A myriad of hard and soft corals compete for space on the substrate of the snorkel site known as the Milky Way, Palau, Micronesia, Pacific

Snorkeller dives down to observe the substrate, St. Peter and St. Paul's rocks, Brazil, South America

Small Tube Worm (Pomatocerous triqueter), group of tiny colourful individuals on rocky substrate, St Abbs, Scotland, UK North Sea

Underwater substrate, St. Peter and St. Paul's rocks, Brazil, South America

Underwater substrate, St. Peter and St. Paul's rocks, Brazil, South America

Underwater substrate, St. Peter and St. Paul's rocks, Brazil, South America

Split image of rocks and underwater substrate, St. Peter and St. Paul's rocks, Brazil, South America

Rocky substrate, in the first few meters below the surface of the ocean. Volcanic underwater bottoms. La Gomera, Canary Islands.