Marine sponges in New Zealand allegedly dissolved prematurely, a phenomenon typically anticipated only by the year 2100 due to global warming.
Marine Heatwaves: An Annual Threat in New Zealand's Waters
Here's a low-down on marine heatwaves, their impacts on our kiwis' underwater world, and how these events are redefining the future of our marine life.
Hop, Skip, and Heatwaves
Marine heatwaves, those prolonged spells of abnormally high ocean temperatures, are becoming all too common in New Zealand waters. According to Dr Vonda Cummings, Principal Scientist of Marine Ecology at New Zealand's National Institute of Water and Atmospheric Research (NIWA), these events can be quite troubling.
"Marine heatwaves can cause heat stress in marine animals, pushing them towards or even beyond their thermal tolerance limits," warns Dr Cummings. This can lead to disrupting the balance of marine food webs and messing with marine ecosystems.
Chilling Reports on the Cup Sponge Catastrophe
In 2022, a heatwave claimed the lives of millions of cup sponges (Cymbastella lamellate) in Fiordland, on the West Coast of New Zealand's South Island. The saddening part? This wasn't an isolated event. Temperatures exceeded 4C above the average, covering 1000 km of Fiordland's coastline and lasting 259 days. This makes it the largest sponge-bleaching event ever recorded worldwide.
Marine ecologist Professor James Bell from the Victoria University of Wellington shares, "Cup sponges play a vital role in Fiordland's rocky, benthic marine community, and their massive demise is a sight to behold – a shocking and saddening one, for that matter."
From South to North: The Bleaching Wave
The sponge's grim fate wasn't limited to the southern regions. Around 10 percent of the sponges were lost in Pātea (Doubtful Sound), with more gone further south in Tamatea (Dusky Sound) and in Te Puaitaha (Breaksea Sound).
A Chilly Twist: The Arctic Giant Sponges
Sponges in the Arctic, though living in extreme temperatures, are fascinating. Professor Bell highlights, "These sponges, on average, occupy around 15 to 20% of the available space, and have quite a significant impact on the carbon cycling." Even though they're small, they circulate substantial volumes of water due to their sheer numbers.
Fiordland's marine ecosystems are chock-full of surprises. The waters are permanently stained the color of tea due to tannins washed down by the steep-sided bush-clad slopes. This leaves the ecosystems "basically animal-dominated and pretty much unexplored in terms of their biodiversity," as defined by Professor Bell.
The Heatwave's Hit List: What's Next?
Sponges, like corals, host photosynthetic microalgal communities that provide their unique colors. However, when these algae disappear due to rising temperatures, it could lead to death by starvation. But what happens exactly when the algae vanish?
Bell posits that "sponges host diatoms, microalgae with silica walls, which produce dissolved organic carbon that sponges probably feed on. We don't know that for sure, because we haven't measured whether the sponge host consumes the carbon those diatoms fix."
However, the microalgal carbon isn't all for naught. It fuels local food webs, particularly microbes in the seawater, but its role as a nutrient source dwindles when sponges are bleached.
Predation may also play a part in the disappearance of these sponges. Bite marks on the bleached sponges suggest the sponges died through predation, with the fish feasting on the sponges that had turned bright white, making them super obvious.
Borrowing From the Extinct: The Power of Microbes
Could the ability to change microbial numbers or types account for the sponges' longevity? Some surviving sponges may have managed to adapt their microbial communities to survive the heatwave. Diatoms found in some living animals after the event were different to those found before. However, we don't yet know if these changes have any functional significance.
The (Not-So-Silent) Storm Is Already Here
Marine heatwaves are no longer a future concern – they're happening in the present. "The heatwave experienced by these sponges was warmer than those predicted as long-term increases," shares Professor Bell. "So, these climate change impacts aren't things that are going to happen in the future; they're already here, right now, in real time."
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Source: Originally published by Cosmos as NZ marine sponges 'melted' in temperatures not expected until 2100. A marine heatwave in Fiordland, New Zealand, caused more of a physiological effect in 2023, with temperatures causing the sponges to "melt." This was not as severe as the 2022 heatwave but still had damaging effects. NIWA now issues monthly sea surface temperature reports.
Marine heatwaves aren't exclusive to the future of ocean life; they're already impacting our waters today, as seen with the sponges in Fiordland, New Zealand in 2022. Furthermore, connections between marine heatwaves and other environmental factors like medical conditions, health and wellness, climate change, and environmental science, are worth exploring to better understand and preserve our marine ecosystems.
