By Lilian Pavani
Illustration by Catarina Mello
Falling in love is unexpected, inexplicable, and incomprehensible. All of a sudden, it’s BANG! You’re in love! Well, this crazy thing happened to me, but with something quite different than another human -- it happened with a sponge (and I’m not talking about our friend Sponge Bob Square Pants).
When I decided to study biology, I knew that I enjoyed marine biology and cellular biology and that I wanted to do research. I left cellular biology behind after my first semester of college, but marine biology was still waiting for me to discover it. As I soon learned, my ideas about what marine biology was were fairly limited and would soon change. What I knew at that point came mostly from what I saw in Porto de Galinhas: beaches and coral reefs filled with tiny fish. I really had no idea about what I was going to study.
As I started to study invertebrate zoology, I was surprised to find out that there are more than thirty phyla of animals, not just the nine that I’d studied in school. This was the first time that I looked at sponges with a new set of eyes.
Can any organism be more obscure than a sponge? Sponges have no true tissue (they don’t have basal lamina), therefore there are no germ layers, coelom or organs. They are practically a cluster of specialized cells with different functions that can organize themselves to create a single asymmetric organism that eats, grows and reproduces. They do all of this without moving, because they’re sessile, and what's more, they decorate the environment with their beautiful colors!! That’s it, I was hooked!
The Tedania ignis sponge, the object of my study (Photo by Renata Goodridge with a CC00 license)
During my invertebrate zoology course, each student picked a phylum to present on. Of course I volunteered to speak about sponges, so I could learn more about these fascinating animals. For instance, because they are filter feeders, they are good bioindicators of environmental quality. Also, since they are sessile, they need a way to compete with other organisms for space, so they can produce secondary metabolites. These metabolites are of pharmaceutical interest!
Around the same time, I read in the college newspaper that someone from the Economics Department had developed a study about the economic effects of the drop in tourism and fisheries in the region of Ilhabela and São Sebastião due to a recent oil spill. Aha! A lightbulb went on: I could use sponges to study beach pollution!
Tedania ignis on a rock (Photo by Eduardo Hajdu)
No one specialized in sponges at my university, but sponges live along rocky shorelines, and practically everybody worked in those regions. Even though the rest of the lab was involved in the Biota Project, my advisor gave me a vote of confidence and allowed me to write a proposal of my own while I was an intern in the laboratory. My only requirements were that I would have to include amphipods (a tiny crustacean that would later provide me with a Masters’ degree) and set the pollution aspect aside for a bit.
At first that bothered me, but only until I realized the world that could fit within a sponge, or even on top of it. Sponges are secondary substrates to marine life, meaning that they expand the area of occupation within rocky shores, allowing many more organisms to live there. The structure of the sponge provides a variety of microhabitats, specifically good for juvenile organisms, therefore contributing to the local biodiversity.
For my study I chose the sponge Tedania ignis, commonly known as the fire sponge, given that it can cause dermatitis that looks like burns on the skin. These sponges live in easily accessible places, so I could collect them without using diving equipment during spring tides (tides of maximal range near the time of full moon and new moon). During these periods of really low tide, the sponge can easily be spotted along the rocky shore.
Back in the lab, while screening my samples, I discovered several marine organisms that I had never seen before, like small hydrozoa and pycnogonida (sea spiders). I also saw “miniature” versions of animals I recognized, including bivalves. It was a great surprise to open a chamber and find a “nest” of nematodes! It was a really fun activity.
My study lasted a year, with monthly sampling. In this time, I was able to analyze the temporal variation of the associated fauna. I also looked at relationships between the fauna present and environmental factors, such as the amount of organic matter at the collection site and within the sponge itself, using the dry weight as a parameter.
Example of bivalve molluscs found inside and on top of the sponge Tedania ignis: a) Modiolos carvalho; b) Sphenia antillensis; c) Isognomon bicolor; d) Lithophaga bisculata (no scale). (Photos by Lilian Pavani).
An interesting thing I found out about this sponge is that most of the organisms live on its surface. These external organisms (epibiont fauna) were more affected by the amount of organic matter present in the environment than the animals inside of the sponge. The epibiont fauna also changed more temporally, showing that environmental factors (specifically food availability) were most important for these external animals.
A curious thing I noticed in this study is that, contrary to what I initially thought, large sponges (heavier dry weight) do not host more organisms inside. While I didn’t study the size of my sponge’s chambers, I found out from other studies that the fauna that live inside of sponges are more influenced by the size and shape of their chambers than by the sponge’s total size, and apparently there’s a preference for small chambers. Probably, when a small sponge grows, its chambers grow as well, which makes its interior less appealing to the endobiotic animals. Big canals may offer smaller niche diversity and less protection than smaller canals.
Longitudinal cut of the sponge T. ignis, detail of the canals. In grey: marine sediments, the main source of filtered food by sponges. (Photograph by Mariana Fernandes and Izadora Mattiello)
And that’s how sponges taught me to write a scientific proposal and initiated me to marine science. I have eternal admiration, gratitude, and love for them!
About the author:
Lilian is a biologist, she holds a Masters in Ecology with a specialty in Environmental Engineering from the University Estadual of Campinas. She is a lover of sponges and other marine invertebrates, especially the colorful ones. After sailing through the world of sponges, algae, amphipods, and petroleum, the winds eventually took her down other literal roads, where she worked studying roadkill and doing environmental management and supervision of highway construction. She has diverse interests including education, innovation, and cooking. Lilian plays the flute with an amateur group of musicians, writes creatively, and enjoys bird watching. She lives with her feet in the sand and sort of between tides.