Effect of biotic stress on diatom neurotoxins: Predation and competition

Algal toxins are bioactive compounds produced by specific microalgal groups, posing significant risks to human and ecosystem health. Reports of their impact have increased worldwide, which reflects a growing concern and research activity. This review provides a comprehensive analysis of the growth, trends, and topics of algal toxin research, using data from ScienceDirect and Web of Science. Although publications have risen steadily since 2001, fragmentation across databases highlights the need for integrative syntheses. In addition, three representative microalgal neurotoxins – domoic acid (DA), β- N -methylamino-L-alanine (BMAA), and 2,4-diaminobutyric acid (DAB) – are examined with emphasis on how biotic stressors, specifically predation and competition, influence their production and biosynthesis in the causative diatoms. Distinct biotic pressures elicit divergent neurotoxin responses: grazing by herbivorous copepods and copepodamides enhances DA production in Pseudo-nitzschia seriata via activation of the dab gene cluster; competition through physical contact induces BMAA production in Thalassiosira minima, mediated by cysteine synthase; and predation pressure stimulates DAB production in Thalassiosira pseudonana through a separate regulatory pathway. Current predator-competition studies have addressed only a limited subset of possible species interactions, underscoring the need for broader experimental matrices and additional model organisms.