Many of the cities’ histories included being ports for transportation and the shipping industry. As well, many of the cities had, and currently have, fishing industries. Over time, the cities’ populations grew to be over 10 million. Today, the major industries of coast mega-cities are; shipping, resource extraction (in many cases, fishing), and tourism. Common problems for coastal cities include; flooding due to rising sea levels and/or tsunamis which may be caused by earthquakes, and erosion of the coastline. These current problems are also potential future problems for coastal cities.