Phd students

Thiviya Nair

Disease-free production of European flat oysters

Camille Saurel and Lone Madsen, DTU Aqua

The Danish Limfjorden was once rich with European Flat Oysters (Ostrea edulis), treasured as a reef engineer and a nutritious source of protein by local and foreign markets. Unfortunately, the spread of the invasive micro-parasite, Bonamia ostreae, and overfishing for the flat oysters in Europe eventually caught up with the region, decimating their populations. In 2020, the Limfjorden lost its disease-free status and relies on the production of Bonamia-free spat to seed shellfish aquaculture and reef restoration efforts. Bonamia-free spat production relies on accurate and early detection of the parasite, as its life cycle outside of its host is unclear, and infections are often diagnosed when it is too late.

My projects will aim to investigate the biotic and abiotic factors that contribute to the activation of bonamiosis in flat oysters and potential treatments that can be applied to limit B. ostreae’s infectivity. The project will also include testing early and non-destructive sampling methods for parasite detection and provide a basis for biosecurity protocols required for successful Bonamia-free oyster spat production in the Danish Shellfish Centre hatchery at Nykøbing Mors.

The discoveries that will be made in this project will fill up the knowledge gaps on the life cycle and behaviour of B. ostreae. The disease testing methods refined in this project will also serve as a potential early alarm system for hatcheries and Bonamia-free sites. Developments from this project will enable shellfish farm managers to formulate the best mitigation strategies and avoid financial losses. The Bonamia-free spat produced through the efforts of this project can go on to seed future reefs and fisheries, thereby reviving the flat oyster populations in the Limfjorden.

Ana Lilia Tovar Aguirre

Title of PhD project
Microalgae production for shellfish hatchery

Supervisors
Camille Saurel, DTU Aqua and Marie Renaudie, Nantes University

Background of the project
Aquaculture, a rapidly growing sector of food production, is crucial for meeting the global demand for seafood. The European flat oyster (Ostrea edulis) is of significant ecological and economic importance. A critical factor in the success of oyster hatcheries is the quality of microalgal feed, which must meet the nutritional needs of oysters at various life stages. While monocultures of microalgae have been the traditional choice, studies highlight the advantages of using mixed microalgae cultures. Native, local, undefined poly microalgae cultures may offer cost-effectiveness, and high-quality nutritional profiles, making them a promising alternative for sustainable oyster farming.

About the project
This PhD project focuses on using local, undefined poly microalgal cultures as a sustainable and effective feed source for Ostrea edulis in hatcheries. The research will explore the potential of these natural microalgal communities by adapting them to controlled hatchery environments. By examining different factors, the project aims to optimize the cultivation of these polycultures to enhance their suitability as oyster feed. Additionally, the study will investigate the scalability of these cultures from lab-scale to larger production systems, assessing their impact on oyster growth, tissue composition, and overall health.

Perspectives
The findings from this project will advance sustainable aquaculture practices by demonstrating the viability of local, native, microalgal polycultures as a high-quality feed option for oyster hatcheries. This approach could lead to reduced feed costs and improved oyster productivity, contributing to the long-term sustainability of the aquaculture industry. Beyond aquaculture, the insights gained could have broader applications in different areas where polycultures could be suitable.

Morten Højen Kristiansen

Title of the PhD project
Horse mussel, Modiolus modiolus, production for restoration

Supervisors
Camille Saurel, Pernille Nielsen and Grete Elisabeth Dinesen, DTU Aqua

Background of the project
Horse mussel beds are marine formations consisting of dense congregations of living mussels, empty shells, and various substrates, all held together by the mussels’ byssus threads. High densities of mussels are vital for their function as ecosystem engineers that stabilize sediment and create habitats, promoting a rich biodiversity and high biological productivity. In addition, horse mussels provide regulating ecosystem services through suspension feeding, removing phytoplankton and particles from the water column, thereby improving water quality. However, historical records reveal a significant decline in the spatial extent of horse mussel beds, mainly driven by physical disturbances from human activities. The management of threatened horse mussel beds can be supported through targeted restoration efforts, with a promising approach being the deployment of cultured juvenile mussels (spat) to boost recruitment.

About the project
Horse mussel spat has been produced in hatcheries before, but not in quantities that are sufficient to meet the demand for horse mussel reef restoration projects. A limitation in production is largely due to a significant lack of research on horse mussel biology and behaviour. Therefore, to close the knowledge gaps, this PhD project will focus on investigating the life-stage-specific demands of horse mussels in aquaculture. This requires refinement of feeding procedures and control of environmental parameters to create an ideal environment in a hatchery that can help maximize reproductive potential and offspring survival and growth. Additionally, the project will explore biological mechanisms or conditions that trigger spawning and larvae settlement.

Perspectives
This project will contribute with new insights into the biology of the horse mussel and the biological responses that aquaculture conditions impose on the species. The development of a novel horse mussel hatchery will provide the means to restore degraded horse mussel beds and potentially establish new ones, contributing to global efforts to enhance biodiversity and ecological health of marine ecosystems. This project has the potential to drive innovation in ecological restoration techniques and setting new standards for sustainable marine conservation.

Anna Steinmann

Title of the PhD project
Evolution, stability and ecosystem services provided by restoration of marine bivalve habitats

Supervisors
Pedro Seabra de Freitas, Daniel Patrick Taylor & Jens Kjerulf Petersen, DTU Aqua

Background of the project
Coastal ecosystems depend on bivalves for several ecosystem services (ES), including the improvement of water clarity and the formation of long-lasting, complex habitat structures to promote biodiversity. However, human activities such as overfishing and climate change have led to a decline of the populations, thereby threatening these ES. While restoration efforts have been made, they often lack standardized monitoring methodologies or monitoring all together. Consequently, it is challenging to evaluate restoration impacts and identify potential issues that require adaptations to the restoration strategy.

About the project
The objective of this project is to assess the impact of restoration efforts, while considering biotic and abiotic pressure factors that shape and determine the evolution and stability of restored bivalve habitats. Thus, different methods for a standardized monitoring will be developed and compared. A combination of imaging-based techniques, side-scan sonar, and traditional physical sampling will be applied to assess metrics such as the footprint area, sediment coverage, and patterns of self-organization. Alongside those assessments, water clarity as an important ES will be investigated. In-situ sensors will be utilized to monitor particle depletion, which will be linked to relevant abiotic factors. This aims at establishing a monitoring protocol for the assessment of water clarity in and around bivalve beds, with considerations of spatialtemporal changes.

Perspectives
A key outcome will be a detailed assessment of the advantages and limitations of different monitoring methods. This will provide an evaluation of their applicability and thereby support the identification of appropriate techniques for assessing restoration impacts. Ultimately, protocols for standardized monitoring across different restoration projects and studies will be proposed. The implementation of the developed methods will provide a detailed understanding of short-term trends, and the ES provided. It should also provide a perspective on assessment metrics and the expected effort required to implement long-term monitoring.

Previous PhD students within the research area Coastal Ecology

Isabelle Johansson
Population Dynamics of Blue Mussels in Subtidal Areas, Longevity, Recruitment, and Productivity, Under Multiple Stressors (link awaits publication of thesis)

Satish Pawar
Eelgrass habitat mapping in Danish coastal waters: a remote sensing perspective (link awaits publication of thesis)

Development of drone-based tools for the monitoring of submerged aquatic vegetation

Restoration and non-invasive monitoring of geogenic reefs in temperate waters

Investigating hatchery and cultivation methods for improved cultivation of Palmaria palmata 

Mitigation culture of mussels: Production and ecological impacts

Helle Torp Christensen
Area-intensive bottom culture production of blue mussels, Mytilus edulis (L.)