2009 Coral Reef Surveys of Marianas Archipelago Completed

Clouds cap the 857 m summit of Ascuncion Island, an uninhabited stratovolcano in the Northern Mariana Islands.

Scientists from the PIFSC Coral Reef Ecosystem Division (CRED) and partner agencies recently completed the 2009 Mariana Archipelago Reef Assessment and Monitoring Program (MARAMP) research cruise, surveying the coral reef ecosystems of Wake Atoll, the Territory of Guam, and the Commonwealth of the Northern Mariana Islands (CNMI). The 66-day expedition by the NOAA Ship Hi'ialakai was sponsored by NOAA's Coral Reef Conservation Program. This was the third biennial Pacific RAMP cruise to Wake and the fourth to the Marianas Archipelago conducted by CRED. Wake Atoll is part of the recently designated Pacific Remote Islands Marine National Monument and the waters of three of the CNMI islands surveyed are part of the recently designated Marianas Trench Marine National Monument.

Unidentified octocoral under a rocky outcropping near Ascuncion Island, Northern Marianas.

A preliminary analysis of data gathered at Wake Atoll indicates a largely healthy reef ecosystem dominated by hard (scleractinian) corals. In shallower reef areas, macroalgae are abundant, and sometimes dominant. Parrotfishes constituted well over half the total fish biomass estimated by both Rapid Ecological Assessment and towed-diver survey methods. The humphead parrotfish (Bolbometopon muricatum), on the IUCN Red List of threatened species, appeared to be ubiquitous and numerous, consistent with findings during Pacific RAMP cruises in 2005 and 2007. The fish surveys also identified nine species previously unknown in the islands.

Preliminary analyses of towed-diver survey data from the Mariana Archipelago reveal a lower density of fish shorter than 50 cm in 2009 compared to previous survey years. In addition, there were smaller differences in relative abundance of fish between the uninhabited northern islands and the populated southern islands of the archipelago than previously observed. The estimated density of sharks continued to exhibit a decline observed since surveys began in 2003.

Fine-scale biological assessments of the marine benthos suggest that levels of coral diversity, percent cover, and disease in 2009 are comparable to levels observed in previous assessments. Diversity of algae was lower in the northern islands, where turf algae replaced macroalgae as the dominant algal form. Surveys also revealed unusually high levels of cyanophytes like blue-green algae, particularly along the western-facing shores of Pagan Island. Although the factors causing these conditions are not understood, it is speculated that they may be related to iron-rich ash originating from recent volcanic activity. Alternatively, an increase in cyanophyte cover may simply be part of a previously undocumented natural cycle.

In addition to surveys by CRED scientists, guest researchers from the University of Guam and San Diego State University conducted detailed surveys of cryptic vertebrates and studies of microbial oceanography.