Top-down and bottom-up regulations in a high nutrient-high herbivory coastal ecosystem

PAULINA MARTINETTO; MIRTA TEICHBERG; IVAN VALIELA; DIANA MONTEMAYOR; OSCAR IRIBARNE

MARINE ECOLOGY PROGRESS SERIES

INTER-RESEARCH

Año: 2011 vol. 432 p. 69 - 82

0171-8630

In this study we use San Antonio Bay (Northern Argentinean Patagonia) to understand the relative importance of bottom-up and top-down controls on macroalgal blooms in a macrotidal system with high nutrient supply and high consumer abundance. Our results show that nutrients, pH, and O2 concentrations were higher during low tide. A field experiment showed that the biomass accumulation rate of Ulva lactuca ranged between 6 and 12% d-1 and was reduced by herbivory by 60%. The biomass accumulation rate did not differ in thalli with different initial internal nutrient pools. There was a negative relationship between the percentage of algae consumed and the N content in algae tissue suggesting compensatory feeding by herbivores. Herbivory reduced the biomass accumulation rate of U. lactuca when PO43- or no nutrients were added, but not when NO3- was added. In the absence of herbivory, the addition of nutrients did not increase U. lactuca biomass accumulation rate. These results suggest that nutrients remain high enough for adequate time intervals to be assimilated by macroalgae and support blooms. Large water exchange during tides, however, can diminish the potential negative effects of macroalgal accumulation (oxygen depletion, high ammonium concentrations) on herbivores so that herbivores can have a large impact on macroalgae.