The rise of in Anthropocene ecosystems 26 October 2018, by James Bell And Nicole Webster

resources reefs can provide for humans.

Marine sponges are found across the world's oceans. They are among the oldest known multicellular organisms and first appeared in the fossil record about 580 million years ago.

Over this long evolutionary history, sponges experienced a range of environmental conditions and have shown remarkable persistence to survive the end- mass extinction, some 200 million years ago. While sponges are found in shallow and deep-water environments from the tropics to the poles, they are particularly important on coral reefs. There, the filter feeders form a critical link between Many Caribbean reefs are now dominated by sponges. the seafloor and the overlying body of seawater. Credit: www.shutterstock.com, CC BY-ND

, Australian Institute of Marine Science

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. Many marine sponges can tolerate ocean warming and In our latest research, we examine how future acidification better than reef-building corals. Credit: reefs that include more sponges might function James Bell compared to the current coral?dominated ecosystems.

Sponges on coral reefs Sponges pump large quantities of water and remove bacteria, and dissolved food. They On the Great Barrier Reef, the amount of living also maintain symbiotic partnerships with diverse coral has declined over the past 30 years. communities of microorganisms that can provide Recurrent bleaching events are having profound them with nutrients and secondary metabolites that impacts on the ecology of reef systems and the bolster their defence against predators and

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infection.

Sponge tolerance and super larvae

The latest report from the Intergovernmental Panel on Climate Change suggests very different outcomes for coral reefs at a 1.5°C or 2.0°C increase in seawater temperature. Even if we manage to keep ocean warming to 1.5°C, corals will nevertheless be seriously impacted.

However, we have shown that many species are more tolerant than corals of the impacts of climate change. We think sponges could be future "winners" on coral reefs.

Our work explored the tolerance of four Great Testing marine sponges in the laboratory. Credit: Holly Barrier Reef sponge species to ocean warming and Bennett, CC BY-ND ocean acidification levels predicted for 2100. All species were unaffected by moderate climate change scenarios where we increased the temperature by 1.5°C. However, the environmental These findings suggest that sponges have an conditions projected under the most extreme inherent capacity to tolerate climate change, but scenarios (4°C increase in temperature) had that this tolerance is not maintained in adult significant adverse effects in some species. populations.

While higher temperatures can decrease the health Sponge resilience and survival of some sponge species, ocean acidification generally appears to have negligible In our most recent research, we explored the effects. Research conducted at natural carbon potential mechanisms that underpin sponge dioxide vents also confirms the overall pH tolerance tolerance to warming and acidification. We of many sponge species. measured the composition of lipids and fatty acids in sponge species with different environmental Our experimental work showed that responses to sensitivities. We found that sponges with greater the combined effects of ocean warming and ocean proportions of storage lipids and certain long?chain acidification vary between different types of polyunsaturated fatty acids were more resistant to sponges. While acidification exacerbated the effect warming. of warming in sponge species that feed on plankton, it mitigated the warming effect in species These specific lipids and fatty acids likely preserve with photosynthetic symbionts. cell membrane function and other cellular processes in the face of temperature stress. Sponges respond differently throughout their life Further exploration of how sponges alter their history stages. Larvae of the abundant sponge membrane lipids in response to rising temperatures Rhopaloeides odorabile have a thermal threshold revealed a potential mechanism through which 4°C higher than their parents. Survival and ocean acidification may increase resistance to settlement of larvae of the common reef sponge thermal stress by increasing production of Carteriospongia foliascens are unaffected by worst membrane?stabilising sterols. Our research shows case climate change predictions. that lipids and fatty acids are an important component of how sponges respond and may support their survival in future oceans.

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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.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Provided by The Conversation APA citation: The rise of sponges in Anthropocene reef ecosystems (2018, October 26) retrieved 25 September 2021 from https://phys.org/news/2018-10-sponges-anthropocene-reefecosystems.html

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