Introduced marine species in Pago Pago Harbor, Fagatele Bay and the National Park Coast, American Samoa

Coles, SL; Reath, PR; Skelton, P; Bonito, V; Defelice, R; Basch, L

The biological communities at ten sites around the Island of Tutuila, American Samoa were surveyed in October 2002 by a team of four investigators. Diving observations and collections of benthic observations using scuba and snorkel were made at six stations in Pago Pago Harbor, two stations in Fagatele Bay, and one tation each in Vatia Bay and Fagasa Bay. The purpose of this survey was to determine the full complement of organisms greater than 0.5 mm in size, including benthic algae, macroinvertebrates and fishes, occurring at each site, and to evaluate the presence and potential impact of nonindigenous (introduced) marine species. These results were compared with all marine organism reports for these areas by previous investigators. A total of 1256 taxa, including 847 identified to species, were identified from the survey. A clear spatial pattern was found for species richness by sampling site, with maximum numbers of taxa occurring at Fagetele and Vatia Bays, with the next highest occurring within Pago Pago Harbor at Onesosopo, the site nearest the east side of the harbor entrance. Numbers of taxa and species decreased dramatically with distance into the inner harbor, with minimal numbers occurring at the stations along the main shipping dock at Fagotogo and near the drydock and tuna canneries at Satala. Using criteria that have been used for similar studies in Hawaii, Guam and North Queensland, Australia, only 28 on indigenous or cryptogenic species (NIS) were detected on the entire survey, considerably fewer than have been determined on harbor surveys in Hawaii or Guam but more than found at each of four North Queensland ports. The distribution pattern by station for these introduced species was in direct contrast to the pattern found for the total taxa, both in numbers of taxa and as a percentage of the total biota. A maximum of 17 NIS occurred at the main dock station, comprising about 10% of the total biota identified at that site, and 5 NIS, or 5% of the total biota, were at the drydock station. Eight NIS were found at the Utulei and seven at the Onesosopo sites near the west and east sides of the harbor, but because of their higher overall diversities, NIS comprised only about 1.6 to 2.1% of the total taxa identified at these sites. Percentages of total taxa composed by NIS were 1.0 and 1.3% at the Aua and Leloaloa sites in the outer harbor. By comparison, NIS at the four coral reef sites outside the harbor ranged only 0.4-0.9%. These results suggest that relatively few introduced species have been propagated in the waters of Tutuila, and those that do occur are mostly restricted to inner portions of Pago Pago Harbor and are not invasive in coral reef areas either within or outside of the harbor. Therefore, no direct intervention or mitigation measures are required or recommended at this time. A program of periodic rapid assessment and monitoring should be implemented to assure that potentially invasive introduced organism that may arrive in the future can be detected and intercepted in their early stages of propagation and spread. Also, a program should be considered to inspect the hulls of large, slow craft such as barges moving between harbors and islands that may transport introduced organisms already occurring in Pago Pago Harbor.