Marine sponges are ancient and diverse animals that live in all oceans, from shallow coral reefs to deep-sea vents.
They are important for the health and functioning of marine ecosystems, as they filter large volumes of seawater, provide habitat and food for other organisms, and produce bioactive compounds with potential medical applications.
However, marine sponges are also vulnerable to environmental changes, especially rising temperatures due to global warming.
Symbiosis: a close and beneficial partnership
BORIS HORVAT/AFP via Getty Images
Symbiosis is a biological phenomenon where two or more different organisms live together in a close and long-term association that benefits at least one of them.
Symbiosis is very common in nature and can be found in animals, plants, fungi, and microbes, as per Phys.org.
Marine sponges are well-known for hosting a rich and diverse community of symbiotic microbes, which can make up to 40% of their biomass.
These microbes include bacteria, archaea, algae, fungi, and protists. They live inside the sponge tissue, in specialized cells called choanocytes, or in the extracellular matrix.
The symbiotic microbes provide various benefits to the sponge host, such as:
Producing energy and nutrients from photosynthesis or chemosynthesis
Recycling waste products and nitrogen compounds
Producing vitamins and hormones
Producing antibiotics and antifouling agents
Enhancing the immune system and resistance to pathogens
In return, the sponge host provides a stable and protected environment for the microbes, as well as organic carbon and other substrates for their metabolism.
Breakdown: a fatal consequence of warming
The symbiotic relationship between marine sponges and their microbes is sensitive to environmental changes, especially temperature fluctuations.
When the water temperature rises above the optimal range for the symbionts, they can become stressed or damaged, affecting their function and performance.
This can have negative consequences for the sponge host, such as:
Reduced energy and nutrient supply
Accumulation of toxic waste products
Loss of vitamins and hormones
Loss of antibiotics and antifouling agents
Reduced immune system and increased susceptibility to pathogens
In some cases, the symbionts can even become harmful to the host, producing reactive oxygen species or toxins that damage the sponge tissue.
This can lead to a breakdown of the symbiosis, where the host expels or digests the symbionts, or where the symbionts escape or invade the host.
This can result in the death of both partners.
A recent study by researchers from Australia and New Zealand revealed how a breakdown of symbiosis can cause the death of a tropical sponge species (Stylissa flabelliformis) when exposed to high temperatures (31.5°C) for eight weeks.
The researchers found that the sponge lost a key symbiont that was responsible for removing ammonia, which is a toxic waste product, from its tissue.
Without this detoxification process, the sponge tissue became poisoned and died.
The researchers also found that this breakdown of symbiosis was not reversible when the temperature was lowered back to normal (28.5°C).
This suggests that once the symbiosis is disrupted, it is difficult or impossible to restore it.
The study by Botté et al. highlights the importance of symbiosis for the survival of marine sponges under warming conditions, as per The Conversation.
It also shows how warming can disrupt this delicate balance, leading to fatal outcomes for both partners.
This has implications for marine biodiversity and function, as marine sponges are key components of many marine habitats.
They support a high diversity of associated organisms, such as fish, crustaceans, mollusks, and worms.
They also contribute to biogeochemical cycles, such as carbon, nitrogen, and phosphorus cycles. They also produce bioactive compounds that have potential applications in biotechnology and medicine.
The loss of marine sponges due to warming could have cascading effects on marine ecosystems, affecting their structure, function, and services.
It could also reduce the genetic diversity and evolutionary potential of both sponges and their symbionts.
