What are Anchialine Pools?
An anchialine pool is a landlocked body of water with a subterranean 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. Water levels in anchialine pools often fluctuate with tidal changes due to the coastal location and the connection with the ocean. The range in water levels fluctuations will be decreased (damped) and delayed compared to the range and time observed for the adjacent tide. The primary control on the damping and lag is the distance from the coast. Anchialine pools are extremely common worldwide especially along Neotropical coastlines where the geology and aquifer system are relatively young, and there is minimal soil development. Such conditions occur notably where the bedrock is limestone or recently formed volcanic lava. In 2018, the Kīlauea eruption created the new black sand beach at Pohoiki and several new anchialine pools. Many anchialine pools are found on the coastlines of the island of Hawaii, on the Yucatán Peninsula, and Christmas Island.
Ecological studies of anchialine pools frequently identify regionally rare and sometimes endemic species. In Hawaii, the pools are home to the ʻōpaeʻula (Hawaiian shrimp, Halocaridina rubra). In karst anchialine pools and the caves that these may be connected to, the fauna are diverse and include crustaceans, including remipedia and copepods. Vertebrates are also found, including several species of blind cave fish.
Logging Tasks:
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What is the shape of the anchialine pools? Are they circular, elliptical, or another shape?
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Describe the water quality of the pools. Is it clear or cloudy? Could you see the bottom of the pools?
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Use your observations at the GZ and the site https://tidesandcurrents.noaa.gov/noaatidepredictions.html?id=1617760 for tide predictions on the Big Island. Was your visit at Poihoiki Beach near high tide or low tide? How does this affect the appearance of the anchialine pools?
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Sources:
https://en.wikipedia.org/wiki/Anchialine_pool
https://www.staradvertiser.com/2019/11/15/breaking-news/state-asks-public-not-to-swim-snorkel-in-seven-new-anchialine-pools-on-big-isle/
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