North Sulawesi is located within the ‘Coral Triangle’, a territory which spreads from western Thailand all the way through eastern Indonesia. This is where many scientists believe life began in the ocean and it is widely thought that it holds the most bio diverse marine habitats on earth.

For this reason diving in Indonesia has been held in high regard amongst the diving community and North Sulawesi is no exception. To the east of Borneo and below the Philippines, Sulawesi is an oddly shaped island in the Celebes Sea. North Sulawesi refers to the most northerly point. Just a few hundred meters offshore the continental shelf plunges towards the deep oceanic trenches which offers nutrient rich waters. The fact that evolution here has been uninterrupted for millions of year means that the marine life in this particular part of the Coral Triangle is extremely diverse

Bunaken Island lies just a few kilometers offshore, a plateau extends from the island before reaching the drop off which descends to hundreds of meters. Coral life on the wall is extremely dense and different species both hard and soft compete for space. These particular walls have gone some way into making diving in Indonesia what it is today and draw traveling divers from all over the world. Large pelagics like Black and White Tip Sharks, Trevally and Napoleon Wrasse work their way up the reef, whilst Green Sea Turtles lodge themselves into the wall to rest. If you’ve got a skillful guide you might be able to see finger nail size Pygmy Seahorses latched onto Gorgonian Fans, not a common site even when you are diving in Indonesia.

The Lembeh Strait is a complete contrast in bottom topography in comparison to the walls Bunaken Island. Located off the eastern coast of North Sulawesi the Strait is a channel of water that lies between the landmass of Sulawesi and Lembeh Island. The shallow black sand slopes have created a truly unique marine habitat for the dwellers that have adapted themselves supremely to this environment. There are some coral reef formations but these are relatively few and far between. This is where life has come to compete against itself in which evolution has created many weird and wonderful creatures divers refer to as ‘critters’. Mimic Octopus have the ability to take the form of up to ten different types of other species including Lionfish, Snake Eels and Flounder in order to confuse predator and prey. Angler Fish dangle a lure just millimeters from their mouth in order to attract potential prey. Carrier Crabs camouflage and defend themselves by placing Sea Urchins on their shell whilst they make their way from one spot to another.
source: here