Perfect coral reefs instead of sushi & koi - The lesser known side of South Japan!

It was a bit of a chance encounter: while visiting the famous koi breeders in Niigata in northern Japan, one of the koi breeders told me about coral reefs. I put this down to the empty sake bottles or some language-based misunderstanding. But Toshiyaki insisted he was right. So I resorted to Google, which had very few reports and those they had were in Japanese. There seemed to be diving centres on the islands of Okinawa and Ishigaki, so a year later I landed on the small island of Ishigaki, 2000 km south of Tokyo and about the same height as Taipei. Even as we landed, the fringing reef was visible in the clear water around the island.

The dive centre PRIME SCUBA took us on daily trips to the surrounding reefs. We piled onto the boat in the morning and returned to the harbour around 4pm every day. At noon we had a delicious Japanese meal on board with unlimited drinks.

But what’s in it for a marine aquarist diving here?

The first view under water is always the most exciting. The visibility in very clear water was perfect, and the reef reached almost to the surface with an enormous abundance of fish. That was really unexpected. Even when you looked closely, you felt like you were in a species-rich reef in the Philippines, even though the Philippines are 1000 km away.

The reefs are dominated by stony corals, but soft corals are also abundant, especially in the strong current areas and on overhanging areas. On the reef top are large stocks of fire corals, as is common. Between these corals such typical inhabitants as anthias and demoiselles can be seen. On one dive the guide showed us the reefs from below. There were several ways to dive into crevices and holes under the reef. It was a bit of a squeeze, but the reef structure was beyond exciting. You could literally see how storms damaged the reef and made room for new corals. These were flattened again and the reef continued to grow. Thus, layer by layer, a reef developed from the seabed at a depth of 25 metres to a shallow 5 metres. In addition such destructive creatures as parrot fish, which would later trickle the kit (chewed corals) between the corals, were clearly visible above the reef. Nowhere else could you do a site inspection like this!

Naturally we are on the lookout for special features and our trained eyes help us to find the jewels of the reefs: pipefish, head-swimming upside-down jellyfish, common and extremely rare sea slug species alike and some rarely found shrimp species.

The clownfish look absolutely magical in the white anemones, but unfortunately there is a sad background! Anemones only lose their colour (due to zooxanthellae) when the water temperatures rise well above 30 °C and a look at the reef shows us that no other corals show bleaching phenomena. So why only the anemones? Our dive guide explains: We've only had 2 typhoons this year - normally there are five! The typhoons have the important job of mixing the water layers and bringing cool deep water to the surface. The anemones with their loss of colour are always the first to show us the lack of typhoons!

It’s always worth taking a look at the reef top. Some places have cleaning stations that are regularly visited by mantas. Even though manta rays are not really suitable for our aquariums, every diver and aquarist is happy to experience these peaceful giants live. Whether you like it or not: with mantas you lose all sense of time and space. The size of the rays alone and their gentle movements really cast a spell over you - no matter how many times you’ve seen them!

But fans of large animals may not feel they’re getting their money's worth at the Ryukyus. There are a few turtles swimming around, the occasional medium-sized Napoleon fish, but rarely a shark - and if there is one it will only be a medium-sized whitetip reef shark. They usually just lie around lazily and become active at night. Large pelagic sharks are the absolute exception, unfortunately!

The dive guides are always surprised how we get out of the water after a dive or after a snorkelling session where there were no large fish, and proceed to tell each other in glowing terms about teeny tiny fish that non-aquarists don't even notice! Who, apart from us, pays attention to combtooth blennies, juvenile marine angelfish with their special colouring, pygmy angelfish and all the bouncing swimming wrasses that hardly anyone gets to photograph? We watch a venusta angelfish (Paracentropyge venusta) carefully, whether it eats corals or not. Does it fight with other species or does it behave peacefully? And suddenly our diving partners have gone and we have to go and look for them.

The same often happens in “boring” sandy areas. During the "quick" crossing of an unloved sandy area, we aquarium fetishists stop and stay at the first sea cucumber. There might be a small imperator shrimp (Periclemenes imperator) living on it. Carefully turn the sea cucumber around and there it is. To the guardians of all sea cucumbers I would like to say briefly: As long as a sea cucumber doesn't blow its Cuvierian tubules around your ears, the process is completely stress-free for the sea cucumber and is perhaps its only highlight of the day. Then there are the shy spotted garden eels (Heteroconger hassi), which slowly but steadily disappear into their sand tube when approached. Lie down carefully on the sand and wait patiently. Next to us, a bizarre-looking snake eel from Star Wars peers into the area. And suddenly our diving partners have gone again.

Even if the dive guides could kill us at times like this, they find us aquarists very pleasant on the ascent. We can happily occupy ourselves anywhere. On anchor lines we watch the growth and find some mini-animals that no one has ever noticed before. And in the open water we are so busy with the plankton that we have to suck the last out of our cylinder because the display has been showing 0 bar for 10 minutes. You shouldn't do that - but we do!

A special feature of the southern Ryuky Islands are the large sea snake populations. On most reefs in Southeast Asia or Australia, you occasionally see a sea snake. At Ishigaki, however, you can count on five to ten snakes per dive! Their venom is extremely strong, but they have no desire to bite us. In fact the animals seem to seek proximity and often stay with us quite long - at close contact. They examine our pockets (-openings), lick the front of our diving goggles and glide licking (i.e. smelling) over our skin, e.g. on our arms and hands. Maybe it's just because they have really bad eyesight and think we're a piece of floating reef with lots of holes and caves (diving jacket). As sweet as the animals are, a bite would be fatal, and you don't really notice it’s happened because their poisonous teeth are so short!

Surprising water values

As an aquarist and leader of the JBL research expeditions, I always have a few water tests with me. Most of the time the values are normal, but sometimes there are little surprises.

Water temperature at the surface: 26.6-26.8 °C (October 2019) Conductance near the beach 52.2 mS/cm, on the reef 50.7 mS/cm  - Difficult to explain, since in shallow water the rain and the river mouths should actually lower the conductance

Density near the beach 1.025, on the reef 1.024 Carbonate hardness near the beach: 7.5 °dKH, on the reef 5.5 °dKH!! - More often we find that the KH is lower on reefs than on the open sea or near the beach. Whether this is due to the many consumers in the reef is not clear.

pH value near the beach: 8.4, on the reef 8.2 Calcium on the beach and on the reef: 440 mg/l Magnesium near the beach 1480 mg/l, on the reef 1360 mg/l - Magnesium values are rarely the same everywhere. There are greater fluctuations than with calcium.

Oxygen everywhere: 10.0 mg/l - Even at greater depths, the O2 content is always at the saturation limit. Nitrogens and phosphates below the detection limits

At the sight of a group of yellow tangs (Zebrasoma flavescens) I had to think for a moment about where I was underwater. Hawaii lies more than 8000 km to the southeast and there is nothing in between, except for battle sites like the Ogasawara mini-islands and the Midway naval base. You would have to look at a map of ocean currents to see if the larvae of the tangs could have drifted there. The adult fish cannot swim such distances in open water. By the way, we can easily tell from an underwater photo whether the yellow tang was photographed in Japan or near Hawaii: There are very few corals near Hawaii! Theoretically, it could also have been the yellow colour variant of the brown tang (Z. scopas). I’m not an expert in this species, but to my knowledge the yellow colour morph shows a thin bluish fin fringe in scopas, but not in flavescens! So the yellow tangs observed were really Z. flavescens!

The Ryukyu Islands are not only worth visiting for divers, they’re also good for snorkellers. Off the north coast of Ishigaki, at Yonehara Beach, there are ideal snorkelling opportunities from the beach. First you walk five minutes through very shallow water over sand and then you snorkel into a beautiful and seemingly endless reef. There you can explore all the marine life, excluding the mantas, by snorkelling. Juvenile batfish, surely one of the most beautiful sea creatures of all, live there at a depth of only 3 metres. Sea snakes are also there in large numbers and the corals know no bleaching. Just please don't forget to organise transport back to the hotel. We stayed there until dark and then stood completely lost on the road next to the beach. Unfortunately, no one drives around there any more. So you are left with a very long walk in diving gear to the hotel or a nice Japanese man who calls you a taxi!

There was one fish I really wanted to see: The butterfly fish Chaetodon daedalma. This butterflyfish, with its metallic painted appearance, had taken my fancy and it only lives near the Ryukyu Islands and the small Ogasawara Islands in the middle of the Pacific. But as it is always the case, when you look for something, you don't find it. It was only in the Tokyo Aquarium that I was allowed to see my dream fish alive for the first time - well, better than nothing ...

If you ever find yourself in Ishigaki, don't miss the neighbouring jungle island of Iriomote (1 h ferry ride). There you can find brackish water dwellers such as silver moonyfish, pufferfish and scats in clear rivers, as well as the world's largest land crab, the palm thief, in the rainforest itself! Now you already have two more good reasons to visit Japan besides sushi and koi!

Travel tips:

Only the Ryukyu islands of Ishigaki and Okinawa have airports; the neighbouring island of Iriomote can be reached by ferry. There are flights from many major airports in Japan and also from Taiwan, which is much closer. Flights to Tokyo cost around €900 and take about 11 hours from Germany. From Tokyo to Ishigaki you fly about 3 hours and pay about €200. On Ishigaki, hotels on the north coast are recommended because you can snorkel from the beach there. One night costs between €80 and €200. Most of the rain falls in August. No visa is required for Japan and there are no vaccination requirements for the islands. Diving in Japan is not cheap, so it’s worth comparing the prices and services of the various dive centres!

© 23.10.2022

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Heiko Blessin
Heiko Blessin

Tauchen, Fotografie, Aquaristik, Haie, Motorrad


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