Coral reefs

Abstract: The geographic partition of genetic variation, also known as population structure, is an essential attribute of a species’ biology and a useful tool for resource managers to make informed decisions for the protection and long-term preservation of the species. Among the most severe deteriorations of coral reefs have been recorded in the Caribbean Sea and such biological knowledge from key species could assist stakeholders to construct sound management plans. The population structure of the iconic Caribbean Sea fan, Gorgonia ventalina Linnaeus, 1758, was estimated from DNA sequences of the mitochondrial marker MutS Like Homolog protein 1 (MSH1) and the nuclear marker Signal Recognition Particle 54 intron (SRP54). Samples encompassed most of the species’ known distribution from Curaçao to Florida, the Lesser Antilles to Panamá, and Bermuda. Analysis of molecular variance revealed a significant amount of population differentiation between the eastern and western Caribbean with the MSH1 gene, however, no such signal was detected with the SRP54 intron. The Old Buoy and Mario reefs of western and southwestern Puerto Rico were the most genetically differentiated among all sites based on the MSH1 gene. Local current patterns at the reef level and low sample sizes are possible explanations for the observed patterns of genetic differentiation. Comparisons with other studies using microsatellites and SNPs, including a study with G. ventalina suggests that faster-evolving genomic areas are more appropriate markers for the detection of fine-scale population differentiation in G. ventalina. 

Dutch below 

ORANJESTAD, ARUBA – Fundacion Parke Nacional Aruba (FPNA) in collaboration with Wageningen University & Research, ScubbleBubbles, and University of Aruba are proud to announce the launch of “Turning the Tide”, apilot project aimed at hands–on rehabilitation of Aruba’s spatially linked coral reefs and mangroves. This 15–month project is co–funded by RESEMBID and Wageningen University & Research with an allocated fund of EUR 713,000 for this project to help turn the tide of environmental degradation and biodiversity loss to a healthy and resilient marine environment for Aruba. During its execution and upon completion, this project is integrated into the management of Parke Marino Aruba to guarantee continuity and lasting impacts for the island.

Rene Henkens (WUR) at press conference

RESEMBID is a 48–project progamme funded by the European Union and implemented by Expertise France – the development cooperation agency of the Government of France and supports sustainable human development efforts in 12 Caribbean Overseas Countries and Territories (OCTs) – Aruba, Anguilla, Bonaire, British Virgin Islands, the Cayman Islands, Curaçao, Montserrat, Saba, Sint Eustatius, Saint Barthélemy, Sint Maarten and Turks and Caicos.

What’s the problem

According to WWF Fund for Nature’s Living Planet Report 2022, thebiodiversity loss by region is declining far greater across Latin America and the Caribbean than any other region. A 94% decrease of biodiversity was seen between 1970 and 2018. The 5th and 6th national reports of the Netherlands for the Convention on Biological Diversity (CBD 2014, 2019) also reported a disturbing message on the condition of the marine environment in the Dutch Caribbean with the conservation status being insufficient with no measurable positive change. A TEEB–study (2018) for Aruba concluded that the ongoing degradation of its marine environment will eventually not only suppress its small but valuable local fishery sector but also reduce tourist numbers and ultimately overall welfare by 50%. More recent studies conclude the same (CBA2020, Oduber 2020, Alberts 2021). Therefore, it is crucial to turn the tide towards a healthy and resilient marine environment where human uses are in harmony with nature.

How do we solve the problem?

To start solving this problem on a national level it is important that it is recognized in the Aruban policy notes and plans. The seriousness ofunsustainable development and the loss of ecosystem services is reflected in the Nature and Environment policy note 2018–2021, the Economic Policy 2019–2021, the National Strategic Plan 2020–2022 and the SDG Roadmap.

In addition, Aruba enacted the Parke Marino Aruba managed by FundacionParke Nacional Aruba in 2018. Aruba is currently in the process of designating an even larger area of its marine coastal areas as protected wetlands under the Ramsar Convention, thereby supported by local NGOs and partner Wageningen Environmental Research (WENR). Fundacion Parke Nacional Aruba is in the process of finalizing its Marine Management Plan for implementation which is put together using valuable input from over 60 different local stakeholders. All the activities carried out under the currentproject will take place in designated nature areas managed by FPNA. Lastly,the on–going “Turning the Tide” project is expected to tackle the lack of human capacity and financial resources by implementing a long–term sustained joint field implementation project which will continue far after the finalization of the project in April 2024.

What does the project entail?

“Turning the Tide” is expected to contribute to the restoration and conservation of a healthy and resilient coastal marine environment for Aruba, in which native marine biodiversity thrives, while its ecosystem services contribute to the welfare of future generations on the island. The EUR713Kfund that has been allocated for the execution of this project will cover: 

Coral Reef Restoration: Aruba’s coral ecosystem has entered a double negative spiral. Due to the disappearance of the stony and branching corals, the three–dimensional structure has disappeared. This leads to an increased vulnerability to erosion, causing even more coral loss and loss of clean hard substrate for coral settlement. In addition, the decline in stony corals causes that the function of shelter and nursery for key herbivorous species such as fish and sea urchins disappear due to the lack of suitable shelter. Grazing herbivorous species are extremely important for the health of corals in Aruba because they prevent overgrowth of the corals by algae. The pilot project will focus on active interventions by placing artificial reefs across 3 different seabed locations located within the Parke Marino Aruba. The artificial reefs will recreate the three–dimensional structure. With these structures in place, key herbivorous species can be restored over time, macroalgae can be grazed more intensively, and new coral can re–establish on the reef. To kick–start the settling of corals on the artificial structures, the project will actively plant coral fragments onto the reefs (Elkhorn and Staghorn corals).

Mangrove Forest Restoration: Aruba’s mangrove forests have also seen a negative spiral caused by sedimentation. This causes reduction in water depthand surface area which in turn causes mortality of mangroves and destroys its fish nursery function. With the pilot project, construction of sediment traps will reduce the influx of sediments, while the reopening of mangrove channels will enhance the flow of clean water, thereby enhancing mangrove ecological rehabilitation. Spaans Lagoen is one of the target sites for mangrove restoration under current project. The Environmental Impact Assessment (EIA) concerning the (silted) mangroves in Spaans Lagoen and the management recommendations will serve as the starting point for the excavations of trapped sediment at this site. The reopening of channels will focus on the thick mangrove forest of Isla di Oro for its nursery function directly adjacent to the sea.

Awareness Building: “Turning the Tide” aims to raise awareness about the conservation status of, and trends in the marine habitats and ecosystem services. In addition, it aims to communicate how these can be restored and what the impact would be on the local community. Above all, the desired impact is to raise awareness of the fact that a healthy marine habitat not only is essential for biodiversity, but also for the local economy and welfare.

Turning the Tide and Parke Marino Aruba

MPA Sero Colorado. Photo credit: FPNA

Parke Marino Aruba is managed by Fundacion Parke Nacional Aruba and consists of four Marine Protected Areas (MPA), namely MPA Arikok, Sero Colorado, Mangel Halto and Oranjestad. The marine protected areas host valuable biodiversity, including many nativespecies, almost all of the island’s mangroves, patches of seagrass beds, coral reefs, reef islets for tern breeding, and nursery and feeding habitats for dolphins, turtles and sharks.

Over the past year, FPNA has been working on its Marine Management Plan which is expected to be implemented later this year. Stakeholder inputcollected during the “SWOT Analysis” workshop in 2021 and the most recent “Zoning and Regulations” workshop has been crucial in the planning of thispilot project. As a result of the workshops, stakeholder input identified six conservation targets that will be the focus for Parke Marino Aruba, with Coral Ecosystem, Reef Fish and Mangrove Ecosystem as top priorities – all of which are focus points within the “Turning the Tide” project. The stakeholder inputwill also contribute to the selection of the most suitable sites for the placement of the artificial reef structures.

The development of the “Turning the Tide” project will be shared externally throughout the 15–month project duration and will end with the publication of a short documentary. For more information visit RESEMBID.

ORANJESTAD, ARUBA – Fundación Parke Nacional Aruba (FPNA) in samenwerking met Wageningen University & Research, ScubbleBubbles en de Universiteit van Aruba kondigen met trots de lancering aan van “Turning the Tide”, een proefproject gericht op hands-on herstel van Aruba’s ruimtelijk verbonden koraalriffen en mangroven. Dit project van 15 maanden wordt medegefinancierd door RESEMBID en Wageningen University & Research met een toegewezen fonds van EUR 713.000 voor dit project om het tij van aantasting van het milieu en verlies aan biodiversiteit te helpen keren naar een gezond en veerkrachtig mariene milieu voor Aruba. Tijdens de uitvoering en na voltooiing wordt dit project geïntegreerd in het beheer van Parke Marino Aruba om continuïteit en blijvende effecten voor het eiland te garanderen.

Rene Henkens (WUR) op persconferentie

RESEMBID is een programma van 48 projecten, gefinancierd door de Europese Unie en uitgevoerd door Expertise France – het agentschap voor ontwikkelingssamenwerking van de Franse regering en ondersteunt inspanningen voor duurzame menselijke ontwikkeling in 12 Caribische overzeese landen en gebieden (LGO) – Aruba, Anguilla, Bonaire, de Britse Maagdeneilanden, de Kaaimaneilanden, Curaçao, Montserrat, Saba, Sint Eustatius, Saint Barthélemy, Sint Maarten en Turks- en Caicoseilanden.

Wat is het probleem

Volgens het WWF Fund for Nature’s Living Planet Report 2022 neemt het verlies aan biodiversiteit per regio veel sterker af in Latijns-Amerika en het Caribisch gebied dan in welke andere regio dan ook. Tussen 1970 en 2018 was er een afname van de biodiversiteit met 94%. Ook de 5e en 6e nationale rapporten van Nederland voor de Convention on Biological Diversity (CBD 2014, 2019) brachten een verontrustend bericht over de toestand van het mariene milieu in Caribisch Nederland waarbij de staat van instandhouding onvoldoende is zonder meetbare positieve verandering. Een TEEB-studie (2018) voor Aruba concludeerde dat de voortdurende achteruitgang van het mariene milieu uiteindelijk niet alleen de kleine maar waardevolle lokale visserijsector zal onderdrukken, maar ook het aantal toeristen en uiteindelijk het algehele welzijn met 50% zal verminderen. Meer recente studies concluderen hetzelfde (CBA2020, Oduber 2020, Alberts 2021). Daarom is het cruciaal om het tij te keren naar een gezond en veerkrachtig mariene milieu waar menselijk gebruik in harmonie is met de natuur.

Hoe lossen we het probleem op?

Om een begin te maken met het oplossen van dit probleem op nationaal niveau is het van belang dat het wordt erkend in de Arubaanse beleidsnota’s en plannen. De ernst van niet-duurzame ontwikkeling en het verlies van ecosysteemdiensten komt terug in de Beleidsnota Natuur en Milieu 2018-2021, het Economisch Beleid 2019-2021, het Nationaal Strategisch Plan 2020-2022 en de SDG-routekaart.

Daarnaast heeft Aruba in 2018 het Parke Marino Aruba uitgevaardigd, beheerd door Fundacion Parke Nacional Aruba. Aruba is momenteel bezig een nog groter deel van zijn mariene kustgebieden aan te wijzen als beschermd wetland onder de Ramsar-conventie, daarbij ondersteund door lokale ngo’s en partnerorganisaties. Wageningen Milieuonderzoek (WENR). Fundacion Parke Nacional Aruba is bezig met de afronding van haar Marine Management Plan voor implementatie, dat is samengesteld met behulp van waardevolle input van meer dan 60 verschillende lokale belanghebbenden. Alle activiteiten die in het kader van het huidige project worden uitgevoerd, vinden plaats in door FPNA beheerde aangewezen natuurgebieden. Ten slotte wordt verwacht dat het lopende “Turning the Tide”-project het gebrek aan menselijke capaciteit en financiële middelen zal aanpakken door de uitvoering van een langdurig duurzaam gezamenlijk veldimplementatieproject dat zal worden voortgezet tot ver na de afronding van het project in april 2024.

Wat houdt het project in?

“Turning the Tide” zal naar verwachting bijdragen aan het herstel en behoud van een gezond en veerkrachtig mariene kustmilieu voor Aruba, waarin de inheemse mariene biodiversiteit gedijt, terwijl de ecosysteemdiensten bijdragen aan het welzijn van toekomstige generaties op het eiland. Het fonds van 713.000 euro dat is toegewezen voor de uitvoering van dit project, zal het volgende dekken:

Herstel van koraalriffen: het koraalecosysteem van Aruba is in een dubbele negatieve spiraal terechtgekomen. Door het verdwijnen van de steenachtige en vertakkende koralen is de driedimensionale structuur verdwenen. Dit leidt tot een verhoogde kwetsbaarheid voor erosie, wat nog meer koraalverlies en verlies van schoon hard substraat voor koraalzetting veroorzaakt. Daarnaast zorgt de achteruitgang van steenkoralen ervoor dat de functie van schuilplaats en kraamkamer voor belangrijke plantenetende soorten zoals vissen en zee-egels verdwijnt door het ontbreken van geschikte beschutting. Grazende plantenetende soorten zijn uitermate belangrijk voor de gezondheid van koralen op Aruba omdat ze overgroei van de koralen door algen voorkomen. Het proefproject zal zich richten op actieve interventies door kunstmatige riffen te plaatsen op 3 verschillende zeebodemlocaties in het Parke Marino Aruba. De kunstmatige riffen zullen de driedimensionale structuur nabootsen. Als deze structuren aanwezig zijn, kunnen belangrijke plantenetende soorten na verloop van tijd worden hersteld, kunnen macroalgen intensiever worden begraasd en kan nieuw koraal zich op het rif herstellen. Om de vestiging van koralen op de kunstmatige structuren een duwtje in de rug te geven, zal het project actief koraalfragmenten (Elkhorn- en Staghorn-koralen) planten op de riffen.

Herstel van mangrovebossen: de mangrovebossen van Aruba hebben ook een negatieve spiraal doorgemaakt, veroorzaakt door sedimentatie. Dit veroorzaakt een vermindering van de waterdiepte en het oppervlak, wat op zijn beurt de sterfte van mangroven veroorzaakt en de viskwekerijfunctie vernietigt. Met het proefproject zal de bouw van sedimentvallen de instroom van sedimenten verminderen, terwijl de heropening van mangrovekanalen de stroom van schoon water zal verbeteren, waardoor het ecologisch herstel van de mangrove wordt bevorderd. Spaans Lagoen is een van de doellocaties voor mangroveherstel in het kader van het huidige project. Het Milieueffectrapport (MER) betreffende de (verzande) mangroven in Spaans Lagoen en de beheeradviezen zullen als uitgangspunt dienen voor het ontgraven van ingesloten sediment op deze locatie. De heropening van kanalen zal zich concentreren op het dichte mangrovebos van Isla di Oro vanwege zijn kinderkamerfunctie direct grenzend aan de zee.

Bewustzijnsopbouw: “Turning the Tide” heeft tot doel het bewustzijn te vergroten over de staat van instandhouding van en trends in de mariene leefgebieden en ecosysteemdiensten. Daarnaast wil het communiceren hoe deze kunnen worden hersteld en wat de impact zou zijn op de lokale gemeenschap. De gewenste impact is vooral om het bewustzijn te vergroten dat een gezond mariene leefgebied niet alleen essentieel is voor de biodiversiteit, maar ook voor de lokale economie en het welzijn.

“Turning the Tide” en Parke Marino Aruba

MPA Sero Colorado. Foto: FPNA

Parke Marino Aruba wordt beheerd door Fundacion Parke Nacional Aruba en bestaat uit vier Marine Protected Areas (MPA), namelijk MPA Arikok, Sero Colorado, Mangel Halto en Oranjestad. De beschermde mariene gebieden herbergen een waardevolle biodiversiteit, waaronder veel inheemse soorten, bijna alle mangroven van het eiland, stukjes zeegras, koraalriffen, rifeilandjes voor het fokken van sterns, en kraam- en eetgebieden voor dolfijnen, schildpadden en haaien.

Het afgelopen jaar heeft FPNA gewerkt aan haar Marine Management Plan, dat naar verwachting later dit jaar zal worden geïmplementeerd. De input van belanghebbenden verzameld tijdens de workshop “SWOT-analysis” in 2021 en de meest recente workshop “Bestemming en Regelgeving” is cruciaal geweest bij de planning van dit proefproject. Als resultaat van de workshops identificeerde de input van belanghebbenden zes instandhoudingsdoelen die de focus zullen zijn voor Parke Marino Aruba, met Coral Ecosystem, Reef Fish en Mangrove Ecosystem als topprioriteiten – die allemaal focuspunten zijn binnen het project “Turning the Tide” . De inbreng van belanghebbenden zal ook bijdragen aan de selectie van de meest geschikte locaties voor de plaatsing van de kunstmatige rifstructuren.

De ontwikkeling van het project “Turning the Tide” zal gedurende de projectduur van 15 maanden extern worden gedeeld en zal eindigen met de publicatie van een korte documentaire. Ga voor meer informatie over RESEMBID naar www.resembid.org.

Published in BioNews 64

Mutualistic associations between benthic marine invertebrates and reef taxa are common. Sponge-dwelling gobies benefit from protection within sponge tubes and greater food availability. Sponge-dwelling gobies are hypothesized to increase sponge pumping rates by consuming polychaete parasites, but such increases have not been demonstrated yet. We investigated the association between sponge-dwelling gobies (Elacatinus horsti) and two species of tube sponge (Aplysina lacunosa and Aplysina archeri) in Bonaire, Caribbean Netherlands. We visually assessed goby presence in sponges and used an in situ method with fluorescein dye to estimate pumping rates. Aplysina archeri was more likely to host a goby than A. lacunosa. For both sponge species, pumping rates of tubes with gobies were higher on average than those of tubes without gobies. Our observations, therefore, suggest that E. horsti associations with Aplysina are consistent with a mutualistic relationship in which sponges benefit from higher feeding rates when gobies are present.

Full article can be accessed here: https://link.springer.com/article/10.1007/s00338-023-02362-y

Abstract
Anthropogenic stressors such as improper wastewater treatment, dump sites and construction sites can increase nutrient input into marine coastal waters, thereby declining water quality conditions for coral reefs and the surrounding marine environment. Increased nutrient flow in the form of dissolved inorganic nitrogen (DIN) and phosphorous (DIP) is taken up by phytoplankton leading to enhanced algal and cyanobacterial growth which can be measured by an increase of Chlorophyll – a (Chla). As part of the project, “Restoration of Nature and Resilience in the Dutch Caribbean”, water quality monitoring has been implemented on Dutch Caribbean islands to determine local stressors effecting costal water quality. Thus far, the role of land-based nutrient pollution has not been assessed on the Dutch Caribbean Island, Saba. This report analyses the water quality surrounding Saba’s coastal waters with a focus on Chla and nutrients and their relation to anthropogenic stressors on the island. We analysed the distribution of Chla and nutrients spatially and temporally. It is shown that Chla frequently exceeds the 0.2-0.3μM threshold around the harbour and in the two bays: Well’s Bay and Spring Bay/Cove Bay. Temporally, the highest elevated values can be attributed to the hurricane season form August-October. The first round of nutrient sampling from the week of 25-05-2022 shows that DIN exceeds its threshold for Cove Bay and Tent Reef, with ammonium contributing the largest to the DIN content. In future, attention needs to be paid to the DIN and DIP balance since high elevated ratios have been found at Tent Reef, possibly indicating DIP - limitation. With only one week of nutrient data available, no correlation between Chla and nutrients could be made. Overall, sites such as Tent Reef, Well’s Bay, and Spring Bay/Cove Bay demonstrate the most severely declining water quality based on frequently elevated Chla and nutrient levels. Further research on water quality data surrounding Saba is necessary to confirm these findings and to address stressors contributing to decreased water quality.

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

Abstract
Since the severe decline of the Acropora populations in Bonaire in the 1980s, no assessment has characterized the distribution of remnant colonies. Because of their patchy distribution, a large sampling effort is necessary to adequately describe their occurrence. However, the spatial scale at which this assessment needs to be carried out makes this prohibitive with approaches such as transects using SCUBA gear and photogrammetry. This internship project aimed to optimize and apply a simple methodology trialed by relevant stakeholders on the island to obtain coarse but spatially explicit data with relatively low time-investment. Snorkelers utilizing a waterproof GPS and a slate to record coarse categorical data outlined patches of Acropora cervicornis and Acropora palmata in-situ. These were processed with an ArcGIS workflow to create shapefiles of coral patches as polygons joined to their corresponding data. The resulting polygons were used to describe the distribution of Acropora spp. along the leeward coast of Bonaire. Furthermore, these were used as ground-truthing data to test whether remote sensing imagery can be used to detect A. cervicornis remotely. 466 polygons along 14.5km of the coast were created, showing a patchy distribution of both species, more frequent occurrence of A. palmata in the northern leeward coast compared to the southern, and vice-versa for A. cervicornis. A multinomial logistic regression, maximum likelihood classification, and forest-based classification all showed a high accuracy in labelling A. cervicornis correctly in remote sensing data, but all showed frequent misclassification of other reef structures as A. cervicornis. The mapping approach presented in this internship could be applied to investigate fragmentation effects in Acropora populations and to gather in-situ ground-truthing data for other benthic habitats.

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

MSc report

Land based nutrient input from anthropogenic sources is a worldwide issue and a threat to coral reef health. Corals found in high nutrient environments are less resistant to global stressors such as rising temperature and extreme weather events. The absence of sewage treatment on St. Eustatius and its erosion prone coastline suggests poor water quality. Chlorophyll-a concentrations were monitored at 11 locations around St. Eustatius twice a month from May to August 2022 (n=7). Preliminary results on spatial and temporal variation of chlorophyll-a show an overall good water quality. Average concentrations did not exceed the environmental threshold of 0.3 μg/L at any of the sampled locations. Concentrations varied between locations and over time. Highest average chla values were found close to STUCO's brine outlet, the oil terminal and Golden Rock Dive & Nature Resort. Towards the end of the sampling period, chlorophyll-a concentrations were more variable between locations, which coincided with the onset of more frequent rain showers. No heavy rainfall occurred during the sampling period, so it was not possible to study the effects of higher precipitation on chlorophyll-a concentrations. Current results do not show reason for concern. However they should be re-evaluated when data on stable isotopes and nutrient concentrations are available. Long-term monitoring that includes the rainy season will show if the water quality around St. Eustatius is suitable for coral reefs or if action is needed to improve it.

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

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

Internship report

Although Bonaire’s waters harbours one of the richest reefs of the Caribbean, it has not evaded the unprecedented global decline of these unique and precious systems. Recent research suggests a significant impact of local stressors on coral reef functioning. Future intensification of Bonaire's coastal activities may increase run-off, sedimentation, and eutrophication, which, potentially could induce detrimental changes to the system. However, identifying adverse effects of for example nutrient run-off on coral reefs in field conditions remains challenging. Nevertheless, a new local monitoring infrastructure may help to evaluate the risks posed by nutrient pollution by detecting the frequency and origin of harmful concentrations. We aim to create an integrated seawater quality management plan on Bonaire. For this, we measured levels and spatiotemporal variation of dissolved inorganic nutrients (NH4+, NO2-, NO3-, PO43-) and physiochemical water quality parameters (chlorophyll-a and turbidity).

Preliminary data (NOV 2021-Feb 2023) are presented of this ongoing 4-year monitoring project. Spatial water quality data from thirty-seven study sites collected from November 22nd to December 1st (2021) at 5 and 10m depth on the reef slope indicated that DIN concentration at site B12 (marina) and at the sites located in the area North of Kralendijk exceeded the 1μM threshold value set for the phase shift from coral to macroalgae-dominated coral reefs. Furthermore, geographical differences between in nutrient concentrations and relative abundance of nutrient species were found. Ammonium dominated the DIN pool in the areas Kralendijk and North of Kralendijk, whereas in the northern part of Bonaire DIN pool predominantly comprised of nitrate.

The temporal monitoring showed mean chlorophyll-a concentrations across Bonaire’s west coast approached the upper range of the safe threshold value (0.3 μg/L), indicating that Bonaire’s reefs are experiencing a chronic state of eutrophication. The data presented here of short-time span and should be considered as preliminary results. The outcome of this multi-year project, however, will provide more thorough insight spatiotemporal variation in nutrient and physiochemical water quality parameters. This data will help build scientific knowledge into both sources and resilience to external nutrient loading of coral reef ecosystems. Understanding this heterogeneity in local water quality conditions, will aid effective management, help restore reef resilience, and increase our chances of mitigating the global decline in coastal reef systems.

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

MSc thesis

Shifts of coral reefs towards alternative states occur due to local and global stressors. Although global stressors are expected to increase due to climate change, anthropogenic local stressors can be addressed to prevent the loss of important ecosystem services. Identifying and understanding how human activities affect the dynamics in the benthic communities in the reef ecosystems could facilitate more effective reef restoration efforts. But how do human activities affect water quality and subsequently the benthic cover? To answer this question we look towards the coral reefs of Bonaire, home to one of the most pristine reefs in the Caribbean. We combine existing data on human activities and environmental variables with new temporal water quality and benthic cover data generated along the west-coast of Bonaire. We created two sets of models: relating the benthic cover to water quality and explaining water quality with human activity. Because our data collection extended into unexplored deeper parts of the reef we have a unique opportunity to consider the effect of local stressors along a more extensive depth gradient.

We hypothesized that areas with high nutrient loads would be reflected by benthic cover with relatively high algae, sponges and benthic cyanobacterial mats. Our results showed this to be the case for sponges and turf algae, but not for benthic cyanobacterial mats (BCM) and macroalgae. The coral and crustose coralline algae (CCA) cover were expected to be related negatively to the selected water quality variables. The models predicting the coral cover give a mixed result. Both significant positive and negative effects of nutrients on the coral cover have been found, and relatively the positive effects are stronger than the negative effects. The expectation that an increase in human activity leads to a decrease in the water quality is a lot more nuanced, but it is clear that terrestrial human activity plays an important role. The influence of depth on the effects of the water quality on the benthic covers seems to be minimal at most. As the few significant differences in water quality effects found, were more likely to be the effect of under sampling than anything else. However, these results might change as more data becomes available, narrowing both the prediction and confidence intervals and thus increasing the chance of finding significant effects of water quality on the benthic cover and clearer effects of human activity. 

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

MSc internship report

The health and abundance of coral reefs are declining worldwide. Coastal development, terrestrial runoff, the temperature rise of the oceans and coral diseases have decreased the health of coral reef systems in the Caribbean. Terrestrial run off has been shown to affect water quality through nutrient influx. The water quality changes and community composition of the reefs of Bonaire have been recorded in the past but only on smaller scales and most of the time in combination with sites on Curaçao. The project “Resilience Restoration of Nature and Society in the Caribbean Netherlands” (the Resilience project) aims to improve the resilience of the coral reef ecosystem on Bonaire, by implementing an extensive monitoring plan for water quality and benthic community composition. This internship project continues surveys of benthic community composition of Bonaire (1), assess the risk of anthropogenic pollution through nutrient influx (2) and relate the water quality assessment of Bonaire to the benthic community data (3).

Benthic community composition was assessed at 8 sites on the leeward coast of Bonaire, between 5 and 60 meters depth. This was done by Remote Operated Vehicle assisted, picture gathering. Dissolved Inorganic Nitrogen (DIN) and Dissolved Inorganic Phospor (DIP) concentrations were also collected at 39 locations around the leeward coast of Bonaire. 11 of the locations were sampled biweekly between November 2021 and May 2022 and nutrient concentrations from these locations were used in a water quality Risk assessment for eutrophic pressure. This was done by calculating a Risk Quotient and comparing it to the percentage of exceedance of a nutrient concentration threshold for eutrophication on coral reefs. Additionally a "Generalized Additive Model" (GAM) was used to explore the relationship between mean coral coverage and mean DIN concentration.

Turf algae showed to be the most dominant functional group between 5 and 20 meters depth, followed by cyanobacteria as the most dominant group between 40 and 60 meters. Coral cover increased until 20 meters depth, up to 25%, and showed a sharp decline afterwards. The benthic index based on AGGRA benthic indicators suggests that the coral reef ecosystem is more dominated by algae and cyanobacteria than corals. DIN concentrations are close to the eutrophic threshold of 1 μm/L and display a relatively high exceedance percentage of that threshold. DIP concentrations stay safely below the threshold value of 0.1 μm/L. Risk assessment of the worst case scenario for DIN shows that almost all locations sampled have low risk or higher for pressure by nutrients. The GAM showed no significant relationship between DIN and coral coverage. Further nutrient concentrations need to be gathered on a temporal scale to get a better view of the water quality over the whole year. The benthic community composition of locations towards the north of the island also need to be mapped to assess the effect of the elevated nutrient concentrations on the coral reef. This study hopes to support the “Resilience Restoration of Nature and Society in the Caribbean Netherlands” project with their extensive monitoring plan.

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