A species is a group of individuals sharing some common characteristics or qualities, and whose offspring also share those characteristics or qualities. All species are specially suited for the lives they lead. An adaptation is a behavioral, structural, or physiological trait that increases a species’ chance of survival in a specific environment. Every living thing has adapted to fit with where it lives. That’s what it takes for life to survive. Aquatic organisms live in water and have adaptations to do so. This chapter talks about life in water and aquatic ecosystems by fish, aquatic invertebrates, zooplankton, phytoplankton, aquatic plants, and algae in freshwater, estuaries, and the ocean, which in Texas is called the Gulf of Mexico.