Category Archives: Wildlife in North Florida- Critters Big and Small

Diversity- Getting by With a Little Help From (Salt) Marsh Friends

2-Minute Video: Marsh cordgrass, needlerush, sea lavender, mussels, periwinkle snails, and fiddler crabs: diversity in the salt marsh.

In Randall’s last post, she looked at whether genetic diversity within the salt marsh foundation species– smooth cordgrass- made for a stronger marsh (and by stronger, of course, we mean better able to shelter yummy blue crabs for people and sea turtles). In today’s post and video, Randall examines how the combination of plants and animals around cordgrass- the species diversity of a marsh- might play a role as well.
Dr. Randall Hughes FSU Coastal & Marine Lab/ Northeastern University

IGOR chip- biodiversity 150Even though salt marshes often look like one big sea of green in the intertidal, there are plants and animals other than marsh cordgrass around. And even though I devote a lot of effort to understanding the effects of diversity just within cordgrass, these other species are also important – no marsh is an island. (Well, actually they are, but you get the analogy.)

Fiddler crab found in a St. Joseph Bay salt marsh.So who is important, and why? There are at least two animals that can be classified as “friends” of cordgrass – fiddler crabs and mussels. Fiddler crabs create burrows that allow oxygen to get down in the sediment, and cordgrass roots appreciate that oxygen. The fiddler crabs also aerate the sediment during their feeding, and they can excrete nutrients that the plants use to grow.

As an aside, fiddler crabs are also irresistible for kids (and maybe adults too!).

Mussels aren’t quite as charismatic as fiddler crabs, but they like to nestle around stems of cordgrass, and the byssal threads that they use to attach to one another and to the sediment can help prevent erosion. In addition, they excrete nutrients and other organic material as a byproduct of their filter-feeding, and the plants take advantage of these nutrients.

While investigating the relationship between mussels and marsh cordgrass, Randall’s graduate student, Althea Moore, noticed that mussels also seemed to often accompany sea lavender in the marsh. This led to a separate study for Althea.

So who is MORE important, mussels or fiddler crabs? We did an experiment to test that question, or really, to test whether having mussels and fiddler crabs together is better than having just one or another. The answer? As with much in ecology – it depends. For one, it depends on what you measure. If you look at the number of cordgrass stems, then fiddler crabs are the better friend – cordgrass with fiddler crabs does better than cordgrass without fiddler crabs, regardless of whether you have mussels or not. But if you look at how tall the plants are (another important characteristic in the marsh), then mussels are the better friend, but only when fiddlers aren’t around. And if you look at the amount of organic content, mussels increase organic content at the sediment surface, whereas fiddlers increase it belowground. In the end, the take-home message is that the more things you measure about the marsh, the more important it becomes that you have both mussels and fiddler crabs in order to be the “best”.

In the process of doing the experiment I described above, Althea (my graduate student) noticed that when she was out in the marsh, she often found mussels in and around sea lavender (Limonium) plants more often than she found them around cordgrass. She became interested in finding out whether the mussels benefit the sea lavender, the sea lavender benefits the mussels, or a little bit of both. She’s still working on the answer, but it just goes to show that although we often tend to focus on who eats who (think Shark Week) or who can beat who (Octopus vs. Shark, anyone? Or, for kids, there’s always Shark vs. Train – a favorite at my house!), there are just as many instances of species helping one another (not that they always intend to).

Of course, it’s not just animals helping (aka, facilitating) plants – plants can help other plant species to. We’ve shown through a series of experiments that cordgrass benefits from having its tall neighbor needlerush (Juncus roemarianus) around, but only if the snails that like to graze on cordgrass are also present. Nothing is ever as simple as it looks in the marsh…

Music in the piece by Revolution Void.

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.

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.

Crown Conchs- Friend or Foe?

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.

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Dr. Randall Hughes FSU Coastal & Marine Lab
The Crown Conch (Melongena corona).

The Crown Conch (Melongena corona).

IGOR chip_ predators_NCE 150If 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?

Periwinkle in Spartina predator experiment

The Marsh Periwinkle (Littoraria irrotata).

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.

Crown conch pursuing periwinkle snail

At the edge of a marsh at high tide, a crown conch approaches a periwinkle snail. As shown in the video above, the conch was soon to make contact with the smaller snail and send it racing (relative term- the video is of course sped up) up a Spartina shoot.

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.

Periwinkle in Spartina predator experimentOn 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.

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.

How Do Predators Use Fear to Benefit Oysters?

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 Kimbro FSU Coastal & Marine Lab

IGOR chip_ predators_NCE 150A 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.

busycon eating moon snail

Busycon spiratum eating an Atlantic Moon snail on Bay Mouth Bar. These seagrass beds off of Alligator Point are home to the greatest diversity of predatory snails in the world. In the late 1950s and early 1960s, Dr. Robert Paine investigated the effect of the horse conch, the most dominant predator among the snails, on the habitat. David and his crew have similarly used the dynamic invertebrate population to test their theories on the ecology of fear. (click the photo for more on Bay Mouth Bar).

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.

Mud crabs (like the one pictured here), oyster drills, and crown conchs are the primary consumers of oysters on the reef.

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.

We’ll be following the Apalach study as well. Here, Stephanie Buhler, who we had previously seen diving in Apalachicola Bay, welds a cage to house an upcoming experiment in that research. It’s a variation of the tile experiments that became such a staple of the NSF oyster study. In a few days, we break down the tile experiment, and David’s collaborator, Dr. Randall Hughes, talks about what the results are telling them so far.

Music in the video by Revolution Void.

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

Notes from the Field: Overwhelmed Oysters

Meagan Murdock is a lab technician in the Hughes and Kimbro Labs, operating out of the FSU Coastal and Marine Laboratory. The experiment she describes in the following post is a central staple in the research conducted by Dr. Randall Hughes and Dr. David Kimbro into oyster reef ecology. They seek to measure factors affecting the health of an oyster at a given location by monitoring the growth of young oysters (spat) in a controlled unit- the spat tile. We’ll be further exploring the use of spat tiles in their NSF funded oystern study in the next couple of weeks. David Kimbro is also gearing up to deploy a tile experiment in Apalachicola Bay, with the goal of measuring conditions there (see photo below).
Meagan Murdock FSU Coastal & Marine Lab

Beautiful reef backing up to red mangroves (Rhizophora mangle) in Mosquito Lagoon, FL. Notice our experiment on the reef!

Mosquito Lagoon of Canaveral National Seashore is in the northern section of possibly the most diverse estuary in North America, the Indian River Lagoon. But don’t let the name “Mosquito” Lagoon scare you off! This lagoon is an expanse of mangrove islands, oyster beds, and home to charismatic animals like manatees and dolphins (maybe a few mosquitoes, but where in Florida can you not find mosquitoes??).  Eight months ago, we set up a rendition of the “Tile Experiment” at three National Park Service units in hopes of elucidating factors contributing to oyster spat (spat=newly settled oyster) survival and growth. Last week we ventured out to Mosquito Lagoon to check on our baby oysters and this is what I found. The tiles were covered in BARNACLES!

Tile 75 pictured after being deployed for 2 months and 8 months.

I felt bad for the little oysters. Not only are these spat expected to survive through adverse environmental conditions and hope they do not become some crab or fish’s dinner, but they also are competing for space and resources with other filter feeders. Geez it must be tough being an oyster! But-yeehaw!-the oysters are persevering and I got to enjoy the nice weather of Central Florida.

Barnacles overtaking the experimental oysters.

As Meagan continues to monitor the growth of her Canaveral oysters, David is having Stephanie Buhler and Hanna Garland deploy some test tiles in the subtidal (always submerged) oyster reefs of Apalachicola Bay.  The tiles will be protected by a steel cage which will allow access to researchers while protecting the experiment from an oysterman’s tongs.  Different prototypes of tiles and cages were deployed last week with the full experiment to begin in the coming weeks:

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

Fear and the Choices Oysters Make

Last week, Dr. David Kimbro broke nutrients and oysters down for us.  But what if oysters are too scared to eat the nutrient fed plankton they need to survive?  David and Randall take us another step closer to understanding the Ecology of Fear, examining oysters’ choices and how their behavior affects the important habitat they create.  Stay tuned over the following weeks as they unravel the relationships between predators and prey on oyster reefs and their neighboring coastal ecosystems.  We’ll also continue to follow David’s crew in Apalachicola, Hanna and Stephanie, as they research the oyster fishery crisis.

Dr. Randall Hughes FSU Coastal & Marine Lab

IGOR chip_ predators_NCE 150I recently moved and was faced with the dilemma of finding a place to live. This can be a touch decision, especially when you’re in a new city or town. Which neighborhood has the best schools? The best coffee shop? Friendly neighbors? Low crime? My solution was to find something short-term while I scope the place out some more, and then I can decide on something more permanent. (As anyone who has me in their address book knows, “permanent” is a very relative term – I have changed residences a lot over the last 15-20 years!) But imagine you had just one shot – one, for your whole life – to decide where to settle down. Talk about a tough decision! That’s what oysters have to do, because once they settle down and glue themselves to their location of choice, they don’t have the opportunity to move around any more. So how do they decide?

This oyster shell, harvested from an intertidal St. George Island reef, had been settled by multiple young oysters called spat. Spat grow into mature oysters with a hard shell, fused with the oyster on which they originally landed. Clumps of attached oysters form a crucial coastal habitat.

It turns out that oyster larvae (baby oysters swimming in the water) can use a number of “cues” to help them in the house-hunting process. First of all, they can detect calcium carbonate, the material that makes up oyster shells (and other things) – if there’s lots of calcium carbonate in an area, that could be a good sign that it’s an oyster reef. (Or it could be a sign that people have put a lot of cement blocks in the water in the hopes that oysters will settle and create a reef – that’s how a lot of oyster restoration projects are started.) Some recent research even shows that oysters can detect the sounds of an oyster reef, and then swim in that direction! Maybe these guys are smarter than we think…

Regardless of how oysters decide, there are times when we are also faced with the question of what makes good oyster habitat, or deciding which area is better than another. As scientists, we turn to experiments. One type of experiment that we have perfected over the years involves getting juvenile oysters- (either from the field, which can be pretty difficult -as you can see from the first round of our tile experiment, or from a hatchery), and gluing them to portable sections of “reef” (ceramic tiles weighed down by bricks). LOTS of ceramic tiles and bricks. We’re talking 800+ ceramic tiles and 700+ bricks last summer alone! That’s enough to make a path that is ~2 football fields long. All moved by truck, hand, boat, hand, kayak, and hand to their temporary location on a reef (and then moved back again when the experiment is done). But I digress.

In the second incarnation of the tile experiment, oyster spat were attached to tiles with an epoxy used in the repair of boat hulls. The tiles in the first version- the ones in the video above- were assembled differently. In a video we’ll premiere later this month, we’ll look at the twists and turns the experiment took.

After attaching the juvenile oysters to the tiles with a lovely substance known as z-spar, we enclose some tiles in cages to protect them from oyster predators, and we leave others with no cage so they are “open” to predators. (There’s also a 3rd group – the “cage control” – that get 1/2 a cage so we can test whether the cage has effects on the oysters other than keeping out the predators.) Then we take our oyster tiles and put them out in the field at different sites that we want to test. By observing the survival and growth of the ones in the cage (where no predators have access), we can get a general sense for whether it’s a good environment or not. Lots of large, live oysters are a sign of a good environment – plenty of food, good salinity (not too salty or too fresh), good temperature, etc. Also, by comparing the survival of the ones in a cage vs. not in a cage, we can get an idea of how many predators are around – lots of live oysters in the cage and none out of the cage is a pretty good sign that oysters are getting eaten. (If oysters in the cage are dead and oysters outside of the cage are missing, it’s a little tougher to figure out exactly what’s causing it, but it’s clearly not a good place for oysters to live!)

Experimental spat tiles at the Guana Tolomato Matanzas National Estuarine Research Reserve- open, closed, and partially open.

Of course, the oysters themselves don’t know whether they are nice and safe inside our cages, or easy pickings for a predator. So if there are lots of predators lurking around the reef, the oysters may try to “hide”. Obviously, hiding for an oyster does not mean packing up and moving elsewhere, but they do have a few tools at their disposal. In the short term, the oysters can choose not to open up their shells and feed (filter water) as often. This strategy has 2 benefits – 1, they are less vulnerable to predators when their shells are closed and 2, they aren’t releasing lots of invisible chemical cues in the water when they’re closed, so it’s harder for the predators to tell they are there. But as any of you who have been sticking to your New Year’s resolution to lose weight will know, there’s only so long that you can go without eating before that strategy loses its appeal! Over the longer term, the oysters can decide to devote more of the energy that they get from eating to create a thicker, stronger, rougher shell, rather than plumping up their tissues.

So, those are the big-time decisions that an oyster faces: where to live, and when to eat. Sounds kind of familiar…

We want to hear from you! Add your question or comment.

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

What’s the deal with nutrients and oysters?

As David & co. start their new research on the Apalachicola oyster fishery crisis, He and Randall (and their colleagues in Georgia and North Carolina) are starting to wrap up the NSF funded oyster study that we have been following over the last couple of years.  Over the next few weeks, we’ll take a look back at that research through a series of videos.  We’ll cover some oyster basics (how does an animal with no brain behave?), explore David and Randall’s ideas on the role of fear on the oyster reef (what makes a mud crab too afraid to eat an oyster?), and see the day-to-day problem solving and ingenuity it takes to complete a major study.  As these videos are released, we’ll also keep tabs on the work being done in Apalachicola Bay, in which many of the same methods will be used.
Dr. David Kimbro FSU Coastal & Marine Lab

After all, nutrients are basically plant food and oysters are animals.  And how could too few nutrients coming down with the trickling flow of the Apalachicola River possibly explain the record low number of Apalachicola oysters?

This is the perfect time to use the favorite idiom of my former mentor Dr. Ted, “The long and the short of it is….”

The short of it: Plants love nutrients and sunlight as much as I like pizza and beer. But unlike my favorite foods, these plant goodies make plants grow fast and strong. This works out well for us because we all need nutrients for basic body functioning, and because we get them by eating plants and/or by the eating animals that previously consumed plants.

For our filter-feeding bivalve brethren, they get nutrients and energy by eating plant-like cells (phytoplankton) that float in the water. So, it is possible that the trickling flow of the Apalachicola River is bringing too few nutrients to support the size of the pizza buffet to which the Apalachicola oysters are accustomed. But this idea has yet to be tested.

Hanna Garland and Stephanie Buhler harvest oysters from sample reefs in Apalachicola Bay. 

The long of it: Long before the flow of the Apalachicola River slowed to a trickle, there weren’t a lot of nutrients. That’s why the numbers of humans used to be so low: too few nutrients meant too few plants and other animals for us to eat.

How could this possibly be the case given that 78% of the air we breathe is made up of a very important plant nutrient, nitrogen? And there is a lot of air out there!

Well, only a precious few plants exist that can deal with the nitrogen in our air and these are called nitrogen-fixers. Think of these as single-lane, windy, and bumpy dirt roads. In order to help create a plant buffet for all of us animals, a lot of atmospheric nitrogen (bio-unavailable) has to travel down this very slow road that the n-fixers maintain. As a result, it naturally takes a long time for the land to become fertile enough for a large buffet. And, it only takes a couple of crop plantings to wipe out this whole supply of bio-available nitrogen that took so long to accumulate.

guano island

Sea birds on a guano island off the coast of Peru. (zand.net)

Turns out that the ancient Inca civilization around Peru was not only lucky, but they were also pretty darn smart. Lucky, because they lived next to coastal islands that were basically big piles of bird poop, which is very rich in bio-available nitrogen. I’m talking thousands of years of pooping on the same spot! Smart, because they somehow figured out that spreading this on their fields by-passed that slow n-fixing road and allowed them to grow lots of food. Once Columbus tied the world together, lots of bird poop was shipped back to European farms for the same reason. That’s when the European population of humans sky-rocketed.

Turns out that humans in general are pretty smart. Through time, some chemists figured out how to create artificial bird poop, which we now cheaply dump a lot of on our farming land. So, in these modern days, we are very, very rich in bio-available nutrients.

Where am I going with the long of it? Well, on the one hand, these nutrients wash off into rivers and then float down into estuaries. This is how the phytoplankton that oysters eat can benefit from our solution to the slow n-fixing road. In turn, oysters thrive on this big phytoplankton buffet.

Slide by Ashley R. Smyth, Piehler Lab, UNC Chapel Hill Institute of Marine Sciences.

But, on the other hand, too much of these nutrients flowing down into our estuaries can create big problems. Every year, tons of nutrient-rich water makes it way down the Mississippi and into the shallow Gulf of Mexico waters. There, this stuff fuels one big time buffet of phytoplankton, which goes unconsumed. Once these guys live their short lives, they sink to the bottom and are broken down by bacteria. All this bacterial activity decreases the oxygen of water and in turn gives us the infamous dead zone. Because nutrient-rich run-off continues to increase every year, so too does the dead zone.

I’ll close with the thought that oysters themselves may help keep the phytoplankton buffet from getting out of control by acting like anti-nitrogen fixers. In other words, they may help convert an excess of useable nitrogen back into bio-unavailable nitrogen. While this might not have been a great thing to have in low nutrient situations, we currently live in a nutrient-rich era. What’s even cooler is that it all has to do with poop again! But this time, we are talking oyster poop.

Oyster Summit 6

Dr. Mike Piehler, presenting to his collaborators Dr. Jeb Byers (Right), Dr. Jon Grabowski (reclined on couch), Dr. Randall Hughes and Dr. David Kimbro (out of frame). These five researchers have worked on oyster reef ecology since their time at the University of North Carolina. Three years ago, the National Science Foundation funded research into their ideas about predators and fear on oyster reefs.

So does this really happen? Yes. Check out an earlier post for the details. But we don’t fully understand it and that’s why it is a major focus of our research. Our collaborator, Dr. Michael Piehler of UNC-Chapel Hill, is leading this portion of our research project. Read more of Dr. Piehler’s work on this topic here.

So, hopefully this post explains why the relationship between nutrients and oysters is not so simple. But it sure is interesting and a worthy thing to keep studying!

Cheers,
David

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

We want to hear from you! Add your question or comment.

Backyard Ecology (Plus new video on Bay Mouth Bar)

Episode 7: Where Everything is Hungry

(Some species names have changed.)
It’s always a good shoot day at Bay Mouth Bar as every animal seems to be eating every other animal.  Oyster reefs, salt marshes, and seagrass beds– the habitats we’ve covered over the last three weeks- reward those who take the time to look closely.  At Bay Mouth Bar, everything is all out in the open.  For a limited time, anyway…
Dr. David Kimbro FSU Coastal & Marine Lab

IGOR chip_ predators_NCE 150IGOR chip- filtration 150Like most kids, I spent a lot of my formative years in the backyard practicing how to throw the game-winning touch down pass, to shoot the game winning three-pointer, and to sink the formidably long putt.  Although my backyard facilities obviously didn’t propel me into the NFL, NBA, or PGA, they never closed, required no admission fee from my pockets (thanks Mom and Dad!), and were only a few steps away.

Now that I’m striving to be an ecologist at Florida State University, I’m feeling pretty darn lucky about my backyard again. Instead of spending tons of time flying, boating, and driving to far away exotic places, I can use a kayak and ten minutes of David-power to access some amazing habitats right here along the Forgotten Coast.

Part of this coastal backyard was first intellectually groomed by one of the more famous and pioneering scientists of modern-day ecology, Dr. Robert Paine. Five decades ago, Dr. Paine noticed that the tip of Alligator Point sticks out of the water for a few hours at low tide. Of course, this only happens when the tides get really low, which happens about 5 days every month. But when the tip of Alligator Point (which is locally called Bay Mouth Bar) did emerge from the sea each month, Dr. Paine saw tons of large carnivorous snails slithering around a mixture of mud and seagrass. When I first saw this place, my eyeballs bulged out at the site of snails as large as footballs!

Fast- forward 2 decades later: Dr. Paine is developing one of the most powerful ecological concepts (keystone species), one that continues to influence our science and conservation efforts to this very day. Using the rocky shoreline of the Pacific North West as his coastal backyard, he is showing how a few sea stars dramatically dictate what a rocky shoreline looks like.

By eating lots of mussels that outcompete wimpy algae and anemones for space, the sea star allows a lot of different species to stick around. In other words, the sea star maintains species diversity of this community by preventing the mussel bullies from taking over the schoolyard. That’s one simple, but powerful concept….one species can be the keystone for maintaining a system. Lose that species, and you lose the system.

Lightning Whelk

A large lightning whelk found on Bay Mouth Bar in December of 2010.

Ok, let’s grab our ecological concept and travel back in time to Dr. Paine’s earlier research at Bay Mouth Bar. Wow, the precursor to the keystone species concept may be slithering around our backyard of Bay Mouth Bar in the form of the majestic horse conch! In this earlier work, the arrival of this big boy at the bar was followed by the disappearance of all of the former big boys (like this lightning whelk). By eating lots of these potential bullies, the horse conch may be the key for keeping this system so diverse in terms of other wimpy snails.

But why should anyone other than an ecologist care about the keystone species concept and its ability to link Bay Mouth Bar with rocky shorelines of the Pacific NW? Well, what if the lightning whelks eat a lot more clams than do other snails, and less clams buried beneath sediments means less of the sediment modification that can really promote seagrass (Read more about the symbiotic relationship between bivalves and seagrasses here)?  Thanks to Randall’s previous seagrass post, we can envision that less horse conchs could lead to less clams, less seagrass, and then finally a lot less of things that are pleasing to the eye (e.g., birding), to the fishing rod (e.g., red drum), to the stomach (e.g., blue crabs), and ultimately to our economy.

For the past two years, I’ve really enjoyed retracing Dr. Paine’s footsteps at Bay Mouth Bar. But lately, I’m feeling a little more urgent about needing to better understand this system because it’s disappearing (aerial images provided by USGS’s online database at http://earthexplorer.usgs.gov/).

To figure this out, we repeat a lot of what Dr. Paine did five decades ago. At the same time, we are testing some new ideas about how this system operates. For example, if the horse conch is the keystone species, is it dictating what Bay Mouth Bar looks like by eating stuff or by scaring the bully snails? How exactly does or doesn’t the answer affect clams, seagrasses, birds and fishes?

Luckily, because this system is so close, with some persistence and some good help, we’ll soon have good answers to those questions.

Cheers,

David

Ps: Many thanks to Mary Balthrop for helping us access this awesome study system every month.

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