Zapperi, G.; Pratolongo, P.; Piovan, M.J., and Marcovecchio, J.E., 2016. Benthic-pelagic coupling in an intertidal mudflat in the Bahía Blanca estuary (SW Atlantic).

Benthic-pelagic coupling was evaluated in a shallow, turbid, and nutrient-enriched estuary in the SW Atlantic. We analyzed the annual trends in turbidity, nutrients, and chlorophyll a (Chl a) concentration in the water column and related those changes to benthic fluxes of dissolved inorganic nutrients, estimated through microcosm incubation experiments, as well as seasonal variations in the abundance and composition of macrobenthic communities. The intertidal mudflats of the estuary are characterized by the presence of two subsystems defined by their macroecological features: crab beds, steep areas dominated by the burrowing crab, and Laeonereis flats, plain areas with low crab burrow density. Peak Chl a concentration in the water column occurred in July after turbidity reached its minimum value in June. Dissolved nutrients decreased after the peak of Chl a. Benthic fluxes of into the water column were very high after the diatom bloom in the Laeonereis flats, whereas the crab beds performed as sinks. Both subsystems were sinks of + before the bloom, and fluxes reversed in the postbloom period. The crab Neohelice granulata and the polychaete Laeonereis acuta were the most represented macrobenthic species in both subsystems. Density of L. acuta in Laeonereis flats was highest in June, whereas that of N. granulata in the crab beds was highest in December. These changes in abundance coincide with changes in benthic fluxes. These results suggest that benthic-pelagic coupling, mediated by biological activity, may play a significant role in creating the window of lower turbidity that allows phytoplankton blooms. As the bloom develops, dissolved nutrients in the water column are consumed, and organic matter is produced. As a counterpart, the local coupling between remineralization in the sediment surface and the benthic flux to the water column as dissolved nutrients allows the recovery of nutrient levels and supports primary production in the forthcoming cycle.