Four years ago, we traveled out into the oyster reefs of Alligator Harbor with Dr. David Kimbro. It was both the start of an ambitious new study and of our In the Grass, On the Reef project. Last June, we went back to those reefs with Dr. Randall Hughes as she, David, and their colleagues revisited study sites from North Carolina to the Florida Gulf. In 2010, they sampled the reefs with nets and crab traps, and harvested small sections of reef. This more recent sampling, which unfolds in the opening scenes of our recent documentary, Oyster Doctors, was conducted with underwater microphones. Randall explains how sound became a tool in further understanding fear on oyster reefs.
In January, David Kimbro’s lab did a preliminary survey of Apalachicola Bay oyster reefs, looking at the overall health of oysters and the presence of predators. They followed this up with an experiment meant to monitor oyster health and predator effects over time. Many of their experimental cages were displaced, likely due to the buoys marking them breaking off. But what they found in the cages that remained intact was that oyster drill numbers appear to be exploding in warmer waters. David is looking for help keeping tabs on them.
Dr. David KimbroNortheastern University/ FSU Coastal & Marine Lab
Wishing that you were wrong is not something that comes naturally to anyone. But that is how I felt at the most recent oyster task force meeting in April. There, I shared some early research results about the condition of the oyster reefs. In our surveys, we found that the oyster reefs in Apalachicola Bay were in really bad shape and that there were not any big bad predators hanging around the reefs to blame. Even though I had originally shot off my big mouth about the oyster fishery problem being caused by an oyster-eating snail, I hoped that our first bit of data meant the snails were never there. Or better…that they were gone. The story of the boy who cried wolf comes to mind.
But an alternative of this David-cries-wolf story is that our January sampling didn’t turn up many predators because it’s cold in January, and because they were hunkered down for a long winters nap. Unfortunately, this option is looking stronger.
Since the task force meeting, we have been figuring out how conduct field experiments in Apalachicola. To be honest, an underwater environment without any visibility is an experimentalist’s worst nightmare. Still, we deployed fancy equipment, big cages, and then little mini experiments inside each big cage to figure out how much of the oyster problem is due to the environment, to disease, or to predators.
Even though we lost over half of our experiment and instrumentation, we recovered just enough data to show that the problem could be predation and that the culprit is a voracious snail. So, after learning some lessons on how to not lose your equipment, we decided to take another crack at it. In fact, Hanna and crew just finished sampling half of our second experiment today. We got the same results….lots of snails quickly gobbled up all of the oysters that were deployed without protective cages. But the oysters that were protected with cages did just fine.
This photo illustrates what Apalachicola oyster reefs are dealing with. This is one clutch of eggs laid by one adult snail. Within each little capsule, there are probably 10-20 baby snails. After a long winter’s nap, these snails are hungry.
We are going to keep at this, because one week long experiment doesn’t really tell us that much. But if we keep getting the same answer from multiple experiments, then we are getting somewhere.
In addition to updating y’all, I wanted to ask for your help. Because my small lab can’t be everywhere throughout the bay at all times, there are two things you could do if you are on the water.
First, if you come upon our experiment, can you let me know when you happened upon them and how many buoys you saw? If you report that all buoys are present, then I’ll sleep really well. And if you alert us that some buoys are missing, then I’ll be grateful because we will stand a better of chance of quickly getting out there before the cages are inadvertently knocked around, so that we can recover the data. Click here for GPS coordinates and further instructions.
Second, if you are tonging oysters, then you are probably tonging up snails. It would really help us to know when, where, and how many snails you caught. Take a photo on your phone (Instagram hashtag #apalachcatch – Instagram instructions here) or e-mail them to email@example.com. We’ll be posting the photos and the information you provide on this blog.
This is kind of a new thing for us, attempting to use technology and community support this way. There may be some bumps along the way. If you’re having trouble trying to get photos to us, contact us at firstname.lastname@example.org.
Thanks a bunch!
David’s Apalachicola Research is funded by Florida Sea Grant
In the Grass, On the Reef is funded by a grant from the National Science Foundation.
Over the last few weeks, we’ve explored the ecology of fear in oyster reefs. What makes oysters too scared to eat, potentially keeping them from reaching market size or filtering water? What makes mud crabs too scared to eat oysters, giving the oysters a better chance to succeed? New research by Dr. Randall Hughes and Dr. David Kimbro might change the way we understand fear in mud crabs.
Dr. Randall Hughes FSU Coastal & Marine Lab
When we started the In the Grass, On the Reef project, Rob (WFSU-TV Producer Rob Diaz de Villegas) embarked on a crash course learning about oyster reefs and salt marshes, biodiversity, and non-consumptive predator effects. While you’re most likely familiar with those first few terms, the last one – non-consumptive effects – is a bit of a mouthful and hasn’t exactly made the list of new slang words of 2013. The term refers to the ability of predators to SCARE their prey even when they don’t EAT them, causing the prey to hide, or eat less, or change their size/shape to make it less likely that they will be eaten. Of course, these changes are only possible if the prey realizes the predator is there before getting eaten! There are several “cues” that prey can use: (1) they can see them (visual cues); (2) they can feel them (physical cues); or (3) they can “smell” them (chemical cues). This last category is really common in the ocean, especially with slimy snail or fish predators that give off lots of chemicals into the water!
As Rob was learning more about the fish predators that we find on our oyster reefs, he discovered audio clips of the sounds that several of these fish make. Putting 2 and 2 together, he posed a simple question to David and me: Can mud crabs use fish sounds as a cue that their predators are near?
To be quite honest, David and I didn’t have an answer. But, we knew how to find out – do the experiment(s)! We enlisted Housam Tahboub, an undergraduate at the University of Michigan Flint, who wanted to do his summer Honors project in our labs. (Little did he know what he was getting into.) And then we set off on a crash course in bioacoustics, underwater speakers, and crab torture chambers (more on that in a minute).
Rob’s question really has 2 parts:
(1) Can crabs hear (anything)? (They don’t have ears.)
(2) Do crabs respond to the sounds of their fish predators?
To answer #1, we paired up with Dr. David Mann at the University of South Florida. Dr. Mann is an expert in bioacoustics, and particularly in evaluating whether marine critters (primarily fish) can hear different sounds. We modified his methods slightly to accommodate our crabs – basically, we needed to immobilize the crabs on a ‘stretcher’ so that we could insert one electrode near the crab’s antennae, and another in the body cavity to pick up any background “noise” the crab may be produce that was not in response to the acoustic stimuli. Although I know it looks like crab torture, all the crabs survived the experiment!
Once the crab was immobilized and the electrodes were in place, we submerged the crab in a tank full of seawater that had an underwater speaker in it. We then played a series of acoustic stimuli of different volumes and frequencies and quantified the response recorded by the electrode. The really nice thing about this method is that we don’t have to train the crabs to tell us when they hear the noise like in the hearing tests that you and I take!
To tackle question #2, we set up a mesocosm experiment at FSUCML. Each mesocosm (aka, bucket) had sediment, a layer of loose oyster shell to serve as habitat for the crabs, and 5 mud crabs that we collected from nearby oyster reefs. We also added some juvenile clams glued to a few marked oyster shells in each mesocosm – this way, we could count the number of clams eaten over time and determine whether crabs were eating more or less in response to the predator sounds.
To run the experiment, we downloaded sound clips of several different crab predators – toadfish, black drum, and hardhead catfish – as well as 2 non-predators to serve as controls – snapping shrimp and a silent recording. Housam put these on his iPod, connected it to an amplifier and underwater speaker, and we were ready to begin.
(Well, let’s be honest, it wasn’t quite that simple. Housam read a lot of papers to figure out the best methods, spent lots of time collecting crabs, and logged lots of hours (both day and night, in the company of mosquitoes and biting flies) moving the speaker from tank to tank before we finally settled on a good protocol. He even tried all of this in the field! But when his summer ended, Tanya, Phil, and Ryan kindly stepped in to run the rest of the trials we needed.)
But we didn’t stop there. We know from our earlier experiments with Kelly Rooker (another undergraduate researcher) that the crabs don’t eat as much when exposed to water that hardhead catfish have been swimming in, most likely because they can detect chemicals in the water that the fish give off. So which cue generates a stronger response – chemical cues or sound cues? Time for another experiment!
In this version, the mesocosms were assigned to one of 4 combinations: (1) a silent recording, paired with water pumped from a tank holding 2 hardhead catfish into the mesocosm; (2) a recording of a hardhead catfish, paired with water that did not go through the catfish tank; (3) a recording of a hardhead catfish, paired with water from the catfish tank; (4) a silent recording, paired with water that did not go through the catfish tank. We again looked at the number of clams eaten over time to see how the crabs change their behavior.
This project has been a lot of fun, and it never would have happened were it not for Rob’s curiosity. We gave a preview of our results at the Benthic Ecology conference in Savannah, GA, last weekend. But we’ll have to wait until everything is reviewed by other scientists and published in a scientific journal before we can share all of the details here. So stay tuned!
Music in the piece by zikweb.
Black Drum recording used in the video courtesy of James Locascio and David Mann, University of South Florida College of Marine Science.
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In the Grass, On the Reef is funded by a grant from the National Science Foundation.
For today’s post, we shift our look at the ecology of fear from oyster reefs to the (often) neighboring salt marsh. We know crown conchs are villains on oyster reefs, but might they redeem themselves “in the grass?” If they live on the Forgotten Coast, it depends on what side of Apalachicola they live.
If you’re a fan of oysters and you read David’s previous post, then you probably don’t like crown conchs very much. Why? Because David and Hanna’s work shows that crown conchs may be responsible for eating lots of oysters, turning previously healthy reefs into barren outcrops of dead shell. And we generally prefer that those oysters be left alive to filter water and make more oysters. And, let’s be honest, we would rather eat them ourselves!
But, in something of a Dr. Jekyll and Mr. Hyde act, crown conchs can take on a different persona in the salt marsh. Here, the exact same species acts as the good guy, increasing the abundance of marsh cordgrass. And more abundant marsh plants generally means more benefits for we humans in the form of erosion control, water filtration, and habitat for the fishes and crabs we like to eat. How exactly does that work?
If you look out in a salt marsh in much of the Gulf and Southeast Atlantic, I can nearly guarantee that you’ll see a marsh periwinkle snail. Usually, you’ll see lots and lots of them. These marine snails actually don’t like to get wet – they climb up the stems of the marsh grass as the tide comes in. While they are up there, they sometimes decide to nibble on a little live cordgrass, creating a razor blade-like scar on the plant that is then colonized by fungus. The periwinkles really prefer to eat this fungus instead of the cordgrass, but the damage is done – the fungus can kill the entire cordgrass plant! So these seemingly benign and harmless periwinkles can sometimes wreak havoc on a marsh.
But wait a minute – if periwinkles cause all the cordgrass to die, then why do you still see so much cordgrass (and so many snails) in the marsh? That’s where the crown conch comes in.
In marshes along the Gulf coast, there are also lots of crown conchs cruising around in the marsh (albeit slowly), and they like to eat periwinkles. Unlike other periwinkle predators such as blue crabs, the crown conchs stick around even at low tide. So when the periwinkles come down for a snack of benthic algae or dead plant material at low tide, the crown conchs are able to nab a few, reducing snail numbers. And fewer snails generally means more cordgrass.
Of course, the periwinkles aren’t dumb, and they often try to “race” away (again, these are snails!) when they realize a crown conch is in the neighborhood. One escape route is back up the cordgrass stems, or even better, up the stems of the taller needlerush that is often nearby. By causing periwinkles to spend time on the needlerush instead of grazing on cordgrass, or by making the periwinkles too scared to eat regardless of where they are sitting, the crown conch offers a second “non-consumptive” benefit for cordgrass. One of our recent experiments found that cordgrass biomass is much higher when crown conchs and periwinkles are present compared to when just periwinkles are present, even though not many periwinkles were actually eaten.
On the other hand, if the periwinkles decide to climb up on the cordgrass when they sense a crown conch, and if they aren’t too scared to eat, then crown conchs can actually have a negative effect on the plants. This is exactly what David found in one of his experiments. In this case, the tides play an important role – west of Apalachicola, where there is 1 high and 1 low tide per day, each tide naturally lasts longer than east of Apalachicola, where there are 2 high tides and 2 low tides per day. The longer tides west of Apalach appear to encourage the snails not only to stay on the cordgrass, but also to eat like crazy, and the plants bear the brunt of this particular case of the munchies.
So even in the marsh, it turns out that crown conchs can be both a friend and a foe to marsh cordgrass, depending on how the periwinkles respond to them. And figuring out what makes periwinkles respond differently in different situations just gives us more work to do!
Music in the piece by Revolution Void.
In the Grass, On the Reef is funded by a grant from the National Science Foundation.
Over the last few weeks, we’ve explored the concept of the ecology of fear on oyster reefs. But, as David asks in the video, “does it matter?” Exactly how much does fear affect oyster filtration, or their ability to support commercially and ecologically important species? And how does fear affect the benefits we receive from ecosystems such as salt marshes and seagrass beds? Coming up, we see how David and Randall took these big questions and broke them down into a series of experiments and investigations geared at creating a clearer picture of fear in the intertidal zone.
Dr. David KimbroFSU Coastal & Marine Lab
A few weeks ago, we had a bayside conversation about the important link between nutrients and oysters. But there is something else that may dictate whether a reef thrives: predators.
Academically, the importance of predators dates back to the 1960s. Some smart people proposed that the world is green because we have lots of big animals, which eat all of the smaller animals that would otherwise consume all the plants…hence the green world.
Now, that’s a pretty simple yet powerful concept. Since then, lots of studies have tested the importance of predators and how they keep our world spinning. For example, Bob Paine relentlessly braved the icy waters of the NW Pacific for a decade in order to chunk ravenous sea stars from one rocky cliff, but not the other. After several years, the cliff with sea stars still had a tremendous diversity of sea creatures (algae, anemones etc.) and the cliff without predatory sea stars did not. The absence of sea stars allowed pushy, bullying mussels to outcompete all other animals for space and this gave the rocky cliff a uniform and boring mussel complexion.
The same concept has been tested on land. Ripple and Beschetta showed us why the national parks out west no longer have the really important and woody trees (aspen, willow, and cottonwood) that they historically had. By suppressing wolves for the last 50 years, we allowed elk numbers to explode and the elk have overrun the really important woody species.
But predators don’t just eat. Enter my vivid memory of trying out for the Nash Central 8th grade football team in rural North Carolina. Contrary to my father in-law’s belief (who is a hall of fame football coach in Georgia), I wanted to play football instead of soccer. But when it came time for try-outs, fear prevented me from pursuing this line of work. To practice breaking tackles, each player had to lie on the ground and the rest of the team formed a circle around this player. Unbeknownst to the guy on the ground, the coach secretly selected three players to tackle the football player at the sound of the whistle. For twenty minutes, I watched physically un-developed friend after late-blooming friend get crushed by other guys who were definitely not late bloomers. The sights and sounds of this drill kept me nauseous until it was my turn. When my turn came, I couldn’t deal with the fear, didn’t perform well, and consequently became a soccer player.
My point is that fear is very powerful. Of course, I knew the charging football players were not going to eat me. But if I was paralyzed with fear from football, then imagine what it’s like for something that has to worry about being eaten. Going to back “the world is green” story: what if we overlay the concept of fear on that? How does the story change?
Well, the next generation of predator studies has examined how the fear of predators can be just as important as the appetite of predators. In addition, because predators can only eat only one animal at a time but can simultaneously frighten many more, fear can create powerful “remote-control effects”. In Australia, the fear of tiger sharks causes dugongs to avoid certain depths in a bay. As a result, only a small portion of the seagrass beds get grazed down by dugongs, possibly being one of the main reasons why areas like Shark Bay still have huge and lush seagrass meadows.
For the next few weeks, we will look at some work that my friends and I have conducted for the past three years on how predators and the fear of predators influence oyster reefs and the services that they provide us throughtout the southeast. Although we have the same predators and things that like to eat oysters from North Carolina to Florida, we suspect that differences in the environment will cause the effect of predators to play out differently.
In parting, I just want to say that this predator stuff is really interesting and I think it’s very important for oyster reefs. But of course, when you are dealing with an ecosystem that may be on the verge of collapse like Apalachicola Bay, the distinction between the appetite and fear of predators may not matter that much. But, we will soon see because we are now investigating this important system too.
Last Thursday morning, an oyster boat departed East Point and disappeared into the fog. Despite the crisis level lack of oysters in Apalachicola Bay, you can still see several boats working for what little is left. That’s not what this boat was doing, however. It was carrying two divers working for David Kimbro out of the FSU Coastal and Marine Lab. A foggy day is appropriate for the first day of a research study. All of the knowledge is out there, just like the St. George Bridge or the island beyond it are out beyond one’s field of vision. Eventually the sun comes out and everything is revealed.
They’ll need a little more than the sun to reveal the specifics of the oyster crisis. It’s easy enough to say that the record low flow of the Apalachicola River combined with harvesting pressure to decimate the reefs. But the forces at work are a little more nuanced than that. That’s why newly hired lab technician Stephanie Buhler and graduate student Hanna Garland are plunging into the murky waters of the bay and monitoring up to 20 sites within it for a Florida Seagrant funded project. The techniques they use will resemble those used by David and his colleague Dr. Randall Hughes in the NSF funded oyster reef study that we have been following over the last two-and-a-half years. The reefs they’ve worked on for that project were exposed at low tide. These are not, and so they’ll be diving. I’m curious to see how it goes in March, when they construct experiment cages on the floor of the bay.
One thing they’ll look at with the cages is the interaction between oysters and one of their predators. So, alongside the environmental data they’ll accumulate- salinity, availability of plankton and nutrients, oyster recruitment (new generations of oysters growing on the reef)- they will look at how the crown conch is affecting oysters in the bay. If you think it’s as simple “they’re just eating them all,” there’s a chance you might be right. But what David and Randall have found is that the fear of being eaten can be even more powerful than just removing an oyster. For a creature with no brain, oysters exhibit behavior and can be influenced by fear. In a couple of weeks, we’ll have a series of videos chronicling their pursuit of this idea over the last couple of years to see, in David’s words, “Does it matter?” It’ll be interesting to see how those dynamics might be at play here, where the higher salinity has invited a larger number of oyster consumers.
Another way this study is different from the NSF study is that one end result will be a recommendation as to how the resource is managed. David’s other collaborator on this project, Dr. J. Wilson White, will develop an Integral Projection Model for the reefs. Essentially they will take the data collected over the next few months and use it to project how the reef will do in different scenarios. Those scenarios will depend on the amount of water that flows down the Apalachicola River, which in 2012 was at an all time low. In these drought conditions, water is low across the entire Apalachicola/ Chattahootchee/ Flint basin. The basin is managed by the Army Corps of Engineers, whose Master Water Control Manual gives priority to stakeholders in the rivers upstream of the Apalachicola. That Manual is being updated, and Monday is the last day that they are taking public comment on it. You can lend your voice to that discussion here.
It’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.
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 KimbroFSU Coastal & Marine Lab
Like 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.
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.
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.
Imagine 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 Sounds of the Oyster Reef→
“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:
no predators (bivalves only),
spat-consuming mud crabs and oyster drills (consumers),
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.