Edexcel iGCSE > Coastal Environments > Coastal Ecosystems
Many different coastal ecosystems exist, including coral reefs, mangroves, sand dunes and salt marshes.
These underwater ecosystems are concentrated in the tropics, typically in warm, shallow waters with plenty of sunlight for photosynthesis. Coral requires sea surface temperatures of 17-33°C to grow. It also requires 30-38 parts per thousand salinity and clear water. They’re mainly located in the Indo-Pacific region and the Caribbean Sea. These vibrant ecosystems are teeming with various marine life and are known for their high biodiversity. Around 25% of the world’s sea fish spawn, grow and breed in coral reefs. Reefs comprise coral polyps that secrete calcium carbonate, forming hard structures that provide habitats for numerous species.
Mangroves are saltwater-tolerant forests that grow in tidal estuaries and muddy, tropical coastlines. These are typically found in tropical and subtropical tidal areas and require sea surface temperatures of over 24°C in the warmest months and annual rainfall of over 1250mm. Countries with the largest mangrove areas include Indonesia, Brazil, and Australia. Mangroves are trees or shrubs that grow in coastal saline or brackish water. They have specialized roots, called pneumatophores, which help them to cope with oxygen-poor muddy soil and frequent inundations. They provide crucial habitat for many species and protect the coastlines from erosion and storm surges.
Sand dunes are found in many coastal areas worldwide, often forming due to wind deposition. These dynamic systems are vital to the coastal environment, acting as natural barriers to sea level rise and storm surge. Their vegetation, adapted to sandy, nutrient-poor conditions, helps to stabilise the dune structure. Vegetation that dominates sand dunes is typically halophytic (salt-tolerant) and xerophytic (drought-resistant).
Salt marshes are productive, fertile ecosystems. These coastal wetlands are found on every continent except Antarctica, primarily in temperate regions. They form in upper coastal intertidal zones between land and open saltwater, such as behind a spit or in tidal river estuaries that are flooded regularly by the tides. They form in coastal areas with high oxygen levels, significant nutrient content, and light availability. Salt marshes are characterised by grasses and other plants adapted to saline conditions. They serve as important habitats for many species, act as natural water filters, and provide a buffer against coastal storms and sea-level rise. Salt marsh vegetation is halophytic (salt-tolerant) and typically has deep roots to anchor the plant in the mud.