Cool Papers! Part 2: Hermit crabs with a not-so ‘hermit’ lifestyle

By Danielle Ludeman

‘Hermit’ crabs seemingly implies that they are just that – hermits – living alone in their own (second-hand) shell, apart from society (i.e. their kin).  But are they as alone as their name implies?

According to a new study by Mark Laidre, terrestrial hermit crabs are forced to socialize if they want to find a new shell to move into! Carrying around giant shells on land would be heavy, and so terrestrial hermits, unlike marine hermit crabs, modify their gastropod shells by eroding the interior and creating a larger and more lightweight home. This also takes time, and so hermits will move into previously modified shells, if they are available, when it is time to move into a larger one.  To look at the consequences of this modification, Mark Laidre placed hermits in either 1) new unmodified shells or 2) previously remodeled shells of the same diameter, and found that only the hermits in the shells passed down from other hermits survived! The hermits in the unmodified shells could not fit into the small amount of space available, and thus they did not have full protection against ant attacks. There are virtually no unoccupied remodeled shells in the population, so when it comes time to moving on up into a bigger shell the hermits benefit from being around others if they want any hope in finding a previously remodeled shell!

Laidre calls this remodeling of the shell ‘niche construction’ (the process in which an organism changes its environment).  According to the fossil record, this ‘niche construction’ has been taking place in terrestrial hermit crabs for millions of years! Laidre argues that that is ample amounts of time for such a trait to start to drive social behavior, so that these remodeled shells become a form of ‘ecological inheritance’, where modification of the environment is reused by many successive generations.  Unlike genetic inheritance, ecological inheritance can be passed on to individuals that are unrelated.  These remodeled shells, therefore,may be a driving force for social dependence, even among unrelated individuals.

As it turns out, the need to find a new shell when a hermit crab grows drives another form of social behavior as well!  When a new shell becomes available in the environment, many hermit crabs gather round forming something called a ‘vacancy chain’. The hermit crabs will essentially line up from biggest to smallest (albeit in a not-quite so elegant fashion), taking the next biggest shell as it becomes vacant!

Waves, Caves & Humpbacks

By Danielle Ludeman

Living in Bamfield definitely has its perks, one of which is being located in the spectacular Barkley Sound. With hundreds of islands separated by deep water channels, Barkley Sound hosts abundant marine and wildlife along its diverse coastlines, which not only makes it an ideal location for doing research, it also makes for an amazing place to explore during days off! The multitude of islands that occur in Barkley Sound, such as the Broken Group Islands and the Deer Group, have become famous among kayakers and divers alike, and a couple of weeks ago I had the opportunity to see why when I did an overnight kayaking trip to the Ross islets in the Deer Group.

Visiting the seals at Wizard island. Photo credit: D Ludeman

Leaving early in the morning from the Bamfield Marine Sciences Centre to avoid the afternoon westerly winds, we packed the graduate kayak hatches full of camping gear, food, and drinking water and headed out across the Trevor Channel.  With a brief stop at Wizard island to visit some seal friends, we made it to the Ross islets within an hour and a half and set up camp at one of the two camp sites.  Lucky for us, even though it was one of the busiest kayaking times of the year, we arrived just as another group was leaving and so snagged one of the two camping spots on the islet!

Kayaking around Fleming Island in Barkley Sound. Photo credit: D Ludeman

One of the many bald eagles spotted on Fleming Island. Photo credit: D Ludeman

We then had the rest of the day to explore, and taking some advice from the departing kayakers we decided to paddle around Fleming, a large island beside the Ross islets.  Just as we were leaving (enjoying the much lighter kayaks to paddle in!) the clouds broke and it turned into an amazingly sunny day – even though the previous week in July had felt like Fogust!  The calm waters along the Trevor Channel side of Fleming made for some peaceful paddling, and we could even see some sea life through the glass-like waters!  On land, the long sandy beaches were stunning, and it wasn’t hard to spot the many bald eagles on the wind-swept trees!

As we rounded the corner at Tzartus island, we glimpsed this amazing sea cave and just had to go have a look.  Although it was tempting, we decided against paddling through it – probably a good thing too as when we were chatting to our fellow Ross islet campers later that evening, one of them had a story of going for a little impromptu swim right in the middle of the same cave!  Instead, we found a nice little beach to have lunch at, and enjoyed the amazing view that Barkley Sound has to offer.

Sea caves are abundant in Barkley Sound, such as this one on the southwest corner of Tzartus island. Photo credit: D Ludeman

After lunch, we left the calm waters of Trevor Channel behind and took off to paddle the side of Fleming along the Imperial Eagle Channel. The waves, although a little challenging, were exhilarating!  And well worth what we were about to see.  As soon as we turned the corner at the North side of Fleming we heard the explosive snort of a humpback whale and looked just in time before it dove back underwater.  We sat there motionless (or as motionless as we could in the waves) waiting for it to grace us with its presence again, and feeling the rush of being so near such a magnificent creature.  After a few more breaths the whale moved on, and so did we to battle the waves and observe the many more sea caves along Fleming.

The many colors of Pisaster. Photo credit: D Ludeman.

Late afternoon we arrived back at the Ross islets, just in time for the low tide! We gave our arms a much needed break and took off exploring the small island on foot, checking out the many tide pools and awesome creatures that they house! From the colorful starfish Pisaster, to the massive californian mussels Mytilus, and the medieval- looking gooseneck barnacle Pollicipes, there was plenty to seek and discover.  And after cooking some dinner on the beach, we sat down and relaxed, watching the tide come up on the rocks, and the sun set behind the Broken Group Islands.

Sunset at Ross islets. Photo credit: D Ludeman

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.