The changing nature of the planktonic community structure and biomass in coastal waters of Scotia Bay (Laurie Island, South Orkney)

ALDER V.A.; PAPARAZZO, F.E.; YAYA M; OLGUIN HF; CAPITANIO F; SANTOFERRARA LF; FRANZOSI C; SPINELLI M ,; HOERMANN I

Kuala Lumpur

Conferencia; XXXIV SCAR OPEN SCIENCE CONFERENCE; 2016

SCAR

The understanding of feedbacks between temperature changes due to global warming and biological responses of marine communities in terms of nutrient and carbon cycles and productivity is still at an early stage. Knowing the size structure of planktonic communities and their key species allows to predict their role in the biological carbon pump and how environmental changes will propagate to higher trophic levels. Within this context, the aim of the present study was to analyse, for the first time, the size structure of Scotia Bay?s (Laurie Island, South Orkney) planktonic communities ranging from pico- to microplankton, and the size-fractioned chlorophyll (0.7-2, 2-10, >10 μm) and macronutrients during an annual cycle -from summer 2014 to summer 2015. Mesozooplankton was sampled only during summer seasons. The study was conducted with logistic support from the Orcadas Research Station (Argentina). Sites with different environmental features (proximity to glaciers, bird colonies, shoreline and deeper points) were selected and sampled by boating operations or through ice holes. From winter to early spring (July to October), the bay was 100% covered by ice.Mean values from each season reveal the following trends: Summer 2014 was characterized by a moderate N:P ratio (16) and higher silicate (54 μM) and chlorophyll (5 μChl/L) values, with a distinct contribution of the >10 μm size-fractioned chlorophyll, mostly due to a bloom of the micro-diatom Odontella weissflogii; diatoms represented 94% of total biomass (> 200 μC/L). During autumn, winter and spring, the contribution to chlorophyll by the three size fractions was quite even but total chlorophyll reached only 1, < 0.5 and 2.3 μChl/L, respectively. Summer 2015, as compared to summer 2014, presented higher values of subsurface sea water temperature and N:P ratio (18.4) while lower silicates (50 μM) and chlorophyll (2.1 μChl/L). There was a remarkable increase of cryptophytes, prasinophytes, pigmented <5 μm flagellates (four-fold increase), nanoplanktonic diatoms (Thalassiosira sp), naked ciliates, and dinoflagellates, while mean biomass values of diatoms and total mesozooplancton decreased in one order of magnitude. Neither planktonic cyanobacteria nor krill larvae were detected in any of these two summer seasons. The structure of the summer planktonic community showed a remarkable interannual fluctuation, with a lineal food web in 2014 -more efficient in terms of carbon pumping- and a microbial food web in 2015 -less efficient but with heterotrophic bacteria playing a more important role. Key species and spatial heterogeneity will be discussed. The results from the present study represent the starting point of the ―Scotia Bay Planktonic Observatory‖, meant to provide the basis to address novel goals at the ecosystem level in areas of relevance, such as high seas Antarctic islands located in the southern branch of the Scotia ArcThe changing nature of theplanktonic community structure and biomass in coastal waters of Scotia Bay(Laurie Island, South Orkney), SCAROPEN SCIENCE CONFERENCE, Kuala Lumpur, Malasia, 430, ISBN 978-0-948277-32-0