There’s so much to see when you snorkel the Bunaken National Park reef that surrounds the tiny island of Siladen in North Sulawesi, Indonesia! In fact, I’ve needed two full posts — one in 2023 and another in 2025—- to share just some of the amazing marine life I’ve come across during the daytime. And a whole new world opens up at night. Snorkeling with just a torch in hand, everything dims to shades of brown and black — but then your light hits a sparkle of color or movement, and it’s like you’ve discovered a different universe.

Here’s what the depths reveal after dark.

Octopuses

I’ve seen octopuses both large and small in the shallows of Siladen — hanging out under rocks, hiding in holes, sitting on starfish…

… and changing color while out on the hunt.

To me, an octopus is one of the holy grails of snorkeling or diving, so I love these finds every time.

Nudibranchs

Here’s my other holy grail: the ever-elusive nudibranch. Fortunately, they’re much easier to spot at night — especially the unusually large and colorful Spanish Dancer, Hexabranchus sanguineus:

Sea Slugs

Technically speaking, all nudibranchs are sea slugs—but not all sea slugs are nudibranchs. These differently colored examples of Forskal’s sidegill slug (Pleurobranchus forskalii)—shown above and below—are good examples of where the two orders diverge: these sea slugs have gills on the sides of their bodies, while nudibranchs have exposed gills on their backs.

Sea Hares

Here’s another animal in the blob-like category, but since these have a hard plate hidden inside, they are considered sea snails rather than sea slugs. If you’re having trouble following these distinctions, don’t worry about it — just know that sea hares, like this wedge sea hare (Dolabella auricularia), are much larger and more visibly active than their smaller, squishier brethren. By the way, if you want to learn some marine fun facts, check out the mating habits of sea hares!

Crabs

Wow, do crabs come out after dark! And these aren’t just any crabs—these are night snorkeling gold. We’re talking about species that live in symbiotic relationships with sea anemones attached to their shells …

… sponge crabs, which cut out pieces of sponge and wear them like a sort of hat …

… porcelain crabs, which peek out from beneath the folds of sea anemone tentacles …

… and dozens of red hairy hermit crabs that use all kinds of discarded shells for protection.

Pufferfish

So cute, no? Most fish hide at night, but pufferfish are easy to find when you’re out snorkeling at night—either curled up in coral (like the black-spotted puffer above) or swimming in the shallows.

Sea Urchins

Sea urchins hide under rocks and coral during the day, then roll out at night to feed. They’re one of my biggest concerns while night snorkeling — their spines always feel a little too close for comfort — but they can be spectacularly beautiful.

The most unusual ones look to me like military mines (but they’re actually slate pencil urchins, or Heterocentrotus mamillatus).

Lionfish

Lionfish also float out to feed at night, and you need to beware of their venomous spines — but they keep to themselves, so there’s not much to worry about. In Bunaken National Park, you’re most likely to run across a more traditional lionfish, like the zebra lionfish above. But if you’re lucky, you might see a wild-looking twospot turkeyfish!

These guys barely register as fish at all—if you see one, you might spend a while asking, “What was that?” The answer is that Dendrochirus biocellatus is a happy member of the Scorpaenidae family, which includes all lionfish species.

Basket Stars

Believe it or not, that’s an animal! Meet Astroboa nuda, also known as the naked or giant basket star—an echinoderm related to sea urchins and sea stars. Basket stars hide during the day and emerge at night to feed, unfurling and waving their branching plant-like arms to catch plankton and larvae.

Eels

Eels are generally nocturnal, so if you want to see them out and about in all their hunting glory, you’ll need to snorkel or dive at night. We had a great time watching what I believe is a fimbriated moray (shown above), but my favorite was this tiger snake eel:

Lobsters

Some critters have shiny, beady eyes in the glare of a flashlight, and this blue lobster — Panulirus versicolor — is a good (if slightly creepy) example.

Shrimp

Here’s another critter with tiny, beady eyes: the banded coral shrimp, also known as a cleaner shrimp for its habit of removing parasites from various fish. You might also get lucky and spot an itty bitty anemone shrimp if you peer hard enough through an anemone’s tentacles.

Stonefish or Scorpionfish

Scorpionfish and stonefish are so good at camouflaging themselves that they’re hard to identify. But they’re more active at night (to the extent that you can call these rock-and-sand-sitters “active”) — so we saw a number of them (probably scorpionfish) on our nighttime snorkeling in Bunaken National Marine Park.

Sole and Flounder

One other type of fish you’re likely to see at night is a sole—like this little guy in the Pardachirus genus (my best guess is that it’s a peacock sole). Sole and flounder use the cover of night to wriggle out of their burrows in the sand and search for prey.

And More!

There’s so much more hiding beneath the inky black! Among other things, you’ll find giant clams with their shells wide open, blue-spotted rays darting from rock to coral, hairy-mantled cowries out feeding, tiny cuttlefish flitting through the water, and black-and-white banded sea kraits slithering along the ocean floor. It may feel daunting to pull out your flashlight and dive in — but it’s always worth it.

Wondering what all of this looks like during the day? I explored snorkeling Siladen’s house reef in this 2023 post— and don’t miss my return to see more creatures in 2025 and my Bunaken clownfish gallery.