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New species of Bacteriastrum (Chaetocerotaceae, Bacillariophyta) in the Adriatic Sea?

This study reports on ecology and description of Bacteriastrum sp. (Chaetocerotaceae, Bacillariophyta) which dominated phytoplankton assemblages in the survey done in the coastal eastern Adriatic Sea. The investigated area is the 40 km long and 4-14 km wide system of Pag and Velebit Channel extending parallel to the coast. The inner part of the Velebit Channel is extended into the karstic Zrmanja River estuary while the outer end communicates with the open sea through Pag Channel and Kvarneric strait. The area is extremely oligotrophic with limited riverine input of nutrients. Water samples were collected at 7 stations along the coast during November 2008 in order to analyze the phytoplankton composition and its relation to environmental conditions. The nutrient concentration was generally low and its wide range confirmed existence of the trophic gradient in this system. Concentration of phosphate varied from 0.001 to 0.1 &micro ; ; ; mol L^ -1, total inorganic nitrogen from 0.85 to 7.0 &micro ; ; ; mol L^ -1, while silicate concentration ranged from 0.3 to 15.4 &micro ; ; ; mol L^ -1. The high Redfield ratio (31 – 3180) indicated strong phosphorus limitation in the area. Total of 80 microphytoplankton taxa were identified. The most abundant groups were diatoms with maximal abundances, from 7.3 x 104 cells L^ -1 at the most oligotrophic, up to 9.6 x 10^5 cells L^ -1 at the least oligotrophic stations. Bacteriastrum sp. contributed to the phytoplankton community in more oligotrophic stations with abundances up to 9.8 x 10^4 cells L^ -1 (92% of total microphytoplankton) while on more eutrophic stations its abundance was 6 x 10^3 cells L^ -1 (1% of total microphytoplankton). Morphological analysis has shown that the dominating Bacteriastrum resembled solitary species B. paralellum but the size was different as well as orientation and morphology of setae. Unlike colonial Bacteriastrum species adjacent cells were distant from each other (15-25 &micro ; ; ; m) forming “ chains” with up to 25 cells while their setae did not connect or fuse. Our observations indicate the possibility of observing a stage in the life cycle of some other Bacteriastrum species since additional analysis of net samples revealed presence of three true colonial Bacteriastrum species (B. furcatum, B. hyalinum, B. mediterraneum) or discovering yet undescribed species from this genus.

Bacteriastrum; taxonomy; Adriatic Sea

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