High abundance and diversity of consumers associated to eutrophic areas in a semi-desert macrotidal coastal ecosystem in Patagonia, Argentina

MARTINETTO, P; DALEO, P.; ESCAPA, M; ALBERTI, J.; ISACCH, J.P.; FANJUL, E.; BOTTO, F.; PIRIZ, M.L.; PONCE, G.; CASAS, G; IRIBARNE, O.

ESTUARINE COASTAL AND SHELF SCIENCE

ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD

Año: 2010 vol. 88 p. 357 - 364

0272-7714

Abstract: Eutrophication due to anthropogenic supply of nitrogen is one of the major impacts of human activities on coastal ecosystems worldwide. As a consequence of the high availabilityof nutrients, primary production is typically enhanced followed by changes in composition andabundance of flora and fauna. Advanced states of eutrophication are characterized by thereplacement of the original vegetation by opportunistic seaweeds and by the reduction ofabundance and diversity of consumers. This process occurs mostly in estuaries, bays, and semiclosed coastal areas where land-derived nutrients (e.g., fertilizer, wastewater) are retained due to the low water exchange, and then can be assimilated by opportunistic seaweeds. San Antonio bay (Patagonia, Argentina, 40º 48´ S) is a macrotidal system (up to 9 m) where signs ofeutrophication (high nutrient concentration, seaweed blooms, high growth rate of macroalgae)have been reported. Here we evaluated the response to eutrophication in terms of abundance and diversity of flora and fauna in this semi-desert macrotidal coastal system. We comparedabundances and species composition of macroalagae, small infaunal and epifaunal invertebrates,and birds associated with tidal channels of the San Antonio Bay subject to contrasting anthropogenic influence. Macroalgae was more abundant and diverse in the channel closer tohuman activity where nutrient concentrations were also higher. In contrast to other eutrophicsites, small invertebrates and birds were also more abundant and diverse in the channel withmacroalgal blooms and high nutrient concentration. The large water flushing during the tidalcycle could prevent anoxic or hypoxic events making the environment suitable for consumers.Thus, this could be a case in which eutrophication supports high densities of consumers byincreasing food availability, rather than negatively affecting the survival of organisms.