Bonaire

This study aims to provide historical information on key environmental parameters and describe the current trends of coral growth in Bonaire. In particular, we aim to reconstruct changes in terrestrial runoff and bleaching stress events and establish their effects on the calcification rates for Siderastrea spp corals around Bonaire over multiple decades. For this coral cores of Siderastrea sppcorals will be used to reconstruct the changes in calcification and environmental parameters along a gradient of terrestrial influence and anthropogenic activity. During March 2023 15 coral cores were collected from Siderastrea spp colonies at four locations around the west coast of Bonaire.

Abstract: The economies of small tropical islands often benefit from large-scale tourism, attracted by
the guarantee of beach facilities, sun and warmth, landscape beauty, and cultural and underwater
life. While these are highly valued assets, it is unclear how local communities benefit from tourism,
or how they perceive their natural environment, which has been the basis for their rich cultural
history. Against this background, the main aim of this article is to investigate inhabitants’ perceptions
about locals’ inclusiveness in tourism and recreation on a small island called Bonaire. A total of
400 households were interviewed during the period November 2021–February 2022. Inclusiveness in
tourism and the welfare it brings are judged as low, based on the findings in this study. With a share
of around 40% of the population of Dutch Caribbean islanders living in poverty, the challenge of
inequality is urgent. While environmental degradation contributes to inequality, inequality can also
contribute to environmental degradation. To reduce inequalities, while ensuring life below water and
life on land, the handling of poverty is one of the most critical bottlenecks in this society.

Abstract: Over the past decades coastal ecosystems have been increasingly threatened and have been reducing at alarming rates. Similar is happening on Bonaire, where increased sediment transport and decrease in the freshwater inflow is responsible for high mortality of the mangrove forest in Lac Bay. Factors, such as Bonaire’s arid climate, past deforestation and overgrazing by feral animals have left the island bare which furtherly increases erosion and sediment rich runoff towards the bay. To come up with interventions to reduce mangrove mortality quantitative and qualitative data on the erosion potential and on the rainfall runoff relationship is required. This research provides information on spatial distribution of potential erosion rates in the catchment of Lac Bay, using the RUSLE equation. Moreover, a portable mini rainfall simulator is used to estimate the surface runoff coefficient and to validate RUSLEs potential erosion rates. Unfortunately, no correlation has been found between the measured data and the estimated soil erosion rates. Median annual potential soil loss is 19,3 t ha1 corresponding to annual soil loss of 41678 t. Spatial variation of potential erosion rates is homogeneous, implying catchment wide conservation measures. Measures such as reduced grazing could decrease the potential erosion rates in Lac Bay up to 5%, by increasing vegetation cover in the catchment. Structural measures such as earth dams could furtherly reduce sedimentation at the point of deposition, however before implementation further research needs to be conducted on the impact of such structures on freshwater inflow to the bay. The median runoff coefficient is 0,24 with 76% of the catchment having runoff coefficients between 0,16 and 0,33.

Summary The Government of Bonaire has requested Wageningen Marine Research (WMR) to research the composition of the sand used to construct the artificial beach of the Chogogo Beach and Dive Resort. The major concern regarding the artificial sand was to evaluate whether the sand used could harm the marine park corals. The sand of the beach of Chogogo was sampled on the 10th of May 2022 and analyzed at the Netherlands Institute of Sea Research (NIOZ) for grain size and organic matter content. Additionally, the natural sand in front of Chogogo and several other places was sampled to better compare the sand that naturally occurs around Bonaire to the artificial sand. The results of the analysis and expert evaluation have provided the following responses to specific questions that have been raised.  

What are the potential effects on marine life, specifically corals, in relation to the constructed beach?  There is already sand being transported into the adjacent sea. Corals may already be affected. If so, then stress on corals will be increased. This will affect their metabolism, influencing coral growth and health. Furthermore, a higher sediment load will lead to a higher cover of the bottom by sand and prevent coral recruits from settling. In the longer term, corals more sensitive to sediment will disappear from the location which may be exchanged for more stress-tolerant corals. Generally, these species are less important for maintaining the reef. However, if the sediment load is high (permanently or incidentally), the sea floor may become fully covered by sand, and all corals may disappear. Thus, it is important to monitor artificial beaches for breaks in the retention walls, accumulation of sand along the walls, and make adjustments when necessary. It is important to note that since corals are long-lived organisms, a short-term assessment, as presented within this report, can barely unravel the longterm quantitative impacts on the health of adjacent corals. Thus, long-term monitoring of the coral communities in front of and up-current from (as control) the artificial beach should be favored.  

What are the potential effects on the health of the corals under normal weather conditions? Currently, the sand is already moving towards the sea, and it cannot be excluded that there are no negative effects. Potentially, visibility is already lower, and sedimentation has increased. In addition to the recommendations under question 3, we recommend installing (natural) windbreakers to decrease the wind-funneling effect between the resort's buildings in order to decrease wind effects on the sand.

What are the potential effects on the health of the corals during a storm or wind reversal? During a wind reversal or a storm, there is a high chance that waves will reach the retention wall and wash over it. Consequently, large amounts of sand could suddenly be transported onto the reef and cause massive mortality of corals by burial. The fine sand is likely to be transported downstream (generally in a northerly direction) and may lead to decreased light levels, increased sedimentation, and possibly mortality of corals. The exact transport of the sand is very difficult to predict without extensive measurements of current patterns at the location. We recommend that the retention wall be raised to the prescribed height. It may also be an option to put additional structures in place that can be deployed during wind reversals or storms to prevent sand from being washed away.

How important is the origin of the sand, the kind of sand (river or carbonate sand), the quantity of sand, the layout of the beach, and the constructed wall for the effects? The origin of the sand is very important. Since the sand is not carbonated, it will probably not be processed similarly to carbonated sand. It may be less likely to be cemented into the reef. Compared with natural sand in front of the artificial beach, the grain size distribution is much finer, indicating that the sand, once it travels over the retaining wall, is likely to be washed away by waves and currents. Once the sand washes away, all the negative effects of increased sediment load and sedimentation may occur. The exact location of the beach and the layout, as well as the buildings around the beach, influence the wind erosion of the beach. In this case, local wind conditions transport the sand toward the sea. Even if the retention wall is raised, the sand will continue to be piled up at the downwind side of the beach and will probably need to be redistributed regularly to not end up in the sea. We recommend periodical reinspection and redistribution to ensure that sand is not transported over the retention wall.

Overall, local wind, waves, and current conditions play a major role in the fate of artificial and natural beaches. Since all artificial beaches are on the island’s leeward side, the prevailing wind always blows the sand seaward. Increasing wall height and constructing wind blockers upwind of the beach may provide extra protection against the sand being blown away. Very high waves can accompany wind reversals. This may lead to massive sand transport onto the reef, consequently smothering and killing coral colonies. A general recommendation is to re-evaluate all artificial beaches given the expected consequences of climate change, such as sea level rise and an increase in the frequency of tropical storms, as this may have strong negative consequences for the reef. Current requirements for artificial beaches may have to be reconsidered.  

Summary

Over the last 10 years, the Caribbean Netherlands fisheries on Saba and St. Eustatius have been monitored and multiple assessment reports have been made by Wageningen Marine Research (WMR) in collaboration with local Data Monitoring Officers (DMOs). However, due to challenges in collecting the necessary data, there are gaps in the data which can lead to large uncertainties in the current stock assessments and make it difficult to deliver a more detailed assessment of the fisheries and the state of the stocks.

The specific objectives of this report were to present the data challenges and provide recommendations to address the shortcomings in the current data collection. By addressing these and providing solutions, improvements of the Caribbean Netherlands fisheries monitoring program can be made.

The main gaps identified in the data are:

- Limited coverage by the logbook data, especially the case in St. Eustatius. This implies that large raising factors are applied when estimating total effort and landing estimates, which leads to more uncertain estimates.

- Landings not reported by species (at least for the main species) and port sampling for species composition not frequent enough to be able to produce landing estimates and abundance indices at the species level (instead of species groups). For instance in Saba, the number of trips sampled to estimate the length-composition of the landings was on average 60 per year (excluding 2011), with mainly lobster and redfish trips being sampled. On average, around 40 trips per year were sampled for species composition, taken representatively from the different fishing methods. This is less than one catch sampled per week. This is too low and needs to be intensified if data availability and quality are to improve.

- While some species are over-sampled for length-composition, others are not sampled enough to be able to compute reliable length-based indicators.

Our key recommendations are:

o Port sampling and biological data collection-frequency must be stepped up to meet minimum targets.

o Going along with fishers on the vessels, in order to measure catches on location. (Then fishermen won’t have to wait at the harbor for the DMOs work to be done.)

o Facilitate working in morning/midday/evening shifts. This enables data collection after regular working hours, e.g. when fishers come home late in the day (5-6pm).

o Set quantitative targets for data collection. We suggest targeting for a minimum of 70% logbook declarations, activity surveys, catch species composition and weight data (tonnes), while doubling the effort on selected species of importance

o Data collection will now need to include exact biometric data to establish length-weight and fecundity curves, sex ratios and reproductive seasons for individual species, as well as the collection of otoliths from a range of sizes for each species as a basis for age and growth studies by the WMR otolith lab.

o Have DMOs sit in a workspace with a clear view of the harbor where fishers arrive with their catches, so they can immediately act when boats arrive with their catches. This is mainly an issue for the St. Eustatius DMO.

o For bycatch measurements photographing the fish on a cm grid surface can save measuring time in port or on vessels. o Increase willingness of fishers to participate in data collection. o Incentivize fishers to participate by organizing regular (bimonthly or quarterly) gettogethers where the DMOs update fishers on some monitoring results, providing snacks and drinks.

o Provide dedicated freezer storage space for fishers at the harbor, enabling DMOs more time for the port sampling. Fishers willingness to wait for port sampling is understandably limited. By providing dedicated freezer storage facility, the DMOs can take extra time needed for sufficient biological sampling (i.e. species composition, length, sex) while the catch of the fishers stays fresh. The same can be done for lobster catches if a port-based holding area is provided. 

o Provide modern technologies to the fishers and/or DMOs, e.g. Electronic Reporting Systems (ERS) such as electronic logbooks, and GPS systems such as the Vessel Monitoring System (VMS).

o Arrange for closer involvement of WMR in work planning for the island DMO’s

ABSTRACT There is a lack of information on presence of vibrios in the marine environment in the Caribbean. The aim of this study was to determine the occurrence of Vibrios in the coastal waters of Bonaire. Fifty samples of marine water collected at different depths from various sources around Bonaire were examined for the presence of vibrios. Species identification was confirmed by KB007 HiVibrioTM, Identification Kit and TOFEL-MALDI. Forty of the samples contained Vibrio alginolyticus, 33 yielded V. parahaemolyticus and 29 showed presence of V. vulnificus / V. cholerae. Regarding total colony counts in the sample, 47.4% of the colonies were V. alginolyticus, 35.2% were V. parahaemolyticus, and 17.4% represented V. vulnificus /V. cholerae. Further, of the 25 surface samples from various sites, 14 had a colony count percentage of 50% or greater number of V. alginolyticus. Another 10 sites had a colony count percentage of 50% or greater for V. parahaemolyticus; three of them had a colony count percentage of 50% or greater for V. vulnificus / V. cholerae. The present study constitutes the first study of its kind providing evidence of the prevalence of pathogenic Vibrio species, viz. V. alginolyticus, V. parahaemolyticus, and V. vulnificus / V. cholerae in marine water from the Dutch Caribbean.

Abstract

The economies of small tropical islands often benefit from large-scale tourism, attracted by the guarantee of beach facilities, sun and warmth, landscape beauty, and cultural and underwater life. While these are highly valued assets, it is unclear how local communities benefit from tourism, or how they perceive their natural environment, which has been the basis for their rich cultural history. Against this background, the main aim of this article is to investigate inhabitants’ perceptions about locals’ inclusiveness in tourism and recreation on a small island called Bonaire. A total of 400 households were interviewed during the period November 2021–February 2022. Inclusiveness in tourism and the welfare it brings are judged as low, based on the findings in this study. With a share of around 40% of the population of Dutch Caribbean islanders living in poverty, the challenge of inequality is urgent. While environmental degradation contributes to inequality, inequality can also contribute to environmental degradation. To reduce inequalities, while ensuring life below water and life on land, the handling of poverty is one of the most critical bottlenecks in this society.

Abstract

Red-billed Tropicbirds have historically been considered rare visitors to the waters around the islands of Aruba, Curaçao, and Bonaire in the southern Caribbean. However, in recent years there has been an increase in documented records. We summarize all known Red-billed Tropicbird records for the region and review broader regional population and movement data to place this increase in records in context. We recommend continued careful documentation of Red-billed Tropicbird records on and around the islands of Aruba, Curaçao, and Bonaire and the implementation of a standardized monitoring pro-gram across the Caribbean range for the species to better understand the species' population status, trends, and breeding and at-sea distribution

Nederlands below.

The mangrove forest of Lac Bay, Bonaire, is experiencing a die-off of trees in its northern area. Increasing the tidal exchange by creek restoration likely increases the living conditions for the mangrove trees. In the first months of 2022, a collaboration between the Mangrove Maniacs and the University of Twente was set up to investigate the hydrodynamic properties of the area and looked into the effects of creek restoration.

Creek in Lac Bay opened by the Mangrove Maniacs. Photo source: Rob van Zee

Lac Bay

Mangrove systems worldwide promote ecological diversity while also being economically valuable for humanity. If a mangrove forest experiences die-back, it loses the services it provides. One such case is the mangrove forest of Lac Bay, Bonaire. The northern side of Lac Bay, also known as Awa di Lodo, is experiencing a die-back of mangroves. Unsustainable overgrazing by livestock on Bonaire has depleted the area of ground cover vegetation resulting in the wind, vehicle traffic, and rainwater mobilizing and transporting sediment into Awa di Lodo. The excess sediment in combination with growing mangrove roots clogs lagoons and creeks, eventually closing off these creeks, reducing the hydrological connectivity between the front and back of the forest. High evaporation rates and a low influx of freshwater create hypersaline conditions in Awa di Lodo. The Mangrove Maniacs are trying to open the mangrove creeks so the tidal exchange (the tide-induced volume of water reaching Awa di Lodo) increases, lowering the salinity values in the area. However, it is yet unclear to what extent the existing creeks contribute to the tidal exchange in Lac Bay and to what extent creek restoration can improve the tidal exchange in Lac Bay.

Research

At the start of the year 2022, a group of researchers from the University of Twente monitored water levels and velocities and mapped topographic characteristics of Lac Bay. One of the goals was to create insight into the hydrodynamics of the mangrove system through in-depth analysis of this data. The propagation of the tidal wave, relations between the water levels and velocities and the tidal asymmetry were investigated. Next, a numerical model was developed to quantify the influence of creeks on the tidal exchange and to investigate the effect of creek restoration on the tidal exchange. To quantify the tidal exchange, the residence time of the water in Awa di Lodo was computed, which is the time it takes (in days) for the tidal exchange to completely replace the total water volume of Awa di Lodo.

Results

The obtained data shows that the diurnal tidal wave has a negligible delay in the open water of Lac Bay. In Awa di Lodo, high water is reached on average more than four hours later than in the open bay. During spring tides, the tidal range in the open water is sufficiently large to create an increasing trend in the water level in Awa di Lodo. The water level in Awa di Lodo lowers again when the tidal range decreases during consecutive neap tides. Flow velocities in the creeks mainly depended on the water level difference between the open water and Awa di Lodo. Both ebb- and flood-dominant peak velocity asymmetries are observed in the creeks. The observed flood-dominant tidal duration asymmetry in Awa di Lodo indicates that sheet flow during high tides is responsible for the fast increase of the water level in Awa di Lodo while during low tides the creeks are responsible for the outflow.

The hydrodynamic model showed that creeks significantly influence the tidal exchange from the open water in Lac Bay to Awa di Lodo (Table 1). A new creek connection to Awa di Lodo, preferably by extension of the creek through the center of the mangrove system, is found to be the most efficient to increase the tidal exchange. It was also concluded that the widening of the creeks, deepening of the creeks or the extension of the eastern creek system would have a limited effect on the tidal exchange. Hence creek restoration is shown to be an effective measure to increase the tidal exchange in the mangrove forest of Lac Bay.

Table 1: Tidal exchange, residence time and the ratio of the residence time of any of the scenarios compared to the reference scenario. Red coloured rows indicate a decrease in tidal exchange and blue coloured rows indicate an increase in tidal exchange. A darker shade implies a greater decrease/increase

Impacts on the future

The data analysis and the developed hydrodynamic model will be important tools for the Mangrove Maniacs to make decisions on where to open new creeks and to study the impact of their work. By having more insight into the hydrodynamics of Lac Bay, the mangrove restoration will become more effective and thus increase the ecological value of the area.

For more information, you can read the full report using the DCBD link below.

More info in the Dutch Caribbean Biodiversity Database

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De invloed van kreken op de getijdenuitwisseling in het mangrovebos van Lac Bay, Bonaire

Het mangrovebos van Lac Bay, Bonaire, ervaart het afsterven van bomen in het noordelijke gebied. Er is een goede kans dat het verhogen van de getijdenuitwisseling door het herstellen van mangrove kreken de leefomstandigheden van de bomen verbeterd. In de eerste maanden van 2022 is een samenwerking opgezet tussen de Mangrove Maniacs en de Universiteit Twente om de hydrodynamische eigenschappen van het gebied en de effecten van kreekherstel te onderzoeken.

Kreek in Lac Bay die geopend is door de Mangrove Maniacs. Photo source: Rob van Zee

Lac Bay

Wereldwijd bevorderen mangrovesystemen ecologische diversiteit terwijl ze ook van economische waarde zijn voor de mensheid. Als een mangrovebos sterft, verliest het een voor een groot deel de waarde die het kan toevoegen aan de wereld. Een voorbeeld hiervan is het mangrovebos van Lac Bay, Bonaire. Het gebied aan de noordkant van Lac Bay, ook wel bekend als Awa di Lodo, ervaart het afsterven van mangroven. Niet-duurzame overbegrazing door vee op Bonaire heeft het gebied ontdaan van bodem bedekkende vegetatie, waardoor wind, autoverkeer en regenwater de kans hebben om sediment naar Awa di Lodo te transporteren. Overtollig sediment in combinatie met de groeiende mangrovewortels verstoppen de lagunes en kreken waardoor deze uiteindelijk dicht komen te zitten. Hierdoor wordt de hydrologische connectiviteit tussen de voor- en achterkant van het bos wordt verminderd. Hoge verdampingswaarden en een lage instroom van zoet water creëren extreem zoute omstandigheden in Awa di Lodo. De Mangrove Maniacs proberen de  mangrove kreken te openen zodat de getijdenuitwisseling (het volume water dat door het getij Awa di Lodo bereikt) toeneemt, waardoor het zoutgehalte in het gebied daalt. Het is echter nog onduidelijk in hoeverre de bestaande kreken bijdragen aan de getijdenuitwisseling in Lac Bay en in hoeverre kreekherstel de getijdenuitwisseling in Lac Bay kan verbeteren.

Onderzoek

Begin 2022 heeft een groep onderzoekers van de Universiteit Twente de waterstanden en snelheden gemeten en topografische kenmerken van Lac Bay in kaart gebracht. Een van de doelen een diepgaande data-analyse om inzicht te krijgen in de hydrodynamica van het mangrovesysteem. Er is gekeken naar de voortplanting van de vloedgolf, relaties tussen de waterstanden en watersnelheden en naar de getijdenasymmetrie. Vervolgens werd een numeriek model ontwikkeld om de invloed van kreken op de getijdenuitwisseling te kwantificeren en om het effect van kreekherstel op de getijdenuitwisseling te onderzoeken. Om de getijwisseling te kwantificeren is de verblijftijd van het water in Awa di Lodo berekend, dat de tijd die nodig is (in dagen) voordat de getijwisseling het totale watervolume van Awa di Lodo volledig heeft vervangen.

Resultaten

Uit de verkregen data blijkt dat de dagelijkse vloedgolf een verwaarloosbare vertraging heeft in het open water van Lac Bay. In Awa di Lodo wordt het hoogwater gemiddeld meer dan vier uur later bereikt dan in de open baai. Tijdens springtij is het getijverschil in het open water groot genoeg om een ​​stijgende trend in het waterpeil in Awa di Lodo te creëren. Het waterpeil in Awa di Lodo daalt weer wanneer het getijverschil afneemt bij opeenvolgende doodtij. Stroomsnelheden in de kreken zijn vooral afhankelijk van het waterpeilverschil tussen het open water en Awa di Lodo. In de kreken worden zowel eb- als vloed-dominante pieksnelheidsasymmetrieën waargenomen. De waargenomen vloed-dominante asymmetrie in de getijdenduur in Awa di Lodo geeft aan dat de stroming tussen de mangrovebomen door tijdens hoogwater verantwoordelijk is voor de snelle stijging van het waterpeil in Awa di Lodo. Tijdens eb zijn juist de kreken verantwoordelijk voor de uitstroom en de daling van het waterpeil in Awa di Lodo.

Het hydrodynamische model toonde aan dat kreken een significante invloed hebben op de getijdenuitwisseling van het open water in Lac Bay naar Awa di Lodo (Tabel 1). Een nieuwe kreekverbinding met Awa di Lodo, ​​bij voorkeur door verlenging van de kreek door het midden van het mangrovesysteem, blijkt het meest efficiënt te zijn om de getijdenuitwisseling te vergroten. Ook werd geconcludeerd dat de verbreding van de kreken, de verdieping van de kreken of de uitbreiding van het oostelijke krekenstelsel een beperkt effect op de getijdenuitwisseling zou hebben. Daarom is aangetoond dat kreekherstel een effectieve maatregel is om de getijdenuitwisseling in het mangrovebos van Lac Bay te vergroten.

Tabel 1: Getijdenuitwisseling, verblijftijd en de verhouding van de verblijftijd van elk van de scenario’s ten opzichte van het referentiescenario. Roodgekleurde rijen duiden op een afname van de getijwisseling en blauwgekleurde rijen duiden op een toename van de getijwisseling. Een donkerdere tint impliceert een grotere afname/toename

Impact op de toekomst

De data-analyse en het ontwikkelde hydrodynamische model zullen belangrijke instrumenten zijn voor de Mangrove Maniacs om beslissingen te nemen over waar nieuwe kreken te openen en om de impact van hun werk te bestuderen. Door meer inzicht te krijgen in de hydrodynamica van Lac Bay zal het herstel van het mangrovebos effectiever worden en zal daarmee de ecologische waarde van het gebied vergroten.

More info in the Dutch Caribbean Biodiversity Database

Published in BioNews 57.

Main Findings

The main climate change vulnerabilities for Bonaire are: an increase in the intensity of hurricanes and tropical storms, an increase in the number and extent of flood events, and an increase in the occurrence of extreme weather

• These impact Bonaire’s natural systems (e.g., destruction of coastal and marine ecosystems and terrestrial environments) and socio-economic systems (e.g., health, income, and food availability) – and thus negatively impact households.

• The average score of the household sample indicates that HCR in Bonaire is not particularly low, but also not high.

• Especially the following drivers of household climate resilience seem to be limited in Bonaire: expected damage to homes, amount of savings, insurance covering damage from climate change (vulnerabilities), dependent income sources, incomes, vulnerable neighbourhoods, alternatives to electricity, water, and food, social resilience, community response, government response, awareness of climate change, information and education on climate change impacts and steps to prepare for this, and steps taken to prepare for this.

• The following households are less inclined to be climate resilient: (possibly) bigger households, households with high kid ratios, households with younger household heads, (possibly) households speaking fewer languages, households not fluently speaking English, and households with a higher level of obtained education.

Recommendations

• Create an action plan in which policy directly aimed at increasing (household) climate resilience is formulated. This should at least include policy to:

>Keep investing in the protection and recovery of Bonaire’s nature

>Create awareness >Increase the availability of insurance covering damage from climate change (vulnerabilities)

>Provide financial assistance to help households prepare for climate change (vulnerabilities)

>Provide income generating opportunities and diversify the economy.

• Incorporate climate change (resiliency) in the design of policy on other themes.

• Increase cooperation• Involve the local community

• Conduct additional research

For more information, please contact Nina Zander nina.p.zander@gmail.com.

Please also see:

Nina Zander's Masters Thesis https://www.dcbd.nl/document/household-resilience-climate-change-vulnera...
Raw data set https://www.dcbd.nl/document/household-resilience-climate-change-vulnera...