Tag Archives: cordgrass

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.

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The Many Personalities of Salt Marsh Cordgrass

2-Minute Video: Do sea turtles and fishermen benefit from a genetic diversity in marsh cordgrass?

As Randall mentioned in her last post, biodiversity can mean many things. In this video, she examines diversity within a species, in particular marsh cordgrass (Spartina alterniflora). Each Spartina plant has its own personality. What Randall wants to know is: are more personalities better for a salt marsh (and the sea turtles and blue crabs that use it)?
Dr. Randall Hughes FSU Coastal & Marine Lab / Northeastern University

Its difficult to see the diversity of the cordgrass in this vast sea of green.IGOR chip- biodiversity 150One of the more striking things about a salt marsh at first glance is how uniform it is. A sea of green. Or maybe a sea of green (cordgrass) in the intertidal and brown (needlerush) further back. But definitely not something that screams “diversity”.  And yet, wondering about the importance of diversity in the salt marsh is what I spend a lot of my time doing.

Often, when scientists talk about diversity, they are referring to different species of plants and animals (= species diversity). But there are actually lots of different kinds of diversity – functional diversity, phylogenetic diversity, genetic diversity. To illustrate what these terms mean, let’s shift to the topic I most like to think about when I’m not thinking about science – FOOD. Functional diversity is one of the broader categories, where different species are grouped by how they look or behave. So, think vegetables vs. fruits. Or, even green leafy veggies vs. root vegetables vs. berries vs. melons. Phylogenetic diversity refers to how related the species are – broccoli and cauliflower are more closely related (and thus have less phylogenetic diversity) than broccoli and zucchini – whereas species diversity refers to how many different species there are. Finally, even a single species can have a lot of diversity within it – apples are a perfect example of a fruit with large numbers of varieties to choose from. It’s this last level of diversity, genetic diversity, that I’m really interested in.

Some of a Spartina plant's below ground root structure.  Many of the plants used in Randall's experiment have sent out rhizomes under the sediment which have sprouted new shoots.  If you're at the edge of a salt marsh and see a line of marsh cordgrass plants sticking out into the water, they're likely connected by such a rhizome.

Some of a Spartina plant’s below ground root structure.  Many of the plants used in Randall’s experiment have sent out rhizomes under the sediment which have sprouted new shoots.  If you’re at the edge of a salt marsh and see a line of marsh cordgrass plants sticking out into the water, they’re likely connected by such a rhizome.

Unfortunately, it’s not as easy to tell different ‘varieties’ (aka, genotypes) of cordgrass apart as it is to tell a Granny Smith from a Red Delicious. Most of the plants look really similar, and it’s impossible to tell by looking from above the ground which ones are connected by roots and rhizomes below the ground. I have 2 solutions to this problem:

1. Take small pieces of cordgrass into the lab and use even smaller snippets of DNA to tell who is who. (As my dad says, think CSI with grass.)

2. Take a single cordgrass stem and grow it in a flowerpot in the greenhouse until it starts to produce lots of other stems. By splitting these up and allowing them to continue to grow (and keeping careful track of which pot is which), I can produce a supply of known cordgrass genotypes to do experiments with.

Neither of these techniques happens overnight. In fact, it took us nearly 2 full years to get enough genotypes in the greenhouse to start doing experiments with! (Proof that even someone without a green thumb – like me – can work with plants, but it takes longer than it should.)

Each bar in these graphs represents a different marsh cordgrass genotype. You can see how each plant differs in "personality" from its number of stems and flexibility.

Each bar in these graphs represents a different marsh cordgrass genotype. You can see how each plant differs in “personality” from its number of stems and flexibility.

The cool thing about spending that much time with these plants is that you start to recognize that they have their own flavors or personalities. Some grow a few really tall stems vs. others with lots of average size stems; some flower in July vs. others that flower in October; some have really flexible stems vs. others that are more rigid (which probably matters if you’re a snail climbing up the stem).

It’s these different personalities that may allow a mixture of multiple genotypes to do better over time than a genotype growing by itself. For one, if some genotypes are better at surviving some sort of disturbance, then having a mixture of genotypes increases the chances that one of those “good” genotypes is included in the mix. Or, if genotypes are all a little bit different, they may be complementary to one another, allowing the mixture to do better than any one of them growing alone. (This “complementarity” can also be referred to as facilitation, and it’s an idea we’ll return to in coming weeks.)

We have several experiments that are wrapping up now that test this very idea – do diverse marsh patches perform better than less diverse patches? If so, why does that happen? Early indications are that the answer is like a lot of things in nature – it depends. Sometimes the diverse patches do better, and sometimes they don’t. So now the trick is to figure out how to predict when diversity will matter, and use that information to help conserve existing salt marshes and restore marshes that have been damaged in the past (which can help provide a steady supply of blue crabs for both sea turtles and us!).

Music in the piece by airtone.  Thanks to Mineral Springs Seafood for letting us tag along as they emptied their crab traps.  And thanks to Gulf Specimen Marine Lab for the underwater footage of Allie the sea turtle (good luck out there, Allie!).

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.

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Crown Conchs- Friend or Foe?

For today’s post, we shift our look at the ecology of fear from oyster reefs to the (often) neighboring salt marsh.  We know crown conchs are villains on oyster reefs, but might they redeem themselves “in the grass?”  If they live on the Forgotten Coast, it depends on what side of Apalachicola they live.
Dr. Randall Hughes FSU Coastal & Marine Lab
The Crown Conch (Melongena corona).

The Crown Conch (Melongena corona).

IGOR chip_ predators_NCE 150If you’re a fan of oysters and you read David’s previous post, then you probably don’t like crown conchs very much. Why? Because David and Hanna’s work shows that crown conchs may be responsible for eating lots of oysters, turning previously healthy reefs into barren outcrops of dead shell.  And we generally prefer that those oysters be left alive to filter water and make more oysters.  And, let’s be honest, we would rather eat them ourselves!

But, in something of a Dr. Jekyll and Mr. Hyde act, crown conchs can take on a different persona in the salt marsh. Here, the exact same species acts as the good guy, increasing the abundance of marsh cordgrass.  And more abundant marsh plants generally means more benefits for we humans in the form of erosion control, water filtration, and habitat for the fishes and crabs we like to eat.  How exactly does that work?

Periwinkle in Spartina predator experiment

The Marsh Periwinkle (Littoraria irrotata).

If you look out in a salt marsh in much of the Gulf and Southeast Atlantic, I can nearly guarantee that you’ll see a marsh periwinkle snail. Usually, you’ll see lots and lots of them. These marine snails actually don’t like to get wet – they climb up the stems of the marsh grass as the tide comes in. While they are up there, they sometimes decide to nibble on a little live cordgrass, creating a razor blade-like scar on the plant that is then colonized by fungus. The periwinkles really prefer to eat this fungus instead of the cordgrass, but the damage is done – the fungus can kill the entire cordgrass plant! So these seemingly benign and harmless periwinkles can sometimes wreak havoc on a marsh.

But wait a minute – if periwinkles cause all the cordgrass to die, then why do you still see so much cordgrass (and so many snails) in the marsh? That’s where the crown conch comes in.

Crown conch pursuing periwinkle snail

At the edge of a marsh at high tide, a crown conch approaches a periwinkle snail. As shown in the video above, the conch was soon to make contact with the smaller snail and send it racing (relative term- the video is of course sped up) up a Spartina shoot.

In marshes along the Gulf coast, there are also lots of crown conchs cruising around in the marsh (albeit slowly), and they like to eat periwinkles. Unlike other periwinkle predators such as blue crabs, the crown conchs stick around even at low tide. So when the periwinkles come down for a snack of benthic algae or dead plant material at low tide, the crown conchs are able to nab a few, reducing snail numbers. And fewer snails generally means more cordgrass.

Of course, the periwinkles aren’t dumb, and they often try to “race” away (again, these are snails!) when they realize a crown conch is in the neighborhood. One escape route is back up the cordgrass stems, or even better, up the stems of the taller needlerush that is often nearby. By causing periwinkles to spend time on the needlerush instead of grazing on cordgrass, or by making the periwinkles too scared to eat regardless of where they are sitting, the crown conch offers a second “non-consumptive” benefit for cordgrass. One of our recent experiments found that cordgrass biomass is much higher when crown conchs and periwinkles are present compared to when just periwinkles are present, even though not many periwinkles were actually eaten.

Periwinkle in Spartina predator experimentOn the other hand, if the periwinkles decide to climb up on the cordgrass when they sense a crown conch, and if they aren’t too scared to eat, then crown conchs can actually have a negative effect on the plants. This is exactly what David found in one of his experiments.  In this case, the tides play an important role – west of Apalachicola, where there is 1 high and 1 low tide per day, each tide naturally lasts longer than east of Apalachicola, where there are 2 high tides and 2 low tides per day.  The longer tides west of Apalach appear to encourage the snails not only to stay on the cordgrass, but also to eat like crazy, and the plants bear the brunt of this particular case of the munchies.

So even in the marsh, it turns out that crown conchs can be both a friend and a foe to marsh cordgrass, depending on how the periwinkles respond to them. And figuring out what makes periwinkles respond differently in different situations just gives us more work to do!

Music in the piece by Revolution Void.

In the Grass, On the Reef is funded by a grant from the National Science Foundation.

Biodiversity and the Apalachicola: Why it’s Worth a Visit

Rob Diaz de Villegas WFSU-TV

Tune into WFSU-TV’s dimensions on Wednesday, February 15 at 7:30 PM/ ET to watch our paddling and wildlife watching EcoAdventure throughout the Apalachicola River system.

Zoom into the clusters of flags to see each site in more detail.
Island 3

This marsh island might be comprised of several genetically distinct cordgrass individuals, or just a few.

IGOR chip- human appreciation 150IGOR chip- biodiversity 150In composing and researching this post, I seem to have stumbled upon a diversity of biodiversity. In Randall Hughes’ salt marsh biodiversity study, you don’t always even physically see it.  Within a salt marsh, you might be looking at a variety of cordgrass individuals, or just one.  You wouldn’t know until you got the DNA results back from the lab.  That’s genetic diversity, the variation of genes within a species.  A little more obvious is the diversity of plant and animal life within a habitat: what other plants are mixed in with the cordgrass, what different predators are eating and terrorizing periwinkle snails, etc.  This species diversity is also crucial to a system’s health, and to the services it provides us. Continue reading