Acoustic Ecology Of Marine Crustacean Zooplankton : Sound Production And The Impact Of Anthropogenic Underwater Noise

The relevance of my thesis lies in its examination of two key aspects of zooplankton acoustic ecology, their natural sound production and their sensitivity to anthropogenic underwater noise (AUN), with Chapter 1 serving as the introductory chapter in which I outline and contextualize this relevance in relation to my research questions.
First, I demonstrate that Northern krill and Calanus copepods actively contribute to marine soundscapes through species-specific acoustic signals that may play roles in intraspecific communication and predator–prey interactions (Chapter 2). My second focus is on how the two different categories of AUN, continuous and impulsive, as defined by the Marine Strategy Framework Directive, affect copepod behaviour. A review (Chapter 3) highlights that behavioural impacts on (holo)zooplankton are poorly studied, despite their ecological importance. Experiments show that continuous harbour noise significantly disrupts feeding, when fed with microalgae, in the coastal copepod Acartia tonsa, reducing feeding rates by 40% in the laboratory on average and by 36% in situ, with additional variance linked to population sex ratios (Chapters 4 and 5).
Offshore, impulsive seismic airgun shots alter the swimming behaviour of the larger copepod Calanus finmarchicus in a non-linear relationship with distance to the source (Chapter 6). Using a unique field setup, in situ exposures from > 4000 m to < 100 m revealed pronounced changes in swimming patterns, including increased swimming speeds and shifts among the behavioural categories: swimming, sinking, and jumping.
Together, these findings reveal that zooplankton shape and are shaped by marine soundscapes. Their ability to produce sound underscores their active ecological role, while their vulnerability to AUN highlights the need for improved consideration of zooplankton behaviour within marine noise management. Chapter 7 synthesises these results and outlines future research directions.