Harmful algal blooms (HABs) in the Johor Strait and adjacent Singapore coastal waters have been associated with recurrent fish-kill events since 2009, yet the species-specific environmental triggers that promote bloom initiation, biomass accumulation, and persistence remain unresolved. This knowledge gap is particularly important in tropical semi-enclosed systems, where nutrient inputs, salinity variability, temperature stress, and restricted water exchange may interact to favour different HAB taxa.
This study examined the trigger responses of two fish-kill-associated dinoflagellates, Karlodinium australe and Karenia mikimotoi, using controlled culture experiments designed to mimic local coastal conditions. Experimental axes included nitrogen form and enrichment, phosphorus enrichment, combined nitrogen–phosphorus enrichment, salinity reduction, and elevated temperature. Species responses were evaluated using specific growth rate, representing short-term population expansion, and maximum yield, representing biomass accumulation and bloom magnitude potential.
Our findings revealed that the two dinoflagellates showed distinct environmental response profiles across nutrient, salinity, and temperature axes. Their responses differed not only in growth rate but also in biomass yield, indicating that bloom potential cannot be inferred from a single environmental driver or growth metric alone. These divergent patterns suggest that fish-kill-associated HAB taxa may require species-specific interpretation when assessing bloom risk under tropical coastal conditions.
This presentation outlines how a trigger-based response profile can provide a laboratory-based framework for linking species physiology with future HAB monitoring data, including nutrients, environmental profiles, automated imaging, microscopy, and molecular community observations. By integrating experimental response templates with field-based evidence, this approach can support Bayesian risk updating and decision-support tools for improved HAB risk interpretation in the Johor Strait.