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How Tiny Sea Urchins Are Saving Kāne‘ohe Bay

February 01, 2017

Video: Hawaiian collector sea urchins are a vital component to cleaning up Kāne‘ohe Bay of invasive algae.

A sea urchin floats in the water, heading for coral.

Video: Hawaiian collector sea urchins are a vital component to cleaning up Kāne‘ohe Bay of invasive algae. This video, produced by Joseph Bennington-Castro, shows the aquaculture process of raising these algae-munchers in a hatchery.

It's around lunch time on a warm day in late November. Several staff members at the State of Hawai‘i's Ānuenue Fisheries Research Center at Sand Island on O‘ahu are gathered around a rectangular folding table, which has about half a dozen clear plastic deli cups lined up on it. Each cup is filled to the brim with a once-transparent liquid that's now clouded with a substance that one staffer describes as "pumpkin-colored" and another says looks like "mango sorbet."

But make no mistake, these cups don't contain the latest deli soup craze. Rather, they hold something far more valuable, at least to the coral reefs in Kāne‘ohe Bay: Tiny eggs from Hawaiian collector sea urchins (Tripneustes gratilla).

Here at the Division of Aquatic Resource's (DAR) sea urchin hatchery, it's spawning day again, a time when staff begin the process of rearing the next generation of sea urchins to be put out to pasture at the patch reefs in Kāne‘ohe Bay. These urchins make up the second step of a multi-agency effort — involving DAR, NOAA Fisheries, and the U.S. Fish and Wildlife Service (USFWS) — to release the reefs from the stranglehold of invasive algae.

Unfortunately, this spawning day has not been going according to plan. The female sea urchins — which rest upside down on the deli cups, their bodies partly sticking out and into the water through the circular holes cut into the cups' lids — have not been spitting out as many eggs, or "spawning," as expected or needed. But now, after more than two hours of trying to coax eggs out of the urchins, things are finally starting to look up for hatchery-manager David Cohen and his team.

"This is what a spawning is supposed to look like!" says Cohen, as he stares at the latest cup set down, its saltwater quickly being filled with an orange murk. "Alright, I think we're nearing the end here."

"End," of course, is relative. This event is the birth of another sea urchin cycle, which has been repeated numerous times over the life of a project that itself will go on for, perhaps, another decade.

Interestingly enough, this environmental restoration project owes its continuation to a completely separate environmental mishap that occurred more than a decade ago

The Flattery Incident

In February 2005, a ship named M/V Cape Flattery grounded on coral reef south of the entrance channel to Barbers Point Harbor at the southwestern coast of O‘ahu. The ship, a hulking 555-foot-long cargo vessel, was carrying about 9 metric tons (nearly 20,000 pounds) of bulk pelletized cement and 147,000 gallons of fuel, which could cause immense environmental damage if released.

To prevent a catastrophe, federal and state responders rushed to the scene. They worked diligently to lighten the vessel (by removing cement cargo and fuel) and manipulate and stabilize it so that it could be freed. After nine days of work, they were able to refloat the ship and tow it off the reef. Though some cement ultimately spilled into the water, the efforts prevented a potentially massive oil spill — but this doesn't mean the reef was left unscathed.

M/V Cape Flattery grounded in ocean.   Removing cement cargo from ship.

Left: Cape Flattery after it grounded at Barbers Point. Right: State and federal responders removed cement cargo to lighten the ship.

"We didn't have an oil spill, which is great," says Dr. Matthew Parry, a fishery biologist with the NOAA Fisheries Restoration Center and the Damage Assessment, Remediation and Restoration Program. "But there was substantial injury to the reef from the physical maneuvering of the vessel."

Under the Oil Pollution Act of 1990, however, any environmental injury that's incurred in response to the threat of oil release is compensable. That is, though the grounding didn't release oil, the efforts to prevent this from happening still resulted in environmental injury, making the vessel managers — Cape Flattery Limited and Pacific Basin (HK) Limited — liable.

After a rigorous damage assessment process that lasted several years, experts estimated that the grounding and response efforts injured 19.5 acres of coral, as well as the animals and algae that relied on the corals for survival. "Anything associated with corals was wiped out," Parry says. Coral reefs are considered essential fish habitat, or areas necessary for federally managed fish and other organisms to reproduce and survive.


The Flattery incident caused a large amount of coral damage (lighter areas in the image).

In March 2013, the Flattery managers reached a settlement with "natural resource trustees" (State of Hawai‘i, NOAA Fisheries, and USFWS), agreeing to pay nearly $6 million for coral reef habitat-restoration projects outlined in a plan put forth by the trustees.

"But at that site, we didn't really have a good methodology for restoring these things," Parry says. "How do you restore coral that is 50 or 100 years old, or even coral that's 20 years old?" What's more, in the time it took to complete the assessment and reach a settlement that area of Barbers Point had begun to recruit new coral and the ecosystem showed signs of recovery.

Rather than messing with the recovering reef, NOAA Fisheries and its partners turned to help other imperiled corals: Those in Kāne‘ohe Bay.

A Deadly Alien Algae

With a barrier reef bounding its seaward side, Kāne‘ohe Bay is the largest sheltered body of water in the main Hawaiian Islands. Its inshore portion contains numerous patch reefs that are, on average, less than 1 meter (3 feet) from the surface of the water — these reefs have been fighting a desperate battle for survival that began decades ago.

In the 1970s, there was a lot of interest in aquaculture in the United States, including in Hawai‘i. For instance, DAR built a greenhouse and hatchery at the Ānuenue Fisheries Research Center for giant fresh-water prawns (Macrobrachium rosenbergii), which they distributed to farmers throughout the state, Cohen says. And in 1979, Hawai‘i actually became the first state to develop a comprehensive aquaculture development plan.

Aside from state and commercial entities, independent scientists were also interested in aquaculture. In 1974, a university aquaculture researcher introduced foreign red algae (seaweed) of the genera Kappaphycus and Eucheuma to Kāne‘ohe Bay in experimental pens. Around the world, these seaweed, which come from southeast Asia, are commonly harvested for their carrageenan, a substance used in medicinal, agricultural, and manufacturing applications, including as a thickening agent in milk products.

But the red algae flourished in its new environment.

750x500-smoothering-seaweed-on-coral1-DAR.jpg   750x500-smoothering-seaweed-on-coral2-DAR.jpg

Without any natural predators, smothering seaweed can carpet Hawai‘i reefs. Credit: DAR.

In its native range, the seaweed is kept in check by sea urchins and certain fish species not found in Hawai‘i. Though collector sea urchins are common among many reefs throughout the state, they only occur in very low numbers in Kāne‘ohe Bay (it's unclear if they were once common and have been overfished or driven out by other physical or biological means). Without natural predators to eat it, the seaweed thrived, spreading far beyond its original pens.

The two genera of red algae grow together in the bay in large knotted mats or clumps, their thick, spiny branches sticking out in erratic directions. They grow quickly, spread easily (via fragmentation, in which a piece of a branch can regenerate into a separate seaweed), and outcompete native algae and corals — on the patch reefs of Kāne‘ohe Bay, they sometimes grow completely over coral, blocking it from the sunlight it needs to survive. These characteristics have earned Kappaphycus and Eucheuma the collective moniker, "smothering seaweed."

In 2005, the Nature Conservancy, University of Hawai‘i, and State of Hawai‘i's Department of Land and Natural Resources, with some funding from NOAA, developed an underwater vacuum device called the "Super Sucker" to clean up smothering seaweed. The Super Sucker consists of a barge-based, 40-horsepower pump and large hose; divers take one end of the hose into the water and use it to literally suck up unwanted algae from the reef, which is spit out back on the mini-barge. Local farmers use the collected algae as a nutrient-rich fertilizer for various crops, including taro and sweet potato, because of its high potassium content and potential ability to repel insects, according to DAR.

Able to suck up some 800 pounds of algae per hour, the innovative method has proven to be a highly successfully tool for removing smothering seaweed from Kāne‘ohe Bay. But the Super Sucker isn't able to — and was never intended to — defeat the alien algae on its own. "It's just like mowing the lawn," Parry says. "Soon after you're done, it will come back."

Diver with a super sucker hose.

Diver with the Super Sucker hose. Credit: Division of Aquatic Resources - Hawaii.

Before (smothered with seaweed) and after (seaweed removed) coral image.

Reef before (left) and after (right) using the Super Sucker. Credit: DAR.

To fully stop smothering seaweed in its track and save the bay's reefs, a two-pronged approach is necessary: First, suck the mass of seaweed off the reef; second, use another control agent to remove algae bits nestled in coral crevices and prevent the seaweed from growing back.

That agent? Sea urchins.

Dawn of a New Aquaculture Project

The challenge of using sea urchins as control agents in the bay goes beyond a straightforward numbers game. Not only are large amounts of urchins necessary to cover the extensive reefs in the bay, the urchins also have to be juveniles so that they're small enough to gorge on the algae hiding in the cracks of the reef. Simply relocating urchins from other reefs across the state was out of the question, leaving just one solution: Rearing them in a hatchery.

During the negotiations for the settlement, the trustees had thought to include such a strategy into the restoration plan for Kāne‘ohe Bay to complement the Super Sucker activities already underway. "The idea was to get the project to be self-sustaining," Parry says. "But at the time, nobody had really raised these sea urchins in Hawai‘i." The money that would come from the Flattery settlement would be, essentially, the public's money (given that it would have to be used for public natural resources), so the trustees had to be sure that whatever strategy they chose was actually possible and would work.

Sea urchin hatchery.

Panorama of the sea urchin hatchery at the Ānuenue Fisheries Research Center.

To that end, in 2009 the State of Hawai‘i put its own resources towards starting a sea urchin hatchery — repurposing the old prawn hatchery at Sand Island — to show that the strategy was viable. It was up and running in 2010. "In early 2011, we had our first urchin release," Cohen says.

Near the end of the settlement negotiations for the Flattery accident, the state had shown that it had a viable sea urchin hatchery for 18 months and that the strategy could be reliably added to the restoration plan for Kāne‘ohe Bay, Parry explains. The settlement secured the project's funding until around 2025, or about 20 years in total since the accident, which is the estimated time it would take for the damaged corals at Barbers Point to recover.

The sea urchin release is currently focused in an area known as Marker 12, a reef at the northern end of Kāne‘ohe Bay that takes about 20 minutes to reach by boat. When the project first began, this area, like some others in the bay, was covered in a thick blanket of smothering seaweed; DAR decided to concentrate efforts on Marker 12 to prevent the algae from spreading to reefs outside of Kāne‘ohe Bay. But once Marker 12 is free of smothering seaweed, they'll move south and tackle other patch reefs in the bay, Parry says.

Coral reef, Marker 12, area.

The reef at Marker 12, where sea urchin efforts are currently focused.

DAR's Flattery field team, led by Justin Goggins of DAR, periodically surveys the reef to make sure the treatment is working (it is) and identify areas that still need urchins. For the most part, Parry says, the animals stay put, but there doesn't appear to be a reproducing population in the bay just yet, which isn't entirely surprising given that sea urchins reproduce through so-called broadcast spawning. Here, adults in an area will release gametes (eggs and sperm) into the water in response to some environmental cue, typically wave action — if enough urchins spawn at once, their gametes will, with luck, mix and result in fertilized eggs.

"We're trying to get to some kind of critical mass that will jumpstart those urchin populations to reproduce naturally in the bay again," Parry says, adding that this effort isn't actually required by the terms of the settlement. "It's a 'pie in the sky,' but it would be a nice benefit [to the project]."

Retaking the Bay

Since the first urchin release in 2011, DAR has since significantly increased its production and release of sea urchins. In 2012, DAR released 60,000 urchins; in 2013, they released 90,000 urchins; and in 2014, they released 110,000 urchins.

"2015 was kind of a bummer year for us," Cohen says. Right now, DAR doesn't have definite answers about what caused 2015's "crash" in numbers.

Cohen estimates they will have released 70,000 to 75,000 urchins in 2016 and they hope to reach the 150,000 to 200,000 range in 2017.

Sounds simple enough, but raising urchins is a long process. In all, it takes about four months to grow sea urchins from tiny larvae to quarter-sized spikey babies that are large enough to get to work in the aquatic fields of Kāne‘ohe Bay.

On release day, Goggins’ team will load about 5,000 urchins into multiple shallow white trays, truck them over to Kāne‘ohe Bay, and then transport them to Marker 12. Using GPS devices, they'll keep careful track of which spots on the reef they're depositing urchins. Over the years, they've covered the entire outer edge of the shallow Marker 12 patch reef, leaving just the central area, which can take some 10 to 15 minutes of swimming to reach from the boat.

750x500-urchins-in-tray-NOAA-PIRO.jpg   750x500-diver-deposit-urchins-NOAA-PIRO.jpg

Left: Urchins are loaded on to these shallow trays on release day. Right: Divers try to deposit 1-3 urchins per meter. 

Getting the urchins to these untreated spots is easier said than done: The divers need to not only keep watch on their GPS location, they also need to make sure the buoyant urchin trays don't get submerged by the rarely still water. If they're scheduled to release urchins on a particularly windy or rainy day, the whole plan may fall apart.

Once at their respective destinations on the reef, the divers will dip down and look for signs of the smothering seaweed. With the large masses of the algae already removed with the Super Sucker, the alien algae look like a kind of patchy greenish-brown carpet on some of the coral and in crevices, and are difficult to identify with an untrained eye. Grabbing a handful of urchins, they'll swim down and try to release one to three urchins per meter — with several divers in the water at time, it takes about a couple of hours to fully empty the trays of urchins.

Release day is a physically demanding and exciting event, at least compared to the process of spawning and raising the urchins, which Cohen describes as a lot of "hurry up and wait." Unless, of course, something goes wrong. As it did today.

Spawning a New Generation of Urchins

This spawning day started off like any other, with the dive team going to the Honolulu Reef Runway to collect about 50 adult urchins. Today, however, they could only find about 20 urchins.

When the team collects the urchins, the jostling drive to the hatchery is normally enough to get them to start spawning. At the hatchery, they make note of which urchins are releasing the off-white sperm and which are releasing the orange-ish eggs (it's not possible to tell males from females otherwise). Today, as is often the case I'm told, more males are releasing gametes than females from the get-go.

The crew, numbering about half a dozen, takes the males out of the holding tank individually to get them to release sperm outside of the saltwater, which would otherwise "activate" the sperm and prevent it from being used later. Holding the urchins with their gonopore (genital pore) face up, the staff induce the urchins to release their sperm by gently agitating them in hand, such as by using a circular hand motion as if they're swirling wine to release its scent or using oscillating hand motions as if they're mimicking a washing machine cycle. They then use pipettes to suck up the sperm and deposit it into a single test tube; once the males stop releasing sperm, they're returned to another tank.

750x500-sperm-collection-male-NOAA-PIRO.jpg   Female sperm in containers.

DAR staff use pipettes to collect sperm from adult male urchins (left), while female adults spawn eggs into deli cups (right).

Division of Aquatic Resources, Hawaii, staff use pipettes to collect sperm from adult male urchins.

"We don't need much sperm," Cohen says. "It's a matter of trying to get a good amount of genetic mix." By the end of the harvesting, the test tube is only filled 5.5 milliliters (ml) with sperm, which is far more than needed.

Females, on the other hand, get agitated in the same manner and then placed on the deli cups. To get stubborn females to spawn, some staff swear by an intern-developed method that involves lightly tapping the female's body, though others are dubious. In many cases, they inject potassium chloride into the female's body cavity to cause contractions and induce egg release.

On a normal spawning day, the team can get a 0.25-inch-thick mass of eggs per female; today, the females are releasing nowhere near that amount. So, after about an hour of getting poor results, Cohen sends the dive team back out to collect more females at a nearby reef — compared with the Reef Runway, this reef is shallow and affected by waves, usually resulting in urchins that have already spawned some before being collected.

Yet, as Cohen exclaimed, these newly collected females are having a surprisingly normal-looking spawning, providing the eggs the team needs for the complicated next step.

From Larvae to Baby Urchins

Cohen and two assistants bring the sperm and eggs into the "larval room," a warm room containing a dozen 6-foot-tall, 200-liter, cone-shaped larval tanks. They divvy up the eggs into roughly equal batches, and proceed to dump the batches through a 90-micron mesh screen (for comparison, a single human hair is between 10 and 200 microns in width) and rinse the eggs with filtered seawater — this process, Cohen explains, filters out gunk, particularly urchin feces. They then put the batches into large buckets filled with filtered seawater.

Next, the trio dilutes some of the sperm with filtered water at a 1:1000 ratio, and squirts about 60 ml of the diluted sperm into each of the egg-infused buckets. They leave the sperm and egg mixture to fertilize for about 30 minutes. When they return, they filter the batches through a 30-micron mesh, which allows excess sperm to pass through, but not the fertilized eggs. "Marine invertebrates can get what's called polyspermy, which means that eggs can be fertilized by more than one sperm," Cohen says. Polyspermy larvae may be less physically fit and able to develop into healthy urchins.

A day later, tiny developing larvae are visibly suspended in the water column, appearing as distinct lines of particles when light is shone on them just right. Later, Cohen explains, the team will siphon out some of the larvae and count them to estimate their numbers. They'll then stock half of the cone-shaped tanks at about 4 larvae per ml, or about 800,000 larvae per tank. These tanks are aerated from the bottom — 1 to 2 bubbles per second are puffed up from the base of the tanks to keep the water moving and prevent the urchins from settling (and collecting harmful bacteria). 


Sea urchin larvae suspended in the water column.

The larvae will spend the next 23 days or so in this tank. During this time, Cohen and his team will exchange the water in the tanks every day and feed the larvae phytoplankton (microalgae), which they grow in stepwise tanks in a separate building in the hatchery. Like many of the protocols and procedures used in the hatchery, this food source — a mixture of Chaetoceros and Rhodomonas algae — was based partly on the few successful urchin hatchery endeavors in the world and partly on trial-and-error, Cohen says.

At the end of the larval run, the team will have 150,000 to 200,000 larvae left per tank, 30 to 50 percent of which will be "competent." These competent larvae have certain physical features that make them likely to successfully settle and survive in the large, rectangular tanks outside of their nursery home.

From the larval room, the immature sea urchins will be transferred to these tanks, which are filled with seawater and have plate racks covered in algal biofilms (mass of algae cells sticking to each other, as well as the rack's surface). The larvae settle on and eat these biofilms and develop into juvenile sea urchins.

When all's said and done, each batch of 800,000 larvae will result in 5,000 little urchins placed in the field — if, of course, there are no unavoidable disasters (like extreme El Niño conditions) or major staff mistakes. "There are a thousand tiny things that we have to get right," Cohen says. "I feel like if we can get 800 to 850 of them right, the other 100 to 150 hopefully will be forgiven."

The young urchins will steadily grow over time as they munch on the algae biofilm. After one to two months, they'll reach a diameter of 5 to 7 millimeters (about the size of a pencil eraser) and start feeding on macro-algae, or seaweed, which DAR grows in-house. Cohen and his crew have several large sunlit tanks outside of the hatchery for Gracilaria parvispora — a native seaweed or limu that's used in numerous Hawaiian dishes, including poke — and Ulva fasciata, which can be found worldwide.

750x500-urchins-in-hatchery1-NOAA-PIRO.jpg   750x500-urchins-in-hatchery2-hands-NOAA-PIRO.jpg

Young urchins in the hatchery. 

After all, the team can always begin the urchin cycle anew, once again filling their deli cups with the urchins' mango sorbet — a new beginning that'll bring the coral reefs in Kāne‘ohe Bay nearer to the end of their battle with smothering seaweed.

Last updated by Pacific Islands Regional Office on October 04, 2023