Tag Archives: salt marsh

marsh-sunrise

Does Diversity Matter in the Salt Marsh? A Look Back

Dr. Randall Hughes has collaborated with WFSU on this blog since 2010. We have spent years visiting her research sites in Saint Joseph Bay, where Randall conducted a multi-year study on salt marsh biodiversity funded by the National Science Foundation. The study has concluded, and Randall has published several papers on her findings. Here is what she has found.

This is Saint Joe Bay week on the Ecology Blog.  Wednesday, August 20th, at 7:30 pm ET: WFSU premieres the eighth season of Dimensions, and our Saint Joseph Bay scalloping EcoAdventure. 

Dr. Randall Hughes Northeastern University
Just a bunch of grass?  Not to the larval shrimp, juvenile mullet, pinfish, fiddler crabs, mussels, periwinkle snails, and blue crabs that make use of the habitat, or the birds and sea turtles that go hunting there.

Just a bunch of grass? Not to the larval shrimp, juvenile mullet, pinfish, fiddler crabs, mussels, periwinkle snails, and blue crabs that make use of the habitat, or the birds and sea turtles that go hunting there.

As you drive along Highway 98 towards St. Joseph Bay (SJB), one of the most common views outside your window is of the salt marsh.  From the car, it looks like a beautiful but monotonous meadow of green and/or brown, depending on the season, often intersected by tidal channels. So I won’t blame you if “diversity” is not the first word that comes to your mind as you gaze out the window. But diversity is exactly what I set out to find out about when this project first started – how much diversity is there in the marshes of St. Joe Bay, and what (if any) effects does it have? And now, several years later, I finally have answers to share!

First, let’s revisit what I mean about diversity. There are 2 main types that I have focused on for my research:

Species diversity, or the number of different species in an area. If you garden, you can think of it as the number of different vegetables or flowers you plant.

Genetic diversity, or the number of different genetic individuals (or genetic variants) in an area. Using the garden example, this would be similar to the number of different tomato varieties you plant in your garden.

Randall Hughes and Ryan Coker in an FSUCML Greenhouse

Randall and technician Ryan Coker tend to plants in an FSU Coastal & Marine Lab greenhouse. Before Randall and her team could begin to test their theories about marshes and marsh grass, they needed to create controlled marsh units of a comparable size, and needed to know the genetic identity of the grass in their plots.  Randall grew this grass for two years before conducting those experiments.

Wait – why so much talk about plants? Don’t animals have diversity too? Animals do have diversity, and this diversity matters – for one, having more species of fish on a coral reef means the corals grow better. But plants are the foundation of the marsh – if you have no plants, you have no marsh. So I have focused on the species and genetic diversity of the plants and tested how it affects the number and diversity of animals that live there (which includes animals that we like to eat, such as blue crabs). The dominant marsh plant species in many areas is cordgrass (Spartina alterniflora), and we created a greenhouse full of known genetic individuals to use in many of our experiments. Here are some of the highlights of what we have learned, with a little background on each, and links to the published articles where you can learn more if you’re interested:

1. Increasing the number of plant species in the marsh, even just from one species to two, can reduce the negative effects of a hungry periwinkle snail.

Periwinkles are really common in the marsh, and when conditions line up just right (the periwinkles are hungry, the cordgrass is already stressed from something like drought) they can mow down the cordgrass. We don’t see this happen very often in SJB, and I wondered if that was because there’s another really common plant species – needlerush – that often grows with the cordgrass, that the periwinkles also seem to like, at least for climbing on to stay out of the water and away from their predators. So we did an experiment where we planted cordgrass with and without needlerush and with and without periwinkles, and we found what I had expected: having needlerush neighbors around means the periwinkles don’t mow down the cordgrass!

Randall published these findings in the Ecological Society of America Journal.

2. Contrary to conventional wisdom that a few cordgrass individuals (also known as “clones”) rule the marsh, genetic diversity can be quite high, with as many as 9 distinct individuals living together in an area the size of a hula hoop.

periwinkles on cordgrass

Smooth cordgrass (Spartina alterniflora), the foundation species of a coastal salt marsh. Before she could understand how the genetic diversity of this species affects the health of a marsh, Randall needed to know how many genetic individuals were present within the ecosystem.

Genetic diversity is really important for the ability of plants and animals to respond to stress or change, and so it’s something we often want to know, but the bummer about it is that it’s not nearly as easy to measure as species diversity. You can’t just look at two cordgrass plants and tell whether they are the same or different genotypes! I teamed up with Dr. Katie Lotterhos to use little snippets of DNA to tell us whether the cordgrass plants we collected from the marshes around SJB were all a few closely related individuals, or whether there were lots of different individuals around. It turns out that even though they all look pretty much the same, there is a lot of genetic diversity in our marshes.

Randall and Katie published these findings in the Inter-Research Science Center’s Marine Ecology Progress Series (link is a PDF).

Monoculture plot- four genetically identical cordgrass individuals.  In this specific experiment, plots are composed off one, two, or four separate individuals.  Do plots with higher diversity fare better?

A monoculture plot of four genetically identical cordgrass individuals. In this experiment, similar to the one described to the right, plots were composed of one, two, or four separate individuals. Did plots with higher diversity fare better?

3. Changing the number of cordgrass clones living together in an area the size of a hula hoop affects how well the plants grow, as well as how many animals share that space. These effects of diversity may be particularly important when plants are first colonizing an area, such as in restoration efforts.

Once we knew how many different genetic individuals shared a hula hoop-sized area in natural marshes, we did an experiment to see how changing that number affects how well the plants grow. This experiment took a long time to prep, because we first had to grow a bunch of plants in the greenhouse so that we could keep track of who was who. After that, the experiment itself was pretty simple: plant 1, 3, or 6 different clones inside a hula hoop (well, in this case it was a modified hula hoop made of less expensive irrigation tubing) at the edge of the marsh, and watch them grow over time.

Randall published these findings in the British Ecological Society’s Journal of Ecology.

4. Just like you and me, different cordgrass clones have unique characteristics – some are tall, some are short, some do well in a crowd, and some like a little breathing room. And the animals that live amongst these plants, such as mussels and fiddler crabs, can go from being friends to enemies depending on which clone they are interacting with.

Even though I said before that all cordgrass plants look similar, it just so happens that when you grow the same clones in the greenhouse for a few years, you start to see slight differences among them. And these differences that seem pretty minor to us are really important to the small animals like fiddler crabs and mussels that live on and around the plants. So, in part to test this idea that different clones have different relationships with fiddler crabs and mussels, and in part just to do an experiment with fiddler crabs because I think they are cool, we set up an experiment using different cordgrass clones growing with just fiddlers, just mussels, or both. And although typically mussels and fiddlers are both “friends” with cordgrass (in that they provide it with nutrients and oxygen in the sediment to help it grow), that is not a universal truth – some cordgrass clones did not benefit (or even were harmed) by having mussels and fiddlers around.

Randall, her graduate student Althea Moore (whose investigation of a similar relationship between mussels and another marsh plant we covered in 2013), and Randall’s oyster collaborator Mike Piehler published their findings in the journal Oikos.

It’s a little disconcerting that ~ 4 years of work can be boiled down into these 4 highlights. Of course there are loads of details I’m leaving out, as well as other ongoing projects that will tell us even more about the effects of diversity in the salt marsh. That’s how the scientific process works – you gain some answers, and those answers lead to new questions! Job security for a curious mind…

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.

Keep up with the latest posts, environmental coverage from the WFSU News department and more at @wfsuIGOR.

Black mangrove propagules.

VIDEO- Mangroves and Cold, & Oyster Doctors Airs on WFSU

Rob Diaz de Villegas WFSU-TV

Wednesday, March 19 at 8 PM on WFSU-TV, catch the broadcast premiere of the new In the Grass, On the Reef documentary: Oyster Doctors.

Withered Black Mangrove

Although it was a relatively mild winter, one or two harsh cold snaps provided Randall an opportunity to test black mangrove survivorship in north Florida marshes, where it has become a more frequent resident.

Lately I’ve been preoccupied with wrapping up the National Science Foundation grant that funds a lot of what appears on this blog, and thinking about the future of the project.  The last major piece of funded content is our latest documentary, Oyster Doctors, chronicling four years of research conducted by Dr. Randall Hughes and Dr. David Kimbro.  On the one hand, the show is about learning how coastal ecosystems work.  And it’s about how the inner workings of salt marshes, oyster reefs, and seagrass beds provide people with jobs, clean water, and protection from erosion and storm surge.  But it’s as much about the ecologists as it is about the ecology.

Randall and David, and their graduate students- Tanya Rogers, Hanna Garland, and Althea Moore- are people who get inspired to pursue a line of research.  They get excited by an idea, like predators affecting prey more through fear than through their eating them.  They get excited about places.  David gets geeked out about predatory snails on Bay Mouth Bar.  Hanna falls in love with Apalachicola and wants to figure out its oyster problem.  Randall makes observations about things she sees in St. Joseph Bay marshes and it sets her on a path.  In one case, that path led her to the video above.

Randall’s interest in black mangroves has unfolded before our eyes on this blog, starting in 2010.  These trees have a range that ends to the south and east of here, yet here they were by her study sites.  To learn more, she started experiments.  Our Oyster Doctor premiere events on March 8 gave her a reason to come down from Massachusetts (she left the FSU Coastal & Marine Lab in January of 2013) and check on her mangrove experiments.  These experiments are growing away in the St. Joseph Bay State Buffer Preserve.  One of our premiere events was a walking tour of the Buffer and a visit to the experiment site.  One reason the trees have been spreading in northern Gulf marshes are the warmer winters we’d been having in recent years.  Recent cold snaps let Randall (and a group of interested parties) better see how certain sets of trees in her experiment might survive up here.  And so, as we finished the show, which has its section on the mangrove research, we went right back into the field and gained a little extra knowledge. Nature’s inner workings never stop unfolding.

Later that day, Randall joined Apalachicola Riverkeeper Dan Tonsmeire for an excursion within the Apalachicola River delta. Exploring the connection between freshwater bodies and coastal ecosystems has become a focus of this project since we started our EcoAdventures segments.

Later that day, Randall joined Apalachicola Riverkeeper Dan Tonsmeire for an excursion within the Apalachicola River delta. Exploring the connection between freshwater bodies and coastal ecosystems has become a focus of this project since we started our EcoAdventures segments.

In the coming months, we’ll get more posts detailing Randall and David’s findings in the studies we’ve been following.  And then… well, certainly more EcoAdventures.  Through those we can explore all of our area, connecting forests with swamps with rivers and back to the coasts, where this project was born.  As people signed up for the premiere and its associated events, we left a spot for people to tell us about their connection to our local wild spaces.  I’ll be looking those over as we move forward.  I love having a window into what all of you care about.  Likewise, this blog has a comments section!  Tell us what gets you excited about the outdoors, what you’d like to see more of, what’s not being covered?

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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.
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.

Dr. Randall Hughes inspects a black mangrove growing in the Saint Joseph Bay State Buffer Preserve.

Black Mangroves: Strangers in a St. Joe Bay Marsh

2-Minute Video: Mangroves don’t love the cold, but relatively mild winters have seen them multiply north of their range.  Randall takes a closer look at black mangroves in  the salt marshes of Saint Joseph Bay.

Dr. Randall Hughes FSU Coastal & Marine Lab/ Northeastern University

IGOR chip- biodiversity 150

A few years ago, I took my colleague Dr. Ed Proffitt to check out the marshes in St. Joseph Bay. He asked to see mangroves, and I thought he was crazy. Mangroves up here? No way! But we had only been in one Buffer Preserve salt marsh together for a few minutes before I realized that the small “shrubs” that I had previously ignored were actually small black mangroves! And the more we looked, the more we found. They aren’t everywhere, but they can be quite abundant in some places.

Shrubby black mangroves (Avicennia germinans) are an increasingly common site in the Saint Joseph Bay State Buffer Preserve.

Shrubby black mangroves (Avicennia germinans) appear to be an increasingly common site in the marshes of the Saint Joseph Bay State Buffer Preserve.

Mangroves typically occur below the “frost line”, or in areas that don’t experience hard freezes. Lore has it that mangroves have become more common in the northern Gulf of Mexico in recent years due to a series of mild winters. I haven’t been monitoring them long enough to say whether or not there are more now than there were, say, 10 or even 20 years ago, but it’s not hard to see that the ones that are here are successfully reproducing, with small seedlings surrounding the adult trees.

There are even red mangroves lingering around – they are less cold-tolerant than the black mangroves and a surprise to find in our marshes!

Dr. Randall Hughes inspects a black mangrove growing in the Saint Joseph Bay State Buffer Preserve.I definitely have not seen any significant dieback in the last 5 winters, even when we have had hard freezes. And I would not be surprised if they become more common and abundant as the climate continues to change.

Mangroves in the marsh raise a number of interesting questions. Will they take over? What will that mean for the services these areas provide to people? Will the fishes and crabs that we like to eat become more or less abundant if mangroves dominate over marsh grasses?

A study conducted in Texas marshes looked at conditions under which mangroves best survived in marshes.

Unfortunately, I don’t have the answer to these questions. But I can say that the mangroves that occur in St. Joseph Bay aren’t necessarily “better” at surviving in the northern Gulf than mangroves from farther down south. And why should they be?  Well, if a group of mangrove propagules arrived in St. Joe Bay, we may expect that only a subset of them would be able to survive the colder temperatures, and when these propagules grew into adult trees and produced propagules of their own, they should pass that “benefit” to their offspring (the process known as natural selection).

Black mangrove propagules.

Black mangrove propagules.

How do we we test whether St. Joe Bay mangroves are better equipped to live here than mangroves from down south? We have 2 ongoing experiments where we’ve planted “propagules” (young mangroves that look a lot like seeds) from different locations throughout FL in St. Joe Bay and followed them through time to see which ones survive and grow the best. There’s a lot of variation, but the St. Joe Bay propagules (which were largely the “runts” of the bunch to begin with) did not do as well as propagules from some of the areas down south such as Cedar Key and Cape Canaveral. These results suggest that it doesn’t take a particularly special propagule to survive in the northern Gulf; instead, there probably aren’t just many propagules that make it up here to begin with.

Of course, we’ve only been monitoring these propagules for 1-2 years; maybe the St. Joe propagules have an advantage when they get old / big enough to reproduce. We don’t want to speed up the mangrove take-over, so we’ll remove the seedlings in our experiment before that happens. But we’ll definitely continue to monitor the ones that already made it here on their own accord to see what they do next!

The Guana Tolomato Matanzas National Estuarine Research Reserve (NERR) south of Saint Augustine is where Randall and David have done a lot of their oyster research.  There, mangroves mingle with marsh cordgrass. Could salt marshes in St. Joseph Bay (or north Florida in general) one day look like something approximating this?

Music in the video by pitx.

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.

marshfriendsbanner

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.