Latest research by iAtlantic scientists reveals that deep-sea mining could significantly impact pelagic animals in the deep ocean, as well as those living on the seafloor. Plumes of sediment in the ocean – an expected byproduct of mining for seafloor mineral deposits – will likely affect the health of organisms such as jellyfish that live in the midwater. These new findings provide another critical glimpse into the poorly understood and highly vulnerable deep-sea environment that is being targeted for mineral extraction.
The study, carried out by scientists at GEOMAR and published in Nature Communications this week, investigated the effects of suspended sediment on midwater animals such as jellyfish. Using the helmet jellyfish (Periphylla periphylla, pictured right) as a representative model for a wide range of related midwater species, they demonstrate that the sediment plumes expected to be generated by mining activity will likely have significant impacts on jellyfish health.
This work represents the first such investigation into the likely stress response of midwater jellyfish. Findings show that, when exposed to increased suspended sediment levels, helmet jellies produced excess mucus to rid themselves of particles accumulating on their bodies — a process that significantly drains the animals’ energy reserves, consuming up to 40% of their daily energy intake and and sapping energy from other important systems including immune response and wound repair. In an environment where food resources are scarce, it’s unlikely the jellyfish could compensate for this energy deficit by increasing their food consumption.
“Since determining ‘stress’ in a jellyfish is not a straightforward process, we investigated their response from multiple angles and combined insights gained from their physiology, gene expression and the microbial symbionts on the jellyfish’s exterior,” explains Vanessa Stenvers, the co-first author on the study and currently working towards her PhD at GEOMAR. “While mucus helped jellyfish maintain a stable microbiome, continuous mucus production is an energetically costly response and can demand a substantial portion of the total energy budget of an animal”.
The scientists also tested the jellyfish’s stress response to warming seawater temperatures (+4°C), which are expected as a consequence of climate change. Whilst warmer seawater did trigger some increased metabolic activity in the jellyfish, it paled in comparison to the reaction seen upon exposure to sediment. This shows that the jellyfish are more likely to be directly and negatively impacted by mining activities than by even the most extreme ocean warming scenario.
Left: The helmet jellyfish (Periphylla periphylla) in the experimental tank. The photo was taken under red light, as helmet jellyfish are highly sensitive to bright light. Image courtesy Vanessa Stenvers
Animals living in the deep pelagic zone are highly diverse, but poorly researched and understood. Results from this work may be indicative of other midwater animals’ response to sediment stress as many other midwater species have a gelatinous body composition and mucus production is a common defence mechanism amongst these species.
Dr Henk-Jan Hoving, senior author and group leader of the Deep Sea Ecology group at GEOMAR, adds: “Midwater species are often fragile, gelatinous and sometimes giant organisms, with low metabolic rates that are difficult to observe in their natural environment and to perform experiments on. Their physical fragility may make them particularly vulnerable to environmental disturbance. At the same we have only scratched the surface when it comes to exploring the midwater and most biodiversity still remains unknown, as well as their function in the ecosystem, and their tolerance to change.”
This research contributes to iAtlantic’s work on understanding the impacts of human activities on the deep-sea environment and ecosystems, and provides a critical glimpse into the potential impacts of deep-sea mining and climate change on animals living in the water column. It highlights the need for a more comprehensive understanding of impacts from human activities on deep-sea ecosystems, including in the wider environment beyond the immediate vicinity of activity, as well as the need for more work on ecosystem response to multiple and cumulative stressors.
Dr Helena Hauss, co-first author of the study and Research Director Marine Ecology at Norwegian Research Centre (NORCE), explains: “The midwater is crucial for the global ocean’s capacity to store carbon, but also its inhabitants are the main food source for many fish, squid, and marine mammal species and therefore resemble a critical link in the marine food web. They have evolved under much more stable conditions compared to surface dwelling animals, under a constant scarcity of food, and are therefore potentially more susceptible to changing conditions in their environment.”
The full study is available as an open access publication:
Stenvers, V.I., Hauss, H., Bayer, T., Havermans, C., Hentschel, U., Schmittmann, L., Sweetman, A. & Hoving, H.J.T. (2023) Experimental mining plumes and ocean warming trigger stress in a deep pelagic jellyfish. Nature Communications. https://doi.org/10.1038/s41467-023-43023-6