Corresponding author: Phanor Hernando Montoya Maya ( email@example.com )
Academic editor: Isabel Sousa-Pinto
© 2016 Phanor Hernando Montoya Maya, Kaylee Pamela Smit, April Jasmine Burt, Sarah Frias-Torres.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation: Montoya-Maya PH, Smit KP, Burt AJ, Frias-Torres S (2016) Large-scale coral reef restoration could assist natural recovery in Seychelles, Indian Ocean. Nature Conservation 16: 1-17. https://doi.org/10.3897/natureconservation.16.8604
The aim of ecological restoration is to establish self-sustaining and resilient systems. In coral reef restoration, transplantation of nursery-grown corals is seen as a potential method to mitigate reef degradation and enhance recovery. The transplanted reef should be capable of recruiting new juvenile corals to ensure long-term resilience. Here, we quantified how coral transplantation influenced natural coral recruitment at a large-scale coral reef restoration site in Seychelles, Indian Ocean. Between November 2011 and June 2014 a total of 24,431 nursery-grown coral colonies from 10 different coral species were transplanted in 5,225 m2 (0.52 ha) of degraded reef at the no-take marine reserve of Cousin Island Special Reserve in an attempt to assist in natural reef recovery. We present the results of research and monitoring conducted before and after coral transplantation to evaluate the positive effect that the project had on coral recruitment and reef recovery at the restored site. We quantified the density of coral recruits (spat <1 cm) and juveniles (colonies 1-5 cm) at the transplanted site, a degraded control site and a healthy control site at the marine reserve. We used ceramic tiles to estimate coral settlement and visual surveys with 1 m2 quadrats to estimate coral recruitment. Six months after tile deployment, total spat density at the transplanted site (123.4 ± 13.3 spat m-2) was 1.8 times higher than at healthy site (68.4 ± 7.8 spat m-2) and 1.6 times higher than at degraded site (78.2 ± 7.17 spat m-2). Two years after first transplantation, the total recruit density was highest at healthy site (4.8 ± 0.4 recruits m-2), intermediate at transplanted site (2.7 ± 0.4 recruits m-2), and lowest at degraded site (1.7 ± 0.3 recruits m-2). The results suggest that large-scale coral restoration may have a positive influence on coral recruitment and juveniles. The effect of key project techniques on the results are discussed. This study supports the application of large-scale, science-based coral reef restoration projects with at least a 3-year time scale to assist the recovery of damaged reefs.
Reef recovery, coral transplantation, coral settlement, coral recruitment, Acroporidae, Pocilloporidae, Western Indian Ocean
A key principle in ecological restoration is to re-establish self-sustaining and resilient ecosystems, similar to their reference ecosystems (
The 1998 mass coral bleaching event severely affected the reefs of the Indian Ocean (
Could coral transplantation have a positive effect on coral recruitment and therefore enhance reef recovery at the restored site? Coral recruitment did not change when comparing sites with coral settlement structures with and without coral transplants (Maldives,
Our aim was to evaluate the effects of large-scale coral restoration on coral recruitment in a no-take marine reserve. We assessed the spatial differences in natural coral recruitment and juveniles after coral transplantation. We quantified coral recruitment and juveniles at the transplanted site and two untouched sites: healthy and degraded. The healthy and degraded sites served as a reference for natural coral recruitment. We hypothesized that coral recruitment and juveniles would be highest at the healthy site, intermediate at the transplanted site, and lowest at the degraded site. This study will contribute to our understanding of the effectiveness of large-scale coral restoration in enhancing natural coral recruitment or in accelerating reef recovery.
The study site was a continuous fringing reef on the south-west side of Cousin Island (Figure
Study area and live coral cover and family composition at each site. A Locations of Seychelles, Cousin Island, donor site (Les Parisiennes) and the three study sites: healthy control, degraded control and transplanted. Lower panel shows the seascape and concrete blocks with tiles at B healthy control (HC) C transplanted (T) and D degraded control (DC) sites. E Change in average (± SE) live coral cover (% of total area) for individual sites between the start (November 2012) and the end (June 2014) of the transplantation project. F Family (ACR =
Our experience in the local conditions indicated strong (~0.5 m s-1) bidirectional currents along the reef with no clear seasonal pattern due to local winds, tides and bathymetry (
We deployed settlement tiles onto the reef between 9th and 15th January 2014, over 14 months after first coral transplantation. Based on our coral reproduction monitoring, this deployment schedule allowed approximately 3 weeks biological conditioning of the tiles prior to the first expected coral spawning in the area, the first week of February 2014 (Montoya-Maya, unpublished data).
Coral recruitment (spat <1 cm) was compared among all three study sites over a six-month period using settlement tiles. Two ceramic tiles (16 × 16 × 0.8 cm) were placed separately on a concrete block and secured with a plastic cable tie. Flat ceramic tiles attached to concrete blocks were used, rather than other more efficient coral settlement methods (e.g. tiles of differing texture and orientation;
Coral juveniles were assessed four times: before transplantation, 12, 18 and 24 months after first transplantation. Abundance and diversity were quantified at genus level for coral juveniles by SCUBA diving and counting the number of juvenile scleractinian corals (<5 cm in diameter) within 1 m2 quadrats on natural substrate. At the transplanted, degraded and healthy sites, six 10-m transects were deployed and within each transect three quadrats were randomly placed (using a random number table) for juvenile coral abundance. The substratum of each quadrat was carefully examined for non-fragmented small colonies. Any obstructive macroalgae was parted when necessary. Colonies resulting from fission, shrinkage or fragmentation of older colonies were excluded. Because individual corals were not being monitored through time and fixed quadrats were not used, estimates were considered as total number of juveniles (i.e. new juveniles and old juveniles) and not as an estimate of recruitment rates (i.e. number of new recruits per unit time).
The experimental design we used was a compromise between scientific objectives and the time required to implement a large-scale coral reef restoration project. We acknowledge the limitations such an approach has in our ability to statistically test the effect of the coral transplantation effort. Accordingly, differences in recruit and juvenile density between the three sites were evaluated using generalized linear mixed models (GLMMs) with a Poisson error structure, with the log link function and site as a fixed effect. There were two types of random factors. In recruit density, we used tile nested within cement block to account for pseudo replication. In juvenile density, we used time and quadrat nested within transects to account for pseudo replication and irregular monitoring intervals. We used the likelihood radio (LR) test to determine the influence of fixed and random effects on recruit and juvenile densities by comparing the fit for models with and without the conditions (
During the six-month study, 326 spat were counted across all sites: 192 (58.9%) recruited on the upper surface of the tile and 134 (41.1%) settled on the sides. Pocilloporid corals predominated at all sites (80.7% of recruits) followed by other families (13.5%) and Acroporidae (5.8%). The average density was 2.8 ± 0.19 spat tile-1 (86 ± 6.1 spat m-2) and ranged from 0 to 13 spat tile-1 (0 - 351.4 spat m-2). Although the contribution of Pocilloporidae to the total number of spat at each site varied slightly (71.6-89.9%), the contribution of Acroporidae at the healthy site (12.6%) was higher than transplanted site (2.0%; Figure
Total recruitment varied significantly among sites (LR test: χ2 = 15.50, df = 2, P < 0.001) and similar results were found for the three coral taxa examined (Acroporidae: χ2 = 6.77, df = 2, P = 0.034; Pocilloporidae: χ2 = 11.2, df = 2, P = 0.004; Other families: χ2 = 12.10, df = 2, P = 0.002). Spat density at the transplanted site was 1.6 times (0.46 ± 0.15, β ± SE on the logit scale; Figure
Estimated influence (marker) and 95% confidence intervals (lines) of each study site (DC – degraded control; HC – healthy control; T – transplanted) on coral recruitment and juveniles of
Estimates of spat and juvenile densities (mean ± SE) of Acroporidae, Pocilloporidae, other coral families (Other) and all families combined (All taxa) for each study site.
|Taxon||Healthy Control||Degraded Control||Transplanted|
|Spat tile-1||0.3 ± 0.08||0.1 ± 0.06||0.1 ± 0.04|
|Spat m-2||9.7 ± 2.61||3.3 ± 1.95||3.3 ± 1.30|
|Juvenile m-2||2.1 ± 0.24||0.7 ± 0.16||1.0 ± 0.19|
|Spat tile-1||1.7 ± 0.22||1.9 ± 0.22||3.1 ± 0.43|
|Spat m-2||55.4 ± 7.17||61.9 ± 7.20||101.0 ± 14.01|
|Juvenile m-2||1.4 ± 0.18||0.4 ± 0.09||0.6 ± 0.11|
|Spat tile-1||0.4 ± 0.04||0.1 ± 0.06||0.6 ± 0.13|
|Spat m-2||13.0 ± 1.30||3.3 ± 1.95||19.5 ± 4.23|
|Juvenile m-2||1.6 ± 0.16||0.5 ± 0.11||1.1 ± 0.21|
|Spat tile-1||2.1 ± 0.24||2.4 ± 0.22||3.8 ± 0.41|
|Spat m-2||68.4 ± 7.82||78.2 ± 7.17||123.8 ± 13.35|
|Juvenile m-2||4.8 ± 0.40||1.7 ± 0.26||2.7 ± 0.38|
Throughout the four sampling periods between November 2012 and October 2014, 527 juveniles were counted in 216 quadrats. The overall juvenile density was 3.1 ± 0.19 juveniles m-2, ranging from 0 to 16 recruits m-2. Acroporid juveniles were 40.2% of the total coral juveniles across sampling periods, followed by other families (37.2%) and Pocilloporidae (22.6%). The family distribution of coral juveniles was similar between sampling periods and between study sites (Figure
Total juveniles varied among sites (χ2 = 35.13, df = 2, P < 0.001) and similar results were obtained for the three coral taxa examined (Acroporidae: χ2 = 27.69, df = 2, P < 0.001; Pocilloporidae: χ2 = 23.48 df = 2, P < 0.001; Other families: χ2 = 18.73, df = 2, P < 0.001). The healthy site had the highest total juvenile density (GLMM, ɀ = 6.74, P < 0.001; Table
Mean (±SE) numbers of juveniles observed at the three study sites by sampling period. Data are presented for all individuals combined and for Acroporidae, Pocilloporidae and other families separately. Dates correspond to the four sampling periods. Statistical significant differences (P < 0.05) between sites are also shown.
Estimates of the effects of sampling period on coral juveniles across the three sampled sites. Estimated coefficient (marker) and 95% confidence intervals (lines) are shown for all individuals combined (ALL) and for
We quantified spatial differences in natural coral recruitment and juveniles after large-scale coral transplantation by comparing two untouched control sites (healthy and degraded) with the transplanted site. Coral recruitment was assessed >14 months after first transplantation using a single tile deployment. Six months after tile deployment, total spat density at the transplanted site was 1.8 times higher than the healthy site and 1.6 higher than the degraded site, but the magnitude of variation in coral recruitment between the transplanted site and the degraded site was up to 6 times for coral families other than Pocilloporidae and Acroporidae. Spatial variation in early coral recruitment is common between and within reefs (
We propose three reasons to explain the increase in coral recruitment at the transplanted site. First, the transplanted corals increase local production of coral larvae. The transplanted colonies were large enough at transplantation time (>15 cm) to have a high probability of being mature (
Coral juveniles were assessed over a 2-year period that included sampling before and after coral transplantation. Total juvenile density and that of the three taxa examined was highest at the healthy site, intermediate at the transplanted site and lowest at the degraded site. Juvenile density at the transplanted site was consistently higher than the degraded site: between 1.1 (Acroporidae) to 1.9 (Pocilloporidae) times higher. Structural complexity is related to higher recovery rates due to enhanced recruit survival (e.g. indirectly reduces competition with algae and erosion by urchins or loose rubble;
The healthy-degraded-transplanted site cluster lacks replication at multiple locations and multiple times which limits the generalization of our results (
Our results are consistent with conclusions and best practices outlined in previous studies of coral reef restoration for species selection and transplant substrate. The use of brooding species in reef restoration projects is seen as a particularly effective form of transplantation (
The effects of project size, duration and location should also be considered. Increasing the size of the transplanted area and expanding the monitoring time are required to observe any positive effects of active reef restoration (
Our approach confirmed the hypothesis that scleractinian coral recruitment and juveniles will be higher at the transplanted site than at the degraded site. As coral reefs continue to degrade, it is imperative that we understand how active reef restoration impacts natural reef recovery. We have shown coral transplantation with colonies large enough to be reproductive results in higher structural complexity, self-recruitment and recruitment of non-transplanted species. These results confirm coral reef restoration can be sustainable in the long-term. Enhanced natural coral settlement and recruitment resulting from coral transplantation holds great promise for the success and long-term sustainability of large-scale coral reef restoration, at least for those projects aimed at assisting the recovery of naturally degraded reefs in the Seychelles.
We thank S. Beach, S.C. Klaus, E. Martin, C. Reveret, K. Rowe and N. Taylor for help during fieldwork. N. Shah and K. Henri at Nature Seychelles for managing the Reef Rescuers Project. A. Hennie from Black Pearl Seychelles, for allowing us to use their stereomicroscope. Several anonymous reviewers gave constructive criticisms improving the manuscript. Funding to Nature Seychelles was received through the United States Agency for International Development (USAID) Reef Rescuers Project 674-A-00-10-00123-00.