Tag Archives: fiddler crab

Are two friends better than one?

Dr. Randall Hughes FSU Coastal & Marine Lab

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Sand fiddler crab.

This summer we’ve been conducting an experiment on our new deck to look at the effects of fiddler crabs and ribbed mussels on Spartina alterniflora (smooth cordgrass).

Past studies by Dr. Mark Bertness have shown that crabs and mussels by themselves can have positive effects on plant growth – most likely because crabs can reduce the stress of low oxygen in the sediments by building their burrows, and mussels can add nutrients to the sediments.

Fig. 3 from Bertness 1984, Ecology 65: 1794-1807

Figure 3 from Mark Bertness's 1984 Ecology study illustrating the positive effects of mussel presence (white bars) on Spartina

Table 3 from Bertness 1985, Ecology 66: 1042-1055

Table 3 from Mark Bertness's 1985 Ecology study. Fiddler removal has a negative effect on Spartina in the marsh flat, but not the marsh edge.

Although both fiddlers and mussels occur together in the field, no studies have looked at how the combination affects the plants. Are the positive effects of each species by itself doubled? Or are they redundant with each other? Do crabs somehow reduce the positive effect of mussels, or vice-versa? How many crabs or mussels do you need to get a positive effect on Spartina? These are some of the questions that we hope to answer with our experiment.

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Our new deck at FSUCML.

But first, we had to get everything set up. There were several long and hot days of shoveling sand into our “mesocosms” (10 gallon buckets) – many thanks to Robyn, Chris, Althea, and all the others who took care of that task! Then there was another day spent transplanting the Spartina.

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Chris, Randall, and Robyn work to transplant Spartina from the greenhouse to the mesocosms.

Finally, it was time to add the fiddlers and mussels, and everything began!

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Mussels nestled among the Spartina stems in one of our experimental mesocosms

Althea and Chris have been leading the charge on this experiment, and they’ve spent a lot of time getting to know (and identify) the fiddler crabs. All in all, a pretty fun study organism!

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Althea working to identify fiddler crab species.

We’ll continue the experiment another month and then measure the height and density of the plants in each treatment to see if there are any differences. Once this experiment is complete, we’ll set up a separate one asking somewhat of the converse question – are two enemies (periwinkle snails and grasshoppers) worse than one? We’ll keep you posted.

Randall’s research is funded by the National Science Foundation.
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Return to the field

Dr. Randall Hughes FSU Coastal & Marine Lab

IGOR chip- biodiversity 150A sure sign of spring for me is an increase in time in the field. (Robyn and Emily would probably disagree with me, since they have been out in the field regularly throughout the winter!) I have been in the lab or office since December, which feels like a long time, and I’m really looking forward to getting back in the field. I find it is so much easier to come up with new research questions and develop insights into what the animals and plants are doing out there when I’m actually there with them. I guess that makes sense!

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Cold and Wet: Field Research in the Winter

Waves on Cape San Blas rocks

Rob Diaz de Villegas WFSU-TV

IGOR chip- employment 150I was driving to Stump Hole with my production assistant Kevin when we saw these waves crashing on the rocks on the beach side of Cape San Blas.  Like any good production people, we knew the only thing to do was to climb the rocks and get footage and stills of the scene.  The same wind pushing the waves at us rocked us a little bit as we balanced- only slightly precariously- on the big stones.  It was a little after 8:30 AM and we had some time to kill before Randall and her team showed up.  And then we would kayak into the bay just across the street.

In early December I made my first winter forays into coastal environments.  Randall has already written about the seasonal shift from Summer to Autumn, where the flora and fauna are reproducing and animals are abundant in the marshes.  Winter is an entirely different beast, as I would see when we got to their sites.  But first, we actually had to get to these sites.

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After everyone was there, we kayaked east from Stump Hole with a stiff north wind pushing us on our left.  Rowing to the left was like rowing into a wall, and there were a couple of marshes in our way where we had to get out and lug the kayaks to the other side.  Saltwater splashed into my eyes and onto my glasses.  I kept my squinty eyes forward and we got to a site that for the purposes of this study is known as Island 4.

The research crew went about their normal survey work, with Randall taking a quadrat to several specific spots within the marsh to see how much grass and other species were within its PVC boundary, how tall the grass is and how many Spartina shoots were dead.  Using markers and a GPS, they’ll have data from these precise spots over a span of three years.  Emily and Hanna vacuumed bugs out of the grass and surveyed seagrass wrack.  They will, as always, search for patterns over time, and I suspect the data collected in the winter months will quantify some of what we saw with our own eyes.

Sea Urchin shell washed up on marsh

While we didn't see the usual critters swimming and crawling about, some cool stuff washed in from the bay, such as sponges, lightning whelk egg casings, and this sea urchin shell.

Last time I was at this site, some male blue crabs were fighting over a female.  They were so engrossed that I was able to get fairly close without their bolting away.  All manner of predatory snails oozed about, little fish darted in and out of the sparse shoots at the periphery, and a ray laid low in an adjacent seagrass bed.  Today it looked like they had all packed up and left for the season.  And, when it came time to go our next site, so had the water in the bay.

A combination of the tide and the strong wind left the south side of the bay somewhat empty.  Taking a few steps with our kayaks in hand, we decided instead to leave them at the island while we walked our gear over to a mainland marsh known as Wrack 5.

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This was another site where I had always seen an abundance of fauna. Hundreds, sometimes thousands of fiddler crabs would scurry away from me into the grass in this one corner of the marsh.  As Randall explained to me, the fiddlers bury themselves in the winter.  Blue crabs swim into the deeper part of the bay, to the north.  Randall didn’t know exactly what happened to the crown conchs, though when digging cordgrass up for an experiment she had come upon a buried conch.  And with their predators all gone, the marsh periwinkles had descended to the bottom of the spartina plants.

Lightning Whelk shellOne thing I did see a lot of were lightning whelk shells.  I picked them up and looked inside, wondering, are they more cold tolerant than the other species?  They’re not.  But their shells were pretty.

The following Monday I went to Alligator Harbor with Tanya and Hanna, and it was a lot of the same.  We dragged our kayaks from the ramp to the first site and walked between the islands to the second and third sites.  It was a much muckier walk than in St. Joe Bay (the oysters like it mucky), and I was breaking in a new pair of crappy old sneakers to be my oyster reef shoes.  This is how they fared:

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Now that I’ve muddied my hands pulling my shoe out, where’s all that water?

Have any of you trekked out into the cold coastal waters this season? Share your stories!

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.

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Operation Noah’s Ark

Rob Diaz de Villegas WFSU-TV

The video above is from our dimensions program. It dovetails nicely with what we care about on this site, which is the ecology of Florida’s Forgotten Coast, in this case salt marshes.  The idea is that, when looking to minimize potential oil damage to our coast, you start with its smallest building blocks.  Operation Noah’s Ark, based out of the Gulf Specimen Marine Lab in Panacea, is collecting a lot of little critters that live in places like salt marshes. The fiddler crab helps maintain the marsh with its burrows, which bring oxygen to cordgrass roots.  In that grass, juvenile mullet find shelter, as do blue crabs and juvenile pinfish.  The Kemps-Ridley Sea Turtle eats those blue crabs, and those pinfish will mature and swim out into the gulf to be eaten by gag grouper.  You can see how one species becoming compromised can have a cascading effect throughout the Gulf.
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