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A fleet of baited remote underwater video stations was set in lagoonal and inter-reef waters of the Great Barrier Reef Marine Park, across 14°of latitude and the entire shelf. Counts of the maximum number seen in any one field of view were used to estimate relative abundance of 347 species of bony fishes, cartilaginous fishes and sea snakes. Boosted regression trees were used to assess the influence of depth and location of sampling sites on species richness. Multivariate regression trees and indices of specificity and fidelity (Dufrêne-Legendre indices) were used to distinguish 17 spatially contiguous vertebrate groups within a hierarchy of spatial scales. Location across the shelf and depth had the greatest influence on species richness, with peaks occurring around the ~35 m isobath in the inter-reef waters of the reef matrix, coinciding with shallow banks and shoals. Richness increased slightly toward the equator. Nine terminal vertebrate communities parallel to the coast were distinguished inshore and offshore in deep and shallow water along a latitudinal gradient. There were important community boundaries at Bowen in the south, Townsville in the centre, and Cape Flattery in the north. Latitudinal groupings were most evident inshore. Offshore communities were spatially extensive and separated lagoonal, mid-shelf and outer-shelf sites. Community boundaries were correlated with knowledge of strong gradients in sedimentary and oceanographic processes influenced by the shape of the reef matrix and regional tides and currents.

The black marlin (Istiompax indica) is one of the largest bony fishes in the world with females capable of reaching a mass of over 700 kg. This highly migratory predator occurs in the tropical regions of the Pacific and Indian Oceans, and is the target of regional recreational and commercial fisheries. Through the sampling of ichthyoplankton and ovaries we provide evidence that the relatively high seasonal abundance of black marlin off the Great Barrier Reef is, in fact, a spawning aggregation. Furthermore, through the tracking of individual black marlin via satellite popup tags, we document the dispersal of adult black marlin away from the spawning aggregation, thereby identifying the catchment area for this spawning stock. Although tag shedding is an issue when studying billfish, we tentatively identify the catchment area for this stock of black marlin to extend throughout the Coral Sea, including the waters of Papua New Guinea, the Solomon Islands, Micronesia, New Caledonia, Kiribati, Vanuatu, Fiji, Tuvalu and Nauru.

We report severe bleaching in a turbid water coral community in north-western Australia. Towed still imagery was used for a benthic survey near Onslow in March 2013 to assess thermal stress in hard and soft corals, finding 51–68% of all corals fully bleached in 10–15-m water depth. Tabulate or foliaceous Turbinaria was the locally most abundant hard coral (46%), followed by massives such as faviids and poritids (25%) and encrusting coral (12%), thus over 80% of the local corals could be considered to be bleaching resistant. All coral groups were bleached in similar proportions (massive hard corals 51%<soft corals 60%<encrusting hard corals 62%<Turbinaria 62%<‘others’ 68%). NOAA data and environmental assessments suggest previous recurrent thermal stress throughout the last 10 years in the study area. On the basis of these records this stress apparently changed the community structure from bleaching vulnerable species such as Acropora, leaving more tolerant species, and reduced coral cover. We could see no evidence for adaptation or acclimation of corals in this area. Towed still imagery was found to be a suitable means for rapid and large-scale bleaching studies in shallow, turbid areas where diving can be difficult or impossible.