Seasonal changes in microzooplankton feeding behavior under varying eutrophication levels in the Bahía Blanca Estuary (SW Atlantic Ocean)

LÓPEZ ABBATE M. C.; BARRIA DE CAO, MS; PETTIGROSSO, R. E.; GUINDER V. A.; DUTTO MS; BERASATEGUI A.; CHAZARRETA, J.; HOFFMEYER M. S.

JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2016 vol. 481 p. 25 - 33

0022-0981

Dilution experiments were conducted during a two-year survey inthe Bahía Blanca Estuary (SW Atlantic Ocean) to evaluate seasonalvariations of microzooplankton grazing (m) and phytoplankton growth (μ).The trophic interactions between these groups were investigated inrelation to anthropogenic eutrophication. For this purpose, two sitesexposed differently to sewage input in the estuary were selected. Thepercentage of primary production grazed by microzooplankton averaged 79%,although this percentage showed high seasonal variability. The lowestconsumer control was found in winter and summer, and was associated withhigh density of chain-forming diatoms. Conversely, the microzooplanktongrazing exerted heavy control on phytoplankton biomass during spring andfall, in concurrence with the highest density of nanoflagellates. Resultsshowed average differences between μ and m close to zero during most ofthe annual cycle, suggesting microzooplankton control of autotrophic preyin the two sites. Under high exposure to sewage, however, experimentalresults evidenced the prevalence of non-linear feeding response, poortrophic phasing at low phytoplankton growth rate and lower reactivity ofmicrozooplankton grazing. Regardless their exposure to sewage input,microzooplankton was an important loss term of phytoplankton in theestuarine system and appear as a primary factor defining phytoplanktonbiomass accumulation.