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Divers vacuum invasive algae off the reef. Photo © Kanako Uchino

"The north end of the bay is where we are focusing our efforts, because that's the leading edge of the invasion."

Eric Conklin
Hawai'i Director of Marine Science

Venture out on the water in O‘ahu’s Kāne‘ohe Bay and you are likely to see an odd-looking boat called the Super Sucker—a giant, barge-mounted vacuum cleaner that sucks invasive algae off the reef.  For Kāne‘ohe Bay, it’s a potential game-changer:  the difference between returning its coral reefs to health or watching them succumb to the chokehold of invasive algae.  

In 2005, The Nature Conservancy partnered with the State and the University of Hawai‘i to develop the Super Sucker, which can remove well over 1,000 pounds of algae an hour.  Today, it is operated by the State Division of Aquatic Resources, whose crew clears invasive algae from about seven acres of reef each year, and then seeds the reefs with native sea urchins that feed on the algae and keep it from growing back.  

It’s a powerful one-two combination, but it is not enough. 

“Up until now, it has been difficult to keep pace with the expansion of the invasive algae problem,” says Suzanne Case, the Conservancy’s Hawai'i executive director.  “That’s why we’ve built a second Super Sucker and are operating it in tandem with the State.  Having a  second Super Sucker gives us the capacity to get ahead of the problem and start reclaiming large sections of the bay.”

The goal is to clear the entire north end of the bay of the most pernicious algae by 2015.

A Bay Out of Balance

Kāne‘ohe Bay is the only bay in Hawai'i containing fringing, patch and barrier reef systems.   Traditionally, the bay was home to some of the highest numbers and greatest diversity of fish and corals on O‘ahu.  But over time these populations have plummeted, in large part due to the threats posed by invasive algae, overharvesting and land-based sources of pollution.  

Invasive algae were introduced into the bay for aquaculture about 30 years ago. Fed by nutrient-rich sediment, and without healthy populations of native plant-eating fish and sea urchins to keep them in check, they quickly spread. Today, they form thick, tangled mats that are destroying the bay’s ecology and turning its reefs into an algae-smothered wasteland.

“The bad news is that these algae species are the very, very worst introduced marine species in the state,” says Eric Conklin, the Conservancy’s Hawai‘i director of marine science.  “They smother and kill native corals, which are the core structural organisms of the entire ecosystem.”

The good news is that their distribution is still restricted.  The algae were introduced and became established in the south and central portions of the bay.  According to Conklin, there are effective natural barriers that prevent the algae from spreading south to Kailua Bay. But to the north there’s one continuous fringing reef that goes up the entire windward coast and, essentially, around the island—a  very real corridor for dispersal. 

“The north end of the bay is where we are focusing our efforts, because that’s the leading edge of invasion,” Conklin says. “The plan is to clear the north end and work our way back, keeping the algae contained inside the bay.  By having two Super Suckers instead of one, we will finally be able to get ahead of the invasion, removing algae faster than it can grow and spread – and that is going to make a big difference for the bay. ”

Sea Urchin Solution

But cleaning the reefs of invasive algae is only half the battle.  The most virulent strains can quickly return.  Experiments in the bay have shown that when patch reefs are cleared and left alone, the invasive algae return within months, while on reefs that are cleared and seeded with native sea urchins, the algae are kept in check. 

The State is now raising sea urchins in captivity at its Anuenue Fisheries Research Center on Sand Island, with the goal of producing tens of thousands of urchins for out-planting onto reefs.  The Nature Conservancy is supporting these efforts.   

Controlling Sediment   

Over the long term, keeping invasive algae in check will also require reducing the flow of sediment and nutrients into the bay.  To that end, the Conservancy is supporting a community-led project to restore a traditional Hawaiian wetland system in Kāne‘ohe’s He‘eia ahupua‘a—a large 2,250-acre mountains-to-sea land division with an historic fishpond at its ocean end.  The He‘eia community is clearing pasture land, planting taro lo‘i (fields) and restoring fresh water fishponds and native wetlands that act as sediment traps.

“Our long-term vision is to restore Kāne‘ohe Bay’s natural resilience and its ability to take care of itself,” says Kim Hum, the Conservancy’s Hawai‘i director of marine conservation.  “The Super Sucker, the sea urchins and the He’eia project are all important parts of restoring that resilience.” 

We Need Your Support

Building and operating a second Super Sucker will cost an estimated $2.5 million over the next three years.  Thanks in large part to a $500,000 challenge grant from the Harold K. L. Castle Foundation, the Conservancy has raised $2 million toward that goal.    

“It’s critical that we stop the failing health of the bay,” says Eric Co, marine program officer for the Castle Foundation.  “The amount of money it takes to confront these problems now is trivial compared to the economic impact of widespread degradation that would result if these species became broadly distributed around O‘ahu or throughout the state.”

The tools and knowledge to stop the invasion and reclaim the bay exist.  But to do it, The Nature Conservancy needs your help.    

“Coral reefs take thousands of years to build, but only decades to destroy,” says Case. “The Nature Conservancy urges you to komo mai kau māpuna hoe:  dip in your paddle and join the effort. With your support, we can reclaim Kāne‘ohe Bay and protect its marvelous marine life for generations to come. “