SUMMARY: Ecological properties and distribution and abundance of medusae were studied over an 18-month period in the Mljet Island seawater lakes, south-east Croatia. Strong stratification during the summer differentiates these lakes from the oligotrophic South Adriatic ecosystem. The lakes are designated as a moderately eutrophicated ecosystem. Very small numbers of hydromedusae were noted, representing only the Anthomedusae and Leptomedusae. A new species of the genus Tima was found in considerable numbers of individuals. High abundance of the scyphomedusa Aurelia sp. was observed throughout the year. This species differs in terms of genetic divergence from Aurelia aurita found elsewhere in the Mediterranean and could be attributed to the boreal origin.

No abstract

The karstic Zrmanja River discharges into the eastern Adriatic Sea, forming a highly stratified estuary with a sharp halocline that divides upper brackish and lower marine layers. Low orthophosphate concentrations and high Redfield ratios indicate that phosphorus limits phytoplankton growth. In addition, high transparency (avg 6.7 m) and oxygen saturation (avg 98.78%) indicate oligotrophy. Maximum phytoplankton abundance reached 3.4 × 106 cells·l−1 in early spring, a period when the community was composed mainly of diatoms. Dinoflagellates and nanoplanktonic phytoplankton dominated in summer; coccolithophorids and silicoflagellates characterized autumn. Stable conditions in the middle and lower estuary provided a suitable setting for development of microphytoplanktonic diatoms, whereas unstable conditions (frequent salinity variations) at the head of the estuary favored nanophytoplankton. Canonical correspondence analysis identified salinity, temperature, and river inflow as the main factors influencing phytoplankton development. Nutrients strongly limited phytoplankton growth in summer when the river discharge was a minimum.

No abstract

No abstract