Gary Bell/ Oceanwide / Kelp holdfasts, Governor Island Marine Reserve, Bicheno, Tasmania, Australia

Nick Hawkins / View of stipe and holdfast of sugar kelp (Saccharina latissima) off Nova Scotia, Canada. September

Olga Kamenskaya / Kelp holdfast attached to rock, underwater, Svalbard, Norway, September.

Adrian Davies / Seaweed (Laminaria sp) holdfast on pebble, Isle of Wight, Hampshire, UK January

Norbert Wu / Giant Kelp (Macrocystis pyrifera) holdfasts, California

Richard Robinson / Bull kelp (Durvillaea antarctica) underwater showing holdfast, Dusky Sound, Fiordland National Park, New Zealand. April 2014.

MYN / Sheri Mandel / Holdfast, Malibu, California, USA, March, meetyourneighbours.net project

Sue Daly / Furbellows holdfast (Saccorhiza polyschides) English Channel, off the coast of Sark, Channel Islands, August

Sue Daly / Furbellows holdfast (Saccorhiza polyschides) English Channel, off the coast of Sark, Channel Islands, August

Nick Upton / Bulbous holdfast and large spreading frond of Furbellows (Saccorhiza polyschides), a large kelp, attached to rocks very low on the shore alongside Thongweed (Himanthalia elongata) and Tangleweed kelp...

Nick Upton / Holdfast of Tangleweed kelp (Laminaria digitata) fronds attached to rocks exposed on a low spring tide alongside Toothed wrack (Fucus serratus), North Berwick, East Lothian, UK, July.

Philippe Clement / Bulbous holdfast of Furbellow kelp (Saccorhiza polyschides) washed ashore on rocky beach. Brittany, France.

Philippe Clement / Bulbous holdfast of Furbellow kelp (Saccorhiza polyschides) washed ashore on rocky beach. Brittany, France.

Jeff Rotman / Giant Kelp (Macrocystis pyrifera) holdfast / haptera with Brittle Stars. Channel Islands, USA, Pacific Ocean.

GEORGETTE DOUWMA / Giant kelp holdfast (Macrocystis pyrifera) California, USA.

Nick Upton / Close up of holdfast and branching fronds of Velvet horn / Spongeweed (Codium tomentosum) growing on rocks low on the shore, Wembury, Devon, UK, August.

Nick Upton / Bulbous holdfast and divided frond of Furbellows (Saccorhiza polyschides), a large kelp, attached to floor of a rockpool alongside red algae: Harpoon weed (Asparagopsis armata) and Coralweed (Corallin...

Nick Upton / Bulbous holdfast of Furbellows (Saccorhiza polyschides), a large kelp, attached to rocks very low on the shore alongside Thongweed (Himanthalia elongata) and Tangleweed kelp (Laminaria digitata), near...

Nick Upton / Bulbous holdfast and large spreading frond of Furbellows (Saccorhiza polyschides), a large kelp, attached to rocks very low on the shore alongside Thongweed (Himanthalia elongata) and Tangleweed kelp...

Nick Upton / Bulbous holdfast of Furbellows (Saccorhiza polyschides), a large kelp, attached to a boulder low on a rocky shore alongside Sea lettuce (Ulva lactuca) and red algae, near Falmouth, Cornwall, UK, Augus...

Colin Monteath / Kelp holdfasts bleached and weathered on beach, Kaikoura, North Canterbury, New Zealand

Ashley Cooper / Lichen covered rock. Mist Rocks, Holdfast Point, Pernik Peninsula, Lallemand Fjord, Antarctica. January.