A new report on the effects of oil pollution from the Rena's grounding has shown few long-lasting impacts on Bay of Plenty maritime habitats, but the environment has not yet returned to its pre-Rena state.
The 460-page report covers the first two years of ongoing survey and research work, and details one of the most comprehensive, multi-disciplinary studies ever undertaken in response to a marine pollution incident.
University of Waikato's chair in coastal science Professor Chris Battershill said initial concerns that oil would have a long-lasting and negative impact on beaches and fisheries could mostly be put to rest.
"While there is still some evidence from time to time of heightened Rena-sourced contaminant levels in kaimoana species on some of the beaches, and northern parts of Motiti, the vast majority of kaimoana and other species have survived, and no evidence has been found of any catastrophic die-off," he said.
The report covered the immediate and medium-term environmental response to the incident, and did not aim to give a comprehensive assessment of the long-term environmental effects, or provide a complete assessment of the "myriad complex interactions" surrounding the Rena grounding, he said.
These assessments would be planned over the coming months, on top of ongoing postgraduate research work initiated by the first phase of monitoring.
"It will be prudent to continue to monitor key locations affected by tar balls and other debris over the next year to pick up any longer-term trends," he said.
"We also want to assess what impact the re-exposure to pollutants is having on kaimoana and other species."
In other findings based on laboratory studies done within the project, the impact of heavy fuel oil and the dispersant Corexit on juvenile finfish such as kingfish and flounder, showed effects at higher exposures.
However as the dispersant was used only briefly on the oil spill at sea, and given the strong offshore wind conditions at the time, there were no environmental effects, he said.
There was now little evidence of remaining oil or tarballs around the Bay of Plenty's coast, and oil washed up on rocky reefs has largely disappeared.
"Very little oil residue has been found in coastal beach sediment cores, which sample deeper down into the beach sands. However, some oil and other debris from the shipwreck and containers continue to wash ashore during storms."
The results back up what scientists suspected when early test findings were released on the first anniversary of the grounding.
At that time, 30,000 samples had shown that levels of PAHs (Polycyclic Aromatic Hydrocarbons) had dissipated in most areas of the Bay of Plenty.
- By Jamie Morton of the New Zealand Herald
