Alex Mustard / RF - Grey seal (Halichoerus grypus) relaxing in a bed of kelp (Laminaria digitata), with two seals in the background. Farne Islands, Northumberland, England, United Kingdom. British Isles. North Sea....

Tony Wu / Female Northern pygmy squid (Idiosepius paradoxus) depositing eggs on a blade of eelgrass (Zostera marina), Yamaguchi Prefecture, Japan.

Tony Wu / Female Northern pygmy squid (Idiosepius paradoxus) preparing to lay another egg on a blade of eelgrass (Zostera marina), Yamaguchi Prefecture, Japan.

Nick Garbutt / Adult humpback whale (Megaptera novaeangliae) diving in deep water channel. Great Bear Rainforest, British Columbia, Canada. COP26 Countdown Photo Competition 2021 Finalist. (digitally stitched image)

Andy Murch / Spiny dogfish (Squalus acanthias) portrait. Rhode Island, New England, USA. August.

Andy Murch / Red stingray (Hemitrygon akajei) with Banded houndshark (Triakis scyllium) group and smaller fish in background. Chiba Prefecture, Honshu, Japan. September.

Andy Murch / Pyjama shark (Poroderma africanum), two in reef, amongst kelp. Simon's Town, Western Cape, South Africa. May.

Andy Murch / Happy Eddy (Haploblepharus edwardsii) amongst Cape sea urchin (Parechinus angulosus) and starfish. False Bay, Western Cape, South Africa. June.

Andy Murch / Cape fur seal (Arctocephalus pusillus) playing with Dark shyshark (Haploblepharus pictus) carcass, seal diving in background. False Bay, South Africa. May.

Andy Murch / Banded houndshark (Triakis scyllium) group above sea floor. Chiba Prefecture, Honshu, Japan. October.

Shane Gross / Cunner (Tautogolabrus adspersus) pair in Eelgrass (Zostera marina) bed. Newfoundland, Canada. September.

Erlend Haarberg / White wagtail (Motacilla alba) reflected in water. Pasvik, Norway. May.

Tony Wu / Male Korean seahorse (Hippocampus haema) giving birth. Kumamoto Prefecture, Kyushu, Japan.

Danny Green / Sea otter (Enhydra lutris) female and pup playing. Alaska, USA, February.

Danny Green / Sea otter (Enhydra lutris) female and pup. Alaska, USA, February.

Brandon Cole / Orca whale (Orcinus orca) spyhopping, British Columbia, Canada, Pacific Ocean.

Brandon Cole / Orca whales (Orcinus orca), three adult male resident killer whales travelling together at sunset. British Columbia, Canada, Pacific Ocean.

Sergio Hanquet / Wide-eyed flounder (Bothus podas) portrait showing eyes above head, Tenerife, Canary Islands.

Sergio Hanquet / Commonstingray (Dasyatis pastinaca ) on sea floor, Tenerife, Canary Islands.

Sergio Hanquet / Pilot whale (Globicephala macorhynchus) close-up of submerged adult. Tenerife, Canary Islands.

Sergio Hanquet / Yellowfin tuna (Thunnus albacares) hunting mackerel (Scomber colias) Tenerife, Canary Islands.

Sergio Hanquet / Atlantic spotted dolphin (Stenella frontalis) juvenile porpoising, Tenerife, Canary Islands.

Sergio Hanquet / Atlantic spotted dolphin (Stenella frontalis) adult and juvenile near surface. Tenerife, Canary Islands.

Sergio Hanquet / Atlantic spotted dolphin (Stenella frontalis) juvenile porpoising, with pod, Tenerife, Canary Islands.

Nick Hawkins / Atlantic sturgeon (Acipenser sturio), Minas Basin of the Bay of Fundy, Canada. July 2019.

Nick Hawkins / American white water-lily (Nymphaea odorata) growing, St. Mary's river, Nova Scotia, Canada. July.

Nick Hawkins / Common shiners (Luxilus cornutus) school below lilly pads in lake, Nova Scotia, Canada. July.

Nick Hawkins / Head of a North Atlantic right whale (Eubalaena glacialis) emerges from the water, Gulf of Saint Lawrence, Canada. July.

Nick Hawkins / Tail of a North Atlantic right whale (Eubalaena glacialis) as it dives, Gulf of Saint Lawrence, Canada. July 2019. IUCN Status: Endangered.

David Hall / Steller sea lions (Eumetopias jubatus), three playing underwater, Inian Island, Alaska, USA. August.

David Hall / Steller sea lions (Eumetopias jubatus) playing underwater, Inian Island, Alaska, USA. August.

David Hall / Split-level of Cormorants (Phalacrocorax sp.) standing on rocks with Sea lettuce (Ulva sp.) seen underwater, Hussar Bay, Nigei Island, Queen Charlotte Strait, British Columbia, Canada. September.

David Hall / Fried Egg Jellyfish (Phacellophora camtschatica) viewed from below; Browning Pass, Queen Charlotte Strait, British Columbia, Canada. September.

David Hall / A Giant rock scallop (Crassadoma gigantea) encrusted with and surrounded by several other invertebrates, including White anemones (Metridium sp.), White mushroom ascidians (Distaplia sp.), Red soft co...

David Hall / Harbor seal (Phoca vitulina) using a large,encrusted boulder as a tool to scratch itself against, Gowland Harbour, Quadra Island, British Columbia, Canada. March.

David Hall / Split level of a Lion's mane Jellyfish (Cyanea capillata) and Feather-boa kelp (Egregia menziesii), Seven-tree Island, Browning Pass, Queen Charlotte Strait, British Columbia, Canada. September.

David Hall / Split level of a Sockeye salmon (Oncorhynchus nerka) in shallow water; Adams River, British Columbia, Canada. October.

David Hall / Split level of Sockeye salmon (Oncorhynchus nerka) during migration; Adams River, British Columbia, Canada. October.

David Hall / Sockeye salmon (Oncorhynchus nerka) migration, Adams River, British Columbia, Canada. October.

David Hall / Sockeye salmon (Oncorhynchus nerka) migration, Adams River, British Columbia, Canada. October.

David Hall / Crimson anemone (Cribrinopsis fernaldi) with Candy-striped shrimps (Lebbeus grandimanus) living symbiotically. Browning Pass, Queen Charlotte Strait, British Columbia, Canada. September.

David Hall / Candy stripe shrimp (Lebbeus grandimanus), a commensal species that associates with crimson sea anemones. Browning Pass, Queen Charlotte Strait, British Columbia, Canada. September.

Franco Banfi / Tiger moray / Fangtooth Moray (Enchelycore anatina), South Tenerife, Canary Islands, Atlantic Ocean.

Franco Banfi / Tiger moray / Fangtooth Moray (Enchelycore anatina) and Black moray eel (Muraena augusti), South Tenerife, Canary Islands, Atlantic Ocean.

Franco Banfi / Bull ray (Pteromylaeus bovinus), South Tenerife, Canary Islands, Atlantic Ocean.

Franco Banfi / Green turtle (Chelonia mydas), South Tenerife, Canary Islands, Atlantic Ocean.

Franco Banfi / Bull ray (Pteromylaeus bovinus), South Tenerife, Canary Islands, Atlantic Ocean.

Franco Banfi / Short-finned pilot whale (Globicephala macrorhynchus) female carrying dead calf, South Tenerife, Canary Islands, Atlantic Ocean. Runner-up in Underwater Worlds category of MontPhoto competition 2020.