Nudibranchs: the macro obsession

Nudibranchs: the macro obsession

At some point in most diving careers, you'll be on a drift dive past a stunning wall full of schooling fish, and you'll realize your buddy stopped moving three meters ago and is just staring at a rock. Look closer: on that rock, smaller than your fingernail, is a nudibranch.

Nudibranchs are soft-bodied marine mollusks — shell-less sea slugs — and they are, bafflingly, the most beautiful animals in the ocean. Thousands of species, each more extravagant than the last, painted in impossible colors as a warning to predators: I am toxic. Do not eat.

Where to see them

Nudibranchs exist everywhere, but muck diving sites are where serious nudibranch hunters go. Silty slopes, rubble, artificial structures — the unexciting-looking terrain is their world.

• Lembeh Strait (Indonesia) — the global capital
• Anilao (Philippines) — rival for the crown
• Puerto Galera (Philippines) — famous for rare species
• Dauin (Philippines) — growing reputation for critter dives
• Ambon (Indonesia) — muck diving at its most obscure

How to find them

Slow down. Dive a site at 1/10th your normal speed. Your guide (always hire a local macro guide in muck-diving regions) will find 90% of what you see. Once you learn the rhythm, you will start to spot them yourself — the flash of color that turns out to be a half-centimeter animal on a sponge.