Integration of remote sensing and in situ data to determine environmental drivers and ecological effects of Noctiluca blooms in Australian waters

Harmful algal blooms (HABs) have been a major concern in recent decades, increasing spatially, as well as in frequency and intensity. One species in particular, Noctiluca scintillans, is considered harmful, as dense aggregations are capable of depleting oxygen at the surface, in turn suffocating sea life. These dinoflagellate blooms are prevalent mostly in spring and summer along Australia’s coast, creating mesmerizing bioluminescent waters at night and red-orange tides during the day. These distinguishable tides make it simple to identify blooms with true color satellite images. However, little is known about the interaction of red Noctiluca blooms with other phytoplankton species, especially those that contain chlorophyll. Here we examine chlorophyll-a (chl-a) values, pre and post blooms, derived from Earth observation satellites: Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua and Sentinel-2 MultiSpectral Instrument (MSI). In situ precipitation, temperature, and wind were also analyzed to determine potential bloom drivers, specifically around Tasmania. Preliminary results show seasonal differences in the frequency and severity of blooms; however, we found no distinct correlations between in situ parameters and N. scintillans density. Blooms may be influenced by southerly winds and increased rainfall, moving nutrients to the coast. A peak in chl-a values along the coast prior to and during bloom periods may be an indicator for an increase in Gymnodinium catenatum, a food source of Notiluca that contains chl-a. Understanding localized bloom characteristics and phytoplankton dynamics is essential for forecasting ecosystem-level impacts, with implications for sustainable aquaculture and fisheries management.