Residents and visitors both revel in Kauai’s lush landscape, and beneath its seascape. However, it’s underwater where things don’t look so healthy—at least not here at Makua Beach.
Scientists from the US Geological Survey got a detailed picture of the coral reef’s physical environment. Understanding just what these reefs are exposed to and for how long, may help explain why some corals here have succumbed to black band disease.
Christina Kellogg: Corals, like us, are an organism that has symbiotic microbes as a critical part of its biology. So disease is when that balance between the microbes and the host gets messed up by something.
This black band clearly delineates live from dead tissues. When a disease forces coral to lose its colorful tissue, a white skeleton remains behind.
Kellogg: We are going to sample out on the coral reef where the disease is, and then inshore right by these rocks that might be indicative of submarine groundwater discharge and compare between the two.
Kellogg: Is it submarine groundwater discharge, is it nutrients, is it is sewage contamination, is it all at once? I don’t know that we can outright answer that, but we are at least addressing each of the components. And hopefully we can put all those pieces together, and get an idea of what’s driving this particular disease outbreak.
So they towed salinity instruments by walking and kayaking, measured the speed of currents with instruments placed in various ways on the seafloor, and they released drifters to track how quickly the ocean flushed through the bay, which tells a story about exposure.
Curt Storlazzi: If there’s bad things like nutrients and contaminants, the exposure is a function of two things: how much of the stuff there is, and how long it is exposed to it.
USGS made the drifters on a 3D printer, saving tens of thousands of dollars. They ingeniously attached a GPS dog collar for tracking.
Kellogg: The submarine groundwater guys are looking to see where is it coming out and maybe how much.
To detect that freshwater running underground, they laid lines to measure the flow of electrical current. They also tracked an element, called radon—a tracer for groundwater— because radon accrues in freshwater flowing through the ground.
Ferdinand Oberle: We are trying to measure a gas called radon, to distinguish if we are looking at just surface run-off, or if it’s actually groundwater.
The team also collected sediment in streams and along the coast, and tested seawater to discover what bacteria lived around the reef. Their DNA gives clues about whether they were reacting to nutrients or freshwater.
Kellogg: So I’m collecting bacteria you can’t see, and then pulling out DNA you can’t see to try and answer questions that you can see.
And if you thought the tropical climate meant this data was easy to collect, it wasn’t.
Josh Logan: It was a little too deep and too rough, and so you couldn’t even hold the two boats…
Storlazzi: The surf was about twice as big as we were expecting it to be, and the wind was blowing probably twice as hard as we were expecting it to be
What’s the swell… it’s like 6-8 feet at 8 seconds offshore. And it’s putting a little too much water over the reef. Currents are 2-3 knots and you can swim, what, a good knot or a knot and half maybe.
Oberle: Water really isn’t our friend because none of these instruments are waterproof!
Dan Hoover: No one ever told me there was so much hard labor involved in science.
Working on a popular beach also gave the USGS a chance to answer questions and interact with public beachgoers.
Oberle: People have been more than just understanding of what we are doing. Most of them have showed great interest and concern for the health of the coral reef.
Pooling the data from biologists, chemists and oceanographers helps narrow down possible reasons—both natural and manmade—for the recent outbreak of black band disease on the north shore of Kauai.
Storlazzi: As the tide drops we have more restricted circulation so that groundwater comes out and is contained very close to the shoreline. However, that process has probably been happening for the past couple thousand years. You know, why are we now having a greater outbreak of BBD? Well one of the things you can see from aerial photos is that there’s a large increase in population development in this area with more septic system and leach fields. And if those nutrients are coming out, they are coming out in higher concentrations at low tide. It’s sitting over those reefs for much longer period of time, and that’s where we are seeing much higher black band disease.
Which brings up another question: if human activity is part of the problem, where do we start to make changes to protect coral reefs?
Thanks to the:
Filmed and produced by Amy West
At-sea drifter footage by Josh Logan, SCUBA footage by Curt Storlazzi
All CC license 3.0:
Footage from https://coralreefs.wr.usgs.gov/CoralDiseaseVideo.html
Music by Blue Dot Sessions (The Zeppelin, Steadfast, Balti), CC BY-NC 4.0