On a trip to the island of Hachijo, an hour south of Tokyo, Richard Smith encountered this Japanese pygmy seahorse (Hippocampus sp.), which measures at around 2.5cm in length from snout to tail. It would have only just stretched across an Australian 10-cent coin.

The tube blenny (Neoclinus bryope) tends to be found in relatively shallow water, where it sits with its head protruding from a hole. Males guard a clutch of eggs that are laid inside the hole. They will attack other small fish or snail that wander within a radius of about 30cm.

Bubble snails (Micromelo undata) are an intermediate between slugs and snail, as the shell almost takes on a vestigial form in these animals.

Japan has a rich diversity of syngnathids, the group to which seahorses belong. Shiho’s seahorse (Hippocampus sidonis) is found only in Japanese waters and individuals can vary dramatically in colour and the predominance of skin filaments.

Kidako moray eels (Gymnothorax kidako) are commonly seen free-swimming over the rocky reefs of Japan, where they are considered a food fish. They reach almost 1m in length. Here a cleaner wrasse searches for parasites on the eel’s skin – this is a symbiotic relationship in which the cleaner earns a tasty snack while the client fish is freed of pesky parasites.

Found only around Hachijo and a few neighbouring islands, the wrought iron butterflyfish (Chaetodon daedalma), or Yuzen as it is locally known, is an extremely range restricted Japanese endemic species.

The Japanese pygmy seahorse (Hippocampus sp.) is distinguished from other members of the group by its reticulate pattern, which often has a dark spot in the middle. Like other pygmies, the male Japanese species becomes pregnant with the young after receiving a clutch of eggs from his partner. As the eggs pass into his brood pouch, the clutch is fertilised and they remain in the pouch for the coming weeks when the tiny fry are released.

This Yatabe combtooth blenny (Parablennius yatabei) was living in an old barnacle shell just below the tide line. This species is found only in Japanese and Korean coastal waters. The filaments, or cirri as they’re properly named, above the eyes are longer in males than females.

This tiny yellow pygmy goby (Lubricogobius exiguus) was guarding the opening of a discarded wine bottle, which was lying out in the open on a sandy patch. Inside the bottle the fish’s partner tended to a clutch of developing eggs stuck to the internal glass. These gobies reach a maximum length of 4cm.

False kelpfish (Sebasticus marmoratus) hide among algal fronds and are extremely well camouflaged. They have venomous dorsal spines.

Richard found the preferred habitat of the Japanese pygmy seahorse (Hippocampus sp.) to be small fronds of algae over volcanic boulders on the shore around Hachijo. Where these boulders formed overhangs and large crevices, the protection from strong currents provided perfect conditions for these tiny fish.

The stunning colours of the Japanese angelfish (Centropyge interrupta) make it highly prized in the international aquarium trade. It is a common species on the rocky reefs of temperate Japan and despite its name, has also been found at Midway in the northwestern Hawaiian Islands.

Harlequin shrimps (Hymenocera elegans) are voracious predators of sea stars. These colourful crustaceans measure just under 4cm in length and are usually found in pairs. Dwarfed by their prey, they work together to prize the sea star’s limbs from the substrate and await the chance to flip them over. Over the coming week or so they slowly consume their prey while it is still alive.

Despite its appearance, the dragon moray (Enchelycore pardalis) poses little threat to humans. Reaching just under 1m in length, the eel feeds on small fish.

The Kuroshio Current pushes water from the equator northwards to Japan. This current has a significant impact on marine ecosystems, bringing with it warm water and the larvae of tropical fishes. In southern Japan’s Okinawa Island, coral reefs predominate and anemonefish (Amphiprion melanopus), such as this black and red species, can be found.

Many small gobies and blennies share the microscopic world of the pygmy seahorse. Richard says life at this scale is only now being explored, resulting in many significant new finds.

Male dragonets (Synchiropus ijimai) tend to have brighter colouration and long dorsal fins, which are used in display. Males typically have a small harem of several females with which they mate daily at dusk, one after the other.

Like its close relatives the stone and scorpionfishes, the Japanese lionfish (Pterois lunulata) has venomous dorsal spines. If stung, the best response is to immerse the area in hot (non-scalding) water, which breaks down the venom, rendering it inert.

This crustacean is known in English as the boxer crab (Lybia tesselata) and in Japanese as the cheerleader crab. Both common names refer to the crab’s habit of attaching tiny anemones to its pincers and waving them from side to side as a deterrent to predators.

The nutrient-rich green waters off Izu’s west coast nourish diverse and vibrant reefs. These colourful soft corals do not require strong sunlight like their stony relatives on the Great Barrier Reef. Instead they feed on suspended matter, which is plentiful in these waters.

Female triplefins (Helcogramma fuscopinna) are a drab beige colour, while the males, such as this one, are a shimmering example of sexual selection.

The striped boarfish is known in Japanese as ‘Tengu’ (Evistias acutirostris), after the big-nosed deity. This unusual looking fish has whisker-like villi on the chin, which presumably have a sensory function. They are considered rare throughout their geographic range, which may be a result of their preference for deep water.

Striated anglerfish (Antennarius striatus) rest motionless for long periods, pretending to be part of the scenery and awaiting their prey to stray too close. They are able to extend a fleshy, worm-like lure ahead of the mouth which is irresistible to small fish. When the fish approaches, the angler rapidly opens its cavernous mouth, sucking the prey inside.