Shallow-water hydrothermal vents in the Azores (Portugal)

Abstract

The impact of global warming has been a major issue in recent years and will continue increasing in the future. Knowledge about the effects of ocean acidification on marine organisms and communities is crucial to efficient management. Island envi- ronments are particularly sensitive to externally induced changes and highly dependent on their coastal areas. This study summarises the published information on shallow-water hydrothermal vents of the Azores. These environments were reported to exhibit high metal concentration and acidified seawater due to the diffusion of acidic volcanic gases (mainly CO 2 ) and a considerable temperature range. In some vents a water input with lower salinity was reported. These conditions result in a depletion of some of the species but can also enhance a diversity gradient between the unique shallow marine hy- drothermal ecosystems and the surrounding common coastal marine environment, potentiating the co-existence of a high vari- ety of metabolisms and so biodiversity. Metal content on species from vent areas was reported to be associated with volcanic activity and signs of organism's chronic stress seemed to result in modifications on their morphometry and internal composi- tion. Species able to survive at vent conditions are indicated as potential sentinels for studying the effects of increasing tem- perature and acidification on marine organisms and as bioindicators of metal accumulation studies at the Azores. Further information on CO 2 flux, metals concentration in the sediments and seawater and on the geochemistry of fluids from active shallow-water hydrothermal systems is needed. Also, research on the productivity of shallow- water vent areas at the Azores and on food chains and interactions between trophic levels at these environments is recommended as it will contribute to a better knowledge of metal bioavailability, accumulation and biomagnifica- tion. This research should be complemented by investigations directed to the venting periodicity and episodicity and metal deposits resulting from hydrothermalism. This would increase the value of the Azorean vents as natural laboratories to the implementation of multidisciplinary research aimed at contributing to predict and/or to infer about ocean acidification effects on marine organisms and communities.