LAUSR

The El Nino–Southern Oscillation (ENSO) strongly influences climate and hydrology on the planet and may drive the structure and functioning of estuarine communities. However, the effects of the ENSO on coastal areas are dependent on the spatial scale and the intrinsic characteristics of the estuary. Over six years (2013 to 2018), we investigated the variability in macrobenthic secondary production of Spartina alterniflora marshes and adjacent unvegetated areas in a subtropical coastal lagoon in Southern Brazil. We tested whether the ENSO events affect the benthic secondary production of these two habitats. Most environmental variables (air temperature, northward surface stress and northward wind component) did not differ significantly between ENSO phases, except for precipitation. Monthly precipitation totals during El Nino months were 70% higher than neutral and La Nina conditions. A total of 25,862 organisms (8,191 in salt marshes and 17,671 in unvegetated areas) belonging to 39 taxa (25 in marshes and 34 unvegetated areas) were collected throughout the study. The tanaid Monokalliapseudes schubarti, and Nereididae polychaeta Laeonereis acuta were largely the most abundant species in both vegetated and unvegetated areas, with higher biomass and productivity. The secondary production in unvegetated areas increased 216%, from a mean of 107.5 g C/m2/y to 336.4 g C/m2/y during El Nino. However, the salt marshes responded differently than the unvegetated areas, with secondary production more stable over the time, with highest value of 164.2 g C/m2/y-1. There is also a distinction in the effects on different species, L. acuta showed an increase only in biomass (from 0.024 to 0.042 g DW/0.03m2), whereas M. schubarti increased both in biomass (more than 4000%) and density (more than 5000%). In contrast, no significant differences in density, biomass and secondary production for both species were detected over time in the salt marshes. Our findings indicate that large scale climatic variations, such as ENSO, can strongly affect estuarine density, biomass and secondary production, but salt marshes buffer El Nino effects on benthic associations.