| Popis: |
The immense diversity of oceanic plankton and its distribution is hard to access with a single method only. Discrete samples, analysed through imaging, pigments or molecular methods, offer a great view of the composition, but offer only a limited resolution of plankton over space and time. Optical tools, deployed on in situ and from remote sensing platforms, allow high spatial and temporal view, but tell very little about plankton composition. However, combination of these techniques offers an all-inclusive view of plankton diversity in the ocean. Winter cruise (February/March 2015) was conducted in oligotrophic waters of the Southern Adriatic Pit. CTD casts were performed and concurrent measurements of temperature, salinity, light, chlorophyll fluorescence, particulate backscattering and beam attenuation were collected. Total phytoplankton and zooplankton abundances were investigated by means of microscopy, flow cytometry and molecular identification methods, and then combined with optical analysis, from which we derived particulate organic and phytoplankton carbon, as well as several optical indices. While diatoms and coccolithophorids were found altering in dominance among different investigated stations, different groups of picophytoplankton, including picoeukaryotes, Synechococcus and Prochlorococcus, demonstrated intriguing and not well defined spatial pattern. Average zooplankton densities showed graduate decrease with depth. Unexpectedly, high numbers of microzooplankton were recorded for the at all stations, with average densities greater than 10 000 ind. m-3 in the upper 300 m of the water column. Encountered distribution of the plankton in the water column reflects an intricate play of the water masses in the studied area. Overall, our results suggest that different portions of plankton community, here separated by their size, respond to different environmental cues in this oligotrophic oceanic ecosystem. |
