Hello! It's Oshin, I'm back here at Yokoyama Sensei's Lab for half a year.
From May 10th to May 14th, I joined a mangrove sampling campaign in Ishigaki Island. I flew out from Narita International Airport and met the team from Kobe University : Kida-san, his students Aki-san and Shimamoto-san, and Khwan from Thailand. Everyone was incredibly kind and welcoming from the very beginning.
The first thing I noticed after landing in Ishigaki Island was the humidity. My hair curled up almost instantly the moment I stepped outside the airport.
After arriving, we rented a car, bought supplies for the next few days, and drove north toward the mangrove site we would be studying: Gaburumata. The scenery already felt completely different from Tokyo as it was tropical, lush, and surrounded by mountains and ocean.
Into the Mangroves
The next morning, we headed to a farm near the mangroves to prepare our equipment. Heavy rain poured down from early morning, and we needed to enter the mangroves by around 8:20 am to make the best use of the low tide conditions. We waited for nearly an hour hoping the rain would lighten.
Then Khwan finally said, “No, let's just go in anyway.”
So we went into the heavy rain.
Carrying a heavy metal corer, we entered the mangrove forest. Almost immediately, it felt like the mud was pulling us downward with every step. There was even an old ladder Kida-san had borrowed years ago to help us get in. Beside us, the water in the stream rushed rapidly because of the storm.
Despite the conditions, we continued downstream to survey and sample near two mangrove species: Bruguiera and Rhizophora. For me, this was one of the most fascinating parts of the trip because Kida-san explained so many ecological processes while we worked. One concept he talked about was stem flow, how rainwater washes nutrients down the trunks and roots of trees into the mangrove system, nourishing the surrounding sediment and ecosystem.
It quickly became obvious that mangroves are far more complex than they first appear.
Once the rain finally calmed, the entire atmosphere changed. Mudskippers emerged from the mud, everything became quiet, and suddenly the mangrove felt peaceful. We continued pulling sediment cores, measuring them, and dividing them into subsamples until the afternoon.
That evening, I walked back to my accommodation from the mangroves. Ishigaki felt incredibly alive: giant frogs, tropical birds everywhere, humid air, dense greenery. Everything felt vibrant.
Core After Core
The next two days were rainy again, but fieldwork continued regardless.
We finished sampling the downstream sites and moved upstream, where coring was slightly easier. That day, I asked if I could try pulling some cores myself. I honestly did not have much strength for it, but I managed to complete a 0–50 cm core on my own. The group cheered me on to try a 50–100 cm core as well. I managed to push the corer halfway down before the others stepped in to help finish it.
When we finally pulled it out successfully, everyone celebrated together.Afternoons were just as busy. After quick showers and lunch, we spent hours subsampling sediment samples and washing root samples through sieves. We often worked until around 8 pm, surrounded by mosquitoes, exhausted but still enjying conversations and learning from each other. Kida-san also spent a lot of time explaining topics beyond mangroves, including Antarctic waters and dissolved organic matter (DOM), which made the trip feel not only like fieldwork but also like an immersive learning experience.
The Final Day
Our last field day finally gave us perfect weather. No rain. Calm water. Quiet mangroves.
This time we entered from the coastal side because Kida-san wanted to show us the full ecosystem transition from ocean to mangrove interior. Along the shore, there were hermit crabs everywhere. We also searched for the famous giant “Yashigani” coconut crabs, though unfortunately we never found one.
From the coast we moved deeper into the mangroves, sometimes walking directly through the river itself. Every single step through the mud required effort.
Our goal that day was to collect water samples along the entire environmental gradient — from the coast into the mangrove system and its end members. We sampled seawater, mangrove water, and pore water from the sediment. Collecting pore water was especially difficult. We had to dig deep into the sediment, wait patiently for water to slowly accumulate, clear it, and finally extract the sample.
After finishing the work, we returned to the ocean side and simply enjoyed the sun and water for a while. After days of rain and mud, it felt like the perfect ending. We went for a quick swim before returning to complete the final subsampling and pack everything up.
Exploring Ishigaki
Since our flights were in the evening on the last day, we spent the morning exploring a bit more of Ishigaki together.
We visited Banna Park for birdwatching, ate local Yaeyama soba for lunch, and explored the beautiful Ishigaki Island Limestone Cave. The cave system was absolutely fascinating.
Before heading to the airport, we stopped to buy omiyage, and then it was finally time to say goodbye to the Kobe team and fly back to Tokyo.
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Ishigaki was hard work — rain, mud, mosquitoes, heavy cores, long days — but it was also unforgettable. Between the mangroves, the ocean, the mountains, and the people, it became one of the most memorable field experiences I have had so far.
