Mesoscale regulation comes from the bottom‐up: intertidal interactions between consumers and upwelling

Abstract

Theory suggests that variation in resource supply should propagate up trophic webs influencing plant-herbivore interactions and abundances. Community regulation models have been tested in several ecosystems, but benthic marine ecologists have largely overlooked bottom-up factors except at the largest spatial scales. We used naturally occurring variation in nutrient supply associated with upwelling intensity (over 10s of kilometre) to test community regulation models. Higher upwelling intensity was strongly associated with increased abundance of late-successional, corticated algae, which in turn had apparent negative effects on ephemeral algae. Corticated algae were resistant to extant levels of herbivory. As a result, corticated algae were more abundant at sites of high upwelling intensity, while ephemeral algae were more abundant at sites of low upwelling intensity. We speculate that human removal of large grazers that can feed on corticated algae may interact with natural variation in nutrient supply to shift community structure over mesoscales.

Interactive effects of grazing and environmental stress on macroalgal biomass in subtropical rocky shores: Modulation of bottom-up inputs by wave action

“…Estimates of nitrate concentration based on SST were exceedingly low, compared to nearshore conditions in other regions (i.e. Bustamante et al, 1995;Menge et al, 1997;Nielsen and Navarrete, 2004;Shirodkar et al, 2009), varying from 0.2 to 0.7 μM, and were much lower in 2008 than 2010 for a large part of the year (Fig. 2).…”

“…The much higher biomass of mesoherbivores in exposed shores, where their effects were not detected, suggest a positive effect of the macroalgal standing stock on limpet and periwinkle populations, with no coupled top-down effects on these macroalgae (Menge, 2000). Contrasting herbivore biomass, however, could also be related to spatial variation of the recruitment intensity of these consumers among shores (Nielsen and Navarrete, 2004), a possibility that should be investigated.…”

“…This high susceptibility to herbivory has been usually associated with the lower biomass of ephemeral macroalgae observed on many temperate shores (Coleman et al, 2006;Hawkins, 1981;Nielsen and Navarrete, 2004;Poore et al, 2012;Steneck and Dethier, 1994) and on a few tropical intertidal shores as well (Kennish et al, 1996;Menge et al, 1985;Vinueza et al, 2006). However, the extent to which grazers control algal biomass may vary substantially at different spatial scales, even within the same shoreline, independently of the general climatic region (e.g.…”

“…However, the extent to which grazers control algal biomass may vary substantially at different spatial scales, even within the same shoreline, independently of the general climatic region (e.g. Coleman et al, 2006;Jenkins et al, 2005;Nielsen and Navarrete, 2004;Sauer Machado et al, 1996). Although several studies indicated that consumption pressure may increase towards the tropics (Vermeij, 1978;Brosnan, 1992;Schemske et al, 2009;Freestone et al, 2011), a recent review of more than 600 studies does not support such a latitudinal trend (Poore et al, 2012).…”

“…Aguilera and Navarrete, 2012;Hawkins, 1981;Nielsen and Navarrete, 2004;Sousa, 1979) and environmental stress, particularly high temperature (Moore, 1972;Williams, 1993), have also been demonstrated to play roles in the seasonal decline of ephemeral algal biomass. Higher temperatures in tropical areas may impose more severe restrictions to intertidal macroalgal assemblages (Moore, 1972;Williams, 1993) and, therefore, environmental factors capable of mitigating heat and desiccation stress, such as orientation to sunlight and exposure to wave splash, may be crucial.…”