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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A merry (subtidal) Bamfield Christmas

Amanda loves tide poolsby 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.

The “decorations”:

Bugula californica

Credit: J Watanabe. Image from http://seanet.stanford.edu/

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!

Calliostoma annulatum (Purple-ringed top snail)

Calliostoma annulatum

Image credit: Steve Lonhart (SIMoN / MBNMS), from Wikimedia Commons.

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.

Pisaster ochraceous

Pisaster ochraceous

Image credit: Jackson Chu, from Flickr

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.

The party guests:

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).

Oncorhynchus nerka (Sockeye salmon)

Sockeye salmon

Sockeye salmon in its brightly colored holiday colors, probably heading upstream to spawn. Image credit: PacificFishing.com

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.

Cryptolithodes sitchensis (Umbrella crab)

Umbrella crab

Image credit: Ken-ichi from Flickr

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.

Haliotis kamtschatkana (Pinto abalone)

Image credit: University of Oregon Museum of Natural and Cultural History

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.”

Lopholithodes mandtii (Puget Sound King Crab)

Lopholithodes mandtii (Puget Sound King Crab)

Image credit: Jackson Chu via Flickr

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.

Anarrhichthys ocellatus (Wolf eel)

Scott's Bay - Wolfeels

Image credit: Jackson Chu via Flickr

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.

There are loads of other animals, and probably seaweeds too, that deserve to be added to this list.  Vote for your favorite 2012 Bamfield holiday creature, and consider recommending another either in the poll or the comments section below!

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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