engleski

Northern Adriatic mesocosm experiment Rovinj 2003: changes in the microphytoplankton community

Background and purpose: The purpose of the experiment was to study species successions within the microphytoplankton community in nutrient balanced and P-deficient conditions. Analyses of macroaggregate samples and laboratory experiments indicated that some diatom species (e.g. Cylindrotheca closterium) could have an important role in the mucilage phenomenon in the northern Adriatic. Materials and methods: Seawater for the experiment was sampled in a frontal zone between oligotrophic and eutrophic waters developed in the open northern Adriatic. Triplicate subsamples (mesocosms), enriched with nutrients (N/P ratios 100:1 and 16:1), and a control one were incubated in free-floating 25 L transparent bottles at the sea surface in an anchored frame. Aliquots were taken mostly every other day and preserved with neutralised Lugol's solution. Microphytoplankton counts were performed within a few days by a Zeiss inverted microscope, using the Utermöhl settling method. Results and conclusions: Diatom Dactyliosolen fragilissimus, the most abundant species in the seawater sample, dominated also the microphytoplankton bloom during the major part of the mesocosm experiment (up to the ~20th day) in both nutrient balanced and P-deficient conditions, in which a fast P recycling was probably due to a significant induction of alkaline phosphatase. Concomitantly, succession of some smaller diatoms occurred (Chaetoceros affinis, Nitzschia longissima and Chaetoceros sp.). In the last experiment week, extreme changes occurred in the microphytoplankton composition, characterized by the decay of the former species and the development of a Cylindrotheca closterium bloom, a diatom very often dominant in northern Adriatic mucilaginous aggregates.

microphytoplankton; mesocosm; northern Adriatic; Dactyliosolen fragilissimus; Cylindrotheca closterium; nutrients

nije evidentirano