Monterey Bay Aquarium employed over 500 people and had 1,200 active volunteers in 2015. Between 1984 and 2014, 8,500 volunteers donated 3.2 million community service hours. The aquarium attracts around 2 million visitors each year and, through 2016, over 50 million people had visited. Out of the 51 accredited public aquariums in the United States in 2015, Monterey Bay Aquariums 2.08 million visitors ranked it second by number of visits, behind Georgia Aquariums 2.2 million. In 2015, it served 290,000 annual members.

Answer this question based on the article: How many more volunteers were there in 2015 compared to employees?
700