Abstract: Bioerosion caused by boring mussels (Mytilidae: Lithophaginae) can negatively impact coral reef health. During biodiversity surveys of coral-associated fauna in Curaçao (southern Caribbean), morphological variation in mussel boreholes was studied. Borings were found in 22 coral species, 12 of which represented new host records. Dead corals usually showed twin siphon openings, for each mussel shaped like a figure of eight, which were lined with a calcareous sheath and protruded as tubes from the substrate surface. Most openings surrounded by live coral tissue were deeper and funnel-shaped, with outlines resembling dumbbells, keyholes, ovals or irregular ink blotches. The boreholes appeared to contain black siphon and mantle tissue of the mussel. Because of the black color and the hidden borehole opening in live host corals, the mantle tissue appeared to mimic dark, empty holes, while they were actually cloaking live coral tissue around the hole, which is a new discovery. By illustrating the morphological range of borehole orifices, we aim to facilitate the easy detection of boring mussels for future research.
There is almost no systematic information about the state of marine ecosystems in Aruba. A recent report commissioned by the United Nations Development Program (Pantin 2011) also noted an almost complete lack of information on Aruba’s ecological resources, carrying capacity, limits of acceptable change and the existing level of environmental stress. The Government of Aruba therefore aims to create an assessment program to monitor the status and changes in the reef communities along its coastline. CARMABI, a Curaçaoan foundation specializing in tropical marine research, was selected to conduct the baseline assessment in collaboration with the Scripps Institution of Oceanography (U.S.A.) and the Global Coral Reef Monitoring Network (U.S.A.).
When juveniles must tolerate harsh environments early in life, the disproportionate success of certain phenotypes across multiple early life stages will dramatically influence adult community composition and dynamics. In many species, large offspring have a higher tolerance for stressful environments than do smaller conspecifics (parental effects). However, we have a poor understanding of whether the benefits of increased parental investment carry over after juveniles escape harsh environments or progress to later life stages (latent effects). To investigate whether parental effects and latent effects interactively influence offspring success, we determined the degree to which latent effects of harsh abiotic conditions are mediated by offspring size in two stony coral species. Larvae of both species were sorted by size class and exposed to relatively high-temperature or low-salinity conditions. Survivorship was quantified for six days in these stressful environments, after which surviving larvae were placed in ambient conditions and evaluated for their ability to settle and metamorphose. We subsequently assessed long-term post-settlement survival of one species in its natural environment. Following existing theory, we expected that, within and between species, larger offspring would have a higher tolerance for harsh environmental conditions than smaller offspring. We found that large size did enhance offspring performance in each species. However, large offspring size within a species did not reduce the proportional, negative latent effects of harsh larval environments. Furthermore, the coral species that produces larger offspring was more, not less, prone to negative latent effects. We conclude that, within species, large offspring size does not increase resistance to latent effects. Comparing between species, we conclude that larger offspring size does not inherently confer greater robustness, and we instead propose that other life history characteristics such as larval duration better predict the tolerance of offspring to harsh and variable abiotic conditions. Additionally, when considering how stressful environments influence offspring performance, studies that only evaluate direct effects may miss crucial downstream (latent) effects on juveniles that have significant consequences for long-term population dynamics.
Algae-derived dissolved organic matter has been hypothesized to induce mortality of reef building corals. One proposed killing mechanism is a zone of hypoxia created by rapidly growing microbes. To investigate this hypothesis, biological oxygen demand (BOD) optodes were used to quantify the change in oxygen concentrations of microbial communities following exposure to exudates generated by turf algae and crustose coralline algae (CCA). BOD optodes were embedded with microbial communities cultured from Montastraea annularis and Mussismilia hispida, and respiration was measured during exposure to turf and CCA exudates. The oxygen concentrations along the optodes were visualized with a low-cost Submersible Oxygen Optode Recorder (SOOpR) system. With this system we observed that exposure to exudates derived from turf algae stimulated higher oxygen drawdown by the coral-associated bacteria than CCA exudates or seawater controls. Furthermore, in both turf and CCA exudate treatments, all microbial communities (coral-, algae-associated and pelagic) contributed significantly to the observed oxygen drawdown. This suggests that the driving factor for elevated oxygen consumption rates is the source of exudates rather than the initially introduced microbial community. Our results demonstrate that exudates from turf algae may contribute to hypoxia-induced coral stress in two different coral genera as a result of increased biological oxygen demand of the local microbial community. Additionally, the SOOpR system developed here can be applied to measure the BOD of any culturable microbe or microbial community.
A dedicated Saba Bank Symposium was organised by the University of Wageningen in December 2016. The Symposium was held in Den Helder and brought together researchers and conservationists from throughout the Kingdom to share their knowledge and to provide an overview of the current state of scientific knowledge about the Netherland’s largest and most remote National Park.
Among others, presentations were given on the following topics:
- Where does our interest in Saba Bank come from? by Paul Hoetjes
- State of the reefs: 3 expeditions to Saba Bank by Erik Meesters
- Fish and fisheries at Saba Bank by Martin de Graaf
- Importance of Saba Bank for local communities, by Kai Wulf
- Research by NIOZ on the Saba Bank, by Fleur van Duyl
- Coral diversity and historical collections of Saba Bank, by Bert Hoeksema
- Shark habitat use, by Erwin Winter
- Listening to the Bank: whales and dolphins, by Dick de Haan
The Symposium ended with a panel discussion on the sustainable use of the Saba Bank and what is needed to protect the Saba Bank for the future.
We have done our best to capture the wealth of information presented at the symposium for you in our BioNews letter and hope, that like us, you are impressed by the depth and diversity of the work that has been done to explore and document our largest National Park: The Saba Bank.
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BioNews is produced by the Dutch Caribbean Nature Alliance and funded by the Ministry of Economic Affairs.
Specific anthropogenic substrates demonstrate the ability to aid new coral growth among Caribbean reefs in Bonaire, N.A. In this study I documented the total percent coral cover on tires, concrete, and metal objects then compared it to nearby natural reef. I also documented the percent cover for individual coral species. Natural substrates exhibited the highest percent total coral cover (mean = 64.5 %), followed by concrete (mean = 21.5 %) and metal (mean = 22.9 %); tires supported the lowest mean coral cover (mean = 3.5 %). Coral species diversity was highest on metal substrates (11 spp.), followed by concrete (9 spp.), natural reef (8 spp.) and tires (2 spp.). These data suggest that concrete may be the most appropriate artificial substrate in efforts to aid reef regeneration and restoration in this region.
This report characterizes the state of Bonaire’s reefs as of March 2005. We pay particular attention to structural and functional attributes of reefs that have changed in so many other Caribbean reefs. We characterize coral reefs by their resident organisms and the forces regulating their distribution and abundance. Thus, corals, algae and fish define the “structure” of coral reefs but climate changes, diseases, hurricanes, overfishing, sedimentation and excess nutrients may affect how they “function”. Recent unfavorable changes in the structural and functional attributes of reefs have caused “the coral reef crisis” (Bellwood et al. 2004). In Caribbean coral reefs the most alarming changes have been the declines in the abundance of corals, sea urchins and reef fishes and the accompanying increases in large harmful seaweeds (called “macroalgae”). The decline in coral and increase in macroalgae, called a “phase shift”, represents a significant change in the structure of coral reef ecosystems that could lower its resilience.
In March of 2005, a team of graduate students from the University of Maine revisited six study reefs on Bonaire to determine the status of those reefs and to detect if any change has occurred since March of 2003 when the last such survey was conducted. The study sites established in 2003 from north to south are: Karpata, Barcadera, Reef Scientifico, Forest on Klein Bonaire, Plaza and Windsock. Bonaire’s shallow (10 m) reefs remain in good condition. Coral cover averaged 47% in 2005 compared to 46% in 2003 (no change). Turf algae have increased and coralline algae have declined slightly over the past two years. Harmful seaweed “macroalgae” abundance remains low (2% in 2005 and 5% in 2003; see Steneck in this report) at the 10 m depth we studied. At depths below 20 m, macroalgae are now and have been (for at least the past 30 years) much more abundant (e.g. Van den Hoek et al. 1975) The absence of macroalgae in Bonaire most likely relates to the abundance of seaweedeating species or “herbivores”. Caribbean-wide, harmful macroalgal seaweed abundance corresponds inversely with the abundance of grazing fish such as parrotfish and tangs (Fig. 1). No comparable plot exists for seaweed abundance and any other measured factor on reefs.
Changes over the past two decades
Comparisons between the status of reefs over a few years tell us little about long-term changes. For example, today there is a distinct demarcation between where Bonaire’s fringing reefs begin at 5 to 10 m depth and the shore. This region today is largely coralfree and dominated by rubble and sediment laden turf algae. However, this may not have always been the case. Prior to whiteband disease that killed nearly 90% of the elkhorn and staghorn corals in the Caribbean (i.e. Acropora palmata and A. cervicornis) (Aronson et al. 1998, Aronson and Precht 2001), most of the near shore zone was coral-dominated.
Coral cover in the near shore zone surrounding Bonaire has declined dramatically and is now dominated by dead coral rubble where once elkhorn and staghorn corals had formed near monocultures prior to white band disease. Five of our six study sites have changed dramatically over the past 20 years except for Karpata. The decline of the Acropora species may have allowed competitively inferior species such as lettuce, pencil, finger and fire corals (Agaricia spp, Madracis spp, Porites porities and Millepora complanata) to expand since all have increased in abundance since the Van Duyl study (1985). Corals are not the only group to have changed dramatically since the 1980s. Diadema antillarum, the dominant grazing sea urchins was abundant in the near shore zone until it succumbed to the mass mortality of the mid 1980s. Today, more than 20 years later it remains below detectable levels at most of the sites we studied (Smith and Malek this report, Steneck this report). These changes, along with the significant declines in large predator finfish (see Bonaire Report 2003) indicate that several key players for the resilience of coral reefs (e.g. Fig. 3) have declined in abundance.
Brief description of the recently started (Feb 2015) coral reef monitoring program in St. Eustatius using the guidelines agreed upon by the Caribbean (Global) Coral Reef Monitoring Network (Caribbean – GCRMN).
The GCRMN baseline scientific monitoring methods provide a basic framework for existing and developing monitoring programs to contribute data that support a regional understanding of status and trends of Caribbean coral reefs. The purpose of these methods is to collect data that will contribute to our understanding of the processes that shape coral reefs and to provide actionable advice to policy makers, stakeholders, and communities. In order to achieve these goals, the GCRMN community seeks to collect comprehensive and inter-comparable data that build from a modern scientific perspective of reef monitoring.
The GCRMN methods have been developed to provide a systematic snapshot of the ecosystem health of coral reefs and, when repeated through time, insight into temporal trends in reef condition. Based on the conclusions of a retrospective analysis of trends in reef health over the past decades, GCRMN members have agreed that there is great value in coordinating and standardizing future monitoring efforts. To date, Caribbean regional monitoring efforts often collect non-overlapping types of data about coral reefs, or the efforts use non-comparable methods for describing similar parts of the reef ecosystem. The goal of this document is to define a set of data and data collection techniques that will be used by Caribbean GCRMN members. These methods reflect long-standing, vetted scientific protocols and provide a compromise between practical applicability and ease of comparison between existing methods and long-term datasets.
The GCRMN methods describe six elements of the coral reef ecosystem – (1) abundance and biomass of key reef fish taxa, (2) relative cover of reef-building organisms (corals, coralline algae) and their dominant competitors, (3) assessment of coral health and (4) recruitment of reef-building corals, (5) abundance of key macro-invertebrate species, and (6) water quality. These elements provide an overview of the current condition of the coral reef ecosystem as well as an indication of likely future trajectories. GCRMN recognizes that by collecting information about these elements across multiple locations, with regular re-sampling through time, it will be possible to more knowingly describe the status of coral reef health in the Caribbean and to assess the effectiveness of local and regional management efforts.
These methods are designed to provide a basic and regional summary of reef health. Importantly, the elements that are included for GCRMN monitoring are not all-inclusive, and many partner members may be interested in collecting more detailed or spatially expansive data. However, the GCRMN methods should be viewed as a minimum set of measurements to provide a reliable snapshot of reef condition – data elements should not be selected individually but instead will be collected in sum. Given the inherent complexity of reef processes, a multidimensional description of coral reef health is essential to provide a coherent ‘baseline’ of coral reef condition in a dynamic and changing world.