Paul Souders/ Worldfoto / Red algae and salt formations, Lake Natron, Ol Doinyo Lengai, Tanzania

Tom Gilks / Zanzibari woman at low tide with harvested seaweed (eucheuma spinosum) Matemwe, Zanzibar, Tanzania

Sven Zacek,Sven Zacek / Fresh snow and ice on Baltic Sea coast. The red colour comes from seaweed beneath the ice. Baltic sea coast, Northern Estonia, December 2012.

Linda Pitkin / 2020VISION / Spiny spider crab (Maja brachydactyla / squinado) pair on rock covered with red algae, Lundy Island Marine Conservation Zone, Devon, England, UK, May.

Linda Pitkin / 2020VISION / Tube worms (Bispira volutacornis) living between rocks covered in Crustose coralline (Corallinaceae) and red algae (Rhodophyceae), Lundy Island Marine Conservation Zone, Devon, England, UK, May.

Daniel Heuclin / 'Laguna Colorada' or 'Red Lagoon' with mountains beyond. The colouration is due to both sediments and red-algae. Eduardo Avaroa national reserve, Bolivian altiplano at 4780 m.

Alex Mustard / 2020VISION / Common / Red sunstar (Crossaster papposus) amongst Dead man's fingers (Alcyonium digitatum) on a rocky reef, beneath kelp. Shetland Islands, Scotland, UK, June.

Michel Roggo / Underwater landscape in peat pond, Fribourg, Switzerland, August

Michel Roggo / Underwater landscape in peat pond, Fribourg, Switzerland, August

Wild Wonders of Europe / Lundgren / Kelp with Common / Red sunstar (Crossaster papposus) and shells, Moere coastline, Norway, February 2009

Tim Laman / Split level of Spotted sea hare {Aplysia dactylomela} on root of Red mangrove tree {Rhizophora mangle} where it was grazing on algae. Tunicate Cove, Belize.

Jack Dykinga / Red algae on seeps along stream, Death Hollow, Grand Staircase-Escalante National Monument, Utah, USA