restoration

Monitoring water quality parameters of the coastal waters of Saba and the possible effects on the coral reef

MSc intership report

Coral reef systems have been declining all over the world. The project “Restoration of resilience of nature and society in the Caribbean Netherlands” focuses on mitigating further decline by improving the resilience of the coral reef. This is done, among other things, through water quality monitoring. In this report, we focussed on the quality of the coastal waters of Saba.

The spatial and temporal variation of chlorophyll a, salinity and temperature was assessed and connected to possible land-based activities and anthropogenic stressors.

The local stressors were assessed through informal interviews. The water quality indicators were measured with sensitive sensor technology. This was done by boat, every two weeks, on 13 locations around Saba, at a depth of 1.5-10 meters.

Both a temporal and spatial variation in chlorophyll a, temperature and salinity have been found. The chlorophyll a values seem concerting when looking at the coral reef threshold. Temperature and salinity are not yet troubling within he period of this research. However, if their temporal trend persists, there would be cause for concern. A baseline for potential local stressors has been identified but more extensive research is needed. Prolonged monitoring of the water quality indicators and more research into local stressors and how these affect one another is needed to fully understand what is going on.
For full report or more information,  please contact erik.meesters@wur.nl or gulsah.dogruer@wur.nl

Date
2022
Data type
Research report
Theme
Research and monitoring
Report number
Department of Animal Sciences Aquaculture and Fisheries Group
Geographic location
Saba

Key Insights for Mangrove Restoration Discovered on Bonaire

Dutch below

 

Since 2016 the Mangrove Maniacs of Bonaire have dedicated themselves to the restoration and conservation of mangroves on the island. Monitoring research has provided key insights into the conditions that favour growth and survivability of these vital ecosystems and provide necessary information in support of management actions and planning.

Lac Bay and its mangroves 

When a mangrove forest experiences die-off, it loses the important services it provides (coastal protection, habitat for marine species, and carbon storage). This is currently the case with the northern part (also called Awa di Lodo) of the mangrove forest in Lac Bay. Unsustainable overgrazing by livestock has resulted in a depletion of ground cover vegetation. Wind, vehicle traffic and rainwater run-off therefore cause a high influx of sediment into Awa di Lodo. The sediment build-up clogs lagoons and creeks, reducing the hydrological connectivity between the front and back of the forest, creating hypersaline conditions and causing the trees to die. 

Figure 1: Outplant event on the southwest coast of Bonaire (23 September, 2022). Photo Source: Josien Hendricksen

To fight this die-off, the Mangrove Maniacs dig channels to increase the tidal exchange and thereby improve the water quality conditions. They also plant mangrove seeds (propagules) of two different species: red (Rhizophora mangle) and black mangroves (Avicennia germinans). The propagules are grown in special ‘nurseries’ and are then planted in degraded areas or along the southwest coast to promote coastal protection (Figure 1). By monitoring propagule growth and survival as well as water quality parameters, we can increase our knowledge on the relationship between these factors and improve management plans for mangrove restoration and reforestation.

Tale of two studies

Study 1: Mangrove Growth

A long-term monitoring research between 2016 and 2020 investigated red mangrove growth by comparing a healthy and a degrading area. The diameter at breast height (DBH; ± 1.3 m above ground surface) and the growth of aerial roots was measured monthly (Figure 2). The results showed a clear difference in mean aerial root growth between the healthy and degraded locations. In general, it was seen that healthier sites had higher aerial root growth whereas the degrading areas had more DBH growth. Since the degrading area  experiences a higher sun exposure (due to a less dense canopy), these results would imply that shade promotes aerial root growth, while tree DBH keeps increasing in more sunny areas. In healthier areas, more energy is dedicated towards growing aerial roots, which could be the reason for the slower DBH growth.

 

Figure 2: Measuring the aerial root length of a red mangrove in Lac Bay. Photo source: Arno Verhoeven

 

Study 2: Mangrove Propagules

Another experiment with black and red mangrove propagules was carried out between 2020 and 2022. Here, the growth and survival of propagules in five different locations in Lac Bay (Figure 3: Pedro, Kaminda Sorobon, Isla Yuwana, Rand and Taco) was monitored, together with the salinity levels at these places. The monitoring took place along the regular hydrological restoration in the area, aiming at a better refreshment of water and improving conditions. During the propagule experiment the salinity levels have decreased over time at all locations, which is an expected result of the hydrological restoration efforts. Survivability rates of red mangrove propagules was found to be higher than that of black mangrove propagules due to inundation times. Further experiments where inundation changes are excluded are needed to assess the effects of salinity. 

Figure 3: Monitoring locations of mangroves in Lac Bay, Bonaire

 

Future implications

The two studies clearly showed that salinity levels have decreased over the last years due to Mangrove Maniacs’ restoration efforts (Figure 4), although the levels are still high. In general, more degraded areas had a higher salinity and also lower growth rates. Red mangrove propagules seem to have a higher resilience for changes in water level and salinity than black mangrove propagules. Their strategy of fast growth under a wide range of environmental conditions would be a reason to prefer red mangroves over other species for outplants in locations more susceptible to environmental change (e.g. the southwest coast with sea level rise). The decrease in salinity over time shows the importance of channel maintenance in the mangrove forest of Lac Bay. To further improve water circulation and thus the health of the forest, new channels would be needed. This is already in the planning of the Mangrove Maniacs.

If you want to learn more, follow the Mangrove Maniacs on social media or come out to volunteer with them on Tuesday mornings (8am @Lac Cai, boat space is limited so please sign up via Facebook).

 

Photo credit: Monique Grol

 

Nieuwe inzichten ontdekt voor mangroveherstel Bonaire

De vrijwilligers van Mangrove Maniacs op Bonaire wijden zich sinds 2016 aan het herstel en behoud van de mangroves op het eiland. Monitoringsresultaten tonen belangrijke inzichten over de condities die de groei en overleving van dit vitale ecosysteem bevorderen en verstrekken daarnaast de nodige informatie ter ondersteuning van beheeracties en planning.

Lac Bay en zijn mangroven

Wanneer een mangrovebos afsterft, verliest het de belangrijke diensten die het biedt (o.a. kustbescherming, leefgebied voor mariene soorten en koolstofopslag). Dit is momenteel het geval met het noordelijke deel (ook wel Awa di Lodo genoemd) van het mangrovebos in Lac Bay. Niet-duurzame overbegrazing door vee heeft geresulteerd in een uitputting van de bodembedekkende vegetatie. Wind, autoverkeer en afstromend regenwater zorgen daarom voor een grote instroom van sediment in Awa di Lodo. De opeenhoping van sediment verstopt lagunes en kreken, waardoor de hydrologische verbinding tussen de noord- en zuidkant van het bos wordt verminderd. Dit resulteert in extreem zilte omstandigheden en het afsterven van de bomen. 

Om deze afsterving tegen te gaan, graven de Mangrove Maniacs kanalen om de getijdenuitwisseling te vergroten en zo de waterkwaliteit te verbeteren. Ook worden er mangrovezaden (propagules) geplant van twee verschillende soorten: rode (Rhizophora mangel) en zwarte mangroven (Avicennia germinans). De propagules worden gekweekt in speciale ‘kwekerijen’ langs de mangrovekanalen en vervolgens geplant in gedegradeerde gebieden of langs de zuidwestkust om kustbescherming te bevorderen (Figuur 1). Door zowel de groei en overleving van propagules als verschillende waterkwaliteitsparameters te monitoren, kunnen we onze kennis over de relatie tussen deze factoren vergroten en beheerplannen voor mangroveherstel en herbebossing verbeteren.

Resultaten van twee onderzoeken

Studie 1 Mangrovegroei

Een langdurig monitoringonderzoek tussen 2016 en 2020 onderzocht de groei van rode mangroven door een gezond en een degraderend gebied met elkaar te vergelijken. Maandelijks werd de diameter op borsthoogte (DBH; ± 1,3 m boven grondoppervlak) en de groei van luchtwortels gemeten (Figuur 2). De resultaten toonden een duidelijk verschil in gemiddelde luchtwortelgroei tussen de gezonde en aangetaste locaties. Over het algemeen werd gezien dat de gezonde locaties een hogere luchtwortelgroei hadden, terwijl de degraderende gebieden meer DBH-toename hadden. Aangezien het degraderende gebied een hogere blootstelling aan de zon ervaart (vanwege een minder dicht bladerdek), zouden deze resultaten impliceren dat schaduw de groei van luchtwortels bevordert, terwijl de DBH van een boom wel blijft toenemen in meer zonnige gebieden. In gezondere gebieden wordt meer energie gewijd aan het groeien van luchtwortels, wat de reden zou kunnen zijn voor de langzamere DBH-toename.

Figure 2: Measuring the aerial root length of a red mangrove in Lac Bay. Photo source: Arno Verhoeven

 

Studie 2: Mangrovepropagules

Een ander experiment met propagules van zwarte en rode mangroven werd uitgevoerd tussen 2020 en 2022. Hier werd de groei en overleving van propagules op vijf verschillende locaties in Lac Bay (Figuur 3: Pedro, Kaminda Sorobon, Isla Yuwana, Rand en Taco) gemonitord, samen met het zoutgehalte op deze plaatsen. De monitoring vond tegelijkertijd plaats met het reguliere hydrologische herstel in het gebied, wat ervoor moet zorgen dat de watercirculatie en daarmee de levensomstandigheden voor de mangroves verbetert. Tijdens het propagule-experiment is het zoutgehalte in de loop van de tijd op alle locaties afgenomen, wat een verwacht resultaat is van de hydrologische herstelinspanningen. De overlevingspercentages van propagules van rode mangroven bleken hoger te zijn dan die van propagules van zwarte mangroven, vanwege overstromingen. Verdere experimenten zijn daarom nodig om de effecten van zoutgehalte op de groei van propagules te meten, waarbij overstromingen en dus veranderingen in waterstand worden uitgesloten.

Figure 3: Monitoring locations of mangroves in Lac Bay, Bonaire

 

Gevolgen voor de toekomst

De twee onderzoeken toonden duidelijk aan dat het zoutgehalte de afgelopen jaren is afgenomen als gevolg van de inspanningen van de Mangrove Maniacs (Figuur 4), hoewel de niveaus nog steeds hoog zijn. Over het algemeen toonden de meer gedegradeerde gebieden een hoger zoutgehalte en lagere groeipercentages. Propagules van rode mangroven lijken beter bestand te zijn tegen veranderingen in waterpeil en zoutgehalte dan propagules van zwarte mangroven. Hun strategie van snelle groei onder uiteenlopende omgevingsomstandigheden zou een reden zijn om de voorkeur te geven aan rode mangroven boven andere soorten voor het uitplanten op locaties die gevoeliger zijn voor veranderingen in het milieu (bijvoorbeeld de zuidwestkust met zeespiegelstijging). De afname van het zoutgehalte in de loop van de tijd toont het belang van kanaalonderhoud in het mangrovebos van Lac Bay. Om de watercirculatie en daarmee de gezondheid van het bos verder te verbeteren, zijn nieuwe kanalen nodig. Dit staat al op de planning van de Mangrove Maniacs.

Als je meer wilt weten, volg dan de Mangrove Maniacs op sociale media of help zelf mee met het vrijwilligerswerk op dinsdagochtend (8 uur @Lac Cai, bootruimte is beperkt, dus meld je aan via Facebook).

Photo credit: Josien Hendricksen

 

Published in BioNews 60

Date
2022
Data type
Media
Theme
Education and outreach
Research and monitoring
Geographic location
Bonaire

Innovative Techniques could be key for Sea Urchin Recovery

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

 

____________________________________________________________________________________________________________________________________________________________________________

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.

 

Date
2022
Data type
Media
Theme
Research and monitoring
Geographic location
Saba
Saba bank
Author

Bionews Diadema Special Edition - Background and Current State

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

 

 

Date
2022
Data type
Media
Theme
Research and monitoring
Geographic location
Aruba
Bonaire
Curacao
Saba
Saba bank
St. Eustatius
St. Maarten
Author

Presentation - Assessing the Relationship between Coastal Currents and Water Quality Indicators on Bonaire: ADCP & CTD approach

Final presentation 

Date
2022
Data type
Media
Theme
Research and monitoring
Geographic location
Bonaire

First Caribbean cultured Diadema sea urchins are great news for coral reef restoration

On October 22st, 2021, the first ever recorded Diadema sea urchins in the Caribbean were cultured on Saba. Diadema sea urchins are important grazers and can facilitate corals by reducing their competition with algae. By culturing them, researchers from University of Applied Sciences Van Hall Larenstein set an important step in restocking sea urchins on Saba’s coral reefs.

 

Long-spined urchins (Diadema antillarum). Photo credit: Hans Leijnse

The long spined black sea urchin, also known as Diadema, has been absent on most coral reefs throughout the Caribbean, since 99% of all populations died to an unknow disease in the early 80s. Before the die-off these sea urchins were the major herbivore in the Caribbean, by scraping off and eating the seaweeds. After the mass mortality, Diadema sea urchin populations never really recovered and most reefs nowadays are dominated by macroalgae. Restoring Diadema populations is therefore seen as key priority in Caribbean coral reef management.

Culturing Diadema and releasing them in the wild would speed up the recovery of this keystone species. Unfortunately, the culture of Diadema is very hard, due to the sensitive nature of the larvae. It has been tried several times, especially in Florida, but despite some successes, a consistent method was never developed. In 2020 a new culture method was developed in The Netherlands by researchers from University of Applied Sciences Van Hall Larenstein, making it possible to consistently culture Diadema from tiny larvae to juvenile sea urchins.

In July of this year the research team moved their culture efforts from the cold and not so tropical Netherlands to the Dutch Caribbean island of Saba, in an attempt to culture juveniles near the reefs where they are much needed. With help of the Saba Conservation Foundation, the first larvae have successfully been cultured and settled, resulting in the first 19 Caribbean cultured Diadema sea urchin juveniles! The first 19 cultured Diadema are raised in captivity until they are big enough for release in the wild, where they can graze away the algae that are smothering the corals and prevent new corals from settling.

First 19 cultured Diadema sea urchins in the Caribbean. Squares are 1×1 mm. Source: Tom Wijers and Alwin Hylkema

The next step is to upscale cultivation, with currently over 3000 larvae being cultured. If this approach is proven to be effective on Saba, it can be copied throughout the Caribbean. By removing their most important competitors, Diadema sea urchins can help coral reefs to cope with other stressors like climate change and pollution.

More information: https://www.vhluniversity.com/research/research-projects/diadema

Or contact researchers Tom Wijers (tom.wijers@hvhl.nl) or Alwin Hylkema (alwin.hylkema@hvhl.nl)

 

https://www.dcbd.nl/document/new-diadema-project-aims-restore-sea-urchin...

 

Article published in BioNews 50

Date
2021
Data type
Media
Theme
Education and outreach
Research and monitoring
Geographic location
Saba

High peak settlement of Diadema antillarum on different artificial collectors in the Eastern Caribbean

The massive die-off of the herbivorous sea urchin Diadema antillarum in 1983 and 1984 resulted in phase shifts on Caribbean coral reefs, where macroalgae replaced coral as the most dominant benthic group. Since then, D. antillarum recovery has been slow to non-existent on most reefs. Studying settlement rates can provide insight into the mechanisms constraining the recovery of D. antillarum, while efficient settlement collectors can be used to identify locations with high settlement rates and to collect settlers for restoration practices. The aim of this study was to compare pre and post die-off settlement rates and to determine possible settlement peaks in the Eastern Caribbean island of St. Eustatius. Additionally, we aimed to determine the effectiveness and reproducibility of five different settlement collectors for D. antillarum. D. antillarum settlement around St. Eustatius was highest in May, June and August and low during the rest of the study. Before the die-off, settlement recorded for Curaçao was high throughout the year and was characterized by multiple settlement peaks. Even though peak settlement rates in this study were in the same order of magnitude as in Curaçao before the die-off, overall yearly settlement rates around St. Eustatius were still lower. As no juvenile or adult D. antillarum were observed on the reefs around the settlement collectors, it is likely that other factors are hindering the recovery of the island's D. antillarum populations. Of all five materials tested, bio ball collectors were the most effective and reproducible method to monitor D. antillarum settlement. Panels yielded the least numbers of settlers, which can partly be explained by their position close to the seabed. Settler collection was higher in mid-water layers compared to close to the bottom and maximized when strings of bio balls were used instead of clumps. We recommend research into the feasibility of aiding D. antillarum recovery by providing suitable settlement substrate during the peak of the settlement season and adequate shelter to increase post-settlement survival of settlers. The bio ball collectors could serve as a suitable settlement substrate for this new approach of assisted natural recovery.

Date
2022
Data type
Scientific article
Theme
Education and outreach
Research and monitoring
Geographic location
St. Eustatius

Carbon Sequestration - Engaging Youth in Science and Conservation

Presentation from the Mangrove Restoration Workshop.  

Date
2021
Data type
Media
Theme
Education and outreach
Research and monitoring
Geographic location
Aruba