Cave-Limited Millipedes Discovered on Rapa Nui!

Originally Drafted 18 August 2008

This cave-limited millipede was collected and discovered from a cave near the Rapa Nui coast. While this specimen has not been identified yet, because it is a cave-limited/ troglobitic animal, it most likely represents a new species or perhaps a new genus.

Last night was incredible. As we all prepared for bed, a storm moved in and a torrential downpour ensued. It was an amazing amount of rain. As the rain was coming down, I wondered what would happen to our access road containing the caves, and whether our caves would be sumped out (i.e., water-filled), and we would not be able to enter them tomorrow. With this type of work, essentially you have to accept the hand you are dealt by Mother Nature, so although this concerned me, I wasn’t overly worried about it. What would be tomorrow, would simply be.

Another incredibly sunrise on Rapa Nui. This is the view from my hotel window.

I woke up early and watched the sun rise. I’ve done this every morning since my arrival, and I plan to do this until I leave. The sun rises are gorgeous, and are incomparable to any other sunrises I’ve witnessed.

Today, we remained soaking wet for the most of the day. As we were driving to our study area, we watched a big storm roll in. Once we assembled our gear and began to hike to the caves, it came down in sideways sheets of rain.

Collecting arthropods from the entrance of one of our study caves. Credit: Dan Ruby.

The plan for the day was to have Christina, Knutt and Pete continue to deploy traps and conduct time-constrained searched at each station, while Dan and I would go to the cave containing a large pool near Ahu Te Pahu. According to Sergio, this cave contained a year round fresh water source, and was thus very important to the prehistoric peoples of Rapa Nui. When I learned there was a year round subterranean water source, I realized this would be an excellent place to look for stygobites (aquatic cave-adapted organisms).

Watching the storm roll in, before we hike across the hills to our next cave. Yes, we were soaked by the rain. Credit: Dan Ruby.

Before Dan and I could go to this cave, we needed to check some of the pitfall traps placed on the surface near the cave we sampled yesterday. I didn’t have the actual trap type that I would have preferred for surface sampling, but I decided to deploy traps here anyway. As I expected, one of our pitfall traps was loaded with ants (and contained one cockroach) – the other two traps, near the cave’s dripline, were empty. I collected several ants, and I attempted to capture the cockroach, but it escaped.

Fabric found out of context sitting on a rock near a cave entrance. Fabric made from bull-rush is often used to wrap burials that are placed in Rapa Nui caves. We do not know if this fabric was used for this or not, but is seems appropriate to suggest that it may have been used for this purpose.

Once we were done here, we moved on to the Ana Kai Ua (Cave of Turning Water). As we were hiking from Moon cave to Ana Kai Ua, it started raining again, and by the time we reached the cave and went it, the bottom fell out of the sky. Although we were in a cave, and one may think there would be less water underground, this was not the case. Cave of Turning Water contained formations with dripping water throughout. This cave contained drip pools, dripping water, a large stream and pool and water vapor throughout.

This is a very fuzzy image of me searching for aquatic organisms in a large pool that consumes the vast majority of one of our study sites. The 100% humidity can cleary seen here. Credit: Dan Ruby.

Because we didn’t know exactly where the “turning water” was actually located, Dan and I began exploring this cave. I had brought my scoop net with me, and I was really hoping I’d get the opportunity to use it.

Broken obsidian projectile point found deep within a Rapa Nui Cave. Credit: Dan Ruby.

As we were exploring the upper passage of this cave, we received a big surprise. I approached what appeared to be a jumbled mass of wood on one of the upper ledges of this cave. Upon closer inspection, I found millipedes! These do not look exactly like

the new genus of millipedes that we found in Grand Canyon,

but they did appear to be cave-limited millipedes. This discovery was a huge boost for the project!

As I have learned the history of the island, the fact the island flora was reduced and dramatically changed by human use, human famine, and the introduction of the rat (Rattus rattus), I began to wonder…what if there were no invertebrates in these caves? What would this mean? Would this feed into the ecosystem collapse paradigm that so many ecology textbooks (as well as Jared Diamond) refer to on Rapa Nui. I am also wondered if perhaps a depauperate cave-fauna could be linked to the degree of anthropogenic environmental change this island experienced. These were many of the questions racing through my head.

While I cannot rule out these latter questions, I am feeling more and more confident that this millipede is a cave-adapted specimen. I will fully investigate these specimens tomorrow, and determine if they have eyes. I will get these specimens to my friend and colleague Bill Shear (a leading cave millipede expert) as soon as possible.

Obsidian tool found within the dark zone of our of our study sites. Credit: Dan Ruby.

Once we were finally able to quell our excitement regarding this new find, we began to search for the passage with the “turning water.” We found another side passage, which we believed was the right passage. So, Dan and I began to mosey down this passage. The deeper we went into the passage, the wetter it became. We continued further down passage and then found the water. We continued on for about 50 meters further; by this time, both Dan and I were soaking wet.

We both began searching for aquatic organisms or evidence of aquatic organisms. After searching for about 30 minutes and finding nothing, we decided to return to the surface. Upon reaching the surface, we found there to be a slight break in the weather, so we made a break to another cave that contained the rest of the team.

Upon our arrival, we learned they had deployed all the traps and microclimate sensors. This meant our day was nearing completion. We decided to have lunch in the entrance of the cave, and then we’d head back to the hotel.

Knutt mentioned that us eating in the entrance of the cave was quite similar to what the ancient Rapa Nui must have done. We continued to eat our chicken, rice and sautéed vegetables, as we contemplated what he had said. However, they had to hide behind fortified protective walls to eat their meals, while we had the luxury of eating in the openness of the cave entrance.

Picture is taken from the road leading to the internet cafe.