Description: Natural pH values in coastal waters vary largely among locations, ecosystems, and time periods; still, there is an ongoing acidification trend. In this scenario, more acidic pH values can alter bioavailability of organic contaminants, to organisms. Despite this, interactive effects between pH and chemical substances are not usually considered in Ecological Risk Assessment protocols. This study investigated the effects of pH on the toxicity of a hydrophobic organic compound on a benthic community using a microcosm experiment setup to assess the response of nematode assemblages exposed to environmentally relevant concentrations of Irgarol at two natural pH conditions. Estuarine nematode assemblages were exposed to two concentrations of Irgarol at pH 7.0 and 8.0 for periods of 7 and 35 days. Lower diversity of nematode genera was observed at the highest tested Irgarol concentration (1281 ± 65 ng/g). The results showed that the effects of Irgarol contamination were independent of pH variation, indicating no influence of acidification within this range on the toxicity of Irgarol to benthic meiofauna. However, the results showed that estuarine nematode assemblages are impacted by long-term exposure to low (but naturally occurring) pHs. This indicates that estuarine organisms may be under naturally high physiological pressure and that permanent changes in the ecosystem's environmental factors, such as future coastal ocean acidification, may drive organisms closer to the edges of their tolerance windows.

Description: Present theories of deep-sea community organization recognize the importance of small-scale biological disturbances, originated partly from the activities of epibenthic megafaunal organisms, in maintaining high benthic biodiversity in the deep sea. However, due to technical difficulties, in situ experimental studies to test hypotheses in the deep sea are lacking. The objective of the present study was to evaluate the potential of cages as tools for studying the importance of epibenthic megafauna for deep-sea benthic communities. Using the deep-diving Remotely Operated Vehicle (ROV) "VICTOR 6000", six experimental cages were deployed at the sea floor at 2500 m water depth and sampled after 2 years (2y) and 4 years (4y) for a variety of sediment parameters in order to test for caging artefacts. Photo and video footage from both experiments showed that the cages were efficient at excluding the targeted fauna. The cage also proved to be appropriate to deep-sea studies considering the fact that there was no fouling on the cages and no evidence of any organism establishing residence on or adjacent to it. Environmental changes inside the cages were dependent on the experimental period analysed. In the 4y experiment, chlorophyll a concentrations were higher in the uppermost centimeter of sediment inside cages whereas in the 2y experiment, it did not differ between inside and outside. Although the cages caused some changes to the sedimentary regime, they are relatively minor compared to similar studies in shallow water. The only parameter that was significantly higher under cages at both experiments was the concentration of phaeopigments. Since the epibenthic megafauna at our study site can potentially affect phytodetritus distribution and availability at the seafloor (e.g. via consumption, disaggregation and burial), we suggest that their exclusion was, at least in part, responsible for the increases in pigment concentrations. Cages might be suitable tools to study the long-term effects of disturbances caused by megafaunal organisms on the diversity and community structure of smaller-sized organisms in the deep sea, although further work employing partial cage controls, greater replication, and evaluating faunal components will be essential to unequivocally establish their utility.

Description: The effects of cold fronts in a shallow sublittoral system at the Island of Santa Catarina, S Brazil, were investigated in June 2002. Atmospheric, pelagic and benthic data were taken daily covering the days before, during and after the passage of two cold fronts, summing 8 days of sampling. The results clearly showed that the passage of cold fronts, a short-term event, promote changes in the whole shallow sublittoral system, from the pelagic to the benthic one. At the pelagic system, both the cold fronts changed seston, nutrients and chlorophyll a concentrations. The increase in chlorophyll a just after the cold fronts probably resulted from phytoplankton retention and accumulation next to the coast, the microphytobenthos resuspension and the increase in nutrients availability. At the benthic system, sediment features and all of the three benthic components studied- microphytobenthos, meiofauna and macrofauna were also affected by the passage of the cold fronts. The sediments from the studied site suffered a clear homogenizing process. While medium grain size decreased, fine sand percentages gradually increased after the cold front passage. In contrast, sediment organic content was significantly higher just after the first cold front. The effects of the passage of cold fronts in the benthos were dependent on the biological component, the vertical distribution and on the cold front magnitude. The sediment chlorophyll a concentration was lower exactly one day after both cold fronts passage while phaeopigments were significantly higher. The results of the study showed that both macrofauna and meiofauna, particularly nematodes, of the upper layer of the sediment exhibited a decrease in density and number of taxa during the passage of the first frontal system. The nematodes, more than suffering erosion and transport, showed a vertical migration process to the deeper layers of the sediment during the passage of the cold fronts.

Description: There is little meiofauna data from the southwest Atlantic, and especially lacking are studies examining deep-seacommunities. In this study, the structure of meiofauna communities, particularly nematodes, was analyzed from dataderived from 101 samples (48 samples on the continental-slope and 53 samples at a deep-sea site) collected at CamposBasin, SEBrazil. Differences in the meiofauna densities and in the number of taxa between continental slope and deepseasites depended on the taxonomic level examined. While total meiofauna abundance did not differ significantlybetween sites, nematode densities were significantly higher in the deep sea (mean of 157 inds.10 cm2) than on the slope(mean of 129 inds.10 cm2). The number of meiofauna taxa was significantly higher at the continental slope site. Yet forthe most abundant meiofaunal group, the nematodes, whilst the number of families did not differ between continentalslope and deep sites, the number of genera was significantly higher in the deep sea. The remarkable resemblancebetween the dominant nematodes (Halalaimus, Acantholaimus, Daptonema, Theristus and Sabatieria) from SEBraziland other deep sea studies confirmed earlier suggestions of a typical deep-sea nematode community with a broadgeographical distribution. Multivariate analysis derived from meiofauna and nematode data showed that the structureof the fauna differed significantly between sites. Correlations detected between meiofauna and some sedimentproperties, such as grain size and sediment heterogeneity, although significant, were very low.