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Ecology and taxonomy of Pseudo-nitzschia in Lim Bay (northeastern Adriatic Sea)

Planktonic diatom species of Pseudo-nitzschia group are common in oceanic and neritic plankton worldwide. Since several Pseudo-nitzschia species have been known as producers of domoic acid, a neurotoxic amino acid responsible for Amnesic Shellfish Poisoning (ASP), considerable scientific interest on its ecology and taxonomy has been generated. The taxonomy and ecology of the diatom genus Pseudo-nitzschia was investigated in 10 km long embayment in the north eastern Adriatic Sea in the period from March 2002 to July 2008. Water samplings for physico-chemical and biological variables were conducted several months per year at three stations along the bay. The phytoplankton was dominated by diatoms throughout the year with minimum species diversity in summer and maximum in autumn. Pseudo-nitzschia spp. was present in 59 % of the samples with abundance up to 1.5 x 10^6 cells L^-1.The maximum abundance of Pseudo-nitzschia was in autumn, when it contributed up to 69% of the total diatom abundance. The timing of Pseudo-nitzschia blooms suggests nutrient stimulation, since the blooms co-occurred with highest concentration of phosphorus and nitrogen. The low Si:N rations in autumn may favour the growth of Pseudo-nitzschia over other diatoms due its lower silica requirement. Since the toxicity is species specific, morphological analysis has been done revealing five different species, four of them known as potentionaly toxic. In August 2007 dominant Pseudo-nitschia species corresponded to P. cuspidata, P. calliantha and P. manii, in October the same year P. calliantha dominated the community, while in February 2008 P. fraudulenta and P. pungens were identified.

Pseudo-nitzschia; taxonomy; Adriatic Sea

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