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Does Diversity Matter in the Salt Marsh? A Look Back

Dr. Randall Hughes has collaborated with WFSU on this blog since 2010. We have spent years visiting her research sites in Saint Joseph Bay, where Randall conducted a multi-year study on salt marsh biodiversity funded by the National Science Foundation. The study has concluded, and Randall has published several papers on her findings. Here is what she has found.

This is Saint Joe Bay week on the Ecology Blog.  Wednesday, August 20th, at 7:30 pm ET: WFSU premieres the eighth season of Dimensions, and our Saint Joseph Bay scalloping EcoAdventure. 

Dr. Randall Hughes Northeastern University
Just a bunch of grass?  Not to the larval shrimp, juvenile mullet, pinfish, fiddler crabs, mussels, periwinkle snails, and blue crabs that make use of the habitat, or the birds and sea turtles that go hunting there.

Just a bunch of grass? Not to the larval shrimp, juvenile mullet, pinfish, fiddler crabs, mussels, periwinkle snails, and blue crabs that make use of the habitat, or the birds and sea turtles that go hunting there.

As you drive along Highway 98 towards St. Joseph Bay (SJB), one of the most common views outside your window is of the salt marsh.  From the car, it looks like a beautiful but monotonous meadow of green and/or brown, depending on the season, often intersected by tidal channels. So I won’t blame you if “diversity” is not the first word that comes to your mind as you gaze out the window. But diversity is exactly what I set out to find out about when this project first started – how much diversity is there in the marshes of St. Joe Bay, and what (if any) effects does it have? And now, several years later, I finally have answers to share!

First, let’s revisit what I mean about diversity. There are 2 main types that I have focused on for my research:

Species diversity, or the number of different species in an area. If you garden, you can think of it as the number of different vegetables or flowers you plant.

Genetic diversity, or the number of different genetic individuals (or genetic variants) in an area. Using the garden example, this would be similar to the number of different tomato varieties you plant in your garden.

Randall Hughes and Ryan Coker in an FSUCML Greenhouse

Randall and technician Ryan Coker tend to plants in an FSU Coastal & Marine Lab greenhouse. Before Randall and her team could begin to test their theories about marshes and marsh grass, they needed to create controlled marsh units of a comparable size, and needed to know the genetic identity of the grass in their plots.  Randall grew this grass for two years before conducting those experiments.

Wait – why so much talk about plants? Don’t animals have diversity too? Animals do have diversity, and this diversity matters – for one, having more species of fish on a coral reef means the corals grow better. But plants are the foundation of the marsh – if you have no plants, you have no marsh. So I have focused on the species and genetic diversity of the plants and tested how it affects the number and diversity of animals that live there (which includes animals that we like to eat, such as blue crabs). The dominant marsh plant species in many areas is cordgrass (Spartina alterniflora), and we created a greenhouse full of known genetic individuals to use in many of our experiments. Here are some of the highlights of what we have learned, with a little background on each, and links to the published articles where you can learn more if you’re interested:

1. Increasing the number of plant species in the marsh, even just from one species to two, can reduce the negative effects of a hungry periwinkle snail.

Periwinkles are really common in the marsh, and when conditions line up just right (the periwinkles are hungry, the cordgrass is already stressed from something like drought) they can mow down the cordgrass. We don’t see this happen very often in SJB, and I wondered if that was because there’s another really common plant species – needlerush – that often grows with the cordgrass, that the periwinkles also seem to like, at least for climbing on to stay out of the water and away from their predators. So we did an experiment where we planted cordgrass with and without needlerush and with and without periwinkles, and we found what I had expected: having needlerush neighbors around means the periwinkles don’t mow down the cordgrass!

Randall published these findings in the Ecological Society of America Journal.

2. Contrary to conventional wisdom that a few cordgrass individuals (also known as “clones”) rule the marsh, genetic diversity can be quite high, with as many as 9 distinct individuals living together in an area the size of a hula hoop.

periwinkles on cordgrass

Smooth cordgrass (Spartina alterniflora), the foundation species of a coastal salt marsh. Before she could understand how the genetic diversity of this species affects the health of a marsh, Randall needed to know how many genetic individuals were present within the ecosystem.

Genetic diversity is really important for the ability of plants and animals to respond to stress or change, and so it’s something we often want to know, but the bummer about it is that it’s not nearly as easy to measure as species diversity. You can’t just look at two cordgrass plants and tell whether they are the same or different genotypes! I teamed up with Dr. Katie Lotterhos to use little snippets of DNA to tell us whether the cordgrass plants we collected from the marshes around SJB were all a few closely related individuals, or whether there were lots of different individuals around. It turns out that even though they all look pretty much the same, there is a lot of genetic diversity in our marshes.

Randall and Katie published these findings in the Inter-Research Science Center’s Marine Ecology Progress Series (link is a PDF).

Monoculture plot- four genetically identical cordgrass individuals.  In this specific experiment, plots are composed off one, two, or four separate individuals.  Do plots with higher diversity fare better?

A monoculture plot of four genetically identical cordgrass individuals. In this experiment, similar to the one described to the right, plots were composed of one, two, or four separate individuals. Did plots with higher diversity fare better?

3. Changing the number of cordgrass clones living together in an area the size of a hula hoop affects how well the plants grow, as well as how many animals share that space. These effects of diversity may be particularly important when plants are first colonizing an area, such as in restoration efforts.

Once we knew how many different genetic individuals shared a hula hoop-sized area in natural marshes, we did an experiment to see how changing that number affects how well the plants grow. This experiment took a long time to prep, because we first had to grow a bunch of plants in the greenhouse so that we could keep track of who was who. After that, the experiment itself was pretty simple: plant 1, 3, or 6 different clones inside a hula hoop (well, in this case it was a modified hula hoop made of less expensive irrigation tubing) at the edge of the marsh, and watch them grow over time.

Randall published these findings in the British Ecological Society’s Journal of Ecology.

4. Just like you and me, different cordgrass clones have unique characteristics – some are tall, some are short, some do well in a crowd, and some like a little breathing room. And the animals that live amongst these plants, such as mussels and fiddler crabs, can go from being friends to enemies depending on which clone they are interacting with.

Even though I said before that all cordgrass plants look similar, it just so happens that when you grow the same clones in the greenhouse for a few years, you start to see slight differences among them. And these differences that seem pretty minor to us are really important to the small animals like fiddler crabs and mussels that live on and around the plants. So, in part to test this idea that different clones have different relationships with fiddler crabs and mussels, and in part just to do an experiment with fiddler crabs because I think they are cool, we set up an experiment using different cordgrass clones growing with just fiddlers, just mussels, or both. And although typically mussels and fiddlers are both “friends” with cordgrass (in that they provide it with nutrients and oxygen in the sediment to help it grow), that is not a universal truth – some cordgrass clones did not benefit (or even were harmed) by having mussels and fiddlers around.

Randall, her graduate student Althea Moore (whose investigation of a similar relationship between mussels and another marsh plant we covered in 2013), and Randall’s oyster collaborator Mike Piehler published their findings in the journal Oikos.

It’s a little disconcerting that ~ 4 years of work can be boiled down into these 4 highlights. Of course there are loads of details I’m leaving out, as well as other ongoing projects that will tell us even more about the effects of diversity in the salt marsh. That’s how the scientific process works – you gain some answers, and those answers lead to new questions! Job security for a curious mind…

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.

Keep up with the latest posts, environmental coverage from the WFSU News department and more at @wfsuIGOR.

Saint Joseph Bay scallop, shucked and ready to eat

Shucking a Saint Joseph Bay Scallop: Video

Wednesday, August 20th, at 7:30 pm ET: WFSU premieres the eighth season of Dimensions.  Tune in to watch our Saint Joseph Bay scalloping EcoAdventure.  We snorkel  seagrass beds, see some fun critters, and breathe underwater with the Snuba.  We also eat some tasty scallops.  But you can’t taste these guys if they’re still in their shells.  Below, Captain Bobby Guilford of Break-A-Way Charters shows us how to shuck our catch.  Captain Bobby took us out on the water in July, and he gave us this quick demo:

Rob Diaz de Villegas WFSU-TV

Another season of EcoAdventures is so close we can almost taste it.  Next week, it’ll taste like bay scallops as we return to Saint Joseph Bay not for science, but to enjoy the products of the seagrass bed ecosystem.  Saint Joe Bay is of course where we’ve been partnering with Dr. Randall Hughes to explore the inner workings of salt marshes and seagrass beds.  Just a bunch of grass?  Not if you like seafood.  Randall will have more about what she’s learned from Saint Joe Bay next week.

P1060980This summer we also spent some time with the WFSU/ FSU Mag Lab SciGirls.  Their annual two week whirlwind through the many aspects of science takes them on a few choice EcoAdventures of their own.  We accompany them to Tall Timbers Research Station as they get to know pine flatwoods ecology in the best way possible- by trapping birds and handling snakes, of course!  Our area is blessed with some of the best examples of longleaf pine forest, an ecosystem that thrives with fire.  We’ll see how various animal species (like those birds and snakes) benefit from burning.

Pied billed grebe at Wakulla SpringsWe also soak the SciGirls in our Water Moves game.  In our last video centering on the game, we followed water from urban Tallahassee to Wakulla Springs, passing through troubled waterways Munson Slough and Lake Munson.  That piece spent most of its time on the game and learning about the Leon County side of the Wakulla Springs watershed.  In our upcoming video, we visit Wakulla Springs itself.  It is an ecological marvel that’s had it’s share of troubles, but can still wow you with impressive sites and an abundance of wildlife.

And there’s more to come.  This year it’s all about connectivity- between lands and waters, between people and the natural spaces around them.  You can see from our new video open that we’ve seen some cool stuff over the last few years.  What would you like to see coming up?

In next week’s video, Captain Bobby also shucks one of these…

Dr. Randall Hughes holds large clam in St. Joe Bay

Keep up with the latest posts, environmental coverage from the WFSU News department and more at @wfsuIGOR.

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Lake Report: Leon County’s Cleanest and Dirtiest Lakes

Rob Diaz de Villegas WFSU-TV

Last week on our Water Moves EcoAdventure, we showed images of polluted waterways south of Tallahassee. We in this area benefit from a large amount of protected lands, which surround us with scenic views as well as protect many of our rivers and streams.  But Tallahassee itself is fairly urban; our paved roadways move pollutants into drainage ditches and sloughs instead of letting them sink into the ground to be filtered by the aquifer.  Some waterways are more affected than others.  Our lakes and rivers provide us with fresh fish and recreation; when they become compromised by algal blooms and other pollutants, they affect the health and economy of the communities around the resources.

With that in mind, I’ve compiled this list of lakes in the area, with data for each on cleanliness and safety concerns. We’re looking at three things:

  1. Nutrient load for each lake. We’ll link to a PDF of a report published by Leon County Public Works, which was compiled by Johnny Richardson (who we interviewed in the Water Moves video). I can’t link to the individual pages, but I will list them with the link back to the document if you’re interested in reading more.
  2. How safe is it to eat the fish in each lake? For this, I’m using a report created by the Florida Department of Health (DOH). This is also a PDF, and I’ll be referencing it in the same way.
  3. Toxic algal blooms. DOH has an Algal Bloom tracker which lists three locations in Leon County. During the rainy season, these blooms will get flushed, but the locations listed have had persistent nutrient problems and are still a risk to bloom when the weather dries.

North Leon: The Red Hills

Our largest lakes are located in the north of the county.  This is a sparsely populated area, protected to the north by over 300,000 acres of forested land held on hunting plantations.  Our recent Red Hills EcoAdventure explored some of these waterways and the land protecting them.  These are the cleanest lakes in Leon County.

Lake Iamonia (5,554 acres, the largest lake in Leon County)

Florida Fish & Wildlife's Michael Hill takes me out on Lake Iamonia near tall Timbers Research Station.

Florida Fish & Wildlife’s Michael Hill takes me out on Lake Iamonia near Tall Timbers Research Station.

Nutrients: The report we cite was issued by Leon County in 2011.  The report uses a measurement developed by FDEP, called a Trophic State Index, to determine the health of a waterbody.  It’s a formula that weighs nutrient levels (phosphorous, nitrogen, and chlorophyl a), with a score of 60 or higher denoting an impaired waterbody (40 for clearwater lakes, which are lower nutrient systems).  Lake Iamonia’s scores over the last few years are well blow that, averaging in the low 40s (chart on Page 64).

Fish Safety: According to the DOH Freshwater Fish Guide, this is a fairly healthy lake.  Florida lakes and rivers are considered to have low to medium mercury levels, so the guide puts limits on how much they recommend that an individual eats.  They recommend most fish caught in Iamonia be eaten no more than twice a week (page 16) for most species (slightly less for children and pregnant/ trying to get pregnant mothers).  This is as high as they go for any Florida waterbody.

Other Concerns: As we learned during the Red Hills Water EcoAdventure, the lake’s sinkhole was impounded in the 1930s.  While the dam has been removed, there is ecological damage that could take generations to fix.

Lake Miccosukee (6,257 acres.  It forms the northeast border of Leon County, but is located in Jefferson County)

Nutrients: It averages in the 50s on the TSI index (page 174-5); below the impairment level but higher than Iamonia due to an elevation of one particular nutrient, chlorophyl a.  This may be related to the dam constructed around its sinkhole in 1954.  It’s a story you see on many area lakes, playing out slightly differently on each.  Impounded lakes end up with floating islands of vegetation, tussocks, which block the sun and add organic material to the sediment.  This vegetation might be responsible for the elevated chlorophyl.

Fish Safety: The high amount of vegetation on the surface has reduced the amount of dissolved oxygen in the water, and so there aren’t a lot of fish in the lake.  Of the two species listed on the DOH document, it recommends no more than twice a week (page 18) for bluegill  and once a week for largemouth bass.  This is typical for bass throughout the document; some fish store more mercury in their fat cells.

Lake Jackson (4,000 acres)

Stormwater runoff in Elanor Klapp-Phipps Park.  This plot of land is adjacent to Lake Jackson, which is why it was purchased by the  Northwest Florida Water Management District.  Having protected land next to the lake reduced urban runoff into it.

Stormwater runoff in Elinor Klapp-Phipps Park. This plot of land is adjacent to Lake Jackson, which is why it was purchased by the Northwest Florida Water Management District. Having protected land next to the lake reduces urban runoff into it.

Nutrients: Over the course of the last few years, the color of the lake’s surface has clarified, so it technically qualifies as a clearwater lake with a lower TSI threshold.  As such, it would be considered an impaired lake, averaging in the 40s on the TSI index (page 95).  The report questions using the lower threshold, citing “the dynamic nature of the lake and the recent drought” (pages 95-96).  Part of the change in color is attributed to changes in stormwater management, which have reduced runoff to the lake.

Fish Safety: Bluegill & redear sunfish, twice a week.  Largemouth bass, once a week (page 16).

Lake Hall (182 acres, a part of the Lake Jackson Watershed)

Tall Timbers' Georgia Ackerman teaches me to stand up paddleboard on Lake Hall, as part of our Red Hills Water EcoAdventure.

Tall Timbers’ Georgia Ackerman teaches me to stand up paddleboard on Lake Hall, as part of our Red Hills Water EcoAdventure.

Nutrients: Lake Hall is one of the cleanest lakes in Leon County, averaging in the high 20s (page 91) on the TSI.  As a clearwater lake, it’s threshold for impairment is 40.  Lake Hall is partially located in Alfred B. Maclay Gardens State Park.  There are some restrictions on the use of motors on Lake Hall.

Fish Safety: Not listed.  The lake is fished pretty regularly, however.

Middle Leon County

Lake Lafayette 

Dead vegetation on the surface of Lower lake Lafayette.  The segmentation of the lake in the early twentieth century has affected its ability to "dry down."  Many Leon county lakes naturally empty every few years, and the plants and animals that live in the lake have adapted to and thrive in such conditions.  Impounding Lake Lafayette has caused floating mats of vegetation to form on its surface, disrupting the lake's ecology.  Clearing it is an involved and expensive process.

Dead vegetation on the surface of Lower Lake Lafayette. The segmentation of the lake in the early twentieth century has affected its ability to “dry down.” Many Leon county lakes naturally empty into sinkholes every few years, and the plants and animals that live in the lakes have adapted to and thrive in such conditions. Impounding Lake Lafayette has caused floating mats of vegetation to form on its surface, disrupting the lake’s ecology. Clearing the vegetation is an involved and expensive process.

As we learned on our Lafayette Heritage Trail Park EcoAdventure last year, the historical Lake Lafayette has been segmented into four smaller lakes by earthen dams.  As with other lakes in our area (Iamonia, Jackson, and Miccosukee), its sinkhole was separated to prevent the lake from draining.  The sinkhole is in Upper Lake Lafayette.  The other lakes are Piney Z. Lake, the Alford Arm, and Lower Lake Lafayette (which feeds the St. Marks River).  Impounding the lake has resulted in tussocks and accumulation of mucky sediment, as in the other lakes.

This lake is north of the Cody Escarpment and is considered a part of the Red Hills.  I classify it differently because of its more urban setting.

Nutrients :

  • Upper Lake Lafayette: Based on its color, its TSI index is 40.  It regularly exceeds that threshold, averaging about 50 TSI (page 132) and going into the 90s in 2005.  This part of the lake drains housing developments and is adjacent to the Walmart/ Costco shopping center on Mahan Drive.
  • Piney Z. Lake: Like Upper Lafayette, Piney Z.’s threshold is 40 TSI.  The lake regularly exceeds that, with scores typically between 50-70 TSI (page 136), and sometimes higher.  In late 2013, WFSU-FM reporter Lynn hatter reported on a toxic algal bloom on Piney Z.  The Department of Health’s Algal Bloom Tracking Tool still has a mark on the lake, though I don’t know how often that data gets updated.  The lake is bordered by Piney Z. Plantation housing development, whose newsletter advised residents on methods to reduce their nutrient contribution to the lake.
  • Alford Arm: Alford Arm drains the Miccosukee Greenway, the J.R. Alford Greenway, and the Welaunee Plantations.  It’s threshold is 60 TSI, and its average TSI is in the low 40s (page 140).
  • Lower Lake Lafayette: Its threshold is 60 TSI, and it has only exceeded that once in the last ten years, in 2004.  While its score came perilously close to 60 for a couple of years after that, since 2006 its TSI score has dropped into the low 40s/ upper 30s (page 146).

Fish Safety: Only Piney Z. is listed, recommending no more than two a week (page 27) for all species. I’m not sure if this data was collected before or after the toxic algal bloom.

Lake Talquin (6,963.  It is a larger lake than Iamonia, but it is an artificial lake created by a hydroelectric dam on the Ochlockonee River)

Nutrients: The lake averages in the low 50s on the TSI index, below its threshold of 60 (page 253).

Fish Safety: Two a week for all species except largemouth bass (page 22).

Lake Talquin is recognized as an outstanding body of water by the Florida Department of Environmental Protection.

The Bradford Chain of Lakes

The Bradford chain is comprised of three connected lakes: Bradford, Hiawatha, and Cascade.

The first time I ever paddled a canoe or kayak was in my mid-twenties, at the FSU Seminole Reservation on Lake Bradford.  Wanting to get my son Max out on the water at a younger age, I took him out there last year.

The first time I ever paddled a canoe or kayak was in my mid-twenties, at the FSU Seminole Reservation on Lake Bradford. Wanting to get my son Max out on the water at a younger age, I took him there last year.

Nutrients:

  • Lake Bradford: It averages in the 40s on the TSI index (page 191), which is below its threshold of 60.  It has risen since 2006; prior to then it had averaged in the 30s (the report theorizes that this may be due to runoff created  by Tropical Storm Faye in late 2008).  Lake Bradford sits between the FSU Seminole Reservation and the Tallahassee Museum, and drains the residential area between Orange Avenue and Capital Circle.
  • Lake Hiawatha: The lake averages in the 40s on the TSI index (page 194), below its threshold of 60.  While paddling the corridor between Lake Bradford and Lake Hiawatha, you pass the Florida panther enclosure in the Tallahassee Museum.
  • Lake Cascade: Lake Cascade Averages in the low 30s on the TSI index (page 197), well below its threshold of 60.  This lake is susceptible to drought.  The report lists gaps where water could not be collected due to low levels.

Fish Safety: Not listed.

South Leon

Lake Munson (255 acres)

The sad thing about Lake Munson is that it is really an attractive lake.  It is believed to have once been a cypress swamp, that had its water impounded in the 1800s.  It is still ringed by cypress trees.

The sad thing about Lake Munson is that it is really an attractive lake. It is believed to have once been a cypress swamp, that had its water impounded in the 1800s. It is still ringed by cypress trees.

Nutrients: “The lake has a history of severe water quality and ecologic problems including fish kills, algal blooms, floating aquatic vegetation, high nutrient and bacterial levels, low game fish productivity, sediment contamination, and depressed oxygen levels (Maristany and Bartel, 1989)” (page 206).  Lake Munson routinely exceeds 60 on the TSI index (page 208), though it will dip below the threshold seasonally, sometimes for over a year.  When I visited the lake earlier in the month, Johnny Richardson told me that the heavy rain we’ve gotten does help to flush the lake.  The DOH Algal Bloom tracking tool reports toxic blooms on both Lake Munson and on Munson Slough to the north of the lake (the slough also continues to the south through the Apalachicola National Forest, partially draining into Wakulla Springs).  The tool merely reports that there have been blooms recently.  The blooms had washed away when I visited, but Mr. Richardson expects them back in the summer.

Fish Safety: The DOH guide recommends no more than twice a week for all species but black crappie (page 19).  This is their recommendation based on mercury level.  There is a warning for PCBs (Polychlorinated biphenyl, an endocrine disruptor, page 35).  It recommends, based on PCB concerns in largemouth bass, no more than one meal a month.  That’s if you’re willing to put any amount of it in your body to begin with.

Additional Concerns: At several points over the last ten years, Lake Munson has exceeded the acceptable levels of fecal coliform (page 216).  Fecal coliform is caused by human or animal waste, and an excess could be due to septic tank failures or sewage overflows.

So that’s the good, the bad, and the ugly of our local lakes.  There is plenty of good recreation and fishing to be had, but it is helpful to know which bodies of water present potential health risks.  Most of the problems are preventable, if people are willing to make changes.  Some of the changes aren’t too much of a burden, and others have benefits beyond reducing personal pollution.  We’ll look at some of those in the coming weeks.

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Water Moves: Into and Out of Your Home and Watershed

Rob Diaz de Villegas WFSU-TV
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Teams of children try to remove water from a central pool without stepping over a red line.

I was happy to hear that our station was going to create a game where children would learn about the movement of water in our area. Not enough people know where their drinking water comes from and where it goes. The short answer is: from the earth, and back into the earth. The longer answer led me to the specific place that drains FSU, FAMU, TCC, and Tallahassee’s downtown. The water we drink and the water we use for recreation in lakes, rivers, and on the Gulf, that water is all part of a system. There are subsystems within that system. There is the manmade network of pipes and treatment facilities that take water from the aquifer and place it in our homes; or the aquifer itself, replenishing with rain and feeding springs.

With Water Moves, WFSU aimed to teach children about systems thinking. Our local game is part of a larger initiative from PBS Kids Digital, which wanted something that had kids running around to compliment an upcoming computer game. Six teams of six kids had the same goal, to fill their buckets (houses) from a central pool (the aquifer) using tools they bought by earning points. Jamie Shakar from the City of Tallahassee then talked with them about the actual system, through which rain sublimes into the ground and is filtered through sand, clay, and ultimately limestone, finally reaching the sites where the city pumps our water.

In our Red Hills EcoAdventure, I made a connection between sinkholes in our lakes and our drinking water . Technically speaking, the water we drink does not come from surface water (lakes and rivers), but from groundwater (filtered and made clean as it makes its way down). To our second presenter of the day, though, all water in the aquifer is connected and must be protected.

Where Munson Slough flows into Lake Henrietta.

Where Munson Slough flows into Lake Henrietta.

Karen Rubin is with the City of Tallahassee’s TAPP (Think About Personal Pollution). She showed that, as rain falls and filters through the ground into the aquifer, it also travels off of lawns and parking lots and down streets, looking for a low point. As this is how water flows, the low points tend to be lakes. For the most urban areas within Tallahassee, that low spot is Lake Munson. It is the most compromised body of water in our county. It is fed by Munson Slough, which runs through Lake Henrietta along the way. I visited Lake Henrietta, where the county has built barriers to catch some of our trash and keep it out of Lake Munson. What I saw, and smelled, kind of surprised me. I thought that the Munson Watershed’s problems would be more subtle, evidencing themselves in water quality readings on a table in a report. I was wrong.

What is being carried into Lake Munson? Think of our roadways, and all of the car exhaust that hits it. Do you notice a little puddle under your car when you run the air? And in and around our homes. People fertilize their lawns and vegetable gardens (As we’ve covered before, an excess of nitrogen from fertilizers ends up feeding algae, which blooms, sucks up oxygen and kills aquatic life). We use pesticides to kill those ant piles that pop up everywhere. We pressure wash our houses with chemicals. Water washes off of our lawns, picking up these chemicals and compounds as it drains to that low spot in our watershed.

Now, if Lake Munson was the final resting place of these pollutants, we might well say “Munson can take one for the team” and let it collect our refuse. We have so many great lakes and rivers already. But Munson Slough continues southward from the lake. It disappears down Ames Sink and a percentage of its water end up in Wakulla Springs.

anhinga-WS

An anhinga, surrounded by hydrilla, on Wakulla Springs. By occupying the space where water runs against vegetation, hydrilla may have prevented apple snails from laying their eggs and ultimately depriving limpkins of  food.

Wakulla Springs has an outline of a limpkin on its sign. And while some comments in a 2012 post regarding limpkins offer some hope for their return, that bird disappeared from the park in the 1990s. No definitive cause has been determined, but many look at invasive hydrilla as a culprit. Fed by excess nutrients, it is a major presence in Wakulla Springs. So much so that it encroached upon the bases of plants where apple snails lay eggs. When its source of food disappeared, there was no reason for the bird to stay.

Johnny Richardson is a water quality scientist with Leon County. He told me that while 11% of the nutrients in Wakulla Springs are known to come from streams and sinks, they don’t know exactly how much comes from the Munson system.

And while the water that flows from Wakulla Springs into the Wakulla River is considered compromised by the Florida Department of Environmental Protection, the system seems to clean it before it reaches the lower Wakulla, where it meets with the St. Marks River. St. Marks is a town that celebrates its fishing heritage with a Stone Crab Festival that we visited last year. While we in Tallahassee are connected through water to this fertile fishing ground, and to the St. Marks National Wildlife Refuge, our pollutants seem to dilute or get filtered out before reaching them.

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A television lies in algae just downstream of a dam on Lake Munson. From here, the lake flows into Munson Slough, through the Apalachicola National Forest, and into Wakulla Springs.

It’s hard to say how much one leaky car or one overzealous gardener might degrade our beloved natural resources. Tallahassee can take the blame for Lake Munson, accept that it has some negative influence on Wakulla Springs, and feel okay that it isn’t contaminating seafood in St. Marks. What we do know is that we can make the problems better or worse. We can control this.

Over the summer, we’ll look at ways to reduce our personal pollution. For instance, instead of leaving a TV and its toxic innards on the curb for a few days, or heaving it into a lake, you can take it to Leon County’s Solid Waste Facility. It’s a little out of the way, but maybe you were going to Tom Brown Park or Walmart anyway?

Also over the summer, we’ll get back to the fun EcoAdventures. Also, Randall Hughes and David Kimbro will look back at the research into salt marsh, oyster reef, and seagrass bed ecology that we’ve been following over the years. Our area has some amazing ecology, and there are places we haven’t been and connections we haven’t yet made. I never tire of learning how it all works.

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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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