A successful method to restore seagrass habitats in coastal areas affected by consecutive natural events.

Background: Seagrass meadows, known for providing essential ecosystem services like supporting fishing, coastline protection from erosion, and acting as carbon sinks to mitigate climate change effects, are facing severe degradation. The current deteriorating state can be attributed to the combination of anthropogenic activities, biological factors (i.e., invasive species), and natural forces (i.e., hurricanes). Indeed, the global seagrass cover is diminishing at an alarming mean rate of 7% annually, jeopardizing the health of these vital ecosystems. However, in the Island Municipality of Culebra, Puerto Rico, losses are occurring at a faster pace. For instance, hurricanes have caused over 10% of cover seagrass losses, and the natural recovery of seagrasses across Culebra's coast has been slow due to the low growth rates of native seagrasses (Thalassia testudinum and Syringodium filiforme) and the invasion of the invasive species Halophila stipulacea. Restoration programs are, thus, necessary to revitalize the native seagrass communities and associated fauna while limiting the spread of the invasive species. Methods: Here, we present the results of a seagrass meadow restoration project carried out in Punta Melones (PTM), Culebra, Puerto Rico, in response to the impact of Hurricanes Irma and María during 2017. The restoration technique used was planting propagation units (PUs), each with an area of 900 cm2 of native seagrasses Thalassia testudinum and Syringodium filiforme, planted at a depth between 3.5 and 4.5 m. A total of 688 PUs were planted between August 2021 and August 2023, and a sub-sample of 88 PUs was monitored between August 2021 and April 2023. Results: PUs showed over 95% of the seagrass survived, with Hurricane Fiona causing most of the mortalities potentially due to PUs burial by sediment movement and uplifting by wave energy. The surface area of the planting units increased by approximately 200% (i.e., 2,459 cm2), while seagrass shoot density increased by 168% (i.e., 126 shoots by PU). Additionally, flowering and fruiting were observed in multiple planting units, indicating 1) that the action taken did not adversely affect the PUs units and 2) that the project was successful in revitalizing seagrass populations. The seagrass restoration project achieved remarkable success, primarily attributed to the substantial volume of each PUs. Likely this high volume played a crucial role in facilitating the connection among roots, shoots, and microfauna while providing a higher number of undamaged and active rhizome meristems and short shoots. These factors collectively contributed to the enhanced growth and survivorship of the PUs, ultimately leading to the favorable outcome observed in the seagrass restoration project.

Demographic and population response of the threatened coral Acropora cervicornis (Scleractinia, Acroporidae) to fireworm corallivory

Introduction: The fireworm Hermodice carunculata is a widespread polychaete that can prey upon many coral species. However, few studies have examined the effect of fireworm predation on coral demographics during non-outbreak periods. Objective: To determine whether predation by H. carunculata compromised the growth, survival, and population performance of the threatened coral Acropora cervicornis. Methods: Nursery-reared coral fragments (n = 99) were fixed to the bottom of Punta Melones reef in the Island Municipality of Culebra, Puerto Rico. Predation activity and its demographic consequences on coral outplants were assessed from December 2020 to August 2022. Susceptibility to predation was compared between colonies collected directly from the reef and those originating from outside sources (e.g., coral nurseries). With the demographic data, simple size-based population matrix models were developed to 1) examine whether fireworm predation led to a significant decline in population growth rate (λ), 2) determine the demographic transition(s) that contribute the most to λ, and 3) determining the demographic transition(s) that accounted for differences in λ when comparing scenarios that considered either only predated colonies or both predated and non-predated outplants. Results: Predation increased over time, being more frequently observed in the area with the highest topographic relief and on colonies foreign to the study site. Outplants that were partially consumed grew significantly slower than non-predated colonies; however, predation did not threaten their survival. The likelihood of being attacked by the fireworm increased with branching complexity. The estimated λ for a scenario considering only predated colonies was 0.99, whereas, for a scenario where both predated and non-predated colonies were considered, λ was 0.91. Population growth, under the two scenarios, was mainly influenced by the probability of a large colony surviving and remaining at the largest size. Conclusions: Although predation can negatively impact coral growth, the relatively high survival rate of predated colonies compensates for the adverse effect. Since survival is the demographic transition that contributes most to population growth, it could be concluded that under a non-outbreak scenario, fireworm predation may not be the primary cause of A. cervicornis population decline.

Introducción: El gusano de fuego Hermodice carunculata es un poliqueto común que puede depredar muchas especies de coral. Sin embargo, pocos estudios han examinado el efecto de la depredación del gusano de fuego en la demografía de los corales durante periodos sin brotes poblacionales. Objetivo: Este estudio tuvo como objetivo determinar si la depredación por H. carunculata compromete el crecimiento, la supervivencia y el desempeño poblacional del coral amenazado Acropora cervicornis. Métodos: Fragmentos de coral criados en vivero (n = 99) se fijaron al fondo del arrecife Punta Melones en la Isla Municipio de Culebra, Puerto Rico. La actividad de depredación y sus consecuencias demográficas en los trasplantes de coral se evaluaron desde diciembre de 2020 hasta agosto de 2022. Se comparó la susceptibilidad a la depredación entre las colonias recolectadas directamente del arrecife y las que se originaron en fuentes externas (p. ej., viveros de coral). Con los datos demográficos, se desarrollaron modelos matriciales simples de población basados en el tamaño para 1) examinar si la depredación del gusano de fuego causa una disminución significativa en la tasa de crecimiento de la población (λ), 2) determinar las transiciones demográficas que más contribuyen a λ, y 3) determinar la(s) transición(es) demográfica(s) que explican las diferencias en λ al comparar escenarios que consideraron solo colonias depredadas o la combinación de colonias depredadas y no depredadas. Resultados: La depredación aumentó con el tiempo, observándose con mayor frecuencia en la zona de mayor relieve topográfico y en colonias ajenas al sitio de estudio. Los trasplantes consumidos parcialmente crecieron significativamente más lento que las colonias no depredadas; sin embargo, la depredación no amenazó su supervivencia. La probabilidad de ser atacado por el gusano de fuego aumentó con la complejidad morfológica de la colonia. El λ estimado para un escenario que consideraba solo las colonias depredadas fue de 0.99, mientras que, para un escenario en el que se consideraron tanto las colonias depredadas como las no depredadas, λ fue de 0.91. El crecimiento de la población, en ambos escenarios, estuvo influenciado principalmente por la probabilidad de que una colonia grande sobreviviera y permaneciera en el tamaño más grande. Conclusiones: Aunque la depredación puede tener un impacto negativo en el crecimiento de los corales, una tasa de supervivencia relativamente alta de las colonias depredadas compensa los efectos adversos. Dado que la supervivencia es la transición demográfica que más contribuye al crecimiento de la población, se podría concluir que, en un escenario sin brotes, la depredación por gusanos de fuego no debe ser la causa principal de la disminución de la población de A. cervicornis.

Population dynamics of diseased corals: Effects of a Shut Down Reaction outbreak in Puerto Rican Acropora cervicornis.

Chronic coral reef degradation has been characterized by a significant decline in the population abundance and live tissue cover of scleractinian corals across the wider Caribbean. Acropora cervicornis is among the species whose populations have suffered an unprecedented collapse throughout the region. This species, which once dominated the shallow-water reef communities, is susceptible to a wide range of stressors, resulting in a general lack of recovery following disturbances. A. cervicornis is a critical contributor to the structure, function, and resilience of Caribbean coral reefs. Therefore, it is essential to identify the factors that influence their demographic and population performance. Diseases are one of the factors that are compromising the recovery of coral populations. In this chapter, we use size-based population matrix models to evaluate the population-level effect of a Shut Down Reaction Disease (SDR) outbreak, one of the less-understood diseases affecting this coral. The model was parameterized by following the fate of 105 colonies for 2 years at Tamarindo reef in Culebra, Puerto Rico. SDR, which affected 78% of the population, led to a rapid decline in colony abundance. The estimated population growth rate (λ) for the diseased population was more than six times lower than would be expected for a population at equilibrium. It was found that colonies in the smaller size class (≤100cm total linear length) were more likely to get infected and succumbing to the disease than larger colonies. Model simulations indicate that: (1) under the estimated λ, the population would reach extinction in 5 years; (2) an SDR outbreak as intense as the one observed in this study can lead to a notable decline in stochastic λs even when relatively rare (i.e. 10% probability of occurring); and (3) disease incidence as low as 5% can cause the population to lose its ecological functionality (e.g., reach a pseudo-extinction level of 10% of the initial population size) 33 years before disappearing. SDR and probably any other similarly virulent disease could thus be a major driver of local extinction events of A. cervicornis.

The role of coral colony health state in the recovery of lesions.

Coral disease literature has focused, for the most part, on the etiology of the more than 35 coral afflictions currently described. Much less understood are the factors that underpin the capacity of corals to regenerate lesions, including the role of colony health. This lack of knowledge with respect to the factors that influence tissue regeneration significantly limits our understanding of the impact of diseases at the colony, population, and community level. In this study, we experimentally compared tissue regeneration capacity of diseased versus healthy fragments of Gorgonia ventalina colonies at 5 m and 12 m of depth. We found that the initial health state of colonies (i.e., diseased or healthy) had a significant effect on tissue regeneration (healing). All healthy fragments exhibited full recovery regardless of depth treatment, while diseased fragments did not. Our results suggest that being diseased or healthy has a significant effect on the capacity of a sea fan colony to repair tissue, but that environmental factors associated with changes in depth, such as temperature and light, do not. We conclude that disease doesn't just compromise vital functions such as growth and reproduction in corals but also compromises their capacity to regenerate tissue and heal lesions.