Pseudo-nitzschia seriata

P. seriata is a cold-water species. Previously known only from the Northern Hemisphere in the Atlantic, but recently also from the Northern Pacific. Recently, it was reported from the Southern cold Pacific. Due to morphological variability of P. seriata and related species, this needs to be confirmed either by molecular data.

P. seriata has been implicated in toxic episodes in the field in Europe (Denmark, Ireland, Scotland) and Canada. It has caused DA in sea scallops and molluscan shellfish in Canada, in blue mussels in Denmark, and associated with DA in king scallops in Scotland. DA levels above the regularory limit (20µm g-1) has been found at concentrations of 50-62,000 cells L-1 in Canada and Denmark.

requires electron microscopy. The main characteristics of P. seriata are the asymmetric valve and the 4 rows of poroids (2 outer rows of larger poroids and 2 inner rows of smaller poroids). P. seriata is phylogenetically and morphologically closely related to P. obtusa and P. australis, two other species with asymmetric valves. The main differences are the number of poroid rows in the striae, poroid density, and valve width. However, in P. seriata number of poroid rows and poroid density has been found to decrease with increasing temperature, making identification difficult. P. seriata: (2)-4 rows - 6-9 poroids/µm - 4.6-8.0µm P. obtusa: 2 rows - 6-8 poroids/µm - 2.9-5.0µm P. australis: 2 rows - 4-5 poroids/µm - 6.5-8.0µm Verified sequences of ITS rDNA (ITS1, 5.8S, ITS2) are: P. seriata (DQ062663); P. obtusa (DQ062667); P. australis (DQ062661)