Sexual propagation of corals specifically for reef rehabilitation remains largely experimental. In this study, we refined low technology culture and transplantation approaches and assessed the role of colony size and age, at time of transfer from nursery to reef, on subsequent survival. Larvae from Acropora millepora were reared from gametes and settled on engineered substrates, called coral plug-ins, that were designed to simplify transplantation to areas of degraded reef. Plug-ins, with laboratory spawned and settled coral recruits attached, were maintained in nurseries until they were at least 7 months old before being transplanted to replicate coral limestone outcrops within a marine protected area until they were 31 months old. Survival rates of transplanted corals that remained at the protected in situ nursery the longest were 3.9-5.6 times higher than corals transplanted to the reef earlier, demonstrating that an intermediate ocean nursery stage is critical in the sexual propagation of corals for reef rehabilitation. 3 years post-settlement, colonies were reproductively mature, making this one of few published studies to date to rear a broadcasting scleractinian from eggs to spawning adults. While our data show that it is technically feasible to transplant sexually propagated corals and rear them until maturity, producing a single 2.5-year-old coral on the reef cost at least US$60. 'What if' scenarios indicate that the cost per transplantable coral could be reduced by almost 80 %, nevertheless, it is likely that the high cost per coral using sexual propagation methods would constrain delivery of new corals to relatively small scales in many countries with coral reefs.
The synchrony of spawning is of paramount importance to successful coral reproduction. The precise timing of spawning is thought to be controlled by a set of interacting environmental factors, including regional wind field patterns, timing of the sunset, and sea surface temperatures (SST). Climate change is resulting in increased SST, which is causing physiological stress in corals and could also be altering spawning synchrony and timing. In this study, we examined the effect of increasing seawater temperature by 2°C for 1 month prior to the predicted spawning time on reproduction in the coral Acropora digitifera. This short period of elevated temperature caused spawning to advance by 1 day. In animals incubated at elevated temperature, egg number per egg bundle did not change, however, egg volume significantly decreased as did sperm number. Our results indicate that temperature is acting both as a proximate cue to accelerate timing and as a stressor on gametogenesis to reduce fecundity. This finding suggests that increasing SSTs could play a dramatic role in altering reproductive timing and the success of corals in an era of climate change.
Due to unregulated blast fishing and episodic bleaching events, the back-reef zone near Barangay Lucero in Bolinao, Pangasinan, Philippines, was reduced to a barren area of unconsolidated sand and coral rubble. Anecdotal accounts from local inhabitants, scientific reports, and examination of rubble on the substratum revealed that the area had been dominated by staghorn Acropora corals prior to degradation. With no significant signs of natural recovery, a low-tech restoration method that is both transferable to the community and cost-effective was devised and implemented. Through the help of local inhabitants, 450 fragments of two staghorn coral species (Acropora intermedia and A. pulchra) were transplanted, without using SCUBA equipment, in a total of six 4 × 4 m plots. There were two transplant density treatments: low and high, receiving 25 and 50 fragments of each coral species, respectively. Survivorship and growth of transplants, as well as the assemblage of fishes and macroinvertebrates inside the transplantation and control plots, were monitored periodically for up to 19 months. Transplant survivorship was generally high (68–89%) at the end of the study. There was also an average of a 15-fold increase in ecological volume of the transplants (from 1784.25 ± 162.75 to 26 540.765 ± 4547.25 cm3). Consequently, a significantly higher number of fish and of macroinvertebrates was recorded inside the transplantation plots than in the control plots, indicating signs of restoration success with the reintroduction of the two coral species. Exhibiting significant differences in coral cover, fish biomass and abundance, high-density is more cost-effective than low-density treatment, attaining optimal effects on key reef recovery parameters. The total cost of restoring a thicket of Acropora in a sandy-rubble field using this low-tech rehabilitation method with community participation was estimated to be US$9198.40 ha−1 (US$0.90 m−2), and thus ∼60% cheaper than without community involvement. Community involvement not only reduced the cost of the restoration activity but also provided the community with a sense of ownership and responsibility for their resources, thus ensuring the long-term success of the intervention.
Background: The technology in the production of sexual coral propagules for coral reef restoration is being actively developed recently to address concerns on the low genetic diversity in coral populations restored through transplantation of coral materials derived from fragmentation. Results: In this study, we produced coral spat attached to rubble and determined the effect of the addition of hatchery-reared trochus, a herbivorous gastropod, at two densities (one and two trochus per cage, equivalent to four and eight trochus per square meter, respectively) on the survivorship of the spat cultured in cages at the hatchery and in situ nursery. After 5 weeks of culture in the hatchery, spat survivorship was significantly higher in the two per cage trochus treatment (18.3% ± 6.7%, mean ± sd) than in the control (5.5% ± 1.7%), with the one per cage trochus treatment having intermediate spat survival (12.6% ± 7.9%). The enhanced spat survivorship, though not apparent in the in situ nursery culture, is attributed to the grazing effect of trochus as significantly lower turf algal cover was observed in rubble placed in two per cage trochus treatment (44.8% ± 3.2%) than in the one per cage trochus treatment and control (80.2% ± 6.5% and 76.3% ± 5.0%, respectively). Conclusions: This study demonstrates that trochus can be used to control algal cover and enhance survivorship of coral spat in caged culture, at least in the hatchery, for the production of sexually derived transplant materials for coral reef restoration.
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