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Echinoderm mass mortality events shape marine ecosystems by altering the dynamics among major benthic groups. The sea urchin Diadema antillarum , virtually extirpated in the Caribbean in the early 1980s by an unknown cause, recently experienced another mass mortality beginning in January 2022. We investigated the cause of this mass mortality event through combined molecular biological and veterinary pathologic approaches comparing grossly normal and abnormal animals collected from 23 sites, representing locations that were either affected or unaffected at the time of sampling. Here, we report that a scuticociliate most similar to Philaster apodigitiformis was consistently associated with abnormal urchins at affected sites but was absent from unaffected sites. Experimentally challenging naïve urchins with a Philaster culture isolated from an abnormal, field-collected specimen resulted in gross signs consistent with those of the mortality event. The same ciliate was recovered from treated specimens postmortem, thus fulfilling Koch’s postulates for this microorganism. We term this condition D. antillarum scuticociliatosis.

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−1, twice weekly, compared to 30,000 and 60,000 cells mL−1. A density of 1 larvae mL−1 resulted in the highest body size and survival compared to densities of 2 or 4 larvae mL−1. Overall survival from larva to settled juvenile urchin increased from 8 to 10% settlement to 32–33% when the initial density was lowered further from 1.2 to 0.4 larvae mL−1. Growth, survival, competency and settlement did not differ between larval cultures kept at 25 °C or 28 °C. We believe that this novel method for culturing D. antillarum larvae, once scaled-up and validated to pilot scale, could provide juveniles for restocking of urchin-depleted reefs that suffer from algae overgrowth.

The 1983-1984 die-off of the long-spined sea urchin Diadema antillarum stands out as a catastrophic marine event because of its detrimental effects on 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.

Description of the establishment of both Gymnophthalmus underwoodi and Indotyphlops braminus on Saba, Dutch Caribbean.

Onderzoekers van Hogeschool Van Hall Larenstein, Wageningen University en Wageningen Marine Research hebben een nieuwe techniek ontwikkeld voor het natuurlijk herstel van Diadema zee-egels. Samen met de Saba Conservation Foundation, vonden zij een nieuw aanvullend substraat voor vestiging op het koraal en toonden aan dat een geschikte vestigingsondergrond heel belangrijk is voor het herstelproces.

Het zijn de schapen van het koraal. Zee-egels, die de riffen met hun gegraas schoonhouden van algen. En dat is belangrijk, want het koraal wordt wereldwijd enorm bedreigd. Maar in het Caribisch gebied gaat het ook niet goed met de zee-egels. Een ziekte dreigt verschillende populaties uit te roeien. Marien ecoloog Alwin Hylkema van de Universiteit Wageningen en tevens werkzaam als onderzoeker aan hogeschool Van Hall Larenstein doet onderzoek naar zee-egels en koraal-herstel. Hij is deze week gepromoveerd.

Het zijn de schapen van het koraal. Zee-egels, die de riffen met hun gegraas schoonhouden van algen. En dat is belangrijk, want het koraal wordt wereldwijd enorm bedreigd. Maar in het Caribisch gebied gaat het ook niet goed met de zee-egels. Een ziekte dreigt verschillende populaties uit te roeien. Marien ecoloog Alwin Hylkema van de Universiteit Wageningen en tevens werkzaam als onderzoeker aan hogeschool Van Hall Larenstein doet onderzoek naar zee-egels en koraal-herstel. Hij is deze week gepromoveerd.

In april 2022, the Dutch Caribbean Nature Alliance (DCNA), together with the University of Applied Sciences Van Hall Larenstein, hosted a sea urchin (Diadema Antillarum) restoration workshop on Saba. During the workshop experts and representatives from the Dutch Caribbean and Jamaica came together to join forces towards coral reef restoration. This workshop helped 21 coral experts from the Caribbean region and more than 65 online attendants, to obtain a comprehensive view of the overall situation of the Diadema sea urchin in the Caribbean, including the current die-off events and restoration techniques. Throughout the workshop important discussions took place to determine the next steps needed to mitigate the loss of Diadema sea urchins on a regional scale.

At Van Hall Larenstein University of Applied Sciences (HVHL) in Leeuwarden, the sea urchin Diadema antillarum has been cultivated to help restore the coral reefs around Saba and St. Eustatius (Caribbean Netherlands). The first young urchins bred in Leeuwarden were released on March 24th to the Rotterdam Zoo (Diergaarde Blijdorp). The ultimate goal is to also breed this species on Saba in order to give the sea urchin populations there a helping hand. These sea urchins keep algae growth under control, giving corals more room to grow. During this project, researchers worked closely with students from the Coastal and Marine Management program.

At Van Hall Larenstein University of Applied Sciences (HVHL) in Leeuwarden, the sea urchin Diadema antillarum has been cultivated to help restore the coral reefs around Saba and St. Eustatius (Caribbean Netherlands). The first young urchins bred in Leeuwarden were released on March 24th to the Rotterdam Zoo (Diergaarde Blijdorp). The ultimate goal is to also breed this species on Saba in order to give the sea urchin populations there a helping hand. These sea urchins keep algae growth under control, giving corals more room to grow. During this project, researchers worked closely with students from the Coastal and Marine Management program.

Diadema sea-urchins play a vital role in maintaining a balanced coral reef ecosystem and their restoration is essential to assist recovery of the degraded coral reefs around Saba and St. Eustatius. A collaborative effort between University of Applied Sciences Van Hall Larenstein, WUR, STENAPA, CNSI and NIOZ studied settlement rates of sea-urchin larvae. The new findings provide insight into why the Diadema population has not been restored since the massive die-off in the mid 1980’s and are important for developing and implementing effective sea urchin restoration projects.

Diadema sea-urchins play a vital role in maintaining a balanced coral reef ecosystem and their restoration is essential to assist recovery of the degraded coral reefs around Saba and St. Eustatius. A collaborative effort between University of Applied Sciences Van Hall Larenstein, WUR, STENAPA, CNSI and NIOZ studied settlement rates of sea-urchin larvae. The new findings provide insight into why the Diadema population has not been restored since the massive die-off in the mid 1980’s and are important for developing and implementing effective sea urchin restoration projects.

The massive die-off of the sea urchin Diadema antillarum in 1983–1984 is one the main reasons for low coral recruitment and little coral recovery in the Caribbean. As the natural recovery of D. antillarum is slow to non-existent, multiple restoration studies have been attempted. There are currently three different approaches to obtain individuals for restocking: the translocation of wild-collected juveniles or adults, lab-reared juveniles cultured from wild-collected settlers, or lab-reared juveniles cultured from gametes. All three methods are costly and can only be applied on a relatively small scale. We here propose a fourth, new, approach, which we term assisted natural recovery (ANR) of D. antillarum populations. ANR, a concept already applied in terrestrial restoration to restore forests and grasslands, can accelerate succession by removing barriers to natural recovery. In this study, performed on the Dutch Caribbean island of Saba, suitable settlement substrate was provided in the form of bio ball streamers that were attached to the reef shortly before the settlement season. At the end of the experiment, reefs with streamers had significantly higher D. antillarum recruit densities than control reefs without additional settlement substrate, indicating that the lack of settlement substrate is an important factor constraining natural recovery. However, D. antillarum recruit abundance was low compared to the measured settlement rates, possibly due to low post-settlement survival. The size distribution of recruits showed that recruits almost never became larger than 20 mm, which is likely due to predation. We conclude that, next to low settlement availability, low post-settlement survival and high predation on recruits also constrain the natural recovery of D. antillarum populations on Saba. To improve the survival of settlers till adults, we propose to 1) reduce predation on settlers by using bio balls or other substrates that can provide shelter to larger individuals and 2) optimize the reef habitat by removing macroalgae, either manually or by facilitating other herbivores. To improve the survival of recruits, we suggest to 1) choose sites with a known lower predation density or 2) protect recruits with a corral around the reef underneath the streamers. The combination of these measures could improve prospects for ANR, and we expect this new approach can contribute to the recovery of D. antillarum populations in the future.

University of Applied Sciences Van Hall Larenstein and Wageningen University and Research recently conducted a comparative study of artificial reefs within the Caribbean. This study provides new insights into the impacts of these structures on local marine life and neighboring ecosystems and highlight the need for comprehensive monitoring and integration into marine management plans.

University of Applied Sciences Van Hall Larenstein and Wageningen University and Research recently conducted a comparative study of artificial reefs within the Caribbean. This study provides new insights into the impacts of these structures on local marine life and neighboring ecosystems and highlight the need for comprehensive monitoring and integration into marine management plans.

Caribbean coral reefs are in decline and the deployment of artificial reefs, structures on the sea bottom that mimic one or more characteristics of a natural reef, is increasingly often considered to sustain ecosystem services. Independent of their specific purposes, it is essential that artificial reefs do not negatively affect the already stressed surrounding habitat. To evaluate the ecological effects of artificial reefs in the Caribbean, an analysis was performed on 212 artificial reefs that were deployed in the Greater Caribbean between 1960 and 2018, based on cases documented in grey (n = 158) and scientific (n = 54) literature. Depending on the availability of data, reef type and purpose were linked to ecological effects and fisheries management practices around the artificial reefs. The three most common purposes to deploy artificial reefs were to create new dive sites (41%), to perform research (22%) and to support ecosystem restoration (18%), mainly by stimulating diversity. Ship wrecks (44%), reef balls© (13%) and piles of concrete construction blocks (11%) were the most-often deployed artificial reef structures and metal and concrete were the most-used materials. The ecological development on artificial reefs in the Caribbean appeared to be severely understudied. Research and monitoring has mostly been done on small experimental reefs that had been specifically designed for science, whereas the most commonly deployed artificial reef types have hardly been evaluated. Studies that systematically compare the ecological functioning of different artificial reef types are virtually non-existent in the Caribbean and should be a research priority, including the efficacy of new designs and materials. Comparisons with natural reef ecosystems are scarce. Artificial reefs can harbor high fish densities and species richness, but both fish and benthos assemblages often remain distinct from natural ecosystems. Studies from other parts of the world show that artificial reefs can influence the surrounding ecosystem by introducing non-indigenous species and by leaking iron. As artificial reefs attract part of their marine organisms from surrounding habitats, intensive exploitation by fishers, without clear management, can adversely affect the fish stocks in the surrounding area and thus counteract any potential ecosystem benefits. This study shows that over 80% of artificial reefs in the Caribbean remain accessible to fishers and are a risk to the surrounding habitat. To ensure artificial reefs and their fisheries do not negatively affect the surrounding ecosystem, it is imperative to include artificial reefs, their fisheries and the surrounding ecosystem in monitoring programs and management plans and to create no-take zones around artificial reefs that are not monitored.

Baseline data on anthropogenic seafloor debris contamination in the year 2000 is provided for 24 submersible video transects at depths of 80-900 m, off the Dutch ABC-islands (Aruba, Bonaire, Curaçao), in the southeastern Caribbean Sea. In total, 202 objects were documented from a combined 21,184 m of transect, ranging from sandy lower island-slope to rocky upper island-slope habitat. Debris densities differed significantly with depth. Highest debris accumulation (0.459 items 100 m(-2) or 4590 items per km(2)) occurred at depths of 300-600 m on more shallow-sloping (20-30°) sand and silt bottoms. The overall average debris density was 0.27 objects per 100 m(2) (or 2700 items per km(2)), which is an order of magnitude higher than most other deepwater debris studies. What we describe may be representative for other small, populated, steep volcanic Caribbean islands. Food and beverage-related items were the single largest usage category identified (44% of objects; mostly glass beverage bottles).

Hogeschool Van Hall Larenstein en Wageningen University en Research hebben onlangs een vergelijkend onderzoek gedaan naar kunstmatige riffen in het Caribisch gebied. Deze studie biedt nieuwe inzichten in de effecten van deze structuren op het lokale zeeleven en aangrenzende ecosystemen en benadrukt de noodzaak van uitgebreide monitoring en integratie in mariene beheerplannen.

Hogeschool Van Hall Larenstein en Wageningen University en Research hebben onlangs een vergelijkend onderzoek gedaan naar kunstmatige riffen in het Caribisch gebied. Deze studie biedt nieuwe inzichten in de effecten van deze structuren op het lokale zeeleven en aangrenzende ecosystemen en benadrukt de noodzaak van uitgebreide monitoring en integratie in mariene beheerplannen.