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News — Marine sponges are vital for oceanic ecosystems. They perform vital functions in the sea by offering refuge and sustenance to numerous marine organisms, rejuvenating nutrients through the filtration of vast amounts of seawater each day, and acting as hosts to microorganisms that could hold the solution to current urgent medical issues.

Recently, researchers from UNSW have unveiled a significant finding: heightened temperatures lead to the depletion of a crucial microorganism in tropical sea sponges, potentially elucidating the demise of sponge tissue. Today's publication in ISME Communications details the study, demonstrating that subjecting sea sponges to a temperature surge of 3°C prompts the departure of a vital microbe, which could result in toxic effects on the sponge's tissues.

The joint efforts of UNSW researchers, Heidi Luter from the Australian Institute of Marine Science, and James Bell from Victoria University of Wellington have contributed a crucial element to the ongoing investigation into the influence of climate change on global sponge populations. Their collaboration has provided a valuable puzzle piece, shedding light on the ramifications of climate change on these marine organisms worldwide.

Dr. Emmanuelle Botte, the lead author of the study and a member of the School of BEES, highlights the concerning observations regarding the vulnerability of sponges to marine heatwaves. She states, "We have witnessed the devastating effects of marine heatwaves on sponge populations in the Mediterranean and the consequential impact on sponges in New Zealand."

The study has uncovered a significant revelation: certain sponge species may not possess the anticipated resilience to climate change. This research exposes the potential consequences of the disrupted symbiotic relationship between the sponge and its microorganisms, leading to a chemical imbalance within the sponge and ultimately resulting in its deterioration.

Living in symbiosis with microbes

Sea sponges, ancient inhabitants of the sea, are frequently misidentified as plants due to their appearance. However, they are actually immobile animals and rank among the oldest life forms on our planet.

According to Dr. Botte, sponges have a remarkable history that traces back 545 million years. These creatures engage in a symbiotic relationship with microorganisms that play essential roles in their survival. These microbes are responsible for recycling nutrients, generating energy, protecting the sponge from predators and diseases, and even detoxifying the sponge's body. In a way, they function akin to the liver and kidneys of the sponge.

The documented connection between sponges and microbes is vital. Moreover, studies have indicated that certain sponge species and their linked microbes are especially susceptible to elevated water temperatures.

"Dr. Botte stated that we undertook this investigation due to our awareness of certain sponges' sensitivity to forthcoming climate conditions. However, we aimed to unravel the underlying reasons behind it."

"Similar to humans, sponges rely on a thriving microbiome for their survival. We hypothesized that alterations in the microbial composition and, more significantly, their functions within sponges, could elucidate the challenges faced by certain sponge species in warmer aquatic environments."

A shift in the microbial makeup of the sponge

"Dr. Botte states that sponges abound across the entire seafloor, spanning from the tropics to the poles. This research concentrated on Stylissa flabelliformis, a prevalent sponge species in both the Great Barrier Reef and the West Indo-Pacific."

The researchers examined the microbial composition of this sponge, renowned for its susceptibility to temperature changes within the range of 28.5°C and 31.5°C.

"Within these identical circumstances, we observed significant disparities in the microbial populations present within a thriving sponge under cooler temperatures compared to a necrotic sponge in warmer waters," Dr. Botte explains.

One particular alteration stood out noticeably. "Among all the microbial communities in the healthy sponge, a distinct group called archaea accounted for 10% of the total population, whereas it was completely absent in the necrotic sponge."

"Our findings revealed that this microbe possessed the unique ability to detoxify the ammonia generated by the sponge. In the absence of this microbe, toxic levels of ammonia would have accumulated within the sponge's tissues."

The symbiotic relationship between Stylissa flabelliformis and its microbial counterparts seems to lack the flexibility required to adapt to the anticipated high temperatures that are projected to become the norm by the end of the century.

It is crucial to note that the potential consequences of warming waters on sponges and marine microbes are not a distant future scenario. "The conditions we utilized not only reflect future average temperatures but also present-day extremes, as we have already witnessed temperature increases of 1.5°C-3°C above the normal range for extended periods in Australia," emphasizes Dr. Botte.

A goldmine for medicinal molecules

"Alongside their role in providing sustenance and refuge for other organisms, sponges play a vital role in drug discovery," highlights Dr. Botte.

"In the marine realm, the overwhelming majority of molecules possessing anti-tumor or anti-pathogen properties are synthesized by marine invertebrates, specifically the microbes residing in symbiotic relationships with sponges," explains Dr. Botte. "These symbiotic associations are not only vital for the well-being of oceans but also represent a treasure trove of pharmaceutical and commercially valuable compounds."

The research team responsible for this recent study aims to highlight the threat that climate change poses to microbial diversity on Earth. They emphasize that climate change doesn't solely affect prominent charismatic animals. There is a genuine risk of diminishing the biodiversity of inconspicuous animals and the crucial microbes they harbor, which play a pivotal role in maintaining the health of oceans and, more broadly, sustaining life on our planet.