The rise of sponges in Anthropocene reef ecosystems

Many Caribbean reefs are now dominated by sponges. Credit:  CC BY-ND

Coral reefs across the world have been altered dramatically in recent decades. Human activities have contributed to mass coral die-offs in tropical oceans.

The degradation of reef-building corals is expected to worsen under current climate trajectories, but our work shows that most reef sponges are resilient enough to tolerate climate conditions projected for 2100.

In our latest research, we examine how future reefs that include more sponges might function compared to the current coral‐dominated ecosystems.

Sponge resilience

In our most recent research, we explored the potential mechanisms that underpin sponge tolerance to warming and acidification. We measured the composition of lipids and fatty acids in sponge species with different environmental sensitivities. We found that sponges with greater proportions of storage lipids and certain long‐chain polyunsaturated fatty acids were more resistant to warming.

These specific lipids and fatty acids likely preserve cell membrane function and other cellular processes in the face of temperature stress. Further exploration of how sponges alter their membrane lipids in response to rising temperatures revealed a potential mechanism through which ocean acidification may increase resistance to thermal stress by increasing production of membrane‐stabilising sterols. Our research shows that lipids and fatty acids are an important component of how sponges respond and may support their survival in future oceans.

How a sponge reef could work

Reefs dominated by sponges will likely function very differently compared to existing coral-dominated systems. Reefs where sponges are already the most abundant taxa have been reported from Indonesia and the Central Pacific. Some researchers also consider many Caribbean reefs to be mostly dominated by sponges.

Recent research modelled how reef ecosystems with increased sponge abundance would function. It highlighted the need to better understand how changes in the dominant group of reef organisms could alter marine food webs. While it is unlikely that sponge-dominated reefs would provide the same resources to humans as coral reefs, they offer habitat and food for some reef species. They are also responsible for nutrient recycling and contribute to structural complexity that should have positive effects on reef biodiversity.

James Bell And Nicole Webster, The Conversation (via, 26 October 2018. Full Article.

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