Coastal upwelling may strengthen the controls of herbivory and light over the population dynamics of Hedophyllum sessile in the Oregon rocky intertidal

Survival of early life history stages is critical to the successful establishment of benthic populations. Although light availability and herbivory are likely to influence passage of marine macroalgae through a “recruitment bottleneck” at the sporeling stage, the interactive effect of these factors on subsequent community patterns of macroalgae is not well studied. We experimentally tested the effect of light and grazing on sporelings of the common intertidal kelp Hedophyllum sessile. Studies were conducted at two sites along the Oregon coast: Strawberry Hill (an intermittent upwelling region) and Cape Blanco North (a persistent upwelling region). Herbivory and light availability were manipulated and kelp performance metrics (density and length) were measured monthly from May to November 2019. We found that the effects of herbivory and light availability were pronounced at Cape Blanco North but negligible at Strawberry Hill. At Cape Blanco North, herbivory had strong but opposing effect...