Marine ecosystems are complex habitats ranges from highly productive near-shore coastal habitats to the deep sea floor inhabited only by specialized organisms. They are important to humankind both ecologically and economically. Unfortunately, human activities are putting marine ecosystems under pressure across world. Worldwide deterioration of marine biodiversity call for Conservation Strategy to conserve the biodiversity which supports the sound structure and function of marine ecosystems to utilize ecological services of the ocean in a sustainable manner. A theme of this teaching manual is intended to provide the best coverage of the subject and comprehensive explanation about marine ecosystems, marine biodiversity and their conservation to students and researchers. To prepare this teaching manual we referred authenticated websites, scientific reports and textbooks. We hope this text could serve as a resource for students during their coursework as well as it may contribute towards the conservation of marine ecosystems.