Day 21: Sponges of the deep.....

Georgios examining sponges on black coral from the Logachev mounds
Yesterday's dives at the Pisces site revealed a plethora of stunning white Lophelia - a great result, since we were not sure what we would find! Although there are still images and videos from John Wilson's 1973 dive, very little research has been conducted in the area in the past 40 years, so we were all very happy to see the white polyps waving in the currents.
Another animal which we are always happy to find are deep-sea sponges, and there amazing abundance means we are never disappointed! So, today's blog is written by Georgios from the University of Aberdeen, about his spongy specimens of the deep.

Cup-shaped sponges
Deep-sea sponge grounds are important deep-water ecosystems. They provide structural habitat, which is home to a great number of species, as well as acting as nursery grounds for commercially important fish. Importantly, sponges are thought to be a source of bioactive compounds, which can be used to make new drugs. Despite these major characteristics, deep-sea sponge grounds have been overlooked for many years. Their presence in areas of intense human exploration (i.e. gas / oil drilling and trawling) makes them particularly vulnerable to destruction. But, over the past few years, conservation of these important species has become a priority, which makes studies on the structure of these ecosystems essential.

Sponges at Mingulay
Sponges are mainly active filter feeders, which means that they pump seawater through their body and remove particles that are in the water that they can use as food, before pumping out any unused excess. Sponges can also play host to symbiotic bacteria, a relationship where the sponge gains important nutrients from the bacteria, and in exchange the bacteria thrive in their sponge tissue home. Recently, it has been shown that sponges with symbiotic bacteria can also use dissolved organic carbon as a food source, which is really important when looking at the role of sponges in the deep sea food web.

Incubation chambers
In this cruise, we have conducted on board experiments on the feeding and respiration of sponges from the Mingulay Reef Complex and Logachev Mounds, where we found them were attached to dead coral fragments. The sponges were placed in incubation chambers equipped with stirrers and optodes (which measure oxygen levels). In the chambers, they were fed with various food sources (glucose/ammonium, microalgae, bacteria), which were labelled with carbon (13C) and nitrogen (15 N) isotopes. After 24 h in the chambers, our samples were frozen so that we can analyse how much of these isotopes were taken up into the sponge tissues.

"If you’d told me you
needed so much filtered sea water
I would have taken more books"
These experiments will (hopefully!!) provide us with important information about the uptake and turnover of each type of food source. In this way, the role of sponge assemblages in carbon cycling in the deep oceans will be illuminated.