Category Archives: On the Reef

Dr. David Kimbro studies predator-prey relationships in the oyster reefs and salt marshes of Florida’s Gulf coast.

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Predator Diversity Loss and Bay Mouth Bar: The Next Stage

David and Randall’s NSF funded oyster study looks to understand how predators control oyster eating animals such as mud crabs and crown conchs. But this dynamic isn’t exclusive to oyster reefs. They are also investigating how predators might help maintain salt marshes and seagrass beds. In their seagrass bed studies, they have focused on a system loaded with predators: Bay Mouth Bar.
Tanya Rogers FSU Coastal & Marine Lab

Tanya RogersThe very first time I drove from Tallahassee to the FSU Coastal & Marine Lab I saw a black bear crossing the Crawfordville highway. No joke. This was in June of 2010, and I had just driven 5 days and 2800 miles from San Francisco to the Florida panhandle to take up my new job on the Gulf Coast. I had just finished college in Washington state, and I had never before been to the Southeast. What sort of wild place had I ended up in?

IGOR chip_ predators_NCE 150IGOR chip- biodiversity 150A very wild and unique one it turns out, and one I’ve come to know better working for the past few years as a research technician for Dr. David Kimbro in the fascinating coastal habitats of this region. Primarily I’ve been traipsing around oysters reefs across the state for the collaborative biogeographic oyster study (now drawing to a close), but for the past year or so I’ve also been managing our side project in the Bay Mouth Bar system, a sandbar and seagrass bed near the FSU Marine Lab. Bay Mouth Bar is a naturalist’s playground filled with surprises and an astonishing diversity of marine creatures that never ceases to amaze me. It is also a unique study system with an intriguing history out of which we can begin asking many interesting questions. This coming fall I’m excited to be starting as Dr. Kimbro’s Ph.D. student at Northeastern University, and for part of my dissertation I’ve decided to conduct some new experimental research this spring and summer out on Bay Mouth Bar.

Horse conch consuming a banded tulip snail on Bay Mouth Bar.

A horse conch in Tanya's experiment consuming a banded tulip snail.

Bay Mouth Bar is known for its especially diverse assemblage of large predatory snails, which the ecologist Robert T. Paine conducted a study of in the late 1950′s. In 2010, we began surveying the snail community on the bar, interested in what changes might have occurred in the 50 years since Paine’s time, a period during which very little research had been done in this system. I began synthesizing some of the data we’ve gathered, as well as talking to some of the long-term residents of the area. So what has changed on Bay Mouth Bar since the 1950’s? A number of things in fact:

  • Of the 6 most common predatory snail species, 2 are no longer present: the true tulip and the murex snail.
  • The number of specialist snails (like the murex, which only eats clams) has declined relative to the number of generalist snails (those that eat a variety of prey, like the banded tulip).
  • There has been a drastic reduction in the overall area of the bar and changes in the coverage seagrass, specifically the loss of large meadows turtle grass (Thalassia testudinum).
  • Surface dwelling bivalves (e.g. scallops, cockles), once enormously abundant, are now very rare.
True Tulip and murex Snails (no longer found at Bay Mouth Bar)

The two main snail species no longer found at Bay Mouth Bar, true tulip (The larger snail on the left, eating a banded tulip) and murex (right). The true tulip was, along with the horse conch, a top predator of the ecosystem, while the murex is a specialist snail, eating only clams.

Why is this interesting? Worldwide, we know that species diversity is declining as a result of human activities, that specialists are being increasingly replaced by generalists, and that consumer and predator species often face a disproportionate risk of local extinction. So what are the consequences of realistic losses and changes to biodiversity? Is having a diversity of predators beneficial (e.g. both horse conchs and true tulips) to an ecosystem as a whole? Do some species matter more than others? And how do the effects of predators depend on the type of habitat they’re in, given that habitats (like seagrasses) are also changing in response to the environmental changes? These are some of the questions I’m hoping to address in Bay Mouth Bar system, in which we have documented historical changes in predator diversity.

Tethered community in Tanya's Bay Mouth Bar experiment

One of communities in Tanya's experiment. At the center are top predators reflecting either the current assemblage (a horse conch alone) or the historic assemblage (the horse conch and true tulip). The predators are tethered to posts and given enough line to reach the lower level predatory snails (murex, lightning whelks, banded tulips, and Busycon spiratum) on the outside. Those snails have enough line to get out of the large predator's reach and forage for food.

This past week, I set up an experiment featuring a menagerie of snails tethered in different assemblages across Bay Mouth Bar. Some assemblages mimic the current assemblage, whereas others mimic the assemblage found on the bar during Paine’s time. These historical assemblages include the snail species no longer found there, which I collected from other locations where they are still abundant. Some assemblages have top predators (e.g. horse conchs) whereas others do not. Some are in turtle grass, others are in shoal grass. We’ll see how, over the course of the summer, these different assemblages affect the prey community (clams, mussels, small snails) and other elements of seagrass ecosystem functioning.

Music in the piece by Donnie Drost.  Theme by Lydell Rawls.

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

 

A mud crab ready for his hearing test.

Can crabs hear? (A testament to the benefits of collaboration)

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

IGOR chip_ predators_NCE 150When 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?

Housam collecting juvenile clams attached to oyster shells for use in the experiment.

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?

A mud crab ready for his hearing test.

A mud crab ready for his hearing test.

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!

A mud crab submerged in the acoustic chamber

A crab submerged in the acoustic chamber.

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!

A marked oyster shell with juvenile clams glued on it as a crab buffet.

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!

Phil checks on the mesocosm experiment at FSUCML

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.

Catfish and toadfish recordings copyright University of Rhode Island.  They were obtained from dosits.org, under these terms:

Copyright 2002-2007, University of Rhode Island, Office of Marine Programs. All Rights Reserved. No material from this Web site may be copied, reproduced, re-published, uploaded, posted, transmitted, or distributed in any way except that you may download one copy of the materials on any single computer for non-commercial, personal, or educational purposes only, provided that you (1) do not modify such information and (2) include both this notice and any copyright notice originally included with such information. If material is used for other purposes, you must obtain permission from the University of Rhode Island. Office of Marine Programs to use the copyrighted material prior to its use.

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

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Notes from the Field: From Technician to Tourist

Lately, the Hugh-Bro (Hughes and Kimbro) Lab has covered a lot of miles.  Dr. David Kimbro and Dr. Randall Hughes have accepted positions at Northeastern University in Boston.  Tanya Rogers is David’s first graduate student at NEU, though her dissertation is on Bay Mouth Bar at the mouth of Alligator Harbor.  Hanna Garland (who had spent a year living in Saint Augustine Beach for her graduate work with David) and Stephanie Buhler are covering Apalachicola Bay, though Stephanie will start her PhD. work in the Bahamas soon.  We’ll let Ryan Coker tell you of his East coast adventures helping Meagan Murdock wrap her National Park Service tile experiment
Ryan Coker FSU Coastal & Marine Lab

Timucuan - Here I am inspecting a tile as we made our way to the next reef. Looks like these particular oysters didn't fare well, but we saw plenty that did!

For the last couple months, a lot of my responsibilities around the lab have shifted from working out in the field to processing samples from our salt marsh projects (recently, measuring the organic content of sediment samples, i.e. setting dirt on fire and calculating the missing weight). This past week I was happy to be recruited from my normal lab duties to help out on Meagan’s National Park Service oyster experiment, recovering our oyster-covered paving bricks from the experimental reefs for analysis. This meant packing my bags to leave for a six-day field trip to visit our reef sites at Timucuan Ecological & Historic Preserve in Jacksonville and Cumberland Island National Seashore, a barrier island off of Georgia’s coastline. I was told to prepare for precarious treks through oystershell, leg-swallowing mud, and swarms of no-see-ums who, in spite of their name, were determined to get noticed. I prepared for these challenges in earnest, with thick boots and quick feet and enough bug spray to at least suggest that eating me alive wasn’t in any insect’s best interest. But what I wasn’t ready for was the sheer beauty of these places. I feel immensely lucky to have found my calling in ecology—I do the work I love, and I get to do it in the loveliest places.

Timucuan - Meagan decided to test the depth of this mudflat to see if we could access one of our oyster reefs at very low tidal height. As she progressed downward at a rate far exceeding her forward gains, it was clear that we were going to have to wait out the tide and try again. Thank you, Meagan, for being such a champ and getting completely mud-covered while I waited on the boat, laughing and taking pictures. Here she is using my leg to pull herself out of the muck as I perched on the ledge of the pontoon boat.

Because we had a free half-day on Cumberland Island while we waited for the National Park Service to come and ferry us back to the mainland, Meagan and I set off to explore the island. We traded our boots and waders for sneakers and shorts long, bug-proof pants. Transitioning from a field tech to a tourist for just a few hours, I ran up and down the island in an attempt to see it all. It was gorgeous.

The forest was intercut with dirt paths canopied by towering palms and the twisting limbs of immense Live Oaks. The infinite beach, its width rolled out flat from delicate high-blown dunes to where it dips below the lapping ocean tide, is home to shorebirds and “wild” packs of roaming horses.

What I found most striking, though, were the crumbling skeletal remains of Dungeness, a mansion built in the 1880s, abandoned in 1925, and burnt to ruins by the 1960s.

Imagining this place in its glory, I filled in the gaps of the walls and floors where they were collapsed and covered by weeds and rubble. There’s not much left, and I didn’t dwell on my fiction overmuch, but I sure would have loved to see that mansion as it stood. It made me think about the impacts we make on the world, the legacies we’re trying to build before we go. I feel really good about the work I contribute to in the lab. To the metaphorical library of scientific knowledge, I’d like to think the work I do is helping to add-on another room. We’re in the ecology wing, expanding it out, adding just a bit to the collection. It’s our mansion, and at the very least, it’s fireproof.

Of course, mostly I just thought “Holy cow, this is gorgeous,” as I snapped away, already daydreaming about the next spectacular place I might have the opportunity to visit with the lab.

In the Grass, On the Reef is funded by a grant from the National Science Foundation.
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Notes From the Field: Hermit Crab/Crown Conch Cage Match

Last week David connected the regional dots, noticing similarities in oyster reefs overrun by oyster eating crown conchs across North Florida, from the Matanzas Reserve south of Saint Augustine to Apalachicola Bay. That included a breakdown of what they found during surveys of the Bay. Below, Hanna Garland details one of her experiments mentioned by David in the post.
Hanna Garland FSU Coastal & Marine Lab

Gaining a better understanding of the beautiful yet complex habitats that border our coastlines require a significant amount of time surveying and manipulating organisms (as you may know if you have been following our research for the past three years!), and even so, there can still be limitations in whether or not we truly know what is “naturally” occurring in the system.  Unfortunately, pristine salt marshes, seagrass beds and oyster reefs are in a general state of decline worldwide; however, this only heightens our incentive to investigate further into how species interact and how this influences the services and health of habitats that we depend on for food and recreation.

For the past two and a half years we have been studying the oyster populations along 15km of estuary in St. Augustine, but it did not require fancy field surveys or experiments to notice a key player in the system: the crown conch.  Present (and very abundant!) on oyster reefs in the southern region of the estuary, but absent in the northern region, it was obvious that there were interesting dynamics going on here…and we were anxious to figure that out!

In hopes of addressing the question: who is eating whom or more importantly, who is not eating whom, we played a game of tether ball (not really!) with nearly 200 conchs of various sizes by securing each one to a PVC pole (with a 1m radius of fishing line for mobility) onto oyster reefs.  After six months (and still ongoing), the only threat to the poor snails’ survival appeared to be the thinstripe hermit crab (Clibinarius vittatus)!

Hypothesized that hermit crabs invade and occupy the shell of a larger crown conch in order to have a better home, we decided to further investigate the interactions between crown conchs and hermit crabs by placing them in a cage together (almost like a wrestling match).

After only a few days, the mortality began, and results showed a weak relationship between species and size, and appeared to be more of a “battle of the fittest”.

The implications of how the interactions between crown conchs and hermit crabs influence the oyster populations are still largely unknown, but knowing that neither species have dominance over one another is important in understanding the food webs that oyster reefs support…and that organisms occupying ornate gastropod shells can be lethal as well!

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

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Predatory Snails Overrunning Florida Oyster Reefs

A couple of years ago, David wrote about what seemed to be a very locally contained problem.  An out of control population of crown conchs was decimating oyster reefs south of Saint Augustine. Now, he’s seeing that problem in other Florida reefs, including those at the edges Apalachicola Bay. In reviewing his crew’s initial sampling of the bay, he sees that the more heavily harvested subtidal reefs are being assaulted by a different snail.

Dr. David Kimbro FSU Coastal & Marine Lab

Along the Matanzas River south of St. Augustine Florida, Phil Cubbedge followed in the footsteps of his father and grandfather by harvesting and selling oysters for a living. But this reliable income became unreliable and non-existent sometime around 2005. Then, Phil could find oysters but only oysters that were too small for harvest. Like many other folks in this area, Phil abandoned this honest and traditional line of work.

In 2010, Phil was fishing with his grandson along the Matanzas River and spotted several individuals who seemed severely out of place. Because Phil decided to see what they were up to, we are one step closer toward figuring out what happened to the oyster reefs of Matanzas and what may be happening to the oyster reefs of Apalachicola Bay.

Before I met Phil on this fateful morning, I was studying how the predators that visit oyster reefs may help maintain reefs and the services they provide (check out that post here). My ivory-tower mission was to see if the benefits of predators on oyster reefs change from North Carolina to Florida. To be honest, I’m not from Florida and I blindly chose the Matanzas reefs to be one of my many study sites. And in order to study lots of sites from NC to Florida, I couldn’t devote much time or concern to any one particular site. In short, I was a Lorax with a Grinch-sized heart that was two sizes too small; I just wanted some data from as many sites as possible.

Hanna Garland (r) discusses with Cristina Martinez (l) how they will set up gill nets as part of their initial oyster reef research in St. Augustine.

But then I met Phil, heard about his loss, and understood that no one was paying attention to it. After looking around this area, my Grinch-sized heart grew a little bigger. Everywhere I looked had a lot of reef structure yet no living oysters. Being a desk-jockey now, I immediately made my first graduate student (Hanna) survey every inch of oyster reef along 15 km of Matanzas shoreline. I think it was about a month’s worth of hard labor during a really hot summer, but she’s tough. Hey, I worked hard on my keyboard!

With these data and lots of experiments, we showed that a large loss of Matanzas oyster reef is due to a voracious predatory snail (crown conch, Melongena corona). This species has been around a long time and it is really important for the health of salt marshes and oyster reefs (in next week’s post, Randall shows the crown conch’s role in the salt marsh). But something is out of whack in Matanzas because its numbers seemed to look more like an outbreak. But, why? Well, thanks to many more Hanna surveys and experiments, we are closing in on that answer: a prolonged drought, decreasing inputs of fresh water, and increasing water salinity.

David took an exploratory trip to Apalachicola Bay with the Florida Department of Agriculture and Consumer Services in the fall of 2012, where they found these snails.

We need to figure this out soon, because we see the same pattern south of Matanzas at Cape Canaveral. In addition, I saw conchs overwhelming the intertidal reefs of Apalachicola last fall. While these reefs may not be good for harvesting, they are surely tied to the health of the subtidal reefs that have been the backbone of the Apalachicola fishery for a very long time. Even worse, the bay’s subtidal reefs seemed infested with another snail predator, the southern oyster drill (Stramonita haemastoma). Is this all related? After all, according to locals and a squinty-eyed look at Apalachicola oyster landings, it looks like Apalachicola reefs also started to head south in 2005.

To help answer my question, my team began phase 1 of a major monitoring program throughout Apalachicola Bay in January 2013.With funding from Florida SeaGrant, my lab targeted a few oyster reefs and did so in a way that would provide a decent snap shot of oysters throughout the whole bay. With the help of Shawn Hartsfield and his trusty boat, a visit to these sites over a time span of two weeks and hours upon hours of sample processing back at the lab revealed the following:

(1) There is a lot more oyster reef material in the eastern portion of the bay;

(2) There are also a lot more adult oysters toward the east;

(3) Regardless of huge differences in adult oyster density and reef structure, the ratio of dead oysters to live oysters is about the same throughout the whole bay;

(4) Although the abundance of snail predators is not equal throughout the whole bay, it looks like their abundance may track the abundance of adult oysters.

These data do not show a smoking gun, because many different things or a combination of things could explain these patterns. To figure out whether the outbreak of  multiple snail predators is the last straw on the camel’s back for Apalachicola and other north Florida estuaries, we are using the same experimental techniques that Hanna used in Matanazas River. Well, like any repeat of an experiment, we had to add a twist. Thank goodness Stephanie knows how to weld!

Luckily, I have a great crew that is daily working more hours than a day should contain. As I type, they are installing instrumentation and experiments that will address my question. If you see Hanna and Stephanie out on the bay, please give them a smile and a pat on the back.

More later,

David

Click here to see graphs illustrating the increase in salinity in the Matanzas National Estuarine Research Reserve (NERR). The NERR System allows you to review data from sensors at any of their reserves, including Matanzas and Apalachicola.

Music in the piece by Philippe Mangold.

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