Tag Archives: oyster reef

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Can crabs hear? (Revisited, with answers!)

P1050260Four 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.

The research in the following post was conducted while Randall and David worked at the FSU Coastal and Marine Laboratory.

Dr. Randall Hughes Northeastern University

A little over a year ago, I wrote about our research project, motivated by a question from WFSU producer Rob Diaz de Villegas, to test whether crabs can hear the “songs” made by their fish predators. At the time, the work had not been published, and so I was not able to share all of the juicy details. But now it has, in the Proceedings of the Royal Society B, so I can finally answer with a resounding YES!

To review a little bit, Rob’s question really had 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. 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 mud 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 it looks like mud crab torture, all the crabs survived the experiment!

Mud Crab Hearing TestWhat did we find? The crabs had a neurological response (i.e., they “heard”) a range of frequencies. They certainly wouldn’t ace any hearing tests, but if a sound is low- to mid- frequency and relatively close by, they can likely hear it. They do this using their statocyst, a structure containing sensory hairs that can detect changes in orientation and balance, and in this case, can detect changes in particle acceleration associated resulting from the acoustic stimuli.

Although cool to someone like me who is fascinated by marine biology, many of you are probably thinking “So what?”. And for that, we turn to the second part of our study, where we tested whether mud crabs change their eating habits in response to the songs made by their fish predators. We compared the number of juvenile clams that crabs ate when we played them either a silent recording or a recording of snapping shrimp (a common organism on oyster reefs that doesn’t eat crabs) to the number of clams that they ate when we played them recordings of songs from 3 fish that DO eat mud crabs – hardhead catfish, black drum, and toadfish. Apparently catfish and black drum songs are the same to a crab as the Jaws theme song is to me, because they hunkered down and did not eat nearly as many clams when they heard the calls of those two predators.

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Phil Langdon feeds a catfish in an iteration of a mud crab hearing experiment.  They had already noticed that mud crabs were eating less when they heard sounds made by catfish and other predatory fish.  Here, they sought to measure whether the response was more intense with chemical cues (pumped via those tubes into tubs), or predator sounds (played from underwater speakers).

So, now we know that mud crabs can hear, and that they don’t eat as much when they hear some of their predators. But we also know from our earlier experiments that these same crabs don’t eat as much when exposed to water that hardhead catfish have been swimming in, most likely because they can “smell” chemicals in the water that the fish give off. So which catfish cue generates a stronger response – sound or smell? Turns out that both cues reduce crab foraging and to about the same degree, although in our experiment the effects of catfish songs were slightly stronger than the effects of catfish smell.

So what’s the take-home message from this work? For one, it highlights that we still have a lot to learn about the ocean and the animals that live in it – we (and others) have been studying these mud crabs for years and never thought to consider their ability to use one of the 5 major senses! In addition, it’s a reminder that in studying the “ecology of fear”, or the effects that predators have on their prey even when they don’t eat them, we need to remember that few predators are silent, and the sounds that they make could be important cues that prey use to escape being eaten. And finally, it demonstrates that science can be really fun!

This material is based upon work supported by the National Science Foundation under Grant Number 1161194.  Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

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RiverTrek 2013 Preview: A Year in the Apalachicola River and Bay

Rob Diaz de Villegas WFSU-TV

RiverTrek paddlers are raising funds for the Apalachicola Riverkeeper, an organization whose mission is to “provide stewardship and advocacy for the protection of the Apalachicola River and Bay, its tributaries and watersheds…” (participating media members do not raise funds).  At the end of the paddle, on October 12, there will be a reception in Battery Park in Apalachicola.  There, people can greet the paddlers and bring non-perishable food items in benefit of Franklin’s Promise.  Franklin’s Promise aids the families affected by the failure of the Apalachicola Bay oyster reefs.

IGOR chip- gastronomy 150“The Good Lord giveth, and Georgia and the Corps taketh away.” Those words were spoken by Jon Steverson, Executive Director of the Northwest Florida Water Management District.  He was testifying before Florida senators Bill Nelson (D) and Marco Rubio (R) during a special field hearing to address the collapse of the Apalachicola Bay oyster fishery.  The high-profile event, held two weeks ago in Apalachicola, marked almost one year into a particularly turbulent era for this region.  Just one year ago, I was preparing to kayak the Apalachicola River for RiverTrek 2012.  The winter bars in the bay were just days away from opening.  When they did, a lot changed, including the nature of the RiverTrek videos we were to make, and the In the Grass, On the Reef project as a whole.

U.S. Senators Bill Nelson (D) and Marco Rubio (R) at the Senate Committee on Commerce, Science, and Transportation field hearing Apalachicola on August 13.

As I prepare to cover RiverTrek 2013 (October 8-12), the answers to the Apalachicola’s water flow problems remain elusive, and frustration remains high.  Much of that frustration is aimed, as one might gather from the first sentence of this piece, at the state of Georgia and the Army Corps of Engineers.  Thirteen days into the job as Mobile District Commander, Colonel Jon Chytka absorbed decades of displeasure at the Corps’ management of the ACF basin.  “I’m going to try to find out why they sent you,” said Senator Nelson, “Why didn’t they send the generals that I’ve been talking to?”  Part of the frustration stems from the rigidity with which the Corps follows the ACF Water Control Manual, and their interpretation of the authority granted them by congress.  The economic impact of fresh water on Florida’s seafood industry is not given as much weight as its economic impact on Georgia agriculture.   The Endangered Species Act of 1973 is the only guarantor that the river flow is not set below 5,000 cubic feet per second (cfs), which is how low it stayed for 10 months starting May 1, 2012.  That qualifies as the lowest river flow in recorded history, and only endangered mussels and gulf sturgeon kept it from being lower.  Senator Rubio asked whether the Apalachicola oyster would qualify for such protection.  Crassostrea virginica, the common oyster, is the main oyster species found on the east coast of this country and in the Gulf of Mexico.  The oysters you see on the fringe of the coast are the same species as the larger ones harvested from the floor of the bay.  Apalachicola oysters are the same species as Chesapeake oysters.  To the letter of the law, and despite massive decline in oyster reefs worldwide, it is not an endangered species.

This oyster was retrieved from Dr. David Kimbro’s oyster experiment in Apalachicola Bay. They found it dead, with its meat having been eaten. Like many of the dead oysters they’ve found, it has oyster drill egg sacs growing on it. Each of the sacs (here growing on the “chin” of the oyster) contains 10-20 drills.  Low freshwater input to the bay increases its salinity, making the bay hospitable to oyster predators such as drills, crown conchs, and stone crabs.

A further source of frustration with the Corps is the speed with which the Manual is being updated.  As Col. Chytka pointed out, the process began in 2008 and was complicated by lawsuits, the amount of input from stakeholders in the affected states (over 3,000 comments), and the “technical complexities” of the system.  He projected that a draft of an Environmental Impact Statement would be ready in the Summer of 2015, after which they’d reopen it to comments and then finalize by 2016.  The oyster industry may not have that kind of time.  “I don’t see any hope for the near future,” said Shannon Hartsfield, President of the Franklin County Seafood Workers Association. “We don’t have a near future.”

The best-case scenario for the bay, as determined by the University of Florida’s Oyster Recovery Team, is full recovery within a couple of years.  That’s dependent on being able to place a significant amount of oyster shell at the bottom of the bay.  So far, Hartsfield estimates that they’ve covered 35-40% of Cat Point, historically one of Apalachicola’s most productive bars.  By the end of the current shelling project, he believes that they’ll have covered 50% of another of the bay’s main bars, East Hole.  So, in addition to fresh water, oysters will still be lacking adequate substrate where spat could settle.  Additional funding will be needed to cover the bars fully.  There is, though, a glimmer of hope.

While frustration has remained high, so too has passion for the ecosystem and compassion for the people affected.  Says Hartsfield, “This is the first time, ever, out of all this disaster that Franklin County has experienced in the commercial (seafood) industry, that we’ve had any recognition.  And we appreciate it greatly.”  That recognition drew dozens to the steps of the Franklin County Courthouse that day to show support.  It has drawn researchers willing to work with oystermen to find solutions.  It has drawn a steady stream of regional and national media.  And it drew the United States Senate to a fishing town on Florida’s Forgotten Coast.  At the very least, lot of people are invested in finding a solution.

RiverTrek paddlers make their way to Sutton Lake, off of the Apalachicola River.  Last year, the water was too low to paddle to where the largest cypress trees in the Apalachicola watershed are found.  With a year of healthy rainfall, this year's paddlers will have better opportunities to explore the creeks and sloughs branching off of the river.

RiverTrek paddlers make their way to Sutton Lake, off of the Apalachicola River. Last year, the water was too low to paddle further into the lake, where the largest cypress trees in the Apalachicola watershed are found. With a year of healthy rainfall, this year’s paddlers will have better opportunities to explore the creeks and sloughs branching off of the river.

I’m one of the media members who have found themselves returning to cover the crisis, and it started with 105 miles of paddling.  Last year at this time, RiverTrek was to be a different perspective on our local ecology than our marsh, oyster reef, and seagrass videos.  A change of pace.  Instead, it kicked off a year of content that connected the river with the coast, and with the people who care for and rely on these resources.  I now find myself getting ready for this year’s journey with a better knowledge and feel for the story, but with much less certainty about the outcome.  RiverTrek will end after five days.  For this other, much larger Apalachicola adventure, we’ll all just have to keep on paddling.

For more information on RiverTrek 2013, visit the Apalachicola Riverkeeper web site.  To watch videos from last year’s Trek, click here.

Music in the video by airtone.  “Salt in the Blood” was written and performed by Brian Bowen.

This material is based upon work supported by the National Science Foundation under Grant Number 1161194.  Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Shark tooth found in Apalachicola Bay buoy marking oyster reef experiment.

Apalachicola Oyster Research: SHARK WEEK

Since they’ve deployed their experimental cages in Apalachicola Bay, David Kimbro’s crew has had some go missing, while others have been found in this condition.  Missing buoys make potentially unharmed cages nearly impossible to find.  Until just yesterday, there have been no leads as to the identities of possible culprits.

Dr. David Kimbro Northeastern University/ FSU Coastal & Marine Lab
Southern Oyster Drill

Shark week? In Apalachicola Bay, oyster drills like this one are the animals that have inflicted the most damage.

I’ll eventually get to how our research on Apalachicola Bay oysters ties into shark week. But first, let me tell you about my history with the annual Shark Week, which is put on by the Discovery Channel. Growing up as a surfer in North Carolina, the best time to surf was in the late summer and early fall. After many warm months of zero waves in the spring and summer, we lived for tropical storms that would make their way into the south east….but not get too close. I hated those suckers that got too close, because fun waves would quickly turn into pigs being on the roof and lots of misfortune for my fellow North Carolinians.

Getting to the point, every August, I was barraged by the Discovery Channel with interesting stories about sharks. Cool… but as soon as the waves start coming up, I’d have all of these thoughts about sharks circling through my head. In fact, in the line-up the next morning, it was looked down upon to talk about the previous evening’s episode of Shark Week. Now, sharks are awesome and they are critical to the health of our marine environments, but I don’t like to think about them when I’m waiting for a wave.

Okay, enter our research on Apalachicola Bay’s oyster reefs. It has been a very wet summer and the waters are very murky… you can’t see squat under water. But that doesn’t deter us, because we have been full throttle this past year and especially this summer on the monitoring and experiments.

Disclaimer: the pronoun we = Nikkie and Hanna, who have to do all the diving and data collection. To be honest, I couldn’t have asked for a better graduate student and employee to lead this research project.

Nikkie with crown conch (and egg casing), found in Apalachicola Bay.

Nikkie with crown conch (and egg casing), found in Apalachicola Bay. Surveys have found that while southern oyster drills have thrived on commercially harvested reefs on the floor of the bay, conchs have been more numerous on fringe reefs.

Now, another disclaimer is that Nikkie DISLIKES not being able to see under water. So, for all of the sites that I can’t free dive to collect the data (my scientific diver certification expired…next on the to-do list to fix), I would serve as shark/alligator bait by swimming on the surface of the water for 1/2 hour while others collected data below.

To be honest, I’ve skewered Nikkie about her fear and about needing me to serve as bait. BUT… then I got an email today from the crew, which happens to be the first mission since I departed from Florida for Massachussettes. This week, my lab is undergoing a Herculean effort to set up another experiment. In doing so today, they solved mystery of who/what has messed with all of our previous experiments and they simultaneously confirmed Nikkie’s fear. These experiments are protected by welded cages and marked with buoys, which have frequently and unfortunately gone missing. This is bad for our research funds, our time and for the data we need to understand Apalachicola and its oyster reefs.

So, in the spirit of the board game Clue...who dunna it?

Freaking sharks. Given Nikkie’s significant fear and my discounting of that fear, I sure felt bad getting this message from Hanna and Nikkie today. But hey, that’s what team Kimbro does for Apalachicola oysters!

(Edit 8/11/13.  FSU Coastal and Marine Lab’s Dr. Dean Grubbs IDs it as a bull shark.  Read more on this fact sheet from NOAA, from which we leave you with this quote: “Bull sharks are one of the three top sharks implicated in unprovoked fatal attacks throughout the world.”- Rob)

Shark tooth found in Apalachicola Bay buoy marking oyster reef experiment.

Cheers,

David

See more posts and videos on the Apalachicola oyster crisis and this research.

This material is based upon work supported by the National Science Foundation under Grant Number 1161194.  Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

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Oyster Research Needs Your Help In Apalachicola Bay

Oyster drills infest one of David Kimbro's Apalachicola Bay experimental spat tile cages.

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 Kimbro Northeastern 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.

Experimental cages to be deployed in Apalachicola Bay.

Experimental cages to be deployed in Apalachicola Bay.

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.

Click the link to the right for GPS coordinates.

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 robdv@wfsu.org.  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 robdv@wfsu.org.

Thanks a bunch!

David

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.

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Recycling Oyster Shells for Choctawhatchee Bay

Rob Diaz de Villegas WFSU-TV
Choctawhatchee Basin Alliance staff from L to R: Brandy Foley, Jeff Murphy, and Rachel Gwin listen as Allison McDowell explains how the reef is to be laid out.  She had previously laid the section visible under the water.

CBA staff from L to R: Brandy Foley, Jeff Murphy, and Rachel Gwin listen as Allison McDowell explains how the reef is to be laid out. She had previously laid the section visible under the water.

IGOR chip- sedimentation 150

I’ve been wanting to do a video on Choctawhatchee Basin Alliance‘s Oyster Recycling program for some time.  I decided to do it now because we’ve been covering restoration efforts in Apalachicola Bay, and while the two efforts appear to have similar goals, they’re both using different methods and aiming at different goals.  In Apalachicola, they’re trying to restore their fishery.  They want oyster spat to settle on their shells and grow into market sized (3 inches or more) adults.  In Choctawhatchee, they’re rebuilding their coastline.  It’s an ecosystem service we have mentioned in the past but have struggled to show, how oyster reefs (and salt marshes) prevent erosion.  You can see in the video above how the coastline is retreating and exposing tree roots where these natural barriers have been removed.  And you can see how the sand just accumulates where they’ve replaced shell.  It’s one of the many beautiful things an oyster reef does.

With 85% of the world’s oyster reefs having already been lost, and with more being threatened, restoration is critical.  Many of those efforts center around what’s left in your basket when you leave the raw bar.  Every part of the oyster is valuable.  The animal itself cleans the water and provides income for oyster harvesters.  But it’s also a builder, and an oyster reef provides shelter for various fish, crab, and snail species, many of which we eat.    The shells that make the reef are the best place for a larval oyster to land.  So those dozen or two shells you walk away from have their value as well.  Thankfully, people like the Choctawhatchee Basin Alliance staff and volunteers are doing the hard work of collecting them and putting them back to work for the reef.

This is a refrigerator at Busters in Santa Rosa Beach.  Donnie Sellers shucked 75 dozen oysters the day we were there, and that was before tourist season.  All of the restaurant's shells end up in blue recycle bins.

This is a refrigerator at Busters in Santa Rosa Beach. Standing behind the bar, Donnie Sellers shucked 75 dozen oysters the day we were there, and that was before tourist season. All of the restaurant’s shells end up in blue recycle bins.

Music in the Piece by Red Lion.

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