Crustose Coralline Algae Cover Research Articles

Benthic communities influence coral seeding success at fine spatial scales

The deployment of engineered substrates seeded with newly settled corals is a technique being developed to increase the numbers of juvenile corals on reefs with the goal of improving reef resilience in response to climate warming. Using a hierarchical sampling design, we explored the spatial scales at which seeded coral (spat) survival and growth varied in situ and investigated the environmental drivers of seeded spat success in the southern inshore Great Barrier Reef. After 10 months, variation in spat survival and size was greatest at the smallest spatial scale (1–2 m) (27 and 11% of variation, respectively), indicating the scale at which the main drivers of post‐settlement survival and growth are occurring. Crustose coralline algae (CCA) cover on seeding units prior to deployment was a significant driver of short‐ and long‐term spat survival (22% of variation). Survival of Acropora millepora and A. muricata spat did not differ according to benthic community variation. Increasing cover of branching Acropora corals was correlated with decreased survival and the size of Montipora aequituberculata spat, although CCA cover on plugs remained the most influential factor determining survival. Interspecific variation in spat survival and size and higher survival and size in the side‐facing orientation of the seeding units suggest natural variation in response to the seeding method, warranting further experiments to refine species selection and deployment methods prior to upscaling. High within‐site variation in seeded spat survival and size highlights the need for future studies of ecological factors driving post‐settlement mortality at fine spatial scales.

A quantitative assessment of the status of benthic communities on US Atlantic coral reefs using a novel standardized approach

As coral reefs decline globally, the need for an objective approach to quantify the status and trends of corals has become increasingly important. Empirical data on predisturbance conditions are rare, and integrating data from multiple and disparate survey designs and methods can be analytically challenging. Our goal was to conduct a holistic, data-driven evaluation of the status of corals and benthic communities in US Atlantic coral reef jurisdictions: Florida, Flower Garden Banks, Puerto Rico, and the US Virgin Islands. A quantitative approach based upon standardized data was used to compare the change in multiple indicators of coral condition (hard coral, macroalgae, and crustose coralline algae cover, coral density, and old mortality) from historic to current conditions in each geographic region. For each indicator, historic, reference baseline conditions from long-term monitoring data or literature data were first identified, reviewed, and classified on a categorical scale from Very Good to Critical by regional experts to account for condition changes that pre-dated current monitoring data. A reference-centering approach then allowed for categorization of statistical changes from historic to current conditions on the same scale to produce results that could be communicated to a broad audience. Our findings show continued declines for multiple indicators in all regions except Flower Garden Banks, illustrate particularly dire declines from regions that had been impacted by Stony Coral Tissue Loss Disease at the most recent monitoring included in this study, and demonstrate the increasingly critical need for effective coral reef conservation.

NAMBER: A biotic index for assessing the ecological quality of mesophotic biogenic reefs in the northern Adriatic Sea

Abstract The aim of the present study was to propose a biotic index (North Adriatic Mesophotic BiogEnic Reefs, NAMBER) suitable for assessing the ecological quality of the mesophotic biogenic reefs of the northern Adriatic continental shelf based on photographic sampling. At each of the 20 study sites, the degree of bioconstruction (expressed as percentage cover of crustose coralline algae), the α‐diversity (expressed as the mean number of taxa), and the degree of sensitivity to human disturbance and climate change (based on literature data and expert judgement) of the benthic assemblages were selected as descriptors and combined in the NAMBER index, using the best values that the three metrics can currently achieve in the studied region as a reference. The study highlighted that there was large spatial heterogeneity among reefs and high variability in the ecological quality values obtained by NAMBER, ranging from bad to high. The index indicates that reefs lying furthest from the coast, under substantially lower anthropogenic pressure, have a generally higher status of environmental quality. However, a clear geographical pattern did not emerge, as reefs close together often had different ecological qualities. The NAMBER index, which combines three ecological descriptors, in accordance with the requirements of the European Marine Strategy Framework Directive, represents a specific adaptation to the northern Adriatic Sea of a multimetric index previously developed for the north‐western Mediterranean Sea, capitalizing on previous knowledge and research efforts. This multimetric biotic index provides an effective standardized tool for monitoring programmes and environmental impact assessments in the northern Adriatic mesophotic biogenic reefs and lays the foundation for ecosystem‐based management and conservation in this basin.

A contemporary baseline of Madagascar's coral assemblages: Reefs with high coral diversity, abundance, and function associated with marine protected areas.

Madagascar is a major hotspot of biodiversity in the Western Indian Ocean, but, as in many other regions, coral reefs surrounding the island confront large-scale disturbances and human-induced local stressors. Conservation actions have been implemented with encouraging results for fisheries, though their benefit on coral assemblages has never been rigorously addressed. In this context, we analyzed the multiscale spatial variation of the composition, generic richness, abundance, life history strategies, and cover of coral assemblages among 18 stations placed at three regions around the island. The potential influences of marine protected areas (MPAs), algal cover, substrate rugosity, herbivorous fish biomass, and geographic location were also analyzed. Our results highlight the marked spatial variability, with variation at either or both regional and local scales for all coral descriptors. The northeast coastal region of Masoala was characterized by the high abundance of coral colonies, most notably of the competitive Acropora and Pocillopora genera and stress-tolerant taxa at several stations. The southwest station of Salary Nord was distinguished by lower abundances, with depauperate populations of competitive taxa. On the northwest coast, Nosy-Be was characterized by higher diversity and abundance as well as by high coral cover (~42–70%) recorded at unfished stations. Results clearly underline the positive effects of MPAs on all but one of the coral descriptors, particularly at Nosy-Be where the highest contrast between fished and unfished stations was observed. Biomass of herbivorous fishes, crustose coralline algae cover, and substrate rugosity were also positively related to several coral descriptors. The occurrence of reefs with high diversity, abundance, and cover of corals, including the competitive Acropora, is a major finding of this study. Our results strongly support the implementation of locally managed marine areas with strong involvement by primary users, particularly to assist in management in countries with reduced logistic and human resources such as Madagascar.

Coral reef erosion: In situ measurement on different dead coral substrates on a Caribbean reef

AbstractWidespread mortality of reef‐building coral substantially reduces the capacity for reef growth and makes available extensive bare substrate areas that in the absence of coral recovery will be eroded by a variety of external and internal bioeroders. Here, we analyze rates of external erosion on six different types of carbonate substrates under in situ conditions over a 2‐yr period. We measure vertical changes in the surface elevation of four species of recently dead corals afflicted by the stony coral tissue loss disease outbreak, and other two common types of calcareous substrates, long‐dead Acropora palmata fronds and bare calcareous hardground, as a reference for “bare” carbonate substrates that occur widely in Caribbean reefs. The surface of the recently dead colonies experienced significant erosion after 2 yr of exposure, but at different rates depending on the species. Dead skeletons of Orbicella faveolata experienced the greatest rates of erosion after 2 yr at −9.9 mm (±3.2 mm); Dendrogyra cylindrus eroded −3.6 mm (±2.8 mm), Pseudodiploria strigosa −3.3 mm (±3.7 mm), and Siderastrea siderea −1.2 mm (±0.9 mm), while long‐dead substrates remained unchanged. There was significant erosion in the presence of parrotfish grazing scars and of short algal turf mats, while crustose coralline algae cover and sand‐and‐high turf mats were not associated with significant changes in elevation, arguably indicating a protective effect. This study provides new insights into how and at what rates external carbonate erosion is shaping contemporary reefs at fine spatial and temporal scales.

Limitations to coral recovery along an environmental stress gradient.

Positive feedbacks driving habitat-forming species recovery and population growth are often lost as ecosystems degrade. For such systems, identifying mechanisms that limit the re-establishment of critical positive feedbacks is key to facilitating recovery. Theory predicts the primary drivers limiting system recovery shift from biological to physical as abiotic stress increases, but recent work has demonstrated that this seldom happens. We combined field and laboratory experiments to identify variation in limitations to coral recovery along an environmental stress gradient at Ningaloo Reef and Exmouth Gulf in northwest Australia. Many reefs in the region are coral depauperate due to recent cyclones and thermal stress. In general, recovery trajectories are prolonged due to limited coral recruitment. Consistent with theory, clearer water reefs under low thermal stress appear limited by biological interactions: competition with turf algae caused high mortality of newly settled corals and upright macroalgal stands drove mortality in transplanted juvenile corals. Laboratory experiments showed a positive relationship between crustose coralline algae cover and coral settlement, but only in the absence of sedimentation. Contrary to expectation, coral recovery does not appear limited by the survival or growth of recruits on turbid reefs under higher thermal stress, but to exceptionally low larval supply. Laboratory experiments showed that larval survival and settlement are unaffected by seawater quality across the study region. Rather, connectivity models predicted that many of the more turbid reefs in the Gulf are predominantly self seeded, receiving limited supply under degraded reef states. Overall, we find that the influence of oceanography can overwhelm the influences of physical and biological interactions on recovery potential at locations where environmental stressors are high, whereas populations in relatively benign physical conditions are predominantly structured by local ecological drivers. Such context-dependent information can help guide expectations and assist managers in optimizing strategies for spatial conservation planning for system recovery.

Warming Alters the Relationship Between Benthic Cover and Herbivores on Hawaiian Reefs

Increases in sea surface temperature impact animal metabolism, which in turn could influence benthic structure and resulting algal-coral balance. We utilized a long-term coral reef dataset from the west coast of Hawai‘i Island to investigate impacts of annual positive and negative sea surface temperature anomalies (SSTA) on benthic cover [algal turf, macroalgae, crustose coralline algae (CCA), and coral], herbivore density (sea urchins, grazers, browsers, and scrapers) and the relationship between benthic cover and herbivore density. Results showed significantly lower coral cover, but higher CCA cover with positive SSTA. Additionally, the density of sea urchins, grazers and browsers increased with increasing SSTA. Warming disrupted the normal relationship between herbivores and benthic cover on reefs, particularly for grazers where higher densities were coupled with lower algal turf cover only during negative SSTA. The direction of the relationship between benthic cover and herbivore type changed with positive SSTA, where increased algal turf cover was associated with increased herbivore density. Here, herbivores are likely responding accordingly to increases in food availability due to increased metabolism under warming. Despite herbivore populations increasing in density over the past two decades, algal turf cover remains on an upward trajectory. These results indicate that warming can alter herbivore-algal dynamics, where greater herbivore densities may be required to cause a reduction in algal turf cover. Protection of herbivores in addition to reducing nutrient input onto reefs will be essential in driving a reduction in algal turf cover on Hawaiian reefs.

Growth and carbonate production of crustose coralline algae on a degraded turbid reef system

Crustose coralline algae (CCA) and other encrusting calcifiers drive carbonate production on coral reefs. However, little is known about the rates of growth and calcification of these organisms within degraded turbid reef systems. Here we deployed settlement cards (N = 764) across seven reefs in Singapore for two years to examine spatio-temporal variation in encrusting community composition and CCA carbonate production. Our results showed that CCA was the dominant encrusting taxa (63.7% ± 18.3SD) across reefs. CCA carbonate production rates (0.009–0.052 g cm−2 yr−1) were less than half of those reported for most Indo-Pacific reefs, but similar to other turbid reef systems. Highest CCA carbonate production rates were observed furthest from Singapore's main shipping port, due to a relative increase in CCA cover on the offshore reefs. Our results suggest that proximity to areas of high industrialisation and ship traffic may reduce the cover of encrusting calcifying organisms and CCA production rates which may have negative, long-term implications for the stabilisation of nearshore reefs in urbanised settings.

Benthic micro- and macro-community succession and coral recruitment under overfishing and nutrient enrichment.

Herbivory and nutrient availability are fundamental drivers of benthic community succession in shallow marine systems, including coral reefs. Despite the importance of early community succession for coral recruitment and recovery, studies characterizing the impact of top-down and bottom-up drivers on micro- and macrobenthic communities at scales relevant to coral recruitment are lacking. Here, a combination of tank and field experiments were used to assess the effects of herbivore exclusion and nutrient enrichment on micro- to macrobenthic community succession and subsequent coral recruitment success. Herbivore exclusion had the strongest effect on micro- and macrobenthic community succession, including a community shift toward copiotrophic and potentially opportunistic/pathogenic microorganisms, an increased cover of turf and macroalgae, and decreased cover of crustose coralline algae. Yet, when corals settled prior to the development of a macrobenthic community, rates of post-settlement survival increased when herbivores were excluded, benefiting from the predation refugia provided by cages during their vulnerable early post-settlement stage. Interestingly, survival on open tiles was negatively correlated with the relative abundance of the bacterial order Rhodobacterales, an opportunistic microbial group previously associated with stressed and diseased corals. Development of micro- and macrobenthic communities in the absence of herbivory, however, led to reduced coral settlement. In turn, there were no differences in post-settlement survival between open and caged treatments for corals settled on tiles with established benthic communities. As a result, open tiles experienced marginally higher recruitment rates, driven primarily by the higher initial number of settlers on open tiles compared to caged tiles. Overall, we reveal that the primary interaction driving coral recruitment is the positive effect of herbivory in creating crustose coralline algae (CCA)-dominated habitats, free of fleshy algae and associated opportunistic microbes, to enhance coral settlement. The negative direct and indirect impact of fish predation on newly settled corals was outweighed by the positive effect of herbivory on the initial rate of coral settlement. In turn, the addition of nutrients further altered benthic community succession in the absence of herbivory, reducing coral post-settlement survival. However, the overall impact of nutrients on coral recruitment dynamics was minor relative to herbivory.

A centuries-old manmade reef in the Caribbean does not substitute natural reefs in terms of species assemblages and interspecific competition

With increasing maritime activities in the proximity of coral reefs, a growing number of manmade structures are becoming available for coral colonisation. Yet, little is known about the sessile community composition of such artificial reefs in comparison with that of natural coral reefs. Here, we compared the diversity of corals and their competitors for substrate space between a centuries-old manmade structure and the nearest natural reef at St. Eustatius, eastern Caribbean. The artificial reef had a significantly lower species richness and fewer competitive interactions than the natural reef. The artificial reef was dominated by a cover of crustose coralline algae and zoantharians, instead of turf algae and fire corals on the natural reef. Significant differences in species composition were also found between exposed and sheltered sites on both reefs. Our study indicates that even a centuries-old manmade reef cannot serve as a surrogate for natural reefs.

Encrusters maintain stable carbonate production despite temperature anomalies among two inshore island reefs of the Pilbara, Western Australia

Encrusting reef organisms such as crustose coralline algae (CCA), serpulid worms, bivalves, bryozoans, and foraminifera (collectively termed encrusters) provide essential ecosystem services and are a critical part of the reef framework. Globally, research into in situ growth and carbonate production of encrusters has focused on clear water fore-reef settings in the Pacific and Caribbean, with limited studies being conducted on marginal reef systems or within the Indian Ocean. Here we examined spatial and temporal variation in CCA coverage (%) and total encruster carbonate production rates (g cm−2 yr−1) across two inshore turbid island reefs of northern Western Australia. We recorded average carbonate production rates of 0.039 ± 0.002 g cm−2 yr−1, which are comparable to healthy reef sites globally. Our results show variation in lateral CCA cover over small spatial scales, with a strong seasonal signature, while constant average carbonate production rates were maintained. Additionally, we recorded in situ water temperatures above predicted coral bleaching threshold of 29 °C for four weeks and found annual patterns of sea surface temperature anomalies (SSTA) of 2 °C or more being a regular occurrence over the hotter months. Encrusters on these reefs are considered to have a vital contribution to the reef carbonate budgets, and if they maintain stable carbonate production through periods of SSTA, they may support net positive reef carbonate budgets.

Recruitment of Postlarval Abalone Haliotis spp. at Santa Catalina Island: Quantifying Natural Recovery

California abalone Haliotis spp., listed as species of concern, have been slow to recover, after 22 years of fishery closure, or are not recovering at all because of low-density populations and recruitment failure. It is not known if there is successful recruitment in populations in the wild in Southern California. This work examines, for the first time, whether newly settled abalones (<3 mm) are present in the wild at Santa Catalina Island to determine if recruitment is occurring. Natural cobbles with crustose coralline algae cover were sampled for recently settled abalones at two sites and at three depths over the reproductive season of green and pink abalone. A total of 128 abalone recruits (Haliotis spp.) were found over a cumulative rock surface area of 7.47 m2, on 325 cobbles, for a total recruitment density of 17.14 recruits per m2. Abalone recruits ranged in size from 220 to 2,120 µm, with an average recruit size of 490 ± 20 µm (mean ± SE, n = 124). Recruitment was similar across depths (2–4, 6–8, and 10–12 m) but differed between the two study sites, and was highest in June and September. Genetic work is needed to confirm species identification of the new recruits; however, they were most likely green abalone which would be consistent with the signs of green abalone recovery at the island. This work quantifies abalone settlement in Southern California, confirming successful recruitment. These methods can aid future restoration efforts empowering managers and restoration practitioners to monitor and quantify recruitment dynamics for abalones in California.

Interannual variability and decadal stability of benthic organisms on an Indonesian coral reef

AbstractThe availability of colonizable substrate is an important driver of the temporal dynamics of sessile invertebrates on coral reefs. Increased dominance of algae and, in some cases, sponges has been documented on many coral reefs around the world, but how these organisms benefit from non-colonized substrate on the reef is unclear. In this study, we described the temporal dynamics of benthic organisms on an Indonesian coral reef across two time periods between 2006 and 2017 (2006–2008 and 2014–2017), and investigated the effects of colonizable substrate on benthic cover of coral reef organisms at subsequent sampling events. In contrast with other Indonesian reefs where corals have been declining, corals were dominant and stable over time at this location (mean ± SE percentage cover 42.7 ± 1.9%). Percentage cover of turf algae and sponges showed larger interannual variability than corals and crustose coralline algae (CCA) (P &lt; 0.001), indicating that these groups are more dynamic over short temporal scales. Bare substrate was a good predictor of turf cover in the following year (mean effect 0.2, 95% CI: 0–0.4). Algal cover combined with bare space was a good predictor of CCA cover the following year generally, and of sponge cover the following year but only at one of the three sites. These results indicate that turf algae on some Indonesian reefs can rapidly occupy free space when this becomes available, and that other benthic groups are probably not limited by the availability of bare substrate, but may overgrow already fouled substrates.

Spatial distribution of benthic algae in the South China Sea: Responses to gradually changing environmental factors and ecological impacts on coral communities

AbstractAimIn this study, we investigated whether environmental factors can effectively control the spatial distribution of various benthic algae and examined the critical ecological impacts of algae on corals across the South China Sea (SCS). Relationships between benthic algae and environmental factors were assessed, and potential ecological impacts of algae on coral communities were evaluated across spatial scales.LocationA total of 104 sites at 12 coral reefs in four coral reef regions (CRRs) of the SCS (latitude range of 9–22° N).TaxaTurf algae, macroalgae (including fleshy macroalgae and Halimeda), crustose coralline algae (CCA), coral and juvenile coral.MethodsUsing diver‐based surveys (2015–2018), we investigated four CRRs with different reef distance to mainland (RDM) across the SCS. We obtained field data on benthic algal composition and cover, coral cover and diversity, and juvenile coral density. We also measured and collected the environmental factors (including seawater environmental parameters and reef fish diversity).ResultsThe cover of turf algae and CCA gradually decreased and increased, respectively, with an increase in RDM, which had a strong relationship with the gradually changing environmental factors. Random forest models suggested that nutrients, reef fish diversity, seawater transparency and temperature were the most important factors for predicting turf algae and CCA cover. Linear regression analyses showed a significant relationship between the turf algae, macroalgae, and CCA covers, and juvenile coral density.Main conclusionsOur results showed that gradually changing environmental factors were correlated with the spatial distributions of turf algae and CCA. However, the natural biophysical relationships between macroalgae and environmental factors may be disrupted by turf algal overgrowth and nutrient subsidies. Increases in all benthic algal groups significantly impacted coral recruitment, highlighting the critical role of benthic algae in determining the recovery trajectory of the Indo‐Pacific reefs that are threatened by human activities.

Rapid relative increase of crustose coralline algae following herbivore exclusion in a reef of El Salvador.

The Eastern Tropical Pacific (ETP) is one of the most isolated and least studied regions in the world. This particularly applies to the coast of El Salvador, where the only reef between Guatemala and Nicaragua, called Los Cóbanos reef, is located. There is very little published information about the reef’s biodiversity, and to our knowledge, no research on its ecology and responses to anthropogenic impacts, such as overfishing, has been conducted. The present study, therefore, described the benthic community of Los Cóbanos reef, El Salvador, using the Line-Point-Intercept-Transect method and investigated changes in the benthic community following the exclusion of piscine macroherbivores over a period of seven weeks. Results showed high benthic algae cover (up to 98%), dominated by turf and green algae, and low coral cover (0–4%). Porites lobata was the only hermatypic coral species found during the surveys. Surprisingly, crustose coralline algae (CCA) showed a remarkable total cover increase by 58%, while turf algae cover decreased by 82%, in experimental plots after seven weeks of piscine macroherbivore exclusion. These findings apparently contradict the results of most previous similar studies. While it was not possible to ascertain the exact mechanisms leading to these drastic community changes, the most likely explanation is grazing on turf by small grazing macroherbivores that had access to the cages during the experiment and clearing of CCA initially covered by epiphytes and sediments. A higher CCA cover would promote the succesful settlement by corals and prevent further erosion of the reef framework. Therefore it is crucial to better understand algal dynamics, herbivory, and implications of overfishing at Los Cóbanos to avoid further reef deterioration. This could be achieved through video surveys of the fish community, night-time observations of the macroinvertebrate community, exclusion experiments that also keep out herbivorous macroinvertebrates, and/or experimental assessments of turf algae/CCA interactions.

Gross calcium carbonate production in Eastern Tropical Pacific coral reefs (Gorgona Island, Colombia)

The production and accumulation of carbonate reef framework is the positive component of reef development. The main organisms participating in this process are corals and crustose coralline algae (CCA) because their combined calcareous skeletons construct and help to consolidate reef frameworks. We assessed the contribution (i.e. gross production) of corals and CCA to the calcium carbonate (CaCO3) budget of the 2 largest and most developed reefs of Gorgona Island (Pacific coast of Colombia). On each zone (back reef [BR], reef flat [RP], reef front [RF], and reef slope [RS]) of these reefs, we measured substrate rugosity, coral (Pocillopora spp.) and CCA cover, colony density for corals, skeletal density for CCA, and growth rates for the estimation of CaCO3 production rates. Pocillopora spp. corals contributed 93.1% of the total carbonate production, while CCA supplied the remaining 6.9%. CaCO3 production was higher at Playa Blanca reef, although CaCO3 production in the RF of La Azufrada (12.31 kg m-2 yr-1) was higher in comparison to the RF at Playa Blanca (8.45 kg m-2 yr-1). Otherwise, CaCO3 production was higher in all other reef zones (BR, RP, RS) of Playa Blanca, although only significantly higher in the BR (2.25 kg m-2 yr-1 at Playa Blanca against 0.29 kg m-2 yr-1 at La Azufrada). The RF contributed the most CaCO3, mainly due to its high live coral cover and rapid coral growth. Although the contribution of CCA is low, they are key for reef stability. CaCO3 production rates reported here (2.86 and 3.80 kg m-2 yr-1 in La Azufrada and Playa Blanca, respectively) are within the limits reported for Eastern Tropical Pacific reefs, and raise hope for the continued existence of coral reefs in an era of increasing threats to this ecosystem.

Ecomorphological divergence and trophic resource partitioning in 15 syntopic Indo-Pacific parrotfishes (Labridae: Scarini)

AbstractAdaptive diversification is a product of both phylogenetic constraint and ecological opportunity. The species-rich parrotfish genera Scarus and Chlorurus display considerable variation in trophic cranial morphology, but these parrotfishes are often described as generalist herbivores. Recent work has suggested that parrotfish partition trophic resources at very fine spatial scales, raising the question of whether interspecific differences in cranial morphology reflect trophic partitioning. We tested this hypothesis by comparing targeted feeding substrata with a previously published dataset of nine cranial morphological traits. We sampled feeding substrata of 15 parrotfish species at Lizard Island, Great Barrier Reef, Australia, by following individuals until focused biting was observed, then extracting a bite core 22 mm in diameter. Three indices were parameterized for each bite core: substratum taphonomy, maximum turf height and cover of crustose coralline algae. Parrotfish species were spread along a single axis of variation in feeding substrata: successional status of the substratum taphonomy and epilithic and endolithic biota. This axis of trophic variation was significantly correlated with cranial morphology, indicating that morphological disparity within this clade is associated with interspecific partitioning of feeding substrata. Phylogenetic signal and phylomorphospace analyses revealed that the evolution of this clade involved a hitherto-unrecognized level of trophic diversification.

Fish farm effluents alter reef benthic assemblages and reduce coral settlement

Fish farming in coastal areas is a rapidly growing industry. However, unregulated fish farming practices that release massive amounts of unconsumed feed and fecal material into the water column, can result in a nutrient-enriched environment that extends to nearby reef systems. To understand the impact of fish farm effluent on coral settlement, we tested the settlement rate of Pocillopora acuta larvae on artificial substrates conditioned for 12 weeks at three sites with increasing distance (2–10 km) from fish farms in Bolinao, Philippines. Sites far from the fish farms had higher biofilm and crustose coralline algae cover. In contrast, the site closest to the fish farms, where nutrient levels were higher, had greater sediment and turf algae cover. Tiles conditioned at the farther sites promoted higher (6–8%) larval settlement whereas tiles from the nearer site had lower settlement (3%). These findings show that fish farm effluents can indirectly affect coral settlement on adjacent reefs by promoting growth of other biota that may inhibit larval settlement and by reducing the availability of suitable substrate.

Native Herbivores Improve Sexual Propagation of Threatened Staghorn Coral Acropora cervicornis

Staghorn coral Acropora cervicornis was once spatially dominant on Caribbean reefs but is now threatened throughout its range. In recent years, advancements in ex-situ sexual propagation of Caribbean corals have increased the viability of this management strategy. Thus, improving culture methods for sexually propagated corals is important to bolster the overall coral restoration portfolio and increase genetic diversity in restored populations. In both natural systems and culture scenarios, algae proliferation negatively impacts coral growth and survival. Growing coral with native herbivores may represent a strategy for increased efficiency. We tested A. cervicornis recruits raised in replicate aquaria with identical densities of juvenile Lithopoma americanum or juvenile Batillaria minima snails plus a no-snail control. Each of three replicates per treatment contained tiles with similar numbers of recently settled, visually healthy, A. cervicornis. Tiles were photographed every three weeks for five months and coral growth, survivability, turf algae cover, and crustose coralline algae (CCA) cover were quantified. Labor time for cleaning was carefully recorded for each treatment. Results indicated improved growth and survival when A. cervicornis recruits were raised with either snail species in comparison to a no-herbivore control. Further, including snails decreased labor and eliminated turf algae cover. Interestingly, L. americanum significantly reduced CCA cover relative to the other treatments. We report some of the highest survival rates observed to date for sexually propagated Atlantic corals. Ultimately, results suggest that rearing sexually propagated A. cervicornis with native herbivores could improve the ability to employ these corals in reef restoration.

Settlement ecology of scleractinian corals of the Northeastern Tropical Pacific

Reproduction and recruitment are essential processes for the continued success of coral communities. Islas Marias Archipelago is considered a connectivity node among coral communities distributed along the Northeastern Tropical Pacific (NTP); as such, sexual reproduction of scleractinian corals affects the maintenance of the local populations and the long-distance connectivity of reefs across the region. In this study, successful sexual reproduction in the species of the three most abundant scleractinian corals genera was demonstrated, in part by documenting gamete presence and maturation in tissues and spatio-temporal variability in juvenile coral settlement, which were quantified across substrate type, habitat quality, and environmental factors. Only 12 larvae recruited (ten Porites, two Pavona) to artificial substrates, and monthly recruitment density of 1.82 ± 0.23 recruits m−2 (n = 383) was recorded on natural substrates. There were significant differences between genera, with Porites producing the highest density of recruits (0.60 ± 0.45 recruits m−2, followed by Pavona (0.52 ± 0.24 recruits m−2) and Pocillopora (0.28 ± 0.06 recruits m−2). The highest coral recruitment was observed at Baby Reef (2.57 ± 0.46 recruits m−2), followed by Cleofas II (1.81 ± 0.21 recruits m−2) and Japanese Garden (1.24 ± 0.46 recruits m−2); the former site was characterized by the highest cover of crustose coralline algae. We found successful recruitment of the main reef-forming species in the Mexican Pacific and suggest that Islas Marias is a region of critical importance in terms of its function as a source of genetic variability, and, the generation of, new individuals that will be key to sustaining coral reef ecosystems in the NTP.