When we think of marine life, we usually picture colourful coral reefs or dense seaweed forests filled with fish and other critters. The ocean that comes to mind is the one touched by sunlight.

However, most of the ocean is not like that. By volume, roughly 95% of the ocean consists of the permanently dark, cold deep sea. Despite such hostile conditions though, there is life in the ocean’s abyss.

Deep-sea marine sponges are among the organisms that live in these mysterious dark waters. They form “gardens” that are among the largest ecosystems on the planet, some spanning thousands of square kilometres on the ocean floor. They act as ecosystem engineers, providing habitats to many other organisms living on the seafloor.

Individual sponges can also pump and filter thousands of litres of water every day through their bodies. The nutrients they release support other organisms. Yet we know remarkably little about how sponges survive, let alone thrive, in the inhospitable environment of the deep-sea.

Symbiosis with microbes is an important part of how marine sponges live. We’ve been studying deep-sea sponges to better understand life in the........

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