The species-rich diatom family Chaetocerotaceae is common in the coastal marine phytoplankton worldwide where it is responsible for a substantial part of the primary production. Despite its relevance for the global cycling of carbon and silica, many species are still described only morphologically, and numerous specimens do not fit any described taxa. Nowadays, studies to assess plankton biodiversity deploy high throughput sequencing metabarcoding of the 18S rDNA V4 region, but to translate the gathered metabarcodes into biologically meaningful taxa, there is a need for reference barcodes. However, 18S reference barcodes for this important family are still relatively scarce. We provide 18S rDNA and partial 28S rDNA reference sequences of 443 morphologically characterized chaetocerotacean strains. We gathered 164 of the 216 18S sequences and 244 of the 413 28S sequences of strains from the Gulf of Naples, Atlantic France, and Chile. Inferred phylogenies showed 84 terminal taxa in seven principal clades. Two of these clades included terminal taxa whose rDNA sequences contained spliceosomal and Group IC1 introns. Regarding the commonly used metabarcode markers in planktonic diversity studies, all terminal taxa can be discriminated with the 18S V4 hypervariable region; its primers fit their targets in all but two species, and the V4-tree topology is similar to that of the 18S. Hence V4-metabarcodes of unknown Chaetocerotaceae are assignable to the family. Regarding the V9 hypervariable region, most terminal taxa can be discriminated, but several contain introns in their primer targets. Moreover, poor phylogenetic resolution of the V9 region affects placement of metabarcodes of putative but unknown chaetocerotacean taxa, and hence, uncertainty in taxonomic assignment, even of higher taxa.

A broad diversity of sex-determining systems has evolved in eukaryotes. However, information on the mechanisms of sex determination for unicellular microalgae is limited, including for diatoms, key-players of ocean food webs. Here we report the identification of a mating type (MT) determining gene for the diatom Pseudo-nitzschia multistriata. By comparing the expression profile of the two MTs, we find five MT-biased genes, of which one, MRP3, is expressed exclusively in MT+ strains in a monoallelic manner. A short tandem repeat of specific length in the region upstream of MRP3 is consistently present in MT+ and absent in MT− strains. MRP3 overexpression in an MT− strain induces sex reversal: the transgenic MT− can mate with another MT− strain and displays altered regulation of the other MT-biased genes, indicating that they lie downstream. Our data show that a relatively simple genetic program is involved in defining the MT in P. multistriata.

Zooplankton molecular analyses allow for accurate species identification with a proper molecular signature, complementing classic phenotypic-based taxonomy (α taxonomy). For the first time in the Mediterranean Sea, cytochrome oxidase I (COI) gene sequences of calanoid copepods were associated with morphological identification, HD and SEM images, using a fully integrated approach to assess taxonomic diversity. Such method was applied to selected species, generating consensus sequences from the Gulf of Naples (Central Tyrrhenian Sea, Western Mediterranean Sea) also including reference barcodes of three target species (Nannocalanus minor, Pleuromamma gracilis and the non-indigenous species (NIS) Pseudodiaptomus marinus) that are new for the Mediterranean area. The new barcodes were selected including: dominant and rare species; species that were originally described in the study area as type locality, but lacking a molecular description; emergent NIS and potential species complex. The integration between morphological and molecular identification by tree placement, using species-specific highly conserved oligonucleotides, also provided new and high-quality references of the most common and abundant copepod genera and species in the Mediterranean Sea. Our regional reference library was then integrated and analyzed with global data reference available on BOLD database to explore the presence of potential cryptic species and biogeographic patterns and links among geographically distant populations of copepods. Overall, this study provides valuable insight into the actual copepod taxonomic diversity and contributes to building baseline knowledge to monitor coastal biodiversity in neritic areas worldwide, where copepods are of paramount ecological importance, paving the way for future metabarcoding studies.

SUMMARY:We characterised the effect of seasonal fluctuations in water temperature (T w ) on the nonventilatory period (NVP) of Mediterranean loggerhead turtles, Caretta caretta. Ten captive turtles, that were subject to the natural variations in T w found in the Gulf of Naples, dived significantly longer when T w decreased. More than 50% of summer and winter dives lasted between 2 and 10 min; the maximum dive duration (120 min) occurred in winter at a T w of 13°C. The longest NVP coincided with a low level of activity and a lower food consumption. This, and a reduced metabolic rate consequent to acclimatisation to a low T w were likely to have influenced NVP. -En el presente estudio se caracterizó el efecto de la fluctuación estacional en la temperatura del agua (T w ) sobre el periodo no ventilatorio (NVP) de la Tortuga Boba del Mediterráneo, Caretta caretta. Diez tortugas mantenidas en cautividad fueron sometidas a las variaciones naturales de la T w del Golfo de Nápoles, la inmersión fue significativamente más larga cuando la T w decrecía. Más del 50% de las inmersiones, tanto en verano como en invierno, duraron entre 2 y 10 minutos; la inmersión de máxima duración (120 minutos) ocurrió en invierno a una T w de 13°C. El más largo NVP coincidió con el bajo nivel de actividad y el menor consumo de alimento. Ésto, y el reducido grado metabólico como consecuencia de la aclimatación a la baja T w probablemente influyeron en el NVP.Palabras clave: tiempo de inmersión, efecto de temperatura, tortuga marina, apnea.

Molecular tools increasingly refine and improve the identification of zooplankton organisms based on phenotypic features, providing a more robust and comprehensive species description. Integration of data helps revealing the hidden diversity of zooplankton and facilitating the detection of rare and non‐indigenous species. This approach, merging morphological characters and a diagnostic marker for specific identification, such as the mitochondrial cytochrome c oxidase I (COI), is here used to characterize key taxa from the zooplankton assemblage of the Gulf of Naples at the Long‐Term Ecological Research site MareChiara (LTER‐MC) (Central Tyrrhenian Sea, Western Mediterranean Sea). Zooplankton biodiversity assessment using integrated taxonomy was focused on selected crustacean groups: cyclopod copepods (Agetus typicus, Oithona plumifera, Oncaea mediterranea, Oncaea scottodicarloi); newly records of cladocerans (Evadne nordmanni), euphausiids (Euphausia krohnii, Nematoscelis megalops, Nyctiphanes spp.) and sergestids (Lucifer typus), with the aim to boost the knowledge of real zooplankton biodiversity. The results of our investigation provide new high‐quality molecular references of the analysed taxa and contribute to unveiling the genetic diversification of zooplankton species and their relevant ecological significance for Mediterranean coastal waters.