It would be nice if OPAE-ULA could live in a safe and perfect world. In a larger sense, it lives under the long-term dire threat of an important part of its habitat becoming less and less accessible to them as anchialine ponds become filled up as part of development, but more significantly have alien predator fish introduced that force them into the subterranean watertable to exist on only a tiny percentage of the food that was once available to them or force them to forage at night when their predators are asleep!
But one way or another opae-ula will survive and never become endangered. Not so lucky is one of the predators that has no common name. It looks like opae-ula being red and only found in anchialine ponds. It's two to three times as large. Opae-ula are the most numerous of the creatures of the anchialine ponds and the smallest. Generally, you may find one metabateus for every 100 opae-ula. They are easy to spot. They are constantly moving, hunting and ambushing opae-ula who seem to have no problem "pop-corning" away as one approaches. I've never seen an opae-ula caught but have been assured that they are sometimes successful. Like opae-ula, they are most often hiding in lava crevices and openings in the watertable.
Metabetaeus lohena was identified by Dr. ____ Banner and Mrs. Dora ___ Banner in 1960 from specimens collected near Lohena Rock near South Point on the Big Island of Hawaii. Since then they have been found in many of the anchialine ponds wherever opae-ula is found. Most believe that it is primarily a carnivore preying on opae-ula. But that may not be totally true. Both opae-ula and metabetaeus are opportunistic omnivores that will eat a wide range of foods including algae, aquatic plants, insects, bacteria, molt shells, fish, meat, or vegetable matter.
|This is one of the first photos that I took of Metabateus at the pond at Hualalai. It's been very heavily retouched as I tried to add detail in a fuzzy photo. But it clearly shows the size relationship compared to opae-ula.|
|This photo shows two metabetaeus with four opae-ula and a dime. The dime is about 3/4" in diameter and the largest adult opae-ula is about 1/2" long. The metabetaeus are still far from fully grown.|
|Two metabetaeus with the one on the left carrying eggs and the one on the right more clearly showing the large pinchers that opae-ula lack.|
|A side view taken in a clear 2"x2" plastic box shows both the metabetaeus and opae-ula in the background. metabetaeus are a darker red and some have white bands at the joints of it's "tail." Some, but not all have a black spot on the carapace shell (the "head"). Unlike opae-ula, it is common to see metabetaeus with a lot of eggs held by the swimmerets.|
|An enhanced pair.|
|A berried metabetaeus female. They seem to carry 2-3 times the number of eggs compared to opae-ula and seem to be carrying eggs more often. But in our tanks, the metabetaeus population does not seem to grow. Is the survival rate low? Are they cannibalistic?|
|A digitally enhancement of metabetaeus from a photo to try to show more detail.|
|METABETAEUS. A close-up showing the underside photographed while it was on the side of a tank. Note one larger and one smaller pincher. Photo taken with a digital camera with a 5X jeweler's loupe held in front of the lens. Cropped and contrast optimized but not digitally enhanced.|
|OPAE-ULA. A similar photo showing the similarities but actually much smaller and without pinchers. Photo taken with a digital camera with a 5X jeweler's loupe held in front of the lens. Cropped and contrast optimized but not digitally enhanced.|
- INITIAL OBSERVATIONS OF A MIXED
- OPAE-ULA / METABETAEUS LANDSCAPED TANK
My initial efforts to grow metabateus failed and after talking to others, I learned that they felt it was more difficult too. To be able to design extraordinary "UTOPIAN OPAE-ULA BREEDING TANKS" I felt it was necessary for me to be able to observe the interaction between opae-ula and metabetaeus and because I can't spend as much time as I'd like at the ponds, I needed to have a specially designed tank here at Fuku-Bonsai. Unlike our other tanks, we felt that we needed to install an air pump to effectively have the equivalent of a standard aquarium "under-gravel filter."
But we wanted to also create a more attractive underwater scene. Anchialine ponds are sometimes openings in lava tubes in which the ceiling collapsed. The walls are almost vertically straight up and down with rubble on the floor. Using a number of pieces of very porous high-velocity pumice ejecta, a vertical "lava tube wall" was cemented together to have openings throughout.
The tank was a 2.5 gallon bow-front aquarium fitted with a light unit and bonsai base to allow picking it up and transporting it for presentations. The back of the tank was painted black. The bottom plate was permanently attached to the tank bottom and the uptake biological filter tube positioned in the back left corner. The reef wall was cured, then also permanently attached to the bottom baseplate. Larger 3/4" pumice was inserted between the reef wall and the back of the tank to form the breeding habitat and over time a breeding colony of 50 opae-ula was successfully established.
Usually, 75% (or more) of the opae-ula population were in the breeding habitat and only 20% to 25% were visible in the open. The ones that were visible were a darker red. But when the unit was fed, many that were in the habitat emerged to feed and these were almost clear or a light pink initially. If they stayed in view, they became red too.
Establishing the colony provided many insights that have contributed to the success of our 1/2-gallon Introductory Mini-Breeder Tank and 3/4-gallon Educational Breeder Tank. Unlike the opae-ula reproduction as reported by researchers and some customers, our larvae never emerged into view. We never saw berried females in this tank! But we saw tiny post-larvae and early juveniles emerging from the base of the reef wall! This is consistent with what happens in nature and differs from observations of successful reproduction in 10-gallon tanks.
After the breeding colony was established, four metabetaeus were introduced into the tank and THERE WAS A COMPLETE AND DRAMATIC CHANGE! It was no longer a Utopia! The opae-ula quickly relearned how to "pop-corn" to escape the predators! They completely abandoned the breeding habitat and stopped reproducing!
It's now been over 3 months since the four metabataeus were introduced. To date I have not yet seen they catch any opae-ula in spite of their constant efforts. Once I saw an opae-ula that was halfway through the molting stage when a predator grabbed him (or her). But it did a "pop-corning flip" that freed it from the molt-shell and allowed it to escape. There does not seem to be any increase (or decrease) in opae-ula or metabataeus. Although a few of the juvenile opae-ula survived and are mini-adults, it is likely that the predators caught and ate the opae-ula larvae, post-larvae, and early juveniles that were in the habitats.
I've noticed that metabataeus are always moving while the opae-ula tend to be almost stationary and hardly ever swimming. There is a very clear difference as all other of our tanks have only opae-ula and they are constantly lap-swimming. Does a stationary opae-ula indicate that it is stressed or "on the alert"?
In a few months, I plan to re-do this tank as the tension of having a mixed tank is uncomfortable for me. I plan to create a tank of only metabataeus with an air stone, less hiding places, and believe that they will do well. Metabataeus are very aggressive feeders and quickly go up to the surface when spirulina powder is floated. I believe they will thrive on flies and small insects dropped onto the water surface. Because they are 2-3 times the size of opae-ula, they appear very awkward as they filter-feed at the surface. I believe that they would be more attractive when a colony of only metabataeus can be established.
Many believe that metabataeus lives only in a symbiotic relationship with opae-ula which is believed to be their primary food source. Most of the time, they are described as carnivorous. I have heard of ponds where there are mostly metabataeus and few if any opae-ula. After observing them for a while, I believe they are opportunistic omniverous scavengers that will eat a wide range of foods and will be testing this theory with an independent metabataeus-only colony.
Opae-ula and metabataeus are both small and red and are both adapted to the epigeal-hypogeal environment of anchialine ponds. But there are twelve or more species of shrimps that are found in anchialine ponds. Some of these are also found in marine environments. Some exist only in dark caves and come out at night to feed. Opae-ula is the smallest and most numerous.