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

Changes in Coastal Benthic Algae Succession Trajectories and Assemblages Under Contrasting Nutrient and Grazer Loads

“…These channels experience contrasting nutrient and grazer loads (Table 1) and have been used in previous studies to evaluate the effects of eutrophication (Martinetto et al 2010(Martinetto et al , 2011Teichberg et al 2010). One channel runs nearby and along the town of San Antonio Oeste (hereafter SAO channel) and is characterized by high landderived nutrient loads that consequently support frequent algal blooms (Table 1, Martinetto et al 2010Martinetto et al , 2011. In contrast, the second channel runs parallel to the SAO channel but is distant from human population (hereafter CONTROL channel) and shows much lower nutrient loads with algal blooms never reported (Table 1, Martinetto et al 2010).…”

“…In fact, San Antonio Bay is inhabited by a large abundance of consumers associated with areas where macroalgae blooms are common (Iribarne et al 2003;Martinetto et al 2010). There, herbivores can reduce macroalgae biomass up to 60 % (Martinetto et al 2011), which is quite high compared to other eutrophic sites (e.g., Lotze and Worm 2000). Thus, it is possible that under these extreme conditions of high nutrient levels, large water movement and high levels of herbivory, benthic succession could differ from what has been reported in other eutrophic sites.…”

“…The large water movement also prevents some negative effects associated with eutrophication such as anoxia. In this case, the large macroalgae biomass supports high densities of herbivores by increasing food availability and nutritional content rather than negatively affecting the survival of organisms (Martinetto et al 2010(Martinetto et al , 2011. In fact, San Antonio Bay is inhabited by a large abundance of consumers associated with areas where macroalgae blooms are common (Iribarne et al 2003;Martinetto et al 2010).…”

“…The bay experiences a large daily water movement, as a consequence of the macrotidal (up to 9 m) semidiurnal regime present in the area. This considerable water flushing partially relieves the land-derived N loads, as well as the accumulation of biological products (Martinetto et al 2010(Martinetto et al , 2011. Despite the large water movement, nutrient concentration pulses during low tide remain in the system long enough to support high biomass and diversity of macroalgae near the town of San Antonio Oeste (Martinetto et al 2010).…”

“…The Argentinean Patagonian coast is composed of a mosaic of several pristine sites mixed with few places subject to locally increased anthropogenic nitrogen (N) loading (Martinetto et al 2011;Piriz et al 2003). The San Antonio Bay (40°43′ S, 64°56′ W, Argentina) is a good example of recent changes related to increases in human population along the coastline.…”