Background: Long-chain polyunsaturated fatty acids (LC-PUFAs) are vital for various physiological processes in marine organisms. While traditionally associated with health benefits in higher trophic levels, recent studies suggest that their presence in toxic harmful algal bloom (HAB) species may be linked to toxicity.

Objective: This study aims to investigate the potential role of LC-PUFAs as proxies for toxin production in the benthic dinoflagellates Prorocentrum lima and Amphidinium carterae, both known for producing bioactive secondary metabolites such as okadaic acid and amphidinols, respectively.

Methods: The toxicity of these dinoflagellate species was assessed through lethal concentration (LC50) tests on marine microinvertebrates (Artemia and amphipods). Additionally, the levels of specific fatty acids were quantified and correlated with the concentrations of common toxins in both species. Cultures were maintained at varying temperatures (15°C, 19°C, and 24°C) until the end of their exponential growth phase.

Results: Strong positive correlations were observed between eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) levels and toxin concentrations in both dinoflagellate species. Conversely, negative correlations were found between saturated fatty acids, such as palmitic (16:0) and stearic (18:0) acids, and toxin levels.

Conclusions: The findings suggest that LC-PUFAs, particularly EPA and DHA, may serve as biochemical precursors or modulators in the biosynthetic pathways of algal toxins. Understanding these mechanisms is crucial for predicting the ecological impacts of HABs and developing strategies to mitigate their effects on marine food webs.