Tag Archives: periwinkle snails

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How Can We Prevent Salt Marsh Die-Off?

2 Minute Video: Do Marshes Combat Die-Off Through Biodiversity?

Data on “cold” and “warm” episodes compiled by NOAA and the National Weather Service correlate warm episodes with events Randall and David care about: the ruining of oyster reefs south of Saint Augustine by crown conchs in 2005, the Apalachicola oyster fishery crash last year, and the die-off of salt marsh habitats at the turn of the millennium.  These episodes are part of a normal climatological cycle, though recent droughts during warm years have been severe.  
Dr. Randall Hughes FSU Coastal & Marine Lab/Northeastern University

Mineral Springs Seafood's Dusty Murray empties a crab trap by a salt marsh off of Ochlockonee Bay.  Blue crabs are one of the many animals that make use of the salt marsh habitat.

Mineral Springs Seafood's Dusty Murray empties a crab trap by a salt marsh off of Ochlockonee Bay. Blue crabs are one of the many animals that make use of the salt marsh habitat.

IGOR chip- biodiversity 150We’re going to shift our attention a bit to another intriguing intertidal habitat – the salt marsh. We’ve focused a lot recently on oysters, and how David is applying what we’ve learnedfrom our oyster research the last few years to try to understand the crash of the Apalachicola oyster fishery. There is something inherently interesting and fascinating about oysters, despite the fact that they look a lot like not much more than really sharp rocks. And of course, there is urgency to understand the oyster problems in Apalachicola because of the very real and immediate human costs associated with the fishery collapse.But now, my goal is to convince you that the salt marsh is just as fascinating as oyster reefs, even if it is not a highly visible fishery in trouble. Think of me as the parent trying to get you to appreciate your broccoli, after David already gave you your chocolate cake. I’m going to get you to LIKE your broccoli.

The “broccoli” in this scenario is none other than salt marsh cordgrass, Spartina alterniflora, a familiar character on this blog. In addition to oysters, cordgrass has been the focus of most of my research in FL. Why, you may ask? Why study broccoli when you could be studying chocolate cake all the time? The parent in me is tempted to use the catch-all phrase “Because it’s good for you!” But I’ll refrain, and instead give you a few actual reasons:

1. Oyster and cordgrass really aren’t all that different.

What do oysters and cordgrass have in common? At first glance, it may not seem like much. Oysters are animals; cordgrass is a plant. Oysters are tasty (depending on your palette); cordgrass is inedible. Oysters support a community of fishermen, at least in better times; cordgrass doesn’t.

Except this last distinction, which may seem intuitive, is not actually true. Cordgrass, and salt marshes more generally, support a wide range of fishery species including blue crabs (as you can see in the video), mullet, and sea trout. Studies in Florida estimate that marshes provide up to nearly $7000 per acre for recreational fishing alone. And like oysters, salt marshes provide more benefits for us than simply what we can eat, including protection from storms, increased water quality, and erosion control.

2. Plants are cool.

I know I don’t have to convince any of you gardeners out there about the beauty of plants. Give them a little sunshine, some nutrients, and a little water, and they do their thing. And cordgrass can even manage in salt water! There’s something to be said for low maintenance study organisms.

An AmeriCorps volunteer waits for students on Choctawhatchee Bay.  They will be planting Spartina alterniflora as part of the Grasses in Classes Program.

A year ago, that full-bodied marsh in the background looked just like the rows of small cordgrass shoots leading up to it. Both were planted by Laurel Hill School students as part of the Choctawhatchee Basin Alliance's Grasses in Classes program.

Not only that, but you can plant a single cordgrass stem, leave it alone for a few months, and return to find that it has expanded to 20 stems, all from the same individual!  (Or, if you’re lucky enough to be part of Grasses in Classes, you can admire successive years of growth from single transplants.) This “clonal expansion” is impressive, and it makes answering some of the research questions that I’m interested in pretty easy to address – I can test whether some individuals are better at expanding than others, or whether they withstand stresses like grazing better, or whether having a mix of individuals is better than lots of stems of the same individual. I can ask these questions using oysters too, but it is a lot more difficult. Even we ‘eat your vegetables’ advocates like taking the easy way out sometimes.

3. Marshes are in trouble too.

Although not in the headlines of the local papers at the moment, cordgrass has experienced significant declines in the Gulf of Mexico in the past, and salt marsh loss is a historic and ongoing problem in many parts of the world. And in some cases, the same problem can contribute to the loss of marshes and oysters. For instance, drought has been linked to salt marsh die-off in the Gulf, and drought-induced stress can make the plants more sensitive to other stresses such as grazing by snails. (As we’ve discussed before, drought and increased salinities can also make oysters more sensitive to predators and disease.) Because of the many benefits that marshes provide, it is in our best interest to understand the causes of these losses and try to prevent / counteract them.

Marsh Periwinkle (Littoraria irrotata) climbing cordgrass (Spartina Alterniflora) in a St. Joe Bay salt marsh.

Marsh Periwinkle (Littoraria irrotata).

For these reasons and more, I’ve been conducting lots of experiments the past few years to (a) understand what factors increase / decrease how sensitive cordgrass is to it’s major grazer, the marsh periwinkle, and (b) figure out if having more cordgrass individuals (or “genotypes”) makes the marsh less sensitive to change. We’ll highlight these experiments in the coming weeks as part of our quest to spark your fascination with the salt marsh!

Music in the video by Cross(o)ver.  The maps used in the animation were generated by the National Drought Mitigation Center.  Special thanks to Mineral Springs Seafood for taking us along as they emptied their crab traps.

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.

Tricks or Treats? And more on the effects of predators in marshes.

Dr. David Kimbro FSU Coastal & Marine Lab

IGOR chip_ predators_NCE 150Unlike most of the experiments that I’ve conducted up to this point in my career, the oyster experiment from this past summer does not contain a lot of data that can be analyzed quickly.

For example, predator effects on the survivorship of oysters can be quickly determined by simply counting the number of living as well as dead oysters and then by analyzing how survivorship changes across our 3 experimental treatments (i.e., cages with oysters only; cages with mudcrabs and oysters; cages with predators, mudcrabs, and oysters).  But this simple type of data tells us an incomplete story, because we are also interested in whether predators affected oyster filtration behavior and whether these behavioral effects led to differences in oyster traits (e.g., muscle mass) and ultimately the oyster’s influence on sediment characteristics.  If you recall, oyster filter-feeding and waste excretion can sometimes create sediment conditions that promote the removal of excess nitrogen from the system (i.e., denitrification)

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As we are currently learning, getting the latter type of data after the experiment involves multiple time-consuming and tedious steps such as measuring the length and weight of each oyster, shucking it, scooping out and weighing the muscle tissue, drying the muscle tissue for 48 hours, and re-weighing the muscle tissue (read more about this process here).

After repeating all of these steps for nearly 4,000 individual oysters, we can subtract the wet and dry tissue masses to assess whether oysters were generally:

(a) all shell…“Yikes! Lot’s of predators around so I’ll devote all of my energy into thickening my shell”

(b) all meat…“Smells relaxing here, so why bother thickening my shell”

(c) or a mix of the two.

For the next two months, I will resemble a kid with a full Halloween bag of candy who cannot wait to look inside his bag to see whether it’s full of tricks (nonsensical data) or some tasty treats (nice clean and interesting data patterns)!  I’ll happily share the answer with you as soon as we get all the data in order.

Because of this delay, let’s explore some new research of mine that examined how predators affect prey traits in local marshes and why it matters.

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There are two main ingredients to this story:

(a) tides (high versus low) dictate how often and how long predators like blue crabs visit marshes to feast on tasty prey.

(b) prey are not hapless victims; like you and me, they will avoid risky situations.

attach.msc1In Spartina alterniflora systems, periwinkle snails (prey) munch on dead plant material (detritus) lying on the ground or fungus growing on the Spartina leaves that hover over the ground.  Actually, according to Dr. B. Silliman at the University of Florida, these snails farm fungus by slicing open the Spartina leaves, which are then colonized by a fungal infection.  If snails fungal farm too much, then the plant will eventually become stressed and die.

So, I wondered if the fear of predators might control the intensity of this fungal farming and plant damage.

For instance, when the tide floods the marsh, snails race (pretty darn fast for a snail!) up plants to avoid the influx of hungry predators such as the blue crab.

After thinking about this image for a while, I wondered whether water full of predator cues might enhance fungal farming by causing the snail to remain away from the risky ground even during low tide.  Eventually, the snail would get hungry and need to eat, right?  Hence, my hypothesis about enhanced fungal farming due to predator cues.   I also wondered how much of this dynamic might depend on the schedule of the tide.

Before delving into how I answered these questions, you are probably wondering whether this nuance really matters in such a complicated world.  Fair enough, and so did I.

Addressing this doubt, I looked all around our coastline for any confirmatory signs and found that Spartina was less productive and had a lot more snail-farming scars along shorelines subjected to a diurnal tidal schedule (12 hours flood and 12 hours ebb each day) when compared to shorelines subjected to a mixed semidiurnal schedule (2 low tides interspersed among 2 high tides that are each 6 hours).  Even cooler, this pattern occurred despite there being equal numbers of snails and predators along both shorelines; obviously density or consumption effects are not driving this pattern.

Marsh_foodweb

Ok, with this observation, I felt more confident in carrying out a pretty crazy laboratory experiment to see if my hypothesis might provide an explanation.

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Enter Bobby Henderson.  This skilled wizard constructed a system that allowed me to manipulate tides within tanks and therefore mimic natural marsh systems; well, at least more so than does a system of buckets that ignore the tides.

Deck_schematic1

Within each row of tide (blue or red), I randomly assigned each tank a particular predator treatment.  These treatments allowed me to dictate not only whether predators were present but whether they could consume & frighten snails versus just frightening them:

-Spartina only

-Spartina and snails

-Spartina, snails, and crown conch (predator)

-Spartina, snails, blue crab (predator)

-Spartina, snails, crown conch and blue crab (multiple predators)

-Spartina, snails, cue of crown conch (non-lethal predator)

-Spartina, snails, cue of blue crab (non-lethal predator)

-Spartina, snails, cues of crown conch and blue crab (non-lethal multiple predators)

attach.msc6After a few weeks, I found out the following:

(1) Predators caused snails to ascend Spartina regardless of tide and predator identity.  In other words, any predator cue and tide did the job in terms of scaring the dickens out of snails.

(2) Regardless of tide, blue crabs ate a lot more snails than did the slow moving crown conch and together they ate even more.  This ain’t rocket science!

(3) In this refuge from the predators, snails in the diurnal tide wacked away at the marsh while snails in the mixed tide had no effect on the marsh.

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Whoa…the tidal schedule totally dictated whether predator cues indirectly benefitted or harmed Spartina through their direct effects on snail predator-avoidance and farming behavior.  And, this matches the observations in nature… pretty cool story about how the same assemblage of predator and prey can dance to a different tune when put in a slightly different environment.  This study will soon be published in the journal Ecology.  But until its publication, you can check out a more formal summary of this study here.

If this sort of thing happens just along a relatively small portion of our coastline, I can’t wait to see what comes of our data from the oyster experiment, which was conducted over 1,000 km.

Till next time,

David

David’s research is funded by the National Science Foundation.

The End of an Era

Dr. Randall Hughes FSU Coastal & Marine Lab
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Randall examines an experiment cage as Robyn looks on.

IGOR chip- biodiversity 150Calling a one year experiment an “era” is probably a bit of an over-statement, but the end of our snail field experiment definitely feels significant. Especially for Robyn, who has traveled to St. Joe Bay at least once a week for the past year to count snails and take other data. And also for the Webbs, who were kind enough to let us put cages up in the marsh right in front of their house and then proceed to show up to check on them at odd hours for the last year!  And finally for this blog, because the beginning of the snail experiment was the first thing we documented last summer when we started this project with WFSU.  It’s nice to come full circle.

So why, you may wonder, are we ending things now? Is it simply because one year is a nice round number? Not really, though there is some satisfaction in that. The actual reasons include:

(1) The experiment has now run long enough that if snails were going to have an effect on cordgrass, we should have seen it by now. (At least based on prior studies with these same species in GA.)
(2) In fact, we have seen an effect of periwinkle snails, and in some cages there are very few plants left alive for us to count! (And lots of zeros are generally not good when it comes to data analysis.)
(3) Perhaps the most important reason to end things now:  it’s become increasingly difficult in some cages to differentiate the cordgrass that we transplanted from the cordgrass that is growing there naturally. Being able to tell them apart is critical in order for our data to be accurate.
(4) The results of the experiment have been consistent over the last several months, which increases my confidence that they are “real” and not simply some fluke of timing or season.

And what are the results? As I mentioned above, snails can have a really dramatic effect on cordgrass, most noticeably when our experimental transplant is the only game in town (i.e., all the neighboring plants have been removed). And not surprisingly, cordgrass does just fine in the absence of snails and neighbors – they’re not competing with anyone or being eaten!

Slide1

Snails also have a pretty strong effect on the experimental cordgrass transplant (compared to when no snails are present) when all of its neighbors are cordgrass.

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Most interestingly, snails do not have a big effect on the experimental cordgrass transplant when some of the neighboring plants are needlerush.

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This result is consistent with some of the patterns we’ve observed in natural marshes, where cordgrass growing with needlerush neighbors is taller and looks “healthier” than nearby cordgrass growing without needlerush.

Having decimated the plants in the cage, the snails move towards the tallest structure they can reach- a PVC pipe.

But why? Those snails are pretty smart. They generally prefer to climb on the tallest plant around, because it gives them a better refuge at high tide when their predators move into the marsh. (We’ve shown this refuge effect in the lab – fewer snails get eaten by blue crabs  in tanks with some tall plants  than in tanks with all short plants.) Needlerush is almost always taller than cordgrass in the marshes around here, so this preference for tall plants means that snails spend less time on cordgrass when needlerush is around. And finally, less time on cordgrass means less time grazing on cordgrass, so the cordgrass growing with needlerush experiences less grazing pressure.

These results – consumer (snail) effects on cordgrass are lower when cordgrass grows mixed with needlerush – are consistent with theory on the effect of diversity, even though in this case we’re only talking about a “diversity” of 2 plant species.  And they could be important in the recovery or restoration of marsh areas where snails are causing a large reduction in cordgrass biomass.

The one thing we still don’t know with certainty – how do the snails determine which plant is taller??

I guess that’s the beauty of this job, in that there are always more questions to answer.

Randall’s research is funded by the National Science Foundation.

The new documentary, In the Grass, On the Reef: Testing the Ecology of Fear had a segment on the snail experiment.  Watch the full program here.  You can also read Randall’s post from the beginning of the experiment, and watch a video, here.

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Horse Conchs Rule the Seagrass Bed

In the Grass, On the Reef: Testing the Ecology of Fear

Premieres on WFSU-TV Wednesday, June 29 at 7:30 PM, 6:30 CT.  In high definition where available.

Rob Diaz de Villegas WFSU-TV

IGOR_chip_predators_NCE_100This clip is a short segment on one of the predators featured in this program: the horse conch.  It’s practically an ecosystem onto itself, as you can see in the video’s poster frame above.  Barnacles, crepidula, bryozoans, and other marine creatures that affix themselves to hard surfaces settle on its shell.  In the video you’ll see its bright orange body as it roams the seagrass beds of the Forgotten Coast.  And you’ll see it eat another large predatory snail, the lightning whelk.

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