American Samoa Bathymetry

Nov 30, 2010 (Last modified Feb 2, 2013)
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Seamounts, ridges, and reef habitats

Knowledge of American Samoan mesophotic (low light level) reefs is very limited.  They are the some of the deepest and farthest in the archipelago from humans, and thus help to delineate what unimpacted coral reefs are like in the territory (1-3).Unfortunately, there are no good examples of shallow, unimpacted reefs around Tutuila, where human impacts are greatest. Therefore, knowledge about natural, unimpacted reefs in the territory – including deep, mesophotic reefs – is very important for gauging the impacts humans have had on reefs there.

The geomorphology of the Eastern Samoa Volcanic Province – which covers 28,446 square kilometers (km2) with depths ranging from ~50-4,000 meters (m) – is revealed in a new compilation of available multi-beam bathymetry data. Details from these high resolution data reveal 51 previously undocumented seamounts. Seamount shapes suggest that morphologies are largely typical of other Pacific intra-plate seamounts, though infrequent departures show forms indicative of mid-ocean ridge type magmas. Analysis results indicate 2.8 (± 0.2) seamounts per 1,000 km2, within the range of expectations for other regions of the Pacific Plate but toward the low end (4-9).

In the current global census of seamount habitats – some of the richest biological “hotspots” in the oceans (10-12) – only 200 have been sampled, and in no systematic fashion (11), but detailed results from these studies hold promise for exploring a possible relationship between seamount shape and habitat. Indeed, studies of topographic/bathymetric position index (TPI/BPI) indicate it is important – in a vertical sense – for species richness along a vertical biodiversity gradient (13-15). Three Pisces V submersible dives were made to the submerged seamount flanks of Tutuila where relatively shallow (~30 m depth), mesophotic (lower light level) reefs with little human impacts occur (16). As a result, the base of extensive live bottom (coral cover ≥20%) was found to be at ~36 m depth; 91 species of fish and 32 species of invertebrates (total of 9 new records) were identified; and small portions of previous benthic terrain maps were ground-truthed (16, 17).

For more information about seafloor mapping efforts in and around the American Samoa region, see the Oregon State University Davey Jones Locker Lab website at


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Lundblad, E., Wright, D.J., Miller, J., Larkin, E.M., Rinehart, R., Battista, T., Anderson, S.M., Naar, D.F., and Donahue, B.T. (2006). Classifying benthic terrains with multibeam bathymetry, bathymetric position and rugosity: Tutuila, American Samoa. Marine Geodesy 29 (2), 89–111.

Wright, D. J. (2005). Cruise KOK0510 - R/V Ka'imikai-o-Kanaloa. NOAA NURP HURL Cruiste Report. (last accessed 29 Nov 2010).

Wright, D.J., Roberts, J., Fenner, D., Smith, J.R., Koppers, A.A.P., Naar, D., Hirsch, E.R., Clift, L.W., and Hogrefe, K.R. (in press, 2011). Seamounts, ridges, and reef habitats of American Samoa. In Seafloor Geomorphology as Benthic Habitat: GeoHab Atlas of Seafloor Geomorphic Features and Benthic Habitats (P.T. Harris and E.K. Baker, Eds.). Elsevier, Amsterdam.

Co-author:   Dr. Dawn Wright

Recommended by Tara Starr Marvin
Jeremiah Osborne-Gowey. 2010. American Samoa Bathymetry. In: Data Basin. [First published in Data Basin on Nov 30, 2010; Last Modified on Feb 2, 2013; Retrieved on Jul 2, 2022] <>

About the Author

Jeremiah Osborne-Gowey
Aquatic/Landscape Ecologist with Conservation Biology Institute

Jeremiah Osborne-Gowey is an aquatic/landscape ecologist with more than 15 years of Federal, State, and educational natural resource experience. His experience includes aquatic and terrestrial species habitat survey and inventory, invasive-species monitoring, natural resource impact analyses, public...