Scardy Snails

Can you scare snails with a sea sear? What if you just have some water that smells like a crab, would that be enough to scare a snail so much that it won’t eat? That’s what we set out to find out this week.

We had some tanks with seaweed in them, and either added snails, snails plus a sea star, or snails plus water that smelled like a crab to make the snail THINK that there was a scary crab nearby. We also had some tanks with just seaweed, to act as a control (a ‘nothing’ treatment for us to compare our results to). Half of these tanks were kept cold in a seawater table, and half were kept at room temperature.

IMG_3300

Our snail (Littorina littorea) eating some seaweek (Ulva). Photo: Emily Lim

HOWEVER. A bunch of pesky shore crabs managed to crawl into the cold tanks and shredded most of the seaweed, so our results are pretty muddled from those treatments. The crabs also escaped the lab completely and were terrorizing the offices down the hall, but that’s neither here nor there.

Screen Shot 2017-03-20 at 3.20.40 PM

A pesky shore crab. photo from Island Nature, edited by Emily Lim

We found that the snails ate a lot of seaweed when they were by themselves, but not very much when there was a sea star with them. Interestingly, smelly crab water didn’t deter them from eating. This is what we call a trophic cascade, where the predator has an indirect effect on the stuff the herbivore is eating (the vegetation) by eating or scaring the herbivore. In our case, this means the sea star keeps the snails from eating seaweed, resulting in more seaweed left over.

Next, we wanted to find out how afraid of our predators the snails are. Our instructions included the phrase: “gently use [the sea star] like a miniature cattle prod” (science is weird, folks), which basically translates to us poking snails with sea stars and seeing how fast they crawl away. We also recorded how fast snails crawled sitting in crab water or plain seawater, and after being poked with a pencil. We found that the snails didn’t really care about the pencil or sea star, because they crawled just as fast (slow) as they did when they were in plain seawater. Interestingly, they crawled even SLOWER in the crab water and we don’t really know why.

In the end what this tells us is that snails are scared of sea stars when they have to live together for a week, so much so that they don’t eat as much seaweed as they do when they’re alone. This is called a trophic cascade, where the presence of a predator indirectly increases the amount of vegetation by scaring or eating the herbivore. And overall, snails don’t really care about smelly crab water.

If you’re interested in learning more about the famous trophic cascade that happens just off our shore, involving kelp, urchins, and sea otters, click here

Picture from: http://islandnature.ca/2011/05/shore-crab-uncertainty/

 

 

 

How much rain could a rainforest get, if a rainforest could get rain?

Bamfield Marine Center is located in a temperate rainforest, which means that it gets a lot of precipitation. But how much precipitation is a lot of precipitation? And why do I say precipitation instead of rain? In temperate rainforests such as Bamfield, moisture can come in the form of rain, hail, snow, and fog. All of this adds up to about 2846 mm per year! In contrast, Vancouver, a city that prides itself on getting a lot of rain, only gets 1,199 mm per year. Luckily when we went on our nature walk through the forest it was a bright clear day, which is unusual since Bamfield receives precipitation 193 days of the year.

So what does all of this rain mean for the kinds of things that can grow here? Because of all the rain, many of the nutrients and things trees need to grow get washed out of the soil by the water. This is good news for the marine systems that receive all of this run off, but for the forests it means that there aren’t a lot of nutrients left. Because of the way dead matter accumulates and decomposes on the forest floor, the top layer of soil is typically the most rich. All of this means that in order for trees to get the nutrients they need to grow, their roots have to grow out instead of down. With the large amounts of precipitation the forest relieves the tree roots don’t have to go very deep to reach moist soil, so they’re quite happy to stay surface level. All this moisture means that the forest floor is quite muddy, which can be a problem if you don’t stick to the trail and get stuck!

image

Stuck in the muck! Photo credit: Emily Lim

Shallow roots work great for getting nutrients and water, but when strong wind storms come along the trees are very poorly rooted and are vulnerable to getting toppled over. In fact, in these forests wind storms are the largest source of disturbance! All of that rain keeps things nice and damp, so forest fires aren’t as much of a risk here as they are in drier climates. When trees are toppled over by storms, they become part of the decomposing matter that will provide nutrients for generations of trees to come. The dominant tree in Bamfield’s forest is the Western Hemlock. It’s quite common to see a bunch of hemlocks all perfectly in a line, and it’s not because of tree planters! Hemlocks will often start growing out of a fallen tree, called a nurse log, such that you end up with a whole line of them along the dead tree. Eventually, the new trees grow and the dead one decays, leaving you with a perfect line of hemlocks.

Check out http://wwf.panda.org/about_our_earth/ecoregions/pacific_temperate_rainforests.cfm if you want to read more about temperate rainforests and the things living in them!