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Seagrass Wrack in the Salt Marsh – Blessing or Curse?

2-Minute Video: Seagrass wrack kills part of the marsh, but do its benefits outweigh the destruction?

Our videos to date have centered on biodiversity in the marsh and how it can make a marsh stronger against disturbances. As we see in this video, at least one type of disturbance might actually promote genetic and/ or species diversity.
Dr. Randall Hughes FSU Coastal & Marine Lab/ Northeastern University
This snake was found in a seagrass wrack experiment in the Saint Joseph Bay State Buffer Preserve. Blue crabs were often found taking shelter in their experimental plots as well.

This snake was found in a seagrass wrack experiment in the Saint Joseph Bay State Buffer Preserve. Blue crabs were often found taking shelter in their experimental plots as well.

This time of year if you look around salt marshes in our area, you’ll probably see a strip of dead plant material, or “wrack”, resting on top of the salt marsh plants around the high tide line. Look closer, and you’ll see that it’s mostly made up of seagrass leaves that have either been sloughed off naturally (seagrasses produce lots of new leaves in the summer and shed the old ones) or, occasionally, uprooted by boats driving through shallow seagrass beds. Look even closer (say, by picking it up), and you may just find a harmless marsh snake (or worse, a cottonmouth!) – in our experience, they like to hang out in the cool, moist areas under the wrack.

So is this wrack “good” or “bad” for the salt marsh? As with many things in life, the answer depends on your perspective. If you’re a snake or other critter that likes the habitat provided by the wrack, then it’s probably a good thing. On the other hand, if you’re one of my crew who finds that snake, and particularly if you’re Robyn who REALLY doesn’t like snakes, then it’s most definitely a bad thing. Or, if you happen to be the plant that the wrack settles on top of for long periods of time, then it’s a bad thing, because many of those plants die. But, if you’re a seed that is looking for a good spot to germinate in the marsh, then the bare spot created by the wrack is likely a good thing.

Bare spot left in salt marsh left by seagrass wrack.Last fall, David and I teamed up with Dr. Peter Macreadie from the University of Technology Sydney to find out how the bare “halos” created when wrack mats smother the underlying marsh plants influence the marsh sediments. It turns out, these bare areas store less carbon in the sediments than the nearby vegetated areas, which makes them less valuable as “sinks” for carbon dioxide. But as I mentioned earlier, the bare areas can also serve as a good spot for new plant species (or new genotype of a given species) to start growing, potentially increasing the overall diversity of the salt marsh. And as the seagrass wrack decays, it can provide valuable nutrients to the marsh sediments that support future plant growth. So what is the net outcome of all these good and bad effects?

We decided to do an experiment to answer that very question. As Ryan and Meagan will attest (along with almost everyone else in our labs who we enlisted to help us), this was a very labor-intensive experiment. First, we had to figure out how much wrack is typically in a given area of marsh. Then, we had to collect a lot of wrack, weigh it, assemble it into bags that could be “easily” moved to our experiment, and add it to cages that would help hold it in place. We’re talking ~1.5 tons of wrack picked up and moved to various spots!

FSU Coastal and Marine Lab technician Megan Murdock spin dries seagrass wrack for an experiment at the Saint Joseph Bay State Buffer Preserve.To make matters even more interesting, we had to soak the collected wrack in water to make sure it was all the same wetness, and then spin it around in mesh bags (think salad spinner on a very large scale) for a set amount of time to make sure we could get a consistent weight measurement on each bag. Anyone driving past the SJB Buffer Preserve in early September of last year must have wondered what craziness we were up to! And since we were interested in whether the length of time the wrack sits in one place influences its effects, or whether the number of times that wrack sits in a particular area matters, we moved all of this wrack around in our cages every 2 weeks for 3 months to mimic the movement of natural wrack by the tides. And then we measured everything we could think of to measure about the marsh.

We’re still going through all the data to determine the net outcome, but as expected, whether the wrack is a blessing or curse depends on who you are:

  • Juvenile blue crabs seem to like hanging out in the wrack (which is a much nicer surprise to find than a snake, even when they are feisty!)
  • Fiddler crabs also appear to like the wrack, with greater burrow numbers when wrack is present.
  • Contrary to our expectation that wrack would kill cordgrass and allow other plant species to recruit into the marsh, it looked like cordgrass actually did better in the wrack cages!
  • Sea lavender, a marsh plant with very pretty purple flowers, does not do so well when covered with wrack (Learn more about sea lavender and its relationship with mussels).

More to come once all the data are analyzed…

This material is based upon work supported by the National Science Foundation under Grant Number 1161194.  Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Music in the piece by Philippe Mangold.

The many personalities of a grad student

Emily Field FSU Coastal & Marine Lab

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IGOR chip- employment 150You’ve heard about research from a lab tech’s perspective from Tanya, and from a Principle Investigator (PI)’s perspective from Randall and David, so I thought I’d give you a graduate student’s insight. Being a grad student is kind of like being a mash-up of a tech, a student, and a PI: you do a lot of the “dirty work,” but you also have to be able to direct other students and manage your own research. You’re taking classes, but you’re also teaching. You’re writing grant proposals for future projects, but you’re also trying to figure out how to analyze data from past projects. And while this might sound hectic enough to create split personalities, I love it! I get to develop my own projects, take challenging and interesting classes, and help Randall with her projects. In fact, my favorite thing about work is that it’s such a tumbled mix of things: my time is split between the lab, field, classroom, and desk. Life as a grad student is never boring!

Emily and Robyn getting gear ready to collect porewater samples

Emily and Robyn getting gear ready to collect porewater samples.

I moved to Florida in May 2009, right after graduating from University of Rhode Island, and worked for Randall as a tech before starting school in the fall. It was a great way to familiarize myself with the system and learn appropriate sampling techniques for the area. I came in thinking that I wanted to work with epiphytes (small seaweeds that grow on other plants/seaweed) on seagrass. I did develop a project working with Chris Stallings on his huge Big Bend survey looking at the epiphytes throughout the region, but as I was working for Randall, I became more and more interested in developing my own project in the salt marsh. I am now studying the effects of wrack in the marsh. The epiphyte project is ongoing, and a marine certificate student, Michele Sosa, took over the project this summer so that I would have more time to develop my wrack research.

Learn more about Emily’s seagrass wrack study.

I think that is one thing I’ve learned as a grad student: there’s so much you could do, that it can be hard at first to pick one thing to develop into an interesting and informative project. If you’re not careful, you might end up with a bunch of semi-related “side projects.” I definitely owe Randall a lot for helping me stay focused and develop a clear project with a solid theoretical basis. As Tanya said, when there is a lot of work to do, it’s easy to get bogged down in the details and forget the big picture –which you definitely can’t do when you’re in charge of the project!

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Dr. Randall Hughes and Emily Field.

The other trick to grad school is balance, which can have a steep learning curve! One of the first things they tell you when you enter school as a graduate student is that you’re expected to work 60 hours a week: 20 on your coursework, 20 on teaching or your advisor’s research (depending on what you’re being paid for), and 20 on your own research. Of course, every week does not break down into this perfect division, but I think the main point to remember is to balance all of your responsibilities. Which is much, much easier said than done. As I’m writing this post, I’m thinking about the various other tasks I should probably be doing. My bugs need sorting, that paper needs reading, those buckets need mending… the list goes on. But, hey, I knew what I signed up for when I decided to go to grad school. I was warned. However, if you ever see me talking to myself, do me a favor and send for the nice men in the white coats?

Watch Emily survey seagrass beds and learn more about epiphytic algae.

Comments are welcome!

Is it over?

Dr. Randall Hughes FSU Coastal & Marine Lab

IGOR chip- biodiversity 150Since my last post, oil has stopped spewing from the Deepwater Horizon well, a very welcome development in what has been a long and grim story. Although it is tempting to feel that we are out of the woods, all one needs to do is consider the amount of oil that has entered the Gulf to realize that it will be a long time before we fully understand the ecological impacts of this disaster, much less fully recover from it.

That said, the probability that the marshes I study in St. Joseph Bay and Apalachee Bay are going to be directly impacted by oil has declined dramatically. You may wonder, were our efforts to collect “pre-oil” data wasted? The answer is no, for a number of reasons:

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