The effects of multidecadal-scale phytodetritus disturbances on the benthic foraminiferal community of a Western Boundary Upwelling System, Brazil

Abstract Benthic foraminiferal assemblages, Shannon diversity, BFAR index, and oxygen and carbon stable isotopes from Cibicides kullenbergi and Uvigerina peregrina were analyzed in three sedimentary cores dating from the last two centuries from an oligotrophic area influenced by Cabo Frio Upwelling System events in the southwestern Atlantic. The geochemistry and ecology of the benthic foraminifera were compared to organic carbon flux and planktonic foraminiferal records in order to understand the impact of phytodetritus produced by upwelling events and disturbances on the benthic community on a multidecadal time-scale. Values of δ 13 C for C. kullenbergi were lower (0.26 ± 0.10‰) compared to δ 13 C DIC , suggesting the presence of phytodetritus in the sediment water where C. kullenbergi calcifies its test. Changes in the benthic foraminiferal assemblage suggest that distinct levels of disturbance differentially influence community-level diversity. Colonization and dominance by opportunistic species resulted in reduced diversity after 1960 CE, with low diversity being observed in areas under the influence of seasonal and intermittent phytodetritus inputs, and higher diversity in a less disturbed area. Certain species can compensate for the negative impact of opportunistic species in terms of disturbance across the community structure, supporting the spatial insurance hypothesis. This community seems to be far from a stable diversity, given the negative interactions between species over the past two centuries, with the r-selective species G. subglobosa and A. weddellensis limiting B. marginata growth during periods of high food availability.