Anchialine pools of La Perouse Maui

Another type of wetland we see in Hawaii is the Anchialine Pool. We have several great examples in South Maui. An anchialine pool is an enclosed water body or pond with an underground connection to the ocean.

Anchialine pools are a feature of coastal aquifers which are density stratified, with the water near the surface being fresh or brackish, and saline water intruding from the coast below at some depth.

These pools differ from your usual tidal pools, as they have a subterranean connection to the ocean and do no rely on the overwash of the waves. These pools can also become brackish from rainwater or seepage from groundwater. Each pool will have slightly different salinity and chemistry.  These pools are unique and specialized environments for a selected group of species that may be uniquely adapted for life in these pools.

Anchialine pools have their own unique ecosystems populated by tiny and often rare species of crustaceans, fish, and eels. Among these species is Hawaii’s legendary red shrimp, the ʻōpaeʻula (oo-PAY-oo-la). Water levels in the pools can fluctuate in response to ocean tides. Due to their subterranean connection to the ocean, anchialine surface waters are often brackish and become more saline (salty) with increasing depth.

The word “anchialine” (AN-key-ah-lin) comes from a Greek word meaning “near the sea.” These typically small pools, which form in limestone or volcanic rock, are located throughout the world but are most common in the Hawaiian Islands and on Mexico’s Yucatán Peninsula.

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