RAAK Pro Diadema project

Project description

Time: July 2023- July 2025

Project leaders: VHL (Alwin Hylkema), SCF (Kai Wulf), STENAPA (Erik Boman), WUR (Dolfi Debrot)

Project summary

Many Caribbean reefs have shifted from coral-dominated to algal-dominated ecosystems. The high algae cover reduces coral recruitment, making the reef unable to recover from other disturbances and resulting in flatter reefs with lower biodiversity. One of the reasons for the proliferation of algae is a mass die-off of the herbivorous sea urchin Diadema antillarum in the early 1980s. Natural recovery of Diadema populations is slow to non-existent, making active restoration of this important grazer a top priority in Caribbean coral reef management, especially since Diadema densities were reduced by another mass mortality event in 2022. The marine park organizations of Saba and St. Eustatius want to restore Diadema populations by restocking cultured individuals. However, important knowledge gaps need to be addressed before large numbers of Diadema can be restocked on the reef. Current culture methods can only produce a limited number of competent larvae. In addition, only 8% of the settlers survive and after restocking, survival on the reef is low as well. In the RAAK PRO Diadema II project, the bottlenecks in Diadema culture will be addressed by comparing larval survival across multiple culture methods and investigating the relation between larval size and post-settlement survival. Growing-out juveniles at sea is likely to help prepare them for life in the wild, while restocking at an optimal size might also increase survival. Finally, a thorough restocking site selection based on high shelter availability and settlement rates will increase the long-term Diadema densities. The acquired knowledge and developed practices will be verified in a larger scale restocking experiment involving at least 5000 Diadema urchins. By restoring Diadema populations through restocking, macroalgae will be more intensively removed and corals will have a chance to settle and to survive, increasing the ability of the reef to cope with other stressors.

Nederlands below.

Researchers from Van Hall Larenstein, Wageningen University and Wageningen Marine Research have developed a new approach to assist Diadema sea urchins’ natural recovery.  In collaboration with the Saba Conservation Foundation, researchers provided additional substrate for settlement on the reef, increasing sea urchin recruitment and thereby demonstrating the importance of suitable settlement substrate for recovery processes.

Diadema antillarum
Photo credit: Alwin Hylkema

Deterioration of Caribbean coral reefs begun in the 1970s when diseases devastated the most important reef building corals in the region.  These issues were then accelerated, when the most abundant herbivore, the long-spined sea urchins (Diadema antillarum), suffered massive die offs in the 1980s. Within days after the Diadema die-off, macroalgae started to dominate Caribbean coral reefs.  This shift from coral dominated to macroalgae dominated reefs have had devastating effects on the biodiversity and overall reef health.

Assisted Natural Recovery

Natural recovery of the long-spined sea urchin has been slow.  A new method for sea urchin restoration, coined Assisted Natural Recovery (ANR), employs similar techniques as those used in terrestrial reforestation. The concept is centered around the idea that by removing barriers to natural recovery, succession can be accelerated. Earlier studies suggested that recovery of Diadema sea urchins might be limited by a lack of suitable settlement substrate for their larvae. With the reefs overgrown with algae, clean substrate with a fresh biofilm, which is thought to be the main cue for settlement, is lacking.

Photo credit: Alwin Hylkema

Bio Ball Streamers

With ANR the researchers provided new settlement substrate in the form of streamers attached to the reef.  In total, nine streamers, made up of 30 bio ball tied on fishing line, were attached to the reef.  Bio balls are normally used in aquarium filters and have a large surface area. A previous study, conducted in the same project, showed that this material is very effective to monitor sea urchin settlement. These streamers provided areas for sea urchin larvae to settle, protecting them until they grew large enough to migrate to the reef. In April 2021, six patch reefs were selected off the coast of Saba, of which 3 were provided with bio ball streamers and 3 were left untouched and served as control.

At the end of the study, it was demonstrated that reefs with bio ball streamers had significantly higher Diadema urchin recruit densities than those without, highlighting the importance of settlement substrate in natural recovery.  Unfortunately, the improved recruitment rate did not equate to a recovered population.  The recruits rarely grew larger than 20mm, suggesting that predation on recruits is also limiting natural recovery.  Once a recruit becomes larger than 5mm they outgrow the bio ball and need to move to the reef, where they are vulnerable to predation.

Implications

Photo credit: Alwin Hylkema

With the latest news of massive Diadema die offs, park authority managers are desperately looking for ways to protect the future of sea urchin populations in the region.  The new approach of ANR might be one of the ways to assist Diadema sea urchin recovery in the future. Researchers from the RAAK PRO Diadema project are now working on optimization of the method. However, future recovery of this sea urchin species will mostly be dependent on the scale and lethality of a new die-off that is currently happening in the Caribbean. Already accounts of these die-offs have been recorded on Saba, St. Eustatius, St. Maarten and Curacao.  Threatened reefs are struggling to combat the spread of macroalgae, and the continued loss of a herbivores would only exacerbate these issues.

You can help authorities track sea urchin health in the Caribbean by adding your observations of healthy, sick or dead urchins by visiting the AGRRA website (https://www.agrra.org/sea-urchin-die-off/).  To read more about the latest in sea urchin recovery methods, you can find the full article on the DCBD using the link below or follow along with the RAAK PRO Diadema project online.

 

 

Figure 2: (A) Patch reef (no. 4) with streamers on which the transect tape is removed after monitoring. (B) Streamer with buoy and (c) close-up of the bio balls

 

 

 

 

More info in the Dutch Caribbean Biodiversity Database

 

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Nederlands

Innovatieve Technieken kunnen de sleutel zijn voor het herstel van de Diadema zee-egels

Onderzoekers van de Van Hall Larenstein Hoge School, Universiteit van Wageningen en het Wageningen Marien Onderzoek hebben een nieuwe ingang ontwikkeld tot de hulpverlening naar het natuurlijk herstel van de Diadema zee-egels. In samenwerking met de Saba Conservation Foundation, hebben de onderzoekers een nieuw aanvullend substraat gevonden voor vestiging op het koraal, waarbij de rekrutering van zee-egels toegenomen is en daarmee het belang van geschikt vestigingsondergrond voor de herstelprocessen hebben aangetoond.

De verslechtering van de Caribische koraalriffen begon in de jaren zeventig toen ziektes de belangrijkste rif opbouwende koralen in de regio hebben verwoest. Deze problemen werden vervolgens versneld, toen de meest voorkomende herbivoor, de Diadema zee-egels, in de jaren tachtig massaal begon af te sterven. Binnen enkele dagen na het afsterven van de Diadema, begonnen macroalgen te domineren op de Caribische substraatkoraalriffen. Deze verschuiving van door koraal gedomineerde naar door macroalgen gedomineerde riffen heeft verwoestende gevolgen gehad voor de biodiversiteit en de algehele gezondheid van het rif.

Assisted Natural Recovery

Het natuurlijke herstel van de Diadema zee-egel is traag verlopen. Een nieuwe methode voor hulpverlenend herstel van de zee-egels, genaamd Assisted Natural Recovery (ANR), gebruikt vergelijkbare technieken als bij herbebossing op het land. Het concept is gecentreerd rond het idee dat door het wegnemen van barrières voor natuurlijk herstel, de opvolging kan worden versneld. Eerdere studies suggereerden dat het herstel van Diadema-zee-egels mogelijk wordt beperkt door een gebrek aan geschikt vestigingsondergrond voor hun larven. Doordat de riffen begroeid met algen is, ontbreekt er een schoon ondergrond met verse biofilm, waarvan wordt aangenomen dat dit de sleutel is voor nieuwe vestiging.

Photo credit: Alwin Hylkema

Bio Ball Wimpels

Met ANR methode hebben de onderzoekers een nieuw vestigingsondergrond aangebracht in de vorm van wimpels die aan het rif waren bevestigd. In totaal werden negen wimpels, bestaande uit 30 bioballen vastgebonden aan een vislijn, aan het rif bevestigd. Bioballen worden normaal gesproken gebruikt in aquariumfilters en hebben een groot oppervlak. Een eerdere studie, uitgevoerd in hetzelfde project, toonde aan dat dit materiaal zeer effectief is om de vestiging van zee-egels te volgen. Deze wimpels boden gebieden aan voor de zee-egellarven om zich vast te hechten en beschermden ze totdat ze groot genoeg waren om naar het rif te migreren. In april 2021 zijn voor de kust van Saba zes gebieden met herstelriffen geselecteerd, waarvan er 3 zijn voorzien van bioball wimpels en 3 onaangeroerd zijn gelaten en als controle hebben gediend.

Aan het einde van de studie werd aangetoond dat riffen met bioball wimpels aanzienlijk hogere rekruteringsdichtheden van Diadema-egels hadden dan die zonder, wat het belang van een nederzettingsondergrond voor natuurlijk herstel benadrukte. Helaas kwam de verbeterde rekruteringsgraad niet overeen met een herstelde populatie. De rekruten werden zelden groter dan 20 mm, wat suggereert dat predatie op rekruten ook het natuurlijke herstel beperkt. Zodra een rekruut groter wordt dan 5 mm, ontgroeien ze de biobal en moeten ze naar het rif gaan, waar ze kwetsbaar zijn voor predatie.

Photo credit: Alwin Hylkema

Implicaties

Met het laatste nieuws over massale Diadema-sterfte, zijn beheerders van parkorganisaties wanhopig op zoek naar manieren om de toekomst van zee-egelpopulaties in de regio te beschermen. De nieuwe aanpak van ANR kan in de toekomst een van de manieren zijn om Diadema-zee-egels te helpen herstellen. Onderzoekers van het RAAK PRO Diadema-project werken nu aan een optimalisatie van de methode. Toekomstig herstel van deze zee-egelsoort zal echter grotendeels afhangen van de omvang en het sterftecijfer van de nieuwe sterfgevallen dat momenteel in het Caribisch gebied voorkomen. Op Saba, St. Eustatius, St. Maarten en Curaçao zijn al verslagen van deze sterfgevallen geregistreerd. Bedreigde riffen worstelen om de verspreiding van de macroalgen tegen te gaan, en het aanhoudende verlies van herbivoren zou deze problemen alleen maar verergeren.

U kunt autoriteiten helpen de gezondheid van zee-egels in het Caribisch gebied te volgen door uw observaties van gezonde, zieke of dode zee-egels toe te voegen door de AGRRA-website te bezoeken (https://www.agrra.org/sea-urchin-die-off/). Om meer te lezen over de nieuwste methoden voor het herstel van de Diadema zee-egels, kunt u het volledige artikel over de DCBD vinden via de onderstaande link of het RAAK PRO Diadema-project online volgen.

Figuur 2 (A) Herstel rif (nr. 4) met wimpels waar de transactie tape is verwijderd na het monitoringsproces. (B) wimpel met boei en (C) Close-up van bioballen.

 

 

 

More info in the Dutch Caribbean Biodiversity Database

 

 

 

 

Published in BioNews 56.

 

Nederlands, Papiamento and Papiamentu below

 

Since February 2022 there have been reports of Long-spined sea urchin (Diadema) die off from a number of islands in the Caribbean, including St. Eustatius, St. Maarten, Saba and Curaçao.  Marine Protected Area authorities within the Dutch Caribbean region are concerned these events could be echoing the massive die-off  of sea urchins that occurred in the 1980s which almost completely wiped out the Caribbean long-spined sea urchin populations. A new edition of the Dutch Caribbean Nature Alliance (DCNA) free digital newsletter Bionews draws attention to the current state of the die-off, what is being done to restore these populations and what you can do to help.

IMPORTANCE FOR CORAL REEFS

Long-spined 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. Long-spined sea urchins help sustain the delicate balance within the reef by grazing on algae, an overabundance of which can damage coral.

CARIBBEAN-WIDE DISEASE

Photo credit: Alwin Hylkema

In the mid-1980s, a disease swept through the Caribbean wiping out nearly the entire sea urchin population. In mid-February 2022, reports started emerging about new extensive die-off events in the Caribbean region. Reports from within the Dutch Caribbean first came in on March 14th from the island of St. Eustatius.  Follow on reports from the remaining Dutch leeward islands of Saba and St. Maarten soon followed.  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.

 

 

DIADEMA WORKSHOP

In April, DCNA, together with the  University of Applied Sciences Van Hall Larenstein (VHL), hosted a Diadema Restoration Workshop. This workshop gave researchers and park authority managers a comprehensive view of the overall situation of the Diadema sea urchin in the Caribbean, including the current die-off events and restoration techniques.

YOU CAN HELP

Citizens and tourists can also help track sea urchin health in the Caribbean by adding their observations of healthy, sick or dead urchins. These reports will help park authority managers to determine the causes and work on restoration approaches. You can report your sightings by visiting the AGRRA website (https://www.agrra.org/sea-urchin-die-off/) or contact your local Park Management Organization.

Other advice to prevent spreading the disease:

• Wash dive gear in lots of fresh water and let sun-dry
• Dive on uninfected sites before (known) infected sites
• Do not step on them or (re)move them: Alive or dead

Photo source: Alwin Hylkema

 

LEARN MORE

Learn more about current state, what is being done to restore these populations and what you can do to help by reading DCNA’s latest edition of its free digital newsletter Bionews available at https://dcnanature.org/news/.

DCNA’s newsletter BioNews is kindly funded by the Ministry of Agriculture, Nature and Food Quality (LNV) and DCNA’s activities by the Dutch Postcode Lottery.

 

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Nederlands

Diadema zee-egels: geen problemen, maar in de problemen

Sinds februari 2022 zijn er berichten over het afsterven van de zee-egels (Diadema Antillarum) op een aantal eilanden in het Caribisch gebied, waaronder St. Eustatius, St. Maarten, Saba en Curaçao. De autoriteiten van beschermde zeegebieden binnen het Nederlands Caribisch gebied zijn bezorgd dat deze gebeurtenissen een weerspiegeling kunnen zijn van de massale afsterving van zee-egels die plaatsvond in de jaren tachtig waardoor de populaties van de Diadema zee-egels in het Caribisch gebied bijna volledig werden weggevaagd. Een nieuwe editie van Bionews, de gratis digitale nieuwsbrief van de Dutch Caribbean Nature Alliance (DCNA), biedt aandacht aan de huidige stand van de afsterving, wat er wordt gedaan om de populaties te herstellen en wat u kunt doen om te helpen.

BELANG VOOR KORAALRIFFEN

Diadema zee-egels spelen een cruciale rol bij het in stand houden van gezonde koraalriffen, welke essentieel zijn voor kustbescherming en een cruciale inkomstenbron voor mensen in het Nederlands Caribisch gebied, doordat ze een magneet zijn voor toeristen. Diadema zee-egels helpen de delicate balans binnen het rif in stand te houden door te grazen op algen, waarvan een overvloed het koraal kan beschadigen.

CARIBISCH-BREDE ZIEKTE

Foto: Alwin Hylkema

Halverwege de jaren tachtig van de 19e eeuw raasde een ziekte door het Caribisch gebied die bijna de hele zee-egelpopulatie vernietigde. Medio februari 2022 kwamen er meldingen over nieuwe omvangrijke sterfgevallen in het Caribisch gebied. Meldingen uit Nederlands Caribisch gebied kwamen voor het eerst binnen op 14 maart vanaf het eiland St. Eustatius. Vervolgberichten van de overige Nederlandse benedenwindse eilanden Saba en St. Maarten volgden snel. Op Curaçao werden begin juni de eerste waarnemingen van zieke zee-egels gemeld. Twee weken later was meer dan 90% van de onderzochte populaties verdwenen.

 

DIADEMA WORKSHOP

In april organiseerde DCNA, samen met de  University of Applied Sciences Van Hall Larenstein (VHL), een Diadema Restauratie Workshop. Deze workshop gaf onderzoekers en parkbeheer managers een uitgebreid beeld van de algehele situatie van de Diadema zee-egel in het Caribisch gebied, inclusief informatie over de huidige afstervingsgebeurtenissen en restauratietechnieken.

U KUNT HELPEN

Burgers en toeristen kunnen ook helpen de gezondheid van zee-egels in het Caribisch gebied te traceren door hun observaties van gezonde, zieke of dode zee-egels te rapporteren. Deze rapporten helpen parkbeheerders en onderzoekers om de oorzaken te bepalen en te werken aan herstelbenaderingen. U kunt uw waarnemingen melden door de AGRRA-website te bezoeken (https://www.agrra.org/sea-urchin-die-off/) of door contact op te nemen met uw plaatselijke parkbeheerorganisatie.

Ander advies om verspreiding van de ziekte te voorkomen:

– Was duikuitrusting in veel zoet water en laat het in de zon drogen

– Duik op niet-geïnfecteerde plekken voordat u duikt op (bekende) geïnfecteerde plekken

– Stap er niet op en verplaats of verwijder ze niet: levend of dood

 

Foto: Alwin Hylkema

LEER MEER

Leer meer over de huidige staat van populaties, wat er wordt gedaan om deze populaties te herstellen en wat u kunt doen om te helpen, door DCNA’s nieuwste editie van diens gratis digitale nieuwsbrief Bionews te lezen, beschikbaar op https://dcnanature.org/news/

DCNA’s nieuwsbrief BioNews wordt mede mogelijk gemaakt door het Ministerie van Landbouw, Natuur en Voedselkwaliteit (LNV) en de activiteiten van DCNA worden mede mogelijk door de Nationale Postcode Loterij.

 

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Papiamento

Bushi di lama spina largo: no ta duna problema, pero ta den problema

Desde februari 2022 tabatin informacion di extincion di bushi di lama di spina largo (Diadema) den varios isla di Caribe, incluyendo St. Eustatius, St. Maarten, Saba y Corsou. Autoridad di Area Protegi Marino di Caribe Hulandes ta preocupa cu e eventonan aki por refleha morto masivo di bushi di lama cu a tuma luga den e decada di 1980 y cu a caba casi por completo cu e poblacionnan di bushi di lama di spina largo di Caribe. Un  edicion nobo di Dutch Caribbean Nature Alliance (DCNA) boletin digital gratis Bionews a hala atencion na e estado actual di extincion, loke ta haciendo pa restaura e poblacionnan aki y loke abo por haci pa yuda.

Importancia pa rif di coral

Bushi di lama di spina largo ta hunga un papel fundamental den mantene rif di coral saludabel, loke ta esencial pa proteccion di costa y un fuente di ingreso crucial pa e hendenan den Caribe Hulandes, ya cu nan ta un magnet pa turismo. Bushi di lama di spina largo ta yuda mantene e ekilibrio delicado dentro di rif door di come e alganan, di cua su sobreabundancia por daña e coralnan.

Enfermedad den henter Caribe

Foto: Alwin Hylkema

Memey di decada di 1980 un enfermedad a extende su mes pa Caribe y a caba cu casi henter e poblacion di bushi di lama. Memey di febrero di 2022, a cuminsa core informacion tocante evento nobo di  extincion masivo den region Caribe. E informenan desde Caribe Hulandes a yega pa prome biaha dia 14 di maart desde e isla di Sint Eustatius. Lihe a sigui e informacionnan di sobra islanan Hulandes di bou di biento di Saba y St. Maarten. Na Corsou e prome casonan di bushi di lama malo a keda raporta den cuminsamento di luna di juni. Dos siman despues mas di 90% di e populacion contempla a disparce.

Tayer di diadema

Den luna di abril, DCNA, hunto cu University of Applied Sciences Van Hall Larenstein (VHL) a organisa un tayer di restauracion di Diadema. E tayer aki a brinda e investigadonan y manager di autoridad di parke un vision integral di e situacion general di bushi di lama Diadema den Caribe, incluyendo e eventonan actual di extincion y  tecnica di restauracion.

Bo por yuda

Ciudadanonan y turistanan tambe por yuda rastrea salud di bushi di lama den Caribe agregando su observacionnan di bushi di lama sano, malo of morto. E informenan ta yuda e managernan di autoridad di parke determinar e causanan y traha riba acercamento di restauracion. Por informa loke bo mira bishitando e sitio web di AGRRA (https://www.agrra.org/sea-urchin-die-off/) of door di tuma contacto cu bo Organisacion di Maneho di Parke local.

Otro conseho pa evita plama e enfermedad:

– Laba e ekipo di buceo den hopi awa dushi y lag’e seca den solo.

– Sambuya na luga limpi no infecta prome cu na sitio infecta (conoci)

– No trapa riba nan ni (re)move nan: Bibo of morto

 

Foto: Alwin Hylkema

Haya sa mas

Pa obtene mas informacion tocante e estado actual, loke ta haciendo pa restaura e poblacionnan aki y loke por haci pa yuda, lesa e ultima edicion di DCNA di su boletin digital grats Bionews disponibel den https://dcnanature.org/news/.

E boletin BioNews di DCNA ta amablemente financia pa Ministerio di Agricultura, Naturalesa y Calidad Alimentario (LNV) y e actividadnan di DCNA pa Loteria di Codigo Postal Hulandes.

 

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Papiamentu

Seapel spiña largu: no ta problema pero den problema

For di febrüari 2022 tin reportahenan ta drenta di murimentu di seapel spiña largu òf seapel pretu (Diadema) na un grupo di isla den Karibe, inkluso Statia, St. Maarten, Saba i Kòrsou.  Organisashonnan responsabel pa áreanan marino protehá denter di e region di Karibe hulandes ta preokupá ku e eventonan akí por ta un ripitishon di e murimentu masivo di seapel ku a tuma lugá den añanan 1980 i ku a hera kaba ku e populashon di seapel di Karibe. Un edishon nobo di Dutch Caribbean Nature Alliance (DCNA) su boletin di informe digital i grátis Bionews ta pone atenshon na e aktual proseso di murimentu, kiko ta hasiendo pa restorá e populashonnan akí i kiko abo por hasi pa duna asistensia.

 

Importansia pa ref di koral

Seapel pretu tin un papel importante den mantenshon saludabel di ref di koral, ku ta esensial pa protekshon di kosta i un fuente di entrada krusial pa hende den Karibe Hulandes komo ku nan ta un atrakshon pa turismo. Seapel spiña largu ta yuda mantené e balansa delikado denter di e ref dor ku nan ta kome alga, ku ora esaki ta den abundansia grandi ta hasi daño na koral.

 

Malesa rònt region di Karibe

Foto: Alwin Hylkema

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. Di Karibe Hulandes e promé reportahenan a drenta riba 14 di mart for di e isla di Statia. Seguidamente pronto reportahenan di e otro islanan di Islariba, Saba ku St. Maarten a drenta. Na Kòrsou, a reportá e promé opservashonnan di seapel malu a drenta na kuminsamentu di yüni. Dos siman despues mas ku 90% di e populashonnan ku tabata bou di investigashon a disparsé.

 

Tayer di Diadema

Na aprel, DCNA a tene huntu ku Hogeschool Van Hall Larenstein (VHL), un tayer di Restorashon di Diadema (Seapel pretu). E tayer akí a duna investigadónan i managernan di parkenan marino un bista amplio di e situashon ku e seapel pretu ta den pa e region di Karibe, inkluso e eventonan aktual di murimentu i téknikanan di restorashon.

 

Abo por yuda

Siudadanonan i turistanan tambe por yuda registrá salubridat di seapel den Karibe dor di manda nan opservashonnan di seapel saludabel, malu òf morto. E reportahenan akí lo yuda managernan di parkenan marino determiná e kousanan i traha riba intentonan di restorashon. Bo por registrá bo opservashonnan dor di bishita e wèpsait di AGRRA (https://www.agrra.org/sea-urchin-die-off/) òf dor di tuma kontakto ku bo Organisashon di Maneho di Parke lokal.

Otro konsehonan pa prevení plamamentu di e malesa:

• Laba ekipo di sambuyá ku hopi awa dushi i laga nan seka na solo
• Sambuyá na sitionan ku no ta infektá promé ku bai sitionan (indiká komo) infektá
• No trapa riba nan òf kita nan for di kaminda nan ta, bibu òf morto

Foto: Alwin Hylkema

Mas informashon

Tuma mas informashon tokante e situashon aktual, kiko ta hasiendo pa restorá e populashonnan i kiko abo por hasi pa yuda, dor di lesa e último edishon di DCNA su boletin di informe digital grátis Bionews disponibel na https://dcnanature.org/news/.

DCNA su boletin di notisia BioNews ta supsidiá generosamente pa e Ministerio hulandes di Agrikultura, Naturalesa i Kalidat di Kuminda (LNV) i e aktividatnan di DCNA ta supsidiá pa De Postcode Loterij.

 

 

 

Published in BioNews 55.

 

Help Protect Sea urchins

Help us track sea urchin health in the Caribbean by adding your observations of healthy, sick or dead urchins. These reports will allow us to determine the causes and work on restoration approaches. You can report your sightings by visiting the AGRRA website (https://www.agrra.org/sea-urchin-die-off/)

The causative agent of the urchin deaths is not known but may be water-borne and may spread through contact. Pathogens can survive on snorkel/dive gear. To potentially help reduce the spread of pathogens, snorkelers and divers can:

– Have good buoyancy and don’t touch any urchins or other reef life.

– Rent gear locally.

– Decontaminate dive gear after each dive.

– Dive on clean sites before (known) infected sites

All divers should use caution to not further spread this potential disease. Never touch any healthy, sick or dead sea urchins, as you could be spreading the disease. Be mindful and careful about your gear and fins, in order to avoid any touching or stirring up sediment.

Special Diadema BioNews Edition Navigation

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

 

The Diadema RAAK Project is a collaborative effort between University of Applied Sciences Van Hall Larenstein, Wageningen Marine Research and Wageningen University, STENAPA, Saba Conservation Foundation, Caribbean Netherlands Science Institute, University of Applied Sciences HZ, ISER Caribe, Wortel Product Design en Golden Rock Dive Center and is funded by Dutch Research Council (NWO). 

This project is working to improve local populations of long-spined sea urchins around Saba and St. Eustatius by collecting larva from the reef and allowing specimens to mature in a lab before being returned to the wild. Culturing Diadema can provide a number of benefits, including the ability to restock reefs which don’t have a natural larvae supply yet and allowing scientists to study the larval development and settlement cues. The results can consequently be used to develop new and more effective restoration methods.

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.

 

 

Presentation Overviews

2022 Diadema Die-off

Presenter: Alwin Hylkema (Van Hall Larenstein)

The first session covers the current status of Diadema populations within the Dutch Caribbean as well as an update on the current Diadema die-off events, scale, symptoms, treatments and update.  Put in the context of restoration, this presentation stressed the importance of RAAK Pro Diadema project and how it can assist in natural recoveries within Caribbean populations.

 

 

Introduction on Diadema Restoration

Presenter: Alwin Hylkema (Van Hall Larenstein)

This portion of the workshop introduced Diadema restoration and the various approaches to restore this important herbivore within the Caribbean.

 

 

Diadema Cultivation

Presenter: Tom Wijers (Van Hall Larenstein)

There are several restoration methods, most of which are dependent on natural larvae supply within the water (translocation, settler collection and assisted natural recovery).  However, for locations lacking adequate natural larvae supply, its possible to cultivate Diadema larvae from gametes to juveniles.  This presentation covers this process and explores its potential within the Caribbean.

 

The Diadema workshop was 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).

 

Special Diadema BioNews Edition Navigation

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

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.

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.

Repopulation of sea urchins for reef conservation

Diadema antillarum sea urchins were the main grazers of Caribbean coral reefs until over 95% of sea urchins were killed by an unknown disease in 1983. Without sea urchins grazing, algae became the dominant group on the coral reef, outcompeting coral. Today, nearly 40 years after their mass death, sea urchins have still not recovered. HVHL is working with the RAAK PRO Diadema project (2019-2023) along with project partners for the restoration of this species on Saba and St. Eustatius (Caribbean Netherlands).

©Tom Wijers

Long awaited breeding method

For the past 40 years, researchers have been trying to breed Diadema in captivity, but unfortunately have only had limited success. Breeding as been found to be very difficult. Larvae of this type of sea urchin float along sea currents for the first 50 days of their life and are sensitive to water quality and nutrient availability. However, in 2020 researchers and students from HVHL in Leeuwarden managed to develop a method for stable and consistent breeding of young Diadema.

Rotterdam Zoo

It is difficult to transport these animals on a large scale to Saba or St. Eustatius, so the first group of young urchins will find a nice new home in the Rotterdam Zoo starting on March 24th. The next step will be to breed urchins on Saba so that they can be released into the wild, strengthening the populations and helping to restore the coral reef.

More Information

For more information about this project, visit the HVHL website. For a video about this project, please visit our YouTube channel. Follow the project on Facebook for updates.

 

 

Article published in BioNews 42