Punalu'u Beach - Anchialine Pools

Anchialine Pools

Anchialine pools of various types occur near and around Punaluʻu and Ninole Cove. These pools are rare and localized brackish waters along coastal lava flows that exhibit tidal fluctuations without a surface connection to the sea. They include open pools near the shore as well as undisturbed pools in collapsed lava tubes, cracks, and caves. Endemic and native shrimp species live in pools and travel between and through them through underground cracks. The orange-black damselfly (Megalagrion xanthomelas) breeds in the anchialine pools while native insects perch on the nearby vegetation. Throughout the state, anchialine species are severely threatened by alien insects, habitat loss due to coastal development, and other human impacts.

Anchialine ponds are one of Hawaii’s most threatened ecosystems. Anchialine pools are landlocked brackish ponds located close to the shoreline connected to the ocean via subterranean tunnels. Characterized by tidal fluctuations, these rare and fragile ponds are home to unusual plants and animals.

In the U.S., this habitat exists only in the Hawaiian Islands and, of the approximately 700 known anchialine pools, the majority are located on the island of Hawaii. Formed by volcanic activity, these pools are home to a unique assemblage of invertebrate and algal species, some of which are known to exist only in this habitat. In the last 20 years, alien fish species have been introduced and/or invaded a majority of the pools. These alien species have gradually destroyed the ecological balance in many of the pools by eliminating many of unique endemic species.