On September 11th, 2020, 1-2 PM UTC, we dived in the marvellous underwater worlds with Sergio Rossi, Associate Professor at the DiSTeBA (Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali) at the Università del Salento and Visiting Professor at the Universidade Federal do Ceará. He talked about Marine Forests and their Role in the Oceans. The moderator was Eduardo Pereira, Assistant Professor at the University of Minho and a member of IB-S (Institute for Bio-sustainability) and ISISE (Institute for Sustainability and Innovation in Structural Engineering). What is an engineer? A person that solves problems for the community, giving tools and services that improve our lives. A tree or a coral are ecosystem engineering species, they benefit the community, and give also essential ecosystem services to the humans. In the case of the forests of the sea (Marine Forests - MFs): kelp forests, seagrasses, coral reefs, sponge grounds, gorgonian forests, hydrothermal vent associated fauna, etc.) their role is giving shelter and food to other species, promote the reproduction and life cycles of many organisms, transform the hydrodynamics and recycle nutrients, immobilize carbon and promote the biomass of fisheries, create physical barriers against wave action and be biodiversity hotspots…they enhance complexity and functionality that is essential for a healthy community in the benthos and also in the plankton.