2, 4-diaminobutryic acid (DAB) and its structural isomer β-N-methylamino-L-alanine (BMAA) are environmental agents associated with neurotoxicity. A variety of aquatic microorganisms, including diatoms, have the capability to produce DAB and BMAA. Previous research has demonstrated an increase in DAB production in the diatom Thalassiosira pseudonana as a result of predation. Therefore, in this study, we investigated whether the production of DAB as a defensive metabolite is a species-specific strategy or a general approach employed by diatoms to counter predation. The diatom species Phaeodactylum tricornutum and Chaetoceros socialis, along with the copepod Tigriopus sp. were used for the experiment. The copepod did not consume C. socialis, and no specific regulation of DAB and BMAA productions was observed in any of the diatom species. The findings show that the production of DAB and BMAA does not contribute to the defense mechanisms of the diatom P. tricornutum.