Fore Reef Research Articles

Dataset of octocoral assemblages in fore reefs in the northwestern region of Cuba.

This dataset accompanies "Spatio temporal variation in octocoral assemblages along a water quality gradient in the northwestern region of Cuba" [1]. Sampling units were quadrats of 1 m2 (each 1 x 1 m), positioned by a random-systematic design at 10 m depth on the rocky-coral substrate. The number of colonies of octocoral species in thirteen fore reefs was counted to determine the composition, richness and abundance (expressed as density) of octocorals for the period from 2008-2015. Density of six species that most influenced spatial variation of octocoral assemblage structure was compared [1]. Species richness of octocorals was determined in each reef and for the 2008-2015 period. The accumulated species richness was calculated based on 100 randomizations without replacement. This dataset can be used in meta-analysis studies on spatial variations of the structure of octocoral assemblages related to anthropogenic activities and climate variability in the Caribbean Sea, as well as, experimental studies on thresholds to specific pollutants.

Habitat associations of settlement-stage crown-of-thorns starfish on Australia’s Great Barrier Reef

Population irruptions of crown-of-thorns starfish (Acanthaster spp.) contribute greatly to the degradation of coral reefs throughout the Indo-Pacific. Effective management of these population irruptions is limited, in part, by incomplete knowledge of their early life history. Importantly, there are very limited data on the distribution and abundance of newly settled crown-of-thorns starfish (0 + starfish, in their first year since settlement). Extensive sampling was conducted around the circumference of three distinct mid-shelf reefs (at 1–18 m depths) in the central Great Barrier Reef (GBR), during active population irruptions, in May–June 2017, to quantify the occurrence and densities of settlement-stage starfish (2–65 mm diameter) and relate patterns of abundance to distinct habitat features at the scale of individual reefs. Overall, 140 settlement-stage starfish were detected across 1242 quadrats (1 m2). Settlement-stage starfish were recorded from 31 out of 42 sites (73.8%) at mean densities of 0–0.77 starfish m−2. Both estimated densities and the likelihood of occurrence of settlement-stage starfish within quadrats increased overall with the proportion of coral rubble (and dead intact corals), were greatest at intermediate depths (8–14 m), but decreased with the proportion of live hard coral. At the scale of individual reefs, settlement-stage starfish occurred most frequently in south-western and northern fore reef habitats. Our results suggest that settlement and/or early post-settlement survival of crown-of-thorns starfish is greatest in relatively shallow waters of obliquely exposed fore reef habitats where there is high cover of coral rubble. The specific occurrence of these habitat types (within spur and groove systems and rubble slips) provides an opportunity to concentrate searches and increase effective sampling of settlement-stage starfish, though these habitats are relatively widespread and unlikely to constrain the population replenishment or population irruptions of crown-of-thorns starfish on the GBR.

Pacific-wide pH snapshots reveal that high coral cover correlates with low, but variable pH

Ocean acidification (OA) is impairing the construction of coral reefs while simultaneously accelerating their breakdown. The metabolism of different reef organism assemblages alters seawater pH in different ways, possibly buffering or exacerbating OA impacts. In spite of this, field data relating benthic community structure and seawater pH are sparse. We collected pH time-series data snapshots at 10 m depth from 28 different reefs (n = 13 lagoon, n = 15 fore reef) across 22 Pacific islands, spanning 31° latitude and 90° longitude. Coincident with all deployments, we measured percent cover of the benthic community. On fore reefs, high coral cover (CC) negatively correlated with mean and minimum pH, but positively correlated with pH variability. Conversely, pH minima were positively correlated to coverage of coralline and turf algae. Benthic cover did not correlate with pH in lagoonal reefs. From 0% to 100% CC, mean pH and aragonite saturation state (Ωarag) declined –0.081 and –0.51, respectively, while declines in minimum values were greater (Δmin pH = –0.164, Δmin Ωarag = –0.96). Based upon previously published relationships, the mean pH decline from 0% to 100% CC would depress coral calcification 7.7%–18.0% and increase biologically-mediated dissolution 13.5%–27.9%, with pH minima depressing dark coral calcification 14.4%–35.2% and increasing biologically-mediated dissolution 31.0%–62.2%. This spatially expansive dataset provides evidence that coral reefs with the highest coral cover may experience the lowest and most extreme pH values with OA.

Differential disturbance effects and phenotypic plasticity among outplanted corals at patch and fore reef sites

Practitioners have outplanted tens of thousands of nursery-reared coral colonies for restoration purposes, and interest in outplanting is increasing. However, restoration outcomes on natural reefs can be variable, and genotype- and site-specific differences have been reported. To systematically explore these differences, performance of restored corals was compared at two site types, and intraspecific variation in phenotype among six genotypes previously characterized in a nursery was simultaneously assessed. Nursery-reared Acropora cervicornis colonies were outplanted to geographically paired fore reef (n = 2) and patch reef (n = 2) sites. Colony growth and condition were monitored over one year. After the first monitoring visit, Hurricane Irma passed directly over outplant sites, providing an opportunity to examine disturbance effects across sites. In contrast to nursery results, growth did not vary among genotypes or sites either pre- or post-hurricane. Plasticity in pre-hurricane growth among sites was observed for one of the six genotypes examined. Stark differences in post-hurricane survival were observed between fore reef and patch reef sites: while 51.04 ± 9.38 % of outplanted colonies survived at patch reef sites, no colonies could be located at either fore reef site. Records from additional sites monitored by practitioners indicated higher outplant survival following hurricane disturbance at patch reef sites compared to fore reef sites. The lack of site or genotype effects on growth in A. cervicornis contrasts with a number of previous studies, however growth results were likely confounded by Hurricane Irma. Reduced structural complexity on Caribbean reefs may contribute to differential hurricane impacts between restored fore reefs and patch reefs. These results suggest that restoration practitioners should consider increasing effort on patch reef sites in restoration programs while also developing new strategies to foster resilience at fore reef sites.

Depth Influences Symbiodiniaceae Associations Among Montastraea cavernosa Corals on the Belize Barrier Reef.

In Belize, shallow populations (10 and 16 m) of the coral species Montastraea cavernosa from the back reef and reef crest are genetically differentiated from deeper populations on the fore reef and reef wall (25 and 35 m). Like many species of scleractinian corals, M. cavernosa has an obligate symbiosis with dinoflagellate microalgae from the family Symbiodiniaceae. Here, we describe the Symbiodiniaceae taxa found within previously sampled and genotyped M. cavernosa populations along a depth gradient on the Belize Barrier Reef by implementing high-throughput sequencing of the ITS2 region of Symbiodiniaceae ribosomal DNA and the SymPortal analysis framework. While Symbiodiniaceae ITS2 type profiles across all sampling depths were almost entirely (99.99%) from the genus Cladocopium (formerly Symbiodinium Clade C), shallow (10 and 16 m) populations had a greater diversity of ITS2 type profiles in comparison to deeper (25 and 35 m) populations. Permutational multivariate analysis of variance (PERMANOVA) confirmed significant differences in ITS2 type profiles between shallow and deep sample populations. Overall Symbiodiniaceae communities changed significantly with depth, following patterns similar to the coral host’s population genetic structure. Though physiological differences among species in the cosmopolitan genus Cladocopium are not well-described, our results suggest that although some members of Cladocopium are depth-generalists, shallow M. cavernosa populations in Belize may harbor shallow-specialized Symbiodiniaceae not found in deeper populations.

Sedimentological Study of the Hartha Formation in Selected Oilfields, Northern Iraq

The Hartha Formation (late Campanian–Maastrichtian) is one of the most important carbonate hydrocarbon reservoirs in Iraq. Previous studies have focused on stratigraphic and lithological characteristics of the Hartha Formation in the middle and southern parts of Iraq, while this study focuses on the reconstruction of its facies architecture and stratigraphic successions in five oilfields the north and northwestern parts of Iraq. Its thicknesses were recorded for all of the wells studied, along with the occurrences of benthonic foraminifera, rudists, echinoderms, coral, algae and peloids. The main diagenetic processes affecting the formation include dolomitization, cementation, silicification, compaction and micritization. Eleven microfacies are recognized, representing four facies association: outer shelf (I), fore reef and shoal (II), rudist reef and restricted platform (III) and (IV) lagoon. These facies associations occur in a predictable order reflecting regressive shallowing-upward sequences. Lateral facies variation shows that fore reef and shoal environments dominate the Hartha succession, suggesting that it corresponds to a ramp-type carbonate platform depositional model.

Spatio temporal variation in octocoral assemblages along a water quality gradient in the northwestern region of Cuba

Rivers are the main sources of nutrients to coastal zones. Therefore, the effects of water quality degradation on octocoral assemblages and their relationship with microbiological and physical-chemical variables were determined in reefs close to river basins in the northwestern region of Cuba. The evaluations were carried out in 1 m2 frames at a depth of 10 m in 13 fore reefs. The highest concentrations of the microbiological variables and hydrochemicals and the lowest horizontal visibility in the water column were detected in the reefs near the river basins. The lowest richness, diversity and octocoral density were related to higher concentrations of fecal coliform, total coliform and fecal streptococcal bacteria, sediment accumulation on the bottom and lower visibility. The structure of the octocoral assemblages varied significantly between reefs due to fecal organic pollution. Water quality deterioration in the reefs near the river basins has negatively affected the octocoral assemblages.

Mechanisms of spur and groove development and implications for reef platform evolution

Contemporary understanding of Holocene coral reef development is based primarily on sub-surface investigations of reef flat, back reef and lagoon zones. Few studies of Holocene fore reef development exist, constituting a significant gap in our understanding of reef evolution. The spur and groove (SaG) zone is a distinct, understudied, feature of fore reefs worldwide. We review SaG development from previous studies and present 29 new SaG short cores with 52 14C and U–Th ages from six fore reef regions of Heron and One Tree reefs, the first such data from the Great Barrier Reef. Remarkably, we found that SaGs do not necessarily accrete in the same direction as their adjacent reef flat. We identified three modes of reef flat and SaG lateral accretion: Mode 1 – lagoonward accretion of both the reef flat and SaGs; Mode 2 –lagoonward accretion of the reef flat but seaward accretion of the SaGs; Mode 3 - seaward accretion of both the reef flat and SaGs. Most SaG zones (five of the six studied) accreted in a seaward direction (Modes 2 or 3). Hydrodynamic conditions and local topography appear to be the dominant factors determining which mode occurs. Episodic high-energy events are also likely to play an important role in SaG formation. Our findings suggest that traditionally held models of reef evolution whereby lagoonal, mature reefs fill, developing into senile platform reefs, may not hold. Rather, reef flats may continue to expand seaward on their leeward, and semi-exposed fronts to increase in size while maintaining their lagoons.

Year-long effects of high pCO2 on the community structure of a tropical fore reef assembled in outdoor flumes

Abstract In this study, fore reef coral communities were exposed to high pCO2 for a year to explore the relationship between net accretion (Gnet) and community structure (planar area growth). Coral reef communities simulating the fore reef at 17-m depth on Mo’orea, French Polynesia, were assembled in three outdoor flumes (each 500 l) that were maintained at ambient (396 µatm), 782 µatm, and 1434 µatm pCO2, supplied with seawater at 300 l h−1, and exposed to light simulating 17-m depth. The communities were constructed using corals from the fore reef, and the responses of massive Porites spp., Acropora spp., and Pocillopora verrucosa were assessed through monthly measurements of Gnet and planar area. High pCO2 depressed Gnet but did not affect colony area by taxon, although the areas of Acropora spp. and P. verrucosa summed to cause multivariate community structure to differ among treatments. These results suggest that skeletal plasticity modulates the effects of reduced Gnet at high pCO2 on planar growth, at least over a year. The low sensitivity of the planar growth of fore reef corals to the effects of ocean acidification (OA) on net calcification supports the counterintuitive conclusion that coral community structure may not be strongly affected by OA.

Small-Scale Variability Dominates Benthic Coverage and Diversity Across the Jardines de La Reina, Cuba Coral Reef System

Coral reefs are complex and biodiverse ecosystems that are undergoing significant change. Understanding reef composition and biodiversity at multiple spatial scales is necessary to track both large-scale and more subtle ecosystem changes. The Jardines de la Reina (JR) archipelago, located offshore of the island of Cuba, contains the largest marine protected area (MPA) in the Caribbean Sea but lacks multi-scale studies. In this contribution, we documented the diversity of scleractinian corals, octocorals, algae, and sponges across nested spatial scales spanning four orders of magnitude (101–105 m). In addition, we tested the hypothesis that species diversity followed a gradient along the ca. 200 km of reef tract. Across the archipelago, we examined benthic cover and species diversity within 255 photo-quadrats (25 × 25 cm) at 13 fore reef sites (two sampling locations per site, and 10 photo-quadrats per location). Small-scale (101 m) variability between photo-quadrats characterized the coral reef community structure in JR compared with local- (102 m) and mesoscale (104–105 m) variability. This finding suggests that biological processes (e.g. recruitment, competition) had primacy over hydrodynamics for driving the differences in reef community composition. However, the dominance of algae and low cover and diversity of scleractinian corals suggests the pervasive effects of global change on coral communities despite potential benefits provided by the MPA (e.g. oligotrophy and abundance of herbivores). There was not a gradient of benthic community structure along the fore reef tract of JR; instead, a patchy distribution occurred in response to more subtle drivers acting at local scales. Overall, our multi-scale comparison was useful for differentiating the impacts of processes potentially impacting the JR reefs, thus providing important information to understand how reef communities are impacted by different environmental and anthropogenic stressors, and the potential benefits of MPAs.

Implementation of coral propagation for coral reef garden in Nusa Dua, Bali

MARRS (Mars Assisted Reef Restoration System) is an artificial reef method that resembles spider webs and has been implemented in several regions of Indonesia, including Samuh beach, Nusa Dua, Bali. Since July - October 2018, 761 MARRS units, supporting a total of ± 10,600 coral fragments, have been installed. The aim of this research is to provide an initial investigation into establishing a mini-coral reef park in Indonesia. Monitoring was done by identifying habitat geomorphology methods with photo transects and coral propagation status in MARRS using the random visual census method. From the process of habitat geomorphology classification in the artificial reef network, there were 9 types of habitat classified on the fringing reef, reef flats and fore reefs. Ten hard coral species from the Scleractinia group were identified from 10 randomly-selected and monitored MARRS units: Acropora formosa, A. hyacinthus, Pocillopora verucosa, P. damicornis, Psammocora sp., Symphyllia sp., Stylophora pistillata, Turbinaria sp., Echinopora sp. and Favites sp. Three significant coral factors were found to be present within the coral propagation system: resistance, competition and predators.

Trophic plasticity in a common reef‐building coral: Insights from δ13C analysis of essential amino acids

Abstract Reef‐building corals are mixotrophic organisms that can obtain nutrition from endosymbiotic microalgae (autotrophy) and particle capture (heterotrophy). Heterotrophic nutrition is highly beneficial to many corals, particularly in times of stress. Yet, the extent to which different coral species rely on heterotrophic nutrition remains largely unknown because it is challenging to quantify. We developed a quantitative approach to investigate coral nutrition using carbon isotope (δ13C) analysis of six essential amino acids (AAESS) in a common Indo‐Pacific coral (Pocillopora meandrina) from the fore reef habitat of Palmyra Atoll. We sampled particulate organic matter (POM) and zooplankton as the dominant heterotrophic food sources in addition to the coral host and endosymbionts. We also measured bulk tissue carbon (δ13C) and nitrogen (δ15N) isotope values of each sample type. Patterns among δ13C values of individual AAESS provided complete separation between the autotrophic (endosymbionts) and heterotrophic nutritional sources. In contrast, bulk tissue δ13C and δ15N values were highly variable across the putative food sources and among the coral and endosymbiont fractions, preventing accurate estimates of coral nutrition on Palmyra. We used linear discriminant analysis to quantify differences among patterns of AAESS δ13C values, or ‘fingerprints’, of the food resources available to corals. This allowed for the development of a quantitative continuum of coral nutrition that can identify the relative contribution of autotrophic and heterotopic nutrition to individual colonies. Our approach revealed exceptional variation in conspecific colonies at scales of metres to kilometres. On average, 41% of AAESS in P. meandrina on Palmyra are acquired via heterotrophy, but some colonies appear capable of obtaining the majority of AAESS from one source or the other. The use of AAESS δ13C fingerprinting analysis offers a significant improvement on the current methods for quantitatively assessing coral trophic ecology. We anticipate that this approach will facilitate studies of coral nutrition in the field, which are essential for comparing coral trophic ecology across taxa and multiple spatial scales. Such information will be critical for understanding the role of heterotrophic nutrition in coral resistance and/or resilience to ongoing environmental change. A free Plain Language Summary can be found within the Supporting Information of this article.

Nitrogen Identity Drives Differential Impacts of Nutrients on Coral Bleaching and Mortality

Nitrogen pollution increases the susceptibility of corals to heat-induced bleaching. However, different forms of nitrogen (nitrate vs. ammonium/urea) may have different impacts on thermal tolerance of corals. We used an 18-month field experiment on the oligotrophic fore reef of Moorea, French Polynesia, to test how different forms of nitrogen (nitrate vs. urea) impacted coral bleaching. The experiment spanned two moderate thermal stress events in 2016 and 2017. Nitrate increased bleaching prevalence in Acropora by up to 100% and in Pocillopora by up to 60% compared to control corals. Urea exposure often had intermediate effects on bleaching (not different from either control or nitrate-exposed corals) in both taxa. Importantly, nitrate prolonged bleaching in both Acropora and Pocillopora as nitrate-exposed corals remained bleached even after thermal stress ended, while control and urea-exposed corals had mostly recovered. Nitrate exposure also increased the prevalence of partial mortality in Pocillopora colonies and more than tripled the number of colonies that completely died. Our data are the first to show contrasting effects of different forms of nitrogen on coral bleaching and mortality in a natural reef environment, linking previous patterns from large-scale correlative studies with results from more mechanistic laboratory experiments. Most importantly, we showed that corals exposed to nitrate exhibited more frequent bleaching, bleached for longer duration, and were more likely to die than corals in low nitrogen conditions. Exposure to excess nitrogen, particularly anthropogenic nitrogen, may lower the temperature threshold at which corals bleach, triggering bleaching events on polluted reefs even when typical thermal stress thresholds have not been crossed.

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.

Limited coral mortality following acute thermal stress and widespread bleaching on Palmyra Atoll, central Pacific

During 2015–2016, an El Nino and associated warm water event caused widespread coral bleaching across the equatorial Pacific. Here, we combine 8 yr of benthic monitoring data from permanent photoquadrats with remotely sensed and in situ temperature measurements to assess the impact of the warming event on benthic communities at Palmyra Atoll. We quantified bleaching prevalence across two distinct reef habitats using the best available data. On the fore reef (~ 10 m depth), we quantified bleaching severity within 100–200 m2 large-area plots using the custom visualization and analysis software, Viscore. On the reef terrace (~ 5 m depth), we used 95 focal colonies across three species that have been monitored annually since 2014. The 2015–2016 warm water event was the most extreme such event recorded on Palmyra in the past several decades with a maximum cumulative heat stress (degree heating weeks) of 11.9 °C-weeks. On the fore reef, 90% of live coral cover exhibited some degree of bleaching (32% severe bleaching). On the shallow reef terrace, bleaching was observed in 93% of the focal colonies across all species. Overall, coral cover declined 9% on the fore reef from 2014 to 2017, whereas coral cover did not change on the terrace. These contrasting results may be associated with typical daily temperature ranges on the terrace that are three times greater than on the fore reef. Permanent photoquadrats showed that turf algae initially colonized skeletons of recently dead corals but transitioned to crustose coralline algae within a year. Collectively, our study emphasizes that comprehensive monitoring of benthic communities over time combined with in situ temperature data can provide taxonomically precise trajectories of community change during and following thermal stress.

Hydrodynamic conditions that favor the settlement of Diadema antillarum to a western Caribbean coral reef

The reduction in the Diadema antillarum Philippi, 1845 population across the Caribbean region in the 1980s had adverse ecological consequences, including coral-algal phase-shifts. Reduced larval supply, and subsequent low recruitment success, has hampered population recovery. To examine larval density and the influence of hydrodynamics on settlement of D. antillarum, monthly plankton tows were conducted from May 2014 to April 2015 in the lagoon and fore reef zones of a western Caribbean coral reef (Xcalak, Mexico). A moored Nortek acoustic waves and currents (AWAC-Nortek) oceanographic instrument recorded wave height, wave velocity, and suspended particles in the water column. To assess settlement of D. antillarum, collectors were placed along the lagoon and fore reef, and inspected monthly. Monthly samples had a mean density of 0.06 larvae per 15 m3 from June to August corresponding to two developmental stages. Five settlers with test diameter approximately 1 mm were collected from August to December. During August, Doppler profiles recorded via the AWAC-Nortek instrument showed the lowest wave height values (<0.3 m) and a low bottom shear stress of <0.15 N m–1. Acoustic signals indicated that the particle displacement was driven primarily by wave action and that currents played a secondary role. During settlement of D. antillarum, wave orbital velocity (Uw ) was below the threshold of motion (Uwr ), allowing deposition of particles at the seabed. These hydrodynamic conditions suggest a window of opportunity for larval transport and benthic settlement. Ours is the first field study documenting the mechanisms that link hydrodynamics to the settlement of D. antillarum to a Caribbean reef.

Physical and Numerical Modeling of Infragravity Wave Generation and Transformation on Coral Reef Platforms

AbstractWave transformation across reef platforms strongly controls sediment transport processes and coral reef island morphodynamics with infragravity (IG) waves playing an important contributing role. A small‐scale (1:50) laboratory experiment and prototype numerical modeling are used to explore the characteristics of IG wave motion on coral reefs. The slope of the fore reef is the key factor controlling the mechanism of IG wave generation. Steep slopes (&gt;1/10) are dominated by landward and seaward propagating breakpoint‐forced long waves, whereas incoming and then released bound long waves become increasingly important for slopes &lt;1/20. The breakpoint‐forced long wave mechanism is the more effective generator of IG energy, and the most energetic IG motion (normalized by incident wave motion) is generated on reef platforms with a fore reef slope &gt; 1/6. The water level relative to the reef platform hreef is also a key factor, and the largest IG waves are generated for a ratio between hreef and offshore significant wave height Hs,o of −0.25 to 0.75, that is, when most waves break across the reef slope and a fully saturated surf zone extends across the reef platform. An island on the reef platform substantially increases the contribution of IG waves to the total wave spectrum, but increased reef surface roughness reduces IG importance. Under the most optimal conditions, the IG wave height averaged across the platform is 20–30% of the incident offshore wave height. The geomorphic influence of IG waves is considered most significant for reef platforms with energetic waves breaking on the steepest fore reefs.

Laboratory study of wave transformation around reef coasts with various rough surfaces

With global climate change and sea level rise, low-lying atoll islands fringed by coral reefs are especially vulnerable to wave-driven inundation during extreme wave events. In recent years, China has implemented large-scale engineering constructions on some low-lying reef atolls in the South China Sea. Hence, accurate prediction of the nearshore waves on the reefs is important to assess the wave runup on such constructed coastal structures. Wave runup near the reef coast is primarily contributed from sea and swell waves (0.04–0.4 Hz), infragravity waves (0.001–0.04 Hz) and wave setup. A typical coral reef profile is characterized by a seaward sloping fore-reef and an inshore shallow reef flat extending towards the coastline, and the reefs have been reported as efficient buffers to the wind-driven wave energy over decades. Reefs often have fully developed coral communities on the fore reef and reef flat, resulting in complex topography and reef surface roughness. The wave energy loss caused by bottom friction maybe even be greater than that caused by wave breaking. This laboratory study modeled a variety of rough surfaces around the reef surfzone by using an array of cylinders with different arrangements. The results show that the swell waves height near the coastline is significantly lower than the incident waves height due to the breaking of the short waves at the reef edge and the continuous attenuation of the friction along the reef flat during the irregular waves propagation to the shore. The infragravity waves height increases significantly at the reef edge due to wave breaking, and then the infragravity waves height are amplified by the resonance effect on the reef flat, and the infragravity waves height increases gradually along the reef until it reaches the maximum value near the coastline. Near the coastline, both the swell waves height and the infragravity waves height increase with the incident waves height and period increasing. The swell waves height increases with reef-flat still water level increasing, while the low frequency long wave height decreases with the increase of reef-flat still water level. Both wave heights with the rough reef surface are found to be smaller than those with the smooth surface. When the roughness of reef surface varies, both wave heights near the shoreline decrease with the increasing surface roughness density. We also analyze the coherence and transfer functions to show that the infragravity waves on the reef flat are generated by the breaker-point shift when the grouped short waves break around the reef edge. Resonant modes exist assciated with the infragravity wave motions on the reef flat. For the smooth reef surface, the infragravity wave energy is amplified due to the first-order resonance when it propagates from the reef edge to the shoreline. For the rough reef surface, the infragravity wave energy is dissipated by bottom friction on the reef flat, and the effect of resonance is insignificant.

Distribution and status of living colonies of Acropora spp. in the reef crests of a protected marine area of the Caribbean (Jardines de la Reina National Park, Cuba).

The reef crests of the Jardines de la Reina National Park (JRNP) are largely formed by Acropora palmata, but colonies of A. cervicornis and the hybrid A. prolifera are also present. This study shows spatial distribution of colonies, thickets and live fragments of these species in the fore reefs. Snorkeling was used to perform the direct observations. The maximum diameter of 4,399 colonies of A. palmata was measured and the health of 3,546 colonies was evaluated. The same was done to 168 colonies of A. cervicornis and 104 colonies of A. prolifera. The influence of the location and marine currents on a number of living colonies of A. palmata was analyzed. For such purpose, reef crests were divided into segments of 500 m. The marine park was divided into two sectors: East and West. The Caballones Channel was used as the reference dividing line. The park was also divided into five reserve zones. We counted 7,276 live colonies of Acropora spp. 1.4% was A. prolifera, 3.5% A. cervicornis and 95.1% A. palmata. There were 104 thickets of A. palmata, ranging from eight to 12 colonies, and 3,495 fragments; 0.6% was A. cervicornis and the rest A. palmata (99.4%). In the East sector, 263 colonies (3.8% of the total), six thickets (5.8%) and 32 fragments (1%) of A. palmate were recorded. In the same sector, there were 11 fragments (50%) of A.cervicornis and two (2%) colonies of A. prolifera. Health of A. palmata was evaluated as good and not so good in the study area. Health of A. cervicornis was critical and health of A. prolifera was good in all five reserve zones. There was a significant increase in the number of colonies from east to west (Χ2 = 11.5, gl = 3.0, p = 0.009). This corroborates the existence of an important abundance differences between the eastern and the western region of the JRNP. A negative relationship was observed between the number of colonies and the distance from the channel (Χ2 = 65.0, df = 3.0, p < 0.001). The influence of the channel, for the live colonies of A. palmata is greater within the first 2,000 m. It then decreases until approximately 6,000 m, and no significant increase beyond. The orientation of the reef crests significantly influenced the abundance of the colonies (Χ2 = 15.5, df = 2.9, p = 0.001). The results presented here provide a baseline for future research on the status of the populations of Acropora spp., considering that there has been a certain recovery of the species A. palmata during the last 10–16 years. Given the current status of the populations of Acropora spp., conservation actions focusing A. cervicornis should be prioritized.

Experimental support for alternative attractors on coral reefs

Ecological theory predicts that ecosystems with multiple basins of attraction can get locked in an undesired state, which has profound ecological and management implications. Despite their significance, alternative attractors have proven to be challenging to detect and characterize in natural communities. On coral reefs, it has been hypothesized that persistent coral-to-macroalgae “phase shifts” that can result from overfishing of herbivores and/or nutrient enrichment may reflect a regime shift to an alternate attractor, but, to date, the evidence has been equivocal. Our field experiments in Moorea, French Polynesia, revealed the following: ( i ) hysteresis existed in the herbivory–macroalgae relationship, creating the potential for coral–macroalgae bistability at some levels of herbivory, and ( ii ) macroalgae were an alternative attractor under prevailing conditions in the lagoon but not on the fore reef, where ambient herbivory fell outside the experimentally delineated region of hysteresis. These findings help explain the different community responses to disturbances between lagoon and fore reef habitats of Moorea over the past several decades and reinforce the idea that reversing an undesired shift on coral reefs can be difficult. Our experimental framework represents a powerful diagnostic tool to probe for multiple attractors in ecological systems and, as such, can inform management strategies needed to maintain critical ecosystem functions in the face of escalating stresses.