I have been trying to write this post for a while, but every time I start to think about what to write about my work on deep sea sponges, I get stuck on where to begin. So, this idea stayed in the back of my mind and, suddenly, in the last couple of months, I met different people from different places who, when they realized what I was working on, asked me two things: “Why sponges?” and “Why the deep sea?”
Most people probably think of sponges (often confused with corals by lay people) as animals that just live on the bottom of the sea filtering water. Such a boring group of animals doesn`t receive much attention, except when Sponge Bob is mentioned, am I right? But those who work with them know very well that they are far from boring. Actually, these animals are so cool! They may appear simple, but they are so hard to identify that they make one either fall in love with them, or become terrified of them. Nicole Boury-Esnault, a French researcher and remarkable spongiologist, is used to saying, “everything is possible with sponges!” All kinds of colors, shapes and an incredible number of different microstructures, which are key components to identifying most of them, occupy the attention of those who work with sponges.
So, let me come back to the first question: Why study sponges? At first look you may think, “ok! Some different shapes and colors... and, so what?” Like all animals, they have their environmental roles and can be found living on the bottom of all oceans, and even in freshwaters too. They have adapted to different kinds of environments and because they cannot run away from predators they have had to adapt in ways to defend themselves. They might be "simple", but we are talking about one of the oldest animal groups known in the world! They must be doing something right. So, what do they do? In terms of "mechanical"/skeletal adaptation, the most gorgeous skeleton structures are produced to make a thick, sometimes prickly, and unpalatable bodies to save themselves from predators. They also have chemical defense adaptations, and it is here where the human interest-point comes in. A lot of chemical compounds are produced by sponges to defend themselves from predation, and these compounds, known as secondary metabolites, are being studied more and more. Nowadays, we have some important medications produced on the basis of chemistry learned from different sponges (e.g. HIV and anti-tumor cocktails).
And speaking about those adaptations to different places, can you imagine how much pressure, darkness and lack of nutrients deep-sea animals have to deal with? How do they survive in such extreme environments? When I say “deep sea”, I mean depths below 200 meters, ~656 ft. There are huge sponge gardens and reefs in deep waters, and such animals not only persist, but succeed wildly, creating structures that support an incredible array of other diverse organisms. Deep sea sponges exhibit amazing body shapes, as in Hexactinellida -- a group that is nearly exclusively found in cold- and deep-waters. One species of hexactinelid sponge in the deep waters from Pacific (east of China sea), Monorhaphis chuni, has been dated as the oldest living animal on Earth (11,000 years old!!). Imagine, individuals of this species have lived for pretty much the entire Holocene, and the rise and fall of so many civilizations. In 2016, another hexactinellid sponge also broke a record -- as the largest sponge ever found -- by being the size of a minivan.
Another exceptional family of sponges are popularly called carnivorous sponges because they have body parts that catch (like velcro) to small and unsuspecting animals that swim around or seek refuge. This is a surprising way for a sponge to make a living given that all the rest filter minute prey (often bacteria) from water that they pump through their bodies. Have I given you a little taste of why I am so in love with these animals?
This is my work: Within all these different forms and structures, I try to answer questions such as what makes this species unique among the others? Or, how many species are there in a particular region or area? How are those groups distributed in the oceans? And how are these distributions to be explained?
By Cristiana Castello-Branco [Edited by Allen G. Collins]
Additional Reading:
Godefroy, N., Le Goff, E., Martinand-Mari, C. et al. (2019) Sponge digestive system diversity and evolution: filter feeding to carnivory. Cell Tissue Res. https://doi.org/10.1007/s00441-019-03032-8
Newman, D.J. & Cragg, G.M. (2004) Marine Natural Products and Related Compounds in Clinical and Advanced Preclinical Trials. Journal of Natural Products 67(8): 1216-1238. https://doi.org/10.1021/np040031y
Van Soest, R.W.M., Boury-Esnault, N., Vacelet, J., Dohrmann, M., Erpenbeck, D., De Voogd, N.J., et al. (2012) Global Diversity of Sponges (Porifera). PLoS ONE 7(4): e35105. https://doi.org/10.1371/journal.pone.0035105
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