High proliferation of Pseudo-nitzschia cf. arenysensis in the Adriatic Sea: ecological and morphological characterisation

Abstract

The aim of the present study isto characterise the diatom Pseudo-nitzschia community during a bloom period together with environmental conditions. High proliferation of Pseudo-nitzschia spp. was observed in September 2017 at the shellfish breeding area in the Krka River estuary (Central eastern Adriatic Sea). The peak of abundance (1.8 x 106 cells L-1) was recorded at 7 m depth, and the increased abundance persisted for four weeks.Morphological analyses of field samples based on scanning electron microscopy (SEM) revealed that Pseudo-nitzschia cf. arenysensis was prevailing (94%) in the Pseudo-nitzschia assemblage. Several strains were successfully isolated from net samples in order to better define morphological features and phylogenetic characterisation. The isolated Pseudo-nitzschia strains corresponded morphologically to the P. cf. arenysensis from the field samples, based on our SEM observations. Phylogenetic analysis demonstrated that the Croatian strains grouped with P. arenysensis using the ITS and LSU rDNA sequences. Spearman rank correlation showed that salinity was an important environmental factor affecting the vertical distribution of Pseudo-nitzschia spp. in this highly variable area. Availability of increased concentration of orthophosphates and ammonium and low Si: TIN ratio may have promoted the bloom of P. cf. arenysensis in the estuary.

Phenological segregation suggests speciation by time in the planktonic diatom Pseudo-nitzschia allochrona sp. nov.

“…Morphological identity and relatively small genetic distance between P. arenysensis and P. allochrona point at a possibly recent speciation event. Despite numerous recent studies focusing on the genus Pseudo-nitzschia all over the world, so far P. allochrona has only been found in the Gulf of Naples 18,19,45 , in the Ionian Sea (this paper) and more recently in the Adriatic Sea [52][53][54] . In the latter area P. allochrona (as P. cf.…”

Phenological segregation suggests speciation by time in the planktonic diatom Pseudo‐nitzschia allochrona sp. nov.

“…However, differently from the latter cases, the area where P. allochrona could have been introduced from cannot be traced. Despite numerous and detailed studies focusing on the genus Pseudo-nitzschia in the Mediterranean Sea and all over the world, so far P. allochrona has only been found in the Gulf of Naples (Lamari et al, 2013;McDonald et al, 2007;Ruggiero et al, 2015), Ionian Sea (this paper) and more recently in the Adriatic Sea (Arapov et al, 2020;Giulietti et al, 2021;Pugliese et al, 2017). In the latter area, P. allochrona (as P. cf.…”