HAENA — Submarine groundwater discharge could be contributing to the black band coral disease outbreak on Kauai’s North Shore.
That’s according to initial evidence discovered during a United States Geological Survey study at Makua (also known as Tunnels) and Haena, conducted July 29 through Aug. 5.
“We don’t have a smoking gun yet, but circumstantial evidence is pointing in that direction,” said Curt Storlazzi, head of the USGS coral reef project and a member of the 8-person USGS research team.
The University of Hawaii’s Christina Runyon was also involved in the study.
The goal of the survey was to examine the environmental factors associated with black band disease outbreak.
The focus was on Makua because the sediment runoff levels are low, which offered a potential for the disease to be linked to submarine groundwater discharge, Storlazzi said.
“What we were looking at were the environmental drivers, the abiotic parts of the ecosystem,” he said. “Why is it that all of the sudden we had this epidemic outbreak?”
UH scientists Greta Aeby and Runyon documented black band coral disease on Kauai’s North Shore in 2014, and since then studies have focused on the disease itself.
“The question is what really caused the outbreak,” Storlazzi said. “Potentially, there’s a linkage between submarine water discharge and black band coral disease.”
The theory sprouted because various scientists are finding the disease is mostly confined to shallower waters; deep-water reefs seem less affected, he said.
That observation was paired with the knowledge that rainfall in the mountains percolates down through the volcanic soil and lava tubes, and the underground water resurfaces on beaches and in nearshore reefs.
Storlazzi said Makua is an old delta, so over time sediment has been dumped in a fan shape throughout the beach and nearshore waters, mixing with the coarser materials.
“There were a number of places where submarine groundwater was coming out at Makua,” Storlazzi said. “Even clean water coming up could stress corals.”
That’s because corals grow in ocean waters that have a very low nutrient content. Both the salinity and nutrient levels are crucial for their survival.
But Dr. Katherine Muzik, Kapaa marine biologist who has been monitoring salinity at “Mala Moana,” her research location off Kauai’s eastern shore, says she’s not as worried about salinity levels as she is about what’s in the groundwater that’s seeping into the ocean.
For more than a year, Muzik has been taking daily readings from a HOBO instrument supplied to her by the Kauai Surfrider Chapter, which is a conductivity logger that calculates salinity in the water.
The instrument’s readings fluctuate from 23 to 29.8, with an average of 28.9 – a lower reading than the normal ocean salinity of 35.
“The data surprised me, that we have such comparatively low salinities here in Kappa, year round,” Muzik said. “Obviously the flow from Waialeale to here at the coast is long and circuitous, but eventually, fresh waters reach the sea, yet I expected us to be, offshore, a normal ocean 35. We are not.”
In the areas where she’s conducting daily research, the corals and fishes have adapted to the low salinity, she said.
“I can’t say there’s a correlation between the average salinity and black band disease at all,” Muzik said. “I’m much more worried about the contaminants in that fresh water.”
Those contaminants, things like bacteria, pharmaceuticals and residue from birth control pills, can seep into the water as it travels underground toward the ocean. When the submarine groundwater released into the ocean, those substances could be released as well.
“There are corals that have adapted to live in low salinity water, but they’re not adapted to pharmaceuticals and birth control and bacteria,” Muzik said. “I would highly favor the deposition that it’s the contaminants in the water.”
Storlazzi said he and his colleagues considered that theory as they were doing their studies at Makua.
“The volumes (of contaminants) are much smaller than what would come out of a stream, but these are pouring out 24 hours a day, 365 days a year, potentially with high concentrations of nutrients,” Storlazzi said.
The nature of the contaminants and nutrients found in the samples gathered by USGS, and the concentration will be determined as further testing and compiling of the survey’s data is completed.
Concentration of the submarine groundwater seepage was the other piece of the USGS investigation, with the purpose of discovering whether currents and tides have anything to do with the dispersion of the disease.
“The question is: Is it carrying nutrients and contaminants, and are the currents concentrating that in areas or ejecting it out of other areas,” Storlazzi said.
Current activity can concentrate substances in the shallows, but tides can do the same thing. As the ocean level drops, it creates a gradient Storlazzi explained, and submarine groundwater seeps out at a quicker rate.
“When tide is low, there’s much more restricted circulation and not much water gets over the reefs. Current speeds are much weaker and that means the submarine groundwater that comes out stays there a lot longer,” Storlazzi said. “That means more exposure of the reefs to that groundwater.”
Though there is evidence pointing in the direction of submarine groundwater seepage contributing to black band disease in corals, Storlazzi said that doesn’t yet mean it’s definitely a driver.
“We need to run lab tests and it’s going to be a while for us to figure it all out,” Storlazzi said.
Once the data is distilled, that will be presented to those “with a horse in the race in terms of management” Storlazzi said, such as Hawaii’s Department of Land and Natural Resources Department of Aquatic Resources.
“We’re trying to understand physical drivers of black band disease and we’re trying to provide unbiased, scientifically sound information,” Storlazzi said.
He continued: “If it’s a nutrient and contaminant issue, then maybe folks can make decisions to reduce those loads and when there’s a heavier rainfall, we’ll be able to say there’s a higher probability of black band disease, because more water is coming out.”
The information discovered during this survey will be made available nationwide as well, in places like Florida, where injection wells are set into limestone with “Swiss-cheese” like qualities that could be dumping nutrients straight into the ocean, Storlazzi said.
“We try to provide science to help the local issue, but also we hopefully understand the process enough to use that science in other areas as well,” Storlazzi said.
Muzik said she hopes to see more invitations for local cooperation when federal or state agencies come to Kauai for research purposes, because it’s difficult to get a clear picture of what’s happening in the oceans from short, infrequent visits to locations.
“I would like to see the recent NOAA (National Oceanic and Atmospheric Administration) and USGS studies invite local observers, especially surfers and fishermen, who are observant and astute, and most important — here and present,” Muzik said. “Of course they, above all, would like to preserve our Kauai shores and marine life.”