Ocean squares are significant barriers to trade and travel until the discovery of Navigation or Magnetism.
Civilopedia Entry
The oceans and seas of the world cover almost three-quarters of our planet. They are home to millions of life forms ranging from microscopic plankton to whales, the largest mammals in the world. The animals and plants that inhabit the sea provide an excellent source of food. For centuries, coastal and island cultures have thrived on the resources and easy access to trade provided by the sea. Unfortunately, in many parts of the world, a combination of over-harvesting of marine animals and increased pollution has begun to threaten fragile coastal ecologies. Some species of marine life are seriously threatened. For example, the whaling industry, which thrived in the 19th and early 20th century, is responsible for hunting certain species of whales to near-extinction. Government regulations concerning the dumping of pollutants and the indiscriminate harvesting of marine life are constantly being updated in response to these growing problems.