New Zealand spilled oil could not disappear quickly, and it will affect the aquatic environment and lift cycle of the marine ecosystem for a certain period of time, an Australian expert said on Tuesday local time. A cargo ship, Rena, struck a New Zealand reef and has been spilling around 50 tonnes of oil into the Bay of Plenty, North Island of New Zealand since Wednesday. New Zealand maritime authorities said on Monday \"fist-sized patties\" of oil have washed up on New Zealand\'s Mt. Maunganui beach and tonnes more expected to land on the Bay of Plenty beaches further south. Professor Ravi Naidu, managing director of the Co-operative Research Center For Contamination Assessment and Remediation of the Environment in South Australia, said the spilled oil will not disappear quickly, and it could impact on the sensitive aquatic environment and life cycle of the marine ecosystem for a while. \"There are volatile hydrocarbons in the oil which will disperse but the oil which is not removed will continue to have an effect,\" he said in an email note to Xinhua on Tuesday. \"There will be some natural remediation by microbes in the coastal environment, but it may be found that these are not as active as they are in warmer tropical waters. \"Oil which is bound to organic matter in the sediments may be the easiest to break down -- the wave action will be an advantage. \" New Zealand authorities said nine birds, including seven little blue penguins and two shags, had been rescued by wildlife response teams, and reports of oil-slicked seals are being investigated. An Australian oil recovery team of 10 has arrived in New Zealand to help local authorities deal with the incident.