The Peruvian sea is one of the most productive ecosystems in the world. Phytoplankton production provides food for fish, mammals, mollusks and birds. This trophic network is affected by the presence of toxic phytoplankton species. In July 2017, samples of phytoplankton were obtained from Paracas Bay, an important zone for scallop (Argopecten purpuratus) aquaculture in Peru. Morphological analysis revealed the presence of the genus Pseudo-nitzschia, which was isolated and cultivated in laboratory conditions. Subsequently, the monoclonal cultures were observed by scanning electron microscopy (SEM), and identified as P. multistriata, based on both the morphological characteristics, and internal transcribed spacers region (ITS2) sequence phylogenetic analysis. Toxin analysis using liquid chromatography (LC) with high-resolution mass spectrometry (HRMS) revealed the presence of domoic acid (DA) with an estimated amount of 0.004 to 0.010 pg cell⁻¹. This is the first report of DA from the coastal waters of Peru and its detection in P. multistriata indicates that it is a potential risk. Based on our results, routine monitoring of this genus should be considered in order to ensure public health.

Currently, there is little information on the genus Pseudo-nitzschia in Peruvian coastal waters available and some species have been misidentified. This is the first study of Pseudo-nitzschia species found in several blooms off the central coast of Peru. The cultures obtained and identified by scanning electron microscopy revealed the presence of Pseudo-nitzschia subpacifica and P. pungens, the first record of P. subpacifica in Peruvian coastal waters. Neither P. subpacifica nor P. pungens cultures contained domoic acid (DA) in detectable amounts using HPLC–MS/MS. Our results suggest that Pseudo-nitzschia species are common off the central coast of Peru. The detection of non-toxic strains of Pseudo-nitzschia does not necessarily mean that other populations or strains of this genus in Peru cannot produce DA. Research is needed to evaluate other strains from different locations along the Peruvian coast and to explore whether environmental factors or genetic variability affect the production of DA.

During the austral winter of 2017, a bloom of Prorocentrum spp. occurred, reaching a cell density of 2.73 × 10⁶ cells L⁻¹, in Paracas Bay, Peru. In order to identify which, type of species generated this event and determine its toxicity, the values of the environmental parameters (temperature, winds and salinity) that induced the rapid growth of the dinoflagellate in this bloom were identified. A clonal culture was established for taxonomic (SEM), phylogenetic (ITS) and toxicological analysis via LC-MS/MS to determine the presence of tetrodotoxin (TTX) and whether the species represents a food safety hazard. This event coincided with the coastal upwelling process, which generated high concentrations of phytoplankton biomass (>10 mg m⁻³ chlorophyll-a) and allowed the rapid growth of P. cordatum (IMP-BG 450) in Paracas Bay. However, toxicological analyses of the IMP-BG 450 strain culture did not show the presence of TTX quantifiable through the technique used. Due to the antecedents of the presence of TTX in mollusks from other latitudes during blooms of this species, it is recommended that analyses of this toxin be carried out both in filter-feeding mollusks and in this species during a new bloom.