Fringing Reef System Research Articles

Effects of onshore development and damselfish (Stegastes nigricans) on coral richness in Opunohu Bay and Cook’s Bay in Moorea, French Polynesia

The fringing reefs in Opunohu Bay and Cook’s Bay in Moorea, French Polynesia are an important component of Moorea’s fringing reef system, as they comprise approximately 20% of the island’s perimeter. The two bays are assumed to have differing benthic communities due to differences in onshore land development and freshwater input, but observational studies of their benthic communities are rarely published. To address this information gap, we conducted a quadrat-based benthic survey to determine important drivers of coral spatial variation throughout the bays. Interestingly, we found that coral taxonomic richness and cover did not significantly vary between bays, and corals only declined at the sites nearest freshwater input. Instead, coral richness was significantly greater when the territorial herbivorous damselfish Stegastes nigricans was present. The majority of the corals we documented were relatively small (88% < 10 cm diameter), thus our results support a positive effect of S. nigricans on young coral diversity. Stegastes nigricans could potentially be creating a refuge inside their territories from scraper herbivores for many non-dominant corals, although other potential mechanisms and the context of these benefits warrant further investigation. We conclude that, on the fringing reefs of Moorea’s two major bays, spatial variation in coral richness is more strongly associated with patches of S. nigricans territories than larger-scale differences in onshore land development and distance from freshwater input.

Clownfish hosting anemones (Anthozoa, Actiniaria) of the Red Sea: new associations and distributions, historical misidentifications, and morphological variability

BackgroundThe Red Sea contains thousands of kilometers of fringing reef systems inhabited by clownfish and sea anemones, yet there is no consensus regarding the diversity of host anemone species that inhabit this region. We sought to clarify a historical record and recent literature sources that disagree on the diversity of host anemone species in the Red Sea, which contains one endemic anemonefish, Amphiprion bicinctus Rüppell 1830.ResultsWe conducted 73 surveys spanning ~ 1600 km of coastline from the northern Saudi Arabian Red Sea to the Gulf of Aden and encountered seven species of host anemones, six of which hosted A. bicinctus. We revise the list of symbionts for A. bicinctus to include Stichodactyla haddoni (Saville-Kent, 1893) and Stichodactyla mertensii Brandt, 1835 which were both observed in multiple regions. We describe Red Sea phenotypic variability in Heteractis crispa (Hemprich & Ehrenberg in Ehrenberg, 1834) and Heteractis aurora (Quoy & Gaimard, 1833), which may indicate that these species hybridize in this region. We did not encounter Stichodactyla gigantea (Forsskål, 1775), although the Red Sea is the type locality for this species. Further, a thorough review of peer-reviewed literature, occurrence records, and misidentified basis of record reports dating back to the early twentieth century indicate that it is unlikely that S. gigantea occurs in the Red Sea.ConclusionsIn sum, we present a new guide for the host anemones of the Red Sea, revise the host specificity of A. bicinctus, and question whether S. gigantea occurs in the central and western Indian Ocean.

Experimental investigation on the infragravity wave on different reef systems under irregular wave action

This paper presents the results of a laboratory investigation into the role of infragravity motions in reef hydrodynamics over different reef systems. Laboratory experiments are performed with reef profiles of a platform reef and a fringing reef under irregular wave conditions. The propagation and the distribution of the infragravity wave are different over these two reef systems. Analysis of the measured time histories of water surface elevation shows that shorter sea-swell (SS) waves, longer infragravity (IG) wave and mean water level on the reef flat are significantly larger in the fringing reef system. The IG wave height is much larger on the fringing reef than that on the platform reef. This marked increase of the IG wave is considered to be due to: (1) the superposition of incoming IG wave and reflected IG wave from shoreline; (2) more violent wave breaking in the surf zone that may enhance the transfer of wave energy from the frequency band of the shorter wave to IG wave. In this experiment, the wave breaking mechanism controls the relationship between IG wave height and water depth.

Canopy effects of octocoral communities on sedimentation: modern baffles on the shallow-water reefs of St. John, USVI

Recent shifts in the presence and abundance of species on shallow Caribbean coral reefs have left octocorals as the dominant functional group on some reefs, creating an ‘animal forest’ with an associated canopy. This transition changes the reef profile potentially affecting flow and sedimentation. We examined the effects of an octocoral forest on the depositional environment on a shallow-water fringing reef system on the south shore of St. John, USVI. The depositional environment was characterized as canopy or non-canopy based on octocoral density. The effect of the octocoral canopy on flow and sedimentation was assessed using clod cards and sediment traps at 15 paired locations. The octocoral canopy altered flow resulting in greater levels of turbulence within the canopy. Sediment traps in areas of dense octocoral canopy accumulated greater amounts of sediment, with coarser, more rounded grains. Organic content of sediments collected in the traps was greater within the canopy than outside of it. The increase in turbulence within the canopy was likely due to wave-driven oscillatory flow interacting with the octocoral colonies. Sediment traps in the canopy likely had greater sediment accumulation due to both resuspension of sediments from within the canopy and deposition of imported sediments as flow decreased within the canopy. The presence of octocoral canopies and the reworking of sediment within them may affect the success of settling larvae and the evolution of reef structure.

WAVE TRANSFORMATION WITHIN A CORAL REEF LAGOON SYSTEM, ERAKOR LAGOON, VANUATU

Coral reefs encircle most of the islands in Vanuatu and provide natural breakwaters for coastal communities by reducing wave energy arriving at the shoreline acting to control both inundation and erosion. Climate Change is projected to both exacerbate coastal hazards and endanger corals. The aim of this paper is to better understand the parameters that govern hydrodynamics on fringing reef systems. The interaction between the depth, waves and currents are studied from measurements conducted in Erakor lagoon, Vanuatu.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/mPrG6NWL4dM

Physical dynamics of the reef flat, channel, and fore reef areas of a fringing reef embayment: An oceanographic study of Pago Bay, Guam

Long-term observations of oceanographic patterns and processes provide necessary context for integrative ecological studies and for assessing and mitigating anthropogenic impacts to coastal ecosystems. The oceanographic patterns and processes of Pago Bay, Guam, a tropical coral reef system with a small estuary, were observed for one year. An array of 50 sensors including current profilers, temperature and dissolved oxygen loggers, and water quality sensors were deployed throughout Pago Bay from 0–26 m depth. Water flow was primarily driven by wave height in the reef flat and channel. In addition, wind and wave directions that were directly across-shore contributed to faster flow speeds throughout the bay. On the fore reef, wave height was the strongest predictor of current speed, but wind direction had a strong influence on current direction. Flow in the channel and on the reef flat was more tightly tied to environmental factors of wind and waves than flow on the fore reef. Extreme daily temperature variations on the reef flat were observed. In deeper water, cold pulses were observed, indicating that large internal waves may propagate around the slopes of Guam. Cold pulses may deliver nutrients to shallower ecosystems and periodically cool deeper areas of the fore reef. In response to heavy rain events, the estimated backscatter in the channel increased sharply along with significant changes in other water quality parameters. Rain events of this magnitude and associated backscatter increases occur frequently. Along with soil-destabilizing land use practices in the Pago River watershed, the current flow and water quality observations presented here indicate that sedimentation may be a risk for the Pago Bay fore reef coral habitat. The understanding of circulation, thermal environment, and rainstorm impacts in this fringing reef system provides a baseline for understanding the ecology, coral reef resilience, and future oceanographic changes in Pago Bay.

Atenuação de Ondas e Proteção à Linha de Costa por um Sistema de Recife em Franja

While knowledge on coastal dynamics is essential to guarantee well-informed decision making, information is still scarce, particularly regarding areas with the presence of coral reefs and other complex ecosystems. The objective of the present study was to contribute towards the understanding of wave attenuation and shoreline protection at different tide moments by a fringing reef system located in a Southwestern Atlantic archipelago. The predominant directions of offshore waves adjacent to the archipelago were ESE, SE, E and SSE. Coral reefs demonstrated high efficiency in wave height attenuation even under higher energy conditions during high tides. Erosion hot-spots along the archipelago were associated with rip currents, which were greatly reduced or absent during low tides. Coral reef conservation is essential to maintain shoreline protection and information on reef geomorphology should be included in reef status protocols to help advance this field of knowledge.

An Alongshore Momentum Budget Over a Fringing Tropical Fore‐Reef

AbstractExisting momentum budgets over coral reefs have predominantly focused on cross‐reef dynamics, lacking analysis of alongshore processes. To complement existing cross‐reef research and enhance our understanding of forcing variability at the semidiurnal period, this study examines the σ–coordinate, depth‐averaged alongshore momentum budget over a fore‐reef as a function of tidal phase. The observations were gathered over a 3‐week timespan, between the 12‐ and 20‐m isobaths of a Hawaiian fringing reef system, focusing on two moorings on the 12‐m isobath, where median drag coefficients estimated from log fits are CD=0.0080[−0.002,+0.004] and CD=0.0023[−0.0006,+0.0009]. Analysis at one location shows that the unsteadiness, barotropic pressure gradient, and bottom drag are equally important, and their combination is sufficient to close the momentum budget. However, bottom drag is less important at the second mooring; the difference between unsteadiness and pressure gradient suggests that advective acceleration plays a significant role.

Temporal Variability in Thermally Driven Cross-Shore Exchange: The Role of Semidiurnal Tides

AbstractWe examine temporal variability of thermally driven baroclinic cross-shore exchange in the context of a tropical fringing reef system focusing on the role of tidally driven alongshore flow. Ensemble diurnal phase averaging of cross-shore flow at the Kilo Nalu Observatory (KNO) in Oahu, Hawaii, shows a robust diurnal signal associated with an unsteady buoyancy/diffusive dynamic balance, although significant variability is observed at subdiurnal time scales. In particular, persistent fortnightly variability in the cross-shore diurnal flow pattern is consistent with modulation by the semidiurnal alongshore tidal flow. The alongshore flow plays a direct role in the cross-shore exchange momentum balance via Coriolis acceleration but also affects the cross-shore circulation indirectly via its influence on vertical turbulent diffusion. An idealized linear theoretical model for thermally driven cross-shore flow is formulated using the long-term time-averaged diurnal dynamic balance at KNO as a baseline. The model is driven at leading order by the surface heat flux, with contributions from the alongshore flow and cross-shore wind appearing as linear perturbations. Superposition of the idealized solutions for Coriolis and time-varying eddy viscosity perturbations are able to reproduce key aspects of the fortnightly variability. Modifying the model to consider a more realistic alongshore flow and considering effects of nightly convection lead to further improvements in comparisons with KNO observations. The ability of the theoretical approach to reproduce the fortnightly patterns indicates that semidiurnal variations in the alongshore flow are effective in modulating the cross-shore flow via Coriolis and vertical turbulent transport mechanisms.

Differential response of corals to regional mass‐warming events as evident from skeletal Sr/Ca and Mg/Ca ratios

AbstractDuring the summer of 2010/2011, a regional marine heat wave resulted in coral bleaching of variable severity along much of the western coastline of Australia. At Ningaloo Reef, a 300 km long fringing reef system and World Heritage site, highly contrasting coral bleaching was observed between two morphologically distinct nearshore reef communities located on either side of the Ningaloo Peninsula: Tantabiddi (∼20% bleaching) and Bundegi (∼90% bleaching). For this study, we collected coral cores (Porites sp.) from Tantabiddi and Bundegi reef sites to assess the response of the Sr/Ca temperature proxy and Mg/Ca ratios to the variable levels of thermal stress imposed at these two sites during the 2010/2011 warming event. We found that there was an anomalous increase in Sr/Ca and decrease in Mg/Ca ratios in the Bundegi record that was coincident with the timing of severe coral bleaching at the site, while no significant changes were observed in the Tantabiddi record. We show that the change in the relationship of Sr/Ca and Mg/Ca ratios with temperature at Bundegi during the 2010/2011 event reflects changes in related coral “vital” processes during periods of environmental stress. These changes were found to be consistent with a reduction in active transport of Ca2+ to the site of calcification leading to a reduction in calcification rates and reduced Rayleigh fractionation of incorporated trace elements.

Multi-scale spatial and partitioning analyses of the reef-fish community composition of the Yucatan fringing reef system

Coral reef and reef-fish communities are complex systems that have spatial structures that are influenced by multiple factors and processes that interact at several scales. We analysed composition data of reef-fish communities in the Yucatan Peninsula fringing reef system using a hierarchical multi-scale survey design to elucidate the origins of the species distribution patterns through multivariate canonical ordination and partitioning analysis. Twelve reef sites were surveyed along the fringing reef system, nested in three sectors, each with distinctive human interests (tourism, fishing, protection). Line transects were placed on reef lagoon, reef front, reef slope and reef terrace habitat for a total of 480 transects. The communities were composed of many rare and some dominant species (e.g., Thalasoma bifasciatum, Acanthurus bahianus, A. coeruleus, Sparisoma aurofrenatum). Redundancy analyses revealed that environmental variables explained between 11% and 22% of the variation in fish community data according to the habitat analysed. Spatial variables, represented by the geographic coordinates of transects, explained a low percentage (2–5%) of variation in the fish community data. Among the environmental variables that significantly explained (P<0.05) the patterns of variation on the fish community were depth, topographical complexity, and the percentage of the substratum covered by algae, calcareous floor, rock and rubble. Although the total explained variation and proportion of the variation explained by each set of variables were consistently low, most of the effects on the fish community composition data were significant. Explanations are proposed concerning those results. Evincing the distribution patterns on the biological systems of multi-species as well as the causes that shape them is key for conservation planning and essential in highly threatened regions, such as the Caribbean coast of the Yucatan Peninsula.

Parametric Investigation of Breaking Solitary Wave Over Fringing Reef Based on Shock-Capturing Boussinesq Model

In this paper, a hybrid finite-volume-finite-difference scheme for the solution of the one-dimensional form of the Nwogu's extended Boussinesq-type equations was developed to investigate the breaking of a solitary wave propagating over a fringing reef system. The adoption of a high-order finite volume WENO schemes with HLL Riemann solver for advection terms as well as the third-order Runge—Kutta time-stepping scheme makes the present scheme shock-capturing. From the validation case, it is shown that the present shock-capturing model could simulate the shoreline movement and wave breaking as well as bore propagation very well. In order to comprehensively understand the hydrodynamic characteristics when a solitary wave travels over a fringing reef system, a parametric study has been carried out to analyze the interaction process under various conditions. Effects of different physical parameters on wave breaking axe analyzed and the reflection, transmission and dissipation (RTD) coefficients are calculated based on the integration of kinetic and potential energies in different zones.

Performance Evaluation of CRW Reef-Scale and Broad-Scale SST-Based Coral Monitoring Products in Fringing Reef Systems of Tobago

Satellite-derived sea surface temperature (SST) is used to monitor coral bleaching through the National Oceanic and Atmospheric Administration’s Coral Reef Watch (CRW) Decision Support System (DSS). Since 2000, a broad-scale 50 km SST was used to monitor thermal stress for coral reefs globally. However, some discrepancies were noted when applied to small-scale fringing coral reefs. To address this, CRW created a new DSS, specifically targeted at or near reef scales. Here, we evaluated the new reef-scale (5 km resolution) products using in situ temperature data and coral bleaching surveys which were also compared with the heritage broad-scale (50 km) for three reefs (Buccoo Reef, Culloden and Speyside) of the southern Caribbean island of Tobago. Seasonal and annual biases indicated the new 5 km SST generally represents the conditions at these reefs more accurately and more consistently than the 50 km SST. Consistency between satellite and in situ temperature data influences the performance of anomaly-based predictions of bleaching: the 5 km DHW product showed better consistency with bleaching observations than the 50 km product. These results are the first to demonstrate the improvement of the 5 km products over the 50 km predecessors and support their use in monitoring thermal stress of reefs in the southern Caribbean.

Coastal acidification induced by tidal-driven submarine groundwater discharge in a coastal coral reef system.

We identified a barely noticed contributor, submarine groundwater discharge (SGD), to acidification of a coastal fringing reef system in Sanya Bay in the South China Sea based on time-series observations of Ra isotopes and carbonate system parameters. This coastal system was characterized by strong diel changes throughout the spring to neap tidal cycle of dissolved inorganic carbon (DIC), total alkalinity, partial pressure of CO2 (pCO2) and pH, in the ranges of 1851-2131 μmol kg(-1), 2182-2271 μmol kg(-1), 290-888 μatm and 7.72-8.15, respectively. Interestingly, the diurnal amplitudes of these parameters decreased from spring to neap tides, governed by both tidal pumping and biological activities. In ebb stages during the spring tide, we observed the lowest salinities along with the highest DIC, pCO2 and Ra isotopes, and the lowest pH and aragonite saturation state. These observations were consistent with a concurrent SGD rate up to 25 and 44 cm d(-1), quantified using Darcy's law and (226)Ra, during the spring tide ebb, but negligible at flood tides. Such tidal-driven SGD of low pH waters is another significant contributor to coastal acidification, posing additional stress on coastal coral systems, which would be even more susceptible in future scenarios under higher atmospheric CO2.

Quantitative diet analysis of four mesopredators from a coral reef

The diets of four common mesopredator fishes were examined in the back-reef habitat of a subtropical fringing reef system during the summer months. Quantitative gut content analyses revealed that crustaceans, represented >60% of ingested prey (% mass) by the latticed sand-perch Parapercis clathrata, brown dottyback Pseudochromis fuscus and half-moon grouper Epinephelus rivulatus. Dietary analyses also provided insights into ontogenetic shifts. Juvenile P. fuscus ingested large numbers of crustaceans (amphipods and isopods); these small prey were rarely found in larger individuals (<1% of ingested mass). Fishes also made an important contribution to the diets of all three species representing 10-30% of ingested mass. Conversely, the sand lizardfish Synodus dermatogenys fed exclusively on fishes including clupeids, gobies and labrids. Differences in the gut contents of the four species recorded were not apparent using stable isotope analysis of muscle tissues. The similarity of δ(13) C values in muscle tissues suggested that carbon within prey was derived from primary producers, with comparable carbon isotope signatures to corals and macroalgae, whilst similarities in δ(15) N values indicated that all four species belonged to the same trophic level. Thus, interspecific differences between mesopredator diets were undetectable when using stable isotope analysis which suggests that detailed elucidation of trophic pathways requires gut content analyses.

Modern fringing reef carbonates from equatorial SE Asia: An integrated environmental, sediment and satellite characterisation study

Abstract Fringing reefs of SE Asia may conservatively comprise ~ 30% of the world's coral reef area, but remain almost unstudied ( White, 1987 , Tomascik et al., 1997 ). This study provides insights into the primary sedimentological and early alteration characteristics of an isolated fringing reef system (Kaledupa-Hoga) from the Tukang Besi Archipelago, SE Asia. A combined multispectral satellite imagery, field and petrographic study allowed for the generation of an environmental facies map, which acts as a model for the distribution of primary sedimentological characteristics in relation to the primary environmental facies. The islands of the Tukang Besi Archipelago are mesotidal ( 71% accuracy when compared with field and sedimentary data. With the exception of the reef crest and reef slope that commonly have widths on a sub-imaging resolution ( Although field and satellite imagery observations reveal ten environmental facies, sedimentological characterisation results in a lower number of distinctive categories due to the similarity of many deposits. Foreshore/backshore and bare intertidal deposits are distinctive and are composed of reef-derived material that has been reworked shorewards. Seagrass-associated facies all show some fine silt–clay sized material (

Effects of reef roughness on wave setup and surf zone currents

ABSTRACT Franklin, G.L., Marino-Tapia, I. and Torres-Freyermuth, A., 2013. Effects of reef roughness on wave setup and surf zone currents. Circulation in reef systems controls an important number of key processes, such as the transport and dispersion of larvae, nutrients, and sediments. In fringing reef systems, where a shallow lagoon backs onto the reef crest, circulation appears to be dominated by wave breaking. Despite the identified importance of wave driven flows within reef systems, there is a lack of detailed knowledge on these processes within the surf zone of reef crests and the effects reef roughness has on these flows. A numerical study, using two-dimensional (2DV) simulations, was carried out in order to improve the understanding of wave-driven flows in the surf zone of a fringing reef. The model used is Cornell Breaking Wave and Structures (COBRAS), which solves the Reynolds-Averaged Navier-Stokes (RANS) equations with a turbulence closure scheme. The effect of different reef roughness on wav...

The combined influence of hydrodynamic forcing and calcification on the spatial distribution of alkalinity in a coral reef system

We investigated the influence of hydrodynamic forcing (waves, tides, alongshore currents and winds) and net calcification by coral reef organisms on the spatial distribution of total alkalinity (TA) in a fringing reef system through a combination of field measurements and numerical modeling. A field experiment was conducted over 10 days in Coral Bay (Ningaloo Reef, Western Australia) during which we measured wave heights, currents, and tides as well as the spatial distribution of TA across the fore reef, reef crest, and lagoon. We used observed changes in TA on the adjacent reef flat, along with synoptic measurements of cross‐reef transport, to estimate in situ rates of net calcification (gcv) using a control volume approach. Based on the gcv estimated, we simulated light‐driven, diurnal variations in benthic net calcification within a three‐dimensional ocean circulation model, ROMS (Regional Ocean Modeling System). By coupling ROMS with a spectral wave model (Simulating Waves Nearshore), we were able to simulate currents within Coral Bay reef‐lagoon system that were in good agreement with the field observations and demonstrate that circulation with the system was wave‐dominated. Both the field measurements and numerical model output confirmed that both residence time (τR) and TA varied primarily with offshore wave heights and location within the bay. However, variations in TA were also affected by the nonlinear interaction between rates of net calcification that varied as a function of diurnally changing light and water residence time that varied as a function of offshore wave heights.

A numerical study of the dynamics of the wave-driven circulation within a fringing reef system

The circulation driven by wave breaking, tides and winds within a fringing coral reef system (Ningaloo Reef) in Western Australia was investigated using the ocean circulation model ROMS two-way coupled to the wave model SWAN. Currents within the system were dominantly forced by wave breaking, with flow driven over the shallow reefs and towards the lagoon, which returned to the ocean through channels in the reef. Hindcast model simulations were compared against an extensive field dataset, revealing that the coupled wave–circulation model could accurately predict the waves and currents throughout this morphologically complex reef–lagoon system. A detailed momentum budget analysis showed that, over the reef, a dominant cross-shore balance was established between radiation stress gradients and a pressure (mean water level) gradient (similar to a beach). Within the lagoon, alongshore currents were primarily balanced by alongshore gradients in wave setup, which drove flow towards (and ultimately out) the channels. The importance of these wave-driven currents to Ningaloo Reef was quantified over a full seasonal cycle, during periods when wave and wind conditions significantly differed. These results showed that wave breaking still overwhelmingly dominated the circulation and flushing of Ningaloo Reef throughout the year, with winds playing an insignificant role.

Nearshore circulation in a tropical fringing reef system

[1] The role of waves, tide, and wind on the circulation of a fringing reef system was investigated using data collected during a 6 week field experiment in a section of Ningaloo Reef off Western Australia. The high correlation observed between current velocities and wave height throughout the system revealed the dominant role wave breaking plays in driving the overall reef-lagoon circulation, whereas the modulation of the currents at tidal frequencies suggested that the wave-driven currents responded to tidal variations in the mean water level over the reef. The influence of the various forcing mechanisms on the current field was investigated for both high- and low-frequency bands. Wave breaking was found to be the dominant forcing mechanism for the low-frequency (subtidal) currents, with the subtidal flow pattern consisting of a cross-reef flow over the reef, alongshore flow in the lagoon, and water exiting back to the ocean through the main channel. The tides controlled the high-frequency current variability via two mechanisms: one associated with the ebb-flood cycle of the tides and the second associated with tidal modulations of the wave-driven currents. Wind-forcing and buoyancy effects were both found to be negligible in driving the circulation and flushing of the system during the observation period. Flushing time scale estimates varied from as low as 2 h to more than a day for the wide range of observed incident wave heights. The results suggest that the circulation of Ningaloo Reef will be strongly influenced by even a small mean sea level rise.