KAILUA-KONA – Coral continues to suffer in western Hawaii, although considerably less after three consecutive years of whitening that decimated the entire coastline, claiming 50 percent of the area's coral reefs.
The Division of Aquatic Resources of the State of Hawaii (DAR), an arm of the Department of Land and Natural Resources, finalized the data last Wednesday at 20 research sites throughout western Hawaii. The findings showed an average relative loss of coral cover of approximately 7 percent throughout the region, with an absolute loss of coral cover ranging from 1-5 percent in specific locations.
Lindsey Kramer delivered the news on Tuesday morning at the "Symposium on West Hawaii Marine Ecosystem: Bridging the Gap between Science and Management," a conference organized at the Kona Beach Hotel of King Kamehameha by the Evaluation Project of Integrated Ecosystems of West Hawaii, a program funded by the National Oceanic Atmosphere Administration. It was the third such symposium in West Hawaii, the other two were held in 2011 and 2014.
"We were really discouraged," Kramer said of the data.
He added, however, that there was no serious whitening in the last year, just a little partial whitening of specific types of corals with which no mortality was associated.
Although not ideal, Kramer said that, contextually, this is good news considering the catastrophic impact of the 2015 whitening, as well as the considerable damage corals in western Hawaii suffered during the bleaching in 2014 and 2016.
"It was really horrible, there was not a species that was immune to this," Kramer said of the multi-year global bleaching event. "There were not many regional patterns or differences in mortality, it really spread along the coast."
However, DAR has been able to identify trends during the last year and not all of them are negative. Kramer explained that there was a "mix" of coral recovery in seven monitored sites, while the coral coverage continued to decrease in the other 13.
At the regional level, the corals performed well in the northern waters, where a relative increase of corals 2.7 percent.
Ross Martin – also employed by DAR, which provided numbers from a coral recruitment study since 2004 and includes nine sites up and down the coast – indicated that those figures are a reflection of higher recruitment rates in northern waters and south Kohala. He explained two probable reasons why
"The northern part of the island is an older part of the island, and the reefs are much wider," Martin said. "Second, the general current comes from the south and pushes north, so many of the southern corals are probably spreading northward."
He added that several southern reefs are healthy, but probably had problems because they sowed in the north and are narrower than their northern counterparts.
These factors were reflected in Kramer's figures, which indicated that there was a relative loss of 12 percent of the coral cover in the southern region.
Kramer said there were some exceptions to the regional trends observed in the DAR investigation. In Puako, located in the northern zone, coral cover decreased. In the waters of the former Kona airport, located in a region that was characterized by a general decline, coral cover increased.
Human activity and impact have been shown to be strongest in the central area of the DAR long-term recruitment study, Martin said, which is one reason why corals may have fought there.
However, Kramer explained that the region around the Old Kona Airport is one of three monitored marine life conservation districts on the west coast of Hawaii. Two of these districts saw coral coverage increase in the last year, which she said is promising and deserves further examination.
Other encouraging news includes the type of algae that replace corals in certain areas. Coralline coral algae (CCA) coverage and light seaweed cover are increasing as coral replacements, which Kramer said is indicative of a potential for coral recovery.
Herbivores are vital agents for eliminating algae that promote coral recovery. The DAR research found that the presence of two important herbivores, sea urchins and parrotfish, correlated positively with the presence of CCA and clear algae turf, respectively.
Martin explained that West Hawaii's recruitment average over the DAR study – ongoing since 2004 – is 27. To put that in perspective, he contrasted it with other recruiting rates in thousands.
He said that the public can help in the recovery and health of the coral by choosing protective clothing on sunscreen, as some chemicals present in most popular brands have proven to be harmful to corals.
He added that the public should do everything possible to protect herbivores crucial to the health of corals and support marine protected areas, as they have proven to be more resistant to climate change and its impacts than protected waters.