Small Talk

Oahu's anchialine ponds host `opae ula

December 21st, 2015

It's a little refuge in the middle of encroaching development: the Kalaeloa unit of the Pearl Harbor National Wildlife Refuge. This 37 acre parcel of land is the only refuge in the state dedicated to the preservation of plants, not animals. The other two units are wetlands set aside for protecting birds.


I was lucky enough to get a tour from Annette Tagawa and Lorena Iwada, who work together- a joint effort between state and federal agencies- to maintain and protect the land and the Hawaiian life on it.


It was a beautiful day - overcast and not too hot, with light winds stirring the broad, flat plains near the ocean. The green mountains in the distance, the bright blue ocean just yards away. Here, in what felt like the middle of nearly-nowhere, it was easy to imagine pre-contact times, despite the occasional sound of plane engines overhead and the ugly sight of a refinery if one looked too far west.

Iwada explained to us two guests that day - David Yoshishige from the Honolulu Aquarium Society (a group of aquarium hobbyists) and me - about how she was part of a move to engage the community to help restore and maintain the land. It's far too large for the government to manage on its own.

In 2006 the feds reached out to schools and colleges. The group worked hard to clear kiawe and reforest it with native vegetation like ewa hinahina and akoko - plants that are part of a dry land ecosystem.

To make sure it was all done with cultural sensitivity, they enlisted a Native Hawaiian advisor who has ancestral ties to the land. Kahu Glen Kila told them to build an ahu - a shrine to invite water - and to have each new visitor add a rock to the shrine as a symbol of the team effort.

They completed the shrine in September. David and I are some of the first visitors!

Because this is federally protected land, nothing can be imported or exported, so the rocks are actually coral from the beach nearby. "It actually keeps with the theme," Iwada elaborated. "The coral is the first animal created in the Kumulipo (Hawaiian creation chant), and here, we're trying to return to our Hawaiian roots."

She directed us to set an intention for how we would take responsibility for this mission, and place the offering on the ahu. I thought it was a beautiful expression- so meaningful. I'm so glad to be a part of this in some way.


Iwada moved our tour along towards a space closer to the ocean. In 2003, workers discovered one anchialine pond (a landlocked body of water with a subterranean connection to the ocean) while working in this area. Tagawa fill in the timeline: "Three experimental pools were excavated in 2005 to see if water would infiltrate into the holes and recruit any ‘opae ‘ula.  One of these pools was excavated deep enough for water to infiltrate and nine months later the first ‘opae ‘ula were seen in this hole.  The other two weren’t successful and were backfilled."

"After the success of the first restored hole, 12 additional holes were excavated and successfully restored between 2006 and 2008, creating the biggest complex of anchialine pools - a total of 14- found on Oahu."

There are other anchialine pools on Oahu, but Kalaeloa has the biggest group of pools in one location on this island.


The feds alerted the state, which came, restored the ponds, and stabilized the population of the little `opae ula that live in them. There are an estimated 300,000 to 500,000 shrimp living in there, but it's actually a rough guess, since the shrimp live in fissures underground, and they can pond-jump since some of the pools are connected.

The red along the rock walls are the shrimp.

The red along the rock walls are the shrimp.

Biologists who study these shrimp found there are two distinct lineages of `opae in these Ewa ponds, called the Ewa and the Waianae lineage. The two are genetically different enough, separated by a five percent mitochondrial difference, such that they're very close to being officially declared two different subspecies.

Red shimp along rock walls.

Red shimp along rock walls.

Interestingly, one out of every ten shrimp sampled for DNA turn out to be from Waianae, and Tagawa was surprised to learn they do not interbreed; they do not hybridize!

It was quite delightful for me to see the creatures in their natural habitat. I've never seen them in the wild, and I liked furthering my understanding of the species I keep as pets.

What they're working on now is to figure out why they have never seen berried females in the ponds. They've seen pregnant females from other species of shrimp, but not the Halocaridina rubra - the `opae ula of pet store fame. (The ones I'm keenly interested in and keep forcing you to read about.)

They have figured out why there are no babies in the ponds; the salinity changes every 24 hours with the ocean tides, and the babies are too sensitive to the osmotic pressure, so they hide underground where it's more stable.


The experiment now is measure the ‘opae ‘ula is to determine if they breed all year long or if there is any seasonality with regard to reproducing. Tagawa brought some instruments of science with her and let us watch as she caught and measured some shrimp. This was the first day of her hypothesis.

Tagawa measuring shrimp.

Tagawa measuring shrimp.

What's so important about these little shrimp? Why all this effort for some little critters that we don't even consider people food?


"The `opae ula are extremely hardy, and by monitoring the stability of their population, we can spot any broader problems in the environment. If they are starting to struggle, it could mean we will start to struggle. It's a bit of a canary in a coal mine effect," explains Iwada.

"In the broader picture, it's important to take care of this land. By learning from our past, we can prepare for the future. It's the beauty of the management of time. What we had, what has changed, and what comes tomorrow. We can determine value and make decisions on what we will give up today for tomorrow," as she gestures in the distance towards the big malls that have risen up in the recent past.

Tagawa adds, "They are endemic to Hawaii; found here and nowhere else in the world, and part of Hawaii’s natural history and heritage."

It's pretty here in a stark way. I'm sure it's pretty here in a hot way on most days. It's a lovely idea, finding a delicate balance between nature and modernization. The land holds ancient wisdom that can still carry us forward into a better future.

I don't want to give this up for more concrete. I want this just like this, a sacred reminder of who we were, and who we can still be. And it's an intriguing thought that the smallest of creatures, a ten millimeter shrimp, can be part of that process.

3 Responses to “Oahu's anchialine ponds host `opae ula”

  1. Dennis Nakashima:

    Diane, that was a really interesting article. Let us hope that opae'ula, with the help of folks like you and Annette Tagawa, will be have a lasting and bright future here in Hawaii. Mahalo, for all that you do for these little creatures.

  2. Diane Fernandez:

    I totally enjoyed your informational article. Well recuperating from a shoulder operation I discovered Opae Ula. Started with a 2.5 gallon which by the way doing great. Am now cycling a 10 gallon. I fly to Honolulu from Maui to purchase these beautiful little creatures. Can't find any on Maui.

  3. Diane Ako:

    Thank you!

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