Long-term survival, growth, and reproduction of Acropora palmata sexual recruits outplanted onto Mexican Caribbean reefs.

Acropora palmata is a foundational yet endangered Caribbean reef-building coral species. The lack of recovery after a disease outbreak and low recruitment has led to widespread use of fragmentation to restore populations. Another option is the production of sexual recruits (settlers) via assisted reproduction to improve the genetic diversity of depleted populations; however, the viability of this approach has not been tested over the long term. In 2011 and 2012, A. palmata larvae were cultured, settled, and the sexual recruits raised in an ex-situ nursery. Survival and growth were monitored over time. In 2014, these two F1 cohorts were moved to an in-situ nursery and after one year, a subset (29 colonies) was outplanted onto Cuevones Reef in the Mexican Caribbean. Growth and survival of these colonies were monitored periodically and compared to colonies that remained in the in-situ nursery. In 2019, samples were collected and analyzed for fertility and fecundity. 53% of the colonies were gravid and fecundity was 5.61 ± 1.91 oocytes and 3.04 ± 0.26 spermaries per polyp. A further 14 colonies from these two cohorts were outplanted in 2020 onto Picudas Reef and monitored during the subsequent spawning seasons. Two years after outplanting onto Picudas Reef, all colonies were alive and spawning of three of these colonies was recorded in 2022 in synchrony with the wild population. Gametes were collected from two colonies and crossed, with 15% fertilization success. Spermatozoa from wild colonies were then added and fertilization success increased to 95%. The resultant larvae followed normal development and symbiont uptake was visible within two weeks. The F2 generation was settled, maintained in an ex-situ nursery, and monitored for survival and growth. Both F1 and F2 generations followed a Type III survival curve with high initial mortality while in the ex-situ nursery and low later-stage mortality. The growth rates of these colonies increased three-fold after outplanting when compared to their growth rates in the ex-situ and in-situ nurseries. All colonies survived while in the in-situ nursery and for an additional nine years after outplanting onto Cuevones Reef. Overall, our results show that colonies produced by assisted breeding, once outplanted, may contribute to the genetic diversity and establishment of self-sustaining sexually-reproducing populations, which is an overarching goal of coral restoration programs.

Coral affected by stony coral tissue loss disease can produce viable offspring.

Stony coral tissue loss disease (SCTLD) has caused high mortality of at least 25 coral species across the Caribbean, with Pseudodiploria strigosa being the second most affected species in the Mexican Caribbean. The resulting decreased abundance and colony density reduces the fertilization potential of SCTLD-susceptible species. Therefore, larval-based restoration could be of great benefit, though precautionary concerns about disease transmission may foster reluctance to implement this approach with SCTLD-susceptible species. We evaluated the performance of offspring obtained by crossing gametes of a healthy P. strigosa colony (100% apparently healthy tissue) with that of a colony affected by SCTLD (>50% tissue loss) and compared these with prior crosses between healthy parents. Fertilization and settlement were as high as prior crosses among healthy parents, and post-settlement survivorship over a year in outdoor tanks was 7.8%. After thirteen months, the diseased-parent recruits were outplanted to a degraded reef. Their survivorship was ∼44% and their growth rate was 0.365 mm ± 1.29 SD per month. This study shows that even diseased parent colonies can be effective in assisted sexual reproduction for the restoration of species affected by SCTLD.

Coral reef restoration efforts in Latin American countries and territories.

Coral reefs worldwide are degrading due to climate change, overfishing, pollution, coastal development, coral bleaching, and diseases. In areas where the natural recovery of an ecosystem is negligible or protection through management interventions insufficient, active restoration becomes critical. The Reef Futures symposium in 2018 brought together over 400 reef restoration experts, businesses, and civil organizations, and galvanized them to save coral reefs through restoration or identify alternative solutions. The symposium highlighted that solutions and discoveries from long-term and ongoing coral reef restoration projects in Spanish-speaking countries in the Caribbean and Eastern Tropical Pacific were not well known internationally. Therefore, a meeting of scientists and practitioners working in these locations was held to compile the data on the extent of coral reef restoration efforts, advances and challenges. Here, we present unpublished data from 12 coral reef restoration case studies from five Latin American countries, describe their motivations and techniques used, and provide estimates on total annual project cost per unit area of reef intervened, spatial extent as well as project duration. We found that most projects used direct transplantation, the coral gardening method, micro-fragmentation or larval propagation, and aimed to optimize or scale-up restoration approaches (51%) or provide alternative, sustainable livelihood opportunities (15%) followed by promoting coral reef conservation stewardship and re-establishing a self-sustaining, functioning reef ecosystems (both 13%). Reasons for restoring coral reefs were mainly biotic and experimental (both 42%), followed by idealistic and pragmatic motivations (both 8%). The median annual total cost from all projects was $93,000 USD (range: $10,000 USD-$331,802 USD) (2018 dollars) and intervened a median spatial area of 1 ha (range: 0.06 ha-8.39 ha). The median project duration was 3 years; however, projects have lasted up to 17 years. Project feasibility was high with a median of 0.7 (range: 0.5-0.8). This study closes the knowledge gap between academia and practitioners and overcomes the language barrier by providing the first comprehensive compilation of data from ongoing coral reef restoration efforts in Latin America.