Marian Hu

Large scale predictions regarding species sensitivities in a changing ocean require identification and understanding of common physiological principles that determine the degree of sensitivity in marine organisms. Larval stages are often the weakest link when a species is exposed to challenging environmental conditions making these life stages particularly interesting for this research. However, very little is known regarding physiological aspects of marine larval stages, primarily due to the fact that these organisms are very small. Recently developed techniques allowed us to study physiological processes in larval stages, and demonstrated that digestive processes in larval stages of early deuterostomes (echinoderms and hemichordates) seem to represent a critical factor for sensitivity towards ocean acidification. Interestingly, the digestive milieu of these organisms is highly alkaline (~pH 10) and acidified conditions decrease digestion abilities, and thus, food assimilation [1]. Thus, the first part (WP1) of the present project aims at deepening our current understanding regarding the mechanisms and energetics of gastric alkalization in selected echinoderms. In a second step (WP2) this knowledge will be transferred to other protostome groups such as lophotrochozoans (e.g. mollusks) in order to create a wider comparative basis to identify unifying physiological processes responsible for sensitivity towards environmental pH/pCO2 fluctuations. There is increasing evidence that the gastrointestinal microbiome is an essential part and specifically influences the performance of organisms. Digestion ability and pH may be determinants of this microbiome. Therefore, this project will identify and characterize bacteria associated with alkaline larval digestive systems (WP3) in order to broaden our knowledge regarding potential host-symbiont interactions under acidified conditions. WP1-3 are well embedded in the cluster of excellence The future ocean, and will integrate scientists from different research areas (e.g. R3 and R4) as well as national and international collaborators.

Shrimp aquaculture leaves a tremendous footprint on the coastal zone of many tropical countries (e.g. via deforestation of mangrove ecosystems) and animals are often treated with heavy doses of antibiotics to fight bacterial diseases1. Recently, a recirculating shrimp aquaculture farm has established itself in Kiel that produces animals that are free from antibiotics. However, due to the high stocking densities necessary to operate economically, the system accumulates CO2, which impacts animal physiology and welfare, as well as system productivity. Here, we propose a transdisciplinary approach to investigate how high CO2 experienced in shrimp farms influences animal acid-base status and how this impacts animal behavior, growth performance, shrimp palatability and shrimp susceptibility to bacterial disease. In addition, we propose to characterize the carbonate system dynamics within the shrimp farm in order to develop measures to help stakeholders create carbonate system conditions that increase animal well–being, productivity and product sensory quality at the same time.