Coral reefs

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

MSc internship report

75% of coral reefs worldwide experience degradation of which 60% is caused by local (anthropogenic) stressors. The human welfare of a small islands like Bonaire strongly depends on coral reef ecosystem services. On a global scale the carbon contribution of Bonaire is neglectable, thus their best course of action is to reduce their local stressors. These local stressors include terrestrial runoff of wastewater, sediment and nutrients to the sea. The Project Resilience Restoration of Nature and Society in the Caribbean Netherlands aims to quantify local stressors by monitoring water quality indicators along the leeward coast of Bonaire. Due to their efforts, the site-specific water quality dataset is expanding. However, research on the nutrient transport between the monitoring sites was lacking. To gain insight on local currents, a boat mounted Acoustic Doppler Current Profiler (ADCP) was deployed along the leeward coast of Bonaire. By sailing transects orthogonal to the shore, the ADCP captured the currents in 3D up till 40 m deep. In addition, temperature, salinity and chlorophyll-a were measured using a CTD. Combined the ADCP and CTD data was used to link currents to water quality indicators. The dominant flow was found to be a longshore at all sites. For Bonaire the current is predominantly northward, yet in the Kralendijk area a southward current occurred closer to shore. Around Klein Bonaire, the flow was counterclockwise. Generally, the water masses closest to shore had the highest temperature, salinity and chlorophyll-a concentrations. Local elevated chlorophyll-a layers were observed either in (1) less saline seawater at the surface near shore or (2) in equal saline seawater at 7m depth further offshore. The former could be attributed to terrestrial runoff (local stressor), whilst the latter may originate from open sea. Surface layers of chlorophyll-a were found in both longshore currents on the main island, implying the transport of land-based effluents to the north and to a lesser extent to the south. Exchange between Bonaire and Klein Bonaire seems limited. These results will provide a foot hold on how terrestrial effluents are (re)distributed around the coastal environment. And, hopefully, contribute to successful management practices and monitoring of local stressors.

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

A new study by researchers from the University of Texas and California Polytechnic State University documented herbivorous fishes feeding on fish fecal pellets off the coast of Bonaire.  This has never been recorded in the Caribbean before and provides a deeper understanding of nutrient recycling and insight into the diverse diets of fishes who work to keep the local coral reefs healthy.

Blue parrotfish (Scarus coeruleus). Photo credit: Marion Haarsma

Coral reefs are one of the most diverse ecosystems on the planet, but they are also limited in nutrients. So, nutrient recycling is a vital part of supporting such reef organisms and their biodiversity. Organisms can’t process all the nutrients from the food they eat, so some of these nutrients come out in their poop. A new study documented a unique upcycling technique, previously unknown within the Caribbean, herbivorous fish feeding on fish feces.

Parrotfishes and surgeonfishes are often praised as the great caretakers of coral reefs, feeding on reef algae and keeping overgrowth in check, which indirectly promotes healthy coral recruitment and growth.  Although it was previously known that Caribbean parrotfishes and surgeonfishes also fed off other food sources, such as cyanobacteria, sponges, and even corals themselves, a recent study added fish feces to this list.

The Study

This collaborative effort was co-led by Hannah Rempel, a Ph.D. student from University of Texas Marine Science Institute and Abigail Siebert, a former undergraduate student from California Polytechnic State University. They studied the foraging rates of parrotfishes and surgeonfishes on fish fecal matter. Because they found that over 99% of feces they consumed were from the Brown Chromis (Chromis multilineata), a plankton eating fish, they also observed Brown Chromis feces to see what other reef fish ate them and studied the nutritional value of these feces. The study was conducted in 2019 between June and September, across six dive sites along the western shores of Bonaire.  This research is the first of its kind within the Caribbean and paves the way for continued exploration into the topic.

Fecal pellet. Photo credit: Hannah Rempel

The Results

Throughout this study, researchers documented that almost 85% of the observed fecal pellets were ingested by fish with over 90% consumed by parrotfish and surgeonfishes alone. “Compared to algae, these fecal pellets are rich in a number of important micronutrients. Our findings suggest they may be an important nutritional supplement in the diets of these fishes” stated Rempel. Taking a closer look at the fecal matter itself, researchers found that these pellets had higher values of proteins, carbohydrates, total calories, and important micronutrients when compared to most algae.  Therefore, consuming fecal matter may play an important role in nutrient transfer within the marine environment.

Future Research

Understanding the intricate dynamics within coral reefs provides information management authorities need to safeguard these environments more effectively. These results highlight the importance of the consumption of fecal matter in upcycling micronutrients, although there is still much to be learned about the nutritional content of other food sources, such as algae mats, cyanobacteria, sponges and corals.  Fish feces may play a vital role in nutrient supply within the reef environment, emphasizing the need for further insight into this topic moving forward.

For more information you can find the full report on the DCBD by using the link below.

More info in the Dutch Caribbean Biodiversity Database

Published in BioNews 53

Abstract.

Much research is being conducted on environmental issues but more knowledge does not necessarily lead to more decisions that take into account such knowledge. A low research uptake can therefore be a threat to ecosystems. An example is research going on about coral reefs and pollution in Curaçao. Coral reefs are vibrant ecosystems and provide many services. They support the economy and protect the coasts. However, they are declining as many hazards threaten them such as sewage that pours out into the sea. Scientific research is being conducted on that topic, but a major issue is the insufficient uptake of research by the policy sphere and the civil society to adopt environmental friendly decisions and behaviours. This master thesis is embedded in the SEALINK project, which aims at understanding how pollution such as sewage impacts the coral reef in Curaçao, and more precisely to its work package on research uptake strategies. This thesis first identifies in the literature the conditions under which research uptake is optimal. Literature highlights three criteria that knowledge should meet in order to have an optimal research uptake: legitimacy, credibility and salience. The salience of the scientific knowledge produced on sewage pollution and its impact on the reef is the focus of this thesis as the legitimacy and credibility of the knowledge produced on sewage are assumed to be met already. Salience refers to the relevance of the knowledge produced for the users of science, such as policy makers. A lack of salience can be the cause of differences in timerames, in the vocabulary used between the scientist and users of knowledge, for instance. The stakeholders that affect sewage in Curaçao, such as the ministry in charge of sewage management, companies that pick up sewage, the tourism industry, or fishermen, were then listed to be interviewed. Interviews of these stakeholders were conducted to explore the behaviours undermining salience of the knowledge produced on the topic at hand. The results show that this knowledge lacks salience because of an operational misfit between the demand for, and supply of knowledge. Recommendations to the local actors and to future researchers on solutions to create more salient knowledge and therefore to have optimal research uptake to protect the reef better, are proposed under the form of science-policy interfaces with an emphasis on knowledge co-production as the main approach to improve the science and practice relationship.  

Part of the larger The impacts of climate change on Bonaire (2022-present) report available here.
 

Summary

Coastal hazards pose a significant threat to small islands, especially in combination with Sea Level Rise (SLR). Currently, the small Caribbean island of Bonaire is poorly protected against coastal flooding and there is a lack of local knowledge on potential adaptation options and their benefits and trade-offs. This study aims to fill this gap by evaluating how different coastal adaptation options to protect Bonaire are valued, considering economic, social, environmental, and technical criteria. This is evaluated using a participatory Multi-Criteria Analysis (MCA) that includes key stakeholders through semistructured interviews and the use of an online questionnaire. A wide variety of coastal adaptation options, ranging from grey infrastructure to softer Nature-based Solutions (NbS), is assessed based on an interdisciplinary set of 10 different criteria, providing a holistic view of the consequences of each option. The results show that NbS, especially mangrove restoration, and spatial zoning measures are overall perceived to be most beneficial. The least favourable adaptation strategies include the construction of any type of seawall and doing nothing. While an MCA does not lead to a final perfect solution, it does provide valuable comparative information about potential future adaptation strategies for Bonaire, which can be used to aid policy makers in the decision-making process. Moving forward, it is important to further strengthen the results of this study by conducting additional quantified analyses, including an evaluation of the spatial suitability of specific measures or combinations of measures. Moreover, to ensure public support for any final policy decisions, regardless of the specific measures that a

Coral reef surveys in 2021 at the leeward side of Curacao (Duthc Caribbean) yielded the discoery of a new worm snail for the Atlantic. With the help of photographs taken during elarlier surveys, its presence on Curacao could be traced back to 2014 and on Bonaire to 2019.  The species cannot be Petaloconchus varians because that worm builds reefs in shallow waters.  

This supplementary data belongs to the article:  Hoeksema, B.W., van der Loos, L.M., van Moorsel, G.W.N.M., 2022. Coral diversity matches marine park zonation but not economic value of coral reef sites at St. Eustatius, eastern Caribbean. Journal of Environmental Management.

https://www.dcbd.nl/document/coral-diversity-matches-marine-park-zonatio...

A B S T R A C T
Stony corals play a key role in the marine biodiversity of many tropical coastal areas as suppliers of substrate, food and shelter for other reef organisms. Therefore, it is remarkable that coral diversity usually does not play a role in the planning of protected areas in coral reef areas. In the present study we examine how stony coral diversity patterns relate to marine park zonation and the economic value of reefs around St. Eustatius, a small island in the eastern Caribbean, with fisheries and tourism as important sources of income. The marine park contains two no-take reserves. A biodiversity survey was performed at 39 sites, 24 inside the reserves and 15 outside; 22 had a maximum depth >18 m and 17 were shallower. Data on economic value per site were obtained from the literature. Corals were photographed for the verification of identifications made in the field. Coral species richness (n = 49) was highest in the no-take reserves and species composition was mainly affected by maximum depth. No distinct relation is observed between coral diversity and fishery value or total economic value. Based on the outcome of this study we suggest that in future designs of marine park zonation in reef areas, coral diversity should be taken into consideration. This is best served by including reef areas with a continuous depth gradient from shallow flats to deep slopes.

Supplementary material 

https://www.dcbd.nl/document/electronic-supplementary-material-1

Abstract

Coral reefs are one of the most biodiverse yet threatened ecosystems on the planet. Our understanding of what contributes to a coral reef’s resilience to adapt to global and local threats is not well established. Thriving reefs in close proximity to anthropogenic impacts indicate there are opportunities for improved understanding of the underlying factors that influence the ability of some coral species to withstand environmental stressors and changing oceanographic conditions. Research suggests that resource availability and a coral’s trophic strategy can improve a coral’s tolerance to environmental stressors. Such discoveries have already been made, but the effects of resource availability on heterotrophic coral species have been minimally explored in the Caribbean; a region that has suffered substantial declines in coral health and cover–. Regardless of these declines, Curaçao, an island in the Southern Caribbean, possesses uncharacteristic coral diversity and cover for the region. One of the most abundant species covering the Curaçao reef tract, Madracis mirabilis, is largely heterotrophic in its feeding strategy. The growth and distribution of this species was tracked across 7 sites spanning approximately 40 kilometers along natural and anthropogenic gradients of nutrients in Curaçao. Our findings suggest that the highest growth and percent cover of M, mirabilis, can be found in regions with the highest exposure to anthropogenic nutrient loading. These data provide insights into how some corals may be better adapted to changing environmental conditions and degradations in water quality

Researchers from University of Amsterdam and CARMBABI Foundation implemented 3-dimensional reef surveying techniques to improve representation of species found within hidden cavities previously overlooked by 2D methods. 12 sites along the coast of Curacao were selected and analyzed. Improved surveying techniques will increase overall understanding of the complexities of these vital ecosystems.

Photo Source: Niklas Kornder

Coral reefs are one of the most diverse ecosystems on the planet.  Coral’s beautiful skeletal structure plays an important role in providing reef habitat, nursery and hunting ground while also protecting coastal zones.  Climate change continues to be a significant threat to these areas, making the need for accurate mapping and surveying techniques vital to researchers’ ability to detect change. Traditional mapping techniques use a 2D approach to project surface cover estimates throughout a 3D structure.  Unfortunately, this technique misses hidden habitats, such as overhangs and cavities, which can result in an under representation of biomass estimates.

Photo Source: Eric Mijts

2D versus 3D

New research from the University of Amsterdam and CARMBABI Foundation compared 2D versus 3D survey techniques. Traditionally, organism abundance was calculated as the percentage of projected reef cover.  Previously, this was done by 2D surveys, however a new strategy hopes to improve on this technique through the combination of photograph analysis, diving surveys and computer modeling. Researchers surveyed 12 coral areas on the island of Curacao, then compared 3D benthic community estimates against traditional 2D projected surface cover analysis.

The Results

During this research, scientists found that while using 2D techniques, the relative contribution of organisms which grow vertically (gorgonians and massive sponges) was up to two times and 11 times lower, respectfully, than their contribution to reef biomass.  In addition, hidden areas represented nearly half of all total reef substrate, meaning two thirds of all coralline algae and almost all encrusting sponges are not included within traditional surveying techniques.

Using a variety of different metrics, this research presents adjustments to current monitoring techniques, highlighting the importance of evaluating the ecological contributions of previously disregarded or underrepresented species.  These metric conversions can be used to complement traditional survey techniques to provide improved estimates for biovolume, biomass and element composition (stocks of organic carbon and nitrogen) within coral reef communities.

Implications

Photo source: Francesco Ungar

Understanding the true composition of coral reefs is vital for designing and implementing effective conservation strategies. Coral’s unique ability to create complex habitats is vital to maintaining high community diversity and abundance in shallow water environments.  It is estimated that nearly 75-90% of coral reef ecosystems are hidden under the surface skeleton.  This means that for every m2 that can be seen, there is up to 8m2 of additional habitat underneath. This study suggests that 2D approaches may be useful to produce relatively fast estimates of reef ‘health’ but a 3D approach is needed to understand coral reef’s true composition.

https://www.dcbd.nl/document/implications-2d-versus-3d-surveys-measure-a...

Article published in BioNews 47