Reef Crest Research Articles

A probabilistic coral rubble mechanical instability model applied with field observations from the Great Barrier Reef

Unstable coral rubble hinders coral recruitment and recovery of coral reefs after damage from cyclones and bleaching events. If coral rubble remains unstable under typical everyday environmental conditions, areas of coral rubble will not be able to recover. Evaluating the probability of rubble instability over regional scale reef systems can assist the optimization of coral reef restoration efforts. Currently, robust and verified models for such applications do not exist. This paper presents a comprehensive assessment method to predict the probability of coral rubble instability, which combines a fluid-structural interaction approach with a statistical regional wave climate model. The hydrodynamic model employs non-linear wave theory to determine near-bed velocity, pressure gradients, and the corresponding drag and inertia forces acting on the coral rubble. The instability model assesses when overturning or sliding forces exceed resisting forces, considering thousands of combinations of different coral sizes and densities to calculate the proportion of instability under a given wave forcing. The model was calibrated and validated using prior laboratory experiments as reported by Kenyon et al. (2023b). The hydrodynamic and instability models use an extensive dataset of non-cyclonic wave climates (hindcast from over 30 years of wind measurements) specific to the region around Heron Reef, Great Barrier Reef, Australia, enabling a comprehensive evaluation of the probability of rubble instability in this area. Results indicate that the overall probability of rubble instability reaches 0.74 in water depths less than 2 meters (typical of reef crests or reef flats), while it declines to below 0.21 at a depth of 12 meters (typical deeper parts of the fore reef). Coral rubble on reef crests near Heron Reef, which are sheltered by surrounding formations, demonstrates low probability of instability. Thus, coral rubble instability is influenced by both its specific location within the reef and the position of the reef relative to other nearby reefs. By integrating the rubble instability model with non-cyclonic wave climate data, a map of the probability of rubble instability was generated for eight reefs in the Capricorn and Bunker Group (CBG). This map provides valuable guidance for coral reef restoration efforts, significantly reducing the need for extensive field-based data.

Utilisation of macroalgal habitats by juvenile rabbitfishes on an inshore reef

AbstractMacroalgal beds are increasingly recognised as nursery habitats for coral reef fish; however, the extent to which they are used as a source of food and/or a refuge from predation remains largely unexplored. Here, we investigate the distribution, feeding behaviour, diet, and predation risk for juvenile rabbitfish in macroalgal habitats on Orpheus Island, Great Barrier Reef. Visual surveys revealed that juvenile and adult Siganus doliatus had different among-habitat distributions with juveniles being largely restricted to the reef flat and positively associated with macroalgal cover, while adults were abundant on the reef crest. Focal feeding observations show that within macroalgal habitats, juvenile S. doliatus targeted epiphytes on Sargassum (80% of bites), with relatively few bites taken on turfs or the Sargassum itself (27% and 8%, respectively). These observations were supported by stomach content analyses with filamentous algae being the dominant item in the stomach content of both small (< 4 cm total length, TL; 58%) and large juvenile S. doliatus (> 4 cm TL; 47%). The stomach content of juvenile S. doliatus, S. canaliculatus, and S. spinus collected from macroalgal habitats was similar, consisting primarily of filamentous algae and detritus. We found no relationship between the abundance of potential predators and juvenile rabbitfishes across the study sites. Collectively, our results suggest that juvenile rabbitfishes are using macroalgal habitats on this, and potentially other, inshore reefs as a food source and add to a growing body of literature highlighting the importance of these habitats for the early life stages of reef fish.

Shifting sands: The influence of coral reefs on shoreline erosion from short-term storm protection to long-term disequilibrium

Climate change is exacerbating shoreline erosion and flooding, posing significant risks to coastal communities. Although traditional coastal defenses such as seawalls, dykes, and breakwaters offer protection from these hazards, their high environmental and economic costs are driving interest in cost-competitive nature-based solutions. Coral reef restoration is a nature-based solution that may be particularly apt to mitigate tropical coastal flooding and shoreline erosion while providing benefits to local tourism, fisheries, and nature. However, the novelty of this field requires studies demonstrating the benefits of reefs for coastal protection. While the flood protection benefits of reefs have been well-documented, their effects on shoreline erosion are comparatively less understood. Here, we investigate the effects of coral reefs on shoreline erosion by comparing tropical beach responses at short and long timescales, as well as identifying important reef structural features influencing coastal erosion rates. Our analyses leveraged two key datasets created in this study: the first derived from a literature review on short-term shoreline erosion due to storm events, and another compiling >80 years of long-term erosion rates, bathymetry, habitat, and wave energy for the Hawaiian Islands of Kauaʻi, Oʻahu, and Maui. Our analyses reveal three key findings regarding the effects of reefs on shoreline erosion. Firstly, we find evidence for the role of reefs in mitigating shoreline erosion during storm events, with coral reef-protected beaches experiencing 97 % less beach volume loss than unprotected beaches. Secondly, a linear regression analysis demonstrates that coral reef structure and wave energy are important predictors of long-term shoreline erosion rates, explaining 34 % of the variation across the Hawaiian Islands. Consistent with prior research, we find beaches protected by coral reefs with shallow reef crests, wide reef flats, calmer offshore conditions, and positioned farther from the shore exhibit lower erosion rates than others. Finally, when comparing historical erosion rates of protected and unprotected beaches in Hawai'i, we find a seemingly incongruous pattern where coral reef-protected beaches eroded up to 2x faster than beaches without reefs. While the cause of the enhanced erosion is yet to be fully understood, a combination of coral reef structural degradation and sea-level rise is likely shifting the equilibrium profiles of reef-protected beaches inshore. These results emphasize the role of coral reefs in reducing coastal erosion during storm events while revealing contrasting erosion patterns over long timescales. Future studies would ideally broaden the scope to include various regions, utilize advanced sediment transport models, and undertake field experiments to deepen our understanding of coral reef-coupled shoreline dynamics.

Patterns of spawning and settlement of reef fishes as strategic responses to post-settlement competition

Settlement is a critical transition in the life history of reef fish, and the timing of this event can have a strong effect on fitness. Key factors that influence settlement timing are predictable lunar cyclic variation in tidal currents, moonlight, and nocturnal predation risk as larvae transition from pelagic to benthic environments. However, populations typically display wide variation in the arrival of settlers over the lunar cycle. This variation is often hypothesized to result from unpredictable conditions in the pelagic environment and bet-hedging by spawning adults. Here, we consider the hypothesis that the timing of spawning and settlement is a strategic response to post-settlement competition. We use a game theoretic model to predict spawning and settlement distributions when fish face a tradeoff between minimizing density-independent predation risk while crossing the reef crest vs. avoiding high competitor density on settlement habitat. In general, we expect competition to spread spawning over time such that settlement is distributed around the lunar phase with the lowest predation risk, similar to an ideal free distribution in which competition spreads competitors across space. We examine the effects of overcompensating density dependence, age-dependent competition, and competition among daily settler cohorts. Our model predicts that even in the absence of stochastic variation in the larval environment, competition can result in qualitative divergence between spawning and settlement distributions. Furthermore, we show that if competitive strength increases with settler age, competition results in covariation between settler age and settlement date, with older larvae settling when predation risk is minimal. We predict that competition between daily cohorts delays peak settlement, with priority effects potentially selecting for a multimodal settlement distribution.

Comparison of juvenile coral assemblages between Australia’s Coral Sea and Great Barrier Reef Marine Parks

Densities of juvenile corals (≤ 50 mm diameter) are expected to vary between geographically isolated and more spatially proximate reefs, and may constrain local recovery potential. This study compared juvenile coral densities and their relationships with local abundance of adult congenerics at geographically isolated reefs within Australia’s Coral Sea Marine Park (CSMP) versus highly connected reefs within the Great Barrier Reef Marine Park (GBRMP). Three latitudinal regions and two habitats (reef crest and slope) were examined within both marine parks to test for spatial variation. Densities of juvenile corals in the CSMP (13.99 ± 0.72 juveniles 10 m−2) were significantly lower compared to those in the GBRMP (23.72 ± 1.86 juveniles 10 m−2). Specifically, there were significantly less Acropora and Pocillopora juveniles on the reef crest in the central CSMP compared to the GBRMP. Relationships between juvenile abundance and percent coral cover were greatest for Acropora and Pocillopora in the GBRMP. This may be due to the low range of coral cover estimates recorded in the CSMP, especially for Acropora (0–15%). Low juvenile coral abundance, and in particular, the lack of fast-growing juvenile corals (e.g., Acropora) in the Central CSMP, in combination with low cover of broodstock (particularly Acropora) on CSMP reefs, poses a significant constraint on post-disturbance recovery capacity, possibly attributable to isolation and limited connectivity among reefs in this region.

The Influence of Coral Reef Spur and Groove Morphology on Wave Energy Dissipation in Contrasting Reef Environments

AbstractCoral reefs protect coastlines from inundation and flooding and serve over 200 million people globally. Wave transformation has previously been studied on coral reef flats with limited focus on forereef zones where wave transformation is greatest during high‐energy conditions. This study investigates the role of forereef spur and groove (SaG) morphology in wave energy dissipation and transmission at the reef crest. Using XBeach on LiDAR‐derived bathymetry from One Tree Island in the southern Great Barrier Reef, we reproduced dissipation rates comparable to SaG field studies. We examined how wave energy dissipation differs between realistic bathymetry and those with SaG features removed, demonstrating an up to 40% decrease in dissipation when SaG features are absent. We then investigated changes to wave energy dissipation and wave transmission at the reef crest based on IPCC AR5 emission scenarios (RCP2.6 and RCP8.5) and a total disaster scenario (TD) for the year 2100. For RCP2.6, an increase in wave heights of 0.8 m and an increase in water level of 0.3 m resulted in a two‐fold increase in dissipation rates. For RCP8.5 and TD, with no increase in incident wave height, dissipation rates were 29% and 395% lower than RCP2.6. This resulted in increased wave transmission at the reef crest by 1.8 and 2.7 m for the RCP8.5‐ and TD based models, respectively, when compared to the RCP2.6‐based model. The results from our novel modeling approach of using long‐shore varying accurate bathymetry on forereefs show increased wave energy dissipation rates with implications for reducing coastal flooding and island inundation on reef‐lined coasts.

How hot is too hot? Thermal tolerance, performance, and preference in juvenile mangrove whiprays, Urogymnus granulatus

Mangrove habitats can serve as nursery areas for sharks and rays. Such environments can be thermally dynamic and extreme; yet, the physiological and behavioural mechanisms sharks and rays use to exploit such habitats are understudied. This study aimed to define the thermal niche of juvenile mangrove whiprays, Urogymnus granulatus. First, temperature tolerance limits were determined via the critical thermal maximum (CTMax) and minimum (CTMin) of mangrove whiprays at summer acclimation temperatures (28 °C), which were 17.5 °C and 39.9 °C, respectively. Then, maximum and routine oxygen uptake rates (ṀO2max and ṀO2routine, respectively), post-exercise oxygen debt, and recovery were estimated at current (28 °C) and heatwave (32 °C) temperatures, revealing moderate temperature sensitivities (i.e., Q10) of 2.4 (ṀO2max) and 1.6 (ṀO2routine), but opposing effects on post-exercise oxygen uptake. Finally, body temperatures (Tb) of mangrove whiprays were recorded using external temperature loggers, and environmental temperatures (Te) were recorded using stationary temperature loggers moored in three habitat zones (mangrove, reef flat, and reef crest). As expected, environmental temperatures varied between sites depending on depth. Individual mangrove whiprays presented significantly lower Tb relative to Te during the hottest times of the day. Electivity analysis showed tagged individuals selected temperatures from 24.0 to 37.0 °C in habitats that ranged from 21.1 to 43.5 °C. These data demonstrate that mangrove whiprays employ thermotaxic behaviours and a thermally insensitive aerobic metabolism to thrive in thermally dynamic and extreme habitats. Tropical nursery areas may, therefore, offer important thermal refugia for young rays. However, these tropical nursery areas could become threatened by mangrove and coral habitat loss, and climate change.

Laboratory and non-hydrostatic modelling of focused wave group evolution over fringing reef

This paper presents physical experiments and numerical simulations to study the propagation of focused waves group across hypothetical fringing reef profiles. A wave flume is 69 m long and 1.0 m deep, and the reef cross section is made up of a reef face, a reef flat and a vertical wall. A reef crest of 0.085 m is optionally constructed on the outside to replicate the reef crown. By focusing wave trains of the JONSWAP or constant wave amplitude spectrum, the transient wave group is generated on the reef slope. Free surface elevations and flow velocity are measured over time along the flume's centreline. The focused wave process and the development of higher harmonics as a result of the nonlinear interaction over the reef face are clearly visible in the wavelet and FFT analyses of the observed free surface elevation. Low frequency wave is increasing on the reef flat while these short-period wave motions are primarily absorbed by rapid breaking on reef edge and crest. On the flat, it is discovered that reef crest has the effect of reducing short-period wave motion and increasing long-period wave motion. A numerical multi-layer non-hydrostatic wave model is employed and its ability to describe the propagation of focused wave groups over fringing reef profiles is assessed.

Wave transformation across impermeable and porous artificial reefs

Porous artificial reefs can function as nature-based solutions for coastal protection, due to their ability to dissipate wave energy while providing habitat for marine species. However, due to the lack of quantitative understanding of wave interactions with porous artificial reefs, there is uncertainty in how to optimize design for coastal protection applications. To address this gap, physical modelling experiments were conducted in a wave flume to investigate wave transformation across both porous and impermeable artificial reefs exposed to a range of regular wave conditions and submergence depths. The results highlight how key changes to wave kinematics (e.g., wave celerity, wave breaking) and wave energy (through reflection, dissipation and transmission) differ considerably between impermeable and porous artificial reefs. These differences in wave kinematic properties and energy balances across each reef can be well characterized by consideration of the effective crest depth (i.e., the total height of water at a point on the reef, including that in the voids) that accounts for the porosity of the reef structure, rather than the actual depth of the reef crest. The ratio of the effective crest depth to the incident wave height, termed the ‘relative effective crest depth’, was used to develop robust formulations to accurately predict wave reflection and transmission coefficients across both reefs over the range of wave and water depth conditions. The new formulations were also compared to other datasets reported in the literature, and were found to provide accurate predictions of both wave reflection and transmission for the broad range of submerged porous coastal structures considered (including artificial reefs and submerged breakwaters).

Seventeen-year study reveals fluctuations in key ecological indicators on two reef crests in Cuba.

Reef crests in the Caribbean have lost approximately 80% of the foundational habitat-forming coral Acropora palmata (Lamarck, 1816), with declines registered as early as the 1950s mainly from anthropogenic causes. We studied two reef crests in the northwestern region of Cuba over 17 years (2005 to 2021) to evaluate temporal changes in coral cover, dominated by A. palmata, and their potential drivers. The density of A. palmata generally showed a negative trend at both reefs, with the lowest density recorded in 2021 at 0.2±0.05 col. m-2 at Playa Baracoa and 1.0±0.1 col. m-2 at Rincon de Guanabo. The mean size of the colonies in the two reefs also decreased over time. In Playa Baracoa, the mean diameter of A. palmata colonies decreased from 2012 at 67±5.9 cm to 2013 at 34±2.2 cm, whereas in Rincon de Guanabo, a change in diameter was evident from 2015 at 44.3±2.3 to 2021 at 21.6±0.9 cm. Adult colonies (10 cm-50 cm diameter) predominated in most years on both reefs. The populations of A. palmata on both reefs were healthy, with an average of 70% colonies in good condition during the study period. However, A. palmata cover decreased by almost half by 2021, to 8.6% in Playa Baracoa and 16.8% in Rincon de Guanabo. By contrast, macroalgal cover increased two-fold to 87.1% in Playa Baracoa and four-fold to 77.2% in Rincon de Guanabo. The density of the sea urchin Diadema antillarum was higher in Playa Baracoa than in Rincon de Guanabo. The highest densities were 2.8±0.2 ind. m-2 in Playa Baracoa in 2005 and 0.1±0.03 ind. m-2in Rincon de Guanabo in 2008. Although our results show an overall decline of A. palmata (density and percent cover) and an increase in macroalgae, these two reef crests are in better condition than most reefs in the Caribbean in terms of the density and health of A. palmata populations, and the density of D. antillarum at Playa Baracoa. Our results are important in establishing a management plan to ensure the condition of these reef crests does not degrade further.

Seasonal dynamics and environmental drivers of tissue and mucus microbiomes in the staghorn coral Acropora pulchra.

Rainfall-induced coastal runoff represents an important environmental impact in near-shore coral reefs that may affect coral-associated bacterial microbiomes. Shifts in microbiome community composition and function can stress corals and ultimately cause mortality and reef declines. Impacts of environmental stress may be site specific and differ between coral microbiome compartments (e.g., tissue versus mucus). Coastal runoff and associated water pollution represent a major stressor for near-shore reef-ecosystems in Guam, Micronesia. Acropora pulchra colonies growing on the West Hagåtña reef flat in Guam were sampled over a period of 8 months spanning the 2021 wet and dry seasons. To examine bacterial microbiome diversity and composition, samples of A. pulchra tissue and mucus were collected during late April, early July, late September, and at the end of December. Samples were collected from populations in two different habitat zones, near the reef crest (farshore) and close to shore (nearshore). Seawater samples were collected during the same time period to evaluate microbiome dynamics of the waters surrounding coral colonies. Tissue, mucus, and seawater microbiomes were characterized using 16S DNA metabarcoding in conjunction with Illumina sequencing. In addition, water samples were collected to determine fecal indicator bacteria (FIB) concentrations as an indicator of water pollution. Water temperatures were recorded using data loggers and precipitation data obtained from a nearby rain gauge. The correlation structure of environmental parameters (temperature and rainfall), FIB concentrations, and A. pulchra microbiome diversity was evaluated using a structural equation model. Beta diversity analyses were used to investigate spatio-temporal trends of microbiome composition. Acropora pulchra microbiome diversity differed between tissues and mucus, with mucus microbiome diversity being similar to the surrounding seawater. Rainfall and associated fluctuations of FIB concentrations were correlated with changes in tissue and mucus microbiomes, indicating their role as drivers of A. pulchra microbiome diversity. A. pulchra tissue microbiome composition remained relatively stable throughout dry and wet seasons; tissues were dominated by Endozoicomonadaceae, coral endosymbionts and putative indicators of coral health. In nearshore A. pulchra tissue microbiomes, Simkaniaceae, putative obligate coral endosymbionts, were more abundant than in A. pulchra colonies growing near the reef crest (farshore). A. pulchra mucus microbiomes were more diverse during the wet season than the dry season, a distinction that was also associated with drastic shifts in microbiome composition. This study highlights the seasonal dynamics of coral microbiomes and demonstrates that microbiome diversity and composition may differ between coral tissues and the surface mucus layer.

Meltwater Pulse 1a drowned fringing reefs around Tahiti 15 000 years ago.

Reconstruction of postglacial sea-level rise using reef cores recovered from Tahiti during IODP Expedition 310 showed that the first major acceleration, known as Meltwater Pulse 1a (MWP-1a), was a 12-22 m rise in 340 years starting at 14.65 ka BP. Although it was reported that the pulse did not drown Tahitian reefs, the subsequent discovery of a fringing reef at the base of several cores implies that its timing, magnitude and impact require revision. Here, we report facies and paleodepth data from this reef, revise sea level, and revisit reef response. We find its reef crest is dominated by surf-adapted corals to a depth of 2.5 m and show that it retreated upslope over an approximately 1000-year interval from 16 ka. Reef development then apparently ceased at 15 ka at -106 m and remained absent for approximately 600 years, before resuming at 14.4 ka further upslope at -93 m. This absence is consistent with reef drowning and requires that MWP-1a had a smaller magnitude of 13.8 ± 1.3 m, and may have started 300 years earlier than previously reported. It confirms MWP-1a was a global event, drowning reefs on Tahiti as well as those in other oceans.

Analysis of the Bottom Topography of the Reservoir Due to Sediment Trapping (According to the Krasnodar Reservoir, Russia)

Morphometric descriptions of reservoirs are usually limited to the type, shape, altitude position, bed size and volume of water in them. The article presents the results of the analysis of the bottom topography of the Krasnodar reservoir and the transformations of this for 2005-2021. The analysis was carried out based on the materials of bathymetric surveys for the usable volume of the reservoir on an area of 224 km2 with the creation of digital elevation models. The topography of the reservoir bottom is represented by flat sections of flooded accumulative plain with prevailing slopes of about 0.2–0.4°, dissected by riverbeds of lower-order tributaries. The transformation of the topography is caused by gradual silting. The total volume of sediments for this area in 2005-2021 amounted to 127 million m3 with an average siltation layer of 0.4 m. To describe the morphological properties of the bottom topography, we used geomorphometry techniques with the calculation of the BPI index (Bathymetric Position Index) and the classification of mesoscale topography forms based on it. For the riverbed, there are topography forms related to three types of surfaces: flat (Lower Bank Shelves), concave (Depressions, Deep Depressions) and convex (Reef Crests, Back Reefs, Mid-Slope Ridges). The constructed maps reflect the differentiated morphology of the bed surface, the evolution of topography forms and the change in roughness under conditions of continuous transformation of the basin and allow judging the prevailing morphogenetic processes. Morphologically, the coastal zone and the shallow part of the riverbed are the most difficult to construct. Here, along with long-shore reef crests of different genesis, deep depressions and simple depressions in the form of underwater channels on the deltas of extension can form on the accumulative shoal.

“Unless we Value the Intangible Heritage, the Tangible will never be Safe!” Linking the Tangible and Intangible Aspects of Heritage Sites in Africa

ABSTRACT A few heritage researchers and protection practitioners in some African countries define heritage sites and cultural objects based on European and North American criteria. Such criteria emphasize visual material remains like monumental structures and their aesthetically pleasing features. This Western view overlooks some critical aspects. For example, to local people, the meanings and associated values make the monuments and sites relevant. Despite the inseparability of the tangible heritage and associated intangible aspects such as spiritual practices, some researchers and heritage practitioners, including antiquities department officials, need to pay more attention to the invisible meanings embedded in the sites and cultural objects. Notably, it is these immaterial aspects which the local people value the most. In this article, we survey three fishing villages: Batini, Mkadini and Winde, on the Swahili coast in East Africa, and document what heritage means from the local people's perspective. We argue that fishing communities value features like reef crests, sacred mangrove forests, the ruins of stone-built tombs and sacred baobab trees not because of their physical appearance but the spiritual practices (e.g., healing, rituals, and offerings) the local people undertake within and around these sites. We further contend that to achieve heritage preservation sustainability, government officials and heritage scholars should pay greater attention to the spiritual aspects associated with these places.

Bio-physical determinants of sediment accumulation on an offshore coral reef: A snapshot study

Sediments are found on all coral reefs around the globe. However, the amount of sediment in different reservoirs, and the rates at which sediments move between reservoirs, can shape the biological functioning of coral reefs. Unfortunately, relatively few studies have examined reef sediment dynamics, and associated bio-physical drivers, simultaneously over matching spatial and temporal scales. This has led to a partial understanding of how sediments and living reef systems are connected, especially on clear-water offshore reefs. To address this problem, four sediment reservoirs/sedimentary processes and three bio-physical drivers were quantified across seven different reef habitats/depths at Lizard Island, an exposed mid-shelf reef on the Great Barrier Reef. Even in this clear-water reef location a substantial load of suspended sediment passed over the reef; a load theoretically capable of replacing the entire standing stock of on-reef turf sediments in just 8 h. However, quantification of actual sediment deposition suggested that just 2 % of this passing sediment settled on the reef. The data also revealed marked spatial incongruence in sediment deposition (sediment trap data) and accumulation (TurfPod data) across the reef profile, with the flat and back reef emerging as key areas of both deposition and accumulation. By contrast, the shallow windward reef crest was an area of deposition but had a limited capacity for sediment accumulation. These cross-reef patterns related to wave energy and reef geomorphology, with low sediment accumulation on the ecologically important reef crest aligning with substantial wave energy. These findings reveal a disconnect between patterns of sediment deposition and accumulation on the benthos, with the ‘post-settlement’ fate of sediments dependent on local hydrodynamic conditions. From an ecological perspective, the data suggests key contextual constraints (wave energy and reef geomorphology) may predispose some reefs or reef areas to high-load turf sediment regimes.

Six years of demography data for 11 reef coral species.

Scleractinian corals are colonial animals with a range of life-history strategies, making up diverse species assemblages that define coral reefs. We tagged and tracked ~30 colonies from each of 11 species during seven trips spanning 6 years (2009-2015) to measure their vital rates and competitive interactions on the reef crest at Trimodal Reef, Lizard Island, Australia. Pairs of species were chosen from five growth forms in which one species of the pair was locally rare (R) and the other common (C). The sampled growth forms were massive (Goniastrea pectinata [R] and G. retiformis [C]), digitate (Acropora humilis [R] and A. cf. digitifera [C]), corymbose (A. millepora [R] and A. nasuta [C]), tabular (A. cytherea [R] and A. hyacinthus [C]) and arborescent (A. robusta [R] and A. intermedia [C]). An extra corymbose species with intermediate abundance, A. spathulata was included when it became apparent that A. millepora was too rare on the reef crest, making the 11 species in total. The tagged colonies were visited each year in the weeks prior to spawning. During visits, two or more observers each took two or three photographs of each tagged colony from directly above and on the horizontal plane with a scale plate to track planar area. Dead or missing colonies were recorded and new colonies tagged to maintain ~30 colonies per species throughout the 6 years of the study. In addition to tracking tagged corals, 30 fragments were collected from neighboring untagged colonies of each species for counting numbers of eggs per polyp (fecundity); and fragments of untagged colonies were brought into the laboratory where spawned eggs were collected for biomass and energy measurements. We also conducted surveys at the study site to generate size structure data for each species in several of the years. Each tagged colony photograph was digitized by at least two people. Therefore, we could examine sources of error in planar area for both photographers and outliners. Competitive interactions were recorded for a subset of species by measuring the margins of tagged colony outlines interacting with neighboring corals. The study was abruptly ended by Tropical Cyclone Nathan (Category 4) that killed all but nine of the more than 300 tagged colonies in early 2015. Nonetheless, these data will be of use to other researchers interested in coral demography and coexistence, functional ecology, and parametrizing population, community, and ecosystem models. The data set is not copyright restricted, and users should cite this paper when using the data.

Effects of the reef roughness on the harbor oscillations induced by low-frequency waves

Low-frequency waves can be captured and amplified within harbors and present a prevalent inducing factor of harbor oscillations. Effects of the rough reef surface and the possible inhomogeneity of the roughness on the oscillating behaviors within an elongated harbor on reef topography are investigated based on numerical simulations. The reef roughness is applied via hydraulic roughness coefficient within the well-recognized empirical range and the inhomogeneity is arranged following the probable location of the coral covers and the possible engineering inventions. With wavelet transformation analysis and bispectral analysis for inspecting energy distribution of oscillating components and their interactions, the lowest oscillation mode is found to be more influenced by the rough extents of the reef surface whereas higher modes, by the location of roughness. The friction induced by rough surface in the vicinity of reef crest is revealed to be effective in reducing the oscillating behaviors by acting on the generation of low-frequency waves on the reef by the incident short ones. In addition to the damping effects of the reef roughness, the transition from smooth reef surface to rougher one may also lead to evolutions of coupling between different oscillating components and consequently affect oscillating energy distributions.

Habitats diversity and MPA regulations are insufficient in promoting healthy coral reef fish assemblages in Punta Francés National Park (Cuba)

Marine protected areas (MPAs) have been implemented on coral reefs as management and conservation tools since coral reefs provide significant ecological and economic values. For instance, Punta Francés National Park (PFNP) constitutes one of the most pristine marine environments in the Cuban archipelago, where recreational SCUBA diving has long been the most important activity. The goods and services provided by this area, the gaps in its biodiversity knowledge, and the putative effect of the MPA, prompted this research aims (1) to characterize reef fish assemblages in the coral reef of Punta Francés and (2) to test the hypothesis that PFNP hosts more abundant and diverse fish assemblages than the adjacent non-protected reef due to the higher habitat heterogeneity and protection level inside the PFNP. We have organized the analysis into four parts: (1) taxonomic and functional variation of fish assemblages; (2) potential factors influencing fish assemblage structure; (3) representativeness of species with special concern; and (4) functional redundancy analysis. The study was carried out from 2011 to 2014 in three reef habitats (reef crest, reef slope, and spur and groove), both inside and outside the PFNP. We found no differences in species and functional composition of fishes between areas with different protection levels. However, reef fish assemblages depended heavily on habitat type, demonstrating the importance of reef slope and reef crest habitats. No strong mangrove-seagrass bed-coral reef connection was evident for the ichthyofauna reported to use mangroves and seagrasses as nurseries. Low biomass and abundance of predatory species and fish families important to conservation is a concerning outcome. Some functional traits were represented by only one or very few species across the entire area, which likely compromised ecological function in the system. The most distressing issue was the non-consistent differences found between protected and non-protected areas, suggesting the necessity of reviewing the management objectives for reef fishes in PFNP and a clear need to update its management plan and perhaps its boundaries.

Numerical Investigation on Hydrodynamic Processes of Extreme Wave Groups on Fringing Reef

The low-lying reef islands distributed in the tropical and subtropical coastal regions are highly vulnerable to the devastating damages of surges and waves during the severe weather events. Over the past two decades, extreme waves have caused tremendous loss and damages to the tropical and subtropical coastal regions. Previous research has focused on the wave hydrodynamics of tsunami waves, as well as regular and irregular waves on the fringing reefs. The complex wave hydrodynamics of extreme waves on the fringing reefs are rarely studied. By applying the nonhydrostatic numerical flow solver (NHWAVE), transformation and breaking process of the crest- and trough-focused wave groups on the fringing reef are analyzed in this study. Influences of the major factors, i.e., water depth, significant wave height, peak wave period, forereef slope and backreef slope, and ridge width, are discussed in detail. The results show that there are complex interactions between the fringing reef and the focused wave group. Breaking waves of high intensity can form at the reef crest. Meanwhile, due to the wave breakings at the reef crest and bottom friction of the reef flat, the local wave height can be effectively reduced. Within the complex wave hydrodynamics of focused waves on the fringing reef, most of the wave energy can be dissipated. In addition, hydrodynamic difference between the crest- and trough-focused waves on the fringing reef is very limited. The research results of this study will further help researchers to better understand the wave hydrodynamics of extreme waves over the fringing reefs.

Морфометрический анализ донного рельефа крупного долинного водохранилища в процессе его эволюции

Until now, the study of the morphology of the bottom of large reservoirs, subject to gradual siltation, received little attention. Morphometric descriptions of reservoirs are limited by the type, shape, altitude position, size of the bed, and the volume of water in them. The article presents the results of the analysis of the bottom relief of the Krasnodar Reservoir and the transformations of this relief for 2005–2021. The analysis was performed based on the materials of bathymetric surveys for the regulated volume of the reservoir on an area of 224 km2 with the construction of the corresponding digital relief models. The relief of the bottom of the reservoir is represented by flat areas of a flooded accumulative plain with prevailing slopes of about 0.2–0.4°, dissected by river channels of lower order tributaries. The transformation of the relief is caused by gradual siltation. The total volume of deposits for the specified area in 2005–2021 amounted to 127 million m3 with an average silt layer of 0.4 m. To describe the morphological properties of the bottom topography, we used geomorphometric techniques with the calculation of the BPI (Bathymetric Position Index) and the classification of mesoscale landforms based on it. For the bed, relief forms have been established related to three types of surfaces: flat (lower bank shelf), concave (depressions, deep depressions) and convex (reef crests, back reefs, mid-slope reefs). The constructed maps reflect the differentiated morphology of the bed surface, the evolution of landforms under conditions of continuous transformation of the basin, and also make it possible to judge the prevailing processes of morphogenesis. The coastal zone and the shallow part of the bed are the most complex in morphological terms. Here, along with reefs of different genesis, deep depressions and depressions in the form of underwater channels in advanced deltas can form on the accumulative shoal.