Tateyama / Sagami Bay
Japan · Pacific
Tateyama in southern Chiba Prefecture is the gateway to Sagami Bay, long regarded as Japan's nudibranch capital with over 150 species recorded from its rocky kelp reefs. Cold Oyashio-influenced water keeps the bay productive year-round, sustaining extraordinary densities of aeolid and dorid nudibranchs, ornate ghost pipefish, and the resident wobbegong sharks that drape themselves across rocky ledges. Winter water temperatures below 15 degrees Celsius reward cold-tolerant macro photographers with species rarely found anywhere else in the world, and spring brings migratory cuttlefish aggregations.
How this reef is doing
ⓘ How we measure thisReef state
Live science signals for this reef are still being gathered.
Coral cover
Fish life
Heat
Fishing
Open to fishing, and the water is busy.
Sources · Global Fishing Watch and reef gravity
What you will see
39 species across the dive sites here
Sea Star (Crown-of-thorns relative)
Seen 1 month ago
at Moroiso
Kelp Filefish
Seen 9 months ago
at Tsurigasaki
Least concern
Hairy Frogfish
Seen Jul 2025
at Hamasakishita
Least concern
Hermit Crab (Japanese Red)
Seen Apr 2025
at Moroiso
Horse Mackerel
Seen Feb 2025
at Jogashima
Near threatened
Warty Frogfish
Seen Dec 2024
at Hamasakishita
Least concern
Black Rockfish
Seen year round
at Jogashima
Coralline Algae
Seen year round
at Jogashima
Coralline Algae Mat
Seen year round
at Moroiso
Cuthona Nudibranch
Seen year round
at Tsurigasaki
Flabellina Nudibranch
Seen year round
at Tsurigasaki
Hydroid Colonies
Seen year round
at Moroiso
Japanese Bryozoan
Seen year round
at Tsurigasaki
Japanese Eel Blenny
Seen year round
at Jogashima
Least concern
Japanese Shrimpgoby
Seen year round
at Hamasakishita
Japanese Wobbegong
Seen year round
at Moroiso
Least concern
Kelp
Seen year round
at Moroiso
Mosaic Lizardfish
Seen year round
at Hamasakishita
Least concern
Ornate Wobbegong
Seen year round
at Tsurigasaki
Near threatened
Painted Frogfish
Seen year round
at Hamasakishita
Least concern
Painted Greenling
Seen year round
at Moroiso
Least concern
Sea Butterfly Hydroid
Seen year round
at Tsurigasaki
Sea Urchin (Purple)
Seen year round
at Moroiso
Spoon Worm (various species)
Seen year round
at Hamasakishita
Striped Pufferfish
Seen year round
at Tsurigasaki
Least concern
Trinchesia Nudibranch
Seen year round
at Tsurigasaki
Wobbegong Shark
Seen year round
at Jogashima
Least concern
Blue Shark
Seasonal visitor
at Jogashima
Near threatened
Bobtail Squid
Seasonal visitor
at Hamasakishita
Dendronotus Nudibranch
Seasonal visitor
at Jogashima
Diorama Nudibranch
Seasonal visitor
at Jogashima
Flatworm (various species)
Seasonal visitor
at Hamasakishita
Ghost Pipefish
Seasonal visitor
at Hamasakishita
Least concern
Japanese Demon Blenny
Seasonal visitor
at Moroiso
Least concern
Japanese Spider Crab
Seasonal visitor
at Hamasakishita
Japanese Spineless Cuttlefish
Seasonal visitor
at Tsurigasaki
Nudibranch (Chromodoris species complex)
Seasonal visitor
at Moroiso
Tritonia Nudibranch
Seasonal visitor
at Jogashima
Yellowtail Amberjack
Seasonal visitor
at Jogashima
Least concern
Dive sites
Tsurigasaki
ornate wobbegong · flabellina nudibranch · trinchesia nudibranch · cuthona nudibranch
Hamasakishita
painted frogfish · warty frogfish · hairy frogfish · ghost pipefish
Jogashima
wobbegong shark · coralline algae · tritonia nudibranch · dendronotus nudibranch
Moroiso
japanese wobbegong · nudibranch (chromodoris species complex) · coralline algae mat · sea urchin (purple)