By Nicole Webster
You can see the lovely holes in urchin tests used creatively. Credit: Norm Wiens
by Amanda Kahn
If you liked the SEM images from Getting to the Heart of Urchin Spine Attachment, then check out this recent post over at the Echinoblog. These echinoderms are not from around Bamfield, but they are done on regular urchins that we do have around BMSC, including Strongylocentrotus franciscanus and S. purpuratus (versus the irregular, or heart, urchins that I wrote about). Those two urchins can become so large, they’re like spikey grapefruits roaming around on the seafloor, mowing down algae in their path (in the case of urchin barrens) or hiding in cracks waiting for algae to drift by (in the case of kelp forests).
by Amanda Kahn
Sand dollars live in aggregations. In the time-series photos below, from research done in part by Dr. Fu-Shiang Chia, a researcher from the University of Alberta, sand dollars that were strewn haphazardly within a cleared area moved together to form dense aggregations. These aggregations can be as dense as 600 individuals per square meter. At that density, having a million sand dollars means having about 1.7 square kilometers of sand. To have a million people, well, that’s about the population size of Calgary.
Sand dollars have two modes of feeding: suspension feeding and deposit feeding. Suspension feeders remove particles from the water, including small drifting pieces of kelp but also smaller particles. Deposit feeding happens when the sand dollars snuffle along the seafloor, removing organic matter from around sand grains. A neat study in 2007 observed something neat about sand dollar feeding: the proportion of time spent feeding either as deposit- or suspension feeders depended on the density of the sand dollars present! A study published in 2007 found that as densities increased, the proportion of sand dollars that depended on deposit feeding (instead of suspension feeding) decreased. That means greater densities had to depend on what was in the water column versus what they could scrabble together from organic material on the seafloor.
This brings in questions about intraspecific competition, something I’ve been thinking a lot about lately. When the sand dollars change their mode of feeding based on density, that makes it seem like there is not enough food from deposit feeding alone that can sustain them. Instead, at higher densities, more sand dollars depend on suspension feeding, meaning food that has moved through the water column and flows and refreshes with the currents. Looking at the figure above, it looks like even at low densities, some sand dollars preferentially rely on suspension feeding anyway. I wonder if there is a point at which even suspension feeding cannot sustain the numbers of sand dollars (or other filter feeders) in a given body of water. Maybe currents change and suddenly there is less food than before, or filter feeders just get too efficient at pulling food from the water and deplete it continually.
All of this thinking is making me hungry. I think I’ll go forage now–some sand dollar cookies sound like good brain food for the train of thought I’ve been following! (Check out the recipe for the cookies below by clicking on the picture of the cookies.)
Hmm, looking back, this post wandered a bit…Getting back to the title of this post, if I had a million dollars…
…they’d probably all be suspension feeding. And cookies are delicious.
Birkeland, C., and F.S. Chia (1971). Recruitment risk, growth, age and predation in two populations of sand dollars, Dendraster excentricus (Eschscholtz). Journal of Experimental Marine Biology and Ecology, 6(3):265-278.
Fodrie, J.F., S.Z. Herzka, A.J. Lucas, and V. Francisco (2007). Intraspecific density regulates positioning and feeding mode selection of the sand dollar Dendraster excentricus. Journal of Experimental Marine Biology and Ecology, 340(2):169-183.
by Amanda Kahn
Hi folks! Just a short post today. I wanted to feature this amazing video I saw, produced by Rendezvous Divers, a diving resort operated in Barkley Sound. Since I recently wrote about the amazing predatory abilities of sea stars, I thought I’d follow up with this video of yet another animal’s dramatic response once it senses a sea star nearby.
Whoa!! That escape response must have cost the sea anemone so much energy! But I guess it’s better than being eaten. Have a great weekend, and keep an eye out for five-armed predators!
by Amanda Kahn
Sea stars are intense invertebrate predators. Like, eat-everything-in-sight voracious. It might be hard to imagine at first. Some sea stars are soft and look cuddly, like the Pteraster pictured below, which always makes me think of the stars from Super Mario Brothers games.
The Pteraster pictured above harbors a more sinister side. Namely, the oral side, where there are five mouth plates with mouth spines on each (that’s right, pentaradial symmetry means they don’t just have TWO jaws like we’re used to, but 5 chompers!).
But sea stars are slow-moving, aren’t they? They couldn’t possibly be effective predators against other invertebrates that can move…right? Well first of all, they’re not that slow. Those little tube feet can stick and unstick quite quickly, easily overtaking other benthic invertebrates. Crabs are quick, and usually can get away…but a race between a snail and a sea star isn’t really a race at all.
But as seen with the sea cucumber above, animals that normally move slowly have special escape strategies that, while energetically quite expensive, can work to free them from a sea star’s inexorable reach. Snails do a similar trick, torquing their shells around and causing them to tumble away downhill and, hopefully, down away from the sea stars. Scallops clap their two valves (shells) together, allowing them to swim away from the area with the offending predator. So there are strategies for avoiding the occasional sea star encounter, at least based on typical densities of sea stars.
However, ChrisM, founder and author of the Echinoblog, pointed out a phenomenon that has been noted a few times in the waters of British Columbia, in which super dense swarms of the tube-footed predators carpet the seafloor.
Check out his post for the full story, amazing pictures from Neil McDaniel, and some hypotheses for why these swarms might occur. I’ve reposted the info here because I’m curious–have any divers noticed this happening in the Barkley Sound area? Other accounts have been off the coast of Vancouver, within the Strait of Georgia, but I can’t imagine it would be too different in Barkley Sound, and we definitely have lots of divers that go out of Barkley Sound who could have noticed something like this. Leave a message in the comments below if you have, do check out the full story of these swarms on the Echinoblog, and try to forget that image of FIVE sets of mouth spines before you go to sleep tonight!
by Amanda Kahn
My first SCUBA dive in Bamfield was at a site called “Aguilar”, although by some it’s also called the “Love Shack.” I don’t know the history of the building that sits perched on the rocky intertidal zone in the cove (maybe a local can chime in on that in the comments below), but the picturesque cove is an interesting, curiosity-inspiring place above- and below-water.
A dive beneath the Love Shack features reveals a shallow field of cobbles housing sea squirts, sponges, snails, sea stars, and TONS of sea urchins. Aguilar sits at the northeastern tip of Bamfield’s West Side, which means that from the marine station, it is accessible only by boat. It is a good site for a training/practice dive, which is what we used it for, because it is protected from swells (it was a stormy day the day we dove), shallow, and there are open expanses on the seafloor where one can practice skills without quite as much worry about bumping into a fragile animal (though buoyancy control should never be undervalued).
This site is an urchin barren, meaning if you go, you’ll find a habitat that’s overrun with urchins. Urchins are often opportunistic feeders who sit in burrows and feed on kelp that happens to drift by. However, urchins in urchin barrens come out of their burrows and scour the benthos (seafloor), eating through live kelps. What results is a habitat that contains mostly urchins, and very few kelps. Pictured in the video below is an urchin barren filmed near BMSC.
Farther south, studies have shown that the loss of one of urchins’ key predators, sea otters, is implicated in facilitating the swap from a kelp forest habitat to one of an urchin barren. Whatever causes urchin barrens up here, once a habitat becomes an urchin barren it is fairly stable–it would be difficult to recover the habitat back to a kelp forest. Likewise, if a kelp forest is robust and healthy, it is difficult to convert it into an urchin barren. In the video below, notice that there are tons of urchins visible, but no kelp in sight.
This interesting phenomenon is called “alternate steady states” by ecologists.and is interesting because it shows that no one habitat is the best for a specific location. Can you think of other habitats, whether in land or in the water, where there can be alternate steady states? The urchin barren/kelp forest is the classic example, and I realize that I haven’t really thought about other possibilities. If you can think of some, please leave a comment below!
On the west coast you may have noticed sea urchins, specifically purple ones (Strongylocentrotus purpuratus) are hidden in crevices in the rocks, some that seem not only the perfect shape, but so deep the urchins can’t escape! This is not a trick of your mind, but ‘intentional’. The purple sea urchin is one of several species of urchin that actively bore into rocks, both by abrading with their spines and grinding with their teeth.
Some species, or younger urchins leave their protective home at night to graze, returning home during the day. In some cases the urchin bores too deep, or grows to quickly and becomes wedged in its hole. I’ve seen that at Keeha beach, but no photo available. In that case it depends on the food to drift into the hole.
The purple sea urchin is quite famous for it’s boring, and has even been noted boring directly into steel pilings in California!
I found another boring urchin in Cuba, I believe it is Echinometer lucunter – the red rock urchin or rock boring urchin. Don’t take this identification too seriously, simply matching photos and biogeography is not the most accurate way to make a positive ID.
by Amanda Kahn
One day while exploring an island in Trevor Channel during a low tide, I happened across this sea star.
Apart from looking like it was dancing a happy dance on a barnacle-encrusted rock, there was something notable about this individual. This species of sea star usually comes in one of three colors: orange, reddish-brown, or purple. However, this one was orange with purple tips on its arms.
The purple tips on the sea star I found made me wonder what causes colors to change in these sea stars. It’s not fully known yet, but people are thinking about it.
Pisaster ochraceus is commonly found in the intertidal zone around Barkley Sound and is known to be a keystone predator for intertidal habitats. This means the sea stars are largely responsible for the way intertidal communities are arranged, with bands of mussels in the middle intertidal zone and very few mussels and barnacles beneath that zone.
What is known is that color variation is not genetically determined, at least not directly. A study done partly in Bamfield by Chris Harley and co-authors found no meaningful distinctions between orange versus red versus purple sea stars, even though they looked very different. Instead, within an area, such as within the San Juan archipelago or the Strait of Georgia, all sea stars had very similar gene sequences, indicating that all color morphs can and do breed freely and easily with other color morphs. Fitting that idea with the commonly-accepted theory that confines individuals within a “species” (two individuals can’t reproduce to create viable offspring that are also capable of reproduction if they are different species), Harley and co-authors concluded that there don’t seem to be multiple similar-but-not-quite-the-same species, called cryptic species, living amongst each other on the intertidal rocks of Barkley Sound.
Orange and purple (and sometimes white) color morphs have also been observed in a deep-sea heart urchin, Echinocrepis rostrata. Urchins are part of the same phylum as sea stars, so they are expected to be similar to each other. The color morphs of E. rostrata were also not genetically distinct from each other, indicating that the colors do not seem to be cryptic species of each other either.
So if colors are not related to the genetics of the sea stars, then what’s left? Well, as in the debate of nature vs. nurture, if the sea stars are not born with the genetic predisposition to be purple or orange (the “nature”), then it must be something in their environment that determines their color (the “nurture”). This is where it gets really interesting, with Harley and co-authors finding that the differences in diet might affect the colors of sea stars (though that was not conclusively tested), while size and location did not. The authors in the paper even noted,
“Notably, small fractions of orange stars have purple coloration at the tips and along the undersides of their rays, especially if a ray is actively growing (e.g., following injury; CH, pers. obs.). Even smaller fractions have a tracework of purple coloration on their aboral surface (CH, pers. obs.). Very small Pisaster are not chromatically differentiated, and some orange adults may turn purple when held for long periods under laboratory conditions (J. Pearse, Long Marine Laboratory, University of California Santa Cruz, pers. comm.). These observations imply that individuals express different pigments as they grow or age; however, the effects of age and diet remain confounded for the time being.”
The idea that sea stars may change colors depending on changes in their diet or age was a new concept to me. Why do you think different color morphs happen? Is it related to diet, like Harley and co-authors suppose? Or age-related? Maybe you’ve read a more recent paper about it in a class? Please let me know in the comments section below–I’d love to learn more about this!
Harley, C. D. G., M. S. Pankey, J. P. Wares, R. K. Grosberg, and M. J. Wonham (2006). Color polymorphism and genetic structure in the sea star Pisaster ochraceus. Biological Bulletin 211(3), 248-262.
Vardaro, M. F. (2010). Genetic and anatomic relationships among three morphotypes of the echinoid Echinocrepis rostrata. Invertebrate Biology 129(4), 368-375.
by Amanda Kahn
Other than those with life cycles shorter than one year, most marine residents are present year-round in tide pools and subtidal habitats in Bamfield. However, as you go tide-pooling this December, keep an eye out for these particular animals whose appearances rival that of the Christmas decorations you find humans have put together on land.
This bryozoan forms spiral tree-like spires and looks like a beige grove of Christmas trees. Find animals living on the bryozoan (called “epibionts”) and you even have decorations!
These colorful snails are brilliantly gilded with orange and purple spirals, making them look like beautiful ornaments for decorating a tree. Calliostoma annulatum are found from tide pools down into subtidal kelp and rocky reef habitats. I’ve seen them both in kelp reefs and urchin barrens, and they are quite abundant in Barkley Sound.
These sea stars come in a variety of colors, mainly shades of purple and orange, and resemble the star that tops Christmas trees on land. Pisaster ochraceous lives mainly in the intertidal zone, where it is an important predator, responsible for enhancing diversity in an area that would otherwise become dominated by mussels.
Like so many attendees to Christmas parties, these animals are adorned in red and green, sometimes tastefully, and other times in a cheesy way (again, just like humans).
Salmon are anadromous, meaning they live in the ocean for much of their lives, but return to rivers to reproduce. The sockeye salmon is silver with a blue back while it lives in the ocean, but in the fall adult males turn red and head up rivers to spawn. The green head ties together with the red body for a festive holiday look.
Umbrella crabs come in a variety of colors, but every so often you find ones that are pink with green patterns dotting the carapace, like a gaudy holiday sweater. The wide carapace hides the softer, more easily damaged appendages beneath.
The pinto abalone is a gastropod with a large shell. The inside of the shell, shown in the right of the photo here, is prized in jewelry for its iridescent colors. The outside of the shell, however, functions more as camouflage and is tougher than the inside, resisting attacks from animals that might bore into the shell. Abalone are grazers that eat algae and, though important food items in the Pacific Northwest, most abalone species are endangered or threatened as a result of overfishing and a disorder called “withering foot syndrome.”
This crab lives in the Pacific Northwest and is quite good at blending into the background. This may come as a surprise, since once viewed under strong sunlight, its colors stand out as brilliantly as any Christmas lights decorating a home.
Bah humbug! The wolf eel is like the great-uncle who comes to the holiday parties and then grumbles about how overcooked the roast is. Wolf eels might not be caught at a holiday party though–they tend to be territorial and remain in the same area most of their lives.
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!