Welcome to the Coastal World!
In this chapter, we are going to explore the amazing "living" part of our coastlines. While rocks and waves are important, the coast is also home to incredible ecosystems like colorful coral reefs and mysterious mangrove forests. We will look at where these are found, what makes them tick, and why they are currently in a bit of trouble. Think of this as the "biology" of the beach!
Note: This chapter focuses on ecosystems. If you are looking for information on how waves carve out cliffs or how to stop coastal flooding, check out the chapters on Coastal Processes or Coastal Management.
1. The Big Four: Key Coastal Ecosystems
The Edexcel syllabus requires you to know about four specific types of ecosystems. Each one has a unique "home address" (distribution) and special look (features).
A. Coral Reefs
Distribution: You won't find these in cold places like the UK! They are found in tropical waters between the Tropics of Cancer and Capricorn. They need very specific conditions: warm water (above \(18^\circ\text{C}\)), shallow water (so sunlight can reach them), and clear, salty water.
Features: Often called the "rainforests of the sea," they are built by tiny animals called polyps. They provide a home for about \(25\%\) of all marine life!
B. Mangroves
Distribution: These are found along tropical and sub-tropical coastlines. They grow in the "intertidal zone"—the area that is covered by water at high tide and exposed to air at low tide.
Features: Mangroves are trees that can survive in salty water. They have amazing prop roots (which look like stilts) that help them stay steady in soft mud and pneumatophores (breathing roots) that stick out of the mud like snorkels to get oxygen.
C. Sand Dunes
Distribution: These are found at the back of wide, sandy beaches all over the world. They need a large supply of sand and a strong onshore wind to blow that sand inland.
Features: This is a story of "succession." It starts with small embryo dunes near the sea and moves back to older, more stable grey dunes. Marram grass is the hero here—its long roots bind the sand together so the wind doesn't blow the dune away.
D. Salt Marshes
Distribution: You’ll find these in sheltered coastal areas, like estuaries (where rivers meet the sea) or behind a spit. They need calm water so that fine mud can settle and build up.
Features: They are flat, muddy areas with halophytic (salt-tolerant) plants. As the mud builds up, the marsh gets higher, and different types of plants start to grow.
Quick Review: Remember, Corals and Mangroves love the tropics (warm), while Sand Dunes and Salt Marshes can be found in temperate areas (like the UK) as well.
2. Inside an Ecosystem: Abiotic vs. Biotic
Every ecosystem is a team effort between living and non-living things. To understand this, let's look at one named example: The Great Barrier Reef, Australia.
Abiotic Characteristics (The Non-Living Stuff):
- Temperature: The water stays between \(23^\circ\text{C}\) and \(29^\circ\text{C}\).
- Light: The water is shallow and clear, allowing \(100\%\) of the sunlight to reach the coral for photosynthesis.
- Salinity: The water is very salty; coral cannot grow where fresh river water dilutes the sea.
Biotic Characteristics (The Living Stuff):
- Coral Polyps: The tiny animals that build the calcium carbonate structure of the reef.
- Zooxanthellae: Microscopic algae that live inside the coral. They give the coral its color and food.
- Biodiversity: Thousands of species of fish, mollusks, and sea turtles that rely on the reef for food and shelter.
Don't worry if these names seem tricky! Just remember: Abiotic = Physical environment (Sun, water, salt). Biotic = Living creatures (Fish, plants, coral).
3. Threats to Coastal Ecosystems
Unfortunately, human activity is putting these beautiful places at risk. The syllabus highlights four main threats:
I. Industrialisation
Factories and power plants are often built on the coast for easy shipping and cooling water.
- The Problem: They can release chemical pollution or "thermal pollution" (hot water) into the sea. Hot water is a disaster for coral reefs, as it can cause coral bleaching (where the coral kicks out its algae and dies).
II. Agricultural Practices
Farming might seem far away from the sea, but everything flows downstream.
- The Problem: Farmers use fertilisers on their crops. When it rains, these chemicals wash into rivers and out to the coast. This causes eutrophication—a fancy word for when too many nutrients cause "algae blooms" that suck the oxygen out of the water and block sunlight from reaching the seabed.
III. Tourism
Everyone loves a beach holiday, but too many visitors cause damage.
- The Problem: Tourists might accidentally kick or step on fragile coral. Hotels are often built right on top of sand dunes or mangroves, destroying the habitat. Furthermore, many resorts dump untreated sewage directly into the coastal waters.
IV. Deforestation
This is a major threat specifically for Mangroves.
- The Problem: Mangrove forests are being chopped down at an alarming rate. Why? Mostly to make room for shrimp farming (aquaculture) or for timber. When mangroves are gone, the coast loses its "natural shield" against storms, and the fish that lived in the roots have nowhere to breed.
Did you know? Mangroves are "carbon sinks," meaning they store more CO2 than most tropical rainforests. Cutting them down actually speeds up climate change!
Key Takeaways for Your Exam
- Distribution: Be ready to describe where these ecosystems are found (e.g., "Mangroves are found in tropical intertidal zones").
- Features: Know one or two special things about each (e.g., "Marram grass stabilises sand dunes").
- Abiotic/Biotic: Use the Great Barrier Reef as your example. Link the warm water (abiotic) to the coral growth (biotic).
- Threats: Be able to explain how agriculture or tourism actually hurts the ecosystem. Don't just say "it's bad"—explain that fertilisers cause algae blooms or tourism leads to physical damage.