Sabine Engel

After the 2021 Workshop on Mangrove Restoration held on Bonaire, Jessica Johnson (Coastal Dynamics; Bonaire), Jimena Samper Villareal (Centro de Investigación en Ciencias del Mar y Limnología (CIMAR) of the University of Costa Rica (UCR)) and Sabine Engel (Internos/Mangrove Maniacs; Bonaire) joined forces to establish the Tropical Restoration Network. The aim of this network is to provide a platform for the collaboration and methodological harmonization of the many efforts for restoration of blue carbon habitats, focused on seagrasses and mangroves, in the Caribbean, Gulf of Mexico and Eastern Tropical Pacific region.

Building off the momentum of the 2021 Workshop, a follow on Tropical Restoration Workshop was planned for 6-8 June 2023 hosted by the University of Costa Rica in San Jose. Participants from across the region were invited to attend, either virtually or in person

4. Discussion and Recommendations
Seagrass

Overall, there has been a decrease in the native species of T. testudinum and an increase in the invasive species H. stipulacea. S. filliforme populations appear to be stable, with a slight increase in coverage. Native seagrass Thalassia testudinum (Tt) has had an overall decrease in coverage from 48.78% in 2011 to 20.61% in 2022 . Over this same time period there has been a slight
increase in native seagrass Syringodium filiforme, from 3.85% in 2011 to 6.44% in 2022.

Lastly, there has been an alarming increase in the invasive seagrass Halophila stipulacea, growing from 6.01% in 2011 to 35.24% in 2022. A table with the annual averages for the three seagrasses can be found below in Table 1.

Sargassum has been an issue within Lac Bay, with several of the survey sites being locations where decaying sargassum has created a thick mat, which in most cases was slowly removed with the tide. Physical impact of the sargassum landings can be seen by the seagrass dieback all along the mangrove border from the south until just north of Punto Kalbas. This is noticeable at G.
Additionally, at location E, a very fluffy sediment was found to be covering the substrate. A likely explanation is that this is the result of decomposed sargassum settling at this site. The overall cover by all species together seems to be stable, but in terms of biomass it would appear to be lower. The ecosystem services provided by Halophila stipulacea are significantly lower than those of
Thalassia testudinum due to its shallow root structure (Smulders et al., 2017) and the fact that it is less nutrient rich than native seagrass species (Boman et al., 2019). The shift towards this nonnative species is of concern and should be closely monitored.

Benthic Species
Since 2018 Halimeda species and in 2022 bioturbation observations were added to the methodology of these surveys. Although bioturbators were noted in 2020, they were not quantified in such a way to allow objective, quantitative comparisons moving forward. Overall cover by Halimeda seems to have decreased but a longer time series is required to draw more definitive conclusions.
Two students have looked into carbonate sand production by Halimeda during the Lac Ecological Restoration project: Laura Timmermans (2018) and Valeria Pesch (2019). Results from these studies were inconclusive, highlighting the need for additional research to fully understand the contribution of Halimeda to carbonate sands and infilling of the bay.

In addition, more information is needed on the influence of eutrophication (Slijkerman et al., 2011) on this process. Table 2 below shows the overall averages for both species of Halimeda from 2018 to 2022. Table 2: Overall Halimeda averages between 2018 and 2022.

Sand particles size in Lac was measured during the Conch Stock Restoration project. Largerfractions often show Halimeda segments next to small shells and other carbonate particles(Figure 5). For this reason, it is believed thatHalimeda sp.are a major contributor of sandwithin the bay.

Sediments have been analyzed for carbonate content in several other studies such as theEHLZK projectand duringthe baseline surveys conducted in 2012 (Debrot et al, 2012).Although the findings have not been published, the data showed that sediments towards thecenter of the bay have a higher CaCO3content, and the distribution sand, silt, clay changes(Appendix VI). In addition, it was foundthat terrigenous sediments were most prevalent alongthe borders of Lac-mainly in the northwestern sector, whereas endogenous sediments werefound in the central part of the bay and towards the reef. 

Bioturbators have also been added to recent surveys as it is believed to be important as itmay cause a loss of sequestered carbon, and new sediment may facilitate settlement ofH.stipulacea. Bioturbators are considered to be ecosystem engineers, changing the substratelandscape.Common bioturbators are callianassid (burrowing ghost) shrimp, the lugworm,mantis shrimp and the burrowing sea cucumber.

1. BackgroundInvertebrates play a critica

l role in maintaining a resilient and healthy environment. These speciesare one of the most globally abundant and diverse animal groups, comprising nearly 80% of alldocumented species to date (Brusca &Brusca, 2002). In fact, these species occupy a wide range oftropic levels, interacting with species throughout the food web.One study (Prather et al, 2020) broke down the importance of invertebrates into the following fourecosystem services:

1) Supporting services. This includes primary production, decomposition, nutrient cycling,hydrologic flux and habitat formation and modification. Within the sediment, invertebratescan dramatically influence water movement, increasing soil porosity (Derouard etal., 1997)and decreasing litter quantity (Wardle, 2002).

2) Providing services. These contributions include serving as a food source, or generatinghousehold goods, inclusion in biochemical or pharmaceutical products as well as a boundlesssupply ofscientific study. For Lac, thequeen conch is an iconic species, whose meat washistoricallyfeatured in local cuisine and shellis still usedas decoration.

3) Regulating services. This includes ability to improve water quality, food web stability,disease regulation within populations as well as pest and invader control. In shallow marineecosystems, bivalves (such as mussels and oysters) can provide substantial water filtrationthroughout the water column.

4) Cultural services. This includes benefits obtained from recreational services and theircultural significance. Many iconic invertebrate species, such as octopus, corals, sponges andconch create a vibrant landscape for scuba divers and snorkelers alike to explore.

Lac Bay has great economic,environmental and cultural value, none of which would be possiblewithout a healthy and robust invertebrate population. These invertebrates are help build resiliencewithin the sandy plateaus, seagrass beds and mangroves, serve as a point of interest forvisitors, andareeither themselves iconic, or vital to the success of other iconic species (such as the flamingo andsea turtle)within the bay.

Historical Data and Background

The first known qualitative seagrass survey in Lac Bay was conducted in 1969. Sincethen, additional quantitative surveys were conducted in 1999 and 2007 and on a regularbasis since 2011 (2011, 2013, 2015, 2017, 2018,2019, 2020).After each survey, raw dataforseagrass observationswereuploaded to the DutchCaribbeanBiodiversityDatabase (DCBD)and have beenreferenced innumerouspublications, most notably the seagrassandsea turtle research byChristianen andSmulders from Wageningen University and Research (WUR).In 2010, the invasive speciesHalophila stipulaceawas first documented in Lac Bay, andhas continued to spread since. This is a concern as this species is fast growing andhas been known to outcompete local species of seagrasses. If left unchecked,Halophila stipulaceais a threat to native seagrasses and the species of which dependon it (such as green turtle and queen conch).

Discussion

In recent monitoring (2019, 2020) pictures were taken of all quadrants surveyed as wellas of the surroundingarea.SeagrassOverall, there has been a decrease in the native species ofT. testudinumand anincrease in the invasive speciesH. stipulacea. S. filliformepopulations appeartobe stable, with a slight increase in coverage.Sargassum has been an issue within Lac Bay, with several of the survey sites beinglocations where decaying sargassum has created a thick mat, which in most cases wasslowly removed with the tide. Two ofthese sites, Locations A and G were completelycovered by sargassum. Physical repercussions of the sargassum landings can be seenby the seagrass dieback all along the mangrove border from the south until just north ofPunto Kalba.Additionally, at location E, a very fluffy sediment was found to be covering the substrate.A likely explanation is that this is the result of decomposed sargassum settling at thissite.The overall cover by all species together seems to be stable, but in terms of biomass itwould appear to be lower. The ecosystem services provided byHalophila stipulaceaaresignificantly lower than those ofThalassia testudinumdue to its shallow root structure(Smulders et al., 2017) and the fact that it is less nutrient rich than native seagrassspecies (Boman et al., 2019).The shift towards this nonnative species is of concern andshould be closely monitored.

Halimeda

Since 2018 Halimeda species and bioturbation observations were added to themethodology of these surveys. 2020Data onHalimeda sp.occurrence can be found inAppendix III.Overall cover by Halimeda seems to have decreasedbut a longer time series isrequired to draw more definitive conclusions. Two students have looked into carbonatesand production by Halimeda during theLac Ecological Restoration project: LauraTimmermans (2018)and Valeria Pesch (2019). Results from these studies wereinconclusive, highlighting the need for additional research to fully understand thecontribution of Halimeda to carbonate sands and infilling of the bay. In addition, moreinformation is needed on the influence of eutrophication (Slijkerman et al., 2011) on thisprocess.

Sand particles size in Lac was measured during the Conch Stock Restoration project.Larger fractions often show Halimeda segments next to small shells and othercarbonate particles (Figure 5). For this reason, it is believed thatHalimeda sp.are amajorcontributor of sand within the bay.Sediments have been analyzed for carbonate content in several other studies such asthe EHLZK project and during the baseline surveys conducted in 2012 (Debrot et al,2012). Although the findings have not been published, the data showed that sedimentstowards the center of the bay have a higher CaCO3content, and the distribution sand,silt, clay changes (Appendix V). In addition, it was found that terrigenous sedimentswere most prevalent along the borders of Lac-mainly in the northwestern sector,whereas endogenous sediments were found in the central part of the bay and towardsthe reef.

Bioturbators

Bioturbators have also been added to recent surveys as it is believed to be important asit may cause a loss of sequestered carbon, and new sediment may facilitate settlementofH. stipulacea. Bioturbators are considered to be ecosystem engineers, changingthesubstrate landscape. Common bioturbators are callianassid (burrowing ghost) shrimp,the lugworm, mantis shrimp and the burrowing sea cucumber. To date, surveys haveonly included rough estimates as to the number of mounds per square meter.After discussing this issue among local researchers, it has been decided to amend theprotocol for next year to count all mounds in the same quadrant as the seagrass cover.If more than half of the mound falls out of the quadrant the mound will not be counted

Historical Data

A study conducted in 1969 by Hummelinck and Roosgave the first qualitative data forqueen conch general distribution throughout Lac Bay. In 2000, a study by Lottpresented the first quantitative data within the same study area. This was followed by asecond survey in 2007. From 2010 onwards (Conch Stock Restoration Project)assessment of queen conch population has been done at irregular intervals (2010,2013, 2015, 2016, 2020).

Results
A total of 43,200 m2 was surveyed and 85 live conchs were found and measured. This resulted in a population density of 19.27 conchs / Ha. To use the Allee effect, only sexually mature conchs should be considered. Over the course of this study, no sexually mature conchs were found , the oldest conch had a lip thickness which measured 6 mm.

Below, Table 1 has been included to summarize the results of the last 5 surveys (2010, 2013, 2015, 2016, 2020). It is interesting to note the dramatic increase between conch populations in 2010 and 2013, and then the rapid decrease in follow on surveys. The results of the 2020 survey highlight a significant issue with only 85 conchs found, none of which having reached sexual maturity. Figure 4 shows a map with the total number of live conchs found per location. There was also a significant number of poached conchs (Table 2/Figure 5) found within the bay. In fact, there were more poached conch shells (100) found than live conch (85), demonstrating that poaching is still an issue which needs to be addressed before the conch population can rebound. 

Each quadrant (quantity 49) equates to 0.09 ha. Using this value, the following densities per year were calculated: 2010 (6.35 conchs/ha), 2013 (51.70 conchs/ha), 2015 (46.49 conchs/ha), 2016 (21.54 conchs/ha), 2020 (19.27 conchs /ha) 

1.Background

The queen conch, orLobatus gigas, is an iconic species found within the Caribbean, beingboth economically andsocially important.Famous for its unique and beautiful shell, alongwith its role as a popular item in local dishes, this species is heavily fishedand, in someareas,highly threatened.A project started in the 1980's, Marcultura, worked to boost localpopulations by cultivating conch to be released in the bay (Hensen,1983). Unfortunately,there were no long-term positive impacts to the conch populations after this project.Since November 1992, queen conch havebeen listed as an CITES Appendix II species,which means it is at risk of endangerment. However, due to concerns over local populations,taking conch from Bonaire has been forbidden since 1985. Only legal imports (from countrieswith CITES export permits) are allowed. Unfortunately, poaching is still an ongoing issue forthe island.The conch middens (old shells) that can be seen in large piles along the Lac Caibeach are from conch caught locally and brought in from the Aves Islands.Other species in the genusLobatusandStrombusareLobatus raninus (hawkwing conch),Lobatus costatus(milk conch) andStrombus pugilus (fighting conch) also occur on Bonaire.Lobatus costatusare taken incidentally but their shell is verythick,and they have very littlemeat.

Nederlands below.

A joint experiment between WWF-Mexico and STINAPA Bonaire found that vegetables grown in soil enriched with sargassum had higher levels of arsenic and cadmium, heavy metals that can be toxic to humans and animals.  Researchers warn that sargassum should not be used to compliment animal fodder, nor used as a fertilizer for consumables until further investigated.

Sargassum influx in Lac Cai

Sargassum is a floating brown seaweed that plays several important ecological roles. Although sargassum occurs naturally, due to shifting ocean currents and increased pollution, the Atlantic is experiencing episodic sargassum blooms.  Since 2011, the Caribbean has experienced several significant sargassum events, leading to a number of social, environmental and economic issues, particularly in the hospitality and fisheries sectors.  Sargassum influxes threaten the already fragile coral reefs, mangroves and seagrass beds.

The Study

To better understand the impact of disposed sargassum, a joint project between WWF-Mexico and STINAPA Bonaire explored whether sargassum-enriched fertilizer promoted faster seed development and if any heavy metals were detectable in the vegetables after harvest. Two planter boxes were used, one filled with 50/50 dried sargassum and potting soil and one with only potting soil.

The Results

Sargassum enriched soil testing set up

Although, in general, there appeared to be no significant physical differences (shape or quantity of vegetable production) between plants grown with or without the presence of sargassum, samples analyzed at the Radboud University laboratory found that arsenic levels were higher in vegetables grown in soil with sargassum. More specifically, bok choy had 37 times, zucchini 21 times, spinach 4 times and soil 13.5 times more arsenic than their counterparts grown in plain potting soil.  Cadmium levels were also higher in plants grown in sargassum enriched soil, with chemical analysis showing bok choy having 2.5 times, zucchini with 3 times, spinach with 1.3 times and soil with 2.7 times the amount of cadmium than samples without sargassum enrichment.

Furthermore, a Wageningen University and Research report titled “Opportunities for valorization of pelagic Sargassum in the Dutch Caribbean”, analyzed sargassum from the same source and found it to have high levels of heavy metals.  This full report is available from the Wageningen University and Research website (https://edepot.wur.nl/543797).

Implications

Decomposing sargassum in water

The health implications of these findings are still unclear. Arsenic can take several forms, namely organic and inorganic, where organic levels can be much higher before negative impacts are observed in people.  It should be noted that the European Food Safety Authority (EFSA) has not yet set official thresholds for arsenic. In fact, the EFSA Panel on Contaminants in the Food Chain (CONTAM) published data in 2010 which stated that there are no ‘safe’ levels of arsenic.  Long term ingestion of inorganic arsenic has been connected to skin lesions, cancer, developmental toxicity, neurotoxicity, cardiovascular disease, abnormal glucose metabolism and diabetes (CONTAM, 2010). More research is needed to understand impacts of these higher levels of heavy metals and the long -term effects when ingested.

As influxes of sargassum are becoming increasingly common, countries and individuals will search for innovative ways to use and dispose of this nuisance. Already, some reports have highlighted its use as a building material, animal fodder or fertilizer for home gardens. Until the health implications are more widely understood, it would be wise to limit sargassum use to non-consumable options.  This leaves the door open for sargassum to be used as building material (dried and pressed into bricks), biofuel or perhaps fertilizer for decorative plants or construction material, such as bamboo.

Submitted by: Jessica Johnson and Sabine Engel, researchers for STINAPA. This project was funded by WWF-Netherlands and received support from Radboud University.

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Nederlands

Zware metalen in sargassum-mest worden door planten opgenomen

De bevindingen van een experiment uitgevoerd door STINAPA in het kader van een gezamenlijk project met WWF Mexico tonen aan dat grond verbeterd met sargassum hogere arseeen (As) en cadmium (Cd) waardes heeft. Arseen en cadmium zijn zware metalen die schadelijk zijn voor mens en dier. De onderzoekers waarschuwen dat sargassum niet gebruikt moet worden als aanvulling voor dier voedsel of als bemesting van groenten, voordat verder onderzoek heeft plaatsgevonden.

Sargassum bij Lac, Bonaire

Sargassum is een drijvend bruinwier dat een aantal belangrijke ecologische functies vervult. Sargassum komt natuurlijk voor, maar door veranderde zeestromingen en toegenomen vervuiling komen er nu periodieke sargassum ‘blooms’ (woekeringen) voor. Sinds 2011 zijn er in de Caraïben verschillende heftige sargassum ‘blooms’ geweest die gevolgen hadden op sociaal-, milieu- en economische gebied, voornamelijk in de horeca, toeristen en visserij sector. De periodieke sargassum aanvoer bedreigt daarnaast ook de toch al kwetsbare koraalriffen, mangroves en zeegras bedden.

De studie

Om meer te weten over het lot of de mogelijke toepassing van het afgevoerde sargassum werd in een gezamenlijk WWF Mexico – Bonaire project door STINAPA onderzocht of planten beter ontkiemden op grond waar sargassum-mest aan toe was gevoegd, en of de zware metalen voor kwamen in de geoogste planten. Twee plantenbedden werden klaargemaakt: één met potgrond, en één met 50/50 potgrond en gedroogd sargassum.

De resultaten

Het kweek experiment

Over het algemeen was er geen zichtbaar verschil tussen de planten gekweekt in de twee bedden maar monsters geanalyseerd aan de Radboud Universiteit toonden hogere arseen waardes aan in groentes uit de bedden met sargassum. Om precies te zijn, bok choy had 37 keer, zucchini 21 keer, malabar spinazie 4 keer, en het groeimedium potgrond sargassum 13.5 keer meer arseen dan de planten en grond uit de bedden met alleen potgrond. Het cadmium gehalte was ook hoger in planten die gekweekt waren in de ‘sargassum’ grond. Bij bok choy was dat 2,5 keer zoveel, zucchini 3 maal spinazie 1,3 maal en het medium 2,7 keer de hoeveelheid cadmium dan de controle planten.

Aan de Wageningen Universiteit werden monsters sargassum van dezelfde bron onderzocht in het kader van de studie “Opportunities for valorization of pelagic Sargassum in the Dutch Caribbean”, en werden ook hoge waardes voor zware metalen aangetroffen. Het volledige rapport is te vinden op de site van Wageningen University and Research (https://edepot.wur.nl/543797)

Implicaties

De gezondheids implicaties zijn nog niet helemaal duidelijk. Er zijn verschillende organische en anorganische vormen van arseen. Pas bij hogere waardes van organisch arseen worden negatieve gevolgen waargenomen voor mensen. De Europese Voedsel Veiligheid authoriteit (EFSA) heeft nog geen drempelwaardes vastgesteld. In feite publiceerde het EFSA Panel Verontreinigingen in de Voedselketen (EFSA Contaminants in the Food Chain (CONTAM)) in 2010 gegevens en stelde dat er geen ‘veilige’ arseen waarden zijn. Verband is gelegd tussen langdurige blootstelling aan anorganisch arseen en huidafwijkingen, kanker, ontwikkelingstoxiciteit, neurologische toxiciteit, cardiovasculaire ziektes, abnormale glucose vertering en diabetes (CONTAM, 2010). Er is meer onderzoek nodig om te bepalen wat de effecten zijn van deze zware metalen bij langdurige blootstelling.

Nu het op de kust ophopen van sargassum steeds vaker voorkomt zoeken landen en organisaties naar innovatieve manieren om van deze sargassum-overlast af te komen. Er zijn al publicaties die hebben aangegeven dat sargassum gebruikt kan worden als bouwmateriaal, veevoer of als huis & tuin grondverbeteraar. Maar zolang de gezondheidseffecten niet duidelijk zijn is het verstandig om sargassum niet te gebruiken voor voedselproductie. Het biedt dus alleen mogelijkheden voor bouwmateriaal (gedroogd en in blokken samengeperst), biofuel en misschien bemesting voor decoratieve planten of bouwmateriaal zoals bamboe.

Samengesteld door Jessica Johnson en Sabine Engel, onderzoekers voor STINAPA. Dit project is gefinancierd door WWF – Nederland, met bijdrages van de Radboud Universiteit.

Published in BioNews 54

EXECUTIVE SUMMARY

The southern wetlands of Bonaire represent a unique environment for the island. Consisting of a wide variety of habitat types including caves, karsts, dry tropical forests, coastal areas, salt pans and mangroves. The Ramsar site Pekelmeer lies completely in this area, as well as a small portion of the buffer zone of the Ramsar site Lac Bay.

Culturally, a number of Bonaire’s historic monuments and tributes to its past can be found as you drive around the perimeter, from ruins of old salt pans to the remains of slave huts and gravestones. Maintaining and respecting these sober reminders of Bonaire’s history is vital to ensuring the sacrifices of the enslaved populations are not forgotten. It would be impossible to separate the historic and cultural identity of Bonaire from this area.

Economically the southern wetlands represent commercial opportunities for salt extraction by Cargill Salt Works as well as a significant driver of tourism, whether it is history enthusiasts, cyclists, kiteboarders, recreational fishers, scuba divers or bird watchers.

The cultural and economic value of this area is only surpassed by its environmental value. The southern wetlands are recognized internationally as an Important Bird Area (IBA), as a site of regional importance by the Western Hemisphere Shorebird Reserve Network, as an area important for sea turtle nesting and as a Ramsar site. The Ramsar site Pekelmeer, which encompasses most of the southern portion of the wetlands, is critical to a number of threatened, endangered or keystone species. Pekelmeer offers a much-needed rest stop for a number of migratory bird species while also serving as an important breeding ground for the Caribbean Flamingo and five different tern species. Furthermore, the southern wetlands constitute most of the natural habitat of the rare and endemic Bonaire Sabal Palm.

This management plan offers a description of the southern wetlands (chapter 1), a legal and legislative overview (chapter 2), a description of resources and utilities (chapter 3), an explanation of the spatial development plan (chapter 4), an overview of conservation target habitats (chapter 5), an analysis of threats and issues (chapter 6), an outline of management actions and strategies (chapter 7), and provides recommendations for the management plan evaluation and review (chapter 8). Conserving this unique wetland will be a major challenge. A critical first step is to designate Pekelmeer as a protected area under island and national legislation, and appoint a management authority.

Presentation given during 2021 Mangrove Restoration Workshop

Presentation given during the 2021 Mangrove Restoration Workshop