27 October 2011 Cold temperatures are all part of the job

Working in temperatures considerably colder than any she had ever experienced in New Zealand became routine for Dr Victoria Metcalf when she spent several summers outdoors undertaking research in the frigid conditions of the Antarctic.

Dr Metcalf, from the Faculty of Agriculture and Life Sciences at Lincoln University, travelled to Scott Base teaming up with other New Zealand and international scientists to study the effect of decreasing pH levels in the Southern Ocean on the survival of the Antarctic bivalve (shellfish), Laternula elliptica.

After her team had collected the shellfish from the mud on the ocean floor Dr Metcalf and the team took them to Scott Base and raised them in purpose built indoor tanks filled with sea water from the local area. The shellfish were then brought back to a New Zealand facility where acidification scenarios were simulated and the effects on the them were analysed.
"As temperatures increase worldwide with more carbon dioxide in the atmosphere, more oceanic carbon dioxide absorption also occurs and the resulting increase in acidification may leave marine fauna less able to cope with other environmental stressors," said Dr Metcalf.

After taking a number of measurements from the shellfish and their environment the team discovered that how much oxygen the shellfish used changed depending on changes in the acidity of the water - lower pH levels meant the shellfish had to use more oxygen - a bit like how humans breathe more deeply when they walk up a hill.

They also confirmed that at pH 7.88 the shellfish had to work harder to calcify their shells in seawater that contained lowered calcium carbonate levels. Ocean waters are usually slightly alkaline at pH 8.20.

"These results are exciting because they show that the shell formation process for L. elliptica is under biological control (it responds to changes in the environment) and this may allow some degree of adaptation or acclimatisation to future changes in ocean acidification scenarios," said Dr Metcalf.

Ocean acidification occurs because of a decrease in pH (meaning the water becomes more acidic), caused by the uptake of carbon dioxide from the atmosphere forming carbonic acid. This means that shellfish find it more difficult to form their protective shells or they develop weakened shells. Organisms living in high latitude regions of the world such as the Arctic and Antarctic circles are affected because of the cold waters and naturally low calcium carbonate saturation levels.

Very little study has been done on the ability of marine organisms to acclimate to these changes.

Collecting the shellfish from the sea floor was a complex task. Two holes had to be drilled in the ice, one as an alternative exit in case the local seals got too curious and came up and blocked a hole. Then two team members encased in dry suits went down to the sea floor together (the buddy system) to collect the shellfish.

"It was challenging working in such low temperatures day after day," said Dr Metcalf. "I felt quite sorry for the guys who had to work in such cold water temperatures."

This project was funded by a subcontract from NIWA as part of the ICE-CUBE FRST IPY project with logistical support provided by Antarctica NZ.