Long-term changes in diversity in a subtropical estuary in southern Brazil

The Patos Lagoon (10,000 km²) is the dominant feature in the coastal plain of Southern Brazil. The estuary of the Patos Lagoon (32° 05' S, 52° 10'W) and adjacent coast were chosen as a SITE (1,500 km²) for the Brazilian Long Term Ecological Research (LTER). This region presents high biological productivity and at the same time is host of important port and industrial activities. From 2000 to 2015, systematic sampling of physico-chemical variables and of the main constituents from plankton, benthos and nekton was conducted monthly. Species diversity index were calculated to express changes in diversity in the estuary. The estuary is a river-dominated system with discharge maxima associated with strong rainfall and low discharge periods occurring during drought years. This has direct influence on the circulation and salinity variations, with low values recorded during El Niño and high salt-water intrusion during La Niña years. Results reveal that species composition of phytoplankton, zooplankton, benthic flora and macrofauna in the estuary are all affected by different scales of variability. The fact that ENSO is a dominant forcing factor in the region highlights the importance of long term monitoring of biological components of coastal and ocean observing systems.