Marine Ecosystem: This is a type of aquatic environment that is based in salty waters such as oceans and seas. It's home to a diverse range of species including fish, mammals like whales and dolphins, birds like penguins and seagulls, reptiles like sea turtles, invertebrates like jellyfish and octopus.
Freshwater Ecosystem: This is another type of aquatic environment found in bodies of fresh water such as lakes or rivers. They are home to organisms such as fish species adapted for freshwater living conditions.
Aquatic Biome: A larger classification that includes all water-based ecosystems on Earth. It's divided into two main groups - marine biomes (oceans) and freshwater biomes (lakes & rivers).