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Restoring Coral Reefs In Bonaire

InDepth editor Amanda White ventures into the depths of coral restoration with Reef Renewals Foundation Bonaire (RRFB)’s Francesca Virdis. To date, the organization has replanted 25,000 corals and is now planning to scale up restoration efforts.

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By Amanda White
Header photo by David J. Fishman of outplanted Staghorn corals.

Coral colonies serve as the foundation of coral reef ecosystems, and their rapid decline could mean a loss of habitat for more than 25% of marine life that depends on them to survive. With coral bleaching and rising ocean temperatures becoming a headlining concern across the globe, what can be done to help save this critical ecosystem? Hope is not lost. We caught up with environmental scientist Francesca Virdis, the coordinator for Reef Renewal Foundation Bonaire, a non-profit organization that is growing and replanting corals around the island of Bonaire, to find out  how they are working to save the reefs. 

InDepth: What is Reef Renewal Foundation Bonaire (RRFB) doing to address the loss of coral reef habitat?

Francesca Virdis: We started in 2012. The first phase of the project was to collect coral samples from the reef from different strains, or genotypes, of two different coral species—staghorn and elkhorn corals. Once the most abundant coral species in the Caribbean region, their populations have now been reduced by over 90% and are currently listed as Critically Endangered on the IUCN Red List and in the Endangered Species Act. This is the most important reason why we chose to work on the restoration of the population of these two species. Furthermore, they are branching and fast-growing corals, so they are easy to propagate and can show visible results in a short time.

After the initial collection, we brought these 200 coral samples to the nursery, and from there on we started propagating thousands of corals every year. 

What is the project’s ultimate goal? 

The ultimate goal is to assist in the recovery of degraded coral reef areas using active coral restoration as a strategy to preserve and enhance the population of coral species. 

Staghorn coral colonies that have been outplanted by Reef Renewal Foundation. Photo by Reef Renewal Foundation.

It’s not just about placing more corals on the reefs to increase coral abundance but also about working in terms of diversity—adding different strains of coral colonies to the wild stocks. When we outplant corals back to the reef, we want to strategically promote genetic diversity. In fact, different coral strains have different strengths and different abilities. For example, some of them could better withstand diseases, be more heat tolerant, or grow faster. 

Environmental conditions are changing, and they will change even more in the near future, so to give the reef a chance and increase its resilience, it’s critical to work on biodiversity. 

How do these nurseries work?

Since 2012, RRFB has grown corals using a “tree” nursery design. It’s called that because the structure resembles an antenna or a Christmas tree. The nursery trees are made of PVC and fiberglass, anchored to the seafloor at a depth of 5-8 m/15-25 ft.

Coral Restoration Project conducted by RRFB (Reef Renewal Foundation Bonaire). Photos and captions by ©Lorenzo Mittiga for National Geographic.

Each tree hosts between 100-160 corals of the same genotype. These are propagated from the same donor colonies that were collected originally in 2012 to populate the nursery. Corals hang on the trees and are suspended in mid-water. New fragments are cut from the growing colonies, using a technique known as “coral gardening,” creating new generations of corals. These corals are re-suspended back in the nursery, and the process begins again. Corals remain in the nurseries until they reach the proper size, and then RRFB selects them from the nurseries and outplants them onto the reef. 

How many corals have you planted since 2012?

From the same parent colonies, we can produce thousands of corals every year. We have more than 110 trees underwater that hold a total of 13,000 corals that you can count at any given time in our nurseries. To date, we have outplanted back to the reef more than 25,000 corals. 

When do you replant the corals outside of the nurseries?

Corals remain in the nurseries until they are reef-ready, meaning the overall health and size will give them a higher chance at survival when exposed to predators and other stressors outside of a nursery environment. Once ready, corals are selected from the nurseries to be outplanted onto restoration sites, which are degraded reef areas where these species of corals were in the past or are still present but in low density. 

As a baseline, we use maps that show how the corals were distributed in Bonaire more than 30 years ago.

Coral Restoration Project conducted by RRFB (Reef Renewal Foundation Bonaire). Photos and captions by ©Lorenzo Mittiga for National Geographic.

How does the replanting process work?

Based on the area size and bottom type, we choose the number of corals, strains, and outplanting techniques. RRFB uses different outplanting methods depending upon the substrate. 

For hard rocky bottoms, we use marine epoxy to attach the corals directly to the substrate. When no hard substrate is available, we use elevated biodegradable bamboo structures that are built-in sand/rubble areas to provide a substrate to attach corals. Corals, which are tied to the structures using cable ties, eventually cover the entire structure and grow down toward the substrate.

How long does it take from the beginning of growing them to when they are replanted? What’s the timeline?

It depends on the coral species and the initial size of the fragments. On average it will take about 6 to 8 months max to get outplanted to the reef.

How do you manage to plant all of these?

With the help of many volunteer divers, tourists, residents, and local dive professionals who work for the four dive shops that are members of the Foundation and support this project. The Foundation at the moment has only two employees, therefore the dive shop support and the community involvement are extremely important for us. 

How do you monitor the corals that you have replanted?

Photomosaic of a restoration site in Bonaire. Photo by Reef Renewal Foundation.

Before we plant, we do a photomosaic of the reef area we want to restore. Photogrammetry allows us to compare how the site looked before and after our work. Then, using image analysis, we can pull out different metrics to evaluate the performance of different strains that have been planted. We do in-water surveys as well to monitor survival and evaluate potential stressors such as diseases, predation, etc. We come back to the restoration sites and monitor their development on a yearly basis. 

What are the major threats facing the coral reefs in Bonaire?

I would say one of the major threats is water quality. We do have a sewer system, but only the buildings in town and within 100 m/328 ft from shore are connected to it. The rest of the buildings have very old septic tanks, which often leak. Untreated water means more nutrients flowing to the ocean, which leads not only to more algae growing on the reef but also the presence of more bacteria and viruses, which potentially can lead to more diseases. Furthermore, in town, there is an increased number of moored boats, which are not required to have their wastewater treated. Because Bonaire is located outside of the hurricane belt, many boats visit us for several months a year and their wastewater gets discharged straight to the ocean. 

Another factor that is affecting the water quality is sedimentation. Bonaire is a dry island with free-roaming goats eating the vegetation; this negatively affects the retainment of sediment. When it rains, a large amount of sediment gets washed away into the sea, contaminating the water and suffocating the corals. In addition, we are witnessing unsustainable coastal development. Often, because of the lack of regulation and enforcement, we have buildings too close to the ocean or artificial beaches with imported sand. If not properly handled, the majority of the sand gets blown into the ocean during or right after the construction process.  

Are the corals you are replanting more likely to survive the water quality? 

Recently outplanted corals. Photo by David J. Fishman.

Reducing stressors is definitely paramount for the success of the project. The Bonaire National Marine Park, together with the government and stakeholders, is working toward improving water quality on the island, educating tourists, and protecting the reefs. We have been successful in the majority of our restoration sites. However, having a long-term water quality monitoring program could help us to better understand why corals are affected more in some areas than in others. Our outplanted corals are also used as bio-indicators of environmental conditions. A lower survival rate after outplanting can help draw attention and actions to preserve degraded reef areas.

Do you think it’s possible to restore coral reefs on a large scale? 

Although it’s crucial to protect what we have by reducing the stressors that are affecting the reefs, restoring coral populations is a tool to buy time, and it’s faster than what people imagine. It depends on the coral species, but some of them are fast-growing, and we have been able to repopulate several sites, some as large as 3000 m2 /32292 ft2in just a couple of years, by outplanting no more than 2500 corals. In Bonaire, we are currently working on a “midscale” but we are looking forward to improving our efficiency and expanding in the future. 

Bonaire Reef Renewal partners with Project Baseline, how does that fit with your mission?

The idea behind the Project Baseline partnership is to promote coral reef awareness and to show people that a positive change is possible. Sadly, most of the Project Baseline projects are currently showing negative trends, which reflects the reality of nature preservation around the world. Through our project, we want to give a message of hope and show people that something can actually be done. Often when witnessing nature degradation, we feel powerless and don’t know what to do. With our work, we want to empower people and show what each of us can do to make a change.

What are your future plans?

We want to scale-up the restoration effort in Bonaire and support other locations to help them to develop successful restoration projects.

We recently started working on three additional boulder coral species—star corals in this case. We have been working on a new nursery design that is able to host these species of corals because they grow in a completely different way than the branching corals we currently work with. We recently obtained the permit to set up the nursery and, within the next two years, we are planning to produce at least 6,000 corals per year of these massive corals. 

Elkhorn coral colonies that have been outplanted by Reef Renewal Foundation. Photo by Reef Renewal Foundation.

We have also recently established a new partnership that allows us to bring an innovative restoration technique, known as larval propagation, to Bonaire. This technique is based on collecting reproductive material during coral spawning, fertilizing the eggs on land, and outplanting recently settled larvae back to the reef. The larval propagation technique uses the corals’ sexual reproduction as restoration method, and, more importantly, gives us the ability to dramatically scale up the number of coral outplants, work with numerous coral species and morphologies, and increase the genetic diversity of corals on reefs.

How can people get involved?

The dive shops that are supporting the foundation are responsible for the training of our volunteers, who are tourists or resident divers. Sometimes people are not interested in volunteering, but they still want to learn about it and support the project, so part of the class fee goes to the foundation as a donation. With the help from our supporting dive shops, so far we have trained more than 1,000 people as coral restoration divers.

Non-divers can also show their support by donating. One of the options is to purchase material from our online wish list and bring it with them when they visit Bonaire. Most of the material is affordable, but it is expensive for us to have it shipped. We invite everybody planning to visit Bonaire to check the wish list on our website.

Additional Resources:

Diving In Bonaire by Manuel Bustelo
Nourishing My Inner Tekkie at Bonaire Tek by Michael Menduno


Amanda White is an editor for InDepth. Her main passion in life is protecting the environment. Whether that means working to minimize her own footprint or working on a broader scale to protect wildlife, the oceans, and other bodies of water. She received her GUE Recreational Level 1 certificate in November 2016 and is ecstatic to begin her scuba diving journey. Amanda was a volunteer for Project Baseline for over a year as the communications lead during Baseline Explorer missions. Now she manages communication between Project Baseline and the public and works as the content and marketing manager for GUE. Amanda holds a Bachelor’s degree in Journalism, with an emphasis in Strategic Communications from the University of Nevada, Reno.

Community

Uncovering A Mass Extinction Event: The Lake Rototoa Mussel Survey

Water quality scientist Ebi Hussain led a Project Baseline citizen science team to determine what was happening to New Zealand’s Lake Rototoa mussel population. Crying cockles and mussels, alive, alive, No!! Here are the deets.

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By Ebrahim (Ebi) Hussain
Header photo courtesy of Oliver Horschig.

Lake Rototoa, a cold, monomictic1 dune lake in a rural area northwest of Auckland, New Zealand, is in peril. With a maximum depth of 26m/85 ft, Rototoa is the largest and deepest of a series of sand dune lakes along the country’s western coastline. Known for its increasingly rare, diverse population of native submerged macrophytes i.e., aquatic plants, and large, freshwater mussel beds, this lake is under increasing threat from a deteriorated water quality. Although the exact cause of this deterioration is unclear, the likely culprit is a combination of factors: eutrophication, land use activities, pest invasion, and climate change.

In late 2019, the Project Baseline Aotearoa Lakes team noted signs of a freshwater mussel population collapse as well as other evidence of environmental degradation. This was alarming, as freshwater mussels are rapidly declining in New Zealand, and globally, with 70 percent of the species considered at risk or threatened.

Many people are unaware that freshwater mussels are an important part of a lake ecosystem; as biofilters and bioturbators, they filter out nutrients, algae, bacteria, and fine organic material which helps purify the water. The loss of these keystone  species has likely contributed to the decline in water quality seen at Lake Rototoa.

The team’s observations prompted the design of a collaborative project between Project Baseline Aotearoa Lakes and the Auckland Council Biodiversity Team. This project is the first of its kind in New Zealand; it aims to fill critical knowledge gaps and, for the first time, quantify mussel populations in Lake Rototoa in a scientific manner. 

Ebrahim Hussain installing the transect. This peg marks the beginning of the first transect across the mussel bed. Photo by Oliver Horschig.

This project is the first of its kind in New Zealand; it aims to fill critical knowledge gaps and, for the first time, quantify mussel populations in Lake Rototoa in a scientific manner. 

The first objective was to assess the mussel population statistics, including species composition, abundance, size class, and recruitment success. The second objective was to determine habitat preferences, bed locations, and bed limiting factors. In order to satisfy the project objectives, the team designed a bespoke survey methodology to collect all the required information in a standardized way.

Digging Into The Data

The initial series of dives focused on habitat mapping and collecting bed scale survey information. The team has mapped almost 5 km2/3.1 mi2 of lakebed and 2.2 km2/1.4 mi2 of mussel bed so far. This information provided critical insight into mussel bed formation and habitat preferences which the team used to inform the site selection for the more detailed follow up surveys. 

The first phase of surveys has been completed and the results are frightening. A total of 1604 mussels (Echyridella menziesii) were counted. The combined density across all three survey sites was 41.4 mussels per m2/3.8 mussels/ft2. Out of the 1604 mussels found, 1320 (82.3%) were dead and only 284 (17.7%) were alive. The dead mussel shells were in a similar condition to the live individuals indicating that they may have all died during a recent mass extinction event.

No juveniles were seen during the surveys and all the mussels were larger than 51 mm/2 in. The surveyed population is composed entirely of mature adults, 64.1% of live mussels were larger than 70 mm/2.8 in in length, 30.6% were between 61 to 70 mm/2.4 to 2.8 in and the remaining 5.3% were in the 51 to 60 mm/2 to 2.4 in size class.

Measuring an adult Echyridella menziesii, this individual is 78mm in length and approximately 15-20 years old. Photo by Oliver Horschig.

Individual dead mussels were not measured but were placed into approximate size classes, all dead mussels were larger than 51 mm/2 in with the majority of them being placed in the 61 to 70 mm and >70 mm size classes. The average age of the mussels surveyed was estimated to be between 20 and 30 years old based on their size. Some larger individuals were 80 to 100 mm long and were estimated to be around 50 years old.  

This aging population and lack of younger individuals indicates limited-to-no viable recruitment in the surveyed area for more than a decade. Considering that most of the live mussels were at the upper end of their life expectancy and that there was no evidence of recent recruitment, the long-term viability of the surveyed population is low. 

While the exact reasons for this population collapse are not known, recent lake surveys (fish, water quality, and macrophytes)  provide some indication of possible causes. Recent fish surveys indicate a significant drop in the number of  the primary intermediate host species. Both galaxiid and bully species are declining due to predation by pest fish species. Without these native fish, the mussels cannot effectively complete their life cycle.

The declining water quality of the lake is also a contributing factor. The lake’s change from an oligotrophic state, which is low in plant nutrients and high oxygen at depth, to a mesotrophic state with moderate nutrients, subjected it to increased eutrophication.  

Eutrophication causes an increase in bioavailable nutrients which stimulates algal growth and in turn causes high organic silting. This silt settles on the lakebed and decomposes creating areas of low dissolved oxygen, which can cause animal die offs. 

Some studies suggest that these mussels cannot survive at dissolved oxygen concentrations below 5mg/L and it is possible that the lake undergoes prolonged periods of low-dissolved oxygen during seasonal stratification. The wide scale coverage of benthic blue-green algal mats further points to periods of anoxia, or absence of oxygen, and general eutrophication. 



Mussel Mania

Due to the low nutrient concentrations and the filtration capacity of the extensive mussel population, Lake Rototoa historically had good water clarity. Mussel filtration rates generally match their food ingestion rate, but once they reach their food ingestion rate, no further filtration will occur. If there is a high concentration of food (phytoplankton and zooplankton) in the water, the filtration rate is likely to be low. This means that as the lake becomes more eutrophic, the algal biomass increases, and the mussel’s filtration rate will continue to decrease. 

An Echyridella menziesii bed, showing a mixture of live and dead adult sized mussels. Photo by Ebrahim Hussain.

This decrease in filtration rates will contribute to the declining visual clarity. The significant loss of mussel biomass and ultimately the loss of mussels in Lake Rototoa exacerbated the situation and may have facilitated a higher rate of eutrophication.

Sediment is also known to affect mussel populations, and there are signs of increased sedimentation; however, no clear evidence of smothering or suffocating was observed. The combination of the organic silt, sediment, and benthic algal growth can clog the mussel gills, so there are likely to be some sediment-induced population stressors.

In terms of bed extent and bed limiting factors, the team made several key observations. The mussels tended to prefer gentle slopes and did not occur in great densities on steep faced slopes/shelves. Water level, riparian vegetation extent, and wind/wave-induced disturbance appeared to dictate the upper extent. Mussel beds were generally established at a depth just below the permanent water line a short distance away from the end of the riparian edge. Fewer mussels were observed in shallow, exposed areas with visible signs of wind/wave-induced substrate disturbance. 

The establishment of aquatic plants, changes in substrate, thermoclines, and potentially anoxia limited the lower bed extent. Mussels were commonly found in lower numbers in amandaphyte stands within the wider bed area and were not found at all within dense charophyte meadows. Mussels tended to establish around isolated macrophyte stands rather than in them. The lower extent of the bed mirrored the start of the deeper charophyte meadows. The littoral zone had clearly defined sections of mussels in the shallower areas (1.5 to 5 m/5 to 16 ft ) and dense macrophyte dominated areas in the deeper portion (6 to 10 m), which were relatively devoid of mussels. 

Ebrahim Hussain counting and size classing mussels in a 0.25m 2 quadrate. Photo by Oliver Horschig.

In the absence of aquatic plants, the thermocline separating the warmer epilimnion above from the colder hypolimnion below appeared to dictate the lower bed extent. Almost no mussels were found past the thermocline, which was between 6 and 7 m/20 to 23 ft deep during the survey period. Since mussel bed establishment is not known to be thermally regulated, the limiting factor here may be anoxic conditions, commonly associated with hypolimnetic water. This assumption has not been validated, and a more detailed investigation of stratification profiles are planned for this upcoming year.

A clear limiting factor is the change in substrate seen past the 7 to 10 m/23 to 33 ft depth contour. The substrate changes from sand with a surficial layer of silt to a semi liquid silt/soft mud. No mussels or macrophytes were found in these areas, and the substrate does not appear to support bed establishment. Benthic algal mats covered the lower extent of some beds but did not clearly limit their establishment; since these mussels are mobile, presumably they will move if they are being smothered.

In Conclusion

Despite the concerning results, this project is a landmark event as it is the first study of its kind in New Zealand and the first detailed survey of the mussel population in Lake Rototoa. This project highlighted the pressures faced by our aquatic environments and exposed the ugly truth of what is going on below the surface. We have uncovered a mass extinction event that is currently occurring in our back yard that no one even knew was happening. 

We have uncovered a mass extinction event that is currently occurring in our back yard that no one even knew was happening.

Now more than ever, projects like this are critical. Our environments are under increasing pressure, and it is up to all of us to take action to ensure that we preserve these ecosystems for future generations.

The follow-up phases of this project are planned to be carried out this summer. The data we have collected thus far has enabled the Auckland Council to make informed decisions on how best to manage these threatened species and preserve native biodiversity. We hope that our continued efforts at this lake will contribute to preserving this ecosystem and prevent the complete extinction of these threatened species.

Footnotes:

  1. Cold monomictic lakes are lakes that are covered by ice throughout much of the year. During their brief “summer”, the surface waters remain at or below 4°C. The ice prevents these lakes from mixing in winter. During summer, these lakes lack significant thermal stratification, and they mix thoroughly from top to bottom. These lakes are typical of cold-climate regions. 

Additional Resources:

InDepth V 1.6: Bringing Citizen Science To Lake Pupuke by Ebrahim Hussain

Learn more about Project Baseline
View their online database
Get involved 


Ebrahim (Ebi) Hussain is a water quality scientist who grew up in South Africa. As far back as he can remember he has always wanted to scuba dive and explore the underwater world. He began diving when he was 12 years old and he has never looked back. Diving opened up a new world for him and he quickly developed a passion for aquatic ecosystems and how they work. The complexity of all the abiotic and biotic interactions fascinates him and has inspired Ebi to pursue a career in this field.
He studied aquatic ecotoxicology and zoology at university, and it was clear that Ebi wanted to spend his life studying these subsurface ecosystems and the anthropogenic stressors that impact them. After traveling to New Zealand, Ebi decided to move to this amazing country. The natural beauty drew him in, and even though there were signs of environmental degradation, there was still hope. Ebi founded Project Baseline Aotearoa Lakes with the goal of contributing to preserving and enhancing this natural beauty as well as encouraging others to get involved in actively monitoring their natural surroundings.

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