Friday, 14 September 2012

Dive 6 – St John’s Umm Aruk at night

Night diving is very different to day diving

Umm Aruk Dive Plan

in that some fish come out to hunt and other fish hide. Many of the hard corals feed at night by putting out flowering blooms which catch the passing plankton and other nutrients.

Our dive plan has been designed to minimise underwater navigation (which is much harder at night – as we were to prove on another night dive). We are concentrating on two blocks close to the boat and circling them at different depths using our torches to seek interesting things. The dive duration has been limited to 50 minutes and we have agreed safety measures to attract attention on the surface if we have to ascend for help.

The boat leaves all of its stern lights on (which you can see from under the water) and also a strobe has been lowered so we can tell our boat from any others.

Certain diving techniques are much more difficult in the dark – doing a 5m safety stop is hard because you have no points of reference for keeping your depth other than shining a torch on your dive computer and trying to remain at the correct depth. Communication with your buddy is also more difficult because they cannot see what you are doing and in a pack of divers, locating them is difficult. I always choose something like fin shape and colour as a marker and in the case of my buddy, the fact that he has a dive computer with an orange band around the dial face is unique in the group.

When doing sign language, you have to manage this whilst shining your torch on your hands – three hands would be very useful at night.

The reef at night Flowering at night

Each of the above photos shows coral in a different colour or state to what it is during the day.

Fire Coral at night with Parrot Fish

In the photo above and below, there is a parrot fish hiding in the folds of the Fire Coral. It hopes this will be a safe nest from predators.

Parrot Fish in Fire Coral

It does not move when we shine our lights on it.

Soft Coral

Soft Anemone

Shades of Brocolli

The colour variations in the soft corals seem more pronounced at night.

Bubble Green aka sailors eyeball

The glass looking bulb in the centre of this coral is called Bubble Green aka “Sailors Eye” and is an algae which produces carbon dioxide which is contained within the bubble.

Fan out at night

Fan corals only come out at night and catch food in their wide fan fronds. If you shine a torch on them, they rapidly curl up and hide because they think daylight has come.

This night dive was unspectacular but quite interesting.

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