Category Archives: Salt Marsh Ecology | In the Grass
Dr. Randall Hughes, among other things, studies biodiversity in salt marshes, and how it affects the habitat’s ability to cope with disturbances. Does having a greater variety of plant species benefit a salt marsh? Does having more genetic individuals of smooth cordgrass help when environmental or man made catastrophes strike? Randall is looking at several factors, from the animals that eat the cordgrass (the foundation species of the marsh), to which combinations of plants work best together, or how seagrass wrack affects the health of a marsh.
Most of her study is centered on St. Joseph Bay, on Florida’s Gulf coast. On this blog you will also see some of her side projects looking at black mangroves are starting to become more prevalent in Gulf salt marshes and why seagrass beds around the world are dying off.
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.
Figure 3 from Mark Bertness’s 1984 Ecology study illustrating the positive effects of mussel presence (white bars) on Spartina
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.
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.
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!
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!
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.
This one is for all you animal lovers! WFSU’s dimensions producer and In the Grass, On the Reef contributor Mike Plummer takes a look at a nonprofit that cares for animals in need, including screech owls and deer, as well as some of the critters we see out along the coast like ospreys and pelicans. Enjoy!
Here is a video from SciGirls II visit with Dr. Randall Hughes at the FSU Coastal and Marine Lab. Enjoy!
Today, the WFSU/ Mag Lab SciGirls visited Dr. Randall Hughes at the Florida State University Coastal and Marine Laboratory.
Randall examines an experiment cage as Robyn looks on.
Calling a one year experiment an “era” is probably a bit of an over-statement, but the end of our snail field experiment definitely feels significant. Especially for Robyn, who has traveled to St. Joe Bay at least once a week for the past year to count snails and take other data. And also for the Webbs, who were kind enough to let us put cages up in the marsh right in front of their house and then proceed to show up to check on them at odd hours for the last year! And finally for this blog, because the beginning of the snail experiment was the first thing we documented last summer when we started this project with WFSU. It’s nice to come full circle.
So why, you may wonder, are we ending things now? Is it simply because one year is a nice round number? Not really, though there is some satisfaction in that. The actual reasons include:
(1) The experiment has now run long enough that if snails were going to have an effect on cordgrass, we should have seen it by now. (At least based on prior studies with these same species in GA.)
(2) In fact, we have seen an effect of periwinkle snails, and in some cages there are very few plants left alive for us to count! (And lots of zeros are generally not good when it comes to data analysis.)
(3) Perhaps the most important reason to end things now: it’s become increasingly difficult in some cages to differentiate the cordgrass that we transplanted from the cordgrass that is growing there naturally. Being able to tell them apart is critical in order for our data to be accurate.
(4) The results of the experiment have been consistent over the last several months, which increases my confidence that they are “real” and not simply some fluke of timing or season.
And what are the results? As I mentioned above, snails can have a really dramatic effect on cordgrass, most noticeably when our experimental transplant is the only game in town (i.e., all the neighboring plants have been removed). And not surprisingly, cordgrass does just fine in the absence of snails and neighbors – they’re not competing with anyone or being eaten!
Snails also have a pretty strong effect on the experimental cordgrass transplant (compared to when no snails are present) when all of its neighbors are cordgrass.
Most interestingly, snails do not have a big effect on the experimental cordgrass transplant when some of the neighboring plants are needlerush.
This result is consistent with some of the patterns we’ve observed in natural marshes, where cordgrass growing with needlerush neighbors is taller and looks “healthier” than nearby cordgrass growing without needlerush.
Having decimated the plants in the cage, the snails move towards the tallest structure they can reach- a PVC pipe.
But why? Those snails are pretty smart. They generally prefer to climb on the tallest plant around, because it gives them a better refuge at high tide when their predators move into the marsh. (We’ve shown this refuge effect in the lab – fewer snails get eaten by blue crabs in tanks with some tall plants than in tanks with all short plants.) Needlerush is almost always taller than cordgrass in the marshes around here, so this preference for tall plants means that snails spend less time on cordgrass when needlerush is around. And finally, less time on cordgrass means less time grazing on cordgrass, so the cordgrass growing with needlerush experiences less grazing pressure.
These results – consumer (snail) effects on cordgrass are lower when cordgrass grows mixed with needlerush – are consistent with theory on the effect of diversity, even though in this case we’re only talking about a “diversity” of 2 plant species. And they could be important in the recovery or restoration of marsh areas where snails are causing a large reduction in cordgrass biomass.
The one thing we still don’t know with certainty – how do the snails determine which plant is taller??
I guess that’s the beauty of this job, in that there are always more questions to answer.
Randall’s research is funded by the National Science Foundation.
The new documentary, In the Grass, On the Reef: Testing the Ecology of Fear had a segment on the snail experiment. Watch the full program here. You can also read Randall’s post from the beginning of the experiment, and watch a video, here.
With the In the Grass, On the Reef documentary done, me, my wife Amy, and our son Maximus took a vacation to visit Amy’s family in Duxbury Beach, Massachusetts. We were picked up at the airport by her cousin, Jim Kennedy. On the ride down, we got to talking about what our respective plans were for the week. One thing he was wanting to do grabbed my attention. He was going to go clamming for quahogs in the marsh by the family’s vacation home and make a chowder. That sounded so cool to me. Go into a marsh without having to lug around a camera, and round up some tasty critters? I told him I wanted to go (I did go into the marsh with a camera last year, which is where the marsh pics you see originated). It’s a strange side effect of working on this project that I now enjoy going into hot, muddy places surrounded by sharp grass.
Low tide was set for 11 AM on the day we chose to go, so we set out between 9:30 and 10 while the tide was still going out. The marsh is at the mouth of the Back River, and when the tide drops, the grass stands a few feet above the bottom of the river bed. Below the cordgrass, the sides of the elevated marsh are pockmarked by fiddler crab burrows. We entered the sand/ mud flats at the head of the river from Gurnet Road, armed with our permit, a rake, and a 12-quart bucket. The quahogs would be buried just below the mucky surface. Here on the Forgotten Coast, we have quahogs as well- ours are the southern quahogs, the more famous New England quahogs are known as the northern quahog:
There were a lot of people out there harvesting the clams. Most of them used a short rake meant specifically for clamming. Jim went to several stores to look for one but couldn’t find it, so we used a garden rake. At the end of the day, though, the best tools we had were our own feet. A mature, legal sized quahog (3-4 years old) is big enough that we could feel them under our feet as we walked up the river bed. Then, with the rake or with our hands, we would dig them out. Around every legal sized clam we found there were usually several smaller ones. I thought back to what David said in the show about what he looked for in an oyster reef. The best ones had several mature oysters as well as several smaller ones to eventually replace them.
Green crab (Carcinus maenas)?
I couldn’t help but note the differences and commonalities between our local marshes and sand flats and this New England marsh. I didn’t see many large predatory snails in or around the marsh, a stark contrast to sand flats in St. Joseph Bay or at Bay Mouth Bar.
Blue crabs are of course common on Florida coasts, but their historic range ends just to the south of here, on the outer coasts of Cape Cod. I believe this mud covered crab is an invasive green crab, and I have seen Atlantic rock crabs on the nearby beach. There were razor clams (Ensis directus) and steamers (soft shell clams, Mya arenaria), each of which are harvested at other times of the year. We also saw the occasional small shrimp, and oysters that had flaked off of reefs deeper out in the bay.
We caught the legal limit and returned, muddied, to prepare the chowder.
Jim Kennedy (left) and WFSU-TV producer Rob Diaz de Villegas (right) shuck and clean quahogs.
A little on how you prepare quahogs for chowder:
You scrub the mud off of the closed shells. Open shells buried in the mud are dead animals and are unsafe for consumption.
After scrubbing them, you boil them until they open. Then you shuck them and remove the contents of their stomachs. In the photo at the lower left of this paragraph, that green stuff is phytoplankton- microscopic plants floating with the other sediment in the water. Good food for clams- and their filtering it is a great way to keep the water clean- but not anything we were interested in eating.
I got to try my hand shucking and cleaning the clams. Jim’s mom, Pam, cut potatoes and onions while Jim cooked the quahogs and fried some bacon. The bacon smell helped with the boiling clam smell. The ingredients would come together in a large pot with milk, cream, and flour. The making of the chowder in the cottage brought out some nostalgia.
Pam recalled that her grandmother’s chowder didn’t contain dairy. When Bertha and Archer MacFarland would camp on Duxbury Beach, they didn’t have refrigeration and so milk and cream weren’t really an option.
“When Max is old enough,” My father-in-law, Chris MacFarland, said to me, “you need to teach him how to go quahogging to keep the tradition going.” Maximus is five months old, so I have a bit of time until I take him out there. When he does go, he’ll represent the fifth generation of the MacFarland family to harvest quahogs from Duxbury Bay.
Duxbury Beach and Duxbury Bay are separated by Gurnet Point, a thin cape down which Gurnet Road runs. The road runs to the town of Saquish at the horn of the cape. Driving there, the beach is on your left, and the bay is to the right. A large marsh is at the North of the bay.
Archer and Bertha started camping on Duxbury Beach around 1920. After some years of camping there, they bought plots of land and built a cottage by the marsh. When their son Robert was sixteen, he built another house nearby. Then, when he was nineteen, he sold his car for $200 to buy a plot. There he built the house where his children, and their children and grandchildren, vacation every summer.
Robert took his children looking for quahogs when they were young. They used the “treading” method to find their clams, much like we did, except that they were barefoot. Jim and I wore shoes to keep our feet safe from broken shells hidden in soft mud that was deep in places. It was deeper as we walked up the riverbed- I sank almost up to my waist at one point. I imagine that they didn’t walk that far up.
Robert also fixed up an old pram, on which he used to take his sons Chris and Doug on fishing trips off of the beach. As Chris (who was 7) and Doug (who was 5) recalled, one of them would row, the other would bail water. They caught cod, threw back pollock and perch, and used mackerel for bait. Of course, North Atlantic cod is not nearly as common as it once was. Nor is flounder as common off of Saquish. Jim remembers going out with his family and spotting them at the edge of seagrass beds from the family’s Boston Whaler. For about ten years now, those haven’t been seen much either. As David points out in the program, the animals in the lower trophic levels see less change over time, and so there are still plenty of clams in Duxbury Bay.
Hopefully that means chowder at the cottage for many more summers.
When the chowder was done, it was served with oyster crackers and crumbled bacon (the bacon Jim made earlier- the grease was used in the chowder).
I’m guessing there are stories like this across the Forgotten Coast: generations of families bonding while they made use of the fish and shellfish swimming outside their back doors. Do you have a story like this? Share it here, in the comments section. We might want to visit some of you and feature your stories in one of our videos.
Photos taken by: Rob Diaz de Villegas, Chris MacFarland, James Kennedy, and Amy Diaz de Villegas. Archival photos provided by Chris MacFarland.
In the Grass, On the Reef: Testing the Ecology of Fear is online in its entirety and in HD. Predators and prey struggle for survival in crucial coastal ecosystems across North Florida.
During their visit to FSUCML, Randall took the SciGirls to the small marsh next to the lab. One SciGirl found this fiddler crab carrying her eggs.
This video is part of the WFSU SciGirls project. SciGirls, for those who haven’t heard of it, addresses an unfortunate reality in the world of science- there are a lot more men doing research than women. It’s a problem that needs to be addressed as interest in science as a career has been waning overall. Every Summer, the SciGirls camp takes groups of teen and preteen girls into labs and into the field with scientists. After visiting Dr. Randall Hughes at the Florida State University Coastal & Marine Laboratory last Summer, a couple of SciGirls returned to conduct this interview.
Randall is a good role model for young aspiring female scientists. Aside from the fact that she herself is a female scientist, most of her lab- and that of her colleague Dr. David Kimbro- are females as well. If you’ve been following this blog, you’ve read about Emily Field’s graduate work on seagrass wrack and Kattie Lotterhos’ graduate work in genetics. In David’s lab, we’ve heard from Tanya Rogers, a lab technician who keeps David’s lab organized, and who is crucial in the planning and implementation of their large field experiments. We have more recently started hearing from Hanna Garland, Tanya’s fellow lab tech who is starting graduate school in the fall and who is looking into the abnormal levels of crown conchs on Randall and David’s Saint Augustine reefs. And we have also heard from Cristina Lima Martinez, an intern who comes to the Kimbro lab from Spain to study the Bay Mouth Bar ecosystem.
We spent one day learning about invasive Hydrilla and alligators at Wakulla Springs, and then of course had to cool off!
For most of the month of May, I was busy teaching an undergraduate course at FSUCML. The course – Marine Biodiversity and Conservation in Florida – was a new offering, and it was lots of fun to put together. And, at least from my perspective, it went pretty well! (I guess you’d have to poll my students to get the true picture of how it went down.)
One of the best aspects of the course, for me, was to learn so much about the special part of Florida that we call home. We spent one day trying our hand at tonging oysters in Apalachicola, Continue reading →
The answer to this seemingly rhetorical question was the subject of a recent review by Edward Barbier and colleagues in the journal Ecological Monographs. They focused not only on salt marshes, but also coral reefs, seagrass beds, mangroves, and sand beaches / dunes. The impetus for the analysis was the recognition that many coastal habitats are in decline – for instance, 50% of salt marshes are lost or degraded around the world – and the belief that we need a better understanding of the true costs of these losses. Continue reading →