The second edition of Marine Biology represents approximately a 15-20% difference from the first edition. There are a few major changes within some of the modules in order to update scientific information (for example, there is a more involved discussion on how tides are created). There are also several minor changes to the material in each module. Some of the experiments have been improved or altered for better explanation of concepts. Some have been removed or replaced to upgrade their quality. On Your Own questions, Module Summaries, Study Guides, and Tests have also been updated and slightly altered. A few questions have been replaced with new ones while others have been reworded or improved in their verbiage. Diagrams and photos have been updated or improved in their quality as well.