American Samoa Bathymetry

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 http://dusk.geo.orst.edu/djl/samoa/.

References

Fenner, D. (2008). The state of the coral reef habitat in American Samoa. In Proceedings of the NOAA Reef Fisheries Workshop. NOAA Coral Reef Task Force, Pago Pago, American Samoa, 74 pp.

Fenner, D., Speicher, M., Gulick, S., Aeby, G., Aletto, S. C., Anderson, P., Carroll, B., DiDonato, E., DiDonato, G., Farmer, V., Gove, J., Houk, P., Lundblad, E., Nadon, M., Riolo, F., Sabater, M., Schroeder, R., Smith, E., Tuitele, C., Tagarino, A., Vaitautolu, S., Vaoli, E., Vargas-Angel, B., Vroom, P., Brown, P., Buchan, E., Hall, A., Helyer, J., Heron, S., Kenyon, J., Oram, R., Richards, B., Saili, K. S., Work, T., and Zgliczynski, B. (2008).The state of coral reefs ecosystems of American Samoa. In The State of Coral Reef Ecosystems of the United States and Pacific Freely Associated States: 2008 (J. E. Waddell and A.M. Clarke, Eds.), pp. 307–351. NOAA Technical Memorandum NOS NCCOS 73, NOAA/NCCOS Center for Coastal Monitoring and Assessment's Biogeography Team, Silver Spring, MD.

Fenner, D.2009.Annual Report for 2008 of the Territorial Coral Reef Monitoring Program for American Samoa, Benthic Section. Dept. of Marine & Wildlife Resources, American Samoa.

Smith, D. K., and Jordan, T. H. (1988). Seamount statistics in the Pacific Ocean. Journal of Geophysical Research 93 (B4), 2899–2918.

Abers, G. A., Parsons, B., and Weissel, J. K. (1988). Seamount abundances and distributions in the southeast Pacific. Earth and Planetary Science Letters 87, 137–151.

Bemis, K. G., and Smith, D. K. (1993). Production of small volcanoes in the Superswell region of the South Pacific. Earth and Planetary Science Letters 118, 251–262.

Scheirer, D. S., and Macdonald, K. C. (1995). Near-axis seamounts on the flanks of the East Pacific Rise, 8ºN to 17ºN. Journal of Geophysical Research 100 (B2), 2239–2259.

Scheirer, D. S., MacDonald, K. C., Forsyth, D. W., and Shen, Y. 1996. Abundant seamounts of the Rano Rahi seamount field near the Southern East Pacific Rise, 15º S to 19º S. Marine Geophysical Researches 18, 13–52.

Rappaport, Y., Naar, D. F., Barton, C. C., Liu, Z. J., and Hey, R. N. (1997). Morphology and distribution of seamounts surrounding Easter Island. Journal of Geophysical Research 102 (B11), 24,713–24,728.

Staudigel, H., Koppers, A. A. P., Lavelle, J. W., Pitcher, T. J., and Shank, T. M.. (2010). Mountains in the sea. Oceanography 23 (1), 18–19.

Etnoyer, P., Wood, J., and Shirley, T.C., (2010). Box 12: How large is the seamount biome? Oceanography 23 (1), 206–209.

Pitcher, T. J., Morato, T., Stocks, K. I., and Clark, M. R. (2010). Box 6: Seamount Ecosystem Evaluation Framework (SEEF): A tool for global seamount research and data synthesis. Oceanography 23 (1), 123–125.

Guisan, A., Weiss, S. B., and Weiss, A. D. (1999). GLM versus CCA spatial modeling of plant species distribution. Plant Ecology 143, 107–122.

Iampietro, P., and Kvitek, R. (2002). Quantitative seafloor habitat classification using GIS terrain analysis: Effects of data density, resolution, and scale. In Proceedings of the 22nd Annual ESRI User Conference. ESRI, San Diego, CA, http://gis.esri.com/library/userconf/proc02 (last accessed 29 Nov 2010).

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. http://dusk.geo.orst.edu/djl/samoa/hurl (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