engleski

Ecology of planktonic diatoms in the low tidal estuary (the Neretva River estuary, NE Mediterranean)

In the frame of the complex ecological investigation, phytoplankton, zooplankton and environmental factor measurements were carried out at fixed station (Vlaška station, 43º 03' N, 17º 29' E, 10 m max. depth) in the estuary of the Neretva River in 1999 and 2000. The estuary of the Neretva River is situated in the Middle Adriatic, NE Mediterranean. It is highly stratified and low tidal (25 cm average daily amplitude) estuary. The annual average flow of the Neretva River is 414 m3 s–1. According to the TRIX trophic index, the estuary can be classified as mesotrophic. Water samples were taken using 5 L Niskin bottles from the surface to bottom at each meter depth at monthly intervals. The aim of the study was to investigate the diatom structure and abundances, and its relationship with physical-chemical conditions in the water column. Seventy-four diatom taxa were identified. Of these, 32 were in at least10% of all samples and eleven rare taxa were in ≤1% of samples. The diatom community, of marine origin, varied over five orders of magnitude (30 - 1.2 x 106 cells L-1) and had three peaks: April 1999 (1.2 x 106 cells L-1), August 1999 (7.9 x 106 cells L-1), and October 1999 (1.3 x 106 cells L-1). The lowest abundance was in November 1999. The most abundant diatoms (exceeding 105 cells L-1) were Nitzschia longissima, Leptocylindrus minimus, Skeletonema marinoi, and Thalassiosira sp. N. longissima (max. 7.9 x 106 cells L-1) dominated the highest peak (August 1999), comprising 54 - 87% of microphytoplantkon (cells longer than 20 μm) abundance. Canonical Correspondence Analysis (CCA) showed that temperature and salinity were the main factors influencing diatom community structure in the estuary. No direct connection was noted between the monthly distribution of diatom abundance, transparency, and small zooplankton taxa (microzooplankton). A main feature of the diatom assemblages was the dominance of more than one species. This likely is owed to the frequent and rapid environmental changes typical of this dynamic estuarine ecosystem.

Diatoms; phytoplankton communities; microzooplankton; environmental variables; CCA; estuary; Croatia; eastern Adriatic Sea.

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