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Deep impacts: Helmet jellyfish foretell the dangers of seafloor mining

A new study led by the GEOMAR Helmholtz Centre for Ocean Research Kiel has uncovered significant insights into the impact of seafloor mining and ocean warming on deep pelagic jellyfish, particularly the helmet jellyfish. 

This research is crucial in understanding the stress responses of midwater organisms, a largely unexplored area in marine biology.

Human pressures 

The deep sea, one of the largest habitats on Earth, is facing increasing environmental pressures from human activities. 

One such activity, deep-sea mining, aims to extract seafloor minerals but inadvertently creates suspended sediment clouds, or plumes, that can spread far beyond the mining sites. 

Midwater ecosystems 

These plumes, which can travel for hundreds of kilometers, pose a significant threat to midwater ecosystems, which typically have low sediment levels and are thus highly sensitive to such disturbances.

Dr. Helena Hauss, co-first author of the study and Research Director Marine Ecology at Norwegian Research Centre (NORCE), expressed her concern about the consequences of deep sea mining. 

“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,” said Dr. Hauss.

“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.” 

Fragile organisms 

“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,” added Dr. Henk-Jan Hoving, senior author and group leader of the Deep Sea Ecology group at GEOMAR.

“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.”

Focus of the research

For the first time, the researchers have investigated the stress response of a midwater organism – the helmet jellyfish – to simulated sediment plumes. 

“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,” explained Vanessa Stenvers, co-first author of the study and doctoral candidate at GEOMAR and the Smithsonian Institution. 

Alarming results

After approximately 1.5 hours of exposure, the jellyfish accumulated sediment particles and produced excess mucus in response. 

“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,” said Stenvers.

Furthermore, the highest sediment treatments triggered a marked expression of genes linked to respiration, innate immunity, and wound repair, indicating a stress response.

Warming waters

Notably, the experts found that sediment-induced stress was more severe than a four-degree increase in sea water temperature, a scenario projected in extreme global warming cases. 

Current climate models predict a one-degree rise over the next 84 years, suggesting that sediment plumes are a more immediate threat.

Broader implications 

The researchers expressed concern that the increased energy expenditure observed in the helmet jellyfish, due to stress responses, might lead to increased food requirements. Given the scarcity of food in deep-sea environments, this could potentially result in starvation.

Gelatinous animals, like the helmet jellyfish, are abundant in deep-sea ecosystems and play a crucial role in these environments. The stress responses observed in the helmet jellyfish may be indicative of broader impacts on similar species.

Understanding the threat

“With deep-sea mining possibly starting in the next decade, which has the potential to disturb nearby water column habitats as well as the seafloor, understanding the combined effects of mining and ocean warming is essential,” concluded study co-author Professor Andrew K. Sweetman from the Scottish Association for Marine Science.

The team hopes that their study, which provides a first glimpse into what some of the possible impacts may be in the midwater zone, will be taken into account by mining companies and the International Seabed Authority (ISA) to develop mining strategies that reduce the environmental damage as much as possible.

Helmet jellyfish 

The helmet jellyfish, named for its distinct hat-like shape, is a fascinating organism residing in the midwater regions of the deep sea. This environment, characterized by its minimal light and immense pressures, is home to a diverse array of species, many of which remain largely unknown to science. 

The helmet jellyfish is an integral part of this ecosystem, and its study offers vital insights into the broader ecological dynamics of deep-sea environments.

Deep-sea food webs

The helmet jellyfish also plays an essential role in deep-sea food webs. Like other gelatinous creatures in the ocean’s depths, it contributes to the cycling of nutrients and serves as both predator and prey within its ecosystem. 

This dual role underscores the importance of ensuring the health and stability of species like the helmet jellyfish, as disruptions to their populations could have cascading effects throughout the deep-sea community.

Adaptive mechanisms 

Furthermore, the genetic responses of the helmet jellyfish to environmental stress, such as changes in genes related to respiration, immunity, and wound repair, provide a window into the adaptive mechanisms of deep-sea life. 

These adaptations are not just vital for the survival of individual species like the helmet jellyfish but are also key to maintaining the resilience of the broader deep-sea ecosystem in the face of global environmental changes.

The study is published in the journal Nature Communications.

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