PhD defence: Biological hotspots in the deep sea. Environmental controls and interactions in deep-sea sponge and coral assemblages

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The deep sea is one of the least studied environments of our planet. It is often considered an unfavorable habitat due to its immense pressure, darkness and low temperatures. Life mostly relies on sinking organic material from the surface as a food source, with only extremely small amounts reaching the seafloor. Surprisingly, in some places we find thriving communities, like cold-water coral reefs and sponge grounds, similar to oases in the desert. To find out why these hotspots appear in certain places, we investigated under which environmental conditions they live and how they sustain themselves.

Environmental conditions in different sponge grounds and cold-water coral reefs within the Atlantic were recorded during long-term deployments of bottom observatories with a multitude of biochemical and hydrodynamic sensors. Measurements showed specific hydrodynamic conditions leading to constant water exchange and delivery of otherwise limited resources. An additional food-web study showed that sponges are not only relying on sinking particulates but also utilise dissolved resources, which are normally inaccessible for animals. Sponges then transfer particulate matter as detritus to the food-deprived associated fauna. Furthermore, sponges take up and release nutrients from the water column and thereby are hotspots of carbon and nitrogen cycling.

This thesis provides for the first-time insights into the environmental variability within deep-sea hotspots and shows that sponges play a pivotal role in their sustenance. It is important to extend our understanding of critical thresholds for these ecosystems to predict how climate change or anthropogenic activities might have negative effects in the future.

Start date and time
End date and time
Location
Academiegebouw, Domplein 29, Utrecht & online (link)
PhD candidate
Ulrike Hanz
Dissertation
Biological hotspots in the deep sea. Environmental controls and interactions in deep-sea sponge and coral assemblages
PhD supervisor(s)
Professor Gert-Jan Reichart
Co-supervisor(s)
Dr Furu Mienis