The occurrence and ecology of the centric diatom Cyclotella choctawhatcheeana Prasad in a Croatian estuary

The centric diatom Cyclotella choctawhatcheeana Prasad has been found for the first time in the Adriatic Sea. It develops dense populations in the highly stratified, oligotrophic, karstic estuary of the Zrmanja River (eastern Adriatic Sea, Croatia). Cyclotella choctawhacheeana contributed to the phytoplankton community in the estuary with high abundance of up to 2 x 10(6) cells L-1. Maximum abundance was found in the marine layer, below the halocline, at a salinity range between 13-28, but it was able to develop over a very wide salinity range. The maximum development appeared in the temperature range of 8-18 degrees C. It was present in 52% of samples throughout the year. The significant negative correlation with silica, nitrates and total inorganic nitrogen showed its preference for a marine, oligotrophic environment. We consider C. choctawhacheeana to be a significant constituent of the phytoplankton of the east Adriatic coast. It can be assumed that its succes is based on species wide tolerance to fluctuations of environmental factors.