PhD defence about the impact of size and growth strategies on structuring marine ecosystems

Global warming and fisheries exploitation are impacting marine ecosystems. Therefore, predicting future changes in marine ecosystems is one of the most urgent challenges in marine science. However, ecosystems are complex, and the classic species-based approach has difficulties predicting global changes because species and species interactions change dramatically among ecosystems.

The trait-based approach provides an efficient tool for understanding ecosystems. This theory ignores the membership of individuals to a species but rather assumes that traits interact together. The variability in growth traits, how fast individuals grow, is known and well described.

However, global models based on traits often do not consider variation in growth traits. In his PhD thesis, Rémy Denéchère, DTU Aqua, therefore investigates how life history traits of growth drive the dynamic and the structure of high-trophic level marine populations and communities by using the example of fast-living squids.

Rémy Denéchère has developed an ecosystem model that includes fast growing squids and slower growing fish. He shows that squid presence strongly depends on pelagic secondary production and that ecosystem structures (trophic interactions and biomass) change in the presence of squid.

He uses this framework to understand the recent global increase in squid and shows that squid increase is not attributed to a rise in temperature, as previously proposed, but rather due to the loss of top predators.

This thesis addresses several aspects of the impact of growth strategies in structuring populations and ecosystems using squid. This shows that better global prediction could be reached by incorporating several growth strategies. Additionally, this thesis gives the first proof-of-concept of the ecological properties of squid based on their traits.

About the PhD defence

Rémy Denéchère will defend his PhD thesis "Metabolism, pace of life, and the dynamics of size-structured populations and communities. The case of fast-living squid" on Wednesday 26 October at DTU, Asmussens Allé, 2800 Kgs. Lyngby, building 303A, auditorium 45. The defence can also be followed on Zoom (find link below). 

Supervisors

• Principal supervisor: Professor Ken Haste Andersen, DTU Aqua
• Co-supervisor: Researcher P. Daniël van Denderen, DTU Aqua 

Examiners               

• Professor Karen Timmermann, DTU Aqua (chair)
• Senior Scientist Patrick Lehodey, Mercator Oceans, France
• Senior Researcher Tobias van Kooten, Wageningen University, The Netherlands

Chairperson at defence

• Senior Researcher Karin Hüssy, DTU Aqua

Learn more

A popular science summary of the thesis can be downloaded here

A pdf of the thesis is available on request. Please contact PhD Secretary Karin Stubgaard, stub@aqua.dtu.dk