A protocol for the simultaneous identification of chitin-containing particles and their associated bacteria.

Chitin is the second most abundant polymer on Earth, playing a crucial role in the biogeochemical cycles. A core issue for studying its processing in aquatic systems is the identification and enumeration of chitin-containing particles and organisms, ideally in a manner that can be directly linked to bulk chitin quantification. The aim of this study was the development of such a technique. We successfully combined the methodology of bulk chitin determination using wheat germ agglutinin (FITC-WGA) for staining chitin-containing particles and organisms along with CARD-FISH staining of either chitin-containing eukaryotic cells or bacteria associated with them. Environmental chitin staining was successfully applied to natural water samples. Fungal hyphae, diatoms, and dinoflagellates, sestonic aggregates and chitin-containing structures derived from metazoa were observed. Also, hybridized bacteria attached to chitinaceous debris were clearly visualized. Finally, as proof of principle, cultured yeast cells were simultaneously-targeted by FITC-WGA and the EUK516 probe without exhibiting any interference between both stains. The presented approach appears as a powerful tool to evaluate the contribution of different size classes and organisms to chitin production and consumption, opening the possibility for application of single-cell approaches targeting the ecophysiology of chitin transformations in aquatic systems.

Biogeochemical and hydrological drivers of the dynamics of Vibrio species in two Patagonian estuaries.

The ecology of the most relevant Vibrio species for human health and their relation to water quality and biogeochemistry were studied in two estuaries in Argentinian Patagonia. Vibrio cholerae and Vibrio parahaemolyticus were reported in >29% of cases at the Río Colorado and Río Negro estuaries. Neither the pandemic serogroups of Vibrio cholerae O1, Vibrio cholerae O139 nor the cholera toxin gene were detected in this study. However, several strains of V. cholerae (not O1 or O139) are able to cause human disease or acquire pathogenic genes by horizontal transfer. Vibrio vulnificus was detected only in three instances in the microplankton fraction of the Río Negro estuary. The higher salinity in the Río Colorado estuary and in marine stations at both estuaries favours an abundance of culturable Vibrio. The extreme peaks for ammonium, heterotrophic bacteria and faecal coliforms in the Río Negro estuary supported a marked impact on sewage discharge. Generally, the more pathogenic strains of Vibrio have a faecal origin. Salinity, pH, ammonium, chlorophyll a, silicate and carbon/nitrogen ratio of suspended organic particulates were the primary factors explaining the distribution of culturable bacteria after distance-based linear models. Several effects of dissolved organic carbon on bacterial distribution are inferred. Global change is expected to increase the trophic state and the salinisation of Patagonian estuaries. Consequently, the distribution and abundance of Vibrio species is projected to increase under future changing baselines. Adaptation strategies should contribute to sustaining good water quality to buffer climate- and anthropogenic- driven impacts.

Global change effects on biogeochemical processes of Argentinian estuaries: an overview of vulnerabilities and ecohydrological adaptive outlooks.

The aims of this work are to provide an overview of the current stresses of estuaries in Argentina and to propose adaptation strategies from an ecohydrological approach. Several Argentinian estuaries are impacted by pollutants, derived mainly from sewage discharge and agricultural or industrial activities. Anthropogenic impacts are expected to rise with increasing human population. Climate-driven warmer temperature and hydrological changes will alter stratification, residence time, oxygen content, salinity, pollutant distribution, organism physiology and ecology, and nutrient dynamics. Good water quality is essential in enhancing estuarine ecological resilience to disturbances brought on by global change. The preservation, restoration, and creation of wetlands will help to protect the coast from erosion, increase sediment accretion rates, and improve water quality by removing excess nutrients and pollutants. The capacity of hydrologic basin ecosystems to absorb human and natural impacts can be improved through holistic management, which should consider social vulnerability in complex human-natural systems.

Mesozooplankton assemblages and their relationship with environmental variables: a study case in a disturbed bay (Beagle Channel, Argentina).

This study focused on the seasonal and spatial analysis of the mesozooplankton community in a human-impacted subantarctic bay in Argentina and aimed to detect assemblages associated with environmental variability. Mesozooplankton samples and environmental data were obtained in the Ushuaia Bay (UB) seasonally, from August 2004 to June 2005, and spatially, from coastal (more polluted), middle (less influenced) and open sea water (free polluted) sampling stations. Remarkable seasonal changes on the mesozooplankton community were observed. Nitrogenated nutrients, chlorophyll a, salinity and temperature were the prevailing environmental conditions likely associated with the different mesozooplankton assemblages found in the bay. The copepods Eurytemora americana, Acartia tonsa, Podon leuckarti and Nematoda were particularly observed on the northwest coast of the bay, characterized by the highest level of urban pollution, eutrophicated by sewage and freshwater inputs from the Encerrada Bay which is connected to it. The stations situated in the northeast area, mostly influenced by freshwater input from rivers and glacier melting, showed low mesozooplankton abundances and an important contribution of adventitious plankton. The copepods Ctenocalanus citer, Clausocalanus brevipes and Drepanopus forcipatus were mostly observed at the stations located near the Beagle Channel, characterized by open sea and free polluted waters. Our findings suggest that the variations observed in the mesozooplankton assemblages in the UB seem to be modulated by environmental variables associated with the anthropogenic influence, clearly detected on the coast of the bay. Certain opportunistic species such as A. tonsa and E. americana could be postulated as potential bioindicators of water quality in subantarctic coastal ecosystems.

Sewage pollution effects on mesozooplankton structure in a shallow temperate estuary.

The effects of a sewage effluent with no treatment on the mesozooplankton structure and the environmental quality were evaluated in the Bahía Blanca Estuary, during June to November 1995. The highest values of particulate organic matter, nutrients and specially phosphate, were observed in the effluent discharge zone. In addition, taxa richness, mesozooplankton abundance and Shannon diversity values were lower in the sewage discharge area compared with the less polluted area. Eurytemora americana and Acartia tonsa as well as larvae of Balanus glandula, Neohelice granulata and Spionidae were found in the discharge area with lower densities. These results highlight the importance of sewage effluent effects on mesozooplankton community providing background data to use in other monitoring programmes.