Differential recruitment of benthic communities on neighboring artificial and natural reefs

Shedding light on the ability of benthic artificial reef (AR) communities to resemble those of a natural reef (NR) is of great importance if we are to harness ARs as tools for rehabilitation and restoration of degraded marine habitats. Studying recruitment processes to experimental settlement plates attached to ARs and NRs reveal the factors that shape community structure at the two reef types, and determine the ability of an AR to support communities similar to those found in adjacent natural habitats. In this study, conducted in Eilat (Red Sea), we used settlement plates to test the hypothesis that differences in benthic communities between ARs and NRs are derived from differential recruitment processes. A monitoring period of 18 months revealed great differences in the recruitment of corals and other benthic communities between the studied ARs and adjacent NRs. The ARs were either made of PVC or metal and 10-17 years old when the study commenced. The recruitment of soft corals reflected the species assemblage found in the area, consisting mainly of the family Nephtheidae and Xeniidae, species, while that of stony corals was mostly determined by the life history traits of the recruited taxa, e.g., the opportunistic nature of the family Pocilloporidae. Benthic organisms, mainly filter feeders like bryozoans, bivalves, sponges and tunicates, were more abundant at the ARs than at the NRs, mainly on the underside of the plates. We suggest that this differential recruitment resulted from a synergistic effect of abiotic and biotic factors, including current regime, sedimentation load and larval settlement preferences, which subsequently differentiated the composition of the benthic communities at the ARs and NRs. Thus, in order to construct an AR for restoration purposes, it must offer similar structural features to those found in the natural surrounding, leading to recruitment of local taxa. However, if the AR and NR will differ structurally, the composition of recruits will also differ and eventually the communities at the two reef types will become distinct, hereby increasing the species diversity in the area.     

Cannabinoids inhibit zebra mussel (Dreissena polymorpha) byssal attachment: a potentially green antifouling technology

Man-made submerged structures, including shipwrecks, offering substrata for fouling organisms and fish, have been classified secondarily as artificial reefs (ARs). The current approach in AR design is that of low-profile structures placed on the seabed and attempting to mimic natural reef (NR) communities with the aim of mitigating degraded marine ecosystems. To examine the validity of this concept, a long-term comparison of the developing AR fouling communities to those of nearby NRs is required. A survey of the fouling reefal organisms was conducted on seven shipwrecks (Red Sea, Egypt), comprising three young (ca 20 years old) and four old (?>?100 years old) unplanned ARs, in comparison to nearby NR communities. The hypothesis tested was that the age of the ARs shapes the structure of their fouling coral communities. The results demonstrated distinct differences between ARs and NRs and between young and old ARs. While the species composition on ARs may resemble that of NRs after approximately 20 years, obtaining a similar extent of coral cover may require a full century. Moreover, differences in structural features between ARs and NRs may lead to differences in species composition that persist even after 100 years.     

Fouling reefal communities on artificial reefs: does age matter?

Man-made submerged structures, including shipwrecks, offering substrata for fouling organisms and fish, have been classified secondarily as artificial reefs (ARs). The current approach in AR design is that of low-profile structures placed on the seabed and attempting to mimic natural reef (NR) communities with the aim of mitigating degraded marine ecosystems. To examine the validity of this concept, a long-term comparison of the developing AR fouling communities to those of nearby NRs is required. A survey of the fouling reefal organisms was conducted on seven shipwrecks (Red Sea, Egypt), comprising three young (ca 20 years old) and four old (>100 years old) unplanned ARs, in comparison to nearby NR communities. The hypothesis tested was that the age of the ARs shapes the structure of their fouling coral communities. The results demonstrated distinct differences between ARs and NRs and between young and old ARs. While the species composition on ARs may resemble that of NRs after approximately 20 years, obtaining a similar extent of coral cover may require a full century. Moreover, differences in structural features between ARs and NRs may lead to differences in species composition that persist even after 100 years.     

Community structure of stony and soft corals on vertical unplanned artificial reefs in Eilat (Red Sea): comparison to natural reefs

In many reef ecosystems, artificial reefs (AR) have become permanent additions to the area, sustaining well-developed benthic communities. Long-term studies on the development of AR coral communities are scarce, and comparisons with their natural surroundings are limited. The present study describes the stony and soft coral community structure of unplanned vertical AR in Eilat (Red Sea) that have progressed beyond the initial successional phases, and compares these to the adjacent natural reefs (NR). Coral communities were characterized using belt transects, conducted on 34- and 14-year-old unplanned AR, and on two proximate NR. Stony corals were the major component in the NR, while soft corals, mainly Nephtheidae, accounted for up to 90% of the total living coverage in the AR. This was attributed to physical and biological features associated with the ARs vertical orientation, which was absent in the NR, and to the life history traits of these soft corals. Community differences between the two AR were related to structural stability and age. The results suggest that AR may increase local heterogeneity and space availability by adding novel habitats, increasing production and elevating species diversity in the surroundings.Communicated by Biological Editor H.R. Lasker     

Effects of habitat relocation on fish community structure- a case study

Local habitat structure and the environment in which it occurs are some of the key components in the development of fish communities. In this case study we examined a snapshot of their relative role following relocation of four artificial reefs (ARs) from a coral reef environment to a sandy area with adjacent sea grass beds. Monitoring the fish communities on ARs and in the surrounding areas revealed that in their new locations, the ARs contained greater fish richness and abundance, with more diurnal than nocturnal fish, but their feeding guilds were similar to those of fish in the reef location. A multivariate analysis showed that the ARs had distinctly different fish assemblage from those of their surroundings regardless of their location. Nonetheless, we identified an effect of the surroundings on AR fish community assemblage. We propose that on a meso- scale, fish community structure is primarily dependent on the properties of the AR rather than on those of the surrounding environment.     

In situ nurseries enhance coral transplant growth in sedimented waters

In situ nurseries have been a crucial part of coral reef restoration initiatives for the past two decades. However, the advantages over direct transplantation in sedimented waters has yet to be examined. In the present study, we showed that Pachyseris speciosa and Pocillopora damicornis fragments reared in in situ nurseries (NR) in Singapore’s sedimented waters grew significantly faster (by three to five times) than those which were directly transplanted (DT) onto the substrates. The increased growth rate during the nursery phase augmented the size of NR transplants, and had a flow-on effect on their performance during the post-transplantation phase. Overall, the maximum diameter of the NR transplants was 1.8–2.7 times larger than DT transplants after 11 months. The growth enhancement of the nursery-reared transplants improved the cost-effectiveness of our restoration effort: the estimated cost per centimetre growth of NR transplants was one-fifth of the DT corals despite the additional costs incurred to construct the nurseries. These results highlight that coral nurseries are beneficial to reef restoration in chronically sedimented waters.     

Optimizing industrial‐scale coral reef restoration: comparing harvesting wild coral spawn slicks and transplanting gravid adult colonies

Accelerating coral reef restoration is a global challenge that has been attempted around the world. Previous attempts show varying levels of success at localized scales, but comparisons of cost and benefits to evaluate large‐scale reef restoration approaches are lacking. Here, we compare two large‐scale restoration approaches: the harvesting, development, and release of wild coral spawn slicks onto a target reef, with the transplantation of gravid coral colonies to provide a seed population and local source of larvae. Comparisons incorporate the best available information on demographic rates to estimate population growth, beginning at embryo production to colony maturity 4 years following deployment. Cost‐effectiveness is considered in a coarse manner. The harvesting, development, and controlled release of coral spawn slicks is anticipated to achieve large‐scale restoration of coral communities with low‐impact technology at low cost per colony. Harvesting wild spawn slicks has the potential to (1) transport billions of larvae up to thousands of kilometers that (2) are relevant to coral restoration efforts at vast geographical scales while (3) benefitting from the use of technology with extremely low impact on wild populations and (4) retaining natural genetic and species diversity needed to enhance the resilience of restored communities. Transplanting colonies is most useful from reefs designated to be impacted by infrastructural development by providing an opportunity for transfer to high value zones, from dedicated nurseries, and for brooding species. Our contribution provides insights into critical elements of both concepts, and we highlight information gaps in parameter uncertainties.     

Differential survival of nursery‐reared Acropora cervicornis outplants along the Florida reef tract

In recent decades, the Florida reef tract has lost over 95% of its coral cover. Although isolated coral assemblages persist, coral restoration programs are attempting to recover local coral populations. Listed as threatened under the Endangered Species Act, Acropora cervicornis is the most widely targeted coral species for restoration in Florida. Yet strategies are still maturing to enhance the survival of nursery‐reared outplants of A. cervicornis colonies on natural reefs. This study examined the survival of 22,634 A. cervicornis colonies raised in nurseries along the Florida reef tract and outplanted to six reef habitats in seven geographical subregions between 2012 and 2018. A Cox proportional hazards regression was used within a Bayesian framework to examine the effects of seven variables: (1) coral‐colony size at outplanting, (2) coral‐colony attachment method, (3) genotypic diversity of outplanted A. cervicornis clusters, (4) reef habitat, (5) geographical subregion, (6) latitude, and (7) the year of monitoring. The best models included coral‐colony size at outplanting, reef habitat, geographical subregion, and the year of monitoring. Survival was highest when colonies were larger than 15 cm (total linear extension), when outplanted to back‐reef and fore‐reef habitats, and when outplanted in Biscayne Bay and Broward–Miami subregions, in the higher latitudes of the Florida reef tract. This study points to several variables that influence the survival of outplanted A. cervicornis colonies and highlights a need to refine restoration strategies to help restore their population along the Florida reef tract.     

Perforated trapezoidal artificial reefs can augment the benefits of restoration of an island and its marine ecosystem

The Gulf of Mannar (GoM) is located along the southeast coast of India. It has a chain of 21 low‐lying uninhabited islands extending from Rameswaram to Tuticorin. These islands are endowed with coral reefs, beds of seagrasses, and other associated marine life. Growing human population has led to accelerated coral mining and destructive fishing practices and this has brought about changes in the bio‐geomorphology of the islands, altered the hydrodynamic conditions, and resulted in severe erosion of the islands. The area of Vaan Island had decreased from 20.8 ha in 1969 to 2.33 ha in 2015. While hard measures have proven successful in preventing erosion, ecosystem‐based measures taking into account the resilience of the flora and fauna yield greater and more natural benefits. A total of 10,600 perforated trapezoidal artificial reef (AR) modules were deployed in clusters along two rows on the windward side of Vaan Island. ARs of 1 and 2 m height were placed respectively along contours of 2 and 3 m depth. The shape and arrangement of the ARs dissipated wave energy through the shoaling effect. As a result, a spit appeared and the area increased to 3.15 ha. The ARs also support epibenthic communities, benthic macrofauna, corals, and fishes. The deployment of an ecosystem‐based multipurpose perforated trapezoidal AR model has been successful not only in restoring the sinking island but also in enhancing the species richness, and it can be adopted as a tool in the restoration of islands and their marine ecosystems.     

Can Coral Cover be Restored in the Absence of Natural Recruitment and Reef Recovery?

With many coral reef areas being degraded whether by anthropogenic or natural causes, a search is on for resilient species of corals that can restore coral cover where needed, if coral reefs are to continue to provide adequate ecosystem services. A series of experiments were undertaken in two sites with different environmental attributes and substrates in a lagoonal area in the northwestern Philippines to test the potentials of a local species, Porites cylindrica, for reef rehabilitation. With the use of asexual fragmentation of donor colonies, different treatments were tested, particularly to determine if the species would survive on different substrates, that is, solid, massive versus digitate/anastomosing, dead colonies. The results after nearly 2 years of the experiment were extraordinarily successful, with survival of transplants ranging from a high of 98% to a low of 80% of colonies, resulting in extensive coral cover on both original and new or different substrate from the original. A subsequent observation after another 16 months showed the coral cover to have been complete or nearly complete in the experimental plots, with the transplanted colonies fusing, and with evident reef fish communities where there were none before. Had there been no intervention, it is highly likely that the reefs would have remained in a degraded state .     

The use of larvae or recruits in coral restoration initiatives: Symbiodinium acquisition does not differ between coral life stages in the wild

Active restoration initiatives are increasingly considered in natural resource management. Laboratory‐reared coral larvae and recruits have been proposed for stock production but it is unknown if their use impacts subsequent symbiosis once transplanted to the reef. We exposed laboratory and field settled aposymbiotic recruits (recently settled <1 month) to Symbiodinium in the wild, then analyzed the acquired communities using ITS‐2 sequencing. There was no significant difference between treatments based on overall community and diversity metrics, or differential abundance of individual taxa. These results suggest that early acquisition is analogous and thus supports the use of either life‐stage as an option for reef restoration.     

Employing a highly fragmented,weedy coral species in reef restoration

A major determinant in reef restoration programs is the choice of species employed. In this paper, we concentrate on the potential use of Montipora digitata (Dana, 1846), a highly fragmented and weedy coral species, for reef restoration and for recreation of reef physiognomy in Bolinao, The Philippines, under the ‘gardening concept’. Coral ramets (n = 1960) were reared in a shallow lagoon nursery for 1 year and then, the resulting nursery-grown colonies were transplanted onto denuded reef knolls at two different sites and according to three transplantation designs (grid design with high or low density and patch design). The nursery grown ramets, which had initially exhibited a 99% survivorship, were reduced to 87% by a super typhoon. Low detachment rates, low mortality (<1% both) and low bleaching (<3% over most months), have been indicating good nursery conditions for corals. Monitoring transplanted colonies for over 15 months showed no significant differences between the sites or among the three different transplantation designs. The major events of mortality and detachment were documented during the first 3 months post-transplantation and in the wake of a bleaching event. M. digitata transplants exhibited rapid growth (a 384% increase in ecological volume) and frequent fragmentation. Some fragments remained by their colonies of origin entangled in the attached branches, while other fragments fell onto the surrounding sandy substrate, forming M. digitata ‘beds’ around the knolls. In both, nursery and transplanted corals, creation of complex 3D structures was followed by recruitment of juvenile fishes into aggregations. Above results reveal that employing fast growing, weedy and easily fragmenting branching species, which are also considered as ‘modifier species’, in reef restoration may result in a fast regeneration of reef physiognomy. Instead of ‘copying’ natural processes, reef managers should therefore concentrate on recovering the reef's ability for self-maintenance.     

象山港典型生境沉积物反硝化细菌群落丰度与结构多样性

通过高通量测序和qPCR技术对象山港4种典型生境(牡蛎养殖区OA、海带养殖区SA、自然岛礁区NR、人工鱼礁区AR)和对照区CK的沉积物反硝化细菌丰度和群落结构进行了测定分析,并探讨了反硝化细菌群落与环境因子之间的相关关系.结果表明:沉积物nirK型反硝化细菌丰度在5种生境间没有显著性差异,而沉积物nirS型反硝化细菌丰...     

Coral reef restoration in the Eastern Tropical Pacific: feasibility of the coral nursery approach

Due to the worldwide degradation of coral reefs, the active restoration of these ecosystems has received considerable attention in recent decades. This study investigated (1) the feasibility of using coral nurseries for restoration projects, (2) the minimum size required for a Pocillopora damicornis (Pocilloporidae) coral fragment to survive and grow in a nursery, and (3) the optimal transplant size of a fragment when transplanted to a degraded reef at Gorgona Island (Colombian Pacific). For this investigation, 230 fragments were transplanted directly to El Remanso reef, and another 150 fragments were maintained in in situ nurseries. Every 2 months, the length, weight, and survival of the fragments were recorded. After growing for 134 days in the nurseries, the 52 surviving fragments were transplanted to El Remanso reef, and after 5 months, the same variables were measured. Among the nursery‐reared fragments, the largest (4 to <8 cm) had the highest survival and growth rates, whereas among the directly transplanted fragments, the smallest fragments (<2 cm) had the highest survival and growth rates. However, the nursery‐reared fragments acquired greater structural complexity (arborescent morphology), and they were all alive 156 days after transplantation and presented a maximum linear growth rate of over 2 cm, which was higher than that of the directly transplanted fragments. Apparently, the arborescent morphology acquired during the nursery period provides advantages to the colonies that favor greater success when transplanted. Therefore, nursery‐reared fragments of P. damicornis between 2 and 4 cm are the most appropriate for use in restoration projects.     

The need for broader ecological and socioeconomic tools to evaluate the effectiveness of coral restoration programs

Coral reef restoration initiatives are burgeoning in response to the need for novel management strategies to address dramatic global declines in coral cover. However, coral restoration programs typically lack rigor and critical evaluation of their effectiveness. A review of 83 peer‐reviewed papers that used coral transplantation for reef restoration reveals that growth and survival of coral fragments were the most widely used indicators of restoration success, with 88% of studies using these two indicators either solely (55%) or in combination with a limited number of other ecological factors (33%). In 53% of studies, reef condition was monitored for 1 year or less, while only 5% of reefs were monitored for more than 5 years post‐transplantation. These results highlight that coral reef restoration science has focused primarily on short‐term experiments to evaluate the feasibility of techniques for ecological restoration and the initial establishment phase post‐transplantation, rather than on longer‐term outcomes for coral reef communities. Here, we outline 10 socioecological indicators that comprehensively evaluate the effectiveness of coral reef restoration across the four pillars of sustainability (i.e. environmental, sociocultural, governance, and economic contributions to sustainable communities). We recommend that evaluations of the effectiveness of coral restoration programs integrate ecological indicators with sociocultural, economic, and governance considerations. Assessing the efficacy of coral restoration as a tool to support reef resilience will help to guide future efforts and ensure the sustainable maintenance of reef ecosystem goods and services.     

Evaluating Methods for Transplanting Endangered Elkhorn Corals in the Virgin Islands

Restoration of rare corals is desirable and restoration projects are fairly common, but scientific evaluation of this approach is limited. We tested several techniques for transplant and restabilization of Acropora palmata (the elkhorn coral), an ecologically important Caribbean coral whose populations have suffered severe declines. In rough weather, fragments break‐off colonies of branching corals like A. palmata as a normal form of asexual reproduction. We transplanted naturally produced coral fragments from remnant populations to nearby restoration sites. Untouched control fragments at the donor site died faster and grew slower than fragments attached to the reef, so attaching fragments to the reef is beneficial. Transplanted fragments grew and died at a rate similar to fragments left at the donor site (both groups were attached to the reef), so there were no effects of moving fragments or differences in habitat quality between donor and restoration sites. Growth and survival were similar using four methods of attaching fragments to the reef: cable ties, two types of epoxy resin, and hydrostatic cement. Corals sometimes compete with the macroalgae that dominate degraded reefs, and clearing surrounding algae improved the growth of fragments. After 4 years, transplanted fragments grew to 1,450 cm² in area and so were potentially sexually active. Because the methods tested are simple and cheap, they could be used by volunteer recreational divers to restore locally extirpated A. palmata populations or to enhance reefs where natural recovery is slow.     

Motivations,success, and cost of coral reef restoration

Coral reef restoration is an increasingly important part of tropical marine conservation. Information about what motivates coral reef restoration as well as its success and cost is not well understood but is needed to inform restoration decisions. We systematically review and synthesize data from mostly scientific studies published in peer‐reviewed and gray literature on the motivations for coral reef restoration, the variables measured, outcomes reported, the cost per hectare of the restoration project, the survival of restored corals, the duration of the project, and its overall spatial extent depending on the restoration technique employed. The main motivation to restore coral reefs for the projects assessed was to further our ecological knowledge and improve restoration techniques, with coral growth, productivity, and survival being the main variables measured. The median project cost was 400,000 US$/ha (2010 US$), ranging from 6,000 US$/ha for the nursery phase of coral gardening to 4,000,000 US$/ha for substrate addition to build an artificial reef. Restoration projects were mostly of short duration (1–2 years) and over small spatial extents (0.01 ha or 108 m²). Median reported survival of restored corals was 60.9%. Future research to survey practitioners who do not publish their discoveries would complement this work. Our findings and database provide critical data to inform future research in coral reef restoration.     

Long-term heightened larval production in nursery-bred coral transplants

The ‘gardening coral reefs’ method is part of the approaches proposed for counteracting the substantial impacts of global climate change on the survival of coral reefs. It incorporates ecosystem engineering strategies for coral nursery farming and coral colonies out-planting. This study explores the reproductive output of three sets of nursery-grown Stylophora pistillata colonies along eight reproductive seasons following transplantation, as compared to that of native corals. When native and transplanted corals grew side by side in a disturbed environment, the nursery-grown transplants showed enhanced larval release (2.6–22.5 times more planulae/colony; multiyear average: 11.6±1.8 planulae/transplant vs. 1.5±0.3 planulae/native colony) with higher percentages of gravid colonies (91±2.1% transplants vs. 34±7.6% native colonies). The inherently enhanced larval production of transplants, maintained for such a long period of time post-transplantation, reveals a possible enduring impact of the nursery conditions on future fitness and ecological traits of transplants. This is further supported by the emerging documentation regarding the enhanced growth of corals under nursery conditions, which continues to be detected even years after transplantation was conducted on the natural reef. The above enhancement of coral reproduction can be harnessed as a human intervention tool for countering global climate change impacts.     

Restoration Strategies for Coral Reefs Damaged by Recreational Activities: The Use of Sexual and Asexual Recruits

The unique marine ecosystems of coral reefs express varying levels of degradation as a result of increasing anthropogenic pressures. This is the main reason why more than 200 coral reef localities were proclaimed as natural reserves or marine parks under varying legislation, rules, and monitoring and management programs. Ironically, the conventional management plans increased accessibility to many reef localities and enhanced dramatically the impact of tourism on reef habitats. Recreational activities including SCUBA and skin diving, fishing, human trampling, sediment re-suspension, and other damage caused by “innocent” visitors are causing a rapid deterioration of many reefs. Their destruction requires years and decades for full recovery. I propose to rehabilitate such damaged habitats by the alternate strategy of “gardening coral reefs” with asexual and sexual recruits. Coral branches, colony fragments, and whole small colonies (asexual recruits) and laboratory or in situ settled planula-larvae (sexual recruits) are designed to be transplanted into denuded reefs for restoration. This approach is further improved when the sexual and asexual recruits are maricultured in situ within special protected areas, before being transplanted. The use of sexual recruits ensures an increase in genetic diversity. I discuss several methodologies and results already accumulated showing the applicability of this gardening strategy for rehabilitation of denuded coral reefs. This restoration strategy should be integrated with proper management similar to that of already established reforestation in terrestrial habitats. The best candidates for employing this strategy are the fast-growing coral species, usually branching forms and species that brood their planulae larvae.     

Coral recruitment and juvenile mortality as structuring factors for reef benthic communities in Biscayne National Park, USA

Coral communities of Biscayne National Park (BNP) on offshore linear bank-barrier reefs are depauperate of reef corals and have little topographic relief, while those on lagoonal patch reefs have greater coral cover and species richness despite presumably more stressful environmental regimes closer to shore. We hypothesized that differences in rates of coral recruitment and/or of coral survivorship were responsible for these differences in community structure. These processes were investigated by measuring: (1) juvenile and adult coral densities, and (2) size-frequency distributions of smaller coral size classes, at three pairs of bank- and patch-reefs distributed along the north-south range of coral reefs within the Park. In addition, small quadrats (0.25 m²) were censused for colonies <2 cm in size on three reefs (one offshore and one patch reef in the central park, and one intermediate reef at the southern end), and re-surveyed after 1 year. Density and size frequency data confirmed that large coral colonies were virtually absent from the offshore reefs, but showed that juvenile corals were common and had similar densities to those of adjacent bank and patch reefs. Large coral colonies were more common on inshore patch reefs, suggesting lower survivorship (higher mortality) of small and intermediate sized colonies on the offshore reefs. The more limited small-quadrat data showed similar survivorship rates and initial and final juvenile densities at all three sites, but a higher influx of new recruits to the patch reef site during the single annual study period. We consider the size-frequency data to be a better indicator of juvenile coral dynamics, since it is a more time-integrated measurement and was replicated at more sites. We conclude that lack of recruitment does not appear to explain the impoverished coral communities on offshore bank reefs in BNP. Instead, higher juvenile coral mortality appears to be a dominant factor structuring these communities. Accepted: 9 September 1999