Intertidal rocky shore seaweed communities subject to the influence of shallow water hydrothermal activity in São Miguel (Azores, Portugal)

Abstract

The volcanic origin of the Azores archipelago (Portugal) gives rise to active deep sea and shallow water hydrothermal activity that affects benthic communities. Intertidal seaweed surveys were conducted at two shores affected by intense shallow water hydrothermal vents. Water temperature, acidity and salinity were monitored. Seaweed communities were found to be species poor and have a disproportionally larger number of filamentous early successional species on shores that are subject to the effect of hot and acidic freshwater of volcanic origin. There is an ecological resemblance between hydrothermally affected seaweed communities in the Azores and those affected by acid mine drainage in the UK, thus indicating that hydrothermalism can be a useful scenario for pollution studies under conditions of ocean warming and acidification.

Indices to monitor coastal ecological quality of rocky shores based on seaweed communities: simplification for wide geographical use

“…Such a scenario forces one to work only with the top end of the quality scale, without the bottom end to calibrate its boundaries. The nearest scenario in the Azores archipelago where coastal communities are subject to environmental conditions comparable to coastal pollution are those coastal communities where shallow water hydrothermal activity leads to increased temperature, acidity and heavy metal concentration within enclosed bays (Wallenstein et al, 2012). …”

Shallow-water hydrothermal vents in the Azores (Portugal)

“…Water fluxes are formed by the venting of meteoric and seawater, which composition has been altered as a result of interactions with the sediments by elevated temperatures and the entrainment of interstitial waters by the rising fluids. Rising gas bubbles can initiate water circulation within the sediment, so that the released water is recharged by overlying water (O'Hara et al, 1995;Dando et al, 1999). Reports on this matter are restricted to D. João de Castro Bank and indicate flow rates of venting water of 773 and 787 mL/min in September 1999 (Cardigos et al, 2005).…”

“…Each vent is associated to a specific substratum type and depth, and the physical and chemical properties of the fluid can be quite variable (Melwani & Kim, 2008). Even the temperature range can be of considerable magnitude (Vedel & Depledge, 1995;Wallenstein et al, 2013). The majority of the data concerns to physical data, revealing the need for more studies regarding chemical water analysis and dissolved gases (e.g.…”

“…Recently, Wallenstein et al (2013) gave an account of the habitat characteristics and associated intertidal seaweed communities subjected to shallow-water hydrothermal activity in the Azores. Seaweed communities were found to be species poor and to have a disproportionally larger number of filamentous early successional species.…”

“…A striking feature of these islands, as a result of their volcanic nature, is the presence of active deep sea and shallow-water hydrothermal activity caused by diffuse degassing from submerged soils (Cruz, 2003;Ferreira et al, 2005). Organisms associated to hydrothermal activity are chronically exposed to extreme environments characterized by "natural thermal pollution", high metal concentrations (Cunha et al, 2007;Cunha et al, 2008;Wallenstein et al, 2009a;Couto et al, 2010;Dionísio et al, 2013;Wallenstein et al, 2013), either in the form of particles or associated with gases from volcanic emissions (Hansell et al, 2006), as well as acidic seawater due to the diffusion of volcanic gases (Cruz & França, 2006). The terrestrial volcanic systems have been well-studied, both because of the long history of devastation caused by their eruptions and because of their geothermal potential (Ferreira, 1994;Cruz et al, 1999;Ferreira & Oskarsson, 1999;Cruz, 2003;França et al, 2003;Ferreira et al, 2005;Cruz & França, 2006;Viveiros et al, 2008;Cruz et al, 2010;Viveiros et al, 2010).…”