At 9 o’clock in the morning groups A and B met alternatively at the harbour, which was only 10 minutes away from the hotel. There the teams split up on two boats. All the participants with a diving licence shared one boat and the snorkelling group took the other one. After a trip of 45 minutes past small islands and fishing villages we reached the diving and snorkelling sites. Sun protection was required in the 28 – 30 °C warm water and you could recognize every snorkeler in the evening by the lobster-red backs of their arms and legs.
The coral reefs we approached were right below the water surface. Thus the snorkelers were able to observe as well as the scuba divers. Only a few shallow water fish species, such as the blue banded surgeonfish (Acanthurus lineatus) remained exclusive to the snorkelers. But for that the divers were able to observe Centriscinae, ghost pipefish and other pipefish at a depth of about fifteen metres.
The hard coral formations were simply stunning, especially in shallow water of 6 m and less depth. They could have been used as a model for an aquascaping competition! Believe me, I have seen quite a few coral reefs in the world but the hard corals of Nha Trang are hard to beat. It is interesting to watch which corals live side-by-side with each other and which ones avoid one another. It shows marine aquarium enthusiasts which socialization patterns are advisable and which not. During the breaks on board we analysed the water values and carried out further measurements. For the first time we were able to determine the UV radiation under water, with the UVA and the UVB measured separately, by means of a newly purchased UV measuring device with waterproof sensors. To measure the light intensity (lux) under water I used the waterproof sensor of the measuring device, keeping it towards the sun in different depths, which were precisely monitored with my depth gauge. Then a second person on board read the value on the measuring device and noted it down. This way we performed measurements down to an 8 m depth. Unfortunately the water surface was so turbulent that it distorted the test results. The stronger the movement of the water surface the stronger the reflection of the sunlight. The comparison between aquarium and nature conditions proved a little frustrating. At midday you can measure about 100,000 lux in the tropics whereas a T8 fluorescent tube of 30 W emits only about 700 lux at a distance of several centimetres. You can double the value with a T5 tube, and a good reflector doubles the lux value again.
We had actually booked 4 dives a day and one night dive, but going local we had to learn that only three dives were possible due to the fact that all boats had to be back in the harbour at 5 p.m. and that night dives off the islands have recently been forbidden. We couldn’t really get a plausible explanation for that, except some confusing rumours about military conflicts in China. Therefore we only managed three dives a day and initiated one night dive from the beach, which you can file under the heading “completely unnecessary” (sight 0, animals 0, nothing but sand).
The time during the day spent in the sun-drenched sea was full of experiences and interesting observations. I wouldn’t recommend Vietnam as a top destination for seasoned divers, there are more beautiful ones! But for marine water enthusiasts who are interested in stony corals I would definitely recommend snorkelling off the coast of Nha Trang.