Anchialine ecosystem painting by Patrick Ching (made for Conservation Council for Hawaiʻi and shared in classrooms across the state as a poster). Shared with Patrick & CCH’s permission.

Hawaiʻi’s Anchialine Pools

Anchialine pools are relatively rare worldwide but common on Hawaiʻi Island (and also present on Maui and Oʻahu!). Anchialine comes from a Greek word meaning “near the ocean” and in Hawaiʻi they are considered wetlands that are “landlocked” and only connected to the sea through underground lava tubes, tunnels, cracks and karst (porous limestone) barriers.  Sometimes referred to as “loko waikai” in Hawaiʻi because they are brackish, and have inputs of fresh groundwater (wai) and saltwater (kai) and also as “loko wai ʻōpae” for the famous anchialine pool shrimp that dwell in many of these ecosystems.

Anchialine pools are unique, fragile habitats that are home to numerous native wildlife species, including ʻōpae ʻula (Halocaridina rubra) the “red shrimp” that as of May 2025 was officially designated the state shrimp of Hawaiʻi. These ecosystems also support seven other anchialine shrimp species (half of which are endemic to Hawaiʻi, and two that are endangered), plus an endangered crab (Pele ramseyi) and a rare endangered eel. Plus, anchialine pools are an important source of drinking water and invertebrate food resources for our resident waterbirds, visiting migratory shorebirds, the ʻōpeʻapeʻa (endangered Hawaiian hoary bat), and pinao (damselflies and dragonflies, including some protected species). Anchialine pools also provide habitat for rare flora like mauʻu ʻōpae (Ruppia maritima, widgeongrass), and a diverse community of cyanobacteria (blue-green algae) mats. The shrimp have a symbiotic relationship with the cyanobacteria, and the species present are often distinct between certain pool systems.

How Hawaiʻi Wildlife Fund works to help Anchialine Pools

HWF has been working to protect Hawaiian anchialine pools since the mid 2000s. We have actively participated in multiple island-wide gatherings, statewide workshops and international conferences on anchialine ecosystems since that time. Learn more about our participation in the International Symposia on Anchialine Ecosystems in the resources section below, including co-hosting the 5th Intʻl event in Kona in November 2022. Anchialine pools and fauna in Hawaiʻi are faced with many threats from coastal development and the introduction of invasive species. Development can directly damage habitats by filling them in or impacting water quality and quantity.  Invasive plant species like pickleweed and seashore paspalum (a.k.a. golf-course grass) can overgrow ecosystems and add leaf litter, and some invasive species including guppies and tilapia directly predate on native species like the ʻōpae ʻula. Learn more about the impacts of invasive species on brackish ecosystems in Hawaiʻi in this YouTube video. Both invasive plants and animals can contribute excess sediments to these habitats that can lead to ecosystem senescence (loss by aging).

Our own journey into anchialine restoration activities began in Waiʻōhinu in 2009 within the Kaʻū Forest Reserve, beginning with invasive vegetation removal and followed by sediment removal from the Hoʻonoua anchialine complex.  Since then, we have been working with state, federal, business and nonprofit partners since to secure permits needed to finalize fish (invasive tilapia) removal from these pools – which are devastating the ʻōpae ʻula population where they exist.

Plus, our dedicated HWF mentors love to teach about anchialine fauna! In fact, anchialine pools are one of the focus habitats of our Hawaiian Coastal Ecosystems unit (geared towards grades 6-8) that we provide in classrooms across Hawaiʻi Island and remotely. Learn more on our Youth Education page and contact us to visit your school.

In 2019, working with fellow members of the Hui Loko: Hawaiʻi Island Fishpond & Anchialine Pool Caretaker Network (coordinated by The Nature Conservancy of Hawaiʻi), we helped to introduce legislation to nominate the ʻōpae ʻula as the state shrimp.  Introduced by Representative Nicole Lowen and 19 other legislators, the bill sat idle and was never scheduled for a hearing.  In 2025, it was re-introduced by Rep. Lowen and colleagues with additional support and advocacy from our partner, Kuaʻāina Ulu Auamo (KUA), and was passed through the House and Senate with nothing but supportive testimony. The bill passed into law on May 19, 2025 with Governor Green’s signature (Act 71) and the ʻōpae ʻula is now officially our state shrimp!