Tag Archives: consumptive_nonconsumptive

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Notes From the Field: Leashing Your Clams

Tanya Rogers FSU Coastal & Marine Lab

IGOR chip_ predators_NCE 150It’s a problem commonly faced by field biologists: You want to put some particular critters out in the field in various places, but how do you keep them from getting swept away or wandering off too far, and how do you ever find them again later to see how they did? Behold the tether! So long as tethers are designed not to interfere too much with the animals’ natural behavior (walking around, burrowing, etc), leashing them to a fixed object is generally a good way to relocate them (provided you study something like crabs or snails and not lions or bald eagles). The other fun benefit of tethering marine invertebrates: you can take them for walks (albeit slow ones).

I recently conducted an experiment in which I put tethered baby clams (sunray venus and quahog, about 12 mm long) out on Bay Mouth Bar to see how their growth, survivorship, and burial depth was affected by (1) their location on the bar (NE, SW, SE, NW) and (2) the type of habitat the clams were in (sand, shoal grass, turtle grass). I checked on the clams a month later: some were still alive and growing, others were dead with clues indicating their likely cause of demise – gaping shell with no damage (stress), cracked shell (eaten by crab), drill hole in shell (eaten by predatory snail). My preliminary analysis suggests that survivorship and causes of death varied between habitat types. Next I hope to do a similar sort of study with tethered snails on Bay Mouth Bar.

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

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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.

At high tide, this reef will be covered in turbid water, and large predators like catfish, blue crabs, and red drum move in to eat smaller animals such as mud crabs.

Sounds of the Oyster Reef

Rob Diaz de Villegas WFSU-TV

IGOR chip_ predators_NCE 150Imagine you’re watching a slasher movie starring mud crabs as the protagonists.  A mud crab leaves the party in the muck under the oyster reef, where the other crabs are chomping down juvenile oysters.  As he pokes his head out from between a couple of shells, you hear a drumming sound and you shout at the screen “Don’t go out there!”

It’s fun to anthropomorphize some of the freaky looking residents of an oyster reef.  But these are the realities of living within the ecology of fear.  Predator cues have a definitive impact on how the smaller, intermediate consumers such as mud crabs behave.  That’s what David Kimbro, Randall Hughes & co. are studying in Alligator Harbor and at their sites across the southeast.  Large predators send certain cues to their prey- perhaps a certain way they move in the water, perhaps.  When the prey species sense that the predators are near, they cease activity- including the eating of juvenile oysters.  That is how large predators help maintain a healthy oyster reef- they make intermediate consumers (mud crabs) eat less of the basal species (oysters, the foundation of the oyster reef habitat). Continue reading

Spat on a Platter

Tanya Rogers FSU Coastal & Marine Lab

IGOR chip_ predators_NCE 150“Spat tiles” are a tool our lab commonly uses to measure the growth and survivorship of juvenile oysters under different conditions, and we’ve used them with varying degrees of success in many of the experiments chronicled in this blog. What these are essentially (in their final form, after a good degree of troubleshooting), are little oysters glued to a tile, which is glued to a brick, which is glued to a mesh backing, which is zip tied vertically to a post. Rob and I have put together a couple interesting slideshows chronicling the growth of these spat over time from two of those experiments. Ever wonder how fast oysters grow? Observe…

This is a time series from our first spat tile experiment, which you can read about in this post. As you may recall, this experiment was largely a failure because the adhesive we used to adhere the spat was inadequate. However, we decided to keep the fully caged tiles out on the reefs to see how they fared over time in different locations. I photographed the tiles every 6 weeks or so, so that we now have a series showing their growth over time. The slideshow shows one of the tiles from Jacksonville. It starts in October of 2010. You’ll notice that not much growth occurs though the late fall and winter, but the spat start to grow noticeably from April-June 2011. From June-September the spat grow explosively and many new spat settle on the tile from the water column and grow equally rapidly. Just as plants (and algae) have a summer growing season, so too do the oysters that feed on them, when conditions are warm and there is abundant phytoplankton in the water to eat.

Next is a series of images from our caging experiment last summer, which you can read about here. Our large cages contained either:

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no predators (bivalves only),

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spat-consuming mud crabs and oyster drills (consumers),

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or mud crabs and oyster drills plus blue crabs and toadfish (predators).

The spat tiles within the larger cages were placed either exposed to potential predators or protected from them in a smaller subcage. Here are typical examples of what tiles looked like at the end of the experiment (about 2 months after starting). You can see how all the spat on the unprotected tiles were wiped out in the consumer treatments, but a good number survived in the treatments with no predators, as we would predict. In the predator treatments, most of the spat on unprotected tiles were removed, but not as fully or quickly as in the consumer treatments, which we would predict if the predators are inhibiting consumption of spat by the mud crabs and drills through consumptive or non-consumptive effects. You’ll see one tiny spat holding on in the predator tile shown. On the protected tiles, most of the spat survived in all treatments, as expected. We plan to further analyze the photographs from the protected tiles though, to see whether spat growth rates differed between them. We may find that protected spat in the consumer treatments grew slower than in the other treatments because of non-consumptive predator effects.

Currently, we’ve recovered most of our arsenal of spat tiles from the field, and I say we have probably amassed enough bricks to pave an entire driveway! Good thing we can reuse them!

The Biogeographic Oyster Study is funded by 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.

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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.