Effects of enhanced temperature and ultraviolet B radiation on a natural plankton community of the Beagle Channel (Southern Argentina): a mesocosm study.

MOREAU, S.; BEHZAD MOSTAJIR; ALMANDOZ, G.O.; DEMERS, S; M. P. HERNANDO,; LEMARCHAND, K.; LIONARD, M.; ROY, S.; I.R. SCHLOSS,; THYSSEN, M.; FERREYRA, G.A.

AQUATIC MICROBIAL ECOLOGY

INTER-RESEARCH

Lugar: Oldendorf/Luhe; Año: 2014

0948-3055

An introductory sentence is lacking; something like ?Global change related temperature increase can affect communities that are in addition submitted to other stresses, like the exposure to UVB radiation that attains polar and sub-polar areas. The goal of this work was to study the synergistic, or antagonistic, effects of increased temperature and ultraviolet B radiations (UVBR, 280-320 nm) on the planktonic community of the Beagle Channel in Patagonia with a mesocosm approach. Eight 2 m3 mesocosms were submitted to four (2 replicates) treatments: (1) control, (2) increased UVBR, (3) increased temperature and (4) increased temperature and UVBR. Chlorophyll-a (Chl-a), nutrients and particulate organic nitrogen and carbon (PON and POC) were studied. Bacterial abundance and richness, phytoplankton (pico-, nano- and microphytoplankton) and microzooplankton abundance and composition were studied by flow cytometry, denaturing gel gradient electrophoresis (DGGE) and inverted microscopy. A phytoplankton bloom was observed in all treatments. Both Chl-a and diatoms abundance were significantly lower in the high temperature treatments during the post-bloom, while no differences between treatments were observed for pico- and nanophytoplankton. In addition, both bacterial abundance and POC were significantly lower during the post-bloom in the high temperature treatments. These differences were probably caused by a cascading trophic effect due to the increase in large ciliates abundance in the high temperature treatments. Overall, no UVBR effects on the Beagle Channel community were detected, possibly because of long-term (i.e. 20 to 30 years) adaptation to ozone hole induced high UVBR. Therefore, only temperature had an impact on the structure of the community, with possible consequences on the carbon pathway towards higher trophic levels and on carbon sedimentation within the deeper layers of the ocean.