Protecting the deep blue

More than 100 scientists have highlighted key targets for conserving and managing the deep sea, including habitat-sustaining species like corals and human activities such as mining, in a survey published in the journal Nature Ecology and Evolution.

Living more than 200 metres below the ocean’s surface is the planet’s “largest and least explored biome”, write Roberto Danovaro, from the Polytechnic University of Marche in Italy, and co-authors from Europe, the US, Australia and China.

Though research has been patchy, it has become increasingly clear that ecosystems of the deep sea and deep seabed are highly complex, housing abundant, diverse life forms, and are intricately connected with the biogeochemical cycles that support all life on the planet.

This includes “a multitude of captivating rare species,” including deep-sea sharks like Mitsukurina owstoni, giant squids such as Arthiteuthis spp, the Dumbo octopus Opisthoteuthis californiana, unique habitats and ecosystem engineers including corals and sponges.

Yet, these vulnerable ecosystems face spiralling threats, indirectly and directly, from a myriad of human pressures including plastic pollution, climate change, fisheries and oil and gas extraction.

“The current scenarios of blue growth anticipate increased exploitation of deep-ocean resources, with associated unknown impacts on deep-sea ecosystems,” Danovaro and colleagues write.

In a quest to identify and prioritise strategies to protect the deep sea, they sent a questionnaire-based survey to experts from around the world and collated responses from 112 scientists.

The survey grouped items researched from the deep-sea literature under five ecological variables deemed essential, comprising biodiversity, ecosystem functions, impacts and risk assessment, climate change and ecosystem conservation. 

Results showed conserving habitat-forming species such as corals, sponges, tube worms and bivalves was considered most important for conservation efforts. 

In line with that, the experts and authors were in mutual agreement that habitat damage needs to be monitored, considering grave concerns about the effects of bottom-contact fisheries and deep-sea mining.

Macro- and megafauna were top priority for survey respondents under biodiversity monitoring, while microorganisms were ranked medium to low priority.

The authors attribute this outcome to biased skillsets and themselves stress the importance of recognising microbial populations as critical contributors to food webs and biogeochemical cycles.

Other priorities included monitoring shifts in the depth ranges of different species as they respond to the effects of climate change, local extinctions and sediment contamination.

Surprisingly, marine pollution – of which 80% is plastics – was ranked low, a result the authors attribute to the erroneous assumption that large quantities of trash don’t reach the ocean’s depths.

Overall, Danovaro and colleagues note that deep-sea conservation approaches need to take a global perspective rather than focus on individual impacts, factoring in the snowballing effects of multiple stressors.

They suggest that adoption of these priorities by industry, government and non-government organisations could help protect and enable sustainable management of the planet’s precious underwater world.