Phytoplankton summer bloom dynamics in the Bahía Blanca Estuary in relation to environmental modifications.

VALERIA GUINDER; CECILIA POPOVICH; JUAN CARLOS MOLINERO; JORGE MARCOVECCHIO

CONTINENTAL SHELF RESEARCH

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2013 vol. 52 p. 150 - 158

0278-4343

We examined austral summer phytoplankton data (December?March) that cover the years 1978?2008 and compared with physico-chemical and meteorological variations in the Bahı´a Blanca Estuary,Argentina. During the years 1978?1982, 1992?1993 and 2006?2008, counts of phytoplankton abundance showed an increase in recent summers; from a mean value of 12103 cells L1 in 1978 to 2239103 cells L1 in 2008, while the chlorophyll concentration remained relatively constant (8.572.5 mg L1, CV¼27%) over the continuous time Series (1978?2008). The rise in the ratio ?cell abundance: chlorophyll concentration? was linked to modifications in species composition, from dominance of phytoflagellates (10?20 mm) and relatively large diatoms (e.g., Cyclotella striata 25?38 mm, Paralia sulcata 15?70 mm, Cerataulina pelagica 18?30 mm, Thalassiosra hendeyi 27?52 mm) towards the dominance of the small (5?15 mm) centric diatom Thalassiosira minima, which reached 480% of the total phytoplankton abundance in summers 2006?2008. The Bahı´a Blanca Estuary has undergone climate modifications and increasing anthropogenic disturbances during the last three decades. In the early 1990s, regional climatic conditions revealed a significant shift. Additionally, dredging activities were initiated to allow the traffic of large ships, rising the levels of suspended sediments, and the invasive copepod Eurytemora americana was introduced via ballast waters into the estuary and has displaced the dominance of the native copepod Acartia tonsa towards summer periods. The examination of physico-chemical conditions of the estuary showed a trend to increase in the minima of water temperature and higher water turbidity, dissolved phosphate, nitrite and nitrate concentrations in the pelagic environment in recent summers. We discuss the potential effects of these changes and trophic interactions on the structure and composition of the phytoplankton summer blooms in this temperate and eutrophic estuary in the Southwestern Atlantic.