Micro- mesozooplankton response to phytoplankton maxima - physical forcing in Potter Cove (King George Island)

GARCIA M. ; HOFFMEYER M.; BARRÍA DE CAO; PETTIGROSSO ; LÓPEZ ABBATE ; ALMANDOZ ; HERNANDO; SCHLOSS I.R.

Congreso; XIth SCAR Biology Symposium; 2013

Global warming increases both the sea ice retreat and glacier melting in most coastal environments of the Western Antarctic Peninsula region, resulting in diverse effects on plankton phenology, spatial-temporal patterns and biochemical-physiological processes. We comparatively examined the features and temporal variability of surface micro- and mesozooplankton as a response to physical forcing and phytoplankton characteristics in Potter Cove during two austral summer periods (January-February of 2010-2011). Sampling was carried out at two zones differently impacted by glacier melting. An exceptional phytoplankton maximum including a conspicuous diatom bloom occurred between 18-28 January of 2010 accounting for more than 10 mg Chl-a m-3; conversely a maximum of lesser magnitude (60%) was registered at similar dates of January 2011. Mesozooplankton composition and species richness (S) (range 18-21) were similar in both zones and periods, dominated by Oithona similis and Calanus propinquus plus scarce holoplankton and meroplankton. Maximal abundances (more than 200 ind m-3) and biomasses were higher close to glacier-affected zone but similar between summer periods and were produced in synchrony with phytoplankton maxima. Composition and species richness of microzooplankton were something different between both zones and periods, observing a lower S close to the glacier and during 2011 than in the previous summer. Codonellopsis balechi dominated the tintinnids while Strombidium spp dominated the naked ciliates and Amphydinium spp - Gyrodinium sp dominated the auto- and heterotrophic dinoflagellates. Maximal abundances (around 1500 to 3000 ind L-1) and biomasses were observed later and uncoupled from the phytoplankton peaks in the two periods, being of lesser magnitude during 2011. Differences in timing and mostly in magnitude of the phytoplankton maxima as well as differences in temperature and salinity during both years were clearly reflected in the micro- and meso- heterotrophes? dynamic behaviour. While microzooplankton seemed to be affected by the lower phytoplankton maxima during 2011, mesozooplankton was not. Predator-prey interactions linking micro and mesozooplankton to phytoplankton and their different tolerance to low salinity conditions appear as the possible explanations to the features and patterns observed.