From fish that can vacuum inhale meals much larger than themselves, to electrified gargoyle looking creatures that lurk beneath the sand, Bunaken Marine Park and the surrounding North Sulawesi area is certainly not short of weird and wonderful critters.
Perhaps among the most fascinating creatures that live in Bunaken Marine Park are cephalopods, which belong to the molluscan class Cephalopoda. This class includes instant crowd-pleasers such as the bobtail squid, long armed octopus, or the infamous blue-ringed octopus. Cephalopods tend to be nocturnal, although there are many exceptions to this â and today we will be discussing one of these exceptions â the Day Octopus.
What is a Day Octopus?
Scientifically known as Octopus cyanea, the day octopus (or reef octopus) is a diurnal (active during the day) species of octopus that can be found on coral reefs and in shallow seas across the entire Indo-Pacific region â from the Red Sea, across to Hawaii.
What does a Day Octopus look like?
Instantly recognisable from their size, day octopuses are the largest octopus (and cephalopod for that matter) that you are likely to encounter on your visit to Siladen Resort & Spa.
The mantle (main body) length grows to just under 20cm, while the arms grow to at least 80cm. Due to their general lack of structure, it can be difficult to assess how big octopus really are, but during a study on the species, one individual was noted to reach a whopping 6.5 kg!
They tend to be dark red to brown in colour with a white trim on their arms, but being an octopus, this can change frequently.
Day Octopus Mimicry and Camouflage
Most people are aware that octopus can change their colour to blend in to their surroundings, but the day octopus is far better at this than most other octopus species. Being active in the day, they rely much more on their camouflage for both hunting and for protection.
As they leave the safety of their nest to hunt, they must try to blend in to their surroundings. They will constantly alter their skin colour to match that of the surrounding sea bed â a process made possible by chromatophores, pigment containing and light reflecting cells that are found in the skin of the octopus. They are known to alter their colouration more frequently than other octopus, with one individual noted to have changed its appearance 1000 times in seven hours.
It is not only the colouration that can be altered â day octopus can also change the patterns on and the texture of their skin. This can make them almost impossible to see, despite their large size.
What does a Day Octopus Eat?
Like all other octopus, the day octopus is carnivorous, feeding on a diet of crabs, shrimp, molluscs, and small fish. They are known to use their colour changing abilities for hunting too â by creating a display that looks similar to that of a passing cloud, to confuse any prey into thinking there is no danger.
Although technically diurnal, they are mostly crepuscular, meaning they are most active at dawn and dusk. They maintain a den which it will return to after each day after feeding. This is most likely under an overhand, among dense coral heads, or in a hole that the octopus has excavated in rubble or sand.
While they will eat the smaller prey as soon they they catch it, they are also opportunistic scavengers and will drag larger finds back to their den to feast on.
Where can I see a Day Octopus?
Being coral lovers, the best bet for finding one of these magnificent creatures is by heading out any of the stunning reefs within Bunaken Marine Park.
We have found them living on almost every dive site in the area, so we are certainly not short of them. The hard bit if finding them â although luckily, our eagle-eyed dive guides are fantastic at spotting them.
Sadly for snorkelers, you may have a harder job finding one unless you snorkel over very shallow water. The abundance of hiding places and their amazing camouflage makes them very difficult to spot from the surface of the water, although you can always be lucky and have one swim out while you are above it. That being said, we have seen them many times over the shallow corals in front of Siladen Resort & Spa, so maybe a late afternoon snorkel session is not the worst idea.
If you do see one, we ask that you do not try to encourage the octopus to come out of its hole. It is well aware that you are there, and should it leave cover, it is because it feels threatened and this is the only course of action left.