Learn & Explore/Habitats/Anchialine Pools
Anchialine Pools: Hawai‘i’s Hidden Coastal Treasures
Small coastal pools with no surface connection to the ocean, yet influenced by tides and groundwater.
What Are Anchialine Pools?
Anchialine pools are small, brackish water habitats found near the coast. They look like isolated ponds, but they are connected underground to the ocean through porous rock and groundwater. This unique connection means they rise and fall with the tides—even though they have no visible link to the sea.
The word anchialine comes from Greek, meaning “near the sea”. In Hawai‘i, these pools are known as wai ‘ōpae, loko wai kai, or loko ‘ōpae ‘ula.
Why Are They Special?
- Hawai‘i has one of the highest concentrations of anchialine pools in the world, with about 700 habitats across the islands.
- These pools occur in lava fields, caves, old lava tubes, and limestone areas.
- They are home to rare and endemic species—plants, animals, and microbes found nowhere else.
The most famous resident is ‘ōpae ‘ula (Halocaridina rubra), Hawai‘i’s official state shrimp. These tiny red shrimp can live for over 20 years and help keep the ecosystem healthy by grazing on algae.
These fragile habitats face growing threats from sea-level rise, coastal development, and invasive species—from guppies to non-native grasses—that degrade water quality and accelerate pool decline.
Cultural Significance
Anchialine pools are deeply rooted in Hawaiian history and culture. For centuries, they provided:
- Fresh water in dry coastal regions
- Aquaculture for food
- ‘Ōpae ‘ula as bait for traditional ‘ōpelu fishing
- Sites tied to Hawaiian royalty and community life
Why Protect Them?
Anchialine ecosystems are fragile. They face threats from development, pollution, invasive species, and climate change. Preserving these habitats means protecting biodiversity, cultural heritage, and the natural beauty of Hawai‘i.