There are so many fascinating things to love about octopuses: they have three hearts,¹ quick-camouflage color-changing skin,² and enormous brains (by invertebrate standards)³ with two-thirds of their neurons found in their arms.⁴ Like squids, cuttlefish, and nautiluses, octopuses are cephalopods, a diverse group of mollusks that evolved over 500 million years ago.⁵ There are nearly 300 species of octopuses,⁶ ranging in size from the Giant Pacific Octopus, with an arm span of 45 feet (14 meters),⁷ to the tiny Octopus wolfi, which measures about one inch (2.5 cm) long.⁸ Although they are most common in tropical waters,⁹ these solitary creatures are found in all of the world’s oceans.¹⁰ Octopuses, like many of their marine neighbors, are placed at risk by the pollution, overfishing and habitat destruction.¹¹ Research also indicates that octopuses may be injured by underwater noise pollution, from sources like offshore drilling and sonar.¹²

Jellyfish, otherworldly and dreamlike, are reminders of the incredible forms life takes in our oceans. Earth’s waters have been host to jellyfish for at least 500 million years, and today there are nearly 4,000 identified species of jellies.¹ While so many marine creatures stand to be lost during the sixth mass extinction, certain adaptable jellyfish species are flourishing in polluted, oxygen-deprived, and warming waters, with less fear of predation and supplies of zooplankton made more plentiful by overfishing.² Jellyfish ‘blooms’ or ‘outbreaks’ are symptoms of an ocean desperately out of balance, beautiful and haunting reminders that so much needs to be done to preserve the biodiversity of all ocean life.

Syngnathidae is a family of bony fishes that includes seahorses, seadragons, pipefish, and pipehorses.¹ These small, charismatic creatures are important symbols of healthy ocean ecosystems, and they are disappearing. Each year, millions are swept up in trawl nets as bycatch,² and millions more are traded illegally for use in traditional medicine and as dried curiosities in souvenir shops.³ Development, pollution, agricultural fertilizer runoff, and ocean warming driven by the climate crisis are all making life untenable for those that evade capture.⁴ By protecting our marine waters, and supporting the work of organizations like Project Seahorse, The Seahorse Trust, and the IUCN SSC Seahorse, Pipefish, and Seadragon Specialist Group, we can preserve these incredible ocean jewels, and the ecosystems they call home, for generations to come.

“To look at the surface of the ocean without knowing the sparkling web of life that is woven through its depths is to be blind to its wonders and the part it plays in making our existence possible.” - Edith Widder, Ph.D., from her book Below the Edge of Darkness

Ninety-five percent of Earth’s living space is found below the surface of the ocean, a realm that remains largely unexplored. In the tiny fraction of seafloor that has been mapped, curious humans have discovered delightfully alien habitats: hydrothermal vents spewing mineral-rich clouds,¹ the rocky base of an underwater mountain cradling an octopus nursery,² and deep sea coral reefs, never touched by sunlight, filtering food from the darkness.³ Above the seafloor, the water column bristles with life: from the “twilight” mesopelagic zone, beginning at 650 feet (200 m), through the “midnight” bathypelagic zone and the “abyssal” abyssopelagic zone, down to the deepest zone of all: the hadalpelagic zone, which extends all the way to the bottom of the Mariana Trench, at a depth of 36,070 feet (10,994 m). Every layer of the ocean plays host to its own particular cast of deep sea characters specially adapted to the light, temperature and pressure of their aquatic home.⁴ The majority of these creatures have yet to be seen by human eyes; estimates from the late aughts placed the number of yet-to-be-discovered deep sea species between 10 and 30 million.⁵

This world, seemingly so far from our own, has nonetheless suffered the deleterious impacts of over-consumption. Plastic has made it to the deep ocean, in the form of heavily-concentrated micro plastics⁶,⁷ and garbage; a plastic bag was even found in the Mariana Trench. Here, researchers discovered that crabs were intensely contaminated with pollutants like PCBs.⁸ Deep-sea trawl nets rip a devastating,⁹ and staggeringly underreported,¹⁰ number of fish from our oceans, causing a cascade of effects through ocean food webs, and a greed-fueled race for new deep-sea mining projects poses untold risks to deep sea habitats.¹¹ It would be an unbelievable tragedy to lose the magic of the deep sea and its unmatched, unknown, biodiversity. Hope can be found in the passionate work of the scientific community. Innovative research and compelling education work by MBARI (whose incredible deep sea footage inspired many of the creatures in the 'Deep Sea' print), the Schmidt Ocean Institute, and the Ocean Exploration Trust's Nautilus Exploration Program, are all helping to connect the public with the wonders of the deep sea.

Over 3,000 species of nudibranchs¹ are found across the world’s oceans, appearing with special abundance in the shallow, tropical waters of the Indo-Pacific. These cheerfully colored sea slugs are predatory, using their sensitive, antennae-like rhinophores to track down prey species: sponges, anemones, corals, barnacles, and even their fellow nudibranchs.² Lacking the shells that provide many other mollusks with safety, nudibranchs have evolved numerous defensive strategies. Nudibranchs are experts at camouflage. By acquiring their color from their prey, some nudibranchs are able to blend in precisely with their meal of choice. Others use bright colors to warn predators of their unappetizing acids and deadly toxins. Perhaps the most impressive defense strategy belongs to select species of aeolid nudibranchs, long, tapering nudibranchs that are covered in waving protrusions called cerata.³ Aeolid nudibranchs feed on stinging jellyfish, sea anemones and corals. These prey species have venom-filled cells called nematocysts that shoot out tiny harpoon-like structures for both hunting and defense. While they are consuming their toxic prey, nudibranchs are able to prevent the nematocysts from firing, potentially through the use of their slug slime. They are then able to store the immature nematocysts that they ingest in cnidosacs: special sacs at the tips of their cerata. These clever nudibranchs can then use the nematocysts to protect themselves against predators.⁴ (The nudibranchs numbered 14, 15, 21 and 25 in the species key below are all aeolid nudibranchs, although it is unclear from my field guide if they display this behavior.)

Nudibranchs are hemaphroditic, allowing any two mature individuals of the same species to mate. Most nudibranchs reproduce by positioning themselves head to tail, exchanging sperm, and then separating to lay their ribbons of eggs. While some nudibranchs develop as miniature adults, most larval nudibranchs have shells which they lose through metamorphosis.⁵ Scientific illustrator Zoe Lawrence has created a great illustration of the life cycle of the nudibranch on her website. Although all of the nudibranchs in the 'Nudibranchia' print are quite small (less than 1 inch, or 3 cm), nudibranchs can grow much larger; the Spanish Dancer, for example, can grow up to 16 inches (40 cm), making it not only the largest nudibranch, but also one of the world’s largest sea slugs.⁶

There are over 500 species of sharks found around the globe.¹ Sharks swim through remote open waters, craggy coral reefs, below frigid North Atlantic ice, and in the darkest ocean depths; marine ecosystems of all kinds are shaped - and protected - by sharks.² Often maligned, these ancient vertebrates are vital to ocean health. Both skilled hunters and filter feeders keep prey populations under control, and scavengers help clean ocean waters. According to the IUCN, at least one-third of all shark species are at risk of extinction. Many species of shark are so poorly understood that they could be lost before they can be classified as endangered.³ The primary threat to sharks is overfishing;⁴ a 2013 Marine Policy study found that between 63 to 273 million sharks are killed each year.⁵ The horrific practice of shark finning claims many of these beautiful creatures.⁶ Some sharks are caught as bycatch in nets meant for fish like swordfish and tuna.⁷ Others are lost to pollution and the degradation of ocean ecosystems. Sharks reproduce slowly, making it difficult for their populations to recover after they have been decimated by irresponsible human practices.⁸ The sharks depicted in ’Sharks of the World’ represent 23 taxonomic families of sharks, illustrating the beautiful biodiversity of these incredible animals. Their loss would not only further imperil the health of the world’s oceans, but would also deprive future generations of the wonder that they inspire.