Coral nursery

Bachelor thesis research project

The previously dominant, reef-building Acropora cervicornis abundance decreased drastically across the greater Caribbean area since the 1970s. This is mainly due to the white band disease (WBD) and coral bleaching events. They have been considered a critically endangered species by the IUCN Red List since 2008 and restoration efforts are paramount to assist recovery of this species population. The exceptionally high growth rate and possibility of fragmenting this species, make it very suitable for coral gardening. This technique grows coral colonies from small fragments in ex- or in-situ coral nurseries before out-planting them into the natural reef. To test which locations are best suited for focusing future out-planting efforts, all previous out-planting trials have been analyzed to select three promising locations. In this research, two rebar frames have been installed at each of these locations. Per location, one frame was equipped with 20 fragments of the genotype ‘HiC’ and the other one with 20 fragments of the genotype ‘LL’. For the following 70 days fragment health, survival, growth rates, sediment settlement, and turbidity have been measured biweekly. The growth rates at location ‘Nursery’ and ‘Big Rock Market’ did not differ, however, at location ‘Hole in the Corner’ the genotype HiC had a significantly higher growth rate compared to the other locations and genotypes. The high amount and variation of turbidity and sedimentation at the Nursery make this location unsuitable for out-planting efforts. Sedimentation at Big Rock Market was exceptionally low and consistent, which could benefit out-planting efforts, but faster growth rates at Hole in the Corner will yield more coral. Because the locations are approximately 1.5km apart and both are considered suitable, it is recommended to outplant at and in between both locations instead of focusing out-planting efforts on one location, in order to increase the resilience of the out-planting efforts against natural stressors such as new outbreaks of the WBD.

Over millions of people around the globe depend on coral reefs for their livelihood and food. Coral reefs also play an important role in coastal protection against strong wave activities and coastal ero-sion. Globally coral reefs have been declining in the past few decades, due to human-induced climate change and anthropogenic disturbances e.g. coastal development, pollution, overfishing, anchoring etc. The worldwide decline in coral abundance along with losses in key ecosystem services, has prompted multiple efforts to mitigate further losses and restore reef function. One of thos efforts is the use of coral nurseries. . The nursery methodology involves three stages: 1. collection of a limited amount of coral fragments from wild populations; 2. growth of the fragments in a nursery setting; 3. out planting of the grown fragments to damaged reefs. In the Caribbean, the RESCQ-project has been organised to help restoring coral reefs and their ecosystem services damaged by mostly white-band disease, with the use of a coral nursery. The goal of this research is to find the optimum fragment size with the highest growth rate of A. cervicornis. Therefore, 50 A. cervicornis fragments were meas-ured over a period of 55 days. During this study, the average growth rate of the fragments in the nursery of Saba was 5,7 cm in total length a month, with a survival rate of 80% of the fragments. Depth shows no significant influence on the growth rate of the fragments. Initial fragment size how-ever did have a significant influence on the growth rate.

Thesis report.

Previously dominant, reef-building Acropora cervicornis and A. palmata abundance decreased dramatically in the Caribbean in the 1970s, mainly due to the white band disease. They have been on the IUCN Red List as ‘critically endangered’ species since 2008, but restoration efforts already date back to the year 2000. Of these methods, fragmentation used in coral gardening seems to be the most productive method for these species, but there is a need for optimisation of this process. This research filled up the nurseries of Saba, Dutch Caribbean, with Acropora, measured growth of both species and of the two staghorn mother colonies. Furthermore, some staghorn fragments were outplanted on an outplanting structure. Growth rates of staghorn differed between some trees, with the highest growth rates in the cut fragments that were ready for outplanting and therefore have lived in the nursery for the longest time. The outplants themselves showed a lower growth rate, which might have to do with the structure itself. There was generally no correlation between initial primary branch length and growth rates of staghorn found except for one tree. Furthermore, branching corals grew faster than non-branching corals, independent of the amount of side branches. Side branches tend to appear from about 10 cm length, but half of the fragments without side branches did not branch at all in the maximum of 79 days. Side branching over time seems to follow an exponential model, but prolonged measurements are needed to prove this. Elkhorn growth in surface area and perimeter was found already in a short period of time, but the method used must be further improved. The results of this research can be used to improve coral gardening of Acropora spp.

MSc thesis.

Reef restoration activities have proliferated in response to the need to mitigate coral declines and recover lost reef structure, function, and ecosystem services. Here, we describe the recent shift from costly and complex engineering solutions to recover degraded reef structure to more economical and efficient ecological approaches that focus on recovering the living components of reef communities. We review the adoption and expansion of the coral gardening framework in the Caribbean and Western Atlantic where practitioners now grow and outplant 10,000’s of corals onto degraded reefs each year. We detail the steps for establishing a gardening program as well as long-term goals and direct and indirect benefits of this approach in our region. With a strong scientific basis, coral gardening activities now contribute significantly to reef and species recovery, provide important scientific, education, and outreach opportunities, and offer alternate livelihoods to local stakeholders. While challenges still remain, the transition from engineering to ecological solutions for reef degradation has opened the field of coral reef restoration to a wider audience poised to contribute to reef conservation and recovery in regions where coral losses and recruitment bottlenecks hinder natural recovery.

Elkhorn coral (Acropora palmata) populations provide important ecological functions on shallow Caribbean reefs, many of which were lost when a disease reduced their abundance by more than 95% beginning in the mid-1970s. Since then, a lack of significant recovery has prompted rehabilitation initiatives throughout the Caribbean. Here, we report the first successful outplanting and long-term survival of A. palmatasettlers reared from gametes collected in the field. A. palmata larvae were settled on clay substrates (substrate units) and either outplanted on the reef two weeks after settlement or kept in a land-based nursery. After 2.5 years, the survival rate of A. palmata settlers outplanted two weeks after settlement was 6.8 times higher (3.4%) than that of settlers kept in a land-based nursery (0.5%). Furthermore, 32% of the substrate units on the reef still harbored one or more well-developed recruit compared to 3% for substrate units kept in the nursery. In addition to increasing survival, outplanting A. palmata settlers shortly after settlement reduced the costs to produce at least one 2.5-year-old A. palmataindividual from $325 to $13 USD. Thus, this study not only highlights the first successful long-term rearing of this critically endangered coral species, but also shows that early outplanting of sexually reared coral settlers can be more cost-effective than the traditional approach of nursery rearing for restoration efforts aimed at rehabilitating coral populations.