The discovery that honu will heavily graze on Chondria tumulosa could be encouraging in the fight against the aggressive red algae, which in the past decade has smothered massive swaths of pristine reef in the remote shoals and atolls several hundred miles northwest of the Main Hawaiian Islands.<\/p>\n
However, in their recent report on the findings, researchers also caution that the turtles\u2019 behavior could put the main islands at greater risk of exposure to the so-called \u201cdevil weed\u201d<\/a> because the turtles migrate south after nesting.\u00a0<\/p>\n If Chondria reaches Hawai\u02bbi\u2019s main islands and blankets its reefs, researchers say, the economic and ecological effects would be devastating.<\/p>\n \u201cMany of the fish that we recreationally fish for like weke, \u02bboama, \u02bb\u014d\u02bbio \u2013 they\u2019ll all go away,\u201d said Randy Kosaki, a retired research ecologist who served as the National Oceanic and Atmospheric Administration\u2019s deputy superintendent for Papah\u0101naumoku\u0101kea. \u201cIt would affect our local lifestyle in every way you could imagine. It would be a major disaster.\u201d\u00a0<\/p>\n More:\u00a0A \u2018Devil\u2019 Seaweed Is Spreading Inside Hawai\u02bbi\u2019s Most Protected Place<\/a><\/p>\n Once a marine invasive species arrives, he added, it\u2019s virtually impossible to eradicate. \u201cReally, prevention is the only practical step.\u201d<\/p>\n The concern raised in the report, published in the journal Coral Reefs<\/a>, is that the honu might eat the invasive Chondria where it\u2019s smothering reefs in the Northwestern Hawaiian Islands and later spread it down the island chain via tiny, undigested fragments of the algae left in their feces.<\/p>\n Key questions remain, local turtle and seaweed experts say, to determine just how big of a risk the honu migrations pose. Would the fragments in the turtle poop be able to plant more Chondria after spending days in the honu\u2019s stomach and digestive tract?\u00a0Would they be viable after a migration to the Main Hawaiian Islands that could take up to several weeks<\/a>?<\/p>\n \u201cThose are all things that we need in order to get a sense of the risk,\u201d said marine botanist and University of Hawai\u02bbi M\u0101noa professor Celia Smith, one of the report\u2019s authors. \u201cAll of these are questions that we wanted to call out so that we could start to frame the scientific questions that would allow us to test this.\u201d<\/p>\n Limu Connoisseurs <\/p>\n Hawaiian green sea turtles are Hawai\u02bbi\u2019s largest marine herbivores, and they\u2019ve been found to eat more than 100 types of seaweed and seagrass<\/a> including invasive species that have spread across the islands\u2019 reefs.<\/p>\n \u201cA turtle will try just about anything,\u201d said Karla McDermid, a marine botanist and professor at UH Hilo\u2019s Marine Science Department. \u201cThey\u2019re gourmands.\u201d\u00a0<\/p>\n In the past decade, as thick mats of Chondria started to envelop the shallow coral reefs across Papah\u0101naumoku\u0101kea, researchers noticed the fish there didn\u2019t seem interested in grazing on the invasive algae.<\/p>\n During more recent visits, however, they noticed turtle-bite-sized holes in those mats. That prompted Smith and her co-researchers from the U.S. Fish and Wildlife Service to station a GoPro camera in the waters off Midway last summer for several hours at a time during their summer expedition.<\/p>\n They set the camera so it would record after they left the area but ran into a few challenges: The GoPro could only record for three hours at a time. It overheated in the sun at one point despite being underwater and shut off. Another time, the camera was knocked out of place \u2014 possibly by a fish \u2014 and filmed an area off the reef for about an hour.<\/p>\n Still, the research team found what they were looking for: nearly an hour of footage of honu scarfing down the Chondria, kicking up sediment as they dug into the mat with their beaks.<\/p>\n One female honu, their report says, took a \u201cremarkable\u201d 18 bites out of the mat in 95 seconds.\u00a0<\/p>\n \u201cNothing of the fish community appears to be able to take the same kind of whack at it that the turtles have,\u201d Smith said.<\/p>\n The research team conducted a necropsy of a separate dead female found stranded on Eastern Island, off of Midway Atoll, and found the Chondria made up 25% of the plant material in its digestive tract.<\/p>\n \u201cI\u2019m not surprised that they are trying the Chondria,\u201d McDermid said, \u201cnow that it\u2019s in enough abundance and they can find it.\u201d<\/p>\n The Worst-Case Scenario<\/p>\n Chondria tumulosa has burst into an invasive menace since researchers first spotted an algae they didn\u2019t recognize in 2016, then found mats of it smothering the reefs off Manawai, or Pearl and Hermes, three years later. <\/p>\n Still, its origins remain unclear. Was it native to the Northwestern Hawaiian Islands but stayed undetected until some ecological change caused it to go berserk? Or, did it arrive from abroad?<\/p>\n One of the main arguments supporting the theory it\u2019s an alien, Kosaki said, is that the local fish seemed unwilling to graze on it. However, Smith said the GoPro footage also shows fish for the first time interested in foraging fragments, at least, of the Chondria kicked up by honu beaks.<\/p>\n \u201cThere\u2019s very few fish that are just going to munch through a thick mat,\u201d McDermid said. \u201cTheir mouths aren\u2019t made that way.\u201d<\/p>\n \u201cA turtle,\u201d she added, \u201cdoesn\u2019t care.\u201d McDermid said she wasn\u2019t aware of any previous studies on whether honu had helped spread invasive plants across the islands via their feces.<\/p>\n The thought of Chondria tumulosa landing in the Main Hawaiian Islands, Smith said, is scary. So far, researchers have witnessed the algae spread and blanket areas with relatively few nutrients in the water to support such aggressive growth.<\/p>\n More:\u00a0Guardians Of The Deep<\/a><\/p>\n Imagine what the Chondria might do, Smith said, if it lands in a nutrient-rich environment such as K\u0101ne\u02bbohe Bay, where manmade runoff has helped fuel coral-killing outbreaks of invasive algae such as Euchema<\/a>.<\/p>\n \u201cIt so just knocked my socks off,\u201d Smith said.<\/p>\n Typically, she and McDermid said, the ocean currents push to the northwest and could help keep the Chondria in place. But other vectors such as marine debris and, possibly, the honu could push it farther south.<\/p>\n When researchers travel to and from the Northwestern Hawaiian Islands, Kosaki said, they soak their diving gear in bleach and take other measures to try and prevent any spread of invasive species.<\/p>\n One hope, he said, is that the aggressive Chondria growth in Papah\u0101naumoku\u0101kea might simply dissipate on its own the way other native and invasive algae has done in Hawai\u02bbi. Then, if it reaches the main islands, Kosaki said, it might repeat that pattern.<\/p>\n \u201cI think that\u2019s the best-case scenario,\u201d Kosaki said. \u201cI wouldn\u2019t call that necessarily a likely scenario.\u201d<\/p>\n![\"Chondria,](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2026\/04\/pmnm-2024-kole-fish-manawai-chondria-1024x768.jpg\")
Chondria, an invasive seaweed, has smothered parts of the reef at Manawai, also known as Pearl and Hermes, in the northwestern part of Papahanaumokuakea Marine National Monument. (Nathan Eagle\/Civil Beat\/2024)<\/p>\n![\"Samples](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2026\/04\/pmnm-2024-chondria-bag-sample-896x1024.jpg\")
Samples of Chondria, an invasive seaweed, were collected at Manawai in 2024. A research expedition the following summer showed that honu will heavily graze on the algae, raising both hopes and concerns. (Nathan Eagle\/Civil Beat\/2024)<\/p>\n![\"Green](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2026\/04\/4280042-1024x808.jpg\")
A green sea turtle cruises off Kahe Point on O\u2018ahu. A new study shows the honu will forage on an aggressive invasive algae plaguing parts of the Northwestern Hawaiian Islands. It also raises concerns the animals could potentially bring the algae back to the Main Hawaiian Islands. (Craig Fujii\/Civil Beat\/2024)<\/p>\n![\"A](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2026\/04\/pmnm-2024-manawai-pearl-hermes-island-reef-aerial-chondria-1024x576.jpg\")
A complex network of reefs encompasses Manawai, also known as Pearl and Hermes Atoll. In recent years that network has been battered by Chondria tumulosa, a highly invasive algae. (Nathan Eagle\/Civil Beat\/2024)<\/p>\n
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