Top-down vs. bottom-up: Grazing and upwelling regime alter patterns of primary productivity in a warm-temperate system

Community structure is driven by biological interactions and physical processes that can vary across environmental gradients and spatial scales. Early ecological models focused on the role of resource availability (i.e. bottom-up effects), predicting that the strength of top-down control varied along gradients of primary productivity and that local species interactions determined community structure. However, the role of regional scale oceanographic processes in determining species interactions and community structure is now widely recognized, with bottom-up effects such as coastal upwelling driving regional scale patterns of resource availability. Such nutrient subsidies can significantly alter primary production and drive changes in algae-herbivore interactions in rocky intertidal habitats. However, despite the potential for upwelling to alter these interactions, studies investigating the effects of upwelling and grazing pressure are scarce, particularly for warm-temperate systems, an..., Experimental design. At each site, 15 experimental plots were established in 5 blocks around the mid-shore level across approximately 100 metres of shoreline, with a minimum of 2 metres between blocks. Each block contained 1 replicate from each experimental treatment. The experiment had a fully factorial design with two factors: 1) upwelling regime (fixed, two levels: upwelling and non-upwelling) and 2) grazing pressure (fixed, three levels: total exclusion, partial exclusion, total access). Grazer exclusion plots were established by enclosing plots with fences (35 x 35 cm, 10 cm high) constructed from stainless steel mesh (0.9 mm wire diameter, 5.16 mm aperture) fixed to the substratum with screws and washers. Fences were chosen instead of enclosed cages with lids to prevent light limitation (Appendix S1: Section S2). This allowed the exclusion of all benthic grazers from the fenced  plots. To test for experimental artefacts affecting on macroalgal production as a result of the presenc..., , # Data from: Top-down vs. bottom-up: Grazing and upwelling regime alter patterns of primary productivity in a warm-temperate system

[https://doi.org/10.5061/dryad.3j9kd51qz](https://doi.org/10.5061/dryad.3j9kd51qz)

This data pertains to a manipulative field experiment in which in-situ stainless steel fences were used to test for the effects of grazing pressure and upwelling regime on the sessile invertebrate community and macroalgal productivity of an intertidal rocky shore in a warm-temperate system. This dataset contains grazer abundance, invertebrate cover and macroalgal cover and biomass data collected at two upwelling and two non-upwelling sites in the presence and absence of grazers on the southeast coast of South Africa during monthly quadrat surveys between January 2021 and December 2021. Grazer access was manipulated using stainless steel fences with three treatments: full fence (no access), half fence (partial access- procedural control) and controls (no fence- full access)....