To support a long-term NOAA Coral Reef Conservation Program (CRCP) for sustainable management and conservation of coral reef ecosystems, from 20110407 to 20110509, marine invertebrate quantitative assessments were conducted, as part of Rapid Ecological Assessments (REA), during the Reef Assessment and Monitoring Program (RAMP) Cruise HA1101 in the Northern Marianas Islands. Such cruises are conducted at biennial intervals by the Coral Reef Ecosystem Division (CRED) at the NOAA Pacific Islands Fisheries Science Center (PIFSC). At specific reef sites, marine invertebrate zoologists along with coral and algal biologists entered the water and conducted a fine-scale (~100 m2) and high degree of taxonomic resolution benthic REA survey for coral, algae, and key invertebrate species. Invertebrate surveys were focused on quantifying key non-coral invertebrate species common to the reef habitats, and were conducted using a belt-transect survey method. In belt-transect surveys, quantitative counts of key invertebrates were recorded along two consecutively-placed 25m long and 2m wide belt transects (total area = 100 m2). For any species that cannot be identified in the field, a photograph and a representative specimen, if possible, is collected for later identification. Based on data from previous REA surveys, a group of target invertebrate species was chosen for quantitative counts at 2 REA sites at Aguijan Island in the Marianas Islands. The species in the list were chosen because they have been shown to be common components of the reef habitats and they are species that are generally visible (i.e.; non-cryptic) and easily enumerated during the course of a single 50-60 minute SCUBA survey.