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The Manell-Geus watershed lies at the southern tip of the island of Guam. Located primarily in the village of Merizo, the rivers and reefs associated with this watershed support the village’s strong fishing tradition.
The extensive seagrass beds and patch reefs in Cocos Lagoon provide important forage and resting habitat for sea turtles. These beds extend eastward into the Achang Reef Flat Marine Preserve, providing valuable nursery habitat for a variety of desirable food fish including:

  • Mafute (Lethrinus harak, the thumbprint emperor)
  • Tiao (juvenile Mullids or goatfish)
  • Manahak (juvenile Siganids)

The area is also an important habitat for both green and hawksbill sea turtles and has the largest aggregation of sea turtles observed on Guam.


While this site has amazing marine resources, the reef ecosystems are impacted by poor water quality linked to erosion on the steep hillsides and along streambanks. Wildland fires, feral animals, and off-roading vehicles have accelerated the erosion. These conditions can lead to flooding in downstream areas, affecting the communities and the adjacent reef in Merizo.

Sedimentation can also have serious impacts to coral health by increasing susceptibility to disease, decreasing growth rates, and affecting coral settlement. These problems may be exacerbated by outbreaks of crown-of-thorns starfish (a carnivorous predator that preys on reef coral polyps) and overharvesting of key species, such as large parrotfish.

Crown of thorns starfish: A threat to Guam coral.



NOAA will now develop an implementation plan for the Manell-Geus watershed.


Please email any questions to Lani Watson at Lani.Watson@noaa.gov.