New Zealand Marine Sponges Allegedly Dissolved at Temperatures Panned for 2100
June 3 – New Zealand is facing an annual marine heatwave crisis
Marine heatwaves are no longer uncommon occurrences in the waters of New Zealand, leading to devastating effects on marine life and ecosystems that rival the impacts seen on the Great Barrier Reef of Australia.
"Marine heatwaves can pose serious issues, as heat stress pushes marine organisms towards their thermal limits," states Dr. Vonda Cummings, Principal Scientist of Marine Ecology at the National Institute of Water and Atmospheric Research (NIWA) New Zealand. "These events can disrupt the balance of marine food webs and wreak havoc on ecosystems."
A significant example of this occurred in 2022, when an estimated 66 million cup sponges (Cymbastella lamellate) bleached and 30 million died in Fiordland, located on the West Coast of New Zealand's South Island. The heatwave lasted 259 days and affected 1000 km of Fiordland's coastline, making it the largest sponge-bleaching event ever documented worldwide.
As a crucial component in Fiordland's rocky, benthic marine community, the massive death of cup sponges has led to far-reaching ecological disruptions. According to marine ecologist Professor James Bell of the Victoria University of Wellington, an estimated 10% of the sponges were lost in Pātea (Doubtful Sound), with even more die-offs further south in Tamatea (Dusky Sound) and Te Puaitaha (Breaksea Sound).
Arctic Giant Sponges and Extinct Ecosystems
"These sponges occupy around 15-20% of the available space and exert a substantial impact on carbon cycling, despite being relatively small in size," affirms Bell. "Despite their diminutive stature, there are millions and millions of them in Fiordland, circulating vast volumes of water."
Research has revealed that Fiordland's unique marine ecosystems are dominated by animals rather than algae, as tannins washed down steep-sided bush-clad slopes by annual rainfall of 6 to 8 meters cause the waters to remain permanently tea-colored.
"These 'mesophotic' (middle-light) ecosystems are primarily animal-based and relatively uncharted in terms of their diversity," Bell told Cosmos. "Limited light penetration through the tannin layer means algal communities don't thrive as well, and animals become more prominent closer to the surface."
In open coastal areas, black coral isn't visible until you're 100-plus meters below the surface. In contrast, in Fiordland, black corals can be seen at a depth of just five to six meters due to the dark, tannin-stained waters.
So, what caused this mass sponge bleaching and death?
Like corals, sponges host photosynthetic microalgal communities that provide them with distinctive colors. When these algae are lost, the sponges lose their colors, appearing bleached, with only limestone or silica skeletons remaining. Corals rely on dinoflagellates called Symbiodinium for nutrition; the loss of algae with rising temperatures can lead to starvation and death. It is believed that sponges host diatoms, microalgae with silica walls, which likely produce dissolved organic carbon that sponges consume.
Factors leading to sponge bleaching and death
Sponges died through various means in Fiordland:
- Starvation: Due to the loss of algae and dissolved organic carbon, sponges potentially faced nutrient deficiencies.
- Predation: Bite marks on bleached sponges suggest lethal predation by fish, possibly due to the sponges' newly bright, contrasting appearance against the dark substrate.
- Physiological Meltdown: In the Hauraki Gulf, a similar marine heatwave caused sponges to essentially dissolve, far surpassing their temperature tolerance limits and slipping off surfaces in some cases, resulting in necrosis and tissue loss.
Resilience in the face of adversity – adaptation to changing microbial communities
Some sponges may have survived the heatwave by adapting their microbial communities. Diatoms found in surviving sponges after the event differed from those found before the heatwave. These differences may provide new pathways for carbon cycling or aid in detoxification of cellular byproducts that are produced under sponge stress.
Sponges have existed for more than 500 million years and survived numerous mass extinctions. The ability to adapt microbial numbers or types to suit changing conditions could be one contributing factor to their longevity.
"This heatwave was extreme, and while there's always some sort of heatwave happening somewhere in New Zealand, the 2022 event was particularly intense," says Bell. "Things on land were basically baked and parched; there were no waterfalls or anything."
As global temperatures continue to rise, New Zealand is experiencing the impacts of marine heatwaves now, not just in the future. Marine heatwaves are becoming an annual event in New Zealand waters, as last year's event in Fiordland was not as severe, with a duration of 270 days in the south of the country, and North Island's Bay of Plenty spent an entire year in heatwave conditions.
NIWA now issues monthly sea surface temperature reports to help monitor these events. To stay informed about scientific developments affecting marine ecosystems, subscribe to our email newsletter, Ultramarine.
Originally published by Cosmos as NZ marine sponges 'melted' in temperatures not expected until 2100
"The destructive impact of marine heatwaves on New Zealand's marine life extends beyond just marine organisms, as these events also disrupt the balance of marine food webs and impact health-and-wellness of the ecosystems. Moreover, the climate-change induced marine heatwaves are becoming an annual occurrence in the country, similar to what happened in 2022, now recognized as the largest sponge-bleaching event ever documented worldwide, with serious implications for environmental-science."
"As global temperatures continue to rise due to climate-change, marine heatwaves are increasingly being observed not just in the future but now, as shown by the annual events in New Zealand's waters. To stay informed about the latest scientific developments affecting marine ecosystems, subscribing to resources such as NIWA's monthly sea surface temperature reports or our email newsletter, Ultramarine, is advisable for anyone interested in health-and-wellness, medical-conditions, and environmental-science."
