Ningaloo Collaboration Cluster: Habitats and biodiversity of the Ningaloo Reef lagoon Part 2: Biodiversity and ecology

Brief description

Surveys were undertaken of key invertebrate and plant groups in lagoon areas throughout the Ningaloo Marine Park, focussing on identifying and quantifying soft corals, sponges, echinoderms (urchins and sea cucumbers) and seagrasses; this information was linked to the underlying habitat structure in the Ningaloo Reef lagoons, used in a parallel habitat mapping project based on hyperspectral aerial photography. The biodiversity surveys conducted throughout the Ningaloo Reef system have shown that there are clear differences in the lagoon systems in different parts of the Marine Park, with clear biogeographic separation of sponges, soft corals and seagrasses. This has important implications for the distribution and abundance of many animals, including some of commercial importance. The northern section of the Marine Park (north of Point Cloates) is more strongly tropical than the southern section, which has many temperate species present. There are also several locations within the Ningaloo Reef system that are quite unique and don’t necessarily match the surrounding lagoon environment. Examples include Coral Bay, Bateman Bay and the Point Cloates region. These observations will be important in the management of the Ningaloo Marine Park; the northern and southern sections of the Marine Park may need to be managed differently. Surveying biological groups over the whole Marine Park is difficult and time consuming; further sampling in more locations and at different times of year are required to build on the findings of our study. There are clear seasonal differences in primary productivity in the lagoons, which likely drive significant community-wide changes throughout the year. These seasonal variations will also affect the validity of the habitat maps, which were based on imagery collected at only one time of year. Seasonal sampling will improve the reliability of the habitat maps and also give a better understanding of how the Ningaloo system operates.

Lineage

Statement: Habitat Surveys To obtain a comprehensive picture of the ecology and biodiversity of Ningaloo Reef, site selection included a latitudinal component and addressed the following major habitats: • Intertidal • Lagoonal/back reef • Seagrass beds • Sand Two major geographical regions were initially sampled: Coral Bay and Yardie Creek-Osprey Bay; the geographic range was subsequently expanded to include Red Bluff-Gnaraloo in the south and Lighthouse Bay-Bundegi in the north, to give better spatial coverage of the entire Ningaloo Reef system. A variety of locations within each of these regions was examined to incorporate as much diversity of habitat as possible, based on aerial photographs. Habitat surveys were conducted within 12 sanctuary zones and adjacent recreation zones within Ningaloo Marine Park. In lagoonal areas, sampling was undertaken at nearshore, lagoon and back reef locations with additional nearshore surveys completed in areas north of Jurabi Point and south of Cape Farquhar. Surveys were carried out using a combination of a nested quadrat design (used to provide validation information for the habitat mapping programme) and haphazardly distributed transects. The nested quadrat design comprised deployment of weighted floats attached to small ropes (~1 m long) to mark the corners of each quadrat, creating a nested 9 m x 9 m “mega-quadrat”, divided into smaller 3 m x 3 m quadrats (the size of the mega-quadrat was predetermined to allow for GPS positional error of mapped pixels, which are approximately 3 m x 3 m). In each quadrat urchins (predominantly Echinometra mathaei), holothurians, tridacnid clams, the corallivorous snail, Drupella cornus and other macroinvertebrates were counted. Visual identification and estimates of substrate % cover were recorded using standard substrate categories. Alternatively, five haphazardly selected 50 m transects were completed at each site, with visual estimates of percent cover and macroinvertebrate counts recorded for ten 50 cm x 50 cm quadrats along each transect. To ensure that sampling was conducted over reasonably homogeneous substrates at each site, transects were swum to suit the individual site characteristics (i.e. when sites were not compatible with swimming straight 50 m line transects, 10 quadrats were haphazardly placed every 5 m within the sampling area). Cross analysis of the two methods was conducted to confirm statistical equivalence of the sampling methods. Qualitative measures of biodiversity Seagrasses were sampled opportunistically while conducting validation field work and quantitative macro-invertebrate sampling. Information collected in this study was combined with existing data obtained in previous studies. Dr Jane Fromont and Oliver Gomez from the Western Australian Museum were sub-contracted to collect and identify soft corals and sponges; soft coral material was subsequently sent to Dr Monica Schlacher at the Queensland Museum for further taxonomic analysis. Sampling for these groups was conducted in line with standard procedures established by the WA Museum. Quantitative measures of biodiversity The composition of benthic communities and relative abundance measures for key organism groups were obtained using photo transects and supplementary techniques; in particular, nested quadrat sampling and analysis permitted quantitative studies of macroalgae, seagrasses and related fauna to be carried out. Sampling for macro-invertebrates was conducted using five 50 m transects at each site, with 0.25 m2 quadrats sampled every 5 m along each transect. A visual estimate was made of substrate cover, using the AIMS long-term monitoring categories. Counts were also made of echinoids, holothurians, tridacnid clams, and the corallivorous snail, Drupella, within each quadrat. The GPS location of all transects was recorded.