Unveiling the spatio-temporal variation of harmful algal bloom (HAB) species assemblages and their relationship with environmental factors in a tidal creek environment

The present study provides complementary information on the harmful algal bloom (HAB) species present in Manori Creek coastal water and tidal channel. A total of 67 HAB species representing 35 genera and 7 taxonomic class groups were identified. Among them, 27 were potentially toxic, while 45 had the potential to form harmful algal blooms. Notable blooms included Chaetoceros socialis in April (8.9 × 10⁵ cells l⁻¹) and May (3.9 × 10⁵ cells l⁻¹), Nitzschia palea in May (4.37 × 10⁶ cells l⁻¹) and June (1.1 × 10⁵ cells l⁻¹), and Coscinodiscus radiatus in (2.7 × 10⁵ cells l⁻¹) in January. The marine ciliate Mesodinium rubrum exhibited bloom formation in May (1.33 × 10⁵ cells l⁻¹) at all stations in Manori Creek. Canonical correspondence analysis revealed that the proliferation of HAB species was facilitated by optimal temperature, salinity, and nutrient levels in creek water. Dinoflagellates responsible for paralytic shellfish poisoning (PSP) and diarrhetic shellfish poisoning (DSP) were rare and found in low abundance. Toxin assessment results, based on the mouse bioassay, revealed that Gafrarium divaricatum samples contained paralytic shellfish toxin (PSP toxin) levels < 0.875 mouse units (MU) per 100 g of clam tissue. The test mice exhibited normal fecal consistency, indicating the absence of high levels of diarrhetic shellfish toxin (DSP toxin). The present study recorded HAB species variability and potential toxin accumulation within G. divaricatum in Manori Creek. The data generated from the creek serve as a pivotal base for the advance monitoring initiatives focused on HAB species and their associated toxins within the creek ecosystem.