Habitat mapping is a useful method for understanding the complex spatial relationships that exist in the marine environment, and is used to evaluate the effectiveness of management strategies, particularly in regards to marine protected areas. This study explored the observed and predicted distribution of an uncommon soft coral species, Dendronephthya australis within the Port Stephens–Great Lakes Marine Park. Dendronephthya australis was mapped by video operated by a SCUBA diver towing a time synchronised GPS. A species distribution model was created to explore the possible occurrence of D. australis outside of the mapped area, using four environmental parameters: bathymetry, slope of seabed, velocity of tidal currents, and distance from estuary mouth. Dendronephthya australis colonies occurred along the southern shoreline in the Port Stephens estuary between Fly Point and Corlette Point, but no colonies were found within sanctuary (no-take) zones within the marine park. The model illustrated limited habitat suitability for D. australis within a larger section of the estuary, suggesting this species has specific environmental requirements survival. Owing to its current threats (anchor damage and fishing line entanglement), implications from these findings will assist future management and protection decisions, particularly in regard to its protection within a marine park.

A threatened and uncommon soft coral species, Dendronephthya australis found in large abundance in PortStephens, within the Port Stephens-Great Lakes Marine Park (PSGLMP), New South Wales, Australia, was hypothesized to be an important habitat for many marine fishes and invertebrates, but is currently under threat from boat anchors, fishing debris entanglement and sand inundation.2. Surveys were undertaken to assess the biodiversity associated with the soft coral habitat and its adjacent habitats (sponge, seagrass and unvegetated sand), using a combination of Underwater Visual Census (UVC) and Baited Remote Underwater Video System (BRUVS) techniques.3. In total, 77 fish species and 21 invertebrate species utilized the D. australis habitat, and multivariate fish assemblages associated with soft corals were significantly different to those associated with nearby sponges, seagrass and sand habitats. Species richness of fishes and invertebrates were significantly higher in soft coral and sponge habitats than seagrass.4. The D. australis habitat was found to be of high importance to juvenile snapper (Pagrus auratus: Sparidae), a species of recreational and commercial fishery importance, which occurred in highest abundance within D. australis, and were significantly smaller in size within the soft coral habitat than the adjacent sponge habitat. 5. Evidently, this rare soft coral habitat supports an extensive marine assemblage, potentially providing a valuable source of food and shelter for fishes and invertebrates, and given it is threatened by human-induced impacts, its protection should be a priority.

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Trade-offs between traits that influence an individual's competitive ability are important in determining community assembly and coexistence of individuals sharing the same resources. Populations of coral reef fish are structurally complex, so it is important to understand how these populations are shaped as a result of an individual's suite of traits and those of its competitors. We conducted a 2 × 2 factorial field experiment that manipulated body condition (high or low, manipulated through a feeding regime) and residency (resident or intruder, where the resident arrived at the habitat 3 h before the intruder) to evaluate effects on competitive ability and survival. Prior residency alleviated the disadvantage of a low body condition with respect to aggression, which was similar between low-condition residents and high-condition intruders. However, high-condition residents displayed a significantly greater level of aggression than intruders, regardless of whether intruders were from high- or low-condition treatments. For intruders to have a high probability of becoming dominant, they needed to have a large body condition advantage. Mortality trajectories suggested that body condition modified the effect of prior residency, and intruders were more likely to suffer mortality if they had a low body condition because residents pushed them away from shelter. Our results highlight that the negative effects of some traits may be compensated for by the positive effects of other traits, and that the specific ecological context an individual faces (such as the characteristics of its competitors) can have a major influence on successful establishment and persistence.