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This study seeks to elucidate the spatial and temporal patterns of toxic phytoplankton in coastal waters of the Balearic Archipelago (NW Mediterranean Sea) in a multivariate approach. We also examine whether there is a direct relationship between the abundance of toxic phytoplankton and the physical-chemical parameters and different human pressure activities. Its magnitude and the species-specific pattern are also evaluated. The study is based on chlorophyll a and phytoplankton composition and abundance, as well as physical and chemical data, to evaluate the ecological status of Balearic waters for the implementation of the Water Framework Directive. A total of 24 taxa included in the Intergovernmental Oceanographic Commission toxic algae checklist and five well-known bloom formers were identified. Principal Component Analysis (PCA) for physical-chemical and human uses revealed the larger phytoplankton variability determined by seasonal patterns. Higher nutrient winter samples were distinguished from those of high transparency and lower nutrient summer waters. The Redundancy Analysis (RDA) separated the toxic species into two groups: Pseudo-nitzschia species, related to winter; and dinoflagellates and other flagellates species, related to spring and summer. The among-islands effect revealed a latitudinal gradient, especially regarding nutrient and human pressures related to Mallorca Island. Meanwhile, the Formentera waters were transparent and far from human activities.

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Five species belonging to the family Prymnesiaceae (one Prymnesium and four Chrysochromulina) have been identified in cultures obtained from water collected in the Bay of Banyuls‐sur‐Mer (Mediterranean Sea, France) using LM, SEM, and TEM. Two are described as new species, Chrysochromulina lanceolata sp. nov. and C. pseudolanceolata sp. nov. Both species are large and lanceolate with an acute posterior and two anterior arms. They are easily detectable with LM but difficult to distinguish to species level with live cells, without experience. EM reveals two completely different scale patterns in the two species. Cells of C. lanceolata are 21–38 μm long, 7–12 μm wide, and 3–7 μm thick. They possess two subequal flagella (30–51 and 29–44 μm), and the haptonema is shorter than the flagella (23–37 μm). The cell body is covered by plate and spine scales. Cells of C. pseudolanceolata sp. nov. are slightly smaller (15–18 × 6–8 μm) with more rounded extremities, two subequal flagella (19–26 and 17–24 μm), and the haptonema is longer than the flagella (about 35 μm). Three types of plate scales are observed in this species. Other findings are C. alifera Parke et Manton and C. throndsenii Eikrem (a new record for the Mediterranean Sea). Prymnesium faveolatum Fresnel, a new toxic species recently described, is illustrated with both LM and SEM.