Plankton features vs environmental quality in the inner zone of Bahía Blanca Estuary (Argentina)

HOFFMEYER, M.S.; BARRIA DE CAO, M.S.; BERASATEGUI, A.A.; PETTIGROSSO, R.; DUTTO, M.S; LÓPEZ ABBATE, M.C.; BIANCALANA, F.; FULCO, V.K; FERNÁNDEZ SEVERINI, M.D.; MENÉNDEZ, M.C.; DIODATO, S.L.; BARNECH BIELSA,G; CHAZARRETA, C.J.

Liverpool

Simposio; European Marine Biology Symposium 2009-EMBS44; 2009

University of Liverpool

The inner zone of Bahía Blanca Estuary is associated with an intense industrial, maritime activity and periodic dredging. A monthly biomonitoring has been carried out as of 2006 in order to determine a planktonic baseline in this area and establish ecological indicators of system health. Environmental data as well as information on the taxonomic composition, biomass, abundance and diversity of phyto, micro, meso- and macrozooplankton were recorded along seven stations of the Principal Channel in 2007. 53 phytoplanktonic taxa were found whereas 22 taxa of the microzooplankton, were observed. 70 meso- macrozooplanktonic taxa were found. Crustaceans were the dominant fraction, the copepods Acartia tonsa (native) and Eurytemora americana (invader) being the dominant ones. Mesozooplankton showed highest mean abundance and biomass values in summer and ending winter. These values coincided with A. tonsa (6,232 ind m-3) and E. americana (18,543 ind m-3) population peaks, the latter being the highest than those recorded to date. Macrozooplankton was scarce and presented maximum abundance and biomass in summer which coincided with the mysidacean Arthromysis magellanica (212.24 ind m-3) population peak. Changes in the temporal and spatial distribution of phyto- and microzooplankton composition which lead to changes in the diversity values, were recorded with respect to data from 1996-1997. In addition, variations in the temporal and spatial composition of micro-, meso- and macrozooplankton, a higher abundance and biomass, and differences in specific diversity were recorded in the present research with respect to those mentioned historic data. Several ecological processes must have been occurring in the studied biotic associations such as changes in predation interactions as well as competition and perturbation of niches, which is evidenced by the recently observed changes in the composition and in the abundance patterns.In addition, the effects of acute pollution by toxic substances, in some punctual sites within this area, could have influenced. The use of bio-ecological monitoring in aquatic ecosystems subjected to anthropogenic pressure, such as rivers and coasts, has intensified since the 90s due to the high sensitivity of the biotic community to respond with some advance to small environmental changes of global or local type.Determine the causes of the observed changes at a systemic level, is a complex and difficult goal to achieve only from field data, mainly due to the likely synergies between the different factors and processes. In this case, it would be neccesary to add experimental works, through which to test hypotheses arising from the observational data.