coral reef

Abstract
The concurrent rise in the prevalence of conspicuous benthic cyanobacterial mats and the incidence of coral diseases independently markmajor axes of degradation of coral reefs globally. Recent advances have uncovered the potential for the existence of interactions between the expanding cover of cyanobacterial mats and coral disease, especially black band disease (BBD), and this intersection represents both an urgent conservation concern and a critical challenge for future research. Here, we propose links between the transmission of BBD and benthic cyanobacterial mats. We provide molecular and ecophysiological evidence suggesting that cyanobacterial mats may create and maintain physically favorable benthic refugia for BBD pathogens while directly harboring BBD precursor assemblages, and discuss how mats may serve as direct (mediated via contact) and indirect (mediated via predator–prey–pathogen relationships) vectors for BBD pathogens. Finally, we identify and outline future priority research directions that are aligned with actionable management practices and priorities to support evidence-based coral conservation practices.

MSc internship report

The project Restoration of resilience of nature and society in the Caribbean Netherlands aims to improve the resilience of the coral reefs in the BES (Bonaire, Sint Eustatius, Saba) islands, by mitigating the local stressors. One of the methodologies used is water quality monitoring. For this research, the focus was on chlorophyll a and turbidity temporal and spatial variability in Saba, and on how this could be related to anthropogenic and natural land-based local stressors. Chlorophyll a is a key water quality parameter which can give an insight on the eutrophic state of an area, while turbidity can be used as an indicator for coastal erosion and run-offs. These parameters were measured in 13 sampling sites, bi-weekly from May to August 2022, using two CTDs, a sensitive sensor technology. The land-based stressors were mapped as a result of qualitative analysis. Chlorophyll a values were highly variable, and often exceeded the safety threshold (0.2 μg/L) previously chosen, suggesting that the area was in a chronic state of eutrophication. Turbidity instead remained more stable and nearly always below the 3 NTU threshold. On one hand, spatial variability was not always directly linked to land-based stressors, and might be better interpreted including the action of sea currents. Temporal fluctuations, on the other hand, can be only partly explained by the amount of rainfall increasing run-offs from land to sea. Moreover, further research is needed to quantify local stressors, and long-term monitoring is necessary to fully understand the amplitude and nature of their influence on water quality.

For full report or more information,  please contact erik.meesters@wur.nl or gulsah.dogruer@wur.nl

MSc internship report

The health of coral reefs is threatened by anthropogenic land-based input, which is a global problem. High nutrient conditions make corals less resilient to environmental stresses like climate change and intense weather. Poor water quality is likely for the island of St. Eustatius due to the lack of sewage treatment and its erodible coastline. However, there are no data on this island’s long-term water quality monitoring. Chlorophyll-a concentrations, used to indicate water quality, were monitored at 13 locations around St. Eustatius twice a month from May to November 2022 (n=13). Additionally, images of the ocean floor at 10m were made using a remotely operated vehicle (ROV) to monitor benthic species communities and their habitat. The main conclusion of this research shows that the reefs are primarily in an algal-dominant state. This may be explained by the frequent, chronic exceedances of the 0.2 g/l chlorophyll-a threshold. Chlorophyll -a thresholds were surpassed more frequently and with higher amounts on the sites with a larger anthropogenic influence. The lower threshold for chlorophyll-a was surpassed at 5 out of the 11 sites by more than 30% of the measurements. This would point to a more pervasive low-level eutrophic condition at all sites. On many of the sand-based substrate areas, seagrass has covered it.

For full report or more information,  please contact erik.meesters@wur.nl or gulsah.dogruer@wur.nl

The 1983-1984 die-off of the long-spined sea urchin Diadema antillarum stands out as a catastrophic marine event because of its detrimental effectson Caribbean coral reefs. Without the grazing activities of this key herbivore, turf and macroalgae became the dominant benthic group, inhibiting coral recruitment and compromising coral reef recovery from other disturbances. In the decades that followed, recovery of D. antillarum populations was slow to non-existent. In late January 2022, a new mass mortality of D. antillarum was first observed in the U.S. Virgin Islands. We documented the spread and extent of this new die-off using an online survey. Infected individuals were closely monitored in the lab to record signs of illness, while a large population on Saba, Dutch Caribbean, was surveyed weekly before and during mortality to determine the lethality of this event. Within four months the die-off was distributed over 1,300 km from north to south and 2,500 km east to west. Whereas the 1983-1984 die-off advanced mostly with the currents, the 2022 event has appeared far more quickly in geographically distant areas. First die-off observations in each jurisdiction were often close to harbor areas, which, together with their rapid appearance, suggests that anthropogenic factors may have contributed to the spread of the causative agent. The signs of illness in sick D. antillarum were very similar to those recorded during the 1983-1984 die-off: lack of tube feet control, slow spine reaction followed by their loss, and necrosis of the epidermis were observed in both lab and wild urchins. Affected populations succumbed fast; within a month of the first signs of illness, a closely monitored population at Saba, Dutch Caribbean, had decreased from 4.05 individuals per m2 to 0.05 individuals per m2. Lethality can therefore be as high as 99%. The full extent of the 2022 D. antillarum die-off event is not currently known. The slower spread in the summer of 2022 might indicate that the die-off is coming to a (temporary) standstill. If this is the case, some populations will remain unaffected and potentially supply larvae to downstream areas and augment natural recovery processes. In addition, several D. antillarum rehabilitation approaches have been developed in the past decade and some are ready for large scale implementation. However, active conservation and restoration should not distract from the primary goal of identifying a cause and, if possible, implementing actions to decrease the likelihood of future D. antillarum die-off events.

A brand new, innovative floating coral fish breeding nursery is being tested at the Dive Friends Sand Dollar location on Bonaire.  This project, led by the startup company RoffaReefs, hopes to improve local coral reef fish populations to enhance the overall coral reef health for the Bonaire National Marine Park.

RoffaReef Floating Nursery. Photo credit: Casper Douma

Coral reefs are extraordinarily dynamic yet fragile ecosystems.  From the microorganisms working to build the reef’s foundation to the more recognizable reef inhabitants at the top of the food chain, this diverse ecosystem faces an incalculable number of threats. It is widely known that globally, reefs are struggling to keep up with the changes due to climate change and increased human activity. Sander van Lopik of RoffaReefs has a unique approach to help strengthen coral reefs in the future.

Photo credit: Casper Douma

Floating Fish Nursery

As part of the larger World Wide Fund for Nature the Netherlands (WWF-NL) “Dutch Caribbean Marine Strategy”, RoffaReefs has designed a system to breed marine fish larvae both in controlled aquarium environments and in the wild. Founded in the Rotterdam Zoo Diergaarde Blijdorp, RoffaReefs will begin testing its fish breeding system in the Bonaire National Marine Park through the use of a floating fish nursery. The goal of this project is to strengthen the overall health of the coral reefs by bolstering the local fish populations. Reef fish help maintain balance throughout the coral reefs as herbivorous fish graze on algae which would otherwise smother the coral while carnivorous fish aid in keeping overall populations in balance.

The floating fish nursery is being tested at the Dive Friends Sand Dollar location along the western coast of Bonaire. Throughout the pilot study, data will be collected to aid in improving the breeding system for the next series of trials. This research is a collaborative effort involving WWF-NL, the Dutch Caribbean Nature Alliance (DCNA), STINAPA, TU Delft, Diergaarde Blijdorp and KKV lijn in water B.V.

DCNA office lab. Photo credit: Casper Douma

DCNA-office lab

During the project, the researchers have their laboratory set-up at the DCNA office on Bonaire. Here, they are bringing fish eggs to determine the species. The goal is to develop an automatic imagery recognition tool to recognize the species with the ultimate goal to develop a “fish spawning calendar” so we know when and where fish species reproduce during the year.

Future

Projects, such as the RoffaReefs fish nursery, can contribute to healthier coral reefs which is important amongst others for local fisheries, tourism, and to mitigate the effects of sea level rise and worsening storm conditions.

Stay up to date on the projects latest developments by following along with the RoffaReefs Facebook page https://www.facebook.com/RoffaReefs/ or by signing up for the DCNA monthly newsletter BioNews (https://dcnanature.org/news/).

Photo credit: Casper Douma

Published in BioNews 59

Summary The Government of Bonaire has requested Wageningen Marine Research (WMR) to research the composition of the sand used to construct the artificial beach of the Chogogo Beach and Dive Resort. The major concern regarding the artificial sand was to evaluate whether the sand used could harm the marine park corals. The sand of the beach of Chogogo was sampled on the 10th of May 2022 and analyzed at the Netherlands Institute of Sea Research (NIOZ) for grain size and organic matter content. Additionally, the natural sand in front of Chogogo and several other places was sampled to better compare the sand that naturally occurs around Bonaire to the artificial sand. The results of the analysis and expert evaluation have provided the following responses to specific questions that have been raised.  

What are the potential effects on marine life, specifically corals, in relation to the constructed beach?  There is already sand being transported into the adjacent sea. Corals may already be affected. If so, then stress on corals will be increased. This will affect their metabolism, influencing coral growth and health. Furthermore, a higher sediment load will lead to a higher cover of the bottom by sand and prevent coral recruits from settling. In the longer term, corals more sensitive to sediment will disappear from the location which may be exchanged for more stress-tolerant corals. Generally, these species are less important for maintaining the reef. However, if the sediment load is high (permanently or incidentally), the sea floor may become fully covered by sand, and all corals may disappear. Thus, it is important to monitor artificial beaches for breaks in the retention walls, accumulation of sand along the walls, and make adjustments when necessary. It is important to note that since corals are long-lived organisms, a short-term assessment, as presented within this report, can barely unravel the longterm quantitative impacts on the health of adjacent corals. Thus, long-term monitoring of the coral communities in front of and up-current from (as control) the artificial beach should be favored.  

What are the potential effects on the health of the corals under normal weather conditions? Currently, the sand is already moving towards the sea, and it cannot be excluded that there are no negative effects. Potentially, visibility is already lower, and sedimentation has increased. In addition to the recommendations under question 3, we recommend installing (natural) windbreakers to decrease the wind-funneling effect between the resort's buildings in order to decrease wind effects on the sand.

What are the potential effects on the health of the corals during a storm or wind reversal? During a wind reversal or a storm, there is a high chance that waves will reach the retention wall and wash over it. Consequently, large amounts of sand could suddenly be transported onto the reef and cause massive mortality of corals by burial. The fine sand is likely to be transported downstream (generally in a northerly direction) and may lead to decreased light levels, increased sedimentation, and possibly mortality of corals. The exact transport of the sand is very difficult to predict without extensive measurements of current patterns at the location. We recommend that the retention wall be raised to the prescribed height. It may also be an option to put additional structures in place that can be deployed during wind reversals or storms to prevent sand from being washed away.

How important is the origin of the sand, the kind of sand (river or carbonate sand), the quantity of sand, the layout of the beach, and the constructed wall for the effects? The origin of the sand is very important. Since the sand is not carbonated, it will probably not be processed similarly to carbonated sand. It may be less likely to be cemented into the reef. Compared with natural sand in front of the artificial beach, the grain size distribution is much finer, indicating that the sand, once it travels over the retaining wall, is likely to be washed away by waves and currents. Once the sand washes away, all the negative effects of increased sediment load and sedimentation may occur. The exact location of the beach and the layout, as well as the buildings around the beach, influence the wind erosion of the beach. In this case, local wind conditions transport the sand toward the sea. Even if the retention wall is raised, the sand will continue to be piled up at the downwind side of the beach and will probably need to be redistributed regularly to not end up in the sea. We recommend periodical reinspection and redistribution to ensure that sand is not transported over the retention wall.

Overall, local wind, waves, and current conditions play a major role in the fate of artificial and natural beaches. Since all artificial beaches are on the island’s leeward side, the prevailing wind always blows the sand seaward. Increasing wall height and constructing wind blockers upwind of the beach may provide extra protection against the sand being blown away. Very high waves can accompany wind reversals. This may lead to massive sand transport onto the reef, consequently smothering and killing coral colonies. A general recommendation is to re-evaluate all artificial beaches given the expected consequences of climate change, such as sea level rise and an increase in the frequency of tropical storms, as this may have strong negative consequences for the reef. Current requirements for artificial beaches may have to be reconsidered.  

Final presentation 

A B S T R A C T
The long spined sea urchin Diadema antillarum was an abundant grazer on Caribbean coral reefs, until
1983–1984, when densities were reduced by ~98% during a region wide die-off. Since then, there has been very
little natural recovery of the species and interest is growing in applying aquaculture as a tool for population
enhancement. In this study we optimized a new shaker bottle cultivation method for D. antillarum. The method
was tested in a series of experiments by culturing D. antillarum from egg to juvenile in the Netherlands as well as
the USA. Larvae were cultured in standard 1-L glass reagent bottles, suspended by gentle constant movement on
an orbital shaking table and fed with either the microalgae Rhodomonas lens or Rhodomonas salina. Effects on
larval growth and survival were evaluated for different microalgal feeding concentrations, larval densities, and
culture temperatures. Larval density and growth were measured twice a week over a period of up to 56 days.
Larvae grew significantly faster on a higher feeding concentration up to 90,000 Rhodomonas sp. cells mL

As I compose this message in 2022, reflecting on Reef Renewal Bonaire’s accomplishments during 2021, and during its first ten years of operation – I find it impossible not to be captivated by the impact that RRFB’s work has had on the shores of Bonaire and Klein Bonaire. For the diver and snorkeler, this work is now easy to see - acres of restored Staghorn corals, stands of majestic Elkhorns thriving and spawning, and providing habitat for a teeming biodiversity of reef life. If you have been lucky enough to tour the Jeff Davis Memorial dive site, just a few yards off Bonaire’s northern coast, you get a sense of what years of hard work and actively managed, successful restoration work can achieve on Bonaire. When RRFB started, these accomplishments were the dream of our Board of Directors, and specifically of our founding President, Martien Van der Valk. As I assume the role of President in 2022 from Martien, I want to take this opportunity to thank him for his hard work, his broad vision, his get-things-done attitude, and for his ability to assemble the diverse team that has executed on behalf of Bonaire’s coral reefs for the past decade. From the beginning, Martien insisted that this vision could not succeed if it was the initiative of a single dive operation or resort. Rather, the whole of Bonaire needed to embrace the restoration vision for RRFB to succeed. Today, RRFB boasts more than 9 dive operators and resort partners who work together on the mission of protecting, restoring, and giving the reefs of Bonaire a helping hand. Together with the Bonaire government, hundreds of volunteer divers and donors, the Bonaire Tourism Board, STINAPA, DCNA, WWF, and other key island partners, the work of RRFB can truly be categorized as a whole, island-wide initiative. Martien helped define RRFB’s “Secret Sauce” – focus on practical goals that are informed by science but made successful and sustainable by a powerful engine of cooperation between local businesses, government, NGOs, volunteers, and the dive community. As we move forward into 2022 and our next decade,  we are setting some very ambitious goals, but we will be guided by Martien’s recipe and his standards as we move forward. Our second secret – in this case, our Secret Weapon - is our Chief Operating Officer, Francesca Virdis. From day one of RRFB, she has been making RRFB’s ambitious vision a reality. She has tirelessly led RRFB’s efforts, pushing it forward in the water, in the lab, and with the scientific community. You will see the impressive results of Francesca’s and her team’s work in this report on our activities in 2021 – but know that RRFB is just getting started. Yes, we will grow more and get more corals in the water but are also looking to significantly scale our outplanting efforts, to push restoration science with new partnerships and new techniques (including building Bonaire’s first full-featured coral Wet Lab), and to continue the push to make Bonaire the global Center of Excellence for coral reef restoration. Thank you to all our partners, donors, and volunteers. As a team, we will continue to execute for Bonaire’s coral reefs and their biodiversity.

David J. Fishman President, RRFB Board of Directors 

Using cryopreserved reproductive cells of elkhorn corals, researchers have crossbreed individuals from Florida and Puerto Rico with those of Curaçao in an important first step to creating more heat tolerant populations. The goal is to increase genetic diversity within at-risk populations of corals to help build resilience for future generations.

Genetic evolution allows entire populations to adapt, over many generations, to their local environments. However, environmental conditions are now changing at an accelerated rate, and in some cases, outpacing the ability of species to adapt. This is where Assisted Gene Flow (AGF) comes into play; this conservation intervention involves directly introducing genetic diversity into at-risk populations. In other words, researchers can now influence the reproductive process of threatened species in order to introduce new genetic diversity and thus facilitate faster evolution.

Elkhorn coral. Photo credit: Hans Leijnse

Elkhorn Coral

Corals are excellent candidates for the Assisted Gene Flow technique, especially the IUCN “critically endangered” elkhorn coral (Acropora palmata). Estimates place the decline in their populations around 95% since the 1980s. Further, they’ve struggled to keep up with changing water conditions and have documented reproductive issues. Mature corals are difficult to relocate for the purposes of AGF and coral gametes (reproductive cells) lose viability within a few hours. Researchers have therefore used cryopreservation to achieve AGF in this species.

Within the region, there are two distinct populations of elkhorn coral, one from the northwestern Atlantic and one from the Caribbean. A central, mixed zone exists near Puerto Rico. Over time, these populations have evolved to their unique thermal and oceanographic environments.

New Techniques

A recently published report highlighted the successful demonstration of using AGF to fertilize elkhorn corals. This research was a collaborative effort by CARMABI, Smithsonian Conservation Biology Institute, Penn State University, Florida Aquarium Center for Conservation, and Mote Marine Laboratory. Using cryopreserved sperm from eastern and central Caribbean (Florida and Puerto Rico) elkhorn corals, researchers were able to fertilize eggs from western Caribbean (Curaçao). By mixing these genetic pools, researchers may be able to accelerate region-wide adaptations to climate change.

Elkhorn coral. Photo credit: Duncan MacRae

Future of Conservation

In addition to achieving the highest ever survival rate for elkhorn coral juveniles, these researchers were able to generate the largest living wildlife population ever created from cryopreserved cells. This research proved the viability of using cryopreserved genetic material to increase genetic diversity. The future of coral conservation will require innovative techniques, such as AGF, to help keep pace with the accelerated changed due to climate change. By identifying and cryopreserving genetic material for threatened corals, crossbreeding with more tolerant populations may be the key to preserving these species in the future.

To read the full report, please use the DCBD link below.

https://www.dcbd.nl/document/assisted-gene-flow-using-cryopreserved-sper...

Article published in BioNews 48