Long carapace spines help larval crabs swim

by Anna Smith and Amanda Kahn

We are used to seeing crabs scuttling across the seafloor or scrambling under rocks in the intertidal zone, but before they settle on the seabed they have larval stages that live in the water column as plankton.  Zoeae (pronounced zoe-EE-uh) and megalopae (MEG-uh-lope-ee) drift through the water, eating food and eventually metamorphosing into bottom-dwelling crabs.

Crab life cycle stages

Life cycle stages of a crab: an egg hatches into swimming zoea stages, then to a megalopa, then metamorphoses into a benthic juvenile and adult crab. Image credit: A Snail’s Odyssey

For her class project in Crustacean Biology (a summer course taught in 2012), Anna Smith worked with instructor Greg Jensen to study how swimming is accomplished by the zoeae of a porcelain crab, Petrolisthes cinctipes. Most crab larvae swim vertically in the water column and are fairly poor swimmers. These zoeae are swept along with the currents and are often taken out to sea with no hope of returning to the shore to settle. Check out the video below to see how zoeae of most crab species move in the water.

Most crab zoeae have sharply pointed spines projecting from their carapace, as pictured below. Previous studies have found these spines to be connected with predator avoidance by making the larvae harder to swallow. The zoeae of porcelain crabs, however, have unusually long spines sticking out the front and back of the carapace. They are also much stronger swimmers than zoeae of many crab species, enabling them to stay close to shore and avoid being swept away from settling grounds. These zoeae swim horizontally through the water column and exhibit much more directional control than most crab zoeae. Anna studied whether the elongated spines of porcelain crabs were connected to their unique swimming by studying their swimming ability with both spines intact, then removed the front, back, or all spines to see how their swimming changed.

Zoea of a porcelain crab

Zoea of a porcelain crab. Image credit: Greg Jensen 2015. This image is from his new book, Crabs and Shrimps of the Pacific Northwest.

The spines were in fact very important to the swimming ability of the zoeae.  Zoeae who had their front (anterior) spine removed could not maintain constant depth in the water.  Zoeae who had their posterior spines removed could not swim backwards or change directions easily and with both front and back spines removed the zoeae could not swim at all. This led Anna and Greg to conclude that the spines contribute to the superior swimming ability of porcelain crab zoeae.

Why is this important? This suggests that the carapace spines are not only used as physical protection from predators, as previously suggested, but also contribute to their survival in other ways. Anna and Greg also hypothesize that the ability to better control direction and water column depth helps the zoeae navigate currents and stay close to shore and may explain their limited dispersal offshore.

Citation:

Smith, AE, and GC Jensen (2015). The role of carapace spines in the swimming behavior of porcelain crab zoeae (Crustacea: Decapoda: Porcellanidae).  Journal of Experimental Marine Biology and Ecology, 471:175-179.

If you want to learn more about the crabs and shrimps along our coast, check out Greg Jensen’s new crustacean guide Crabs and Shrimps of the Pacific Northwest.

To learn more about this course and others offered at BMSC, check out the University Programs website.

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Flat foram

Windy ride
By  Nicole Webster

I had a thin section made of one of my shells, and it came back with a serendipitous hitchhiker. A foraminiferan, you know, those single celled protists that make a gorgeous test (shell) usually out of calcium carbonate? Well it was at just the right place to be beautifully sectioned itself. The section is 30um thick of a 5cm shell, and the foram itself is only 0.5mm wide.

Foram thin section in plane polarized light. Credit N. Webster

Foram thin section in plane polarized light.  The darker spots inside the test are probably dried up tissue, and the little balls underneath the test are probably the glue used to attach the foram to the shell. Credit N. Webster

Foram thin section in cross polarized light. Credit N. Webster

Foram thin section in cross polarized light. Credit N. Webster

Thin sections are typically used in geology to identify different crystals, and thus the rocks that they are made up of. I recommend a quick Google image search, some are really quite pretty. Here I was using it to see how many layers and in what orientation the crystals are layed down in my snails.
A chunk of rock (or shell) is ground down as smoothly as possible to 30um (0.03mm) so that it is transparent. Once under the microscope, a polarizing filter is used to see crystal features better. A cross polarizing filter is used to see interference colours, allowing greater characterization of the mineral. That is why the second image looks a little like something from the 60s. Although the CaCO3 is relatively clear, the glass of the slide refracts the light quite a bit, making a psychodelic pick rainbow. This is a very simplistic view of thin sectioning, please correct me if I’ve misunderstood something.

PS I learned a new word making this post. Arenaceous. It means sandy, or likes sand (for plants), and specifies a geologic grain size ranging from 2 to 0.625mm. In this context it means those foraminifera that don’t grow their own shell, but rather glue bits (read:sediments particles) together to make a shell.

References
1. Rock-Forming Minerals in Thin Section. Steve Dutch, Natural and Applied Sciences, University of Wisconsin. https://www.uwgb.edu/dutchs/Petrology/thinsect.htm
2. Corliss, B. H. 1985. Microhabitats of benthic foraminifera within deep-sea sediments. Nature 314:435-438.

Sandy Mussel beds II

Windy ride

By  Nicole Webster
I was back at Ross this Spring, and am here to update you on the state of the mussel bed on the beach. Short form: It’s still there! (last year’s post)

Overview of the bed, facing the point. Credit: N Webster

Overview of the bed, facing the point. Credit: N Webster

 

Close up of the mussels. They are about 5cm in length. Credit N. Webster

Close up of the mussels. They are about 5cm in length. Credit N. Webster

The mussels are big enough, I could believe they are the same as last year’s, and if so, must have survived the winter storms without a good anchor due to the very protective nature of the beach.

Sensory organ discovered in sponges helps them respond to their environment despite having no nervous system

by Amanda Kahn

Sponges are animals, but they do not have the features we’re used to seeing when we think of animals: no gut, no head or tail, no nerves, and no stomachs or other organs.  And yet despite not having a nervous system, sponges are able to respond to their environment by changing the canal sizes in their filter-feeding system, in an action called the “inflation-contraction response.”  It’s basically akin to what we do when we sneeze.  This was observed in the mid-1900’s, but scientists have only been able to speculate what could be helping the sponges sense and coordinate various cells in their body when there are no nerves or sensory organs observed.  Danielle Ludeman, one of the authors here at the Madreporite, has just published an article describing the sensory organ that she and her coauthors, Nathan Farrar, Ana Riesgo, Jordi Paps, and Sally Leys, discovered in many different species of sponges: primary cilia used to detect changes in water flow.  Check out the time-lapse video below to see how responsive sponges are to irritants (in this case sediments) in the water.

Danielle tested if those cilia are used to detect changes in water flow by using drugs that target and knock out the cilia.  When the cilia were knocked out or knocked down, the “sneeze” response couldn’t be initiated.  If cilia were permitted to grow back following treatment, the “sneeze” response could be initiated.  In our kidneys, primary cilia are used to detect water flow.  The structure of the paired cilia Danielle found aligns well with those of primary cilia in other animals, further supporting that these are sensory cilia that allow the sponges to detect their environment.

The cilia line the osculum, the chimney-like opening of the sponge.  If that osculum is removed, the sponge also is not able to initiate a sneeze response.  This led Danielle and co-authors to determine that the osculum can be thought of as a sensory organ, and not just a giant chimney.

Figure 4 from Ludeman et al. 2014

The “sneeze” response is shown by an increase in canal diameter followed by a rapid decrease (the black lines in the graphs). Various drugs that affect the cilia also affected that inflation/contraction. Source: Ludeman et al. (2014).

Why does this matter to us, and how does it apply to evolutionary theory?  Sponges are one of the earliest branches off of the animal tree of life (the Metazoa).  While they are animals, their distant relation to us and to all other animals (collectively called the Eumetazoa) means they diverged from whatever last common ancestor the Metazoa shared and evolved into something quite different and independent of what other animals have evolved into.  This isn’t unique–every animal phylum is very different from every other.  What is unique is their placement at the base of our collective “family tree.”  If a sponge shares a feature that we also have, it’s likely that the proto-animal–the last common ancestor that all animals shared–had that feature as well.  It brings us a little bit closer toward understanding how we evolved from single-celled organisms to the multicellular, fantastically complex and coordinated animals we are today.

Still think sponges are boring?
(Hint: they are, but only in one way that word is defined!).

Citation:

Ludeman, D.A., N. Farrar, A. Riesgo, J. Paps, and S.P. Leys (2014).  Evolutionary origins of sensation in metazoans: evidence for a new sensory organ in sponges.  BMC Evolutionary Biology, 14(3).  doi:10.1186/1471-2148-14-3.

To learn more about sponges and research on the origin of animal body plans, check out the Leys lab website.

My first time at a conference

by Susan Anthony

I’m unsure as to why I have never been to a conference before, but I haven’t. I have almost completed my 2nd year as a graduate student at U of A, having done 2 field seasons, and finally have data worth presenting. So I ventured onto unchartered territories.

Palm trees

Classic California shot. Credit: S. Anthony 2013

The conference I chose was the Western Society of Naturalists. This year it was held at the Embassy Suites in Oxnard California.

Oxnard marina

Oxnard marina. On my afternoon off, I went for a walk along the boardwalk. Credit: S. Anthony 2013

After frantically analyzing data and producing graphs, formatting Powerpoint and practicing my talk, I hit the road and air for sunny Southern California. The conference was at a swanky resort on the beach, which allowed very brief beach walks at lunch break. The mornings were busy with symposia, and the afternoons were packed with back-to-back 15 minute presentations: you were running out of one talk to get to the next.

WSN name tag

It’s official. Credit: S. Anthony 2013

It was a great experience. I met some wonderful people, and learned about research that was being conducted, and results that were being found. There were lots of parties, a lively auction, and inspirational talks: most notably the final speech by the secretariat, on the subject of being a naturalist.

Presidential banquet

Figure 5: A toast at the Presidential Banquet on the last night of the conference. I was lucky enough to get a ticket from someone who couldn’t make it, and in return placed bids on many books in the silent auction. Credit: S. Anthony 2013

The speech reminded me about the joys of being a naturalist (along with the annoyance faced when people mistake “naturalist” for “naturist”). He spoke of the history of naturalists; those that observed and wondered. They were interested in how things are in the natural world. This type of science is falling out of favour, perhaps because funding has declined. If we lose naturalists who can tell us how things are, and as our Earth gets damaged, how things might react.

Sunset in Oxnard

Sunset on my last night in Oxnard. The weather was beautiful. Credit: S. Anthony 2013

New article about glass sponge reefs

By Amanda Kahn

Glass sponges are in the news!  A lot lately…  This is fine by me–the more we all know about these amazing deepwater animals, the better.  Maybe one day I’ll have a conversation with a stranger that doesn’t involve me explaining that glass sponges are not the same as “sponges used for scrubbing wine glasses” (though there is such a thing).

Glass Castles in the Sea
Reef-building sponges are giving up their long-held secrets.

by Cheryl Lyn Dybas
Published in Natural History magazine

Anyway, check out the article, which features a lot of the research done by the Leys Lab at the University of Alberta (with some of the work done at BMSC), including how they feed, what they eat, how and where reefs form, how humans may impact them, and why CPAWS-BC is pushing to have them considered for protection.

Studying the globally unique glass sponge reefs

By Amanda Kahn

[Cross-posted on the Students Ensuring our Oceans’ Future blog.]

One month ago, we were busy in the lab at the University of Alberta preparing and calibrating instruments, gathering GPS waypoints, and preparing dive plans. Three weeks ago, we drove and flew to Vancouver Island with our equipment and plans. Two weeks ago, we boarded a ship to study the glass sponge reefs in the Strait of Georgia in B.C.

CCGS Vector

Heading out on CCGS Vector, our home away from home. Credit: A Kahn 2013

The main reef we were studying on this trip was on Fraser Ridge. If you drained the water from the SoG, you’d be able to see the ridge and the reef about 14 km away from Vancouver. Fraser Ridge reef is too deep for us to study directly by scuba (150 to 180 meters deep), so instead we study it with the help of the remotely operated vehicle (ROV) ROPOS. ROPOS is piloted and run by the Canadian Scientific Submersible Facility (CSSF) and functions as our eyes and hands underwater.

ROV ROPOS

ROPOS, our eyes and hands underwater. Credit: A Kahn 2013

With those eyes and hands, we studied the energy use and water pumping capacity of the glass sponges that build the reef. Glass sponges are really amazing animals—they can move huge amounts of water through their bodies, which are basically modified to be amazing filters. 9,000 liters of water can pass through a single sponge osculum (the “chimney” that water is released from by the sponge) each day! And from that, the glass sponges can feed on tiny particles, especially bacteria. This is pretty unique among animals—most other animals that feed on particles suspended in the water (called “suspension feeders”) can only capture particles that are larger by 10 times or more.  We did a lot of great science while on board the ship, and I’m now at the field station in Bamfield, British Columbia, to work with other sponges.  We will all spend the winter back in Edmonton working up the samples and data collected from this trip.

Glass sponge reef

Glass sponges in a reef–check out all of those oscula! Credit: CSSF 2011

I’m happy to be a part of SEOF because I can feel connected to other folks who are near the ocean full-time, can ask questions about logistics before I arrive, etc.  I’m the regional representative for Alberta and in this post wanted to show that being far from the ocean does not mean that we cannot have access to marine animals or study ocean-related issues.  Logistics may be more tricky than driving down to beach for the weekend to do some intertidal sampling, but it’s definitely doable and totally worthwhile.  Contact me if you have questions about the reefs or if you’re in Alberta and have questions about how you can get involved in the marine science community across Canada.

To learn more about the reefs, check out these videos, compiled by Sameena Sherman, a student from our lab: