Spatial heterogeneity of Pelagia noctiluca ephyrae linked to water masses in the Western Mediterranean.

Pelagia noctiluca is the most common jellyfish in the Western Mediterranean Sea, living in oceanic waters with a holoplanktonic lifecycle. Frequent outbreaks have been well documented in coastal areas, yet little is known about their offshore distribution. In this study we address the relationship between oceanographic structures and the distribution of P. noctiluca ephyrae along the central continental slope of the Western Mediterranean, covering a wide latitudinal gradient, during July-August 2016. The region is characterized by a rich and complex mesoscale surface circulation driven by the inflow of Atlantic Water into the Western Mediterranean through the Strait of Gibraltar. The results revealed a high variability in the ephyrae spatial paterns related with different water masses and the resulting mesoscale hydrographic features. Their horizontal distribution showed a clear latitudinal gradient with high abundances in the south, associated with recent Atlantic Water, and low abundances or absence in the north, in coincidence with the old Atlantic Water transported by the Northern Current. Ephyrae showed diel vertical migrations of short-extent in the first 50 m, with a wide distribution above the thermocline and the Deep Chlorophyll Maximum during daytime, being more concentrated towards the surface at night. The results suggest the population connectivity of P. noctiluca between the Atlantic and the Mediterranean. In that case, the abundance variability of the species in the Mediterranean could be modulated by its entrance associated with the inflow of Atlantic Water through the Strait of Gibraltar.

Sex and tissue specific gene expression patterns identified following de novo transcriptomic analysis of the Norway lobster, Nephrops norvegicus.

BACKGROUND: The Norway lobster, Nephrops norvegicus, is economically important in European fisheries and is a key organism in local marine ecosystems. Despite multi-faceted scientific interest in this species, our current knowledge of genetic resources in this species remains very limited. Here, we generated a reference de novo transcriptome for N. norvegicus from multiple tissues in both sexes. Bioinformatic analyses were conducted to detect transcripts that were expressed exclusively in either males or females. Patterns were validated via RT-PCR. RESULTS: Sixteen N. norvegicus libraries were sequenced from immature and mature ovary, testis and vas deferens (including the masculinizing androgenic gland). In addition, eyestalk, brain, thoracic ganglia and hepatopancreas tissues were screened in males and both immature and mature females. RNA-Sequencing resulted in >600 million reads. De novo assembly that combined the current dataset with two previously published libraries from eyestalk tissue, yielded a reference transcriptome of 333,225 transcripts with an average size of 708 base pairs (bp), with an N50 of 1272 bp. Sex-specific transcripts were detected primarily in gonads followed by hepatopancreas, brain, thoracic ganglia, and eyestalk, respectively. Candidate transcripts that were expressed exclusively either in males or females were highlighted and the 10 most abundant ones were validated via RT-PCR. Among the most highly expressed genes were Serine threonine protein kinase in testis and Vitellogenin in female hepatopancreas. These results align closely with gene annotation results. Moreover, a differential expression heatmap showed that the majority of differentially expressed transcripts were identified in gonad and eyestalk tissues. Results indicate that sex-specific gene expression patterns in Norway lobster are controlled by differences in gene regulation pattern between males and females in somatic tissues. CONCLUSIONS: The current study presents the first multi-tissue reference transcriptome for the Norway lobster that can be applied to future biological, wild restocking and fisheries studies. Sex-specific markers were mainly expressed in males implying that males may experience stronger selection than females. It is apparent that differential expression is due to sex-specific gene regulatory pathways that are present in somatic tissues and not from effects of genes located on heterogametic sex chromosomes. The N. norvegicus data provide a foundation for future gene-based reproductive studies.