Last week was Northeastern Spring Break! Woohoo! This meant I had no class, and no TAing and therefore more time for research! I saw this as the perfect opportunity to do experiments, uninterrupted by the usual commitments of the week.
I study seasonal nutrient cycling in coastal ecosystems and based on data I have collected over the past couple years, I know that this time of year is the time when essential nutrients like nitrogen are most abundant in coastal waters. This means that seaweeds can take up more nutrients, and store these in their tissues, to prepare for the summer when there will be limited amounts of these essential nutrients.
Work by other scientists (and some of my own previous experiments) shows that snails and other animals that eat seaweed might choose to eat different seaweed based on a variety of things, including the amount of nutrients they can get from the seaweed. Also seaweeds living at different places on the beach have different access to nutrients because they spend different amounts of time underwater when they can absorb nutrients.So a seaweed living low on the shore might be more tasty to a snail because it has more time to absorb nutrients and therefore has more nutrients in its tissues. Finally, seaweed might be more tasty to snails depending on whether the seaweed is an adult or a baby.
The experiment that I did tested these factors that might change the way that snails and seaweeds interact. I chose to do the experiment in March, because I have done similar experiments in April and June and I want to see how the interactions I observe change with season. For the experiment, I put seaweeds and snails in “mesocosms” (fancy word for reusable plastic containers – see photo) to see which seaweeds snails like to eat: seaweed living high or low on the shore, and seaweed that is an adult or baby. I let snails choose between all combinations of these types of seaweeds, and weighed the seaweed before and after the three-day experiment to see how much of each seaweed the snails ate.
My favorite part of this experiment is that it also allows me to test the positive effects of the snails on the seaweed. So, I know right now your asking“What? Positive? I thought the snails were eating the seaweed?!”, but in addition to eating seaweed, snails can also benefit them by excreting ammonium AKA snail pee! The ammonium can be an important source of nitrogen for the seaweeds – facilitation! The experiment is set up so that I can measure how the seaweed grows when it’s being eaten, when it’s benefiting from extra nutrients via snail pee and when no snails are around at all. Positive interactions are neat, and understudied in the field of ecology, because negative interactions are much more obvious. Its easy to see a lion eat a gazelle, but much harder to see a snail pee on a seaweed, increasing its growth.
Why do you care about which seaweeds snails eat, you might ask. Well, these seaweeds and snails provide important nutrients to the whole community of organisms living on a rocky beach, so learning more about how they interact, and how those interactions can change with season, is essential to predicting how the whole rocky shore ecosystem might be affected by human impacts like pollution and climate change.
This experiment was very labor intensive – I weighed 480 pieces of seaweed, twice! But luckily I had some help from an awesome high school student volunteering in our lab – thanks Hannah! Also, I’m sure the neat results will make all the hard work worth it. So get excited for ground-breaking conclusions about seasonal, tide height and seaweed life-stage impacts on seaweed-herbivore interactions and rocky shore nutrient cycling – once I analyze the data!