Science Perspectives – Climate Change and Native Hawaiian Shrimp

We're on a beautiful reach of Umauma stream and this is one of our study sites where we're looking at how climate change and invasive species are affecting stream habitat. This is one of nine sites that we have located on along the Hamakua coast of the Hawaii Island. The streams span a precipitation gradient. And so as you move along the gradient, you go from streams that are perennial like this where there's high flow, to streams that tend to become ephemeral, where there's little flow occurring due to less rainfall. What we're doing is looking at how the streams are responding to that and we have several parameters that we are measuring and one of them has been looking at native shrimp that live in these streams. Native shrimp is a dominant component of Hawaiian streams, the scientific name is Atyoida Bisulcata, and in Hawaiian, they're referred to as opae ka'ahole. Opae means shrimp and ka'ahole, kala is without, ole is color, so they are these clear shrimp that grow up to be about two inches long. They're unique not only from the perspective that they're only found here, but they have a unique lifecycle.

They are what we refer to as amphidromous and what that means is that they require a connection between this stream reach behind us and the open ocean. The adults will spawn upstream and when the eggs hatch, the larval forms will get flushed down the stream. We think that typically happens during storm flows because they need two to three days to get to the ocean. They are adapted to live in saltwater, so any longer than two to three days, they'll die in the freshwater and so it is critical that they get flushed out as fast as they can down to the ocean. Once they reach the ocean then, they can start to feed and they grow and they develop into juvenile shrimp. And when they get to be a certain point, they'll actually settle out and they will start to migrate back up the streams and we think they use either freshwater as a cue, they might use odor, they might be able to smell other shrimp, we're not sure. Downstream of us about 30 feet, there's a waterfall that is maybe 50 feet high and so those opae, those shrimp, had to come back and climb back up that waterfall to recolonize this area.

And then they feed and they reproduce and the whole lifecycle starts all over again. And so we're looking at the opae across this gradient sort of as a model organism because we see them in all these streams and they rely heavily on flow, it's important for them to feed, it's important for them to reproduce, it's just overall important for their lifecycle and so we can see how changes in stream flow will affect the native shrimp in these streams. We have essentially a natural lab setting where we can document how decreased stream flow is going to affect shrimp, gobies, algae, nutrients. We know based upon precipitation records that rainfall is decreasing and they're forecasting a warmer, drier climate which means less water for the streams. What our research is showing us is that across this precipitation gradient, this invasive tree, the strawberry guava, is significantly reducing water input to these streams. And so while we might not be able to do anything about decreased rainfall, by replacing exotic forests with native Ohia and Koa that can trap that water and put it back in the streams, we can maintain some, some base flow that will continue to provide critical habitat.

And so that, that aspect is really exciting to me, because it is really applied. It's not just understanding the ecology but it is saying: "hey, what can we do, what can we do to help maintain the water in these streams for the gobies and the shrimp?" As well as for the downstream end users-the farmers, the industries, the homeowners that require fresh water. Our overall goal is to take all of the information that we're collecting, the hydrology, the water data, the water quality, the ecology and integrate it into a user-friendly watershed decision support tool. And that tool can be used by our partners at the watershed partnerships, at the State Department of Land and Natural Resources and various other NGOs or private land owners such as Kamehameha Schools. They can take this user-friendly, transparent tool, take it back to their organization and use it to more effectively manage their watersheds, so they can identify, they can create a virtual watershed of interest and they can run various management scenarios and identify which scenario will have the greatest impact on water quality or water quantity.