Surface chlorophyll patchiness across Sepanggar Bay: relationships with turbidity and depth

The prevalence of harmful algal blooms (HABs), poses a considerable risk to public health and the livelihood of local fishers centred on Sepanggar Bay (Sabah). While HABs appear ostensibly during the NE Monsoon, there is no information on what may control their mesoscale distribution and production across Sepanggar Bay. For this study, we hypothesize that shallow sediment resuspension of a viable microphytobenthic population, along with potential germination of encysting harmful algae, control the mesoscale surface patchiness of chlorophyll-a across Sepanggar Bay. A ‘snapshot’ over the NE Monsoon, of surface chlorophyll-a, together with turbidity and oxygen concentrations was produced from of 34 sampling stations chosen randomly across the bay’s regions. For rapid processing and measurement, chlorophyll-a, and turbidity were taken from surface colour reflectivity, using the phone app HydroColor™. The remaining variables surface temperature, salinity, and oxygen concentrations came from a probe. Both turbidity and chlorophyll-a showed considerable structure across the bay with depth. In general, there were good correlations between depth (inverse), turbidity (positive), and surface oxygen concentrations (positive) with chlorophyll-a across the bay, but with low chlorophyll-a outliers near a water village. The reasons behind the structure and the above correlations are elaborated in the paper.