Macroalgae, plants and animals like corals and sponges create complex habitats that provide resources, shelter and nursery grounds for many marine organisms.
Marine forests of seaweeds are mainly formed by large brown algae (not plants) such as kelp or fucoids, but also by red and green algae.
Seagrasses are plants that evolved and adapted to live in the sea. They have roots, leafs and produce flowers and fruits.
Marine animal forests are mostly formed by invertebrates that live attached to rock, such as coral reefs and gorgonian gardens.