CROWN-OF-THORNS
OUTSIDE MENEHUNE WALL
SUMMER, 2023
In Summer 2023, there were thousands of juvenile Hawaiʻi’s native cauliflower coral (P. meandrina) outside the Menehune Wall breakwater of Kahaluʻu Bay. There were also reports of crown-of-thorns (COTS) in the area.
This page shares contributions to the Digital Coral Ark containing observational and video records of the reef outside the Mehehune Wall pertaining specifically to cauliflower coral and COTS.
This was not a scientific study, but rather a collection of observations over time to help spot trends and inform future conservation efforts.
June 17th, 2023
The stark white corals are just outside the channel leading out of the bay (by the pyramid rock). COTS predation was suspected in this area. One crown-of-thorns was noted to the south.
Video footage and compilation by Dear Ocean.
July 1st - 7th, 2023
VIDEO SUBMITTED BY JAN WAR WITH THESE OBSERVATIONS:
“One of the most significant observations we have made recently concerns the increase in the number of Crown of Thorns (COTS) sea star individuals that we are currently seeing within the Study Area. Up until the past three months, we rarely ever saw COTS starfish during our snorkel excursions outside the Menehune Wall. The number of COTS observed seems to have increased significantly in the past three weeks.
Most significant to mention is the relationship we have observed between bleached coral juveniles in the Impacted Areas and the presence of COTS starfish within those same areas. We have seen COTS presence in nearly each of the ten (10) designated Impact Areas. Most of the COTS are seen on vertical surfaces and bleached corals tend to be close by.
The colonies outside the Menehune Wall do not appear to have been impacted by sea surface temperature increase (El Nino effects). It is also early in the summer season for thermal bleaching to occur.”
READ JAN WAR’S FULL REPORT.
Video compilation by Dear Ocean from original footage contributed to the Digital Coral Ark by Jan War.
MAP OF AREA THAT JAN WAR OBSERVES REGULARLY:
“We have established a rectangular Study Area so that we can more easily concentrate our observing activity to a specific location. The Study Area is approximately 50 feet wide between the shallow rock wall area to where the reef drops off into deeper (>15 ft.) depths and is approximately 525 feet along a parallel pathway to the shoreline. The size of the Study Area is approximately 26,250 square feet or 0.6 acres.”
July 15th, 2023
VIDEO SUBMITTED BY JAN WAR WITH THESE OBSERVATIONS:
“We snorkeled outside the Menehune Wall between 11:15 a.m. to 12:50 p.m. in overcast clouds
Most COTS and white coral colonies are still occurring at the northern end of Study Area.
In this area three COTS were seen relatively close (within 50 ft.) of each other
The formerly bleached juveniles are rapidly getting invaded / fouled with algae. This turns them a light brown color and makes it difficult to tell what the COTS impact really is. Only the currently white colonies are obvious.
We saw 12 COTS in the study area.
We saw signs of white colonies further south, yet impact is much less there.
Impacted areas are now less isolated and hard to tell apart.”
RAW FOOTAGE OUTSIDE MENEHUNE WALL - 15 MINUTES | JAN WAR
Original raw footage taken on 07/15/23 and contributed to the Digital Coral Ark by Jan War.
July 16th, 2023
PAM MADDEN | CLOSE-UP VIDEOS OF PREDATED CORAL OUTSIDE MENEHUNE WALL - 7/16/23
Original raw footage taken on 07/16/23 and contributed to the Digital Coral Ark by Pam Madden.
PAM MADDEN CLOSE-UP VIDEOS OF COTS OUTSIDE MENEHUNE WALL - 7/16/23
Original raw footage taken on 07/16/23 and contributed to the Digital Coral Ark by Pam Madden.
VIDEO SUBMITTED BY PAM MADDEN WITH THESE OBSERVATIONS:
“My follow up comments based on my observation today: no difference in COT distribution between North and South end of Menehune wall. I went a little further south than the study site outlined in box. I popped up before turning around snapped a couple GoPro pics, hopefully the GPS is in the meta data (south of the building, just north of the north heiau). Appeared to be that when I came across a white patch of coral, I had good success finding COT in the area. Areas where the reef “drop off” had vertical walls appeared to be preferential habitat for COT. Based on my observations in other parts of West Hawaiʻi, I am not yet ready to say there’s a significant increase in COT. The eaten cauliflower coral maybe makes up 5% (at most) of the total number of cauliflower coral colonies present. There’s still a really good number of healthy CC colonies of all sizes out there. Water temperature was 80-82 degrees outside the Menehune Wall. Coming back into the bay, the water was 83 degrees.”
July 16th, 2023
JAN WAR’S OBSERVATIONS 7/16/23:
“We snorkeled within the Study Area today around noon. Although sunny, the conditions in many places were turbid and cloudy. This included inside the lagoon where we also swam into several warm patches near shore. It was very crowded.
Before moving on, Kelly wanted me to clarify that although we saw twelve (12) COT yesterday and those were each associated with an Impacted Area, she counted 15 impacted sites in total.
Here are a few bullet points we would like to mention as a result of today’s excursion.
Kelly counted over 500 white (dead) colonies today. She stopped counting after 500 and by that time we were near the southern boundary of the Study Area. This is the most we have seen so far.
As mentioned yesterday, most of the Impacted Areas are now near to or overlapping each other. This would account to seeing more dead colonies today. As we move south we can see the next Impacted Area coming into view.
Nearly all of the Impacted colonies are near a ledge that drops into deeper water. This also corresponds to where we are seeing COT. The COT seem to be using the ledge to move up, down or hide. Most do not seem to move into shallower areas.
I tried to count the algae fouled dead colonies within the Impacted Areas, although soon realized that it was an impossible task. The white colonies stand out, but the dead and fouled colonies blend in a lot with the other healthy new recruits.
An area inside the “wall” near the Triangle Rock had a few (3-5) white colonies close to each other. No COT were seen, although there was a cushion starfish close by.”
July 18th, 2023
After receiving several reports that crown-of-thorns (COTS) and multiple predated cauliflower coral colonies had been observed in the area, the Hawaiʻi Division of Aquatic Resources (DAR) quickly responded:
“DAR staff conducted a response effort to evaluate the impact to resources and whether the density of COTS individuals was at the level of an outbreak and may warrant mitigation efforts. Staff members surveyed approximately 7,100 m2 of reef area and observed a total of seven (7) COTS individuals and 346 colonies of coral with predation on at least a portion of the colony. DAR staff members computed a density of 0.000987 COTS per m2 of reef. Because this density is well below the densities recorded during documented outbreaks in Hawai’i and elsewhere in the Pacific, it was determined that the COTS event at Kahalu‘u is likely an aggregation of individuals rather than an outbreak.”
The conclusion was welcome news to everyone who had been observing the COTS and the juvenile cauliflower coral colonies. Still, continued monitoring was recommended:
“The DAR Kona staff plan to continue periodic survey efforts outside the Menehune Wall at Kahalu‘u Bay and monitor the COTS situation. The team will collect new survey data during each visit and investigate COTS density as well as percentage of live coral population affected to determine if the COTS population has reached an outbreak level or if a concerning percentage of the live coral population is dying as a result of predation.”
This was a wonderful example of how community members can work with government bodies to help monitor, understand, and protect Hawaiʻi’s near-shore reef environment. DAR completed a exceptionally detailed and educational report as part of this response, for which they have given Dear Ocean permission to share here [Report compiled by Chris Teague M.S., DAR Aquatic Biologist and Ashley Wills M.S., DAR/HCRI Habitat and Fish Monitoring Planner. GPS coordinates (survey starting point): 19.58073, -155.96909].
September 23rd, 2023
JAN WAR’S OBSERVATIONS FOR AUGUST AND SEPTEMBER, 2023:
“We have been seeing less COT and effects of COT since the middle of August. Most recently (September 2023) we are seeing 1-2 COT per dive and often none. We do not know where they have gone.”
AND… SOME FINAL SUMMER OBSERVATIONS OUTSIDE THE MENEHUNE WALL FROM JAN:
“If Cauliflower corals are available as prey, COT does not prey on mounding (Porities sp) corals. They appear to mostly prey upon juvenile Cauliflower corals colonies 1-3 inches in diameter. It is unknown how many colonies they prey upon or eat per day.
Each COT creates a trail of 10-12 white (preyed upon) colonies of Cauliflower corals within the immediate proximity of where it has been feeding. The easiest way to find a COT is to look for the white trail of dead colonies around it. We have not seen any COT within Kahalu’u Bay.
It has been noticed that preyed upon colonies begin to foul with algae (possibly first bacteria and other microorganisms) within a day (sooner) and are completely fouled within a period of 3-5 weeks. The final fouling process is a sequence of progressive layers of different alga and eventually includes various types of sediment. The fouled colony eventually turns into a black tombstone. [Dear Ocean Note: Jan has shared with us an interesting time-series photo summary of algal growth on recently predated cauliflower corals outside the Menehune wall.]
New recruits of Cauliflower corals continue to populate the area outside the Menehune Wall. There continue to be thousands of colonies of young Cauliflower growing outside the wall. Three years ago (2020) the largest colonies were in the range of 4-6” in diameter and height. The juveniles of 2 years ago are now 1-3” in diameter and height. The growth of colonies once established appears to grow 1.0 – 1.5 inches per year.”
September 24th, 2023
CLOSING THOUGHTS FOR THE SUMMER:
Given that community members’ observations in the ensuing months since DAR's survey suggest decreased numbers of COTS in the area, continued monitoring may yield some clues as to the pattern. For instance, a Triton's Trumpet was documented in the area in July, so perhaps the COTS were victims of predation, themselves. Alternatively, perhaps timing or conditions drew the COTS to the Menehune wall, either due to a mating event or because of the unusually large numbers of juvenile cauliflower corals present.
Triton’s Trumpet outside the Menehune Wall in July, 2023. Photo by Jan War.
This aggregation of COTS, along with the predation preferences and patterns, was certainly interesting to observe over the summer. The same is true for both the changes in numbers of COTS sighted as the summer progressed, as well as the changes in appearance of the recently predated cauliflower coral colonies in the weeks that ensued. Comparing observations throughout the year, and in particularly in the summer of 2024, may yield further insights into this phenomenon.
Do You Have Any Photos/Videos to Share?
IF SO, PLEASE VISIT OUR PHOTO/VIDEO CONTRIBUTOR PAGE AND GET IN TOUCH!
WE’RE LOOKING FOR PHOTOS AND VIDEOS OF KAHALUʻU BEACH PARK (INCLUDING THOSE TAKEN OUTSIDE THE MENEHUNE WALL) THAT:
have sufficient clarity and resolution to visually identify species of fish and/or coral.
can be identified by date and location (either by personal knowledge or embedded camera data).
are owned by adults 18 and over willing to grant permission to use in the historical database.
are from 2016 or earlier, especially.
EDUCATIONAL RESOURCES
- https://phys.org/news/2020-11-crown-of-thorns-house-home.html
- https://www.aims.gov.au/research-topics/marine-life/crown-thorns-starfish
- https://sharkresearch.earth.miami.edu/crown-of-thorns-starfish-a-threat-to-coral-reefs/#
- https://www.livingoceansfoundation.org/science/crown-of-thorns-starfish/managing-cots-outbreak/
- https://www.livingoceansfoundation.org/science/crown-of-thorns-starfish/coral-killers/#
We welcome observations you would like to share or corrections you might note. Contact us!
Image/Video Credits: Jan War, Christine Zalewski and Pam Madden for Dear Ocean, & Google Maps.