The sea is the largest habitat on Earth. Here, the evolution of organisms began, and it is also where the greatest diversity of organismal designs can be found. Presented in a learner-friendly format and written in an easily understandable manner, this textbook provides a fundamental and comprehensive overview of the various habitats and communities of the sea. Ecological processes such as competition, predation, symbiosis, and food webs are central themes. Numerous illustrations encourage reading and learning.