Diadema antillarum

As previously mentioned, a new wave of long-spiced sea urchins (Diadema antillarum) die-offs are happening throughout the Caribbean, including reports from the northern three islands of the Dutch Caribbean.

In mid-February 2022, the first reports of extensive Diadema die-offs came in from St. Thomas of the U.S. Virgin Islands. Within a month, additional mortality events had been independently observed on Saba, St. Eustatius, Dominica, Jamaica, St. Vincent. On St Maarten, Diadema loss has been recorded on the dive sites Little Bay (fort Amsterdam), Frenchman’s Reef and Cowboy Reef (Indigo Bay). In Curaçao, the first sightings of diseased sea urchins were reported in early June.  Two weeks later, more than 90% of the surveyed populations had disappeared.

On March 14th, 2022, St. Eustatius’ STENAPA was alerted by dive shops of a significant number of dead long-spined sea urchins in the artificial harbor area.  After conducting a survey, it was determined that 44% of the urchins were dead and 6% appeared to be sick, leaving only half the population in a healthy state.  The sick urchins were unable to stay attached to the substrate and had very minimal spine movement.

The video below was taken on St. Eustatius in March of 2022 by Kitmani Kitson-Walters (CNSI) and shows a number of sick and dying urchins across the seafloor.

A collaborative region-wide effort – the Diadema Response Network – has quickly formed to track and try to understand the cause of this recent die-off of Diadema (and possibly other sea urchins).

Special Diadema BioNews Edition Navigation

• Introduction
• Background and Current State
• Restoration Efforts
• What you can do to help

Nederlands, Papiamentu and Papiamento below

Last week, the Dutch Caribbean Nature Alliance hosted a sea urchin (Diadema Antillarum) restoration workshop on Saba. This workshop was led by University of Applied Sciences Van Hall Larenstein (VHL). 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. Important discussions have taken place to determine the next steps needed to mitigate the loss of Diadema sea urchins on a regional scale.

Coral Reef Restoration

Coral reef restoration methods are showing promising results in supporting regional efforts for restoring degraded coral reefs in the Dutch Caribbean. Coral reef restoration in the Dutch Caribbean has focused heavily on corals. This workshop was built upon research and innovation that introduces the restoration of the important algae grazer: Long-spined Sea urchins (scientific name Diadema antillarum).

Photo credit: Stella Grau

Diadema sea urchins

Diadema sea urchins play a critical role in maintaining healthy coral reefs, which are essential for coastal protection and a crucial source of income for people in the Dutch Caribbean as they are a magnet for tourism. Diadema sea urchins help sustain the delicate balance within the reef by grazing on algae, which

are the main competitors of corals. In the mid-1980s, a disease swept through the Caribbean, wiping out nearly the entire sea urchin population. In mid-February 2022, reports started getting in about new extensive die-offs in the Caribbean region. By restoring Diadema sea urchins alongside corals and solving local threats such as wastewater issues, corals will have a higher chance to survive.

Photo credit: Stella Grau

Workshop outcomes

In the RAAK Pro Diadema project VHL works closely together with other research institutes and local partners to restore long spined sea urchin populations on the coral reefs around Saba and St. Eustatius. This project is showing promising results. The lead researchers Alwin Hylkema and Tom Wijers shared their impressive tools, techniques, and latest scientific findings to facilitate the restoration of Diadema in the Wider Caribbean region during the DCNA workshop.

Several topics were discussed, including the status of these reduced Diadema sea-urchins, recent Diadema die-off events and Diadema restoration techniques. The participants also received hands-on training sessions, to improve practical skills related to Diadema restoration. Besides the 21 participants present on Saba, over 65 people followed the open presentations online.

Multi-island project

During the workshop, there was intense dialogue between the Caribbean islands. Important partnerships have been established and knowledge and capacity gaps identified which needs to be solved to restore the Diadema sea urchins in the Dutch Caribbean. VHL, DCNA and the organizations present are now looking into the possibility to set-up a multi-island Diadema restoration project to accomplish a common goal: Restoring one of the most important and damaged marine ecosystems, the coral reefs.

This workshop was generously funded by the Ministry of Agriculture, Nature and Food Quality (LNV) as a support to the Nature and Environmental Policy Plan for the BES-islands, the Dutch Postcode Lottery and SIA, part of the Dutch Research Council (NWO).

Stay up to date

If you would like to learn more about the Diadema workshop and DCNA’s activities, follow DCNA through their free digital newsletter BioNews (https://dcnanature.org/news/), Facebook (Dutch Caribbean Nature Alliance) or Instagram (DCNAnature). For more information about the RAAK PRO Diadema project follow https://www.facebook.com/reefrestorationVHL/ or contact project leader alwin.hylkema@hvhl.nl.

For more information on the Diadema workshop, please contact:

Tineke van Bussel, Research Communications Liason at research@dcnanature.org and

Dahlia Hassell – Knijff, Projects Officer at projects@dcnanature.org

Downloads & links >

____________________________________________________________________________________________________________________________________________________________________________________________________________________________

Nederlands

Vorige week organiseerde de Dutch Caribbean Nature Alliance een workshop voor het herstel van de zee-egels (Diadema Antillarum) op Saba. Deze workshop was onder leiding van de Hogeschool Van Hall Larenstein (VHL). Tijdens de workshop kwamen de deskundigen en vertegenwoordigers uit het Nederland Caribisch gebied en Jamaica samen om de krachten te bundelen voor het herstel van koraalriffen. Deze workshop hielp 21 koraalexperts uit het Caribisch gebied en meer dan 65 online aanwezigen om een uitgebreid beeld te krijgen van de algehele situatie van de Diadema-zee-egel in het Caribisch gebied, inclusief de huidige voorvallen van afsterving en restauratietechnieken. Er hebben belangrijke besprekingen plaatsgevonden om te bepalen welke volgende stappen nodig zijn om het verlies van de Diadema-zee-egels op regionale schaal te beperken.

Herstel van koraalriffen

 Herstelmethoden voor koraalriffen laten veelbelovende resultaten zien bij het ondersteunen van regionale inspanningen voor het herstel van aangetaste koraalriffen in de Nederlandse Cariben. Het herstel van koraalriffen in de Nederlandse Cariben is sterk gericht op koralen. Deze workshop was gebaseerd op onderzoek en innovatie die het herstel van de belangrijke algengrazer introduceert: de zee-egel Diadema antillarum.

Photo credit: Stella Grau

Diadema zee-egels

De Diadema-zee-egels spelen een cruciale rol bij het in standhouden van gezonde koraalriffen, die essentieel zijn voor kustbescherming en een cruciale bron van inkomsten zijn voor de mensen in de Nederlandse Cariben omdat ze een magneet zijn voor het toerisme. Diadema-zee-egels helpen het delicate evenwicht in het rif te behouden door te grazen op algen, de belangrijkste concurrenten van koralen. Halverwege de jaren tachtig raasde een ziekte door het Caribisch gebied en vernietigde bijna de hele zee-egelpopulatie. Medio februari 2022 kwamen er berichten binnen over nieuwe grootschalige gevallen van afstervingen in het Caribisch gebied. Door de Diadema-zee-egels naast koralen te herstellen en de lokale bedreigingen zoals afvalwaterproblemen op te lossen, hebben koralen een grotere kans om te overleven.

Photo credit: Stella Grau

Resultaten van de Workshop

In het RAAK Pro Diadema-project werkt VHL nauw samen met andere onderzoeksinstituten en lokale partners om de populaties van langdoornige zee-egels op de koraalriffen rond Saba en St. Eustatius te herstellen. Dit project laat veelbelovende resultaten zien. De hoofdonderzoekers Alwin Hylkema en Tom Wijers deelden tijdens de DCNA-workshop hun indrukwekkende tools, technieken en nieuwste wetenschappelijke bevindingen om het herstel van de Diadema in het bredere Caribische gebied te vergemakkelijken.

Verschillende onderwerpen werden besproken, waaronder de status van deze gereduceerde Diadema-zee-egels, recente Diadema-afstervingsgebeurtenissen en Diadema-restauratietechnieken. De deelnemers kregen ook hands-on trainingen om praktische vaardigheden met betrekking tot Diadema-restauratie te verbeteren. Naast de 21 aanwezigen op Saba volgden ruim 65 mensen de open presentaties online.

Multi-eilandenproject

Tijdens de workshop was er een intense dialoog tussen de Caribische eilanden. Er zijn belangrijke samenwerkingsverbanden tot stand gebracht en kennis- en capaciteitslacunes geïdentificeerd die moeten worden opgelost om de Diadema-zee-egels in het Nederlands Caribisch gebied te herstellen. VHL, DCNA en de aanwezige organisaties onderzoeken nu de mogelijkheid om een multi-eiland Diadema restauratieproject op te zetten om een gemeenschappelijk doel te bereiken: het herstel van een van de belangrijkste en meest beschadigde mariene ecosystemen, de koraalriffen.

Deze workshop werd gefinancierd door het Ministerie van Landbouw, Natuur en Voedselkwaliteit (LNV) ter ondersteuning van het Natuur- en Milieubeleidsplan voor de BES-eilanden, de Nationale Postcode Loterij en SIA, dat een onderdeel is van de Nederlandse Onderzoeksraad (NWO).

Stay up to date

Blijf op de hoogte

Als je meer wilt weten over de Diadema-workshop en de activiteiten van DCNA, volg de DCNA dan via haar gratis digitale nieuwsbrief BioNews (https://dcnanature.org/news/), Facebook (Dutch Caribbean Nature Alliance) of Instagram (DCNAnature). Voor meer informatie over het RAAK PRO Diadema project volg dan https://www.facebook.com/reefrestorationVHL/ of neem contact op met projectleider alwin.hylkema@hvhl.nl.

Voor meer informatie over de Diadema workshop, neem a.u.b. contact op:

Tineke van Bussel, Research Communications Liason op research@dcnanature.org en

Dahlia Hassell – Knijff, Projects Officer op projects@dcnanature.org

Downloads & links >

____________________________________________________________________________________________________________________________________________________________________________________________________________________________

Papiamentu

Siman pasá, Dutch Caribbean Nature Alliance a organisá un tayer di restorashon di seapel (Diadema Antillarum) na Saba. E tayer akí tabata bou di guia di Hogeschool Van Hall Larenstein (VHL). Durante e tayer ekspertonan i representantenan di e área di Karibe Hulandes i Jamaica a bini huntu pa uni forsa pa restorashon di ref di koral. E tayer akí a yuda 21 eksperto di koral di e region di Karibe i mas ku 65 partisipante ‘online’, pa haña bista amplio di e situashon general di e seapel Diadema den Karibe, inkluso e kasonan aktual di murimentu i di téknikanan di restorashon. Diskushonnan importante a tuma lugá pa determiná e siguiente pasonan nesesario pa moderá e pèrdida di seapel Diadema na nivel regional.

Restorashon di Ref di Koral

Métodonan di restorashon di ref di koral ta dunando resultadonan prometedor pa sosten di esfuersonan regional pa restorá refnan di koral na Karibe Hulandes. Restorashon di ref di koral na Karibe Hulandes a enfoká grandemente riba koralnan. E tayer akí tabata basá riba investigashon i inovashon ku ta introdusí restorashon di e komedó importante di alga: Seapel ku spiña largu (nòmber sientífiko Diadema antillarum).

Foto: Stella Grau

Seapel Diadema

Sea Diadema tin un papel importante den mantenshon di ref di koral saludabel, ku ta esensial pa protekshon di kosta i ta un fuente di entrada krusial pa hende na Karibe Hulandes komo ku ta forma un magnet pa turismo. Seapel Diadema ta yuda mantené e balansa delikado denter di e ref dor di kome alga, ku ta un kompetidor importante di koral. Medio di añanan 1980 un malesa a skeiru rònt di region di Karibe, kabando ku kasi hinter e populashon di seapel. Medio febrüari 2022, tin reportahenan a kuminsá drenta tokante kasonan ekstensivo di murimentu di seapel den region di Karibe. Dor di restorashon di Diadema den área di koral i solushonando menasanan lokal manera kasonan di awa di kloaka, koralnan lo tin mas chèns di sobrebibí.

Foto: Stella Grau

Resultadonan di e Tayer

Den e proyekto di RAAK Pro Diadema project, VHL ta traha estrechamente ku otro institutonan di investigashon i partnernan lokal pa restorá e populashonnan di seapel spiña largu riba e refnan di koral rònt di Saba i Statia. E proyekto akí ta dunando resultadonan prometedor. E lidernan di investigashon Alwin Hylkema i Tom Wijers a kompartí nan hèrmèntnan i téknikonan impreshonante i e e deskubrimentunan mas resien pa fasilitá restorashon di Diadema den e region di Karibe Amplio durante e tayer di DCNA.

A diskutí diferente tópiko, inkluso e status redusí di seapel Diadema, kasonan di murimentu resien di Diadema i téknikanan di restorashon di Diadema. E partisipantenan a risibí tambe seshonnan di training den práktika relashoná ku restorashon di Diadema. Ademas di e 21 partisipantenan presente na Saba, mas ku 65 persona a sigui e presentashonnan habrí ‘online’.

Proyekto di Múltiple Isla

Durante e tayer, tabatin diálogo intenso entre e islanan Karibense. A establesé lasonan di koperashon importante i a identifiká burakunan di kapasidat pa kua mester buska solushon pa restorá e seapel Diadema den Karibe Hulandes. VHL, DCNA i e organisashonnan presente ta investigando e posibilidat pa krea un proyekto di múltiple isla di restorashon di seapel Diadema pa realisá un meta komun: Restorashon di un di e ekosistemanan marino mas importante i deteriorá, e refnan di koral.

E tayer akí a haña sosten generoso di parti di Ministerio di Agrikultura, Naturalesa i Kalidat di Kuminda (LNV) di Hulanda komo un sosten di e Plan di Maneho pa Naturalesa i Medio Ambiente pa e islanan BES, Postcode Loterij Nederland i SIA, un parti di Nederlands Wetenschappelijk Onderzoek (NWO).

Keda bon na altura

Si bo ke haña sa mas tokante e tayer di Diadema i di DCNA su aktividatnan, sigui informashon di DCNA pa medio di nan boletin di notisia digital grátis BioNews (https://dcnanature.org/news/), Facebook (Dutch Caribbean Nature Alliance) òf Instagram (DCNAnature). Pa mas informashon tokante e proyekto RAAK PRO Diadema bishitá https://www.facebook.com/reefrestorationVHL/ òf tuma kontakto ku lider di proyekto alwin.hylkema@hvhl.nl.

Pa mas informashon tokante e tayer di Diadema, por fabor tuma kontakto ku:

Tineke van Bussel, Research Communications Liason na research@dcnanature.org i

Dahlia Hassell – Knijff, Projects Officer na projects@dcnanature.org

Downloads & links >

____________________________________________________________________________________________________________________________________________________________________________________________________________________________

Papiamento

Siman pasa Dutch Caribbean Nature Alliance (Aliansa pa Naturalesa di Caribe Hulandes a organisa un tayer di restauracion di bushi di lama (Diadema antillarum) na Saba. E tayer aki a wordo dirigi pa University of Applied Sciences Van Hall Larenstein (VHL).  Durante e tayer experto y representante di Caribe Hulandes y Jamaica a bini hunto pa uni forsa pa restauracion di e rifnan di coral. E tayer aki a yuda 21 experto den coral di e region di Caribe y mas di 65 siguidonan online a haya un bista amplio di e situacion di bushi di lama Diadema den Caribe, incluyendo evento actual di murimento di e bushinan y e tecnicanan di restauracion. Discusionnan importante a tuma luga pa determina e proximo pasonan necesario pa mengua perdida di bushi di lama Diadema riba escala regional.

Restauracion di e rifnan di coral

E metodonan di restauracion di e rifnan di coral ta mustrando resultado prometedo den apoyo na e esfuersonan regional pa restaura e rifnan di coral afecta den Caribe Hulandes. Restauracion di e rifnan di coral den Caribe Hulandes a concentra su mes den gran medida riba e coralnan. E tayer aki a basa su mes riba investigacion y innovacion cu ta introduci restauracion di e herbivoro di alga importante: e bushi di lama di spina largo (nomber cientifico Diadema antillarum).

Foto: Stella Grau

Bushi di lama Diadema

Bushi di lama Diadema ta hunga un papel crucial den mantene e rifnan di coral saludabel, cualnan ta esencial pa proteccion di costa y un fuente di ingreso crucial pa e personanan den Caribe Hulandes, ya cu nan ta un magnet pa turismo. Bushi di lama Diadema ta yuda mantene e delicado ekilibrio dentro di rif door di alimenta su mes cu alga, cu ta e principal competido di e coralnan. Memey di e decada di 1980, un enfermedad a pasa den Caribe y a caba cu casi henter e poblacion di bushi di lama. Memey di februari di 2022, a cuminsa yega informe tocante caso di morto masivo nobo den region Caribe. Restaurando bushi di lama Diadema hunto cu e coralnan y resolviendo e menasanan local, manera e problema di awa residual, e coralnan lo tin mas posibilidad di sobrevivi.

Foto: Stella Grau

Resultado di e tayer

Den proyecto RAAK Pro Diadema, VHL ta traha den estrecho colaboracion cu otro instituto di investigacion y socio local pa restaura poblacion di bushi di lama di spina largo den e rifnan di coral alrededor di Saba y Sint Eustatius. E proyecto aki ta mustrando resultado prometedo. E investigadonan principal Alwin Hylkema y Tom Wijers a comparti nan hermentnan impresionante, tecnica y e ultimo hallazgonan cientifico pa facilita restauracion di Diadema den region di Gran Caribe durante e tayer di DCNA.

A discuti varios tema, incluyendo e estado reduci di e bushinan di lama Diadema, e eventonan reciente di die-off di Diadema y e tecnicanan di restauracion di Diadema. E participantenan tambe a ricibi sesion di capacitacion practico pa mehora e habilidadnan practico relaciona cu restauracion di Diadema. Ademas di e 21 participantenan presente na Saba, mas di 65 persona a sigui e presentacionnan habri online.

Proyecto multiisla

Durante e tayer tabatin un dialogo intenso entre e islanan di Caribe. A establece asociacion importante y a identificado gap di conocemento y capacidad cu mester wordo resolvi pa restauracion di bushi di lama Diadema den Caribe Hulandes. VHL, DCNA y e organisacionnan presente ta analisando e posibilidad di establece un proyecto di restauracion di Diadema na varios isla pa logra un obhetivo comun: restaura un di e ecosistemanan marino mas importante y afecta, e rifnan di coral.

E tayer aki tabata generosamente financia pa Ministerio di Agricultura, Naturalesa y Calidad Alimentaria (LNV) como apoyo na  Plan di Maneho Ambiental y di Naturalesa pa e islanan BES, Loteria di Codigo Postal Hulandes y SIA, parte di Conseho di Investigacion Hulandes (NWO) .

Keda al tanto

Si ta desea di ricibi mas informacion tocante e tayer di Diadema y e actividades di DCNA, sigui DCNA via su boletin digital gratuito BioNews (https://dcnanature.org/news/), Facebook (Dutch Caribbean Nature Alliance) of Instagram (DCNAnature). Pa mas informacion tocante e proyecto RAAK PRO Diadema, sigui https://www.facebook.com/reefrestorationVHL/ of comunica cu e lider di proyecto alwin.hylkema@hvhl.nl.

Pa haya mas informacion tocante e tayer Diadema, por comunica cu:

Tineke van Bussel, Liason di Comunicacion di Investigacion den research@dcnanature.org y

Dahlia Hassell – Knijff, Oficial di Proyecto den projects@dcnanature.org

Downloads & links >

Published in BioNews 52

Nederlands below:

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 urcin settler (~0.5 mm) on a bio ball, one of the settlement substrates studied. Credit: Alwin Hylkema

Long-spined sea urchins (Diadema antillarum) play a critical role in maintaining healthy coral reefs. They help sustain the delicate balance within the reef by grazing on algae, which are the main competitors of corals. Unfortunately, in the mid-1980s, a disease swept through the Caribbean, wiping out nearly the entire sea urchin population. Soon after, reports of rapid algae growth were documented throughout the Caribbean. The algae occupy all available space, preventing coral recruitment and limiting the coral reef’s ability to recover from other disturbances. So far, recovery ofD. antillarum populations has been very slow to nonexistent. In the few areas where sea urchins were able to naturally recover, these trends were reversed, highlighting the importance of restoring this keystone species.

Studying sea-urchin settlement

A collaborative study between Van Hall Larenstein, Wageningen University and Research (WUR), STENAPA, Caribbean Netherlands Science Institute (CNSI) and NIOZ Royal Netherlands Institute for Sea Research worked to unravel the mystery behind the slow recovery rate of these vital species. As both juveniles and adults are absent from most reefs, it is likely that the bottle-neck in D. antillarum recovery occurs in the first phase of the life cycle. Sea urchins start their life as larvae and remain the water column for 30-60 days, until they find a suitable place to settle. Understanding settlement rates and patterns will help understand the slow recovery and guide recovery efforts moving forward.

Effectiveness of settlement collectors

Diadema sea urchin juvenile on a settlement panel, one of the studied settlement collectors. Credit: Alwin Hylkema

Settlement collectors were set up in five different locations around the island of St. Eustatius. Between April and December 2019, researchers carefully monitored and analyzed the settlement rates by counting each individual sea urchin larvae which settled on the collectors. Over these 10 months, more than 890 sea urchin settlers were collected. Furthermore, this study compared different materials to identify the most suitable settlement collector for Diadema sea urchins. These materials included panels, artificial turf, bio balls, frayed ropes and a doormat collector. Results showed both the bio ball and doormat collectors were most effective, especially when placed mid-water column.

The mystery behind the slow recovery

Despite high settlement densities on several locations, no juvenile or adult sea urchins were observed on the reefs around the settlement collectors. This hints that there are likely other reasons these populations have been unable to recover around the island. Furthermore, previously conducted reef surveys from 2017 through 2019 found less than 0.01 sea urchins per square meter, far below pre-die-off densities. The fact that this study proves there are sea urchin larvae in the water paired with the lack of juveniles on reefs could be an indication of high predation pressures on settlers on the reef.

Future Populations

One solution which may aid in the restoration of this species would be to collect settlers from the reef and raise them in land-based nurseries. This would protect them from predation early in life and allow them to grow to adequate size before being returned to the reef. In order for this to be economically feasible, high numbers of settlers would need to be collected. Studies such as this can help the islands design and implement effective methods to restore Diadema sea urchins, which can help coral reefs to recover from disturbances naturally.

To learn more, you can read the full article on the DCBD by using the link below.

See also the recent item in Atlas (NPO2) in Dutch- starts at 22 min:

https://www.npostart.nl/atlas/02-02-2022/VPWON_1335373

More info in the Dutch Caribbean Biodiversity Database

____________________________________________________________________________________________________________________________________________________________________________

Belangrijke nieuwe inzichten voor het herstel van zee-egels

Diadema-zee-egels spelen een belangrijke rol binnen een gezond koraalrifecosysteem en hun herstel is essentieel voor het herstel van de aangetaste koraalriffen rondom Saba en St. Eustatius. Hogeschool Van Hall Larenstein, WUR, STENAPA, CNSI en NIOZ onderzochten de vestigingssnelheid van zee-egellarven. De nieuwe bevindingen geven inzicht in waarom de Diadema-populatie niet is hersteld sinds de massale sterfte in het midden van de jaren tachtig en zijn belangrijk voor het ontwikkelen en uitvoeren van effectieve herstelprojecten voor zee-egels.

De zee-egel (Diadema antillarum) speelt een cruciale rol bij het in stand houden van gezonde koraalriffen. Ze helpen het evenwicht in het rif te behouden door te grazen op algen, de belangrijkste concurrenten van koralen. Helaas raasde halverwege de jaren tachtig een ziekte door het Caribisch gebied, waarbij bijna de hele zee-egelpopulatie werd uitgeroeid. Kort daarna werd in het hele Caribisch gebied toename in algengroei waargenomen. De algen nemen alle beschikbare ruimte in beslag, waardoor nieuwe koralen zich moeilijk kunnen vestigen en het vermogen van het koraalrif om te herstellen van andere verstoringen wordt beperkt. Tot op heden is het herstel van D. antillarum-populaties erg traag tot niet-bestaand. In de weinige gebieden waar zee-egels zich op natuurlijke wijze wel konden herstellen, werden deze trends omgekeerd, wat het belang van het herstel van deze soort benadrukt.

Bestuderen van zee-egels

Diadema zee-egel (~0,5 mm) gevestigd op een biobal, een van de onderzochte vestigingssubstraten. Credit: A. Hylkema

Een gezamenlijke studie tussen Van Hall Larenstein, Wageningen University and Research (WUR), STENAPA, Caribisch Nederlands Instituut voor Wetenschappelijk Onderzoek (CNSI) en NIOZ Koninklijk Nederlands Instituut voor Onderzoek der Zee heeft het mysterie achter het trage herstel van deze vitale soorten ontrafeld. Aangezien zowel juvenielen als volwassenen afwezig zijn op de meeste riffen, is het waarschijnlijk dat het knelpunt bij het herstel van D. antillarum optreedt in de eerste fase van de levenscyclus. Zee-egels beginnen hun leven als larve en blijven 30-60 dagen in de waterkolom, totdat ze een geschikte plek hebben gevonden om zich te vestigen. Het bestuderen van deze eerste levensfase zal helpen bij inzicht te krijgen in het langzame herstel en helpen bij herstel projecten.

Verzamelen van zee-egellarven

Diadema zee-egel juveniel op een vestigingspaneel, een van de bestudeerde vestigingsverzamelaars. Credit A. Hylkema

Op vijf verschillende locaties rond het eiland Sint Eustatius werden verzamelaars geplaatst waar zee-egellarven zich op kunnen vestigen. Tussen april en december 2019 hebben onderzoekers de vestigingspercentages nauwkeurig gevolgd en geanalyseerd door elke individuele zee-egellarven te tellen die zich op de verzamelaars vestigden. In deze 10 maanden werden meer dan 890 zee-egelkolonisten verzameld. Bovendien vergeleek deze studie verschillende materialen om de meest geschikte verzamelaar voor Diadema-zee-egels te identificeren. Deze materialen waren onder andere panelen, kunstgras, bioballen, gerafelde touwen en deurmatten. De resultaten toonden aan dat zowel de biobal ​​als de deurmatverzamelaars het meest effectief waren, vooral wanneer ze midden in de waterkolom werden geplaatst.

Het mysterie achter het langzame herstel

Ondanks de hoge vestigingsdichtheid op verschillende locaties, werden er geen juveniele of volwassen zee-egels waargenomen op de riffen rond de verzamelaars. Dit wijst erop dat er waarschijnlijk andere redenen zijn waarom deze populaties zich rond het eiland niet hebben kunnen herstellen. Bovendien vonden onderzoekers bij eerder uitgevoerde rifonderzoeken in 2017 -2019 minder dan 0,01 zee-egels per vierkante meter, ver beneden de dichtheden voor de massale sterfte. Het feit dat deze studie aantoont dat er zee-egellarven in het water zijn in combinatie met het gebrek aan juvenielen op de riffen, kan een indicatie zijn van hoge predatiedruk op de zee-egels op het rif.

Toekomstige zee-egel populaties

Een oplossing die kan zou kunnen helpen bij het herstel van deze soort zou zijn om gevestigde jonge zee-egels van het rif te verzamelen en ze op te kweken in aquaria op het land. Dit zou hen op jonge leeftijd tegen predatie beschermen en hen in staat stellen om voldoende groot te worden voordat ze naar het rif worden teruggebracht. Om dit economisch haalbaar te maken, zouden grote aantallen jonge zee-egels moeten worden verzameld. Studies zoals deze kunnen de eilanden helpen bij het ontwerpen en implementeren van effectieve methoden om Diadema-zee-egels te herstellen, wat koraalriffen kan helpen om op natuurlijke wijze te herstellen van verstoringen.

Lees meer over over deze studie in Dutch Caribbean Biodiversity Database

Of zie het recente item in Atlas (NPO2) – start bij 22 min:

https://www.npostart.nl/atlas/02-02-2022/VPWON_1335373

More info in the Dutch Caribbean Biodiversity Database

Published in BioNews 51

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.

Abstract 

Before its mass-mortality in the 1980’s, Diadema antillarum was the most important benthic herbivore on Caribbean reefs. Since then, reefs have experienced an increase in turf/macroalgae abundance. Despite the approximate 40 years that have past, natural recovery is slow and variable. Therefore efforts are taken to boost D. antillarum recovery artificially. Several bottlenecks for recovery have been found, but in the last decade a new potential problem has risen: massive influxes of floating Sargassum species. Studies have shown that algae or its biofilm can induce sea urchin settlement to a certain extent, but no in vivo experiments have been conducted for D. antillarum. Here we investigated if these Sargassum floats interfere with the recruitment of D. antillarum by measuring the abundance of D. antillarum settlers in submerged and floating, rinsed and unrinsed Sargassum units and comparing values with a positive control. While the amount of data collected with the low sample sizes did not suffice to answer the research question in any statistically significant manner, hypothesis could be formulated.   

D. antillarum certainly is attracted to sargassum patches, whether as post-settler only or also as settler is however still debatable. Cues by conspecifics could possibly play a role in increased settlement in Sargassum, blurring the effect of Sargassum solely. A large variation in D. antillarum abundance was found for the unrinsed submerged treatment, which was possibly the result of migration from nearby existing ecosystems with older D. antillarum into the experimental units, or it was an artefact of the low sample size. To confidently distinguish signal from noise in a similar study, some alterations to the research design need to be made and drifting sargassum patches need to be sampled to get a sense of D. antillarum settler abundance on naturally occurring Sargassum. 

This report characterizes the state of Bonaire’s reefs as of March 2005. We pay particular attention to structural and functional attributes of reefs that have changed in so many other Caribbean reefs. We characterize coral reefs by their resident organisms and the forces regulating their distribution and abundance. Thus, corals, algae and fish define the “structure” of coral reefs but climate changes, diseases, hurricanes, overfishing, sedimentation and excess nutrients may affect how they “function”. Recent unfavorable changes in the structural and functional attributes of reefs have caused “the coral reef crisis” (Bellwood et al. 2004). In Caribbean coral reefs the most alarming changes have been the declines in the abundance of corals, sea urchins and reef fishes and the accompanying increases in large harmful seaweeds (called “macroalgae”). The decline in coral and increase in macroalgae, called a “phase shift”, represents a significant change in the structure of coral reef ecosystems that could lower its resilience.

...

In March of 2005, a team of graduate students from the University of Maine revisited six study reefs on Bonaire to determine the status of those reefs and to detect if any change has occurred since March of 2003 when the last such survey was conducted. The study sites established in 2003 from north to south are: Karpata, Barcadera, Reef Scientifico, Forest on Klein Bonaire, Plaza and Windsock. Bonaire’s shallow (10 m) reefs remain in good condition. Coral cover averaged 47% in 2005 compared to 46% in 2003 (no change). Turf algae have increased and coralline algae have declined slightly over the past two years. Harmful seaweed “macroalgae” abundance remains low (2% in 2005 and 5% in 2003; see Steneck in this report) at the 10 m depth we studied. At depths below 20 m, macroalgae are now and have been (for at least the past 30 years) much more abundant (e.g. Van den Hoek et al. 1975) The absence of macroalgae in Bonaire most likely relates to the abundance of seaweedeating species or “herbivores”. Caribbean-wide, harmful macroalgal seaweed abundance corresponds inversely with the abundance of grazing fish such as parrotfish and tangs (Fig. 1). No comparable plot exists for seaweed abundance and any other measured factor on reefs.

...
Changes over the past two decades
Comparisons between the status of reefs over a few years tell us little about long-term changes. For example, today there is a distinct demarcation between where Bonaire’s fringing reefs begin at 5 to 10 m depth and the shore. This region today is largely coralfree and dominated by rubble and sediment laden turf algae. However, this may not have always been the case. Prior to whiteband disease that killed nearly 90% of the elkhorn and staghorn corals in the Caribbean (i.e. Acropora palmata and A. cervicornis) (Aronson et al. 1998, Aronson and Precht 2001), most of the near shore zone was coral-dominated.
...
Coral cover in the near shore zone surrounding Bonaire has declined dramatically and is now dominated by dead coral rubble where once elkhorn and staghorn corals had formed near monocultures prior to white band disease. Five of our six study sites have changed dramatically over the past 20 years except for Karpata. The decline of the Acropora species may have allowed competitively inferior species such as lettuce, pencil, finger and fire corals (Agaricia spp, Madracis spp, Porites porities and Millepora complanata) to expand since all have increased in abundance since the Van Duyl study (1985). Corals are not the only group to have changed dramatically since the 1980s. Diadema antillarum, the dominant grazing sea urchins was abundant in the near shore zone until it succumbed to the mass mortality of the mid 1980s. Today, more than 20 years later it remains below detectable levels at most of the sites we studied (Smith and Malek this report, Steneck this report). These changes, along with the significant declines in large predator finfish (see Bonaire Report 2003) indicate that several key players for the resilience of coral reefs (e.g. Fig. 3) have declined in abundance.

Bonaire’s reefs remain among the best in the Caribbean. However, our monitoring has revealed some potentially troubling trends that may require management action. In 2005, we reported to the Bonaire Marine National Park on the status of Bonaire’s coral reefs, and we suggested a strategy for monitoring trends among four key reef attributes we believe track the health and resilience of Bonaire’s reefs (Steneck and McClanahan 2005). Here we report the results of monitoring studies conducted 2003, 2005 and now 2007 at each site. Where appropriate, we drew from Bonaire’s first AGRRA assessment conducted in February 1999 (Kramer and Bischof 2003) to extend temporal trends over a period of eight years. 
Troubling trends
We see three troubling trends of increased macroalgae, declining herbivory from parrotfish, and increases in damselfish populations. Of these, the first two are most serious (see Chapters 1, 2 and 3). Secondary trends of concern, increases in damselfish populations (Chapter 4) and declines in coralline algae (Chapter 1), could lead to reduced recruitment of reef corals (Chapter 7), but to date this is not evident (Chapter 7). Importantly, coral cover remains relatively high (Chapter 1). The monitored group of carnivorous fishes, the lutjanid snappers, are holding constant but we remain concerned about the past (Steneck and McClanahan 2003) and continued loss of other larger bodied reef carnivores such as groupers and barracuda. The positive ecological role of parrotfish is well documented (e.g. Mumby et al. 2006) so their decline is troubling. It is unclear exactly why their population densities are declining. While parrotfish are not currently a widely sought group of reef fish (Chapter 8), fishing pressure on them is growing. It is possible they are vulnerable to even modest fishing pressure, particularly from fish traps. Accordingly, we recommend that the capture and killing of parrotfish be stopped because of their key ecological role on Bonaire’s coral reefs. Further, other groups of grazing herbivores such as the longspined sea urchin (Diadema antillarum) are increasing but too slowly to effectively replace the functional role of parrotfish (Chapter 1). We suggest continued monitoring of key drivers of reef health (coral cover, algal abundance, herbivory and coral recruitment). Some standard protocols such as the Atlantic and Gulf Rapid Reef Assessment (AGRRA) are entirely commensurable with the data presented in our reports in 2003, 2005 and 2007 (this report). A streamlined monitoring protocol is likely to be most useful to managers to alert them as a potential problem is growing and, perhaps more importantly, to show improvement when it occurs.
 
 

Bonaire has long been considered to have amongst the healthiest reefs of the Caribbean. However, at the 2002 Annual Meeting of Pew Fellows for Marine Conservation in Bonaire, several scientists with a long history of research on Bonaire’s coral reefs, expressed concern over the future of the island’s reefs. Specifically, they identified the decline in large predatory fish such as groupers as a noticeable change during the past decade. They suspected that this change resulted from increased fishing pressure on Bonaire’s reefs. They also suggested the Bonaire authorities take action to protect the reef-fish stocks. In response to those concerns, officials of the Bonaire Marine Park consulted with scientists and fishermen on Bonaire to explore the possibility of establishing fish protected areas (FPAs), as a way to protect the reef fish stocks. If FPAs improve both fish stocks and the condition of the coral reef, all stakeholders will profit. If fish stocks increased significantly in FPAs, a “spill over” of these fish to adjacent fished areas would be expected. Also, fish that perform important ecological functions could improve the quality of the coral reef ecosystem. Therefore, areas protected from fishing should have healthier coral reefs, which would also improve the island’s valuable ecotourism businesses. The Pew Fellows program funded a research project designed to identify potential FPAs. The Bonaire Marine Park authority, in consultation with the local fishing community would determine the location and size of the FPAs. To monitor the effects of fish protection areas so fishing impacts can be isolated from other factors (such as natural changes, shore-based impacts or effects of scuba divers), an equal number of similar reef sites were selected for study, with half closed to fishing while half remaining open (as “control” reefs). This report reviews the status and recent trends of coral reefs in the Caribbean and Bonaire. It identifies the key features of healthy reefs and how Bonaire’s reefs compares with those elsewhere in the Caribbean. The seven chapters go into scientific detail on factors contributing to the condition of Bonaire’s reefs as of March and April 2003. Special focus will be on factors that threaten reef health or are critical to reef resilience such as seaweed overgrowth, nutrient inputs from land and the ecology of juvenile corals. The report concludes with chapters on the socioeconomic effects of Bonaire’s coral reefs on the fishing and diving industries that depend on them.
Summary Results 2003: The Biological Status of the Coral Reefs of Bonaire & Socioeconomic Implications
 In March and April of 2003, teams of researchers studied the coral reefs of Bonaire to establish the baseline conditions that currently exist and against which trends can be determined and future changes from fish protection areas be assessed. Six study sites were chosen with advice from the Bonaire Marine Park. They represent a range of comparable reefs minimally affected by the 1999 Hurricane Lenny. The sites selected for this study were: Windsock, Plaza, Forest on Klein Bonaire, Scientifico, Barcadera and Karpata (Fig. 0.4). When feasible, parallel studies were conducted at 5 and 10 m depths, however, only the latter depth had fully developed reefs at all sites. The study was designed to quantify the patterns of abundance of the dominant reef organisms as well as to study the processes that control their abundances or threaten their stability. This was done to establish a baseline and to determine if significant differences exist among any of the study sites that would make them a poor choice as a FPA. We also examined some socioeconomic factors related to fishing and scuba diving activities if FPAs are established in Bonaire.

The sea urchin Diadema antillarum commonly occurs on Caribbean reefs in densities sufficiently high to influence characteristics such as community composition and reef growth. We observed an outbreak of mass mortality in this species reducing population densities by 98 to 100 %. Mortality spread from the Curacao harbour mouth along the coast, most rapidly advancing in the down-current direction. Our calculations show a pronounced effect on the carbonate budget of the reef. Recovery of Diadema populations may be facilitated by parthenogenesis. There is continuing recruitment on affected reefs, a possible location of the parent population being up-current unaffected reefs of Bonaire.

Abstract:

Recruitment of the sea urchin Diadema antillarum philippi, 1845 was studied on artificial recruitment panels along the leeward coast of the island of Curaçao, southern Caribbean. data were compared with historical data from the same coast that were collected before (1982–1983) and after (1984) the Caribbean-wide mass mortality of Diadema in October 1983. Average recruitment rates observed in 2005 were equal to 2.2 times lower compared to those observed before the D. antillarum die-off (1982 and 1983), but 56.5 times higher than those observed after the die-off in 1984. The increase in recruitment rates between 1984 and 2005 was 5–51 times greater than the increase in abundance of adult individuals over the same period. This suggests that despite the largely recovered recruitment rates of this important reef herbivore, unknown sources of high post-settlement mortality currently prevent a similar recovery of its adult population.