Tag Archives: St. Joseph Bay

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.

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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.

The Path Less Paddled

Take a photo tour of the Forgotten Coast segment of the Florida Circumnavigational Saltwater Paddling Trail.  Watch a video on the trail on Wednesday, September 14 at 7:30 PM/ ET on WFSU-TV.

Rob Diaz de Villegas WFSU-TV

IGOR chip- human appreciation 150IGOR chip- habitat 150IGOR chip- gastronomy 150It all happened in about five minutes. The gull swooped down and grabbed a soft-shell blue crab about half its size, abandoned it to a swarm of small fish, whose activity may or may not have attracted a shark coming in from Apalachicola Bay.  I was standing at Sugar Hill, a beach campsite in the St. George Island State Park, the last campsite along the Forgotten Coast segment of the Florida Circumnavigational Saltwater Paddling Trail.  You can see this video on tomorrow’s dimensions.

(watch a video on the making of a blue crab molting its shell)

Were a kayaker to try to make the five or six day paddle from Cape San Blas to St. George Island, they would likely see a few of these little dramas play out.  As Doug Alderson (Paddling Trails Coordinator for the Florida Office of Greenways and Trails)  says in the piece, it’s one of the wildest stretches of the statewide trail.  That means it has a lot of nice scenery of coastal habitats.  Much more interesting, though, is that they are functioning habitats.

Predatory snails on Sugar Hill Beach at St. George Island State Park

Large predatory snails congregating on a tree stump at Sugar Hill camp site.

For instance, Doug loves to catch redfish when he camps on St. George; and they’re always there for him.  But why are these fish so abundant in Apalachicola Bay?  The answer is in those tasty oysters that put the name Apalachicola on the map.  Oyster reefs are a refuge for all kinds of animals like stone crabs, blue crabs, and various predatory snails and small fish.  It’s an all you can eat buffet for larger fish looking for those small fish and little mud crabs.  The action I described above happened by a seagrass bed not far offshore.  Those beds thrive in water that oysters filter clean, and so they provide another habitat for marine life in the bay.  I ate Apalachicola oysters for years without realizing just how much they give, and give, and give…

Rob and Debbie by kayak

Rob photographs small fish and crabs that Debbie scooped out of St. Joe Bay.

At the other end of the trail, In Saint Joseph Bay, we caught up with Dan and Debbie VanVleet of Happy Ours Kayak and Canoe Outpost.  When WFSU first started the In the Grass, On the Reef project, we rented our kayaks from Dan and Debbie.  Debbie’s been wanting to take us snorkeling for a while, to get some video of some of the critters living in seagrass beds in St. Joe Bay.  Kayaking over the shallow waters in the bay, you can see the turtlegrass from where you’re sitting, as well as rays, horseshoe crabs, and snails making their way about the sandy bottom.  To see the creatures living in the seagrass beds, you have to get out of the kayak.  This is where you have to be careful.

It is illegal to remove shells from St. Joseph BayWhen I say be careful, I’m not just talking about your safety, though you should shuffle your feet to alert stingrays that you’re coming, or if you kayak to St. Vincent Island, definitely stay out of the way of charging boars.  You also have to be careful with these habitats, and the marine life within them.  Dan and Debbie (and local law enforcement) are very big on people not taking seashells out of the bay.  Taking a bunch of whelks and crown conchs out of the bay means taking out critical predators, removing a top layer in the local food web.  And, as the sign implies, even a dead shell has a role to play (any hermit crab would agree).  It’s called the “leave no trace” approach, and there are tips on how to best accomplish this on the trail website.  There are also safety tips and maps.  If you’re attempting anything more than a day trip along this trail, it’s a pretty comprehensive resource.

Doug has put a lot of work into mapping the trail- it took three years- and assembling resources so that people could best enjoy it.  You can hear the love he has for paddling when he reads from his book, Wild Florida Waters.  You’ll hear a couple of passages in the show tomorrow.  Even hearing him read about paddling in a strong wind kind of gets me excited about going out again.  It reminds me of paddling to safety in St. Joe Bay after a sudden thunderstorm erupts, or paddling in December when the cold water numbed my hands.  It’s not as predicable a form of recreation as visiting a beach resort.  But it’s never boring.

Doug and Josh

Thanks to Doug (L) for talking to us, and Park Ranger Josh Hodson for driving us around St. George Island State Park.

Dan and Debbie from Happy Ours

Thanks to Debbie and Dan for taking us out.

Have fun out there.  And share your stories with us!  Click on the Ecotourism North Florida link above if you have an eco-adventure you’d like to see us cover.

Kayaking, anyone?

Rob Diaz de Villegas WFSU-TV

IGOR chip- human appreciation 150

Here’s a vacation idea for you.

If you had the time, didn’t mind camping for months on end, and were physically up to paddling fifteen hundred miles, you could paddle around the entire state of Florida using trails mapped out by Doug Alderson.  He coordinates the Florida Circumnavigational Paddling Trail for the Florida Department of Environmental Protection (Visit the trail’s web site).  You would pass by major urban centers like Tampa and Miami.  You would make your way through the entirety of the Florida keys.  And you would see a lot of amazing coastal habitats.

Ready to go?

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The Forgotten Coast segment of the trail starts in St. Joseph Peninsula State Park.

I’m guessing the vast majority of people reading this are saying no, though we would certainly want to hear from you if you were doing this.  Luckily, the trail breaks down into twenty six segments, and over one hundred individual day trips.  The one I’m interested in is Segment 4: The Forgotten Coast.  It takes you through some of my favorite places.  St. Joseph Bay has clear water and lively seagrass beds and salt marshes.  Many of St. Vincent Island’s most interesting animals aren’t aquatic, but if you look over as you paddle past you might see wild hogs running or even one of those elusive red wolves (not likely, but it doesn’t hurt to look).  Once you pass there, you could choose to either go along St. George Island or stick to the mainland and pass by Apalachicola, where you can try to find a place to land your kayak while you pick up some oysters.

We’ll be kayaking part of this trail for September 14 episode, and talking to Mr. Alderson about it.  Have any of you done this?  Are any of you attempting this, or any section of it, any time in the next month?  We want to know.  We want to see your photos.  We want to watch your videos. Leave a comment below, with links to any videos or photos if you like.  If you’ll be out that way in the next couple of weeks, we may want to interview you.

Leave your comments!

And we want to keep hearing from you.  If you have any ideas for stories we might do related to coastal ecotourism, leave a comment on our Ecotourism North Florida page.

 

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.

Slide3

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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