All posts by David

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What’s the deal with nutrients and oysters?

As David & co. start their new research on the Apalachicola oyster fishery crisis, He and Randall (and their colleagues in Georgia and North Carolina) are starting to wrap up the NSF funded oyster study that we have been following over the last couple of years.  Over the next few weeks, we’ll take a look back at that research through a series of videos.  We’ll cover some oyster basics (how does an animal with no brain behave?), explore David and Randall’s ideas on the role of fear on the oyster reef (what makes a mud crab too afraid to eat an oyster?), and see the day-to-day problem solving and ingenuity it takes to complete a major study.  As these videos are released, we’ll also keep tabs on the work being done in Apalachicola Bay, in which many of the same methods will be used.
Dr. David Kimbro FSU Coastal & Marine Lab

After all, nutrients are basically plant food and oysters are animals.  And how could too few nutrients coming down with the trickling flow of the Apalachicola River possibly explain the record low number of Apalachicola oysters?

This is the perfect time to use the favorite idiom of my former mentor Dr. Ted, “The long and the short of it is….”

The short of it: Plants love nutrients and sunlight as much as I like pizza and beer. But unlike my favorite foods, these plant goodies make plants grow fast and strong. This works out well for us because we all need nutrients for basic body functioning, and because we get them by eating plants and/or by the eating animals that previously consumed plants.

For our filter-feeding bivalve brethren, they get nutrients and energy by eating plant-like cells (phytoplankton) that float in the water. So, it is possible that the trickling flow of the Apalachicola River is bringing too few nutrients to support the size of the pizza buffet to which the Apalachicola oysters are accustomed. But this idea has yet to be tested.

Hanna Garland and Stephanie Buhler harvest oysters from sample reefs in Apalachicola Bay.

The long of it: Long before the flow of the Apalachicola River slowed to a trickle, there weren’t a lot of nutrients. That’s why the numbers of humans used to be so low: too few nutrients meant too few plants and other animals for us to eat.

How could this possibly be the case given that 78% of the air we breathe is made up of a very important plant nutrient, nitrogen? And there is a lot of air out there!

Well, only a precious few plants exist that can deal with the nitrogen in our air and these are called nitrogen-fixers. Think of these as single-lane, windy, and bumpy dirt roads. In order to help create a plant buffet for all of us animals, a lot of atmospheric nitrogen (bio-unavailable) has to travel down this very slow road that the n-fixers maintain. As a result, it naturally takes a long time for the land to become fertile enough for a large buffet. And, it only takes a couple of crop plantings to wipe out this whole supply of bio-available nitrogen that took so long to accumulate.

guano island

Sea birds on a guano island off the coast of Peru. (zand.net)

Turns out that the ancient Inca civilization around Peru was not only lucky, but they were also pretty darn smart. Lucky, because they lived next to coastal islands that were basically big piles of bird poop, which is very rich in bio-available nitrogen. I’m talking thousands of years of pooping on the same spot! Smart, because they somehow figured out that spreading this on their fields by-passed that slow n-fixing road and allowed them to grow lots of food. Once Columbus tied the world together, lots of bird poop was shipped back to European farms for the same reason. That’s when the European population of humans sky-rocketed.

Turns out that humans in general are pretty smart. Through time, some chemists figured out how to create artificial bird poop, which we now cheaply dump a lot of on our farming land. So, in these modern days, we are very, very rich in bio-available nutrients.

Where am I going with the long of it? Well, on the one hand, these nutrients wash off into rivers and then float down into estuaries. This is how the phytoplankton that oysters eat can benefit from our solution to the slow n-fixing road. In turn, oysters thrive on this big phytoplankton buffet.

Slide by Ashley R. Smyth, Piehler Lab, UNC Chapel Hill Institute of Marine Sciences.

But, on the other hand, too much of these nutrients flowing down into our estuaries can create big problems. Every year, tons of nutrient-rich water makes it way down the Mississippi and into the shallow Gulf of Mexico waters. There, this stuff fuels one big time buffet of phytoplankton, which goes unconsumed. Once these guys live their short lives, they sink to the bottom and are broken down by bacteria. All this bacterial activity decreases the oxygen of water and in turn gives us the infamous dead zone. Because nutrient-rich run-off continues to increase every year, so too does the dead zone.

I’ll close with the thought that oysters themselves may help keep the phytoplankton buffet from getting out of control by acting like anti-nitrogen fixers. In other words, they may help convert an excess of useable nitrogen back into bio-unavailable nitrogen. While this might not have been a great thing to have in low nutrient situations, we currently live in a nutrient-rich era. What’s even cooler is that it all has to do with poop again! But this time, we are talking oyster poop.

Oyster Summit 6

Dr. Mike Piehler, presenting to his collaborators Dr. Jeb Byers (Right), Dr. Jon Grabowski (reclined on couch), Dr. Randall Hughes and Dr. David Kimbro (out of frame). These five researchers have worked on oyster reef ecology since their time at the University of North Carolina. Three years ago, the National Science Foundation funded research into their ideas about predators and fear on oyster reefs.

So does this really happen? Yes. Check out an earlier post for the details. But we don’t fully understand it and that’s why it is a major focus of our research. Our collaborator, Dr. Michael Piehler of UNC-Chapel Hill, is leading this portion of our research project. Read more of Dr. Piehler’s work on this topic here.

So, hopefully this post explains why the relationship between nutrients and oysters is not so simple. But it sure is interesting and a worthy thing to keep studying!

Cheers,
David

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

We want to hear from you! Add your question or comment.
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Split the Difference: Applied vs. Basic Science

Dr. David Kimbro FSU Coastal & Marine Lab
Looking over the catch

Shannon Hartsfield and Colonel Donald Jackson of the Army Corps of Engineers South Atlantic Division look over their catch during an oystering demonstration at Cat Point Bar. This demonstration was meant to show the problems caused by low fresh water input into the bay. Below, David talks about starting to work towards a possible solution.

Tonight on WFSU-TV’s Dimensions program, watch Part 2 of RiverTrek 2012.  Tune in at 7:30 PM/ ET on WFSU-TV. In case you missed it, you can watch Part 1 of RiverTrek 2012 here

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Spread offense or Power-I formation? Man-to-Man or Zone defense? Austerity or Stimulus spending? And most importantly, Batman or Batgirl?

Whether leading a team of athletes or a population of countrymen, deciders frequently confront such either-or decisions or binary outcomes (i.e., yes or no).

Because time is one of our most limiting resources, natural scientists confront such a dilemma right out of the gate: should I pursue Applied or Basic scientific research?

By applied, I mean research that focuses on immediate solutions to societal problems: How can we deal with a new infectious disease (e.g., avian flu)? Where did the BP oil go?

By basic, I mean research that focuses on improving our knowledge about the nuances of the natural world: How many galaxies are there in the observable universe and how were they formed (I just saw a must-see iMax movie, Hubble 3D, at the JFK Space Center Visitor Complex)? Why is biodiversity so much greater in the tropics?

Flashing back to my childhood hero, I realize that Michael Jordan will likely remain the best basketball player to ever play not solely because of his offense (which was certainly top tier), but also because he worked relentlessly to become a top-tier defender as well. Obviously, few people can master both sides of a spectrum, and sometimes a focus on both or on splitting the difference can come with great cost. For example, my favorite college football team (UNC) is implementing a hybrid defense (i.e., a 4-2-5 instead of a 4-3 or a 3-4) this year; we LOST 68-50 this last Saturday…in FOOTBALL!

Because my plans for playing in the NBA and NFL obviously aren’t working out, let’s get back to science and the merits of focusing on both ends of the science spectrum.

Recently, I talked about this topic with a leading research and clinical Psychologist at Florida State University, Dr. Thomas Joiner. Ignorantly, I thought FSU was only great in Football…turns out that they also have the best Psychology department in the nation. In a recent book Lonely at the Top, Dr. Joiner weaved together many interesting and Basic research studies to show how gender and evolutionary forces cause nuanced interactions all the way from neurons and one’s health to one’s social behavior. It was fascinating to learn how these interactions can promote the loneliness that facilitates suicides.

But while all of these powerful connections lined up well for the main argument of his book, I am equally interested by a conversation we recently shared together about there being many applied problems that can’t wait around for further testing of nuanced ideas. For instance, Dr. Joiner recently began working with the US military to study and reduce the causes of suicide within the military. As Dr. Joiner indicated, the military probably couldn’t give a darn about Basic research findings. They just want some realistic solutions and they want them yesterday.

If you stuck it out this far, you are probably wondering, “how does this relate to oysters, predators, etc.?” Well, the motivation of my Basic research is to increase our knowledge about how predators keep the lights on for many of the natural systems that we depend on like oyster reefs, salt marshes and seagrass beds. But in pursuing this research over the past three years, I have confronted a very important applied problem that needs immediate solutions: the oyster fishery of Apalachicola, Florida presently contains too few oysters to support the local economy (Download a PDF of the Department of Agriculture and Consumer Services report here).

So, if you follow this blog, you’ll get to see whether my attempt to be like Mike (if you’ve seen my vertical leap, it’s obvious we’re talking research and not b-ball), to emulate the approach of Dr. Joiner, and to split the Applied–Basic difference is a success or a bust. I’ll be working with a lot of good researchers (Florida Sea Grant, UF Oyster Recovery Task Force), state organizations – Florida Department of Agriculture & Consumer Services (FDACS) and Florida Fish & Wildlife Conservation Commission (FWC)- and the local community to examine the following:

David accompanies FDACS on a sampling trip in Apalachicola Bay as part of a new collaboration.

(1) How in the heck do you work in such a large and logistically challenging system?

(2) What is the extent of the problem…how far gone is the resource?

(3) After getting some research under our belts, what our some realistic options to this problem?

(4) Because we all want answers to these questions yesterday, can we explore the existing data, which was impressively collected by FDACS for the past 30 years, to get a head start?

Finally, I suspect that this Applied perspective may help inform the merits of my Basic interests. There are a ton of things that could be contributing to the failure of the oyster fishery such as climate change, drought, fresh-water extraction, over-harvesting, disease, nutrient inputs, and water quality. Whether or not any of our predator ideas help explain the lost of this fishery represents a very big test. In other words, relative to other explanations, is all of this predator stuff really important?

Ok, as the locals along the Forgotten Coast say “let’s get’er done”.

Best,
David

Take the RiverTrek 2012 photo tour down the Apalachicola River. You can zoom in and scroll across the map for greater detail. Later we’ll post a map with more of the basin and bay as well, from our other EcoAdventures in the area (River Styx, Graham Creek, etc.). Also, many of the locations are approximate. We did not geotag the location of every houseboat on the river, but the photos do show up in the same general vicinity (with the exception of more recognized landmarks such as Sand Mountain, Alum Bluff, etc.).

Related Links

For more information on the Apalachicola RiverKeeper, visit their web site.  (They’re also on Facebook).

The Army Corps of Engineers is updating the Apalachicola/ Chattahoochee/ Flint Master Water Control Manual, and they are taking public input.  You can let your voice be heard here.

The Franklin County Promise Coalition is coordinating aide efforts for families that are being affected in Franklin County through their Bay Aid program.   As Dan told us in his original interview, over half of the residents of Franklin County depend on the river for their livelihoods.  Learn more about volunteering and other Bay Aid opportunities here.

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

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

 

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Backyard Ecology (Plus new video on Bay Mouth Bar)

Episode 7: Where Everything is Hungry

It’s always a good shoot day at Bay Mouth Bar as every animal seems to be eating every other animal.  Oyster reefs, salt marshes, and seagrass beds- the habitats we’ve covered over the last three weeks- reward those who take the time to look closely.  At Bay Mouth Bar, everything is all out in the open.  For a limited time, anyway…
Dr. David Kimbro FSU Coastal & Marine Lab

IGOR chip_ predators_NCE 150IGOR chip- filtration 150Like most kids, I spent a lot of my formative years in the backyard practicing how to throw the game-winning touch down pass, to shoot the game winning three-pointer, and to sink the formidably long putt.  Although my backyard facilities obviously didn’t propel me into the NFL, NBA, or PGA, they never closed, required no admission fee from my pockets (thanks Mom and Dad!), and were only a few steps away.

Now that I’m striving to be an ecologist at Florida State University, I’m feeling pretty darn lucky about my backyard again. Instead of spending tons of time flying, boating, and driving to far away exotic places, I can use a kayak and ten minutes of David-power to access some amazing habitats right here along the Forgotten Coast.

Part of this coastal backyard was first intellectually groomed by one of the more famous and pioneering scientists of modern-day ecology, Dr. Robert Paine. Five decades ago, Dr. Paine noticed that the tip of Alligator Point sticks out of the water for a few hours at low tide. Of course, this only happens when the tides get really low, which happens about 5 days every month. But when the tip of Alligator Point (which is locally called Bay Mouth Bar) did emerge from the sea each month, Dr. Paine saw tons of large carnivorous snails slithering around a mixture of mud and seagrass. When I first saw this place, my eyeballs bulged out at the site of snails as large as footballs!

Fast- forward 2 decades later: Dr. Paine is developing one of the most powerful ecological concepts (keystone species), one that continues to influence our science and conservation efforts to this very day. Using the rocky shoreline of the Pacific North West as his coastal backyard, he is showing how a few sea stars dramatically dictate what a rocky shoreline looks like.

By eating lots of mussels that outcompete wimpy algae and anemones for space, the sea star allows a lot of different species to stick around. In other words, the sea star maintains species diversity of this community by preventing the mussel bullies from taking over the schoolyard. That’s one simple, but powerful concept….one species can be the keystone for maintaining a system. Lose that species, and you lose the system.

Lightning Whelk

A large lightning whelk found on Bay Mouth Bar in December of 2010.

Ok, let’s grab our ecological concept and travel back in time to Dr. Paine’s earlier research at Bay Mouth Bar. Wow, the precursor to the keystone species concept may be slithering around our backyard of Bay Mouth Bar in the form of the majestic horse conch! In this earlier work, the arrival of this big boy at the bar was followed by the disappearance of all of the former big boys (like this lightning whelk). By eating lots of these potential bullies, the horse conch may be the key for keeping this system so diverse in terms of other wimpy snails.

But why should anyone other than an ecologist care about the keystone species concept and its ability to link Bay Mouth Bar with rocky shorelines of the Pacific NW? Well, what if the lightning whelks eat a lot more clams than do other snails, and less clams buried beneath sediments means less of the sediment modification that can really promote seagrass (Read more about the symbiotic relationship between bivalves and seagrasses here)?  Thanks to Randall’s previous seagrass post, we can envision that less horse conchs could lead to less clams, less seagrass, and then finally a lot less of things that are pleasing to the eye (e.g., birding), to the fishing rod (e.g., red drum), to the stomach (e.g., blue crabs), and ultimately to our economy.

For the past two years, I’ve really enjoyed retracing Dr. Paine’s footsteps at Bay Mouth Bar. But lately, I’m feeling a little more urgent about needing to better understand this system because it’s disappearing (aerial images provided by USGS’s online database at http://earthexplorer.usgs.gov/).

To figure this out, we repeat a lot of what Dr. Paine did five decades ago. At the same time, we are testing some new ideas about how this system operates. For example, if the horse conch is the keystone species, is it dictating what Bay Mouth Bar looks like by eating stuff or by scaring the bully snails? How exactly does or doesn’t the answer affect clams, seagrasses, birds and fishes?

Luckily, because this system is so close, with some persistence and some good help, we’ll soon have good answers to those questions.

Cheers,

David

Ps: Many thanks to Mary Balthrop for helping us access this awesome study system every month.

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

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Oyster reefs. Huh! What are they good for!

Episode 4: The Hidden Value of an Oyster Reef

Weeks ago, we came up with a schedule for posts and videos and somehow had our video on oysters due for the week after Governor Scott declared this year’s oyster harvest a failure.  This led to one minor alteration in the above video, but the video was meant as an overview to the services provided by oyster reefs.  There will be content related specifically to Apalachicola Bay in the coming weeks.

Dr. David Kimbro FSU Coastal & Marine Lab

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There are a lot of things that a marine scientist can study such as charismatic animals (dolphin and turtles) or the waves and currents that fuel my surfing addiction. So, why do I spend most of my time mucking around in mud to study the uncharismatic oyster?

Short answer: because they can provide the foundation for a lot of things that we depend on. Now, some of these benefits or services are obvious and many others aren’t.

Let’s start with the obvious. Just like raising cattle supports tons of jobs and our appetite for hamburgers (I recommend reading Omnivores Dilemma if you want to see how eating meat can be environmentally friendly), the harvesting of oysters financially supports many folks as well as the scrumptious past time of tasting oysters on the half shell as the above video just showed me doing at my local favorite, the Indian Pass Raw Bar!

Unfortunately, the importance of this service was made all to clear to us when the Florida governor recently declared this year’s harvest to be a failure and applied for federal relief for the local economy (Download a PDF of the Department of Agriculture and Consumer Services report here). It’s also unfortunate that this type of bad news has a history of indicating that this natural resource is in trouble and that more trouble may be on the way. To see why, check out a study by Dr. Michael Kirby that showed how this service progressively collapsed from New England down to Florida over the past three centuries. In a nutshell, the pattern of collapse mirrors the increasing number of humans that have over-used this service.

But even if there are no questions about the importance and collapse of the previous service, many folks are asking great questions about whether oysters provide other important services in the form of protected reefs that may offset or exceed their commercial/restaurant value. In other words, what good are oysters to us if they don’t make their way to the raw bar?

A sand flat oyster reef in 2002

An oyster reef built by Dr. Jon Grabowski and Dr. Randall Hughes in 1997, pictured in 2002.

Well, my good buddy Dr. Grabowski’s research used relatively tiny oyster reefs to highlight one less obvious service that involves reefs really ramping up the numbers of commercially and recreationally important fishes (drum) and crabs (stone crabs and blue crabs)….yum!  Given that the oyster reefs used to be 12 feet tall and as long as football fields, can you imagine how many crabs and fishes hung around those really big reefs way back then? Heck, even I could have caught a fish!

Another thing that charismatic and good tasting animals need in order to keep our eyes and tummies happy is some healthy coastal water. Having too much plant-like material (phytoplankton) floating around in the water, sinking to the bottom, and decaying can deplete all of the water’s oxygen. Because such a place is very uninviting for lots of sea life, low oxygen areas will not have many animals that are pleasing to the eye, the fishing rod, or our palette.

Columbia River Water Diatoms

Diatoms, single celled phytoplankton. © Pacific Northwest National Laboratory

Enter the filter-feeding oyster.

While it’s hard to know if today’s tiny amount of oysters reefs sufficiently filter enough water, we do know that the really big reefs of our grandparents and their grandparents time were essentially like huge skimmers in swimming pools as big as the Chesapeake Bay.

As the ESPN football talking heads like to say: C’mon Man! Really?

I kid you not, because Jeremy Jackson and colleagues dug through some Chesapeake mud to figure this out for us. Preserved in the mud is stuff that settled out from the water over time, with deeper mud containing older stuff and shallower mud containing newer stuff. It turns out that as we over-ate and turned the larger oyster reefs into small ones, the stuff in the mud transitioned from sings of healthy water to symptoms of unhealthy water. And because the oyster crashes came before the drop in water quality, it’s more likely that oysters maintained the good water signs as opposed to the reverse scenario of the good water signs maintaining the big oyster reefs.

So this points to a third type of service that oyster reefs CAN provide in the form of water-quality. Admittedly, it’s hard to put a dollar amount on that as opposed to the dollar amount that a dozen raw oysters brings in at a raw bar.

But another less obvious way that oysters can help maintain water quality is by removing the nutrients that a lot of the unwanted phytoplankton depend on.

C’mon Man!

Slide by Ashley R. Smyth, Piehler Lab, UNC Chapel Hill Institute of Marine Sciences.

You see, after oysters suck in the water, filter out their preferred phytoplankton (some are good, but some probably taste as bad as my poor attempt of making southern biscuits), they eventually “poop” their waste out into the mud. Some of this waste makes all sorts of bacteria do all sorts of different things. One of these cool things involves taking a form of nitrogen (think fertilizer on your lawn) that is readily sucked up by nasty phytoplankton and converting it into a form that phytoplankton can’t use (think bad fertilizer that you want to return for a refund).  This is called de-nitrification, and it’s a way that oyster feeding and pooping can help maintain healthy coastal conditions. Even cooler, we can slap a dollar amount on it if we think about how much money it costs a waster-water treatment facility to remove the same amount of nitrogen. My buddy in North Carolina Dr. Mike Piehler did just a study and found that the value of this service is about 2,718.00 dollars per acre of oyster reef. And unlike a dozen raw oysters, this service keeps on giving like the energizer bunny.

Finally, and we are now at service 4 in case you are counting, oyster reefs can buffer the waves and storms that eat away at our shorelines, coastal roads, and homes.

Before signing off, I have to also acknowledge that not every oyster reef performs each of these services. Just like my brother and I look pretty darn similar to someone outside of my family, when you look closer, we are really different. Individual oyster reefs are the same way. Heck, while I can do different things well if you catch me in the morning with a cup of coffee, I often really stink at those same things if you check in with me after a too big and sleep-inducing lunch!

This point segues nicely into my research interest about the “context-dependency” of the obvious and not so obvious services that coastal habitats can provide. In other words, why are some reefs doing some services but others are not? This question really crystallizes the essence of a collaborative project that I’m working on with colleagues from FSU, Northeastern University, University of North Carolina, and University of Georgia.

In our crazy-fun, at times maddening, and democratic research team, we are testing whether the answer depends on differences in big hungry and scary predators like drum and crabs lurking around the reefs. Sure, some of these might eat an oyster that doesn’t make it on to my plate at the raw bar. But overall, they may benefit some reefs by eating a lot of the smaller crabs that really like to munch on oysters. And even if they don’t eat all of these oyster munchers, we’re thinking that their presence may sufficiently freak out oyster munchers so that they spend more time watching their backs and less time munching. Hence, the ecology of fear!

Thanks for wading through this long post. If I promise to write shorter posts in the future, then I hope you’ll follow our journey of testing whether predators help maintain services not only in oyster reefs, but also in the marshes and mudflats of the southeast Atlantic and Gulf coastlines.

Cheers,

David

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)

oyster_exp_3box

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.

diurnal-mixed_2box

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.