Hilo Bay and other Hawaii shorelines are being plagued by invasive seaweed species, which University of Hawaii researchers have discovered are outcompeting native species.
While Hawaii has a great diversity of native seaweed species, they are increasingly being muscled out by a handful of invasive breeds, such as gorilla ogo and spiny seaweed.
Veronica Gibson, a UH-Manoa postdoctoral researcher, said these invasive species are believed to have been introduced to the islands from ships landing at Hilo Bay in the early 1900s, when the seaweed was inadvertently included in the vessels’ ballast.
Since then, the plants have spread around the state, crowding out native seaweed species and degrading the habitats of native fish.
“The most important problem is that they grow too quickly and outcompete our limu (seaweed) species,” Gibson said. “And it turns out our local fish species don’t prefer to eat these invasive species. And people don’t prefer it, either.”
Gibson added that gorilla ogo is able to form mounds in order to collect nutrients, which has the side effect of capturing sediments that cloud the water when the seaweed is disturbed. Gorilla ogo also grows directly over coral reefs, she said, which has additional ecological impacts.
“If we were to restore our limu populations, it would be overall better for fish and for us,” Gibson said.
A study that Gibson co-authored was published earlier this month that found the invasive species are better able to respond to fluctuating salinity levels at a cellular level. In watershed areas — where water salinity fluctuates wildly — they are able thrive despite local species failing.
Meanwhile, Gibson said, human impact is exacerbating the problem, because draining natural aquifers reduces the available habitats for native species.
“So, we’re reducing the available habitats for our limu, and then in the habitats they have, they’re being outcompeted by these invasives,” Gibson said. “So, it’s a rough life for our limu species.”
As for how to fix the problem, Gibson said there is no solution. She said large-scale invasive removal efforts over the last decade have had some impacts in Waikiki, but she said the best strategy for the time being is to avoid spreading the invasive seaweed inadvertently by moving rocks from an affected harbor to another.
Currently, Gibson said Hilo is where the majority of the invasive plants are on the Big Island, and that Kona shores have largely escaped them — for now.
But, she added, the true impact of invasive seaweed has yet to be determined. While Gibson said there are more than 400 known local limu species, there is not enough data on any of them to know if any are endangered.
“Unfortunately, unlike the charismatic sea turtles, we don’t know that much about our humble limu,” Gibson said.
Email Michael Brestovansky at mbrestovansky@hawaiitribune-herald.com.