Sea sponges play a critical role in the ocean, and they are rapidly vanishing

Sea sponges serve as critical pillars in our oceanic ecosystems. These stationary animals, often mistaken for plants, offer sanctuary and sustenance to countless marine organisms. They also act as diligent recyclers, filtering copious amounts of seawater daily, which facilitates nutrient cycling.

On top of that, they harbor microbes within their bodies that hold potential solutions to pressing medical challenges. However, recent findings by scientists at UNSW shed light on a sobering reality: our warming oceans may be disrupting this delicate balance.

Warming waters are killing microbes that are vital to sea sponges

The latest study, now available in ISME Communications, indicates that as sea temperatures increase, tropical sea sponges could lose essential microbes, possibly causing tissue decay. The researchers found that a 3°C temperature increase causes one crucial microbe to abandon its sponge host, a change that may ultimately lead to the sponge’s demise.

This significant finding stems from a collaborative endeavor involving experts from UNSW, Heidi Luter from the Australian Institute of Marine Science, and James Bell from Victoria University of Wellington. Their combined efforts provide a vital insight into the impact of climate change on sponge populations worldwide.

“We’ve witnessed marine heatwaves decimate sponges in the Mediterranean and affect those in New Zealand,” comments Dr. Emmanuelle Botte, from the School of BEES and the lead author of the study.

“We’re finding that certain sponge species are more susceptible to climate change than we initially thought. Our research suggests that the breakdown of symbiosis between the sponge and its microbes could upset the sponge’s chemical balance and lead to its decay.”

Microbes and sea sponges have symbiotic relationship

Sea sponges, among Earth’s most ancient creatures, date back approximately 545 million years. Dr. Botte explains, “Sponges live in symbiosis with microbes. These microbes fulfill vital roles for the sponge, recycling nutrients, generating energy, and protecting the sponge against predators and diseases. Some microbes even serve to detoxify the sponge’s body. They’re somewhat like the sponge’s liver and kidneys.”

Researchers have widely recognized this intricate relationship between sponges and their microbial inhabitants. Past studies show certain sponge species, along with their microbial partners, are especially vulnerable to rising water temperatures.

“We initiated this study knowing some sponges were sensitive to future climate conditions, but we wanted to understand why,” Dr. Botte says. “Much like humans, sponges require a healthy microbiome to survive. We theorized that changes in the microbes and their functions might explain why some sponge species falter in warmer waters.”

Researchers found a change in the microbial makeup of sea sponges

The study focused on the Stylissa flabelliformis, a sea sponge species commonly found in the Great Barrier Reef and the West Indo-Pacific Ocean, known for its sensitivity to increased temperatures. Dr. Botte’s team analyzed the microbial composition of this sponge under temperature conditions ranging from 28.5°C to 31.5°C.

“We noticed major differences in the types of microbes found in a healthy sponge in the cooler temperatures, and in a necrotic, or dying, sponge in the warmer waters,” Dr. Botte reveals. The team observed a significant change: a group of microbes, known as archaea, made up 10% of all microbes in the healthy sponge. However, in the necrotic sponge, these microbes were absent.

“This microbe was the sole detoxifier of the ammonia produced by the sponge,” Dr. Botte adds. “Without it, toxic ammonia accumulates in the tissue.”

The findings suggest that the symbiosis between the Stylissa flabelliformis and its microbes lacks the flexibility required to adapt to higher temperatures, expected to become the norm by the century’s end. But this is not a distant prospect.

Dr. Botte warns that the potential impacts of warming waters on sea sponges and marine microbes are already evident. “We used conditions representing today’s extremes, as we have already witnessed temperatures 1.5°C-3°C above normal for weeks in Australia,” says Dr. Botte.

Sea sponges contain a treasure trove of medicinal molecules

These findings highlight the importance of sponges, not only as facilitators of biodiversity but also as potential sources of medical innovation. “Sponges are instrumental for drug discovery,” Dr. Botte emphasizes.

She continues, “The vast majority of molecules with antitumor or antipathogen properties come from marine invertebrates, particularly from microbes living in symbiosis with sponges. These symbiotic relationships are key for maintaining healthy oceans and are a treasure trove for pharmaceutically and commercially relevant molecules.”

The researchers behind this work stress the potential risks climate change poses to microbial diversity on Earth. They want to ensure that we understand this threat extends beyond the noticeable, large marine creatures. There’s a danger that the biodiversity of inconspicuous creatures, like sea sponges and the vital microbes they host, may also erode.

“Climate change impacts more than just the big, charismatic animals. There is a risk of eroding the biodiversity of unassuming animals and the microbes they host, which are key for healthy oceans and more generally life on our planet,” concludes Dr. Botte.

By delving deeper into the impacts of warming oceans, these scientists underscore the intricate, often unseen, connections within our world’s ecosystems. The stakes are high, and understanding these relationships is crucial if we are to protect and preserve the biodiversity of our oceans and, in turn, our planet.

More about sea sponges

Sea sponges, or Porifera, are one of the most primitive forms of multicellular life, dating back at least 540 million years. Despite their simple structure, they possess remarkable biological diversity and play important roles in marine ecosystems.

Structure and Classification

Sponges are primarily marine animals, but some freshwater species exist. They exhibit a wide range of shapes, sizes, and colors. Despite their plant-like appearance, sea sponges are animals. They are sessile, meaning they attach themselves to a surface and do not move. Sponges are organized into three classes based on their skeletal makeup: Calcarea (calcium carbonate spicules), Demospongiae (spongin and/or silica spicules), and Hexactinellida (glass sponges).

Anatomy and Physiology

Sponges have a unique cellular structure. Unlike other animals, they do not have true tissues or organs, but are instead composed of specialized cells that perform various functions. They possess an internal system of pores and channels, which allow water to circulate through their bodies. Sponges filter the water to extract small particles of organic material for nourishment. They breathe by absorbing oxygen directly from the water as it flows through their bodies.

Reproduction

Sponges can reproduce both sexually and asexually. Asexual reproduction often occurs through budding, where a new sponge grows out of the parent sponge. Some species also produce gemmules, resistant structures that can survive harsh conditions. For sexual reproduction, most sea sponges are hermaphrodites, possessing both male and female reproductive cells. Fertilization often takes place inside the sponge, with larvae later released into the water where they drift until finding a suitable surface to attach to and grow.

Ecological Role

Sponges play a crucial role in marine ecosystems. They provide habitats and protection for various small marine organisms. They’re also significant contributors to the process of bioerosion, the breakdown and recycling of coral reefs. Moreover, sponges help maintain water quality by filtering bacteria and other particulates from the water.

Biomedical Importance

Sea sponges have become a focus of scientific interest due to their symbiotic relationship with various microorganisms and their production of bioactive compounds. Some of these compounds have demonstrated anticancer, antiviral, antibacterial, anti-inflammatory, and immune-suppressing properties. Therefore, sponges hold considerable potential in the field of drug discovery and development.

Threats and Conservation

Like many marine organisms, sea sponges are threatened by climate change, ocean acidification, pollution, and destructive fishing practices. Warming sea temperatures can lead to the loss of the symbiotic microorganisms that some sponges rely on for survival. Conservation efforts are necessary to protect these fascinating and important components of marine ecosystems.