Since we will have oceans and waterways that attach to mainland that surely has lakes and rivers, it would make sense to have brackish water ecosystems in the areas where ocean water and fresh water meet. Saltwater swamps, tidal pools, wetlands, marshes and salty mudflats have many interesting flora and fauna.
for animals there is Mudskippers, Alligators, Shrimp, Gobies, Clams, Fiddler Crabs
for plants there is Sea Asparagus, Mangrove Trees, Dulse, Sea Lavender
probably tons more too, just thought it would be a cool new little group of biomes