enshrined in legislation, but losses continued to hasten. The implementation of marine and coastal reserves or national parks can help to protect these ecosystem from direct damages. But alas, the loss of key target systems continues in even some of the most heavily regulated marine reserves on earth. Why is that?

The effects of the centralization of people in the coastal zone extends beyond just the urbanised parts of the coast. All around these urbanised areas agricultural lands are required to provide food for people. These areas have sources for sediment and nutrients that run off into coastal areas via rivers and streams, causing coastal eutrophication and smothering key coastal ecosystems. Recent analyses by Griffith University have shown that rapidly declining trajectories of seagrass meadows extend across the world were most strongly associated with high pressures from destructive dismissal fishing like trolling and also poor coastal water quality. But the good news is that when these two pressures are lowered, that seagrass has a great chance of natural recovery.

Urban areas are also significant sources of nutrients, sediment and pollutants. It has been shown that runoff from construction sites in cities significantly increases sedimentation in some estuaries. polluted runoff from urban areas including firefighting, chemicals, pharmaceuticals and sewage effluent, significantly degrade coastal ecosystems and reduce the health of animals in the coastal zone. In addition urbanised areas are significant sources of marine debris. Plastic rubbish in the sea can be centralised around urbanised areas and then float off into other parts of the sea, leaving a trail of destruction So this all seems pretty bleak. But what is being done to arrest the effects of urbanisation on coastal biodiversity? Coastal restoration is wrapping up all around the world.

People are planting mangroves and seagrasses, restoring marshes and oyster reefs and growing coral. Indeed, recent global analyses have indicated that the number of active coastal restoration projects throughout the world has increased by an order of magnitude for most ecosystems since the turn of the century. These interventions are having huge benefits. They’re reconnecting fragmented mangrove forests and seagrasses, providing people that live in the coastal zone with jobs, enhancing coastal fisheries, having real and tangible benefits for coastal communities. Such efforts must continue to ramp up in future decades. There are also fascinating coastal engineering interventions that people are starting. For example, sea walls, which are typically flat and provide much less value for fish and invertebrates.

The natural shorelines are being improved by installing more complex structure that attract and support biodiversity. nooks and crannies which enhance coastal biodiversity and support some of the services people have lost due to this coastal urbanisation. Artificial reefs are being installed underneath and around jetties to encourage fish communities to thrive. Wetlands are being restored specifically to soak up excess sediments, nutrients and pollutants from waterways. Wetlands are fantastic sponges. And these sorts of projects can have the potential to absorb significant amounts of carbon from the atmosphere, thereby contributing towards climate change mitigation. So globally, coastal urbanisation is continuing to worsen.

But we have interventions and strategies which can help us to either reverse some of its effects or to mitigate negative effects just enough when we have no other choice. The interventions are there. We just need to implement them more cleverly, and invest in them more effectively right across the world.