Tiny life at the Rio Grande Rise

By Natascha Menezes Bergo – oceanographer, PhD student at The Universidade de São Paulo (USP) - Brazil

Microbes are everywhere. In the air, soils, rivers, seas, on trees and on you and me. You can’t see them but they are there. Can you imagine how many are there at sea? What are they doing? Or why are they there? Some scientists estimated about 100 millions of microbial cells per milliliter of seawater. Do you remember when you were at the beach and accidentally swallowed some seawater? Oops...

This picture is from an epifluorescence microscope. All these big and tiny green dots represent tiny life forms in water drop such as bacteria and viruses. Can you count them?

Yet scientists have many questions about microbes in the ocean. Ecologically, microbes play a vital role in marine food chains and global nutrient cycling. These diverse tiny life forms help the health of the oceans. They are primary producers in the ocean’s upper layers where sunlight penetrates around 200 m. These autotrophic microorganisms use the sunlight to do photosynthesis. When gets dark, the microbes’ metabolism changes becoming heterotrophic just like us. In the dark ocean, microbes can be primary producers too.

 So, how are they producing energy and food, if isn’t light out there? These tiny microorganisms can convert some organic and inorganic compounds into food and energy, chemosynthetic microorganisms. Microbes living at deep-sea habitats such as canyons, seamounts, ridges and rises with Fe-Mn crusts are mostly chemosynthetic.

HyBIS dive at Rio Grande Rise with fishes, black corals and an abundant world of tiny microbes that we can’t see. However, this tiny life form is there.

Fe-Mn crusts deposits in Rio Grande Rise can host highly diverse and rich microbial communities. The main scientific question is if these microbes are just living there or whether they are actually involved in the formation of the Fe-Mn crusts. Microbiologists have some hypothesis how these tiny life forms act on the crusts formation, but it is still unproven.

Fe-Mn crust with a shiny biofilm collected during a HyBIS dive at Rio Grande Rise, a tiny microbe’s world.

On board of the RRS Discovery we collected Fe-Mn crusts, corals, calcarenites and crust biofilms at Rio Grande Rise. These samples will be analyzed at the Microbial Ecology Laboratory in the Oceanographic Institute of the University of São Paulo (Brazil). The diversity of microbial habitats will help us to understand how the tiny lives can influence the Fe-Mn crust formation and the deep-sea life.

Final note from Prof. Bramley Murton, Chief Scientist.

Finally, we have a cruise logo – made by Arthur Guth – this will be made into a cruise T-shirt after we get back to Santos, tomorrow.

That is it from Expedition DY094, RRS Discovery cruise to the lost land of the Rio Grande Rise. We have found a lot, learnt a lot, made new friends and great plans for future collaboration.

A stroll in the sponge gardens.

By Arthur Güth – biologist @ Universidade de São Paulo (USP) - Brazil

The HyBIS dives have held a great deal of expectation for everyone on board. Geologists are waiting to see the features shown during multibeam survey and biologists are expecting to spot the life that inhabits these depths.

So, it is during these dives that we keep learning how the relief of the Rio Grande Rise shapes the distribution of the animals on it.

A view from a terrace of FeMn crusts covered in colonies of S. oculata. Here the currents are higher, bringing more food.

Typically, we see “gardens” of the branching sponge Sarostegia oculata at the edges of terraces and rocky outcrops where the currents pickup bringing more food. Like other sponges, these animals are filter feeders, living on small food particles floating in water. But what is the most interesting about them is the association with a zoanthid – a coral relative. These zoanthids, Thoracactis topsenti, are spread along the sponge probably benefiting from the body structure and habitat chosen by Sarostegia.

The robotic arm of the HyBIS sampling near these colonies. Notice also the dead colonies on the bottom

To the untrained eye, the sponge and its hitchhiking polyps look like a coral colony. The typical branching and the spacing between the polyps can fool even an experienced biologist. But what is most intriguing is that this kind of association between cnidarians and sponges is not found anywhere else but in the deep sea. And it is still not clear whether this relationship is mutualistic, with both animals benefiting mutually, or that the zoanthid simply finds a very nice place to settle and live.

 

A colony of Sarostegia oculata obtained from a dredge (left). Detail of the sponge and its associated Thoracactis topsenti polyps (right).