Response of phytobenthic communities towards top-down and bottom-up controls in an eutrophied coastal system

ANNA FRICKE; GERMÁN KOPPRIO; MARIANELA GASTALDI; MAITE NARVARTE; DANIELA ALEMANY; MARTINEZ A; RENDAS D; ELISA PARODI; RUBEN J. LARA; FERNANDO HIDALGO; OSCAR IRIBARNE; PAULINA MARTINETTO

Bremen

Conferencia; Estuarine Coastal and Shlef Science (ECSA) 56: Coastal systems in transition: From a 'natural' to an 'anthropogenically-modified' state; 2016

ECSA

The coast of San Antonio Bay (40° 43´ S, 64° 56´ W, Argentina) is an example of the changesthat a coastal ecosystem may experience under high nutrient conditions. A paired channel system,with a channel close to the town of San Antonio Oeste (SAO-channel) with high nutrient loads/herbivory pressure conditions and a pristine channel (CONTROL-channel) with lowernutrients loads/herbivory, provides the opportunity to study in situ eutrophication processes. Themain aim of our study was to investigate to which extend increased anthropogenic nutrient loadsaffect composition and growth of early algal communities (EAC). We conducted the followingstudies during spring (October) and autumn (March). 1) testing the interactive effect of  NUTRIENT (ambient, N/P and N/P/Fe) and GRAZING (ambient, exclusion) on algal recruitment for a period of 6 days, 2) testing the effect of NUTRIENT on algal biomass accumulation in SAO and CONTROL, 3) testing the interactive effect of NUTRIENT and initial internal algal nutrient content (EACs from SAO and CONTROL channels), by cross-transplanting EACs in the SAO and CONTROL channel, exposed for a period of 12 days, and 4) testing between-channel differences in the natural benthic succession over a year (October 2012-September 2013). Results showed a strong nutrient effect occurring after 6 days, increasing algal recruit numbers and altered taxa composition under N/P/Fe, regardless of CAGE treatment (study 1). N/P/Fe decreased biomass accumulation in the SAO channel in both seasons (study 2). N/P enrichment significantly altered the taxa composition of EACs, which differed according to their origin from each other (study 3). Overall the communities of the SAO- and CONTROL-channel differed significantly all along the succession, visible already after 3 days in biofilm communities (study 4). Findings of this study provide valuable information, which might help to set a baseline and improve the coastal zonemanagement of the area.