Surveys of shallow reef biodiversity were undertaken in the Norfolk Marine Park (NMP) in 2009, 2013 and 2021 by a team of skilled divers participating in the Reef Life Survey program (www.reeflifesurvey.com) and from the University of Tasmania. A total of 74 transects were surveyed for reef fishes, mobile invertebrates and benthic cover at 16 sites in 2009 (n = 31 transects), 2013 (n = 11), and 2021 (n = 32).
Relatively little change was observed in most elements of reef biodiversity, although large variation in measures of reef fish biomass and benthic cover within sites reduced the ability of the surveys to quantify subtle regional changes. Qualitative declines in fish biomass at Phillip Island sites, and increases along the southern exposed coast, from 2009 to 2021 were not statistically significant. Doubleheader (Coris bulbifrons) and black cod (Epinephelus daemelii) became less frequently observed. Fewer mobile invertebrate and cryptic fish species were observed per transect in 2021 than in earlier surveys, and differences in invertebrate and cryptic fish community structure between localities around the island were reduced (i.e. making communities more similar across sites around the island). Benthic cover changed little through time in most locations around the island, but a shift from turfs to macroalgae and a slight increase in coral cover were observed at the lagoon sites. Ongoing surveys through the long-term are needed to determine if these trends continue and require targeted management intervention.