Helena Coelho

Endogenous versus environmental control of vertical migration by intertidal benthic microalgae

The vertical migratory behaviour of estuarine microphytobenthos, i.e. the biofilm-forming microalgae inhabiting intertidal sediments, is probably a significant factor for their success in this extreme and unstable environment. The present work aimed to assess the relative role of endogenous versus environmental control of benthic microalgal vertical migratory behaviour. This was done by comparing the patterns of vertical migration in undisturbed sediment samples kept under constant conditions of darkness and low light with those in ambient light conditions, by measuring the changes in the surface microalgal biomass during daytime low-tide periods. The results showed that the formation of a biofilm was a two-phase process. It began with a relatively small accumulation of cells at the surface, starting hours before the beginning of the light period and endogenously driven. However, the full formation of the biofilm required exposure to light by the expected beginning of the photoperiod, which further promoted upward migration and accelerated the cell accumulation at the surface. In the absence of light, upward migration was interrupted and the incipient biofilm began to disaggregate. The relative importance of the endogenously controlled behaviour varied during the spring–neap tidal cycle, reaching a maximum on those days when low tide occurred in the middle of the day, suggesting its entrainment by the duration of light exposure on previous days. The regulation of the surface cell concentration during daytime low tides was found to be strongly dependent on exogenous factors, particularly irradiance. The spontaneous disaggregation of the biofilm shortly before the end of the low-tide period (due to tidal flood or sunset), both under constant as well as ambient light conditions, suggested the presence of an endogenously controlled positive geotaxis.

Photosynthetic activity and ecology of benthic diatom communities from streams affected by Acid Mine Drainage (AMD) in pyritic mines

The authors are grateful to the Biology and Geosciences Departments of University of Aveiro, Portugal and to the Fundacao para a Ciencia e Tecnologia, Portugal (grant number SFRH/ BD/36137/2007) for their financial support during this study. We thank Helena Novais for the valuable help with the software (ArcGis) to do the sites’ location map. We thank the two anonymous reviewers and the editor for critical comments on the manuscript.

Arsenic accumulation in intertidal macroalgae exposed to sewage discharges

Arsenic is a widely distributed element in marine ecosystems. The main anthropogenic sources of this contaminant are domestic and industrial wastewaters, and since it can be harmful to humans even at low concentrations, it has been ranked as one of the top hazardous substances. Therefore, the analysis of arsenic is an essential task to assess the potential environmental and human health risk associated with sewage discharges. The accumulation of total arsenic on intertidal rocky shore macroalgae exposed to contaminated sewage discharges was measured in five macroalgae species (Asparagopsis armata, Codium sp., Plocamium cartilagineum, Saccorhiza polyschides and Ulva sp.). Differences in the concentrations of arsenic were examined in the seawater and in the macroalgae species. The results showed significantly higher concentrations of arsenic near the sewage discharges in all the species except S. polyschides. Although the information obtained from total arsenic determination is not enough to assess the toxicological risk in the environment, this paper gives an important contribution on contamination risks and helps in choosing potential good biomonitors.