Night Dive!

Location: Lighthouse Reef Atoll - Belize

Day 11
by Wayne & Karen Brown

Tonight we are taking you on a night dive. We will be making our night dive on the same reef where we made our afternoon dives. This way we can easily see what is different about the reef compared to the day. After dinner we go out to the dive deck, put on our dive gear and our special waterproof dive lights. We are not taking our underwater scooters because they don't have headlights and we want to move slowly over the reef to look carefully for any strange sea creatures that may be out at night.

Jumping into the water, we discover that the temperature is the same as during the day – a warm 81ºF. Descending underwater, everything around us is black. Our dive lights make beams of light, but shine on nothing. The only things we can see are the bright lights under the ship shining down into the water above us. We swim down to 60 feet underwater and our dive lights reveal the coral reef at night. During the day colors are filtered out by the water as we dive deeper underwater. Below 50 feet underwater, everything usually looks kind of blue-green. Now we see lots of bright colors on the reef because our dive lights are shining close to the reefs. The lights reveal the colors that are always there, but can’t be seen unless you have a light.

Here’s another surprise: at night the corals look fuzzy! During the day, the tiny coral polyps ("paul-ups") are sleeping. Even though they’re sleeping, they get food from sunlight made by the plant cells, which are called zoothanthalee ("ZOH-than-thell-ee"). These cells live under the corals’ skin. At night, the corals wake up and reach their tiny sea anemone-like tentacles out into the sea to catch tiny floating animals called plankton. Coral polyps have tiny stingers on their tentacles, like jellyfish, called nematocysts ("new-MAT-oh-cists"). These stingers paralyze the plankton that the polyps catch and eat. The corals look fuzzy because thousands of coral polyps have their tentacles sticking out.

Do fish sleep? Yes, they do! As we swim across the fuzzy corals of the reef, we find that some of the fish we saw swimming around during the day are between the corals sleeping. We see a stoplight parrotfish, but it looks different than before. Many fish change color when they go to sleep. It’s as if the fish put on pajamas when they go to bed!

Sleeping fish are in danger because some of the fish that were hiding during the day are out at night looking for sleeping fish to eat! We see a moray eel (a fish, not a snake) slithering across the reef looking for sleeping prey. Moray eels can’t see in the dark, but they have an excellent sense of smell. They swim between the corals and when they bump into something that smells like a fish, they bite it before it can get away.

As we swim over the underwater drop-off and look down the wall that drops into the deep, Karen finds a strange creature on top of some soft coral.. It's a basketstar, about one foot across! Basketstars have five arms that look like branches of a tree. They are related to sea stars. Basketstars only come out at night. During the day they curl-up and hide in sponges or under corals. At night basketstars climb up on top of corals or sponges and extend their long branching tentacles, which they use like baseball glove. They catch zooplankton floating by in the ocean currents.

As I take a picture of the basketstar it slowly starts to move. It is curling-up! The basketstar is so sensitive to light that even the light from our diving lights is enough to make it curl-up. We don't want to stop it from feeding so we turn our lights away and leave the basketstar to catch its dinner.

We’ve been underwater for about almost an hour. Now it’s time for us to swim back to the boat, and jump into the hot tub to warm up before we go to bed. As we fall asleep we’re happy that animals don’t slink around at night, looking for sleeping people to eat!

Best Sleeping Fishes,
Wayne & Karen Brown


Lighthouse Reef Atoll, Belize

Position: 17º 13' N / 87º 36' W
Air Temp: 87ºF
Weather: light breeze, sunny with scattered clouds and calm seas.
Water Temp: 81ºF

The polyps of this star boulder coral are reaching out to catch planktonic animals floating by at night.

Our diving lights attract planktonic worms, so we hold our lights close to the corals so the coral polyps can catch the worms for dinner!

We found this stoplight parrotfish sleeping between the corals.

We saw this spotted moray eel poking around the coral reef looking for sleeping fish to catch for its dinner.

This yellow basketstar has just started to curl up its long branch-like tentacles because it is trying to hide from the our lights.


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