OBSERVATIONS REGARDING THE POHIKI SPECIMENS
The size and the ratios of metabataeus and opae-ula were as predicted but varied greatly from other ponds! To obtain an accurate count, I sucked up one at a time with a roaster-baster, placed the specimen into a small clear plastic box, examined it with a 5x jewelers loupe, then tallied and placed into different containers. With the loupe, it was easy to identify the two species. Metabataeus has a large black spot on the top of the carapice and longer legs. Although the distinguishing feature is larger pinchers, the pinchers of smaller younger metabataeus were almost transparent and harder to see.
While both were small, the metabataeus was much smaller than I expected. In the Kona ponds that I had visited more often, the few predators that I saw were always twice the size of the opae-ula, were aggressively hunting, and had pinchers that were very prominent. In the Pohiki pond they were just a little larger and did not exhibit aggressive hunting behavior. Maybe the ones I was observing were younger and older larger ones were hiding.
The final count: 29 opae-ula and 19 metabataeus! That's the highest ratio that I've ever heard of! Based upon past experience, even though they were actively walking across the bottom, I placed an airstone into the metabetaeus gallon jar. In contrast, the opae-ula hardly moved and were piled up into the corners of a plastic box.
SECOND DAY MINI CRISIS!
In the morning, the metabataeus were not moving. Even when viewed with the loupe, they seemed to be dead or dying! The first day or so is always the most difficult and besides getting used to a different water chemistry, they had to adjust from the pond water temperature of about 93° F to the estimated night water temperatures of about 65° F to 70° F.
I guessed that they would be able to make the temperature adjustment if the water was strongly oxygenated and they were transferred into a smaller 2.25" x 2.25" x 5" clear plastic box with the airstone. It seemed to help and after an hour or two there was more movement with increasing movement throughout the day.
The opae-ula had spread out across the bottom of their container and while they were not moving around, they looked okay.
THIRD DAY PHOTOGRAPHY
Compared to the opae-ula that we grow in our tanks, the collected Pohiki opae-ula are smaller and photos were taken to compare against the size of a dime. A dime is about 3/4" in diameter and the largest Pohiki opae-ula is about 3/8". In our tanks, the largest are about 5/8"
These Pohiki metabataeus are significantly smaller that the large ones that are seen in West Hawaii. There you'll usually see just one metabataeus for every 100 opae-ula and the predators have very prominent pinchers, are much larger, and are very aggressive. The largest Pohiki metabataeus in this photo is about 1/2" long.
The Pohiki metabataeus are larger than the Pohiki opae-ula, but both are smaller than what I consider normal.
AN EARLIER ARCHIVE PHOTO
The three below the dime are opae-ula. The largest opae-ula shown is almost 5/8" long (about 40% larger than the Pohiki opae-ula).
Also compare two larger metabataeus collected in Kona against the Pohiki metabateus in the photo above. The largest metabataeus in the photo is over 3/4" long and it has since grown to over 1" long or twice the length of the Pohiki metabataeus shown in the photo above (About 100% larger than the Pohiki metabataeus).
WHAT CAUSED THESE DIFFERENCES?
Being geothermally heated may be a factor. John Chan and I believe that diet plays a large role. John has studied the stomach contents with strong magnification instruments and believes that decomposing leaf litter is a larger factor. Decomposition increases the number and kinds of bacteria, diatoms, protozoa, etc. Micro-invertibrates such as amoebas, tiny worms, copepods, etc. make up a larger portion of the Pohiki diet compared to the West Hawaii anchialine ponds.
Metabataeus evolved to better exploit this food source and there is, therefore, a larger metabataeus ratio. John's previous research showed when metabataeus and opae-ula are the same size, they ignore each other. His previous research also showed that larger metabataeus will eat smaller opae-ula but actually seem to prefer smaller metabataeus over opae-ula!
This is similar to African land predators that aggressively eliminate other predators within their hunting range.
This is also consistent with observations of our first mixed tank that was created in January 2004. That tank was a 2.5 gallon bowfront aquarium fitted with an airline and an undergravel filter. It began with 50 opae-ula and 4 metabataeus. Several times, berried metabataeus were seen, but to date, no juvenile metabataeus have ever been seen. The opae-ula population is relatively stable, but the metabataeus population may have actually gone down.
Although our greatest area of interest is opae-ula (Halocaridina rubra), to better understand them, it was also necessary to study the larger predator metabataeus lohena. The first Metabataeus article is posted at www.fukubonsai.com/M-L2b3.html