An in vitro cellular model for measuring the impact of thermal stress on Florida reef sponges.

Coral reefs are threatened by recurrent mortality incidents in their native habitats brought on by natural and anthropogenic stressors. Elevated temperature has been indicated as a major causing factor. Although ongoing research is focused on corals, sponges are an important benthic organism on coral reefs and are often overlooked. An accurate and standardized method is needed to determine the environmental limits and thresholds of sponges commonly found on coral reefs. We established an in vitro sponge cell model and evaluated the effect of elevated temperatures on primary cell cultures of five common Florida reef sponges-Agelas clathrodes, Aplysina fulva, Cliona varians, Geodia neptuni, and Xestospongia muta. Analysis of the results revealed that the impact of increased temperatures had no significant effect at the cellular level, but there are changes at the molecular level. Shifts in the sponges' transcriptomic profiles induced by increased temperatures, trigger processes related to signal transduction, apoptosis, and cell repair pathways. Further elevation of temperature corresponding to local extremes activated the immune response and programmed cell death. The results of the present study are based on both cellular and molecular data obtained from the in vitro cell model which highlight the minimal response of all five species to thermal stress, providing an insight into the mechanisms involved in the adaptive process. Furthermore, they suggest a resilience of these sponges to the current thermal extremes, but a combination of factors could still lead to a loss of sponges on reefs. This study forms the basis for use of in vitro sponge cell models to evaluate other environmental parameters and stressors on additional sponge species.