Dr. Ryota Nakajima

A biological oceanographer

What happens after drilling the deep-sea floor?

Ryota and his team monitored the benthic ecosystem at 1,060 m depth of hydrothermally active areas in the Okinawa Trough, off Japan, where a scientific drilling by the Deep Sea Scientific Drilling Vessel Chikyu was performed on September 2010.

This monitoring was started before the drilling operation and lasted 40 months thereafter.

As a result, it led to elucidate impacts of variation in deep-sea habitats on hydrothermal vent communities.

Prior to drilling, the seabed was covered by soft silty sediment, where Calyptogena clam colonies dominated.

After the drilling operation, the clam colonies were completely buried under the drilling deposits.

Then, at 11 months after the drilling, drilling-induced hydrothermal fluid discharges and numerous tiny chimneys were observed on the seafloor.

In addition, benthos communities on the artificial hydrothermal vent fields occupied by Shinkaia crosnieri galatheid crabs were also found.

It is presumed that they have been migrated from the nearby habitats.

The previously soft sediment had hardened probably due to chemical reaction of fluid composition, becoming rough and undulated with many fissures after 25 months of the drilling operation.

The image shows how a new ecosystem is formed around the hydrothermal vent areas.

 

Nakajima R, Yamamoto H, Kawagucci S, Takaya Y, Nozaki T, Chen C, Fujikura K, Miwa T, Takai K (2015) Post-drilling change in seabed landscape and megabenthos in a deep-sea hydrothermal system, the Iheya North field, Okinawa Trough. PLoS ONE 10: e0123095.

The first multi-hectare scale 3D survey of a deep-sea vent community

Blair Thornton and his colleagues investigated the distribution of megabenthos over multi-hectare regions (2.5 ha) of the seafloor of a deep-sea hydrothermal vent site off Japan for the first time.

The study region was the target of scientific drilling during the IODP Expedition 331 in 2010.

The research team surveyed biomass of megabenthos using high- and low-resolution 3D image reconstructions (it goes with Blair Scan) 3 years and 4 months after the site was drilled.

They found more than 100,000 organisms from 6 taxa. The study showed the biomass of the drilled site was lower than observed in nearby naturally discharging areas.

 

Thornton B, Bodenmann A, Pizarro O, Williams SB, Friedman A,  Nakajima R, Takai K, Motoki K, Watsuji T, Hirayama H, Matsui Y, Watanabe H, Ura T (2016) Biometric assessment of deep-sea vent megabenthic communities using multi-resolution 3D image reconstructions. Deep Sea Research I 116: 200-219.