Tag Archives: salt marsh

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.

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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.

Video: Paddling the Forgotten Coast

If you missed it on dimensions, here is our video on the Florida Circumnavigational Saltwater Paddling Trail.

If you have an eco-adventure you’d like to share or have covered, leave a comment on our Ecotourism North Florida page.

Happy Ours kayaksFor more information on the trail, visit the trail web site.

Are two friends better than one?

Dr. Randall Hughes FSU Coastal & Marine Lab

IGOR chip- biodiversity 150

Sand fiddler crab.

This summer we’ve been conducting an experiment on our new deck to look at the effects of fiddler crabs and ribbed mussels on Spartina alterniflora (smooth cordgrass).

Past studies by Dr. Mark Bertness have shown that crabs and mussels by themselves can have positive effects on plant growth – most likely because crabs can reduce the stress of low oxygen in the sediments by building their burrows, and mussels can add nutrients to the sediments.

Fig. 3 from Bertness 1984, Ecology 65: 1794-1807

Figure 3 from Mark Bertness's 1984 Ecology study illustrating the positive effects of mussel presence (white bars) on Spartina

Table 3 from Bertness 1985, Ecology 66: 1042-1055

Table 3 from Mark Bertness's 1985 Ecology study. Fiddler removal has a negative effect on Spartina in the marsh flat, but not the marsh edge.

Although both fiddlers and mussels occur together in the field, no studies have looked at how the combination affects the plants. Are the positive effects of each species by itself doubled? Or are they redundant with each other? Do crabs somehow reduce the positive effect of mussels, or vice-versa? How many crabs or mussels do you need to get a positive effect on Spartina? These are some of the questions that we hope to answer with our experiment.

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Our new deck at FSUCML.

But first, we had to get everything set up. There were several long and hot days of shoveling sand into our “mesocosms” (10 gallon buckets) – many thanks to Robyn, Chris, Althea, and all the others who took care of that task! Then there was another day spent transplanting the Spartina.

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Chris, Randall, and Robyn work to transplant Spartina from the greenhouse to the mesocosms.

Finally, it was time to add the fiddlers and mussels, and everything began!

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Mussels nestled among the Spartina stems in one of our experimental mesocosms

Althea and Chris have been leading the charge on this experiment, and they’ve spent a lot of time getting to know (and identify) the fiddler crabs. All in all, a pretty fun study organism!

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Althea working to identify fiddler crab species.

We’ll continue the experiment another month and then measure the height and density of the plants in each treatment to see if there are any differences. Once this experiment is complete, we’ll set up a separate one asking somewhat of the converse question – are two enemies (periwinkle snails and grasshoppers) worse than one? We’ll keep you posted.

Randall’s research is funded by the National Science Foundation.
We want to hear from you! Add your question or comment.

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.

We want to hear from you! Add your question or comment.

From Bay to Bowl: Making New England Quahog Chowder

Rob Diaz de Villegas WFSU-TV

Mouth of the Back RiverIGOR chip- human appreciation 150

With the In the Grass, On the Reef documentary done, me, my wife Amy, and our son Maximus took a vacation to visit Amy’s family in Duxbury Beach, Massachusetts.  We were picked up at the airport by her cousin, Jim Kennedy.  On the ride down, we got to talking about what our respective plans were for the week.  One thing he was wanting to do grabbed my attention.  He was going to go clamming for quahogs in the marsh by the family’s vacation home and make a chowder.  That sounded so cool to me.  Go into a marsh without having to lug around a camera, and round up some tasty critters?  I told him I wanted to go (I did go into the marsh with a camera last year, which is where the marsh pics you see originated).  It’s a strange side effect of working on this project that I now enjoy going into hot, muddy places surrounded by sharp grass.

P1000595Low tide was set for 11 AM on the day we chose to go, so we set out between 9:30 and 10 while the tide was still going out.  The marsh is at the mouth of the Back River, and when the tide drops, the grass stands a few feet above the bottom of the river bed.  Below the cordgrass, the sides of the elevated marsh are pockmarked by fiddler crab burrows.  We entered the sand/ mud flats at the head of the river from Gurnet Road, armed with our permit, a rake, and a 12-quart bucket.  The quahogs would be buried just below the mucky surface. Here on the Forgotten Coast, we have quahogs as well- ours are the southern quahogs, the more famous New England quahogs are known as the northern quahog:

quahog- north and south

There were a lot of people out there harvesting the clams.  Most of them used a short rake meant specifically for clamming.  Jim went to several stores to look for one but couldn’t find it, so we used a garden rake.  At the end of the day, though, the best tools we had were our own feet.  A mature, legal sized quahog (3-4 years old) is big enough that we could feel them under our feet as we walked up the river bed.  Then, with the rake or with our hands, we would dig them out.  It seemed like a healthy population.  Around every legal sized clam we found there were usually several smaller ones.  I thought back to what David said in the show about what he looked for in an oyster reef.  The best ones had several mature oysters as well as several smaller ones to eventually replace them.

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Green crab (Carcinus maenas).

I couldn’t help but note the differences and commonalities between our local marshes and sand flats and this New England marsh.  I didn’t see many large predatory snails in or around the marsh, a stark contrast to sand flats in St. Joseph Bay or at Bay Mouth Bar.  And instead of blue crabs, there were green crabs.  There were razor clams (Ensis directus) and steamers (soft shell clams, Mya arenaria), each of which are harvested at other times of the year.  We also saw the occasional small shrimp, and oysters that had flaked off of reefs deeper out in the bay.

We caught the legal limit and returned, muddied, to prepare the chowder.

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Jim Kennedy (left) and WFSU-TV producer Rob Diaz de Villegas (right) shuck and clean quahogs.

IMG_6441A little on how you prepare quahogs for chowder:

You scrub the mud off of the closed shells.  Open shells buried in the mud are dead animals and are unsafe for consumption.  After scrubbing them, you boil them until they open.  Then you shuck them and remove the contents of their stomachs.  In the photo at the lower left of this paragraph, that green stuff is phytoplankton- microscopic plants floating with the other sediment in the water.  Good food for clams- and their filtering it is a great way to keep the water clean- but not anything we were interested in eating.  I got to try my hand shucking and cleaning the clams.  Jim’s mom, Pam, cut potatoes and onions while Jim cooked the quahogs and fried some bacon.  The bacon smell helped with the boiling clam smell.  The ingredients would come together in a large pot with milk, cream, and flour.  The making of the chowder in the cottage brought out some nostalgia.

Pam recalled that her grandmother’s chowder didn’t contain dairy.  When Bertha and Archer MacFarland would camp on Duxbury Beach, they didn’t have refrigeration and so milk and cream weren’t really an option.

Archer MacFarland“When Max is old enough,” My father-in-law, Chris MacFarland, said to me, “you need to teach him how to go quahogging to keep the tradition going.”  Maximus is five months old, so I have a bit of time until I take him out there.  When he does go, he’ll represent the fifth generation of the MacFarland family to harvest quahogs from Duxbury Bay.

Duxbury Beach and Duxbury Bay are separated by Gurnet Point, a thin cape down which Gurnet Road runs.  The road runs to the town of Saquish at the horn of the cape. Driving there, the beach is on your left, and the bay is to the right.  A large marsh is at the North of the bay.

Archer and Bertha started camping on Duxbury Beach around 1920.  After some years of camping there, they bought plots of land and built a cottage by the marsh.  When their son Robert was sixteen, he built another house nearby.  Then, when he was nineteen, he sold his car for $200 to buy a plot.  There he built the house where his children, and their children and grandchildren, vacation every summer.

Robert MacFarlandRobert took his children looking for quahogs when they were young.  They used the “treading” method to find their clams, much like we did, except that they were barefoot.  Jim and I wore shoes to keep our feet safe from broken shells hidden in soft mud that was deep in places.  It was deeper as we walked up the riverbed- I sank almost up to my waist at one point.  I imagine that they didn’t walk that far up.

Robert also fixed up an old pram, on which he used to take his sons Chris and Doug on fishing trips off of the beach.  As Chris (who was 7) and Doug (who was 5) recalled, one of them would row, the other would bail water.  They caught cod, threw back pollock and perch, and used mackerel for bait.  Of course, North Atlantic cod is not nearly as common as it once was.  Nor is flounder as common off of Saquish.  Jim remembers going out with his family and spotting them at the edge of seagrass beds from the family’s Boston Whaler.  For about ten years now, those haven’t been seen much either.  Luckily, as David points out in the program, the animals in the lower trophic levels see less change over time, and so there are still plenty of clams in Duxbury Bay.

Hopefully that means chowder at the cottage for many more summers.

When the chowder was done, it was served with oyster crackers and crumbled bacon (the bacon Jim made earlier- the grease was used in the chowder).

I’m guessing there are stories like this across the Forgotten Coast: generations of families bonding while they made use of the fish and shellfish swimming outside their back doors.  Do you have a story like this?  Share it here, in the comments section.  We might want to visit some of you and feature your stories in one of our videos.

Photos taken by: Rob Diaz de Villegas, Chris MacFarland, James Kennedy, and Amy Diaz de Villegas.  Archival photos provided by Chris MacFarland.