Microbial and Metabolic Dynamics in Sponges under Ocean Acidification

Efremova, Jana (2023). Microbial and Metabolic Dynamics in Sponges under Ocean Acidification. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.00016761


Ocean acidification (OA) poses a significant threat to marine ecosystems, and benthic organisms must develop adaptive strategies. Despite being frequently regarded as ‘winner taxa’, we lack a comprehensive understanding of how sponges tolerate stress and undergo positive acclimatization. Marine sponges can be categorized as high or low microbial abundance (HMA or LMA) species, which may adopt distinct strategies to maintain homeostasis and fitness under changing conditions.This study investigated adaptive traits of the HMA sponge Chondrosia reniformis and the LMA sponge Spirastrella cunctatrix by comparing microbial and metabolic shifts in sponge holobionts collected from a natural CO2 vent system and a control pH site in Ischia, Italy. Microbial diversity and core microbiomes changed for both species in response to OA. Morphologically, S. cunctatrix exhibited tissue necrosis accompanied by reduced oscula and water canal sizes, indicating a stress induced dysbiosis and microbial instability. In contrast, C. reniformis appeared to benefit from a highly diverse microbiome with functional redundancy and local microbiome stability, promoting acclimatization to OA. NMR-based metabolomics revealed stable metabolite profiles across sites for C. reniformis, indicating metabolic homeostasis, whereas metabolic shifts in S. cunctatrix suggested OA interference in several pathways, including osmoregulation and energy metabolism. To expand on organismal acclimatization processes towards biochemical exchanges with the environment, a new in situ sampling methodology was developed. The study of inhaled and exhaled water fluxes of filter-feeders was improved using a submarine peristaltic pump, which was tested on C. reniformis. The new methodology can be applied to various ecological research topics, such as nutrient cycling, filter-feeding fluxes, plankton dynamics, and seawater metabolomics. This dissertation compares diverse OA acclimatization strategies of two co-occurring Porifera species in a CO2 vent system based on microbiome and metabolic patterns. Moreover, parallel studies of biochemical exchanges with seawater are crucial to reconstruct these adaptation mechanisms.

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