Forereef Sites Research Articles

Corals survive severe bleaching event in refuges related to taxa, colony size, and water depth

Marine heatwaves are increasing in frequency and duration, threatening tropical reef ecosystems through intensified coral bleaching events. We examined a strikingly variable spatial pattern of bleaching in Moorea, French Polynesia following a heatwave that lasted from November 2018 to July 2019. In July 2019, four months after the onset of bleaching, we surveyed > 5000 individual colonies of the two dominant coral genera, Pocillopora and Acropora, at 10 m and 17 m water depths, at six forereef sites around the island where temperature was measured. We found severe bleaching increased with colony size for both coral genera, but Acropora bleached more severely than Pocillopora overall. Acropora bleached more at 10 m than 17 m, likely due to higher light availability at 10 m compared to 17 m, or greater daily temperature fluctuation at depth. Bleaching in Pocillopora corals did not differ with depth but instead varied with the interaction of colony size and Accumulated Heat Stress (AHS), in that larger colonies (> 30 cm) were more sensitive to AHS than mid-size (10–29 cm) or small colonies (5–9 cm). Our findings provide insight into complex interactions among coral taxa, colony size, and water depth that produce high spatial variation in bleaching and related coral mortality.

Ecological and environmental predictors of juvenile coral density across the central and western Pacific

The persistence of Pacific coral reefs is threatened by large-scale mortality resulting from heat stress, storms, overfishing, disease, and land-based pollution. While reefs have demonstrated the ability to recover from these disturbances, recovery potential is highly variable; in part driven by the high spatial variability in the abundance of coral juveniles. However, our understanding of the patterns and predictors of juvenile coral density is hampered by the limited geographic scope of previous studies. Our objectives in this study were to: (1) explore the spatial and temporal patterns of juvenile (1- < 5cm in diameter) colony density across the U.S.-affiliated Pacific islands and atolls; and (2) identify the potential role of ecological and environmental factors which may influence coral juvenile abundance. Juvenile density was quantified as part of NOAA’s National Coral Reef Monitoring Program between 2013 and 2019 using a stratified sampling design across 1,405 forereef sites on 34 islands and atolls. Regional mean juvenile density varied from 1.4 to 10.5 colonies m-2 with the highest densities observed in the northern Mariana Islands, Northwestern Hawaiian Islands, and southern Mariana Islands. Juvenile density significantly increased between sampling periods in the Main Hawaiian Islands, Line Islands and northern Mariana Islands. Survey-weighted generalized linear modeling demonstrated that juvenile density was best predicted by the interaction between time since a heat stress event and heat stress severity, depth, site and sector-level percent coral cover, human density, percent unconsolidated substrate, macroalgal cover, herbivore biomass, and the interaction of sector coral cover area and heat stress, and the interaction of wave power (combination of wave height and period) and heat stress. With the unique scale and gradients across the U.S. Pacific, our study found that the high latitude regions have enhanced juvenile density compared to their lower latitude counterparts. Our results also suggest density is most dependent on the timing and severity of heat stress, depth, stock-recruitment with an open adult population, availability of suitable habitat at the site-scale, and the number of humans in the system.

Ontogenetic Migration of Juvenile Grunts (Haemulon) across a Coral Reef Seascape: Pathways and Potential Mechanisms

Many coral reef fishes undergo ontogenetic migrations from inshore nurseries to offshore reefs. Quantifying cross-habitat connectivity is important for understanding reef fish spatio-temporal dynamics, essential habitat and spatial planning. Past studies show connectivity is mediated by distance and habitat arrangement. Few studies have documented the pathways linking juveniles and adults, nor suggested underlying orientation/navigation processes important for a more generalized understanding of ontogenetic habitat use. Ontogenetic movements of juvenile grunts, primarily Haemulon flavolineatum, in Puerto Rico were studied using mark-recapture. Small juveniles were tagged at a back-reef site designed to determine their potential movement through a series of size-specific daytime resting schools and posing a choice of direction in migration. Larger juveniles were tagged at mid-shelf reefs to capture off-reef migration to adult locations, including a proposed marine reserve. Small juveniles moved toward more exposed areas, accomplished by progressively shifting locations through existing resting schools. Movement was size-related and alongshore, but direction was primarily parallel to the coast, leading fish away from adjacent areas more directly offshore. Direction may have resulted from the potential mechanism of fish transfer between resting schools rather than by orientation cues. Larger juveniles were tracked from back-reef to fore-reef sites, but no fish were recaptured off-reef. Slower growth than predicted may have contributed to the perceived lack of movement. Localized behavior and habitat distribution appear important in determining the initial pathways of ontogenetic migration, and these may fix later directional movements to unexpected areas.

Spatiotemporal Variation in Coral Assemblages and Reef Habitat Complexity among Shallow Fore-Reef Sites in the Florida Keys National Marine Sanctuary

With the unprecedented degradation and loss of coral reefs at multiple scales, the underlying changes in abiotic and biotic features relevant to the three-dimensional architecture of coral reefs are critical to conservation and restoration. This study characterized the spatiotemporal variation of habitat metrics at eight fore-reef sites representing three management zones in the Florida Keys, USA using visual habitat surveys (2017–2018) acquired before and after Hurricane Irma. Post-hurricane, five of those sites were surveyed using structure-from-motion photogrammetry to further investigate coral morphology on structural complexity. Multivariate results for visual surveys identified moderate separation among sites, with fished sites characterized by complex physical features such as depth and vertical hard relief while protected sites generally harbored high abundances of live coral cover. Three-dimensional models of mapped sites showed within site variation as another driver in site separation. Additionally, fine-scale orthoimage analyses identified significant differences in dominant coral morphologies at each mapped site. This study suggests protected reef sites generally harbor higher live coral cover despite some fished sites being structurally similar in seabed topography. Our work provides fine-scale spatial data on several managed sites within a marine sanctuary and highlights the contribution of diverse coral assemblages to the coral reef framework.

Twenty years of change in benthic communities across the Belizean Barrier Reef.

Disease, storms, ocean warming, and pollution have caused the mass mortality of reef-building corals across the Caribbean over the last four decades. Subsequently, stony corals have been replaced by macroalgae, bacterial mats, and invertebrates including soft corals and sponges, causing changes to the functioning of Caribbean reef ecosystems. Here we describe changes in the absolute cover of benthic reef taxa, including corals, gorgonians, sponges, and algae, at 15 fore-reef sites (12-15m depth) across the Belizean Barrier Reef (BBR) from 1997 to 2016. We also tested whether Marine Protected Areas (MPAs), in which fishing was prohibited but likely still occurred, mitigated these changes. Additionally, we determined whether ocean-temperature anomalies (measured via satellite) or local human impacts (estimated using the Human Influence Index, HII) were related to changes in benthic community structure. We observed a reduction in the cover of reef-building corals, including the long-lived, massive corals Orbicella spp. (from 13 to 2%), and an increase in fleshy and corticated macroalgae across most sites. These and other changes to the benthic communities were unaffected by local protection. The covers of hard-coral taxa, including Acropora spp., Montastraea cavernosa, Orbicella spp., and Porites spp., were negatively related to the frequency of ocean-temperature anomalies. Only gorgonian cover was related, negatively, to our metric of the magnitude of local impacts (HII). Our results suggest that benthic communities along the BBR have experienced disturbances that are beyond the capacity of the current management structure to mitigate. We recommend that managers devote greater resources and capacity to enforcing and expanding existing marine protected areas and to mitigating local stressors, and most importantly, that government, industry, and the public act immediately to reduce global carbon emissions.

A doubling of stony coral cover on shallow forereefs at Carrie Bow Cay, Belize from 2014 to 2019

To better understand the decline of one of earth’s most biodiverse habitats, coral reefs, many survey programs employ regular photographs of the benthos. An emerging challenge is the time required to annotate the large volume of digital imagery generated by these surveys. Here, we leverage existing machine-learning tools (CoralNet) and develop new fit-to-purpose programs to process and score benthic photoquadrats using five years of data from the Smithsonian MarineGEO Network’s biodiversity monitoring program at Carrie Bow Cay, Belize. Our analysis shows that scleractinian coral cover on forereef sites (at depths of 3–10 m) along our surveyed transects increased significantly from 6 to 13% during this period. More modest changes in macroalgae, turf algae, and sponge cover were also observed. Community-wide analysis confirmed a significant shift in benthic structure, and follow-up in situ surveys of coral demographics in 2019 revealed that the emerging coral communities are dominated by fast-recruiting and growing coral species belonging to the genera Agaricia and Porites. While the positive trajectory reported here is promising, Belizean reefs face persistent challenges related to overfishing and climate change. Open-source computational toolkits offer promise for increasing the efficiency of reef monitoring, and therefore our ability to assess the future of coral reefs in the face of rapid environmental change.

Wave exposure shapes reef community composition and recovery trajectories at a remote coral atoll

In a time of unprecedented ecological change, understanding natural biophysical relationships between reef resilience and physical drivers is of increasing importance. This study evaluates how wave forcing structures coral reef benthic community composition and recovery trajectories after the major 2015/2016 bleaching event in the remote Chagos Archipelago, Indian Ocean. Benthic cover and substrate rugosity were quantified from digital imagery at 23 fore reef sites around a small coral atoll (Salomon) in 2020 and compared to data from a similar survey in 2006 and opportunistic surveys in intermediate years. Cluster analysis and principal component analysis show strong separation of community composition between exposed (modelled wave exposure > 1000 J m−3) and sheltered sites (< 1000 J m−3) in 2020. This difference is driven by relatively high cover of Porites sp., other massive corals, encrusting corals, soft corals, rubble and dead table corals at sheltered sites versus high cover of pavement and sponges at exposed sites. Total coral cover and rugosity were also higher at sheltered sites. Adding data from previous years shows benthic community shifts from distinct exposure-driven assemblages and high live coral cover in 2006 towards bare pavement, dead Acropora tables and rubble after the 2015/2016 bleaching event. The subsequent recovery trajectories at sheltered and exposed sites are surprisingly parallel and lead communities towards their respective pre-bleaching communities. These results demonstrate that in the absence of human stressors, community patterns on fore reefs are strongly controlled by wave exposure, even during and after widespread coral loss from bleaching events.

Effects of habitat, fishing, and fisheries management on reef fish populations in Palau

Palau has a rich tradition of fisheries management and stewardship of its waters, and as in many island nations, small-scale coral reef fisheries are a vital part of the local culture, economy, and food security. However, reef fisheries in Palau are data-poor and there is increasing concern that reef fish stocks are declining. To evaluate the current and future status of these resources, information is needed on the abundance, biomass, and size structure of reef fish resource species. To this aim, the Palau International Coral Reef Center (PICRC) conducted a nation-wide study to investigate the status of commercially important reef fish stocks in 2017. Fishery-independent surveys were conducted by diver operated stereo-video (stereo-DOV) at 94 sites across the archipelago. Results showed that fish biomass varied from 0.13 to 293 g m−2. Habitat was the most significant predictor of fish biomass, with the highest biomass found at western fore-reef sites and the lowest at inner reef sites. Region also affected fish biomass, with significantly higher biomass found in the Northern Reefs compared to those around Babeldaob (the largest island in Palau). In channel habitats, marine protected area (MPA) proximity, fishing pressure from Koror (Palau’s main population center), and local fishing pressure significantly influenced fish biomass. In western fore-reef habitats, fish biomass was significantly affected by region, with differences observed between the Northern Reefs and Babeldaob, and between the Southern Reefs and Babeldaob. Fishing pressure from Koror had a significant effect on fish biomass in inner reef habitats, with a weak negative relationship observed. Using length frequencies from the stereo-DOV surveys we also estimated spawning potential ratio (SPR) for seven species and found the majority had SPR values between 20 % and 40 %. Overall, the low fish biomass and SPRs suggests that many of Palau’s principal fisheries species have been overexploited. This is the first study to evaluate the status of resource reef fish stocks across the main islands of Palau and provides a baseline to assess changes in fish populations over time.

Hurricane impacts on a coral reef soundscape.

Soundscape ecology is an emerging field in both terrestrial and aquatic ecosystems, and provides a powerful approach for assessing habitat quality and the ecological response of sound-producing species to natural and anthropogenic perturbations. Little is known of how underwater soundscapes respond during and after severe episodic disturbances, such as hurricanes. This study addresses the impacts of Hurricane Irma on the coral reef soundscape at two spur-and-groove fore-reef sites within the Florida Keys USA, using passive acoustic data collected before and during the storm at Western Dry Rocks (WDR) and before, during and after the storm at Eastern Sambo (ESB). As the storm passed, the cumulative acoustic exposure near the seabed at these sites was comparable to a small vessel operating continuously overhead for 1–2 weeks. Before the storm, sound pressure levels (SPLs) showed a distinct pattern of low frequency diel variation and increased high frequency sound during crepuscular periods. The low frequency band was partitioned in two groups representative of soniferous reef fish, whereas the high frequency band represented snapping shrimp sound production. Daily daytime patterns in low-frequency sound production largely persisted in the weeks following the hurricane. Crepuscular sound production by snapping shrimp was maintained post-hurricane with only a small shift (~1.5dB) in the level of daytime vs nighttime sound production for this high frequency band. This study suggests that on short time scales, temporal patterns in the coral reef soundscape were relatively resilient to acoustic energy exposure during the storm, as well as changes in the benthic habitat and environmental conditions resulting from hurricane damage.

Extracellular Reef Metabolites Across the Protected Jardines de la Reina, Cuba Reef System

Coral reef ecosystems are incredibly diverse marine biomes that rely on nutrient cycling by microorganisms to sustain high productivity in generally oligotrophic regions of the ocean. Understanding the composition of extracellular reef metabolites in seawater, the small organic molecules that serve as the currency for microorganisms, may provide insight into benthic-pelagic coupling as well as the complexity of nutrient cycling in coral reef ecosystems. Jardines de la Reina (JR), Cuba is an ideal environment to examine extracellular metabolites across protected and high-quality reefs. Here, we used liquid chromatography mass spectrometry (LC-MS) to quantify specific known metabolites of interest (targeted metabolomics approach) and to survey trends in metabolite feature composition (untargeted metabolomics approach) from surface and reef depth (6 – 14 m) seawater overlying nine forereef sites in JR. We found that untargeted metabolite feature composition was surprisingly similar between reef depth and surface seawater, corresponding with other biogeochemical and physicochemical measurements and suggesting that environmental conditions were largely homogenous across forereefs within JR. Additionally, we quantified 32 of 53 detected metabolites using the targeted approach, including amino acids, nucleosides, vitamins, and other metabolic intermediates. Two of the quantified metabolites, riboflavin and xanthosine, displayed interesting trends by depth. Riboflavin concentrations were higher in reef depth compared to surface seawater, suggesting that riboflavin may be produced by reef organisms at depth and degraded in the surface through photochemical oxidation. Xanthosine concentrations were significantly higher in surface reef seawater. 5′-methylthioadenosine (MTA) concentrations increased significantly within the central region of the archipelago, displaying biogeographic patterns that warrant further investigation. Here we lay the groundwork for future investigations of variations in metabolite composition across reefs, sources and sinks of reef metabolites, and changes in metabolites over environmental, temporal, and reef health gradients.

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.

Dietary and habitat niche partitioning in congeneric cryptobenthic reef fish species

Ecological niches hold critical information concerning the eco-evolutionary dynamics that govern biodiversity and abundance patterns. Cryptobenthic reef fishes account for approximately half of all reef fish species and are an abundant and important group on coral reefs worldwide. Yet, due to their small size and inconspicuous lifestyles, relatively little is known about the ecological niches of most cryptobenthic species. Here, we use gut content DNA metabarcoding to determine dietary niche overlap and prey richness in four sympatric species of cryptobenthic reef fishes in two genera (Acanthemblemaria aspera, A. spinosa, Enneanectes altivelis, and E. matador). Furthermore, we test whether dietary differentiation corresponds with differences in species distribution patterns across twelve sites on the Mesoamerican Barrier Reef in Belize. Our approach reveals dietary partitioning among the four species, which is further supported by low edge density and high modularity in the resulting trophic network. A. spinosa and E. matador consume a significantly higher richness of prey items than their congeners. This result corresponds with non-random distributions and co-occurrence patterns in both species pairs: the two high prey richness species (A. spinosa and E. matador) co-occur more frequently than predicted by chance, but they are exclusive to exposed forereef sites with high wave action. In contrast, their congeners occur across exposed forereef and sheltered backreef sites, but they do not increase in numbers at sheltered sites. Our findings suggest that A. spinosa and E. matador monopolize a wide variety of prey in exposed habitats, but they are unable to meet the energetic demands of their adaptation to high-flow habitats in sheltered areas, possibly due to lower prey availability. This, in turn, indicates strong ecological differentiation among closely related species of cryptobenthic fishes, driven by links between diet, physiology, prey availability, and wave exposure.

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.

Diel population and functional synchrony of microbial communities on coral reefs

On coral reefs, microorganisms are essential for recycling nutrients to primary producers through the remineralization of benthic-derived organic matter. Diel investigations of reef processes are required to holistically understand the functional roles of microbial players in these ecosystems. Here we report a metagenomic analysis characterizing microbial communities in the water column overlying 16 remote forereef sites over a diel cycle. Our results show that microbial community composition is more dissimilar between day and night samples collected from the same site than between day or night samples collected across geographically distant reefs. Diel community differentiation is largely driven by the flux of Psychrobacter sp., which is two-orders of magnitude more abundant during the day. Nighttime communities are enriched with species of Roseobacter, Halomonas, and Alteromonas encoding a greater variety of pathways for carbohydrate catabolism, further illustrating temporal patterns of energetic provisioning between different marine microbes. Dynamic diel fluctuations of microbial populations could also support the efficient trophic transfer of energy posited in coral reef food webs.

Baseline Assessment of Net Calcium Carbonate Accretion Rates on U.S. Pacific Reefs.

This paper presents a comprehensive quantitative baseline assessment of in situ net calcium carbonate accretion rates (g CaCO3 cm-2 yr-1) of early successional recruitment communities on Calcification Accretion Unit (CAU) plates deployed on coral reefs at 78 discrete sites, across 11 islands in the central and south Pacific Oceans. Accretion rates varied substantially within and between islands, reef zones, levels of wave exposure, and island geomorphology. For forereef sites, mean accretion rates were the highest at Rose Atoll, Jarvis, and Swains Islands, and the lowest at Johnston Atoll and Tutuila. A comparison between reef zones showed higher accretion rates on forereefs compared to lagoon sites; mean accretion rates were also higher on windward than leeward sites but only for a subset of islands. High levels of spatial variability in net carbonate accretion rates reported herein draw attention to the heterogeneity of the community assemblages. Percent cover of key early successional taxa on CAU plates did not reflect that of the mature communities present on surrounding benthos, possibly due to the short deployment period (2 years) of the experimental units. Yet, net CaCO3 accretion rates were positively correlated with crustose coralline algae (CCA) percent cover on the surrounding benthos and on the CAU plates, which on average represented >70% of the accreted material. For foreeefs and lagoon sites combined CaCO3 accretion rates were statistically correlated with total alkalinity and Chlorophyll-a; a GAM analysis indicated that SiOH and Halimeda were the best predictor variables of accretion rates on lagoon sites, and total alkalinity and Chlorophyll-a for forereef sites, demonstrating the utility of CAUs as a tool to monitor changes in reef accretion rates as they relate to ocean acidification. This study underscores the pivotal role CCA play as a key benthic component and supporting actively calcifying reefs; high Mg-calcite exoskeletons makes CCA extremely susceptible changes in ocean water pH, emphasizing the far-reaching threat that ocean acidification poses to the ecological function and persistence of coral reefs worldwide.

Assessing relative resilience potential of coral reefs to inform management

Ecological resilience assessments are an important part of resilience-based management (RBM) and can help prioritize and target management actions. Use of such assessments has been limited due to a lack of clear guidance on the assessment process. This study builds on the latest scientific advances in RBM to provide that guidance from a resilience assessment undertaken in the Commonwealth of the Northern Mariana Islands (CNMI). We assessed spatial variation in ecological resilience potential at 78 forereef sites near the populated islands of the CNMI: Saipan, Tinian/Aguijan, and Rota. The assessments are based on measuring indicators of resilience processes and are combined with information on anthropogenic stress and larval connectivity. We find great spatial variation in relative resilience potential with many high resilience sites near Saipan (5 of 7) and low resilience sites near Rota (7 of 9). Criteria were developed to identify priority sites for six types of management actions (e.g., conservation, land-based sources of pollution reduction, and fishery management and enforcement) and 51 of the 78 sites met at least one of the sets of criteria. The connectivity simulations developed indicate that Tinian and Aguijan are each roughly 10 × the larvae source that Rota is and twice as frequent a destination. These results may explain the lower relative resilience potential of Rota reefs and indicates that actions in Saipan and Tinian/Aguijan will be important to maintaining supply of larvae. The process we describe for undertaking resilience assessments can be tailored for use in coral reef areas globally and applied to other ecosystems.

Efectos de la posición en el arrecife y del linaje en el crecimiento de Acropora cervicornis (Scleractinia:Acroporidae) en una plantación de vivero en Bahía Montego, Jamaica

The reef-building coral Acropora cervicornis was a dominant ecosystem element on the Caribbean reef until the 1980s, when it declined by some 97% due primarily to anthropogenic ecosystem changes and disease. This branching species expanded its colony footprint and achieved local dominance largely through fragmentation and regrowth, thus is suited to nursery culture towards restoration. In this experiment, fragments of Acropora cervicornis of four lineages or genets were followed and measured for growth and health over 12 months in 2006 and 2007 on buoyant drop-loop line nurseries at one shallow and one deep fore-reef site in Montego Bay, Jamaica. Sixty-five of these corals were then out-planted to wild reef sites of similar depth and condition to their respective nurseries and monitored photographically for 11 months through 2007 and 2008. A period of rapid death was seen in the out-planted material at both sites over the first four months, followed by a period of relative stability or recuperation. Hermodice carunculata predation was the primary problem in the shallow fore-reef, and was combined with a banding syndrome at the deeper site. This syndrome was noted in the samples prior to planting, during a one week storage period on the seafloor. Continued slow decline occurred in the subsequent seven months in the shallow fore-reef site; however, regrowth was noted in the deeper site in the remaining material. Including these losses, final total live coral length was more than fourfold greater than the initial wild harvest: a net increase through multi-stage propagative restoration or coral gardening. Returns were noted particularly in the faster-growing genets of the nursery and larger planted corals tended to retain more material at eleven months, suggesting that propagative restoration programmes invest in stronger genets and larger corals. Adaptive management and maintenance gardening of the planted material and reef would likely have greatly improved outcomes. Rev. Biol. Trop. 62 (Suppl. 3): 95-106. Epub 2014 September 01.

Increased Algal Dominance Despite Presence of &lt;I&gt;Diadema Antillarum&lt;/I&gt; Populations on a Caribbean Coral Reef

Populations of Diadema antillarum (Philippi, 1845) have been slow to recover after their 1983 Caribbean-wide massive mortality. The continued absence of this important coral reef herbivore as well as further impacts on local and regional-scales have severely threatened the health of coral reefs. From 2008 to 2011, the population of D. antillarum and structure of the benthic community were monitored within Akumal Bay, Mexico, a heavily impacted ecosystem. Across the 4 yrs of the study, densities of adult D. antillarum did not significantly change and were highest on backreef sites (mean 1.30 and 1.44 m−2). Coral cover was low at all sites (maximum 14%) and decreased during the 4 yrs of the study. Changes in crustose coralline algae (CCA) cover varied by year but was significantly higher on forereef sites, while cover by turf-algal-sediment (TAS) increased at all four sites. Diadema antillarum densities correlated positively with coral and CCA cover in the backreef sites where sea urchin densities were higher but no correlation occurred with TAS and turf. Where Echinometra lucunter (Linnaeus, 1758) sea urchins were more prevalent, their densities correlated negatively with coral and positively with CCA. Although densities of adult D. antillarum were comparable to other regions of the Caribbean, increases in TAS over the 4 yrs of this study may be evidence that even an important herbivore cannot prevent continued decline of a reef in an impacted ecosystem. Coral reefs in the Caribbean have experienced major disturbances over the past few decades and continue to be under a combination of stressors including bleaching, overexploitation of herbivores, coral diseases, and declining water quality, which has resulted in an increase in macroalgae cover (Knowlton 1992, Aronson and Precht 2001, Hughes et al. 2003, Bellwood et al. 2004). The importance of long-spined sea urchin, Diadema antillarum (Philippi, 1845), in removing macroalgae cover became evident after their massive mortality in 1983, when algal biomass abruptly increased (de Ruyter van Steveninck and Bak 1986, Carpenter 1988, Hughes 1994). As the populations of D. antillarum recover after their 1983 Caribbean-wide massive mortality (Lessios et al. 1984b, Lessios 2005), it remains unclear if grazing by this herbivore provides a suitable driver from which to expect a decrease in macroalgal cover on impacted coral reefs. Modeled scenarios indicate that sea urchins impart significant resilience to Caribbean reefs such that continued decline is inevitable when sea urchins are scarce (Mumby et al. 2006). However, abundant literature indicates it is a combination of factors which impacts the benthic dynamics on coral reefs and the propensity for shifts between dominant states [e.g., competition for space (Sandin and McNamara 2012), herbivore diversity (Cheal et al. 2010), biotic histories (Aronson et al. 2004), global climate change and marine diseases (Aronson and Precht 2006)]. CORAL REEF PAPER FastTrack➲ publication

Coexistence of congeneric spiny lobsters on coral reefs: differential use of shelter resources and vulnerability to predators

The notion, previously generated from laboratory experiments, that the local coexistence of spiny lobsters Panulirus guttatus and Panulirus argus on Caribbean reefs may be promoted by a differential use of shelter resources and/or vulnerability to predators was explored in a coral reef in Mexico. Multiple regressions with data collected on 11 occasions on fixed back-reef and fore-reef sites suggested that the densities of the congener, other crevice-dwellers, and predators did not significantly affect the density of P. argus in either reef zone, or of P. guttatus on the back-reef, where coexistence of both lobster species was greatest. In contrast, there was a significant negative relationship between predators and the density of P. guttatus on the fore-reef, where this species was dominant. Congeneric cohabitation in dens was less than expected by chance, but this pattern may reflect a differential use of shelter resources rather than interspecific competition. P. guttatus was more prevalent in dens over the middle and upper third of the reef profile, and P. argus over the lower and middle third of the reef profile. Whether individuals cohabited with conspecifics, congeners, or resided solitarily, P. guttatus was more prevalent at the walls and/or ceiling and P. argus on the floor of dens. This differential use of shelter resources may be related to the differential vulnerability to predators, which may have promoted local coexistence of these congeners in reef habitats.

Boundary layer turbulence and flow structure over a fringing coral reef

Measurements of velocity and rates of turbulence were made across a fringing coral reef in the Gulf of Aqaba, Red Sea, to determine the effect that the rough topography has on boundary layer mixing and flow dynamics. Observations were made at two fore-reef sites and a nearby sandy slope. The friction velocity, u*, and drag coefficient, CD, were determined directly from turbulent Reynolds stresses measured using acoustic Doppler velocimeters. Values of CD for the coral substrates ranged from 0.009 to 0.015, three to five times greater than over the sandy bottom site. The turbulence dissipation rate, ε, was determined by fitting spectra of vertical velocity to the theoretical “5/3” law expected for the inertial subrange of turbulence. There was a local balance between production and dissipation of turbulent kinetic energy, signifying that we could estimate u* from either the mean velocity profile, turbulence, or dissipation rate of turbulent kinetic energy. Estimates from all three measures agreed well with mean u*/Uo ranging from 0.10 ± 0.03 to 0.12 ± 0.03, indicating that existing turbulent boundary layer flow theory can be applied to flows over the rough topography of coral reefs. The bottom topography, by enhancing both reef scale and local drag and mixing levels, allows reef biota to more effectively exchange dissolved and particulate matter with oceanic waters.