Acidification effects on the benthic metabolism and trophodynamics

Abstract

Growing concentrations of atmospheric CO2 is affecting the oceans in two important modes: 1) Increase in the mean temperature and 2) pH reduction. The former may impact the biology and ecology of marine species in different ways, such as changing niche breadth or causing coral bleaching and diseases. The latter is modifying a characteristic that has been stable for the last 25 million years and may have dramatic effects over the biota. Calcium carbonate forming organisms may suffer tremendous losses resulting from changes in the chemical equilibrium of sea water due to the absorption of anthropogenic CO2, which have reached ca. 30%. The vast majority of studies on acidification encompass organism level research and very little is known about the effects of acidification on ecosystem services, i.e. on the marine ecological processes. Among these, benthic remineralization and flux rates are fundamental, since marine sediments are the main depositories of organic matter (OM) in the ocean. Benthic organisms degrade OM and supply nutrients that estimulate benthic and planktonic primary production. This process is of paramount importance in continental shelves that receive a substantial proportion of OM and keep a tight benthic-pelagic coupling owing to the shallower depths. The present proposal is an experimental study on the possible effects of ocean acidification on the sediment OM remineralization and benthic organic carbon foodweb pathways. Experiments will be carried out in shallow waters off Ubatuba-SP (10-20 m depth) through SCUBA diving for in situ measurements and sediment sampling for laboratory experiments. Analyses include sediment-water nutrient flux measurements and pulse-chase experiments to determine benthic trophodynamics. We intend to test the following hypotheses: 1) Ocean acidification (OA) significantly reduces OM degradation and, consequently, nutrient fluxes from the benthos to the water column; 2) OA alters organic carbon pathways in the benthic system; and 3) Under lower pH there is a shift in the sediment procariont community composition. The results will serve not only to measure unknown present day fluxes but also to evaluate the possible impacts of OA in a important process for the carbon cycle in the ocean. Direct and unequivocal data on the herbivore/detritivore food chain will also be generated, which will be unvaluable for understanding how climate change will affect the marine ecosystem. (AU)