A hardhead catfish, one of a mud crab's primary predators on North Florida oyster reefs.
As David has mentioned previously, predators can affect their prey by eating them (a very large effect to the prey individual concerned!) or by changing their behavior. And exactly how the prey change their behavior can have large consequences for the things that they eat. For instance, if you’re out camping and hear a bear lumbering around, do you quickly pack up all your food and put it out of reach of the bear and yourself? Or do you quickly eat as much as you can?
This summer we worked with Kelly, an undergraduate from Bridgewater College, to document how mud crabs deal with this dilemma of getting enough to eat but not getting eaten themselves.
Kelly with the broken down truck on an ill-fated return trip from St. Augustine.
Specifically, we wanted to know how they respond to the presence or absence of catfish, and how this response affects the survival of juvenile oysters. Sounds straightforward, right? Well, yes, in concept, but as Kelly quickly discovered, putting that “on paper” concept into reality at the lab took a lot of time and effort!
First, she had to get the “mesocosms” (aka large tubs) ready to serve as adequate habitat for the crabs, with plenty of sand and dead oyster shell for them to hide in.
Next, Kelly took individual juvenile oysters, or “spat”, and used a marine adhesive to attach them to small tiles that we could distribute among all of the mesocosms.
Juvenile oysters attached with Zspar (a marine adhesive) to a tile so we could assess mud crab predation.
You may have noticed that I mentioned catfish, and that these mesocosms are not particularly large relative to the size of a catfish. Never fear – because we wanted to separate the effects of catfish cues from the effects of catfish actually eating mudcrabs, the catfish were kept in a much larger tank, and then water from this tank was pumped into the mesocosms receiving catfish cues. (Setting up the pump and tubing to 60+ tanks was a several-day effort in itself!)
The catfish tank, with tubing carrying catfish "cues" to individual mesocosms.
Once everything was in place, it was time to collect the mud crabs. We couldn’t collect the crabs gradually, because they like to eat each other when confined in small spaces in the lab, so we garnered as much help as we could and held our own little mud crab rodeo. (And got caught in quite a thunderstorm in Alligator Harbor, but that’s another story).
Finally, it was time to start the experiment! We measured the size of each of the mud crabs, added them to the mesocosms, and let them eat (or not). Each day, Kelly would count the number of live oysters remaining, and she would remove a few mud crabs from some of the mesocosms to simulate catfish predation. There were a lot of moving parts to this experiment, and Kelly did a great job managing it!
And what did we find? Turns out that individual mud crabs actually eat more juvenile oysters when they are exposed to catfish cues and the removal / disappearance of some of their neighboring mud crabs, compared to just the removal of neighboring mud crabs or the absence of catfish cues. But overall, the the removal of mud crabs have a positive effect on oyster survival. (Even though individual crabs may eat more, there are not as many crabs around, so it’s a net positive for oysters.)
Mud crabs ate more oysters per individual in buckets with exposure to catfish cues and high rates of manual removal of mud crabs (to simulate predation).
Kelly has returned to classes, so we’ve now recruited a new assistant, Meagan, to help us with an experiment to address the additional questions that inevitably arise as you learn more about a system – for example, do mud crabs behave differently if catfish are around all the time versus only some of the time? We’ll keep you posted…
Randall and David’s research is funded by the National Science Foundation.
David's collaborators, from left to right- Dr. Jeb Byers, Dr. Mike Piehler, Dr. Jon Grabowski, and Dr. Randall Hughes.
As you can see from the video that summarized our efforts over 2010, it was a busy 6 months of research. After taking a great break during the holidays, the entire oyster team (Jon = Gulf of Maine Research Institute, Mike = University of North Carolina at Chapel Hill, Jeb = University of Georgia, Randall = Florida State University and me) met for a long weekend to figure out what we accomplished and where we are going in the future.
You might think that our 2011 research plans should already be set given that we received funding. Well, we did receive funding to carry out some outlandish field experiments in 2011, but these experiments were dreamed up in our offices and may not address the most ecologically relevant questions for our system. Checking in with the monitoring data is probably the best way to determine if our planned experiments were on target or if they needed to be adjusted and hopefully simplified!
Prior to the oyster summit last weekend, I hounded all of the research teams for all of their data. Given the huge volume of data and everyone’s busy schedules with teaching classes and other research projects, this was quite the task. Once Tanya meshed all the data together (also not a simple task), I then moved on to the next task of analyzing our data.
Well, the initial excitement quickly turned into a stomach churning feeling of….where the heck do I begin? Similar to the way that too many prey can reduce the effectiveness of predators, the data were swamping me…I was overwhelmed and the draining hourglass wasn’t helping (people were flying into town in two days…yikes!).
After multiple cups of coffee, the anxiety passed and I decided to revisit some basic questions:
David's team used gill nets to catch the larger fish around the reefs, many of which are top predators in that habitat.
(1) With the gill nets, we obtained predatory fish data. So how do the abundance and biomass of these fishes vary across latitude? And does this pattern change with season (i.e., summer versus fall)?
(2) Then I thought back to the fond memories of ripping up oyster habitat to check out the abundance of things that consume oysters (e.g., mud crabs). Oh…the memory of that work gives me a warm and fuzzy feeling; I bet Tanya, Hanna, Linda and everyone else that helped feel the same way! How do the abundances of these things change across latitude? Are there larger crabs up north or down south? How does the mud crab picture mesh with the predatory fish picture?
This spat stick is made of calcium carbonate, the same substance as oyster shell, and is ridged to simulate the ridges in those shells. That makes it an attractive landing spot for oyster spat (larval oysters), which tend to settle on oyster shells.
(3) Working our way down the food web and sticking with the oyster samples we ripped up back in August, how do oyster densities and oyster size change across latitude and how do these patterns mesh with the mudcrab and predatory fish data?
(4) Finally, I wanted to revisit the data from our instrumentation to see how temperature and salinity changed across latitude and with season, as well as the data from our spat sticks to see how oyster recruitment differed.
It’s pretty amazing that six months of work can be summarized so quickly into four topics. Well, I kept hitting the coffee and got all of these data worked up in time for the first portion of our oyster summit. Surprisingly, all inbound flights arrived on time and we all assembled last Friday to go over the data. I’ll briefly lift the research curtain to illustrate what our data looked like:
The Georgia reef gill nets trapped a lot of sharks. Here Dr. Jeb Byers is removing blue crabs (also an oyster reef predator) from shark bellies. The trapping done on these reefs is clarifying the food web for these habitats.
(1) Although we predicted predator abundance to increase at lower latitudes, predator abundance and the number of different predators peaked in Georgia/South Carolina. This is because lots of the species we have in Florida were also in Georgia. And, Georgia has lots of sharks! Needless to say, Jeb’s crew has been the busiest during gillnet sampling. Jon and Mike’s crew have had it pretty easy (no offense)! The workload reduced for everyone in the fall, but the differences across latitude stayed relatively the same. The really cool result was the pattern that hardhead catfish are extremely important and the most abundant predatory fish on Florida reefs; I love those slimy things.
(2) Interestingly, mudcrab biomass peaked up north where predatory fishes were less abundant.
(3) And the abundance of large, market size oysters was highest where predatory fish were most abundant (GA/SC).
(4) Amazingly, we all did a good job selecting oyster reefs with equivalent salinities (this can vary a lot just within one estuary) and temperature was the same across all of our sites until December….instrumentation up north got covered in ice! Glad I was assigned the relatively tropical reefs in Florida. Finally, oyster recruitment in NC and Florida appears to proceed at a trickle while that of GA/SC is a flood-like situation during the summer.
A month after first being deployed, Tanya and Hanna inspect an Alligator Harbor tile. You can see that some of the oysters have definitely started growing, but also that some of the spat became unglued. When they run the experiment again, they'll use a different adhesive more suitable for a marine environment.
After we all soaked that in, we then talked about the tile experiment. While these data were really cool (mortality presumably due to mudcrabs was lowest where predatory fish were most abundant = GA), we worried about being able to tease apart the effects of flow, sedimentation, and predation. Unfortunately, this experiment seems to uphold my record with experiments: they never work the first time. We’ll probably repeat this in fall of 2011 with a much better design to account for flow and sedimentation.
Before breaking for a nice communal dinner at my place, Mike summarized the nutrient cycling (sediment) data that we have been collecting. In short, having lots of living oysters really promotes de-nitrification processes and our sampling picked this up.
Putting this all together, it looks like there are latitudinal patterns in fish predators that may result in mudcrab density and size patterns. Together, these may help account for latitudinal patterns in oysters (highest in GA). This all matters because more oysters = more denitrification = healthier estuarine waters.
END DAY 1
On day 2 of the summit, we worked through what made us happy about the monitoring data, what things we could add on to make us happier, and that we should continue this monitoring through the summer of 2011. This actually took all morning.
On day 2, the oyster summit moved into the more comfortable location of the Marine Lab guest house.
After a quick lunch break, we then reconvened in another room with a better view (nice to change up the scenery) to go over how we should experimentally test the linkages I mentioned above. This is where the saw blade of productivity met a strong wood knot. Personally, I became horribly confused, fatigued and was utterly useless. This resulted in lots of disagreement on how to proceed and possibly a few ruffled feathers. But nothing that some good food and NFL playoff football couldn’t cure.
After taking in a beautiful winter sunset over the waters off the lab, we ditched the work and began rehashing old and funny stories about each other.
Amazingly, we awoke the next morning and fashioned together a great experimental design that we will implement beginning June 2011. To Jeb’s disappointment, this will not involve large sharks, but we will get to play with catfish!
But now it’s time to prepare for our winter fish and crab sampling. It will be interesting to see what uses these reefs during the dark and cold of winter!
Thanks for following us during 2010, and please stick around for 2011 as I’m sure things will get really interesting as we prepare for our large field experiment.
David’s research is funded by the National Science Foundation.
The following is the first of three or so videos on the big October oyster trip. In this one, you get a long busy day in the field condensed into two minutes (it’s much less exhausting that way). We’ll have videos in the next couple of weeks on David’s co-collaborators (including video of the Georgia/ S. Carolina team and all the sharks they caught) and a video on David’s own team.
The "October Oyster Push" had many objectives, but none took as much time to implement than the tile experiment. Seeing how these baby oysters- spat- grow over the next few months will give David an idea how oysters typically fare at each reef over the course of their lives.
I spent most of this past week feeling pretty darn good about having just finished our October sampling and experimental objectives out on the oyster reefs. Of course, this glow continued into the weekend as my football team pulled out a W in Tallahassee.
But back to the science. Although Rob chronicled each day of our crazy road trip, I want to relive it once more just to give the trip from my perspective. So, here are my top-ten thoughts:
Number 1: Planning the details of the road trip (housing, which team is going where and when) as well as figuring out how to set up the tile experiment (see video) was pretty stressful. Thank goodness I had Tanya around to bounce scheduling ideas off of. Because I kept chaning my mind, I think Tanya made like 6 different versions of our schedule.
Number 2: I talked the NC and SC/GA teams into doing the aforementioned experiment with oyster spat to examine how actual predation and the fear of being eaten affects oysters up and down the coast. I successfully convinced the teams partly because I emphatically claimed that the additional work load would only be five hours of more work at each site. Well, I got that wrong. It was probably triple that estimate. That’s one of my flaws: I always underestimate how long research tasks take, which is bad because you constantly feel behind as a result of being over-scheduling. Rule of thumb: always multiply my work estimates by at least 2.
Number 3: I never want to see a dremel again. With dremel in hand one evening at Saint Augustine, I had only extracted ¼ the spat I needed for the experiment but the time spent on this task had already surpassed my previous estimate. That’s when coffee and the ability to lose yourself in the task become extremely important. I guess I took it one oyster spat at a time.
(L to R) Tanya, Hanna, and Cristina pick up the slack while David dremels away back at the lab space.
Number 4: I could not have lost myself in the task of setting up the experiment if it hadn’t been for Tanya, Hanna and Cristina. Knowing that they were fully trained to carry out the sampling objectives, I did not have to busy myself with those numerous tasks, such as setting gill nets and traps (and retrieving the catch), taking sediment and water samples, etc. In fact, after finishing the sampling objectives and follow-up lab work, they would immediately begin helping me with the experiment by cleaning adult oysters and identifying spat for me to extract with the dremel. With that help, I was able to focus solely on dremeling.
Number 5: Dremeling 1080 spat out of adult oyster shell stinks. Did I already say that? Well, this task deserves two spots on the top-ten list. In tact, I probably attempted to extract over 2,000 oysters because I would often slip with the dremel and accidentally kill the oyster spat that I had spent five or so minutes on.
Hardhead and sail catfish seem to be the dominant predator of the Florida Gulf sites. By eating mud crabs that predate oysters, these fish perform an important function on oyster reefs.
Number 6: we couldn’t have asked for better weather. In fact, I think there were some temperature records being set. Despite these warmer than usual temperatures, there was about ½ the diversity and number of predatory fish on our reefs. So, going against my expectations, these Florida sites are experiencing some seasonality in the assemblage of predators. Interestingly, all teams were catching red drum on their reefs; guess it’s their time of year. The red drum mostly had smaller fish in their stomachs. The SC/GA team was still catching lots of sharks. And catfish was still the most abundant predator on our reefs. Those slimy things are definitely major players on southern oyster reefs because they had lost of mud crabs (who eat oysters) in their guts. Final detail about the Florida sites is that my northern locations (Alligator Harbor on Gulf and Jacksonville area on Atlantic) had more predatory fishes than did the more southern sites in Florida…. intriguing.
Number 7: We had to change plans at the end of the week and this mid-course change actually went smoothly. This change came about because the housing space near our Jacksonville site was not conducive for setting up the tile experiment. Luckily, Hanna and Cristina ventured up to Jacksonville to figure all of this out for me. This “divide and conquer” strategy allowed Tanya and me to finish up the sampling and experimental objectives in Saint Augustine, while Hanna and Cristina began sampling in Jacksonville to keep us on schedule. And rather than resting up in Jacksonville, Hanna and Cristina ripped up oyster habitat and drove it back down to Saint Augustine. They looked pretty rough upon that later return to Jacksonville. But after a good dinner and a few hours of sleep, their oyster delivery allowed us to work on the materials for the Jacksonville experiment in a much better laboratory setting.
Number 8: Team morale and will to finish objectives hit a low point once we reached Jacksonville. The lodging for the first evening was haunted with cockroaches: this is Hanna’s kryptonite. Luckily, Tanya whipped us up some good pasta to help keep our minds off of the roaches. The next morning, cockroaches began to seem not so bad. When we got to the boat-launch and found there to be no wind, I knew it was trouble because this site had the reputation for being particularly buggy. So, we headed into the mouth of our creek and hit the first reef. Not too bad… actually, no fish in the nets. Only a few bugs and two free hands to swipe them away. But as we ventured further into the belly of the creek/bug hell and found tons of fish in our nets, I began to worry about mutiny. As I was exhorting the crew to extract tons of fish from the next set of nets, I realized that freeing this many fish would take twice as long because we needed to spend an equal amount of time cursing the no-see’ums and keep them out of our ears and noses; kind of hard to do with fish in your hands. While taking fire from the no-see’ums, we then began sustaining additional injuries from other natural agents. I suffered my first good-sized oyster cut. Hanna got her finger nearly cut off by a large stone crab. For the pain finale, a decent sized catfish stabbed my hand with the barb of its dorsal fin. I don’t blame it, but daggum that hurt. At this point, the unpleasantness was almost comical. Note to self: buy hats with bug nets to combat no-see’ums.
Number 9: All of the pain and stress of that week is now good fodder for the lab to laugh about and bond over. That’s one of the perks of conducting research as a team. And that’s one of the reasons why Big Jon, Randall and I are still collaborating.
David walks away from the tiles he and his team spent so much time putting together. He won't know how successful the experiment was until he travels back to these sites.
Number 10: Now that we have all caught up on sleep, have relived our stories, and have begun to look at the data, I now stress about whether the tile experiment will actually work. Like most experiments I conduct, I put a lot of effort into something that has a 50% chance of not succeeding. For example, the spat that I extracted and adhered to tiles may have been overheated by the dremel/extraction process…are they dead already? And then, oh boy…what if the glue doesn’t hold? That’s what really keeps me up at night.
Randall gets back to her roots, placing traps on a reef with Hanna.
When I worked as a technician for our current collaborator Jon Grabowski back when he was in graduate school, one of his favorite sayings as we headed out to the field was “This is where the magic happens”. Yesterday and today I got to experience that magic again as I made my first visit to our oyster sites in Cedar Key. Though I spend a lot more time with plants these days, I do love oyster reefs. Maybe it’s because the first field research I did was on reefs (with Jon), or maybe it’s because of the mystique they seem to hold for nearly everyone, but it sure was fun to hear those shells crunch as I stepped out of the boat.
Of course, in addition to “the magic”, there’s also the cuts and scrapes, the no see-ums, and frustrating way that nets get caught on every oyster clump within 2 ft. But something about the reefs wins me over every time!
Enough of all the nostalgia – what did we actually accomplish? Hanna and I started about midday on Sunday, deploying traps at each of the sites. We realized as we headed back to the boat ramp that the return trip we were scheduled to make later that evening after deploying nets would have been pretty challenging in the dark, so we spent most of the afternoon seeking out a plan B. Thanks to some wonderful people in Cedar Key, we ended up docking the boat for the night at a home just near our sites! Around 6pm we headed out to pick up the traps. We didn’t find a whole lot – a few speckled seatrout and some killifish – but we were able to deploy our nets without any trouble (other than the previously mentioned no see-ums). By 9:30pm we were back at the rental house eating our frozen pizza dinner.
This morning we got up and headed back out to see what was in our nets. Somewhat surprisingly, it was all mullet and catfish! Not that we didn’t expect those fish to be there, but we thought we’d get a greater variety of species. There were also 2 red drum, 1 blue crab, and a couple of crown conchs, but mostly it was mullet, mullet, mullet.
After we got turned around heading back to the boat ramp, I was really glad that we hadn’t tried that trip in the dark last night! All in all, it was a trouble-free trip to the field, and a welcome opportunity for me to see some of “the magic” again myself.
David & Randall’s research is funded by the National Science Foundation.
The first leg of David Kimbro’s Roctober oyster push is now complete. If you look at the schedule below, you’ll see the first day was intensive, starting in the wee hours and going late into the night. As David mentioned in his post, the head of the NC team (Jon Grabowski) was along for the fun. David was Jon’s lab tech once upon a time, as was Dr. Randall Hughes (In the Grass). So tagging along I definitely got some “family reunion” vibes, with lots of good natured ribbing (let’s just say it was good-natured).
For this October push, David will be breaking in a new boat to help his team cover ground more efficiently while lugging traps and samples around. In order for the boat to move in shallow water, David replaced the motor with a lawnmower engine. It worked fine on Thursday, when the water was higher, but it had a few problems Friday morning at low tide:
Jon Grabowski drags the boat- along with and Tanya and Alicia- after not being able to drive the boat through shallow waters.
Finally, they were able to get it to go. The solution? As David’s tech, Hanna, said- “Just Gun it!”
The catch this time was a little different than the last, with new fish like Red Drum ending up in the gill nets and no juvenile fish being caught in the minnow traps. They also started looking into the stomachs of some of the predators (they have a permit to do so if the fish die in the net) and are seeing that the catfish here are eating mud crabs. Mud crabs, of course, are key oyster predators.
Early Friday morning, Hanna Garland kayaks to "site 1" in Alligator Harbor.
We’ll be heading out with David’s crew throughout the week. On top of all of the other arrangements they have to make to move their crews around multiple sites hundreds of miles apart, they have to accommodate our camera crew. So thanks for finding a way to drag us along! Hopefully we can show people the kind of work that goes into making this kind of research happen. There’s a lot of work to go along with the science, and with every subsequent sweep and new experiment, the patterns will hopefully clarify and our understanding of these ecosystems- and how to best conserve them- will be that much further advanced.
David’s crew has been split into two teams, the Net/Trap team (N/T) and the Tile team (TI). For a closer look at how David’s team nets and traps larger fish and crabs, click here. To learn more about what the Tile team will be doing, click here. And if you click On the Reef under categories in the sidebar, you can track David’s progress over the course of this study.
5:07 PM- Retrieve traps. High tide activities: reference water level, water samples, replace spat sticks. Unlike in the previous sampling done in Alligator Harbor, there were no juvenile pinfish or pigfish.(N/T)
8:00 PM- Deploy nets. The nets will be retrieved Friday morning to give David an idea about what was swimming around over night. (N/T)
Tide Times and height (ft.) for Alligator Harbor, October 21, 2010
Low- 8:07 AM (0.2)
High- 2:12 PM (2.7)
Low- 8:07 PM (0.9)
Friday, October 22- Alligator Harbor
8:00 AM- Retrieve nets, data logger. Today there were a lot of red drum (redfish) and of course, catfish (hardhead and sail). On site dissection reveals that the catfish eat mud crabs, thus serving the same role that toadfish serve in North Carolina reefs. (N/T)
8:30 AM- Return tiles/ oysters. The tiles for the new spat experiment mentioned by David go out today. (TI)
Tide Times and height (ft.) for Alligator Harbor, October 21, 2010
Low- 8:40 AM (0.1)
David and his team are taking Saturday off. Bright and early Sunday morning, the Net/ Trap team heads for Cedar Key while the Tile team heads to Saint Augustine.
David’s research is funded by the National Science Foundation.
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