Tag Archives: snails

The search for patterns

Dr. Randall Hughes FSU Coastal & Marine Lab

IGOR chip- biodiversity 150The end of summer is a good time to pause and think about any general patterns that emerge from observations over the course of the last year(s). Sometimes it is easy to get swept up in the minutiae of individual projects and forget about the big picture. Of course, these patterns aren’t definitive (i.e., don’t quote me on this!), but they can be useful to think about, particularly when considering future avenues of research.

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Marsh island in St. Joe Bay viewed from the waterand marshes on the edge of the mainland.

So what sort of patterns can I describe to you after two summers in the marshes of St. Joe Bay? One that doesn’t take a PhD to recognize is that there are two distinct types of marshes that we sample: marsh islands and marshes on the edge of the mainland.

But aside from the obvious fact that one is an island and the other is not, there are some additional interesting differences:

1. The slope of marsh islands is typically greater than mainland marshes, so that you move quickly from plants that can tolerate frequent flooding (cordgrass) to plants that are more “terrestrial” (pickleweed, saltwort, etc.). On islands this transition can occur within a few steps of the water’s edge, whereas mainland marshes typically have a large area (I like to think of it as a football field) dominated by cordgrass.

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Elevation on islands changes rapidly compared to the mainland. Even slight differences in height can influence plant communities.

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Sampling a mainland marsh in St. Joe Bay.

2. Marsh islands tend to have fewer periwinkle snails than mainland sites, although they are certainly present.

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Abundant snails in a mainland marsh.

My guess is that the snail predators (blue crabs, crown conchs) that lurk just at the water’s edge have greater access to snails on the islands at high tide, because they can move in from all sides of the island. In contrast, the predators near mainland sites have only one point of entry into the marsh.

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Blue crab lurking in the seagrass at the edge of the marsh during low tide.

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Crown conch foraging for snails in a lab experiment.

3. Perhaps not surprisingly given that they are surrounded by water, the marsh islands typically have fewer grasshoppers jumping around. We’ve also had far fewer snake encounters on islands, which I consider a good thing. Probably because land-based predators such as snakes, raccoons, etc., are less frequent on islands, we also observe greater numbers of nesting birds on the islands than at mainland sites.

4. One clear difference that I can’t explain but hope to examine in the future is that cordgrass plants collected from the islands (which can only be done with a special permit from the Department of Environmental Protection) survive better in our greenhouse at the lab than those from mainlands. It may simply be the growing conditions, or island plants may be hardier overall. Stay tuned.

As we continue to process, enter, and analyze data, there should be additional trends emerging. And we’ll likely find out that some of the patterns we think we see don’t hold up to the test of actual data. And so goes the process of science!

Randall’s research is funded by the National Science Foundation.
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Autumn in the marsh

Dr. Randall Hughes FSU Coastal & Marine Lab

Marsh periwinkles climbing on a cordgrass reproductive stem

A cordgrass reproductive stem stands above the surrounding plants.

IGOR chip- biodiversity 150 One doesn’t need to look at a calendar to realize that fall is upon us – recent cool mornings are a welcome sign. The marsh is also showing signs of change, with cordgrass flowering shoots springing up everywhere.

These stems are quite noticeable – they are taller than non-reproductive plants, and they have a “feathery” appearance due to the reproductive structures at the tops of the stems.

As I’ve mentioned before, cordgrass is one of those plants (like strawberries) that can spread by underground rhizomes, putting up new stems along the way. Alternatively, it can reproduce the “traditional” way, with reproductive stems that broadcast and receive pollen via the wind, ultimately producing seeds that fall to the sediment, get buried, and then germinate to produce new seedlings. Though conventional wisdom is that most new cordgrass stems are produced vegetatively by spreading rhizomes, it’s clear at our sites that these plants are investing a lot of energy in the other form of reproduction! Continue reading

A walk “in the grass”

Rob Diaz de Villegas WFSU-TV

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Last week we had a post on what it was like on an oyster reef, the idea being that many people have never really seen one.  Continuing with that theme, I thought it might be interesting to take a closer look into a salt marsh.  This is a trickier proposition because, well, what is a typical salt marsh?  Some of them grow in muddy waters next to oyster reefs, or they can be found along beaches, in wide expanses or in small islands just off the coast.  I’ll keep today’s imaginary journey confined to marshes in St. Joseph Bay, where Randall Hughes conducts her biodiversity study- that is what I am most familiar with.

Continue reading

What were we doing before Deepwater Horizon?

Dr. Randall Hughes FSU Coastal & Marine Lab

Watch the “snail experiment.”
Snails in the marsh

Periwinkle snails climbing on cordgrass

IGOR chip- biodiversity 150One of the marsh animals that we have been studying for the last year (in the absence of oil) is the marsh periwinkle, Littoraria irrorata. This snail is very abundant in many marshes and is particularly visible at high tide when it climbs the plant stems to get out of the water and away from its predators, primarily crown conchs and blue crabs.

While hanging out on the cordgrass stems, the snails will often create grazing scars that look much like a razor blade cut through the grass. Even though they don’t remove much plant tissue, they can have a big impact – fungus colonizes their grazing scars, and if the fungus becomes abundant enough, it can kill the entire plant, leading to marsh loss. (See the excellent work done by Brian Silliman at UF on this topic.)

One of the interesting aspects of many Panhandle marshes is that needlerush, a taller plant than cordgrass that usually occurs closer to land, can grow side-by-side with cordgrass at the water’s edge.

When needlerush is there, lots of snails climb on it despite the fact that they don’t eat it. (We think they like needlerush because it is taller and provides a better escape from predators than cordgrass.)

Because we noticed that the cordgrass that occurs with needlerush is taller and healthier than cordgrass that occurs in patches by itself, we are currently conducting an experiment to see if this pattern is due to the snails spending less time on cordgrass when needlerush is around. Each experimental plot is surrounded by a cage that serves to keep snails either in or out so that we can test their effects on the plants. You may notice the snails are very fashionable – we ‘tag’ them with nail polish so that we can differentiate the ones we put in the cages from ones that get in from the surrounding marsh. Some cages contain cordgrass only, whereas others contain a mix of needlerush and cordgrass. Finally, in some of the cages we have clipped the above-ground portions of all of the neighboring plants – this allows us to see whether the cordgrass simply prefers the environment that needlerush grows in, or if the needlerush must be present for the cordgrass to benefit.

As long as our experiment isn’t prematurely interrupted by oil, then we should have an answer to our question by the end of the summer!

Randall’s research is funded by the National Science Foundation. The song used in the video is Florida Breeze, by Craig Reeder.

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The unsung heroes of the muck

Roberto Diaz de Villegas WFSU-TV
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photo by John Spohrer

Let’s talk about the little guys.

Think a little smaller than this pelican here.  Obviously, pelicans are a symbol of our coastal areas, flying in those long rows as they do while we’re driving down Highway 98.  Pelicans covered in oil have become the poster-species of the environmental toll of the Deepwater Horizon oil spill.  It’s horrifying to think of animals as evolved as dolphins washing up on the shores, and people of course are always concerned about sea turtles.  As they should be.  They are all important parts of the Gulf ecosystem.

But they are not the only important parts.  There are other creatures that probably won’t make it on to that oil spill tragedy poster because, let’s face it, they already live in muck.  Those are the species that we’ve been most concerned with on this site.  They are worth worrying about, and I’ve come to find them cute in their way.  I keep thinking I need to try to get Disney to make a movie based in a salt marsh or oyster reef, where mud crabs and periwinkle snails sing and hide from predatory blue crabs (who, like those sharks in Finding Nemo, might be sympathetic characters themselves).  When kids are carrying plush fiddler crab dolls, maybe the little guys would get some consideration.  As it turns out, however, I have no pull at Disney.  So I’ll just talk about them right here on this blog.

Like the fiddlers.  They eat sand.  They shovel it in their mouths with their smaller claws, while they do the mating dance for which they’re better known with their larger “fiddle” claws.  I see thousands of them at a time in a salt marsh, always scurrying away and making that sound, a little bit like trickling water and a little bit like tiny bubble wrap being popped.  Of what importance are these silly little guys?

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Fiddler crabs are crucial to the survival of a salt marsh

Other than being food for blue crabs, their importance has to do with the muck in which they live.  They live in the sediment collected by the cordgrass root system; you can see the holes they call home throughout the marsh.  As Dr. Hughes explained in this video, these burrows provide oxygen to the soil in which the cordgrass grows.  So their presence helps the cordgrass grow, just as the cordgrass provides them shelter.

So maybe the fiddler crab hasn’t found himself at the center of any teary oil spill montage.  But he’s an animal, and a fairly popular pet.  Spartina alterniflora- aka smooth cordgrass- may never gain a foothold in the popular imagination proportionate to its ecological importance.  It is the foundation species of a Gulf salt marsh.  These marshes act as a filter for pollutants flowing into the ocean, protecting important estuaries such as those at the mouth of the Apalachicola River.  Marshes provide shelter to a number of commercially important species (shrimp, mullet, and blue crab, for instance).  And marshes also help absorb storm surges and prevent erosion.

Those are just a couple of examples.  There are, of course, more.  Tasty, tasty oysters filter water and prevent algal blooms lethal to other species.  Toadfish have faces even other toadfish may not love, but they eat animals that would decimate oyster reefs if left unchecked.  Those oyster predators are interesting as well.  Mud crabs might get as large as 4 cm and have these thick little claws which tear through oyster shells.  Oyster drills are small snails whose tongues (radula) are covered with thousands of small razor-like teeth.

As we move forward with this project, we’ll see more and more of all of these coastal denizens.  So far oil has not reached the areas Dr. Hughes and Dr. Kimbro are studying, and so there is always hope that they may be spared.  If oil does arrive, many of these species could be severely affected.  And while some of them may not look like much, the harm that would come to them would have repercussions felt beyond their own habitats.

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This snail lives on an oyster reef

Interested in seeing a fiddler crab plush toy as a WFSU-TV pledge premium?  Well, that isn’t likely to happen. But we will take comments and questions, as usual.