Abstract
Similar environmental driving forces can produce similarity among geographically distant ecosystems. Coastal oceanic upwelling, for example, has been associated with elevated biomass and abundance patterns of certain functional groups, e.g., corticated macroalgae. In the upwelling system of Northern Chile, we examined measures of intertidal macrobenthic composition, structure and trophic ecology across eighteen shores varying in their proximity to two coastal upwelling centres, in a hierarchical sampling design (spatial scales of >1 and >10 km). The influence of coastal upwelling on intertidal communities was confirmed by the stable isotope values (δ13C and δ15N) of consumers, including a dominant suspension feeder, grazers, and their putative resources of POM, epilithic biofilm, and macroalgae. We highlight the utility of muscle δ15N from the suspension feeding mussel, Perumytilus purpuratus, as a proxy for upwelling, supported by satellite data and previous studies. Where possible, we used corrections for broader-scale trends, spatial autocorrelation, ontogenetic dietary shifts and spatial baseline isotopic variation prior to analysis. Our results showed macroalgal assemblage composition, and benthic consumer assemblage structure, varied significantly with the intertidal influence of coastal upwelling, especially contrasting bays and coastal headlands. Coastal topography also separated differences in consumer resource use. This suggested that coastal upwelling, itself driven by coastline topography, influences intertidal communities by advecting nearshore phytoplankton populations offshore and cooling coastal water temperatures. We recommend the isotopic values of benthic organisms, specifically long-lived suspension feeders, as in situ alternatives to offshore measurements of upwelling influence.
Highlights
Environmental context has a large influence on ecosystem functioning [1,2,3], often setting the limits within which a general trend, such as the positive relationship between species richness and primary productivity [4], may hold
Consumer diet was significantly dominated by particulate organic matter (POM) in Antofagasta Bay relative to the Mejillones Peninsula
We identified evidence that at the time of sampling (Summer 2012), the relative contribution of POM to consumer diets was reduced, and assimilation from macroalgae increased over the Mejillones Peninsula and Bay relative to Antofagasta Bay and Coloso Point
Summary
Environmental context has a large influence on ecosystem functioning [1,2,3], often setting the limits within which a general trend, such as the positive relationship between species richness and primary productivity [4], may hold. The relative importance of different environmental processes may vary among geographical regions [6] and with spatial scale [7], making their influence on communities difficult to predict at all but macroecological scales [8]. Certain general scenarios, dominated by similar environmental conditions, appear to characterise multiple geographical regions (c.f. biomes [8, 9]). These merit investigation to identify the extent, and underlying driving processes, of ecological similarities (e.g. trophic structure [10])
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