Identifying nutrient sources to three lagoons at Ofu and Olosega, American Samoa using δ15N of benthic macroalgae

This paper is not subject to U.S. copyright. The definitive version was published in Marine Pollution Bulletin 54 (2007): 1830-1838, doi:10.1016/j.marpolbul.2007.08.016.Degradation of nearshore habitats is a serious problem in some areas of American Samoa, such as in Pago Pago Harbor on Tutuila Island, and is a smaller but chronic problem in other areas. Sedimentation, pollution, nutrient enrichment from surface runoff or groundwater, and trampling are the major factors causing the changes. On the outer islands of Ofu and Olosega, there is an interesting contrast between relatively pristine lagoon habitats not far from comparatively degraded lagoon habitats. To’aga lagoon on the southeast side of Ofu Island has clear waters, a high diversity of corals and fishes, no human habitations, and an undeveloped watershed with no streams. To’aga lagoon is within the boundaries of the National Park of American Samoa and is the site of long-term research on coral reef resilience and global climate change. Only 3 km to the east of To’aga is a degraded lagoon that fronts Olosega Village. The Olosega lagoon is similar in size but has significantly less live coral than To’aga, and blooms of filamentous algae have been reported to cover the Olosega lagoon/reef flat bottom. The islands are influenced by the same regional-scale and biogeochemical regimes, and both islands are remnants of a volcanic caldera