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Assessment of species composition, diversity and biomass in marine habitats and subhabitats around offshore islets in the main Hawaiian Islands
Coles, S.L., Louise Giuseffi, and Melanie Hutchinson. (2008)

The marine algae, invertebrate and fish communities were surveyed at ten islet or offshore island sites in the Main Hawaiian Islands in the vicinity of Lanai (Pu'u Pehe and Po'o Po'o Islets), Maui (Kaemi and Hulu Islets and the outer rim of Molokini), off Kaulapapa National Historic Park on Molokai (Mokapu, 'Okala and Namoku Islets) and Oahu (Kaohikaipu Islet and outside Kapapa Island) in 2007. Survey protocol at all sites consisted of an initial reconnaissance survey on which all algae, invertebrates and fishes that could be identified on site were listed and or photographed and collections of algae and invertebrates were collected for later laboratory identification. Following the reconnaissance surveys, quantitative estimates of coral and algal coverage and size and biomass of fishes along 25 m transects were conducted at each site and their locations were recorded using GPS. A total of 1486 total taxa were identified for all sites ranging from 181 at Po'o Po'o to 126 at Kapapa. The most algal taxa occurred at Kapapa and Hulu and the fewest at 'Okala, the most invertebrates at Po'o Po'o and the fewest at Hulu, and the most fish at Namoku and the fewest at Kaemi. Substantial variation was found in the coral species richness, total cover and size class distributions among the islets, with the highest values in cover occurring at Molokini rim, with nearly as high coverage occurring at Kapapa, where the largest corals also occurred. Coral cover was lowest at Po'o Po'o, where the bottom was largely covered by fine sand/silt, in contrast to all other sites where limestone or basalt was the primary substratum. Highest algal cover was at the normally turbulent site at Kaemi where basalt boulders had abundant macroalgae, especially of Dictyopteris australis and Sargassum sp. Fish biomass for total fish, primary consumers and targets species was highest at Kapapa and highest for secondary consumers at other the Oahu site Kaohikaipu. Values for all of these categories were lowest at Po'o Po'o, Hulu and Pu'u Pehe, the latter site lying within a limited take MLCD where all but shore-based pole fishing is restricted. Therefore, for all but apex predators highest fish biomasses occurred at the two O`ahu sites, near populated shoreline areas. No introduced or cryptogenic algae were found on the surveys, and the only invasive introduced invertebrate was the snowflake octocoral Carijoa riisei, which occurred at seven of the ten sites and was abundant in caves at Po'o Po'o and 'Okala. The introduced fishes Lutjanus kasmira, Lutjanus fulvus and Cepholopholis argus were infrequently observed at six, four and three sites respectively. No endangered or threatened species were observed at any site, but four rare or uncommon algae species were recorded at one to three sites. The overall condition of the reef communities at all but one site (Po'o Po'o) was considered good to excellent, and the high coral cover and fish biomass at the Oahu sites was surprising. Equally surprising was the contrast in reef characteristics at some sites such as Pu'u Pehe and Po`o Po'o off south Lanai and Kaemi and Hulu off north Maui that were near each other and had very similar environmental characteristics but had starkly contrasting biological communities and sediment cover. The low fish biomass values at Pu'u Pehe within the Manele MLCD suggest that poaching may be occurring in this area, and we recommend that enforcement be strengthened and the MLCD boundary be extended to Po'o Po'o. We strongly recommend that the Islets within the Kaulapapa National Historic Park be designated a restricted take Marine Protected Area, that this MPA and the Park boundary be extended to include Mokapu Islet, and that a cooperative agreement be developed between the National Park Service and the State of Hawaii that would enable enforcement of fishing and access regulations by on-site park rangers.