Data collected from more than 30,000 samples has so far shown that levels of PAHs (Polycyclic Aromatic Hydrocarbons) from Rena oil appear to have dissipated in most areas in the Bay of Plenty.
However scientists say there is still a significant amount of work to be done before any final conclusions on long-term environmental impacts can be made; this includes more sample information to be collected from Astrolabe Reef (Otaiti).
Professor Chris Battershill, Waikato University Coastal Chair who is overseeing the Rena Recovery monitoring programme, said there are still thousands of samples expected to be collected and tested over the coming months to provide a full picture of any long-term effects from the Rena grounding in October 2011.
Samples of kaimoana species including tuatua, pipi, p?ua, kina, crabs and cockles have been tested from along the Bay of Plenty coastline including the east coast and from offshore islands to gain full coverage of the region.
"We want to be able to get a full picture of how the environment has been affected and pinpoint exactly what impacts are from the Rena grounding," Professor Battershill said.
"Shellfish are a key focus because they are one of the biggest concerns for the community. They are also a good indicator of water quality because they sit on the sea floor and act as a filter. If there are contaminants in the water it is likely you would trace these in common shellfish."
Professor Battershill said that it is important to note that these results are just the first pieces in the puzzle.
"It is important to understand that we need to process a large amount of data to make a complete analysis of the situation," he said.
The long-term environmental recovery monitoring programme is being overseen by Professor Chris Battershill of Waikato University and Professor David Schiel of Canterbury University who will present an overview to the public tonight [Thursday 11 October]. The programme involves sampling and monitoring of rocky shore and sandy coastline marine communities as well as offshore reef systems including Astrolabe Reef (Otaiti), where the Rena is lodged.
The Rena Long-Term Environmental Recovery Plan is nearly one-third of the way towards completion. The multi-disciplinary partnership between four New Zealand tertiary institutes, iwi and a large contingent of other stakeholders is a unique aspect of this programme. The forthcoming summer programme involves dozens of students, volunteers and iwi-based projects to better understand recovery and on-going effects.
Professor Schiel said that while they would like to be able to give the community final results one year on, it is important to complete the sampling and tests over the summer period to gain a true understanding of the state of the environment.
"However, we want to make sure we keep people informed while we continue our work, and that is why we are giving this update today," Professor Schiel said.
Following are the key discoveries from data sampled as at 11 October 2012.
One of the key priorities of sampling has been to identify contamination of edible seafood by PAHs (Polycyclic Aromatic Hydrocarbons) from Rena oil. The chemical tests for PAHs are very sensitive and can detect nanograms (billionths of a gram), so finding PAHs at low levels does not necessarily indicate toxicity to humans. There were elevated levels of PAHs in some species immediately after the oil spill. From the samples taken so far, PAHs appear to have dissipated over the past year in most areas.
We know that a wide range of coastal species, including kaimoana and animals resident on the sea shore, have been exposed to Rena oil, but we are pleased to see that most have survived and now show little or no evidence of residual PAHs.
Juveniles of some kaimoana species are reduced in some areas we have sampled. Because there is large seasonal variation in many species, this reduction in numbers is not proven to be caused by Rena oil but we are doing continued investigations to be able to make a conclusive judgement.
To determine the maximum effects on marine communities, we focussed some studies on intertidal rocky reefs that had been heavily fouled by oil. Up to 20 percent mortality was experienced by mussels and some other attached organisms; areas are being monitored over the next several months to determine if there is full recovery.
Because of the extent of the oil across the ecosystem, there is potential for sub-lethal effects on reproduction and population dynamics of many species. To resolve this, ecotoxicological assays will be done over the summer months.
Astrolabe Reef itself has been impacted by the Rena and its cargo. Considerably more work will need to be done over the next several months to determine the full extent of environmental damage and recovery there and in the surrounding area, which has had limited access because of the salvage operation.
Already more than 30,000 tuatua have been collected and measured, with representative samples from throughout the Bay analysed for PAH and heavy metals content; more than 1,000 specimens across most relevant kaimoana species have been collected to date for contaminant chemistry tests, and more than 100 cubic meters of sand has been sieved and processed as part of the sampling programme. All this is now being repeated for the spring seasonal survey.
Please note: There is currently a shellfish toxin warning in the Bay of Plenty regarding a separate issue of Paralytic Shellfish Poisoning (PSP). People should take note of the areas that still contain high levels of paralytic shellfish poison and avoid collecting shellfish in these areas.