Nick Upton / Velvet swimming crab (Necora puber) in a rock pool, hiding among Coralweed (Corallina officinalis), Cornwall, UK, March.

Nick Upton / Strawberry anemone (Actinia fragracea) in a rock pool alongside Coralweed (Corallina officinalis), Cornwall, UK, March.

Nick Upton / Common shore crab (Carcinus maenas) hiding among Coralweed (Corallina officinalis) in a rock pool, Cornwall, UK, March.

Nick Upton / Coralweed (Corallina officinalis) from Atlantic Ocean. Cornwall, England, UK. September.

Sue Daly / Maerl (Phymatolithon calcareum) Jersey, British Channel Islands, June.

Nick Upton / Close up of Coralline crust (Lithophyllum tortuosum) an encrusting coralline red algae growing on intertidal rocks exposed at low tide, Asturias, Spain, August.

SCOTLAND: The Big Picture / Common whelk (Buccinum undatum) on maerl (Corallinales) bed, a priority marine feature. Within a Marine Protected Area, Shetland, Scotland, UK, September.

SCOTLAND: The Big Picture / Maerl (Corallinales) and Sea grass (Zostera marina) beds, Orkney, Scotland, UK, January.

SCOTLAND: The Big Picture / Maerl (Corallinales) and Sea grass (Zostera marina) beds, Orkney, Scotland, UK, January.

Philippe Clement / Common Coral Weed / Coralweed (Corallina officinalis) washed ashore on beach, Normandy, France. September

Alex Hyde / Claigan 'coral beach', the beaches are not actually coral, but formed from bleached skeletons of a red coraline seaweed (Lithothamnion corallioides) known as maerl. Claigan, Isle of Skye, Inner Hebrid...

Alex Hyde / Close up of Claigan 'coral beach'. The beaches are not actually coral, but formed from bleached skeletons of a red coraline seaweed (Lithothamnion corallioides) known as maerl. Claigan, Isle of Skye,...

MYN / Carsten Krieger / Common Limpet (Patella vulgata) with Red Alga (Corallina sp) County Clare, Republic of Ireland, December. Meetyourneighbours.net project

MYN / Sheri Mandel / Coralline algae (Corallinales spp.), Malibu, California, USA, February, meetyourneighbours.net project

Franco Banfi / Neptune grass (Posidonia oceanica) with flower, and encrusting algae, Ischia Island, Italy, Tyrrhenian Sea, Mediterranean

Alex Mustard / Wrinkled swimming crab (Liocarcinus corrugatus) displaying its claws on a Maerl (Phymatolithon calcareum) bed, Fal River Estuary, Cornwall, UK.

Alex Mustard / Edible crab (Cancer pagurus) foraging on a Maerl (Phymatolithon calcareum) bed, Fal River estuary, Cornwall, UK.