Induced Dysbiosis Modifies Physiological Responses to Warming in a Temperate Sponge.

Marine sponges host complex and specific microbiomes, yet the role of these microbial symbionts in sponge responses to acute environmental stress is not fully understood. We investigated how altering the microbiome influences physiological responses to temperature in the temperate calcareous sponge Rowella lancifera under simulated marine heatwave (MHW) conditions. Sponges were treated with broad-spectrum antibiotics to disrupt their microbiome and then exposed to sub-lethal MHW temperatures. Microbial community composition was analysed using 16S rRNA gene sequencing, including assessing diversity and differential abundance, while sponge physiological response to temperature was quantified via respiration rates. Antibiotic treatment significantly altered microbial community structure but did not independently induce a physiological response. Heat exposure increased respiration rates, with a stronger response observed in microbiome-altered sponges. Multivariate analyses revealed a relationship between microbial community structure and respiration rate, suggesting an association between microbiome composition and host physiological responses. Overall, these findings indicate that sponge-microbe symbioses may play a role in modulating physiological responses to increased temperatures. As MHWs become more frequent and severe under climate change, understanding sponge-microbe partnerships will be important for predicting responses of sponges and the stability of benthic ecosystems.