A spongy habitat

By Danielle Ludeman

The world is full of organisms, living on organisms, that are living on other organisms.  You just have to take a moment to think about the complexity of life that can occur to start to appreciate all of the life around us.  Take a tree in your front yard – at first glance you may just see a tree, but when you start to look closer you notice the bird nest that will be home to baby chicks in the spring, and the squirrel that runs up and down the branches.  Then you notice all the different types of moss, lichen, and mushrooms that are growing on the tree.  And upon closer inspection you realize that this creates even more space for a variety of spiders and insects to thrive.  And we can keep going on and on to include all of the life that we need a microscope to see. And this is just on a single tree!

This summer, while doing some field studies at Bamfield, I began to appreciate all of the life that can be found on a single sponge.  Now it is well known that sponges can be very important habitat for many organisms, with some species being obligate commensals of sponges, meaning they can ONLY live on a sponge to survive.  But when I started to look closer at some of the sponges in my studies, I began to realize just how many other organisms call a sponge its home!  One species of sponge in particular – Suberites sp.  that I collected off of Brady’s beach – seemed to have a surprise guest visiting every time I looked at it!  I managed to photograph a few of these, and thought I would share these with you in the slideshow below!

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Cool Papers! Part 1: An appetite for glass

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.

Graduate Student Research at BMSC

by Travis Tai

Below is a subsample of what graduate students are studying RIGHT NOW at BMSC. This isn’t a complete survey of all graduate students at BMSC and it’s also not a complete summary of each person’s research.  If you’re interested in hearing more about anyone’s particular projects, leave a comment below and we’ll feature that student’s research in a separate post.

Suz Anthony, University of Alberta, MSc student with Dr. Rich Palmer

Sea slugs. Delicate, beautiful, DEADLY! These squishy creatures, most notably the opalescent sea slug, have the ability steal stinging capsules (cnidae) from their cnidarian prey, and sequester them in their colourful back projections (cerata). These cnidae are then used to defend the sea slugs from their own predators, including crabs, sea stars, and fish. But not all cnidae are equal; some cnidae can inject toxins, some are long and stringy and will entwine the mouthparts of arthropods, and some are more suited to piercing soft tissue. What I want to know is: If the sea slug is in the presence of a specific predator, will the sea slug preferentially select cnidae that will be most effective against that particular predator?

Mónica Ayala-Díaz, University of Victoria, MSc student

Monica in the field

Credit: M Ayala-Diaz

My name is Mónica Ayala-Díaz. I am doing my Masters degree at the University of Victoria. The purpose of my study is to evaluate the changes in behaviour of the marine snail Littorina sitkana due to the presence of trematodes, as these parasites can alter the behaviour of the snail in order to favour its predation by the next host so they can complete their life cycle. I am focusing on trematodes that have birds as their final host and I am testing if the parasite can get to the bird via direct predation of the snail or if it has another intermediate host. To achieve this, I am performing survival experiments in the field. To test changes in behaviour, I am tracking movement and grazing performance of L. sitkana.

Amanda Kahn, University of Alberta, PhD student with Sally Leys

Amanda on a ship

Credit: A Kahn 2012

I’m studying hexactinellid, or glass, sponges: a unique group of sponges that are unique because they are syncytial, meaning that instead of cells they have many nuclei all encased within a common cell membrane.  While other animals have small syncytial regions in their bodies (for example, human muscles), for the most part other animals (and even all other sponge groups) are composed of cells.  I’m studying how hexactinellid syncytia form and grow–from food capture to assimilation to growth of tissue, and finally excretion–which, beyond being really cool because it’s so unique to this group, is important to understand because a small group of glass sponges form reefs, just like corals, off the coast of British Columbia.  The reefs aren’t known to form anywhere else in the world today and are habitats for fish, crabs, sharks, and invertebrates; however, they are fragile and how the reefs grow and why they are so rare (the same sponge species can be found as individuals elsewhere, but only form reefs in a few places) isn’t understood.  Human activities such as trawling can destroy the fragile glass skeletons that form the reef, so understanding more about how the sponges work and what their effects are on animals living alongside them are the aims of my research.

Danielle Ludeman, University of Alberta, MSc student with Dr. Sally Leys

Danielle in the intertidal

Credit: D Ludeman

I study how the canal system in sponges (Porifera) is designed to allow both water flow and particle capture, and then how sedimentation can impact these filtration systems. Sponges are found in high densities worldwide, and as suspension feeders, they play an important ecological role in the recycling of nutrients.  A single 20-hectare glass sponge reef is estimated to filter 80,000 litres of a second!**  Increasingly, sedimentation from resource exploitation such as oil exploration or fishing trawls is having severe impacts on benthic suspension feeders including sponges, which, as filter feeders, are sensitive to materials that can clog their filtration system.  By understanding how their water filtration system works, we can begin to understand the potential impact of sedimentation. This knowledge can be used to predict what level of sedimentation sponges can tolerate to help manage important ecosystems such as the glass sponge reefs off the coast of British Columbia and the ‘ostur’ in the fjords of Norway.

** Chu WF and Leys SP 2010 MEPS 417:97-113

Travis Tai, University of Victoria, MSc student with Dr. Brad Anholt

Travis in the field

Credit: T Tai

I am a Master’s student at UVic, currently working on the evolution of sex-ratios in Tigriopus californicus.  T. californicus has a natural sex-ratio distribution that is extra-binomial, which suggests a polygenic sex-determination mechanism—multiple genes (environmental and/or heritable) contributing to sex-determination.  I am interested in Fisher’s theory of frequency dependent selection and modelling the heritable and environmental effects on sex-determination.  Fisher predicts that selection should select for balanced sex-ratios with respect to the relative costs of sons and daughters.  If sex-ratio should deviate from the balanced equilibrium, individuals of the less abundant sex will have a higher per-capita genetic contribution and frequency dependent selection will drive the sex-ratio towards equilibrium.  After many rounds of artificial selection for sex-biased genes, I have established population lines with male- and female-biased sex-ratios.  With relaxed artificial selection, I have been measuring brood sex-ratios for each treatment population for 8 generations.

Nicole Webster, University of Alberta, PhD student with Dr. Rich Palmer

Snails

Credit: N Webster

I am a PhD student working on the growth and development of shell ornamentation (ridges, ribs, lamellae, varices) in gastropods (snails). I want to know how a snail controls when and where to put ornaments, and how that affects them. My work at Bamfield is on two species, Ceratostoma foliatum, that has three, regularly spaced varices, that are precisely placed in the same position on each whorl, and Nucella lamellosa, that has many varices placed in a less controlled fashion. It is thought that Ceratostoma knows where to place each varix by encountering the previous one, and growing a new one in the same place, which I am testing with some shell manipulation experiments. I am repeating the experiments in Nucella lamellosa to determine how these less constrained varices differ in their growth pattern.

Want to learn more about any of these students’ research?  Or do you have questions about what you read about here?  Leave your questions or comments below!