A recent study led by Annette Samuelsen investigated environmental change at deep-sea sponge grounds in the North Atlantic. She and her team were able to establish a baseline for water conditions in four different areas through simulations – over 67 years. Such a baseline is important for future studies. Sponges have far-reaching implications for life both in the ocean and on land, and their wellbeing is dependent on their environment.

Bubblegum Coral surrounded by deep-sea sponges at Stjernsund (northern Norway). Credit: ROV Ægir6000 Team, NorMaR

Deep-sea sponges live in the ocean, below 250 m and down to several km depth. You can find many different species around the globe. They are not dependent on light, and they grow on the seafloor filtering ocean water to get their nutrients. Many species have crystal needles making up their skeleton, while others have soft protein skeletons instead. When they occur in large quantities, that area is called a “sponge ground”. Sponges in the deep sea have not received much scientific attention historically, but that has changed in the past years, for multiple reasons.

In the now completed SponGES Horizon2020-project led by the University of Bergen, Annette Samuelsen and Çağlar Yumruktepe from NERSC contributed to studying the environmental conditions at deep-sea sponge habitats, resulting in several articles, including this recent publication: Environmental Change at Deep-Sea Sponge Habitats Over the Last Half Century: A Model Hindcast Study for the Age of Anthropogenic Climate Change.

Why do deep-sea sponges matter?

Before we get to the study’s findings – let’s see why scientists now care about sponges: Sponge grounds serve as habitat for fish and other marine life, providing shelter, boosting the ecosystem, and contributing to greater biodiversity. They also play a role in nutrient cycling in the ocean. So, the ocean benefits from their presence.

But we do too because deep-sea sponges contain chemical components that are mostly unexplored. Some of the ones scientists have studied have already led to improvements in the medical field: Several medicines are based on some of those components, and they are used against breast cancer and leukemia! Other sponge components are likely to become useful for different medical areas, and some of the sponge types have inner structures which are interesting for bone tissue engineering and regenerative medicine. Deep-sea sponges and their features may hold even more exciting secrets to be investigated in the future.

Despite their huge potential, they are quite sensitive to human activity in the deep sea such as bottom trawling to catch fish or potentially deep-sea mining. Such drastic changes in the environment are detrimental to sponges as they grow very slowly, but what about long-term changes in the environment that could affect them, you wonder?

How can we investigate the long-term environmental conditions?

The water temperature, salinity, as well as nutrient and oxygen concentrations are important for sponges, so how these factors change over time is important to know for studying sponge grounds in the future. Annette Samuelsen, together with Çağlar Yumruktepe from NERSC and co-authors from the University of Bergen and Hereon in Germany, set out to study the environmental change at four sponge grounds in the deep sea. It is difficult to do that over long timeframes using real observations, there simply is not much data available. Therefore, setting up an ocean model (HYCOM), combined with a biogeochemical model (ECOSMO), to produce a hindcast is the best way to get a good overview of long-term changes. That is what the researchers did: They simulated the deep-sea conditions between 1948-2014 in four different regions in the North Atlantic where there are many sponges around. The sparsely available ocean data was used to evaluate and tune the hindcast to make it as realistic as possible. This way, they created a 67-year-long baseline for the ocean water conditions for the four locations.

What Annette and her team also found was that for three of the four locations, changes in the water occur every 4-6 years, with varying salinity and temperatures. They interpret that those changes happen when surrounding water masses are mixed with the water in the sponge grounds. At the fourth sponge ground, they found a gradual warming of 0,4 °C over the 67 years. This baseline therefore shows interesting features of environmental change at different sponge grounds. Since this baseline for these regions is the first one ever created, it will be useful for investigating environmental changes in the future, which can impact the health of the ecosystem on the sea floor.

Reference:

Samuelsen, A., Schrum, C, Yumruktepe, VÇ, Daewel, U, and EM Roberts. Environmental Change at Deep-Sea Sponge Habitats Over the Last Half Century: A Model Hindcast Study for the Age of Anthropogenic Climate Change. Frontiers in Marine Science. 2022;9. doi: https://doi.org/10.3389/fmars.2022.737164

Dataset analyzed in the study: https://doi.pangaea.de/10.1594/PANGAEA.889396