Fore-reef Slope Research Articles

Effects of reef morphology variations on wave processes over fringing reefs

Many low-lying tropical and sub-tropical atolls fringed by coral reefs are susceptible to coastal inundation during extreme wave events. Previous studies have shown that the infragravity (IG) wave is the dominant component of shoreline run-up compared to the sea and swell (SS) wave and the wave-induced setup. To better understand both the SS and IG wave dynamics over a fringing reef with various morphologies, a series of laboratory experiments were conducted in a wave flume based on an idealized fringing reef profile. The shoreline responses of waves to different reef morphologies with/without the reef crest, the lagoon and the reef surface roughness were examined. IG wave resonance on the reef flat was identified by a spectral analysis of the shoreline wave records. Subsequently, a numerical model based on the Boussinesq equations was validated by the experimental data. The model was then applied to investigate the impacts of varying reef morphologic features (fore-reef slope, reef-crest width, lagoon width, and reef roughness coefficient) on the shoreline wave motions.

Occurrence and life history characteristics of tropical flatfishes at the coral reefs of Curaçao, Dutch Caribbean

In this paper, life history characteristics of tropical flatfishes occurring at the fringing reefs of Curaçao to a depth of 20 m were studied. In total four flatfish species were caught, three common Bothidae species: the eyed flounder Bothus ocellatus, the mottled or maculated flounder B. maculiferus and the peacock flounder B. lunatus, and –in small numbers- the channel flounder Syacium micrurum. B. ocellatus and S. micrurum only occurred in sandy moats on the shallow reef terrace and fore reef and between coral patches on the terrace and fore reef slope. The other species could also be found on coral patches. The depth distribution of the various species overlapped: all species were caught over a depth range from a few meters up to 20 m. All Bothus species were carnivores, preying on a variety of mobile benthic animals such as fishes and crustaceans. Reproduction seemed to occur year round in all three Bothus species. Growth between the species varied considerably with a maximum age found in B. maculiferus and B. lunatus of a little over 1 year, and in B. ocellatus of about 2 years. Growth was lowest in B. ocellatus and highest in B. lunatus: after one year B. ocellatus was about 10 cm in size, B. maculiferus 25 cm and B. lunatus about 35 cm. After correction for differences in water temperature, the Bothus species showed a similar variability and range in growth rate as some temperate and subtropical flatfish species. These observations do not fit the hypothesis postulated by Pauly (1994) of an increasing importance of food-limitation in juvenile flatfish with decreasing latitude, despite the low densities and biomass of benthic in- and epifauna in the soft sediments in mangroves, seagrass beds and the reefs of Curaçao.

Giant ooids in a Neoproterozoic carbonate shelf, Simla Group, Lesser Himalaya, India: An analogue related to Neoproterozoic glacial deposits

Abstract This study is the first comprehensive documentation of giant ooids and related facies associations in the Kunihar Formation, Proterozoic Simla Group Lesser Himalaya, Himachal Pradesh, analysing the understanding of processes and controls on development of giant ooids. Based on field observations, supplemented by outcrop based facies analysis, petrography and delineation of environmental variations, four facies associations have been delineated: (i) Peritidal siliciclastic-carbonate (FA1) (ii) Shelf lagoon (FA2) (iii) Reef complex (FA3) (iv) Fore reef slope (FA4). Deposition of giant ooids and associated facies associations of Kunihar Formation occurred in a carbonate rimmed shelf with high tidal influence. Size of giant ooids from Kunihar Formation is the largest as compared to giant ooids from other geological formations. Kunihar giant ooids developed when normal ooids were washed from ooid shoals (intertidal) into slightly deeper regions (shallow subtidal) resulting in the increased dimension of ooids in suspension due to higher hydrodynamics. Scanning electron microscopy (SEM) studies support microbial origin of ooids, giant ooids and stromatolites of Kunihar Formation. Increased microbial activity in Kunihar Formation is attributed to increase in nutrients by virtue of weathering of underlying Darla volcanics. Abundant carbonate and Microbially induced sedimentary structures (MISS) deposition in lower part of Simla Group points to increased microbial activity which likely increased the volume of oxygen in Neoproterozoic atmosphere ushering in Ice House conditions during the subsequent deposition of Blaini Group. Giant ooids associated with Neoproterozoic glacial deposits throughout the world, occupy stratigraphic positions below, above or between glaciations. Simla Group is another example where giant ooids lie stratigraphically below Marinoan Blaini Tillites. Increased magmatic activity and weathering before and during the Neoproterozoic glaciations increased nutrients in marine waters which increased algal growth. Thus, giant ooids were deposited due to such phases of increased microbial activity before/after glaciation, and during interglacial periods.

Parametric study of solitary wave propagation and runup over fringing reefs based on a Boussinesq wave model

In this paper, a fully nonlinear Boussinesq wave model FUNWAVE-TVD is applied to study solitary wave propagation and runup over fringing reefs. Validation with newly performed laboratory experiments indicates that the wave motions over the forereef slope and reef flat and the runup/rundown process on the backreef slope are reasonably reproduced by the present model with a calibrated bottom friction coefficient for both non-breaking and breaking solitary waves. Sensitive analysis of grid size reveals that the grid spacing is important in capturing the runup height accurately in this study. Predicted spatial distributions of maximum surface elevations from the validation cases also show that compared with the plane beach without fringing reefs, bore propagation processes induced by the wave breaking over reef bathymetry are important in decay of solitary wave and consequent runup height. To comprehensively understand the solitary wave propagation and runup processes over fringing reefs, a parametric study was carried out to analyze the wave–reef interactions under various conditions through a series of numerical experiments. The effects of different hydrodynamic and reef morphological parameters, including the incident wave height, water depth over the reef flat, forereef slope angle and backreef slope angle, on the wave runup were mainly focused on and investigated in this study.

Wave-induced setup and wave-driven current over Quasi-2DH reef-lagoon-channel systems

The primary action of near-shore waves at many field reef sites is to produce a wave-induced setup and 2DH reef-lagoon-channel circulation cells. Instead of using wave basin to study the behaviors of the wave-induced setup and wave-driven flow in such systems, an experimental technique was introduced to achieve the same objective through wave-flume tests. A pipe with a valve was installed underneath the wave flume to connect the lagoon and the ocean side, which makes it possible to simulate a rip channel connecting the lagoon and the offshore side. Experimental results for two reef systems with a fore-reef slope (1V:6H) were obtained under a series of monochromatic wave conditions: one simulating a closed lagoon and the other simulating an open lagoon. Compared with the reef system with a closed lagoon, connecting the lagoon to the ocean side was found to have the following effects: (i) producing a wave-driven current on the reef flat, (ii) reducing the maximum wave setup on the reef flat by 10%–40%, and (iii) causing the wave setup to decrease continuously along the reef flat all the way to the lagoon. For the reef system with an open lagoon, the wave-driven current was found to increase with increasing wave height and wave period, and there appeared to be a peak value of the current within the tested range of reef-flat submergences. The experimental results for the two reef systems were compared with a set of existing wave-basin results for similar reef systems, but with a much steeper fore-reef slope (1V:1H). The dimensionless parameters used in the literature were found to be insufficient to describe both the wave setup and wave-driven current on the reef flat for the reef system with an open lagoon. A semi-analytical quasi-2DH model, which was devised according to the balances of momentum and mass, was also included to understand how the reef and channel morphology and the bottom roughness affect the wave setup and wave-driven current in a reef-lagoon-channel system. The semi-analytical model was validated by our laboratory data as well as field observations reported in the literature.

The role of the reef–dune system in coastal protection in Puerto Morelos (Mexico)

Abstract. Reefs and sand dunes are critical morphological features providing natural coastal protection. Reefs dissipate around 90 % of the incident wave energy through wave breaking, whereas sand dunes provide the final natural barrier against coastal flooding. The storm impact on coastal areas with these features depends on the relative elevation of the extreme water levels with respect to the sand dune morphology. However, despite the importance of barrier reefs and dunes in coastal protection, poor management practices have degraded these ecosystems, increasing their vulnerability to coastal flooding. The present study aims to theoretically investigate the role of the reef–dune system in coastal protection under current climatic conditions at Puerto Morelos, located in the Mexican Caribbean Sea, using a widely validated nonlinear non-hydrostatic numerical model (SWASH). Wave hindcast information, tidal level, and a measured beach profile of the reef–dune system in Puerto Morelos are employed to estimate extreme runup and the storm impact scale for current and theoretical scenarios. The numerical results show the importance of including the storm surge when predicting extreme water levels and also show that ecosystem degradation has important implications for coastal protection against storms with return periods of less than 10 years. The latter highlights the importance of conservation of the system as a mitigation measure to decrease coastal vulnerability and infrastructure losses in coastal areas in the short to medium term. Furthermore, the results are used to evaluate the applicability of runup parameterisations for beaches to reef environments. Numerical analysis of runup dynamics suggests that runup parameterisations for reef environments can be improved by including the fore reef slope. Therefore, future research to develop runup parameterisations incorporating reef geometry features (e.g. reef crest elevation, reef lagoon width, fore reef slope) is warranted.

Atlas of benthic foraminifera from coral reefs of the Raja Ampat Archipelago (Irian Jaya, Indonesia)

Raja Ampat (Indonesia) is a remote archipelago west of Papua mainland and situated at the eastern edge of the Coral Triangle. The archipelago is considered one of the species-richest and most pristine localities and home to the world’s most diverse coral reefs. For centuries, reefs of Raja Ampat have enjoyed natural protection and remained largely untouched due to their isolated location. The region represents a key area for evaluating richness and biogeographic patterns of tropical shallow-water organisms, yet the foraminiferal fauna of Raja Ampat is virtually unexplored. Benthic foraminifera are an integral part of the reef fauna, prolific carbonate producers and essential for reefal accretion and substrate stability. Previous studies on Indo-Pacific benthic reef foraminifera indicate that diversity is highest in the Central Indo-Pacific and broadly correlates with diversity patterns of other tropical marine taxa. This report presents the first illustrated catalog and comprehensive analysis of the structure, composition, and diversity of the species-rich benthic foraminiferal biotas of the Raja Ampat Archipelago including an assessment of local reef vitality with the Foraminifera in Reef Assessment and Monitoring (FoRAM) Index. We examined shallow-water sediment samples from fringing reefs, reef platforms, sheltered bays and reef-associated environments to cover the full range of existing micro- and macrohabitats. Atotal number of 421 species were recovered, among them five new species and one newly described genus of the porcelaneous Miliolida. The fauna is dominated by hyaline taxa but the Miliolida represent the species-richest order and are especially diverse in fine-grained sediments of deep fore-reef slopes. Extraordinary high diversity of the benthic foraminiferal communities indicates that the waters of Raja Ampat probably represent one of the world’s biologically richest locations in reefs.We identified a total of 35 species of larger symbiont-bearing benthic foraminifera, a number that is among the highest reported so far for reefs in modern oceans. The analysis of the FoRAM Index revealed that water quality at all sites examined is suitable for reef growth and recovery. The results of our study show that the Raja Ampat Archipelago harbors unique and particularly diverse assemblages of modern benthic foraminifera and provides a protistan perspective for the hotspot of diversity in the Central Indo-Pacific.

A study of tsunami-like solitary wave transformation and run-up over fringing reefs

After the 2004 Indian Ocean tsunami, the effectiveness of fringing reefs in protecting coastlines from tsunami-induced inundation has aroused great attention in the post-tsunami surveys. To better understand the role of fringing reefs in the mitigation of a tsunami hazard, laboratory experiments were conducted in a wave flume to study the transformation and run-up of tsunami-like solitary waves over various fringing reef profiles. The effects of incident wave height, reef-flat submergence, lagoon width and reef surface roughness were examined. Cylinder arrays were employed to create artificial roughness elements on the reef surface. Empirical formulas based on the experimental data were also proposed for the wave run-up. The ratio of the reef flat submergence to the incident wave height was always found to be the dominant parameter to characterize the wave run-ups over various tested reef profiles. Subsequently, a numerical model based on the improved Boussinesq equations including the drag effect of roughness elements was validated by the experimental data. The validated model was then applied to investigate the impacts of variations of reef morphologies (fore-reef slope, back-reef slope, reef-flat width, reef-crest width) on the solitary wave run-up.

Palaxius salataensis Brönnimann, Cros and Zaninetti, 1972, the oldest crustacean microcoprolite from the early Carboniferous of Guangxi, South China

Palaxius salataensis Bronnimann, Cros and Zaninetti, 1972 is described from early Carboniferous stromatolite mounds of a fore-reef slope setting from Laibin, Guangxi, South China. This is the oldest occurrence of internally structured crustacean coprolites. The geographic distribution and stratigraphic range of the ichnospecies as well as paleoecological implications of this new record of P. salataensis are discussed.

DOC concentrations across a depth-dependent light gradient on a Caribbean coral reef.

Photosynthates released by benthic primary producers (BPP), such as reef algae and scleractinian corals, fuel the dissolved organic carbon (DOC) production on tropical coral reefs. DOC concentrations near BPP have repeatedly been observed to be elevated compared to those in the surrounding water column. As the DOC release of BPP increases with increasing light availability, elevated DOC concentrations near them will, in part, also depend on light availability. Consequently, DOC concentrations are likely to be higher on the shallow, well-lit reef terrace than in deeper sections on the fore reef slope. We measured in situ DOC concentrations and light intensity in close proximity to the reef alga Dictyota sp. and the scleractinian coral Orbicella faveolata along a depth-dependent light gradient from 5 to 20 m depth and compared these to background concentrations in the water column. At 10 m (intermediate light), DOC concentrations near Dictyota sp. were elevated by 15 µmol C L−1 compared to background concentrations in the water column, but not at 5 and 20 m (high and low light, respectively), or near O. faveolata at any of the tested depths. DOC concentrations did not differ between depths and thereby light environments for any of the tested water types. However, water type and depth appear to jointly affect in situ DOC concentrations across the tested depth-dependent light gradient. Corroborative ex situ measurements of excitation pressure on photosystem II suggest that photoinhibition in Dictyota sp. is likely to occur at light intensities that are commonly present on Curaçaoan coral reefs under high light levels at 5 m depth during midday. Photoinhibition may have thereby reduced the DOC release of Dictyota sp. and DOC concentrations in its close proximity. Our results indicate that the occurrence of elevated DOC concentrations did not follow a natural light gradient across depth. Instead, a combination of multiple factors, such as water type, light availability (including the restriction by photoinhibition), and water movement are proposed to interactively determine the DOC concentrations in the close vicinity of BPP.

Study on wave-induced setup over fringing reefs in the presence of a reef crest

It has been well observed that a reef crest (ridge) may be present at the reef edge, but so far very few published studies focusing on the effects of such reef-crest on the wave dynamics over fringing reefs. To understand the role of a reef-crest configuration in determining breaking-wave induced setup over the reef flat, a series of experiments were carried out in a wave flume using an idealized fringing reef model with a reef crest. Experimental results were reported for a trapezoidal reef crest with five reef-crest widths under a series of monochromatic waves. Also examined was the reef without a reef crest. Data analysis shows that larger energy dissipation associated with smaller surfzone width around the reef edge occurred with a wider reef crest. The maximum wave-induced setup on the reef flat in the presence of the reef crest was significantly larger than that without, and it also increased with increasing reef-crest width. The reef-crest submergence was found to be a primary parameter controlling the magnitude of wave setup on the reef flat provided that the reef crest was sufficient wide. An alternative semi-analytical 1DH model based on the balance of cross-shore momentum was proposed. The model was validated by present laboratory data as well as three existing 1DH laboratory studies. Comparing with other two representative semi-analytical models in the literature showed that the proposed model was capable of better reproducing the maximum wave-induced setup on the reef flat for a variety of reef profiles with/without a reef crest, different reef-crest water levels, as well as both monochromatic and spectral waves. The model parameter was physically related to the two characteristic lengths in the surf zone and its value was dependent on the fore-reef slope as well as the presence of a reef crest. The 1DH model was also satisfactorily applied to a fringing reef in field conditions where the effects of fore-reef friction and back-reef lagoon were not important.

Microencruster-microbial framework and synsedimentary cements in the Štramberk Limestone (Carpathians, Czech Republic): Insights into reef zonation

The Stramberk Limestone (Tithonian–lower Berriasian) was developed on a northerly located, isolated intra-Tethyan carbonate platform. It is composed of various facies that can be observed in olistoliths and blocks embedded in the Cretaceous flysch of the Outer Carpathians in Moravia (Czech Republic). Corals, microbialites, microencrusters and synsedimentary cements contributed on various scales to the reef framework. The importance of corals and some microencrusters to the formation of the Stramberk reef complex is well recognized, while other components received less attention in previous studies. Two end members of boundstone types are described from the Kotouc Quarry, near Stramberk. Boundstone type A is dominated by phaceloid (branching-type) corals, encrusted by microbialites and microencrusters, in particular photophile species (“ Lithocodium-Bacinella”, Koskinobullina socialis Cherchi et Schroeder, Iberopora bodeuri Granier et Berthou). Boundstone type B is composed of microencrusters, microbialites and synsedimentary isopachous fibrous cements, while corals are absent or subordinate. Microencrusters [ Crescentiella morronensis (Crescenti) , Labes atramentosa Eliasova , Perturbatacrusta leini Schlagintweit et Gawlick , Radiomura cautica Senowbari-Daryan et Schafer , thin encrusting calcified sponges] are main biotic components of the microencruster-cement boundstone. Some identified microencrusters are known only or mostly from intra-Tethyan carbonate platforms. Except for C. morronensis, other common microencrusters in the coral-microbial boundstone (type A) are rare in the microencruster-cement boundstone (type B). The depositional setting of boundstone type A corresponds to a low-energy environment of an inner platform. Boundstone type B, until now not recognized in the Stramberk Limestone, was developed in a high-energy, upper fore-reef slope environment. Other important facies in the Kotouc Quarry are reef-derived breccias: matrix-supported breccia and clast-supported breccia with radiaxial-fibrous cement (showing some similarities to Triassic “evinosponges” cement), interpreted as being dominantly synsedimentary (pre-burial). The preliminary studies by the present authors, supported by observations under cathodoluminescence, highlight the significance of synsedimentary cementation for the formation of a boundstone framework (type B) and the stabilization of fore-reef, slope deposits.

A Semi-Analytical Model on Wave-Induced Setup over Fringing Reefs with a Shallow Reef Crest

The vulnerability of low-lying reef-fringed atolls to coastal inundation in extreme wave events is of increasing concern in the context of global sea level rise. Wave-induced setup is an important component of wave runup along reef shorelines. We improved a semi-analytical model to investigate wave-induced setup over fringing reefs crested by a shallow reef. Using mass balance and hydraulics, we developed the model based on flow around reef crest kinematics. We proposed a scaling factor to account for flow unsteadiness and reef-crest shape effects. Our solution showed that wave setup on the reef flat is a function of both offshore wave steepness and the wave refection coefficient. Validation of the model by laboratory data shows that the model reproduces the maximum wave-induced setup on the reef flat in the presence of a reef crest with diffident crest widths. Applying the model to experimental data under various reef configurations and wave conditions were also successful. We found that the scaling factor in the model increased with increasing fore-reef slope but was insensitive to variations in reef-crest width. A key requirement for the model to do is that the reef-crest submergence must be small enough or nearly emergent so that an approximate critical flow condition exists.

Reef core insights into mid-Holocene water temperatures of the southern Great Barrier Reef

The tropical and subtropical oceans of the Southern Hemisphere are poorly represented in present-day climate models, necessitating an increased number of paleoclimate records from this key region to both understand the Earth's climate system and help constrain model simulations. Here we present a site-specific calibration of live collected massive Porites Sr/Ca records against concomitant in situ instrumental water temperature data from the fore-reef slope of Heron Reef, southern Great Barrier Reef (GBR). The resultant calibration, and a previously published Acropora calibration from the same site, was applied to subfossil coral material to investigate Holocene water temperatures at Heron Reef. U-Th-dated samples of massive Porites suggest cooler water temperatures with reduced seasonal amplitude at ~5.2 ka (2.76–1.31i?½C cooler than present) and ~7 ka (1.26i?½C cooler than present) at Heron Reef. These results contrast the previous suggestion of a mid-Holocene Thermal Maximum in the central GBR around 5.35 ka and 4.48 ka, yet may be explained by differences in temperature of the shallow ponded reef flat (central GBR) and the deeper reef slope waters (this study) and potential large reservoir correction errors associated with early radiocarbon dates. Combining coral-based water temperature anomaly reconstructions from the tropical and subtropical western Pacific indicates a coherent temperature response across the meridional gradient from Indonesia and Papua New Guinea down to the southern GBR. This similarity in reconstructed temperature anomalies suggests a high probability of an earlier expression of a mid-Holocene Thermal Maximum on the GBR between ~6.8 and 6.0 ka.

Parrotfish erosion underpins reef growth, sand talus development and island building in the Maldives

Parrotfish play a key functional role on coral reefs as external bioerosion agents and produce large quantities of carbonate sediment as a by-product of grazing on reef surfaces. Parrotfish are therefore an important potential source of sediment for island construction and maintenance within atoll reef environments, particularly under future scenarios of sea level rise and island morphological change. Here, we present the first field-based estimates of excavating parrotfish erosion (Chlorurus sordidus and Chlorurus strongylocephalus) within the Indian Ocean and quantify the contribution of parrotfish to the carbonate and sediment budgets of an atoll interior reef platform in the Maldives. We note that parrotfish erosion rates are high (6.3kgm−2 y−1), generating large amounts of new coral-based sediment (2.6kgm−2 y−1) that has a comparable grain size distribution to island deposits. Mean erosion rates by individual C. strongylocephalus (405kg individual y−1) were higher than C. sordidus (55kg individual y−1), but their contribution to erosion per unit area of reef was less due to a lower relative biomass (C. strongylocephalus: 1.3kgm−2 y−1; C. sordidus: 5.0kgm−2 y−1). Parrotfish also facilitate sediment export from reefs (0.7kgm−2 y−1), which contributes extensively to the development of the sand talus on the fore-reef slope and to the evolution of the wider atoll basin. Our results provide strong evidence that parrotfish erosion (and sediment generation) underpins island morphology on Maldivian reefs and highlight the importance of larger parrotfish as producers of island-grade sediment. Ecological processes must therefore be considered within future coastal management strategies for enhancing island stability.

Phytoplankton transport to coral reefs by internal solitons in the northern South China Sea

Evidence is presented that waters containing high concentrations of chlorophyll are transported by internal waves to the fore-reef slope of Dongsha Atoll in the northern South China Sea. High vertical resolution mooring measurements of temperature, pressure, and chlorophyll fluorescence revealed that the internal soliton cores could transport chlorophyll vertically downward and increase concentrations by an order of magnitude near the seafloor, compared to background levels. The reef areas that are potentially nourished by the pulses of phytoplankton are dominated by alcyonacean soft corals, while other reef areas that are less or not at all affected by internal waves are dominated by scleractinian hard corals. This suggests that the delivery of phytoplankton by internal solitons provides a plentiful food source that benefits the growth of soft corals.

Acropora interbranch skeleton Sr/Ca ratios: Evaluation of a potential new high‐resolution paleothermometer

The majority of coral geochemistry-based paleoclimate reconstructions in the Indo-Pacific are conducted on selectively cored colonies of massive Porites. This restriction to a single genus may make it difficult to amass the required paleoclimate data for studies that require deep reef coring techniques. Acropora, however, is a highly abundant coral genus in both modern and fossil reef systems and displays potential as a novel climate archive. Here we present a calibration study for Sr/Ca ratios recovered from interbranch skeleton in corymbose Acropora colonies from Heron Reef, southern Great Barrier Reef. Significant intercolony differences in absolute Sr/Ca ratios were normalized by producing anomaly plots of both coral geochemistry and instrumental water temperature records. Weighted linear regression of these anomalies from the lagoon and fore-reef slope provide a sensitivity of −0.05 mmol/mol °C−1, with a correlation coefficient (r2 = 0.65) comparable to those of genera currently used in paleoclimate reconstructions. Reconstructions of lagoon and reef slope mean seasonality in water temperature accurately identify the greater seasonal amplitude observed in the lagoon of Heron Reef. A longer calibration period is, however, required for reliable reconstructions of annual mean water temperatures.

CORAL REEFS OF GORGONA ISLAND, COLOMBIA, WITH SPECIAL REFERENCE TO CORALLIVORES AND THEIR INFLUENCE ON COMMUNITY STRUCTURE AND REEF DEVELOPMENT

This study offers an overview of the distribution and structure of coral reefs and coral communities at Gorgona Island, off the Pacific coast of Colombia. Biotic interactions, mainly the effects of corallivores, are examined and compared with coral communities elsewhere in the eastern Pacific in order to provide a basis for understanding regional differences in community structure. Located at the south end of the Panamá Bight and ca. 30 km offshore, Gorgona is largely removed from the influence of upwelling and freshwater dilution. The key corallivore Acanthaster, which is widely distributed in the tropical eastern Pacific, is absent from Gorgona, probably a result of unfavorable physical conditions (low temperatures and low salinites) for larval development in the Panamá Bight area. True fringing coral reefs are present at Gorgona and are best developed on the eastern or leeward side, but they also occur in one area on the western and exposed side of the island. The La Azufrada reef, the largest of the fringing reefs, was about 1 km long and 150 m wide, had a minimum thickness of 8 m and supported live corals to a depth of 15 m. Pocilloporid corals predominated on the reef crest and upper to mid forereef slope, and massive and small species increased in relative abundance in the deep forereef and sand plain zones. A corallivorous pufferfish and ovulid gastropod were abundant, but other known corallivores (e. g., Acanthaster, hermit crabs and Eucidaris) were either absent, uncommon or not feeding on live coral. Damage inflicted on live massive colonies by a damselfish, in order to "farm" algae, could play an important role in altering the relative abundances of corals in shallow reef zones. A comparison of coral reefs at Gorgona and Panamá, in areas with and without Acanthaster, show that nonpocilloporid corals, which are preferred prey items, have a higher relative abundance on reefs where the predatory sea star is absent.

The influence of coral reefs and climate change on wave‐driven flooding of tropical coastlines

AbstractA numerical model, XBeach, calibrated and validated on field data collected at Roi‐Namur Island on Kwajalein Atoll in the Republic of Marshall Islands, was used to examine the effects of different coral reef characteristics on potential coastal hazards caused by wave‐driven flooding and how these effects may be altered by projected climate change. The results presented herein suggest that coasts fronted by relatively narrow reefs with steep fore reef slopes (~1:10 and steeper) and deeper, smoother reef flats are expected to experience the highest wave runup. Wave runup increases for higher water levels (sea level rise), higher waves, and lower bed roughness (coral degradation), which are all expected effects of climate change. Rising sea levels and climate change will therefore have a significant negative impact on the ability of coral reefs to mitigate the effects of coastal hazards in the future.

Boussinesq modeling of spatial variability of infragravity waves on fringing reefs

Spatial variations of infragravity waves on fringing reefs are studied using a fully nonlinear Boussinesq equation model FUNWAVE-TVD. The effects of bottom roughness, forereef slope and tidal water level on significant wave height, wave setup and infragravity wave motion are investigated. Model results show that the cross-shore distributions of significant wave heights and setups are reasonably reproduced using the calibrated bottom friction coefficient. However, the infragravity wave heights over the reef flat are under-predicted. Spatial variations of infragravity waves at different tidal water levels exhibit distinct patterns. Spectral peaks and valleys on the reef flat, indicative of the generation of standing infragravity waves, are observed in the measurements and reproduced by the model. It is demonstrated that the model is capable of simulating the generation and propagation of infragravity motions on fringing reefs. The effects of relative submergence and inverse wave steepness on infragravity waves are investigated through a series of numerical experiments. The results demonstrate that the relative submergence has significant effects on the distributions of infragravity waves on the fringing reef. The maximum infragravity wave height decreases with increasing relative submergence at the reef edge. However, it increases with increasing relative submergence at the inner reef flat.