By Danielle Ludeman
As scientists, we all have to keep up to date on the happenings in our field. Although reading papers is not usually my favorite part of doing research, I love that moment when I stumble across a really cool paper and immediately want to run and share my find with someone. Whether you react that way or not, cool papers help to remind us of why we do what we do, and motivate us to keep plugging away at our own research, because we just might get a cool paper out of it too. So to share some of the cool papers in marine science that are out there, I am going to post them to this blog. And what better way to start off the cool papers section than to post about a paper from the Bamfield Marine Science Station’s very own Jackson Chu (and former member of the Leys lab) and his recent paper on predators of glass sponge reefs published in Invertebrate Biology. Now I may be a little biased in thinking this paper is really cool because it’s about sponges. And I was part of the 2009 research cruise when the first nudibranchs on the glass sponges were found. But seriously – glass-eating nudibranchs?! Super cool.
Alright let’s back up a second here – glass sponge reefs? Yup, glass sponges (Class Hexactinellida) in the deep, deep waters off of British Columbia form huge reefs, much the same way that corals form reefs in tropical waters! These vast and majestic glass sponge reefs span hundreds of kilometers along the coast – one of them even lies just at the doorstep to Vancouver, at the base of the Fraser River. Yet even though they live just below our feet, their deep-water habitat of about 100-200m deep meant that we only discovered them about 25 years ago, and we still have much to learn about this important ecosystem!
Glass sponge reef in the Strait of Georgia, viewed from ROPOS. Photo credit: A Kahn
Glass sponges are made out of just that – glass. They form a silica-based skeleton that comprises >90% of their body weight, leaving less than 10% to organic living tissue. Because of this, very few animals are expected to feed on them. But in 2009 and 2011, while surveying the reefs aboard a research vessel equipped with the remotely operated vehicle ROPOS, Chu and Leys noticed two species of large dorid nudibranchs, Peltodoris lentiginosa and Archidoris odhneri, sitting on top of some of the glass sponges on two of the three reefs visited. Now because nudibranchs are notorious sponge-eaters, they had a hunch that these cute little guys may actually be voracious predators in disguise.
Glass sponge-eating dorid nudibranchs found during the 2009 cruise of the Strait of Georgia glass sponge reefs. Photo credit: D Ludeman
So how do you know the nudibranchs are actually eating the sponges? By looking inside their stomachs! By doing so, Jackson found that their stomach and fecal contents were full of spicules unique to both of the main reef-forming species of glass sponges, making these two species of dorid nudibranchs the first known predators of BC’s glass sponge reefs. And the small amount of organic tissue compared to glass in the sponges must mean the nudibranchs have to eat A LOT of glass to sustain their large size! Nom nom nom.