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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - SCOOBA (Symbiotic COOperation and Boring Activity of Cliona sponges under a climate change context)

Teaser

Summary

Rising atmospheric CO2 concentrations are changing the chemistry of the oceans. Specifically, seawater pH is in decline â€“ a process known as ocean acidification (OA). Coral reefs are particularly susceptible to OA. The carbonate structures comprising reefs are built by corals, but OA threatens to weaken and erode calcareous reefs. Another key element in reef dissolution, bioerosion (i.e. the process of sponge growth into calcareous structures causing reef degradation) may increase under future ocean conditions, particularly as a result of warming. The major bioeroding organisms on reefs are sponges belonging to genus Cliona. Under historic conditions, corals and sponges were involved in a healthy balance between reef growth and decline. However, future environmental conditions may shift coral reefs to a state of perpetual decline. It is essential that we understand the role sponges play in that process. The most aggressive bioeroding sponges are those that harbor algal symbionts belonging to the same group found in corals (i.e. Symbiodinium). In corals, the algal symbionts provide the nutrition they need to precipitate calcium carbonate and form large reef structures. In sponges, the energy is used to increase rates of bioerosion. In addition to the interaction with Symbiodinium, most of the sponges host a wide range of bacteria, which are crucial to the sponge behavior.

Globally, the surface of the sea is 1ÂºC warmer than 140 years ago and warmer water bleaches corals, starving them of food. The combination of ocean warming with ocean acidification causes that corals (and other calcifying organisms in temperate regions) are undergoing a significant decline worldwide, however, bioeroding sponges may have an ecological advantage under future conditions. This might have dramatic consequences because reefs, although they cover 1% of the ocean floor, support 25% of marine life. The impact would be not only in terms of food resources obtained from the sea but also tourism would be severely affected. The economic impact is valued in $3.4 billion only in the USA. So, the focus on bioeroding sponges is especially important given how ocean acidification may accelerate the rate of boring into calcium carbonate structures by these type of sponges.

The scientific aim of this project is to study how symbionts interact with each other and with their host in terms of the sponge performance under a climate change context. We want to characterize the symbiotic community associated to Cliona species from tropical and temperate habitats and determine the effect of future environmental conditions on sponge bioerosion from multiple perspectives, estimating bioeroding activity and assessing expression of potential genes related to this process.

Work performed

In the first year of the project, we published a chapter entitled Molecular and Functional Ecology of Sponges and Their Microbial Symbionts (Hill and SacristÃ¡n-Soriano 2017) in the book Climate Change, Ocean Acidification and Sponges, published by Springer Nature, addressing the importance of sponge-microbe symbiotic interactions for marine ecosystems.

For the study of sponge-associated microbial communities, we developed a standardized methodology and analytical pipeline, which is described in the publication SacristÃ¡n-Soriano et al. (2019) Ontogeny of symbiont community structure in two carotenoid-rich, viviparous marine sponges: comparison of microbiomes and analysis of culturable pigmented heterotrophic bacteria. Env. Microbiol. Reports.

There are four different bioeroding sponges in the subtropical region we studied (Florida Keys, FL USA). We characterized genetically and compared the associated microbial community of those species to infer their potential function and relationship with their host. A specific and particular combination of microbes was observed in all the species analyzed but the functional inference remains to be evaluated.

We focused on the highly abundant sponge Cliona varians. We cultivated this sponge ex situ by attaching small sponge fragments to calcium carbonate blocks (Figures Close_view_sponge and Experiment). Two seawater temperatures and three pH conditions were used to mimic present and future environmental conditions and test their effect on the sponge bioerosion and physiology and determine potential shifts in its symbiotic community. An evident sign of bleaching (i.e. loss of Symbiodinium) was observed throughout the experiment in those sponges maintained in high seawater temperatures irrespective of the seawater chemistry. We are currently assessing the potential implications of climate change on the sponge bioerosion and its symbiotic community.

Final results

The original idea of the project was to use sponge cell aggregates to test current and future climate projections on the sponge development and performance. However, the difficulty of obtaining viable cell aggregates forced us to change our workplan and we decided to use small sponge fragments to accomplish our goals (Figure Sponge_clones). Hurricane Irma impacted Florida Keys in the summer of 2017 affecting consequently our research. Nevertheless, we could conduct the experiment planned during the summer of 2018. Besides this unfortunate event, the outgoing phase in the United States has been a complete success.

During the forthcoming year (ingoing phase), we will determine the potential effect of climate change on the sponge bioeroding activity from different perspectives. We will assess the physical erosion of the calcium carbonate blocks, we will also estimate shifts in the morphology of the carbonate â€œchipsâ€ that the sponges expel as a result of their boring activity, and finally we will evaluate changes in the gene expression patterns of the environmental combinations tested, so we could gain insights into the potential genetic pathways related to the bioerosion process. At the same time, we will devote special attention to the symbiotic community to see how it is affected by climate perturbations and compare it to that from temperate relatives.

We foresee mid-term and long-term impacts coming out of this project. Once we know how ocean acidification and ocean warming affect the bioerosion of these sponges into calcareous structures build by corals and determine the potential genetic pathways related to this process, we could anticipate the fate of coral reefs and will have the knowledge of how the eroding activity is regulated. So, we could provide the scientific bases for a good management and protection of coral reefs and other environments where boring sponges are abundant. We could also suggest detailed actions for the conservation of these marine ecosystems and get politicians involved in developing a new protection policy. Although coral reefs cover around 1% of the ocean floor, they support 25% of marine life. Degradation of these habitats means that local marine food resources are threatened but also tourism would be severely affected. So, the economic impact could be enormous (billions of euros).

The wider societal implications of the project will be fundamentally to increase the awareness of the society towards the consequences of climate change in the marine life using an emblematic system, the coral reefs. We Will also point out the knock-on effect on socio-economic issues, and give tips about how a person as individual can contribute to diminish the effects of global warming.