The Indo‑Pacific bottlenose dolphin (Tursiops aduncus) inhabits shallow coastal and estuarine environments across the Indian and western Pacific Oceans, including South Australia’s Adelaide Dolphin Sanctuary (ADS). In early 2025, South Australia experienced an extensive harmful algal bloom (HAB) dominated by a brevotoxin‑producing Karenia species (K. cristata), which entered the ADS in July 2025 and was associated with widespread fish mortalities across Gulf St Vincent. To assess dolphin responses to this event, we analysed 24 months of boat‑based survey data, spanning 12 months before and after bloom onset, focusing on body condition, behaviour, and pod composition. Preliminary results indicate a marked increase in emaciated individuals several months after the HAB onset, likely reflecting reduced prey availability. This period was also characterised by increased foraging behaviour, reduced socialising, and smaller pod sizes. These patterns are consistent with anecdotal reports of elevated dolphin mortality of emaciated dolphins across the region during the bloom.
In parallel, water quality was monitored, and we explored a simple, low-cost approach for tracking bloom intensity using near-surface pH measurements collected during daylight hours. pH was positively correlated with HAB species counts across all sites, suggesting it may provide a practical proxy for bloom intensity under active bloom conditions.