CRED REA Invertebrate Quantitative Assessments at Nihoa Island, NW Hawaiian Islands, in 2000

To support a long-term NOAA Coral Reef Conservation Program (CRCP) for sustainable management and conservation of coral reef ecosystems, from 08 September - 06 October 2000, marine invertebrate quantitative assessments were conducted, as part of Rapid Ecological Assessments (REA), during the Reef Assessment and Monitoring Program (RAMP) Cruise TC0011 in the NW Hawaiian 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 combination of different survey techniques to quantify the diverse communities. These methods included belt-transect surveys, roving-swim surveys, and quadrat surveys. 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. Roving-swim surveys were conducted in the general area with the goal to collect qualitative data for rare, larger, and cryptic organisms, such as Crown of Thorns Starfish and Triton's Trumpet snails which may not be seen during belt-transect surveys, and to survey any additional habitats present at the site, e.g. sand, sea grass, pavement, etc. This was accomplished by swimming a zig-zag pattern that extends roughly 5 m on either side of the two transect lines (total length = 500 m). Quadrat surveys were used to quantify the smaller, more cryptic invertebrates which were sometimes overlooked or too numerous to count during belt-transect surveys. Ten 0.25-m2 quadrats were laid out at 2-m intervals along two of the 25-m transects (total area = 5 m2). For each quadrat the percent cover of sponges, octocorals and zoanthids was recorded, as well as urchins, hermit crabs of the genus Calcinus, trapezid crabs, and coralliophilid snails. In addition, up to 25 cm diameters of all urchin species are measured. Based on data from previous REA surveys, a group of target invertebrate species was chosen for quantitative counts at 2 REA sites at Nihoa Island in the NW Hawaiian 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.