eutrophication

Assessing water quality and the benthic species communities around the Dutch Caribbean Island Sint Eustatius.

Summary
The health of coral reefs is threatened by anthropogenic land-based input, which is a global problem. High nutrient conditions make corals less resilient to environmental stresses like climate change and intense weather. Poor water quality is likely for the island of St. Eustatius due to the lack of sewage treatment and its erodible coastline. However, there are no data on this island’s long-term water quality monitoring. Chlorophyll-a concentrations, used to indicate water quality, were monitored at 13 locations around St. Eustatius twice a month from May to November 2022 (n=13). Additionally, images of the ocean floor at 10m were made using a remotely operated vehicle (ROV) to monitor benthic species communities and their habitat. The main conclusion of this research shows that the reefs are primarily in an algal-dominant state. This may be explained by the frequent, chronic exceedances of the 0.2 g/l chlorophyll-a threshold. Chlorophyll -a thresholds were surpassed more frequently and with higher amounts on the sites with a larger anthropogenic influence. The lower threshold for chlorophyll-a was surpassed at 5 out of the 11 sites by more than 30% of the measurements. This would point to a more pervasive low-level eutrophic condition at all sites. On many of the sand-based substrate areas, seagrass has covered it.

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
Geographic location
St. Eustatius
Author

Assessing Water Quality and the Benthic Species Communities around the Dutch Caribbean Island Sint Eustatius

MSc internship report

The health of coral reefs is threatened by anthropogenic land-based input, which is a global problem. High nutrient conditions make corals less resilient to environmental stresses like climate change and intense weather. Poor water quality is likely for the island of St. Eustatius due to the lack of sewage treatment and its erodible coastline. However, there are no data on this island’s long-term water quality monitoring. Chlorophyll-a concentrations, used to indicate water quality, were monitored at 13 locations around St. Eustatius twice a month from May to November 2022 (n=13). Additionally, images of the ocean floor at 10m were made using a remotely operated vehicle (ROV) to monitor benthic species communities and their habitat. The main conclusion of this research shows that the reefs are primarily in an algal-dominant state. This may be explained by the frequent, chronic exceedances of the 0.2 g/l chlorophyll-a threshold. Chlorophyll -a thresholds were surpassed more frequently and with higher amounts on the sites with a larger anthropogenic influence. The lower threshold for chlorophyll-a was surpassed at 5 out of the 11 sites by more than 30% of the measurements. This would point to a more pervasive low-level eutrophic condition at all sites. On many of the sand-based substrate areas, seagrass has covered it.

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
Wageningen University & Research Aquaculture & Fisheries Group (AFI)
Geographic location
St. Eustatius
Author

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

Seagrass as bioindicator for eutrophication and pollution in the coastal bays of Bonaire, Caribbean Netherlands

MSc thesis

The economy of Bonaire is highly dependent on tourism. Tourists are drawn to Bonaire because of the beautiful nature and biodiversity in the coastal ecosystems, e.g, mangrove forests, seagrass meadows, coral reefs. Therefore, it is important to protect these coastal ecosystems. Currently, eutrophication and pollution are serious threats to Bonaire’s mangrove forests and seagrass meadows through terrestrial run-off and influx of Sargassum. Seagrasses are known to be sensitive to local environmental changes by bioaccumulation of chemicals and nutrients through absorption in their tissues. In this study, we used turtle grass (Thalassia testudinum) as a bioindicator of spatial and temporal variation in eutrophication and pollution in five different bays on Bonaire. We found that T. testudinum is a good bioindicator of eutrophication and pollution. Analysis of stable isotope signatures (δ13C, δ15N), nutrient (%N, %P, %S) and trace metal content (%As, %Cd, %Co, %Fe, %Mn, and %Ni) in T. testudinum leaf samples
revealed that Lagun was the most eutrophic and polluted bay on Bonaire. The high eutrophic and polluted state in Lagun is mainly due to a nearby landfill, large catchment area, and influxes of pelagic Sargassum spp.. In Lac Bay, higher sulfide stress was observed in T. testudinum leaf tissues in 2019 compared to 2015, which may have hindered the uptake of N and P by T. testudinum. The difference in sulfide stress between 2015 and 2019 is due to the massive influx of Sargassum that occurred in 2018. However, we suggest a possible recovery given better uptake of N and P and lower sulfur content in T. testudinum leaf tissues in 2022. This may indicate less sulfide stress in 2022 compared to 2019. In Lac Bay in 2022, biochemical content of T. testudinum leaf tissues collected at fixed sampling sites where the direct cumulative effect of Sargassum influxes was assumed to be highest (i.e., west of Lac Bay), were similar to tissues collected in areas with no or intermediate direct impact of Sargassum. This may also suggest recovery of T. testudinum that has survived the most severe influx in 2018. We showed that Bonaire’s coastal ecosystems are threatened by eutrophication and pollution through land-based run-off and the influx of pelagic Sargassum. Hence, we want to encourage the local government with this study that nature restoration measures need to be taken immediately to protect their coastal ecosystems.
 

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

Abundance of coral-associated fauna in relation to depth and eutrophication along the leeward side of Curaçao, southern Caribbean

A B S T R A C T
Coral-associated invertebrates contribute much to the biodiversity of Caribbean coral reefs. Although the nature
of their symbiotic relation is usually not fully understood, they can cause damage to their hosts, especially when
they occur in high densities. The abundance of seven groups of coral-associated invertebrates was investigated on
reefs along the leeward side of Curaçao, southern Caribbean. In particular, coral barnacles (Pyrgomatidae),
boring mussels (Mytilidae: Leiosolenus spp.), gall crabs (Cryptochiridae), and Christmas tree worms (Serpulidae:
Spirobranchus spp.) were recorded together with their host corals by means of a photo survey at four depths (5,
10, 15, 20 m) and across seven sites with high and five sites with low eutrophication values (based on δ15N
isotope data). Feather duster worms (Sabellidae: Anamobaea), coral blennies (Chaenopsidae: Acanthemblemaria),
and worm snails (Vermetidae: Petaloconchus) were insufficiently abundant for thorough quantitative analyses.
The results show a decrease in the number of barnacles and Christmas tree worms per host over depth, which
could be related to the availability of their host corals. Sites with high δ15N values show a higher abundance of
barnacles and Christmas tree worms per host than sites with low values. This indicates that eutrophication could
be favourable for these filter feeding organisms but when their densities become too high, they tend to overgrow
their hosts and may become a threat to them.

Date
2022
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Curacao

CO2 and inorganic nutrient enrichment affect the performance of a calcifying green alga and its noncalcifying epiphyte

Abstract Ocean acidification studies in the past decade have greatly improved our knowledge of how calcifying organisms respond to increased surface ocean CO2 levels. It has become evident that, for many organisms, nutri- ent availability is an important factor that influences their physiological responses and competitive interactions with other species. Therefore, we tested how simulated ocean acidification and eutrophication (nitrate and phosphate enrichment) interact to affect the physiology and ecology of a calcifying chlorophyte macroalga (Halimeda opuntia(L.) J.V. Lamouroux) and its common noncalcifying epi- phyte (Dictyota sp.) in a 4-week fully crossed multifacto- rial experiment. Inorganic nutrient enrichment (+NP) had a strong influence on all responses measured with the excep- tion of net calcification. Elevated CO2 alone significantly decreased electron transport rates of the photosynthetic apparatus and resulted in phosphorus limitation in both spe- cies, but had no effect on oxygen production or respiration. The combination of CO2 and +NP significantly increased electron transport rates in both species. While +NP alone stimulated H. opuntia growth rates, Dictyota growth was significantly stimulated by nutrient enrichment only at elevated CO2, which led to the highest biomass ratios of Dictyota to Halimeda. Our results suggest that inorganic nutrient enrichment alone stimulates several aspects of H. opuntia physiology, but nutrient enrichment at a CO2 con- centration predicted for the end of the century benefits Dic- tyota sp. and hinders its calcifying basibiont H. opuntia.  

Date
2015
Data type
Scientific article
Theme
Research and monitoring
Journal
Geographic location
Curacao

Nutrient Enrichment and Eutrophication on Fringing Coral Reefs of Bonaire and Curaçao, Netherlands Antilles, 2006-2008

Land-based nutrient pollution is a major stressor on coral reef communities around the Caribbean region and globally. To assess the status of nutrient enrichment and eutrophication on Bonaire and Curacao’s coral reefs, we conducted a comparative nutrient monitoring program that included seasonal sampling for nutrients (ammonium, nitrate, DIN, SRP, TDN, TDP), phytoplankton biomass (Chl a), stable nitrogen isotopes (ð15N) in reef macroalgae, and biotic cover (point count analysis of video transect data) of shallow and deep reef sites between March 2006 and June 2008. Ammonium dominated the DIN pool on both islands and the highest concentrations (~10 µM) occurred on Bonaire’s reef sites adjacent to the Cargill salt ponds. DIN concentrations averaged > 1 µM on both shallow and deep reefs of both islands, indicating that these reefs are now above the DIN threshold noted to support expansion of algal turf, macroalgae and coral diseases. SRP concentrations averaged ~ 0.1 µM on both islands, a level that also represents the SRP threshold for eutrophication on coral reefs. DON and DOP dominated the TDN and TDP pools; TDN/TDP ratios averaged 52 on Bonaire and 45 on Curacao, indicating strong P-limitation of algal growth. Mean Chl a concentrations were higher on Curacao (0.25 µg/l) than Bonaire (0.19 µg/l) and the highest Chl a concentrations on both islands occurred on reefs adjacent to urbanized, nutrient enriched areas. In contrast, low Chl a values of ~ 0.05-0.1 µg/l occurred at the upstream reef sites and the offshore reference site, underscoring the importance of land-based nutrient enrichment to microbial growth and eutrophication on fringing reefs of both islands. The highest macroalgal ð15N values (> + 3 ‰) occurred at the MegaPier and Piscadera Bay on Curacao, which reflects the highest watershed sewage nitrogen inputs of all reef sites in the study. The lower ð15N (< + 2 ‰) values at the other reef sites reflect lower levels of sewage treatment as well as contributions from other nitrogen sources (nitrogen fixation, atmospheric inputs) that have lower source ð15N values. Reefs on both islands were dominated (~ 75 % cover) by benthic algae but showed distinct differences in algal composition; Bonaire’s reefs had high cover of turf and low cover of macroalgae compared to the opposite pattern on Curacao. Our results suggest that the recent expansion of benthic algae and loss of coral cover on reefs in Bonaire and Curacao are not simply the result of top-down human pressures (e.g., overfishing) alone, but also reflect strong bottom-up effects from land-based nutrient pollution.

The data of the study can be found here

Date
2011
Data type
Other resources
Theme
Research and monitoring
Geographic location
Bonaire
Curacao