sheets still nutrient rich rock pools

Size
Length: 10–30 cm
Lifespan
1–2 years
Diet
Photosynthetic marine algae. Draws energy from sunlight and nutrients from surrounding water. Requires clean water and good light.
Habitat
Intertidal rock pools, sheltered mudflats, and calm estuarine shallows with still, nutrient-rich water and ample sunlight.
Range
Found throughout North and South Islands on rocky shores, mudflats, and sheltered estuaries. Most common in sheltered bays and estuaries.
Endemism
Native
Main Threats
None significant. Localised threats include coastal development, pollution, and climate change affecting water temperature and clarity.
Population
Not Threatened. One of most common seaweeds in world. Found on every continent except Antarctica. Abundant in sheltered estuaries and rock pools.
Conservation Status
Not Threatened
Human Risk
harmless
Handling Note
marine algae, safe to handle
Conservation Note
Native green algae; not assessed by NZTCS as marine algae are outside the scope of current threat classifications.
Te Ao Māori
No recorded Māori name distinguishes green sea lettuce from other green seaweeds. Likely grouped with edible seaweeds called karengo or rimu. Traditional food of coastal Māori. Gathered from rock pools and estuaries. Washed and eaten fresh or dried. Used as medicine applied to wounds. Sign of clean water and healthy nutrients. Still grows in rock pools today.
Tide recedes slowly. Ulva lactuca is the salad of the sea. Green sea lettuce grows in thin, flimsy, bright green fronds. Like a piece of lettuce washed up by the tide. Only two cells thick in places. So delicate you can tear it with a gentle tug. Grows in small patches or large mats. Floating just beneath the surface. Waving in the current like underwater grass. What makes it special is its simplicity. One of the simplest seaweeds in the world. Body is a flat sheet of cells. No complex structures. No floats. No specialised parts. Absorbs nutrients directly from water through entire surface. Photosynthesises through every cell. A living sheet of green. Nothing more. But this simplicity is a superpower. Green sea lettuce can grow almost anywhere. On rocks. On mud. On mussel shells. On boat hulls. Tolerates wide range of temperatures, salinities, and nutrient levels. Even grows in brackish water where sea meets river. It is the weed of the sea. The pioneer of the disturbed shore. Reproduction happens by releasing spores. Also by fragmentation. A piece broken off by a wave can grow into whole new plant. This is why it appears so quickly in new areas. Single fragment can colonise whole rock pool within weeks. Green sea lettuce is also edible. Eaten fresh in salads. Dried as seasoning. Cooked in soups and stir-fries. Rich in vitamins and minerals. Mild, slightly salty flavour. In New Zealand, it is the free salad of the shore. To find a patch at low tide is to find flash of bright green in dark rock pool. Thin, flimsy fronds float just beneath surface. Waving in gentle current. Looks delicate. Insubstantial. Almost trivial. But it is a survivor. Able to grow anywhere. Tolerate anything. Feed anyone who cares to pick it. The salad of the sea. Whether you ordered it or not. No one told it otherwise.