Tag Archives: sea lavender

wrack

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.

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Diversity- Getting by With a Little Help From (Salt) Marsh Friends

2-Minute Video: Marsh cordgrass, needlerush, sea lavender, mussels, periwinkle snails, and fiddler crabs: diversity in the salt marsh.

In Randall’s last post, she looked at whether genetic diversity within the salt marsh foundation species- smooth cordgrass- made for a stronger marsh (and by stronger, of course, we mean better able to shelter yummy blue crabs for people and sea turtles). In today’s post and video, Randall examines how the combination of plants and animals around cordgrass- the species diversity of a marsh- might play a role as well.
Dr. Randall Hughes FSU Coastal & Marine Lab/ Northeastern University

IGOR chip- biodiversity 150Even though salt marshes often look like one big sea of green in the intertidal, there are plants and animals other than marsh cordgrass around. And even though I devote a lot of effort to understanding the effects of diversity just within cordgrass, these other species are also important – no marsh is an island. (Well, actually they are, but you get the analogy.)

Fiddler crab found in a St. Joseph Bay salt marsh.So who is important, and why? There are at least two animals that can be classified as “friends” of cordgrass – fiddler crabs and mussels. Fiddler crabs create burrows that allow oxygen to get down in the sediment, and cordgrass roots appreciate that oxygen. The fiddler crabs also aerate the sediment during their feeding, and they can excrete nutrients that the plants use to grow.

As an aside, fiddler crabs are also irresistible for kids (and maybe adults too!).

Mussels aren’t quite as charismatic as fiddler crabs, but they like to nestle around stems of cordgrass, and the byssal threads that they use to attach to one another and to the sediment can help prevent erosion. In addition, they excrete nutrients and other organic material as a byproduct of their filter-feeding, and the plants take advantage of these nutrients.

While investigating the relationship between mussels and marsh cordgrass, Randall’s graduate student, Althea Moore, noticed that mussels also seemed to often accompany sea lavender in the marsh. This led to a separate study for Althea.

So who is MORE important, mussels or fiddler crabs? We did an experiment to test that question, or really, to test whether having mussels and fiddler crabs together is better than having just one or another. The answer? As with much in ecology – it depends. For one, it depends on what you measure. If you look at the number of cordgrass stems, then fiddler crabs are the better friend – cordgrass with fiddler crabs does better than cordgrass without fiddler crabs, regardless of whether you have mussels or not. But if you look at how tall the plants are (another important characteristic in the marsh), then mussels are the better friend, but only when fiddlers aren’t around. And if you look at the amount of organic content, mussels increase organic content at the sediment surface, whereas fiddlers increase it belowground. In the end, the take-home message is that the more things you measure about the marsh, the more important it becomes that you have both mussels and fiddler crabs in order to be the “best”.

In the process of doing the experiment I described above, Althea (my graduate student) noticed that when she was out in the marsh, she often found mussels in and around sea lavender (Limonium) plants more often than she found them around cordgrass. She became interested in finding out whether the mussels benefit the sea lavender, the sea lavender benefits the mussels, or a little bit of both. She’s still working on the answer, but it just goes to show that although we often tend to focus on who eats who (think Shark Week) or who can beat who (Octopus vs. Shark, anyone? Or, for kids, there’s always Shark vs. Train – a favorite at my house!), there are just as many instances of species helping one another (not that they always intend to).

Of course, it’s not just animals helping (aka, facilitating) plants – plants can help other plant species to. We’ve shown through a series of experiments that cordgrass benefits from having its tall neighbor needlerush (Juncus roemarianus) around, but only if the snails that like to graze on cordgrass are also present. Nothing is ever as simple as it looks in the marsh…

Music in the piece by Revolution Void.

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.

Autumn in the marsh

Dr. Randall Hughes FSU Coastal & Marine Lab

Marsh periwinkles climbing on a cordgrass reproductive stem

A cordgrass reproductive stem stands above the surrounding plants.

IGOR chip- biodiversity 150 One doesn’t need to look at a calendar to realize that fall is upon us – recent cool mornings are a welcome sign. The marsh is also showing signs of change, with cordgrass flowering shoots springing up everywhere.

These stems are quite noticeable – they are taller than non-reproductive plants, and they have a “feathery” appearance due to the reproductive structures at the tops of the stems.

As I’ve mentioned before, cordgrass is one of those plants (like strawberries) that can spread by underground rhizomes, putting up new stems along the way. Alternatively, it can reproduce the “traditional” way, with reproductive stems that broadcast and receive pollen via the wind, ultimately producing seeds that fall to the sediment, get buried, and then germinate to produce new seedlings. Though conventional wisdom is that most new cordgrass stems are produced vegetatively by spreading rhizomes, it’s clear at our sites that these plants are investing a lot of energy in the other form of reproduction! Continue reading