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The lagoon of Tarawa harbors the richest benthos documented for any Pacific atoll. The biota is strongly influenced by its setting in the equatorial upwelling zone and the unusual geomorphology of the atoll, with a submerged western rim, but largely closed and islet-strewn eastern and southern sides. As the metropolitan center of the Republic of Kiribati, Tarawa also has the largest human population of any Pacific atoll. These three attributes impose a strong influence on all aspects of the lagoon. The high regional productivity supports unusually high population densities of heterotrophic mollusks and irregular echinoids for an "open" atoll. The dense human population on the atoll relics largely on marine resources for its protein needs. The lagoonal sand flat harbors dense and diverse mollusk communities, particularly in seagrass beds. These communities support an intensive subsistence fishery with an annual harvest of ca. 1,000 tons in South Tarawa. Much of the available biomass of the two preferred species, the blood cockle Anadara uropigimelana (te bun) and the small conch Strombus luhuanus (te nouo), is taken. Both the seagrass and shellfish beds appear to have expanded considerably in the past 50 years, likely as a result of nutrient enrichment from the rapidly growing human population. Dense mollusk communities along the southeastern lagoon slope at 2-8 m depth support an intensive commercial fishery that harvests approximately 1,000 tons of Anadara per year, again representing much of the available production. Three species of irregular echinoids are conspicuously abundant on the floor of the eastern lagoon, with combined densities > 100 m-2 in the muddy facies of the inner lagoon. All aspects of the benthos follow a marked west-to-east and north-to-south zonation, reflecting the one-sided exchange of oceanic waters along the western atoll rim. While mollusk and echinoid biomass increases southeastward, coral diversity and cover decreases in that direction.

The purpose of the present study is to: 1/ list the presently known heterodont bivalve fauna of the Cook Islands, 2/ document the habitat specificity of the species involved in as much detail as possible, and 3/ investigate the correlation between a species' habitat specificity and its distribution among the various islands. While several studies have been done on the molluscan fauna of inner reef environments on Pacific islands (though bivalves are often neglected), there has been little work on the fauna of the outer reef slope. An important part of this study involved documenting the bivalve species living on this slope, and thus a large portion of my survey was carried out there.

Between 1892 and 1930, 58 percent (30 taxa) of Hawaiian endemic forest birds either were greatly reduced or became extinct. The order in which the islands experienced major declines ofseveral forest birds is Oahu (ca. 1873-1887), Hawaii (1892-1900), Mo10kai (1893-1907), Maui (18941901), Kauai (after 1900), and Lanai (1926-1932). Loss of habitat, reduced food supply, introduced avian diseases, as well as predation by man, feral cats, mongooses, and Norway rats (Rattus norvegicus) all appear to have reduced some species ofbirds, but none ofthese factors adequately explains the accelerated rates ofdecline offorest birds that occurred after 1892. Although it has been assumed that roofrats (Rattus rattus) reached Hawaii with the first European ships at the end of the 18th century, there is circumstantial evidence, independent of the bird decline data, that indicates that this rat did not arrive until after 1840, probably between 1870 and 1880. The hypothesis is advanced that after its establishment on Oahu in the 1870s, R. rattus spread to the remaining large islands in the group, resulting in a stepwise accelerated decline offorest birds on each island in turn. Hawaii thus parallels some other Pacific islands where major reductions of birds have followed the establishment of R. rattus. The need for precautions to prevent rats from reaching rat-free islands in the Hawaiian group is emphasized.