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Seven units at a glance
| Unit | Key idea | Main pressures | Useful number or fact |
|---|---|---|---|
| 1. Tides, waves and erosion | Moon and sun make tides; wind makes waves; together they shape coasts | Less sediment, structures, rising sea | High tide about 50 minutes later each day; global sea level up about 20 cm, 1901 to 2018 |
| 2. Tide pools | Life lives in bands; stress limits the top, competition and predators limit the bottom | Trampling, heat, pollution, acidification | Sea star removal showed a keystone effect |
| 3. Salt marshes | Salt-tolerant plants in stripes; mud builds up with the plants | Drainage, nutrients, coastal squeeze | Marshes slow waves and store carbon |
| 4. Mangroves | Trees with special roots in tidal mud | Clearing, aquaculture ponds | About 138,000 km² in 118 countries (around 2000) |
| 5. Seagrass meadows | Flowering plants underwater; feed and shelter many animals | Cloudy water, dredging, heat | About 70 species; about 29 per cent of known area lost since 1879 |
| 6. Coral reefs | Animal and algae partnership builds limestone reefs | Heat, acidification, runoff | Bleaching can start about 1 °C above the usual summer maximum |
| 7. Plankton and food webs | Drifting life feeds the sea; energy falls at each step | Warming, harmful blooms | Phytoplankton make roughly half of Earth’s photosynthesis |
Ten terms to know
- Intertidal zone: the shore between high and low tide.
- Spring tide: large range around new and full moon.
- Neap tide: small range around the quarter moons.
- Longshore drift: sand moving along a coast in a zigzag.
- Halophyte: a salt-tolerant plant.
- Pneumatophore: an air-breathing root of some mangroves.
- Rhizome: a creeping underground stem.
- Bleaching: coral losing its algae under stress.
- Trophic level: a step in a food web.
- Blue carbon: carbon stored in coastal wetlands.
Shore safety in five lines
- Never go alone; take an adult.
- Check the tide table and weather; go on a falling tide.
- Wear shoes with grip and avoid wet seaweed.
- Look and sketch; leave animals and plants in place.
- Leave early: the tide can cut off a route.
Reading carefully
Numbers here are rounded. Where a figure is widely quoted but cannot be checked, the unit says so. For exact figures, use the sources listed on the about page.