When researchers came across seamounts in the central Arctic that contained dense arrays of sponges, their interests peaked. What is the source of the energy that sustains this dense mass? The Seamounts they examined contained three sponge species, Geodia parva, Geodia hentscheli, and Stelletta rhaphidiophora. Sponges in the genus Geodia are known to house large amounts of microbes within their tissues. These microbes can aid the sponge in a number of ways, providing antibiotics, processing waste, and transferring nutrients.
They sampled carbon (δ13C and Δ14C), nitrogen (δ15N) isotopes, and fatty acid (FA) isotopes of the sponge tissue. They also did the same on suspended food particles.
Another potential energy source is degassing or hydrothermal venting; no measurements of these processes were found in or close to these seamounts.
It turns out that the sponges sit on a mat of organic matter. The researchers found that a large proportion of this organic matter is the remnant material of past seep biota, apparently produced during a phase of active venting of the seamounts several thousand years ago. Thus much of the food the sponges feed on is extinct fauna leftovers. Interestingly, remnant organic matter from hundreds or thousands of years ago still feeds an ecosystem.
Seamounts and More Seamounts:
On a similar subject, a recent paper mapped a lot of new small seamounts. Mapping the ocean floor is still a big deal since we know little about it. Using satellite topography researcher observed 19,325 new seamounts. The satellite uses a vertical gravity gradient, which indicates the physical features under the water by the change in the height of the water (altimeter reading). The new seamounts have been added to the seamount catalog; there is a seamount catalog? Knowing where these seamounts are is just the first step; seamounts often hold biodiverse or abundant fauna, as we have seen with sponges. However, only about 700 seamounts have been explored in any detail.
Sources and Further Reading:
Cardenas P, Rapp HT, Schander C. and Tendal OS. 2010. Molecular taxonomy and phylogeny of the Geodiidae (Porifera, Demospongiae, Astrophorida) – combining phylogenetic and Linnaean classification. Zoologica Scripta 39, 89–106.
Gevorgian J, Sandwell DT, Yu Y, Kim S-S, and Wessel P. 2023. Global distribution and morphology of small seamounts. Earth and Space Science, 10, e2022EA002331. https://doi.org/10.1029/2022EA002331
For more on the organic carbon of the oceans, see this review:
Kharbush JJ, Close HG, Van Mooy BAS, Arnosti C, Smittenberg RH, Le Moigne FAC, Mollenhauer G, Scholz-Böttcher B, Obreht I, Koch BP, Becker KW, Iversen MH and Mohr W. 2020. Particulate Organic Carbon Deconstructed: Molecular and Chemical Composition of Particulate Organic Carbon in the Ocean. Frontiers of Marine Science 7:518. doi: 10.3389/fmars.2020.00518
Morganti M, Slaby BM, De Kluijver A, Busch K, Hentschel U, Middelburg JJ, Grotheer H, Mollenhauer G, Dannheim J, Rapp HT, Purser A, and Boetius A. 2022. Giant sponge grounds of Central Arctic seamounts are associated with extinct seep life. Nature Communications 13: 638. https://doi.org/10.1038/s41467-022-28129-7
Seamount Catalog: https://earthref.org/SC/
VCG imagery: http://portal.gplates.org/cesium/