A field-ready molecular workflow for sample-to-result detection of the harmful dinoflagellate species Prorocentrum cordatum (Prorocentraceae, Dinoflagellata) in coastal Brazilian waters

Conventional monitoring of toxic phytoplankton is time consuming, requires large sample volumes and depends on expert taxonomic identification, highlighting the need for faster, more sensitive and widely accessible methods. The globally distributed dinoflagellate Prorocentrum cordatum contributes to harmful algal blooms, posing serious risks to marine ecosystems and coastal economies. This study presents a sample-to-result molecular assay for the detection of P. cordatum using the polymerase chain reaction (PCR) and loop-mediated isothermal amplification (LAMP) targeting the ITS and psbA genes. Analyses were performed on small volumes of water (5–50 ml), from Santa Catarina Island, southern Brazil, which were concentrated with syringe filters and membranes. Sensitivity was evaluated through 10-fold serial dilutions of P. cordatum DNA, and specificity tested against three other potentially harmful dinoflagellates, P. lima, P. hoffmannianum and Takayama acrotrocha. Detection limits were 5.3 × 102 cells l−1 for ITS-PCR and 5.3 × 103 cells l−1 for psbA-PCR; and 5.3 × 105 and 5.3 × 106 cells l−1 for ITS-LAMP and psbA-LAMP, respectively. In field tests (n = 48, all <106 cells l−1), P. cordatum was detected in 32 samples by ITS-PCR and 29 by psbA-PCR. In contrast, ITS-LAMP detected the species in only three samples, and psbA-LAMP in none. Overall, PCR proved highly sensitive and specific for detecting low cell densities, while LAMP, although less sensitive, offers a possible portable option for field monitoring during moderate-to-high bloom conditions.