Project
Enhancing early life stages success of Orbicella faveolata in a climate change era
Motivation
Millions of people across the world depend on coral reefs and the benefits that they provide, such as income through tourism, coastal protection and food. Woefully, decline of key reef-building coral species is major concern worldwide, particularly because of climate change. Their recovery may be facilitated by massive settlement of larvae of the most heat tolerant species. Unfortunately, corals are facing many reproductive challenges, including low abundance of adult corals and the exposure of intense marine heatwaves, which lead to impaired fecundity, bleaching and mortality. Therefore, understanding coral reproductive strategies and improve the use of sexual reproduction in coral restoration is critical to actively enhance coral reef resilience and ensure the long-term survival of keystone coral species. Applying active coral restoration and selective breeding could be a first step to rehabilitate their populations. Gaining understanding on how to enhance survival of early life stages, their symbionts, thermo-tolerance and health is crucial to improve population recovery. Strategic research conducted through this thesis, may lead to resilient corals that will thrive on future reefs.
Aim & Objectives
The aim of this thesis is to establish a thermo-resilient population of the Caribbean boulder coral Orbicella faveolata, an important reef-building species, through selective breeding. To this end, five research questions will be addressed using field and lab experiments in The Bahamas:
- How could rearing and survival of at early life stages be improved? Currently, this is a major bottleneck in sexual coral propagation, also under non-heat stress conditions.
- Does bleaching affect reproductive success of surviving ? Answering this question will determine to what extent collection of coral gametes for selective breeding should be restricted to years with normal summer temperatures.
- Do larvae selected for thermo-tolerance become thermo-tolerant recruits?
- Can thermo-tolerant symbionts further improve the resilience of recruits/juveniles?
- Do restocked thermo-tolerant recruits thrive on natural reefs?
The improvement of corals to restore reef functions in a resilient manner will fulfil the WIAS mission of understanding animals and their role for mankind.
Methodology
The study will be conducted in the southern part of Eleuthera (The Bahamas), using the wet lab facilities at the Cape Eleuthera Institute – Island School as ex-situ location, and three dive sites offshore of South Eleuthera, characterized by high coral cover for the in-situ part of the study.
An important key reef building species with ecological significance, will be used for larval propagation. The species commonly known as Mountainous star coral (Orbicella faveolata) is a broadcaster spawner. With assisted larval propagation in the laboratory, fertilization rates can be improved, but unfortunately the survival after settlement remains low, creating a bottleneck for restoration purposes. Larval propagation techniques applied on the study species will be optimized, improving settlement and enhancing growth.
Health surveys will be conducted in reefs where spawning was observed during consecutive years. Photogrammetry will be applied in permanent plots to determine bleaching and disease susceptibility of O. faveolata colonies, complemented by measurements of photochemical yields using a PAM fluorometer, creating a photomosaic with the values obtained. Fertilization rates and survival of coral offspring will be determined in healthy, bleached and recovered coral colonies. Before, during and after bleaching events. Thermotolerance in early life stages will be identified, to be used for selecting breeding and adding known thermo-tolerant symbionts, could improve survival and capacity to resist heatwaves. It is therefore crucial to study the impact of selecting breeding when thermo tolerant recruits are placed on natural reefs, in particular the role of potential trade-off between heat tolerance and other traits, such as vulnerability of the recruits to diseases, predation and competition.
Media
See the coral spawning predictions of 2024 and 2025.
