Coral Reef Project: Tutuila

Science Center Objects

As part of the USGS Coral Reef Project, the USGS is working on Tutuila with its partners: 1.) in Faga’alu Bay to better understand the impacts of land-based pollutants on the coral reefs, and 2.) on the north coast to help determine the effects of circulation on nearshore waters.

Island as viewed from satellite, with visible clouds, an airport and other land features, and shallow ocean waters.

IKONOS satellite image of Tutuila

Overview

Tutuila encompasses 140 square kilometers (54 square miles) and is the largest and main island of American Samoa, an organized unincorporated territory of the United States. The island is located in the central south Pacific Ocean, about 4,000 kilometers (2,500 miles) northeast of Australia. Formed from Pliocene-age volcanic rocks, Tutuila has a rugged southwest-northeast trending mountain ridge that hugs the northern part of the island and reaches an elevation of 653 meters (2,142 feet). The southern part of the island, however, is relatively flat. Tutuila boasts nearly 100 kilometers (62 miles) of coastline, with the deep embayment of Pago Pago Harbor on the south shore nearly dividing the island into two parts. 

Tutuila’s nearshore coral reefs are home to more than 250 different species of coral, including hard “table” corals nearly 3 meters (10 feet) in diameter. Impacts from poor land-management practices are threatening the health of these ecosystems. Marine protected areas include the Tutuila unit of the National Park of American Samoa on the northern coast and Fagatele Bay National Marine Sanctuary on the southern tip of the island.

Motivation

Human activity has significantly increased the volume of land-based pollution (sediment, nutrients, and contaminants) along much of Tutuila’s southern coastline. These human activities are related primarily to land-management practices, including urban development, wastewater discharge, and poor land use. Because of these land-based pollution impacts to the coral reefs, the U.S. Coral Reef Task Force (USCRTF) designated Faga’alu Bay on the south shore of Tutuila as the third USCRTF Priority Study Area. The USGS is working with San Diego State UniversityNOAA, and other U.S. Coral Reef Task Force (USCRTF) partners to better understand the impacts of these land-based pollutants on the coral reefs in Faga’alu Bay.

Starting in the late 2000s, a significant outbreak of Crown-of-Thorns (COTS) sea stars (Acanthaster planci) began on the western side of Tutuila and decimated many of the coral reefs. This COTS outbreak has now spread to the north coast, and is threatening National Park waters between Fagasa and Afono Bays. In addition to our studies in Faga’alu Bay on the south shore, the USGS is working with the National Park Service on the north coast of the island to help determine the effects of circulation on the nearshore waters, and how it may influence the spread of COTS.