By Kelvin Gorospe
The Pacific Islands Fisheries Science Center’s (PIFSC) Coral Reef Ecosystem Division (CRED) recently completed the Phoenix Islands portion of their Pacific Reef Assessment and Monitoring Program (Pacific RAMP) research cruise. The areas they surveyed included: Johnston Atoll, Howland Island, and Baker Island. All three islands are part of the Pacific Remote Islands Marine National Monument, which is co-managed by NOAA and the U.S. Fish and Wildlife Service (USFWS), as well as the National Wildlife Refuge System administered by the USFWS. These areas are among the most remote locations under U.S. jurisdiction and offer a unique opportunity to study and better understand coral reef ecosystems removed from direct human impacts.
During the expedition, small boats were launched from NOAA ship Hi‘ialakai carrying teams of scientists to survey reef fishes, benthic and microbial communities, and study the effects of ocean acidification and warming on reef ecosystems (Fig 1). A total of 17 scientific divers, one data manager, and two terrestrial biologists participated in operations (Fig 2). For the U.S. Phoenix Islands portion of the cruise, fish data are highlighted below. Blog posts from the upcoming legs of this 103-day research expedition will highlight information from other reef assessment surveys.
Over the course of 13 diving days, the fish team surveyed a total of 102 rapid ecological assessment (REA) sites (31 at Johnston Atoll, 35 at Howland Island, and 36 at Baker Island). The team used a stratified random survey design, whereby the reefs around each island are divided into three depth zones (0-6 m; 6-18 m; and 18-30 m) and the total number of sites surveyed in each depth zone is proportionate to the total amount of reef area found in that depth zone. Site locations are then spatially randomized around the island. Click here for more details on the methodology of fish REA surveys.
At Howland and Baker Islands, the subsurface eastward-flowing Equatorial Undercurrent encounters the submerged portions of these undersea mountains to create areas of intense upwelling of nutrient-rich waters that help sustain high biomasses of reef fishes. This is clearly shown in the bubble plots above (Fig 3 and Fig 4), depicting high levels of fish biomass around both islands. Each circle on the graph is centered on a dive site.
Among other large-bodied species, schools of manta rays were frequently reported around both Howland and Baker Islands (Fig 5). At each site, two fish divers collected replicate data on the sizes and numbers of fish species that swam through their survey area over the course of five minutes (Fig 6). The size of the circle is proportionate to the calculated total biomass of fish (g per m2) at each site. These graphs demonstrate the high reef fish biomasses in these upwelling areas of the Pacific Remote Islands Marine National Monument.
In contrast, Johnston Atoll, which doesn’t experience this strong upwelling of nutrients (Fig 7), sustains lower levels of reef fish biomass than Howland and Baker. However, its importance is highlighted by the fact that it is known to be an important genetic stepping stone between the central Pacific and the Hawaiian Islands, maintaining evolutionary connectivity between these areas. During our time at Johnston on this cruise, CRED scientists spotted three coral species (Acropora speciosa, Acropora retusa, and Pavona diffluens) recently listed as threatened under the Endangered Species Act.
In addition, CRED scientists reported frequent sightings of overturned Acropora table corals and observed that much of the coral on the northwest side of the atoll experienced recent damage, likely as a result of the large ocean swell from the northwest that came through as we were leaving Oahu at the end of January. Protection of these areas from the degrading effects of fishing and extraction is important to ensuring that the reef can recover from natural environmental impacts such as these large ocean swell events.
The CRED team will remain at sea until May 3, 2015, continuing to conduct coral reef ecosystem monitoring surveys throughout American Samoa (Tutuila, Ofu, Olosega, Ta‘u, and Swains Islands and Rose Atoll) as well as the U.S. Line Islands (Jarvis Island, Palmyra Atoll, and Kingman Reef). Stay tuned for more updates from the field.