Preliminary results

We've accomplished a lot since this project was funded ~1.5 years ago! In May 2024 we traveled to Hawaii and collected environmental DNA (eDNA) samples from ~20 different anchialine habitats across Hawaii by filtering water from different habitats (see pics). We brought these samples back to our laboratory at the University of Texas @ Austin and extracted DNA from them. We then used a technique called digital PCR to quantify the amount of DNA in each sample that was from the anchialine endemic shrimp species Halocaridina rubra.

 

Sampling near Isaac Hale Park on the island of Hawaii

 

Hiking to sample a pond near Hilo, Hawaii

We didn't find what we expected! We had expected to find lots of shrimp DNA in the habitats where we saw lots of shrimp at the time of sampling, while in habitats with few or no shrimp we expected to see little DNA or perhaps still a decent amount, suggesting eDNA would be a good way to detect species in this habitat that were confined to underground water sources (or just hard to spot).

What we found was no clear signal of shrimp DNA in any of our samples, even those collected right next to a ton of shrimp! At first, we thought our laboratory methods might not be working for some reason, but we can get a good signal when we use filtered water from aquaria with shrimp in them that are housed in our lab. And we get a great signal when we use pure DNA extracted directly from shrimp, so our methods our valid.

 

Halocaridina rubra at a habitat on Hawaii

 

Sampling on the Kona coast of Hawaii

So what do we think is going on? We're still not sure, but one possibility is that shrimp DNA just isn't that abundant in anchialine habitats. This might be because it is quickly swept away from the habitats due to water flow and currents in the ponds, or maybe its degraded super fast in nature, but sticks around longer in the lab. Either way, it doesn't seem super promising that we'll be able to use eDNA monitoring in Hawaiian anchialine habitats to look for rare, or maybe even common species.

 

Sampling on the Kona coast of Hawaii

So, what was the point? Conservationists and governmental agencies were anxious to know if eDNA would be a way to target specific habitats for conservation or management actions. Although disappointing, our research is important because it suggests our limited conservation efforts should be used on something more feasible than eDNA.

 

Sampling on the Kona Coast of Hawaii

So what's next? We're not done yet! Our current plan to wrap up this project is to continue some lab-based eDNA experiments. We want to know if the eDNA signal we get from tanks is stronger when more shrimp are housed in the tanks, which would be further conformation that our methods are sound. We're also planning to subject our field samples to a more sensitive form of detecting DNA than dPCR - high-throughput sequencing. This would allow us to determine if any shrimp DNA was in our samples, and if not, what DNA are we actually collecting from these water samples?

 

Performing "lab" work in our AirBnb after a day of field work

Thanks for all of your support! This project has become the basis for a chapter in one of our PhD students' dissertations, Cecilia Fitzgerald-Cook! Stay tuned for more updates and hopefully a publication describing our study in the next year or so.