Human impact on the 'last great wilderness'

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We may be significantly damaging the deep-sea environment even as we understand only a tiny fraction of it.

This is the conclusion drawn in a study conducted as part of the Census of Marine Life and published in a recent issue of the online journal PLoS ONE.

Eva Ramirez-Llodra and colleagues assess past, present and future impacts of human-related activities on deep-sea habitats and their communities, from disposal, through exploitation to climate change (including ocean acidification) using a semi-quantitative analytical approach.

The deep sea has often been considered a habitat that is out of sight and out of mind. This has resulted in its historical (and current) perception as a convenient site for the disposal of waste (especially in cases where it was not ethical for the waste to be disposed on land) and as source of potential mineral and biological resources over which no national jurisdiction exists.

Basing their information on published sources and their own experience, the authors assessed the past, present and future human impacts on 12 different types of deep-sea habitats.

The main human impact in the past has been dumping; much of this has been curtailed due to the legal ban on routine dumping of many types of waste from ships imposed since 1972, but illegal dumping is still being carried out.

There is some evidence that the effects of the wide variety of waste introduced to the deep sea (such as plastics, and chemical and organic pollutants) are not benign, although comprehensive studies are lacking and the long-term effects remain largely unknown.

Although dumping and the cascading effects of overfishing in shallow waters remain threats to deep-sea ecosystems, new direct threats in the form of the exploitation of biological, mineral and petrochemical resources are increasing in recent years as a result of expanding technological capabilities.

Another largely unstudied threat has been the effect of alien invasive species, one that the deep sea has been thought to be immune.  

Future threats that may become increasingly important include ocean acidification, deoxygenation, and warming. These are predicted to lead to the loss of important deep-water fisheries habitats and thus fishery resources. More worryingly, these threats are predicted to act synergistically in negatively impacting deep-sea ecosystems.

The authors concluded from their study that the overall anthropogenic impact in the deep sea is increasing and has evolved from mainly disposal and dumping in the late 20th century, to exploitation in the early 21st century.

Although exploitation is currently the most important human-related activity that affects the deep-sea ecosystem, the major impact in the deep sea predicted for the remainder of the century will be climate change.

The authors conclude "Conservation in the deep sea offers challenges in the form of knowledge gaps, climate change uncertainties, shifting jurisdictions and significant enforcement difficulties. With time, technological advances can help address these challenges. It remains to be seen whether new approaches must be developed to conserve the biodiversity and ecosystem services we value in the deepest half of the planet."

For more information, see the paper: Ramirez-Llodra, E, PA Tyler, MC Baker, OA Bergstad, MR Clark, E Escobar, LA Levin, L Menot, AA Rowden, CR Smith and CL Van Dover (2011) Man and the last great wilderness: human impact on the deep sea. PLoS ONE 6, e22588. doi:10.1371/journal.pone.0022588

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