Alex Mustard / Portrait of a male short snouted seahorse (Hippocampus hippocampus) in sea oak seaweed (Halidrys siliquosa). Devon, England, United Kingdom. British Isles. English Channel. North East Atlantic Ocean.

Pete Oxford / Broadleaf Gulfweed (Sargassum fluitans) floating mat, Ambergris Caye, Belize

Solvin Zankl / Tiny crab on Broad-toothed Gulfweed (Sargassum fluitans) Sargassum Community. Sargasso Sea, Bermuda

Alex Mustard / A raft of sargasso weed (Sargassum natans) in open ocean. Off shore, Grand Cayman, Cayman Islands, British West Indies. Caribbean Sea.

Tony Wu / Korean sandlance (Hypoptychus dybowskii) egg clusters on Sargassum (Sargassum horneri). Fish produce sticky secretion in kidneys that adheres eggs to Sargassum. Hokkaido, Japan. May.

Gary Bell/ Oceanwide / Seaweed (Scaberia agardhii), Yorke Peninsula, South Australia, Australia

Nick Upton / Japanese wireweed (Sargassum muticum), invasive non-native species in Atlantic Ocean. Cornwall, England, UK. September.

Nick Upton / Japanese wireweed (Sargassum muticum), invasive non-native species in Atlantic Ocean. Cornwall, England, UK. September.

Nick Upton / Brown tuning fork / Brown forking weed (Bifurcaria bifurcata) from Atlantic Ocean. Cornwall, England, UK. September.

Nick Upton / Japanese wireweed (Sargassum muticum), invasive non-native species in Atlantic Ocean. Cornwall, England, UK. September.

Robin Chittenden / Japanese Wireweed (Sargassum muticum) in rock pool, Isle of Wight, Hampshire, UK August

Solvin Zankl / Algae scientist studying invasive Japanese wireweed (Sargassum muticum) Norway, May 2015.