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Of course not everything is perfect here and we also came across sections of reef that looked more like debris. Here, too, the reasons for coral death are usually too high water temperatures, caused when hurricanes fail to occur.
The typhoons have the important task of mixing the water layers and exchanging cold deep water for warm surface water. On average, the islands experience five hurricanes a year. In 2016, four out of five typhoons failed to occur and the water temperatures rose. Global warming is likely to be responsible for the absence of the hurricanes.
Highly poisonous and playful – sea snakes
Every dive we saw unbelievable numbers of sea snakes! At least five, usually ten or more sea snakes accompanied our diving or snorkeling trips.
Emydocephalus ijimae
Mating
They meandered leisurely through the reef, flicked into every hole between the corals and swam to the surface to catch their breath from time to time. Sometimes the snakes (Emydocephalus ijimae) confused us with a coral reef and searched our equipment for hidden fish or fish eggs. This took some getting used to, because their neurotoxin is considered extremely dangerous. But their teeth are very short and they don’t bite readily. If you let them examine your body and equipment in peace, nothing will happen. No other deadly poisonous snake species can be handled so cooly!
Slugs everywhere
Everywhere you could admire beautiful slugs under water! The variety of their species is enormous and almost approaches the slug top spots of the Philippines and New Guinea.
Halgerda diaphana
However, you need time and a good eye (or a good guide or both) to discover the beauties, some of which are only millimetres to a few centimetres in size. When we look at our photos of these colourful animals, it is hard to imagine how hard they are to find. But in the brightly coloured reefs the tiny creatures are perfectly camouflaged despite or because of their colours! Their colours signal poisonousness, which usually comes from their food. An octopus lay very still and let a slug crawl slowly over its bladder without groping or eating it, as it would have done with any other animal!
If you are not a specialist, flatworms can easily be mistaken for slugs! There are tropical flatworms, which are in no way inferior in colour to the slugs and are usually only later identified as worms on the basis of photos.
Protoceros sp.
Protoceros sp.
Boring sand – or can it be exciting?
Divers and snorkelers love the species-rich reefs and are usually disappointed when they have to swim over sandy ground. But the sand’s exposed structure has produced some very special inhabitants.
Amblyeleotris steinitzi
Stonogobiops xanthorinica
Brightly coloured gobies live as chaperones in symbiosis with bustling crabs; 80 cm long, creepy-looking snake eels wait, vertically buried, for careless prey; gorgeous, orange-white coloured imperator shrimps, a mere 2 cm in length, live on 60 cm long sea cucumbers, which chew the ground sluggishly for food, and many more animals wait to be discovered by trained eyes. If you simply glide quickly over sandy ground, you have already missed the best!
Ophichthus melanochir
Periclemenes imperator
What does it actually look like UNDER a reef?
We had saved something special for our last dive. In a reef area between Ishigaki and Iriomote there were numerous breaches that went deep under or into the reef. Cave diving "light" so to speak. Biologically interesting here was seeing the structure of the reef from below. A reef only grows when something is destroyed or dead at the top. Only then is there room for a new coral, which grows on the dead one.
This is how the reefs are formed over centuries, always growing towards the sunlight. Not all of us were experienced divers and I pay respect to our beginners who undauntedly dived or crawled into a black and narrow hole at the bottom of the reef in a dark passage. Sometimes it was so narrow that we got stuck to the ceiling with the cylinders on our backs or it was so narrow at the sides that we had to stretch out our arms to get through a passage. But the experience to see the huge basic structures of the corals once from below was very special and absolutely recommendable!
Are there yellow tangs in Japan?
We were quite astonished at the end of a dive when we saw three completely yellow coloured surgeonfish swimming together, eating algae. The yellow tang (Zebrasoma flavescens) lives in a region between Hawaii, the Marshall Islands, the Philippines and southern Japan!
Zebrasoma flavescens, juvenile
Zebrasoma scopas, juvenile
Since this surgeonfish is so popular in aquariums, it was really nice to quietly observe it in its natural habitat! After the dive we debated intensely on board whether it was really the Zebrasoma flavescens or the yellow colour morph of Zebrasoma scopas, the blue-lined Tang. It seems to be very difficult to distinguish the two species (in the yellow variant). Doing internet research, we noticed that the yellow Z. scopas variant has a slight blue seam on the fin edge. "Our" animals did not have this edge. Therefore we are now of the opinion that it really was the yellow tang!
Even five meters of fish need to be cleaned – the manta cleaning station
Mantas are definitely not ideal aquarium dwellers. They can only be kept for long periods of time in very large public aquariums and it is of course a question of whether aquarium keeping is at all necessary for these gentle giants. But this is part of the ongoing discussion about zoo animals in general. The fact is, EVERY diver or snorkeler is pleased as pie to see manta rays under water!
The elegant swimming style of the rays, which can grow up to seven meters wide, is one of the most impressive things you can experience under water. Normally they swim past the divers without paying attention to them. Only when manta rays have caught a spot rich in plankton do they turn their loops with their mouth wide open. Another way to observe manta rays in peace and quiet are at cleaning stations like the one we visited.
The mantas float up close, let themselves quietly be cleaned of cleaner fish, and continue to swim, or return several times. The whole thing had nothing to do with aquarium keeping, but it was definitely one of the most exciting moments of the whole expedition!
Do reef inhabitants in the wild eat JBL food?
On every expedition we test whether wild fish "voluntarily" eat the JBL food. It is always amazing to see how many fish species, which are considered very fussy in aquariums, eat the JBL granulated food (JBL MariPearls) offered in the wild either immediately or with a slight hesitation. However, the problem is that damselfish are always the fastest to learn when something is free and that other species then hardly stand a chance, as the photos show!
Water analyses:
Measured near the beach (25/10/19, 17:05)
Position
24°28'17.77 N
124°07'31.06 E
Water temperature (surface):
Conductivity:
Density:
KH:
pH:
Calcium:
Magnesium:
Oxygen:
26.8 °C
52.2 mS
1.025
7.5 ° dKH
8.4
440 mg/l
1480 mg/l
10 mg/l
Measured at the reef on the boat off the northwest coast (26/10/19, 12:00):
Position
24°24'20.52 N
124°07'04.44 E
Water temperature (surface):
Conductivity:
Density:
KH:
pH:
Calcium:
Magnesium:
Oxygen:
26.6 °C
50.7 mS
1.024
5.5
8.2
440 mg/l
1360 mg/l
10 mg/l
The relatively low carbonate hardness of 5.5 °dKH is striking here. There have not been heavy rainfalls and it was not clear why the KH was so low here.
While the others slept: sea snakes ashore and giant crabs
Some of our indefatigable group were still so lively (and curious) in the evening that they wanted to investigate the surrounding biotopes near the hotel. With flashlights, headlamps and cameras they went along the beach towards the mangrove areas. We made our first find before we got there. Some of the sea snakes we had observed under water in the reefs during the day, were now swimming here in shallow water a few centimeters deep, or had even crawled ashore!
Emydocephalus ijimae
Emydocephalus ijimae
Then we left the beach and followed a river course into the mangroves. The snakes avoided the brackish water and stayed in the pure marine water. But more and more crabs were running around: small crabs, medium crabs and then – a really big crab!
Ocypode cordimana
Scylla olivacea
We also found some nocturnal predators in the river. The result was jumping prey fish!
Japan’s most beautiful animals: the marine plankton!
With a specialist like Anke Morbitzer from the Bresser company present, it seemed an obvious thing to catch the smallest creatures and observe them under the microscope. The new Bresser expedition microscope took up hardly any space and did its job admirably!
Microscoped plankton organisms can only be roughly determined. Since almost all sea dwellers go through a planktonic stage, we found crabs, polyps and a lot of diatoms, which really belong to the most beautiful organisms in the world when seen under the microscope!
Sometimes things go completely wrong!
Before going on a trip, you should, of course, change all your batteries and take a test photo, too. And still things can go wrong. In our case, new, small 3.6 V batteries for battery signal converters in two underwater housings all packed up at the same time. And our reserve batteries did not bring any improvement! The cause was probably that we had batteries which had exceeded their shelf-life at the supplier. So we only managed 1-2 photos with the right flash power and even then the batteries did not reach the right voltage. We were sick as parrots…
And what else lives on the reef?
Once all the measurements have been taken, the feeding trials are finished and all the other jobs are done, then it’s time to simply enjoy a reef and to enter into communication with some of the reef inhabitants like cephalopods.
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