The hydrodynamics of Lizard Island lagoon, Great Barrier Reef

Caitlin Philipps & David Bellwood

Abstract:

Hydrodynamic processes are a major driver for marine systems, linking marine organisms with their environment. However, a lack of hydrodynamic data at an ecologically relevant spatial resolution has stymied our understanding of reef function, as exemplified by Lizard Island on the Great Barrier Reef. To address this gap, 23 to 27 Marotte HS current meters were deployed over three periods, collecting 15 months of current velocity data. Combining these data with wind and tide datasets, we provide a preliminary description of the circulation in the Lizard Island lagoon, examining wind and tide influence, and flushing time. During south-easterly trade winds, flood tides flow through the Lagoon Entrance, while wind-induced waves cross the Bird-South crest, driving a north-westerly flow through Loomis Channel and across the western lagoon. Ebb tides flow east–south-east through the Lagoon Entrance and south-west through the Palfrey-South channel. Tides contribute a mean of 20.4% to the overall current speed, particularly in deeper sites with less reef interference, while shallow sites were more influenced by wind. Lizard Island lagoon flushing times ranged from a few hours to 10 days; longer during periods with low wind speeds. Hindcast flushing times during the 2016 coral bleaching event (following 8 Degree Heating Weeks) were approximately 22 h, suggesting that flushing time likely had minimal influence on bleaching. Our analyses provide initial insights into the circulation of the Lizard Island system and aid understanding of the potential relationships between reef organisms and their physical environment, bridging the gap between ecology and hydrodynamics.