John Chan / Western gull (Larus occidentalis) feeding on a California two-spot octopus (Octopus bimaculoides) on a mudflat at low tide, Southern California, USA, November.

Pedro Narra / Aerial view of low tide in Sado estuary, Portugal. November

Juergen Freund / Timelapse of the tide rising at Cape Leveque, with Mangroves (Rhizophora) in the foreground, Kimberley, Western Australia, 2016

Juergen Freund / Timelapse of the tide rising in a Mangrove (Rhizophora) forest, Daintree, Wet Tropics World Heritage Area, North Queensland, Australia.

Juergen Freund / Timelapse of Periwinkle snails (Littoraria) climbing up Mangrove (Rhizophora) roots at lowtide, Daintree, Wet Tropics World Heritage Area, North Queensland, Australia.

Seth Patterson / A compilation of items found washed up along a half mile stretch of the high tide line of South Padre Island, Texas. October 2016. Some of the plastic bottles and bags of signs of nip marks from hun...

Chris Gomersall / Large flock of Red knot (Calidris canutus) moving at high tide roost, in winter plumage, Snettisham RSPB Reserve, Norfolk, England, UK, September.

Guy Edwardes / St. Michael's Mount, Marazion, Cornwall, England, UK. September 2016.

Five Films / Aerial view of tide coming in on beach, Pembrokeshire, Wales, UK, January 2017.

Five Films / Aerial view of tide coming in on beach, Pembrokeshire, Wales, UK, January 2017.

John Waters / Large mixed flock of Knot (Calidris canutrus), Dunlin (Calidris alpina) and Golden plover (Pluvialis apricaria) in flight at high tide, Steart Marshes WWT Reserve, Somerset, England, UK, December.

Frederique Olivier / Group of Adelie penguins (Pygoscelis adeliae) swimming in a tide crack, lots jump out, Adelie Land, Antarctica, January.