Tag Archives: Florida State University

Pea crabs at various stages of development. The ones in the center are young crabs, as they appear in the stages immediately following infection of an oyster. The ones on the right are older, harder-carapaced crabs (most likely males, which may leave their hosts in search of oysters harboring females). The crab on the left is a mature female. The developing, orange-colored gonads are visible through the female’s thin carapace. Since mature females never leave the their host oyster, their carapaces (shells) are very soft and thin. This makes them very… squishy and pea-like.

Pea Crab Infestation!

Tanya Rogers FSU Coastal & Marine Lab

IGOR chip- biogeographic 150Serendipitous results are surely one of the most rewarding parts of experimental research. This past winter, I spent many weeks processing various frozen components of great cage experiment of last summer, including the several hundred spat tiles placed inside the different cages at all sites along the coast. It was while delicately measuring and shucking these little spat that I made one such unanticipated finding: Our oyster spat, unbeknownst to us, had become infested with pea crabs.

Pea crabs at various stages of development. The ones in the center are young crabs, as they appear in the stages immediately following infection of an oyster. The ones on the right are older, harder-carapaced crabs (most likely males, which may leave their hosts in search of oysters harboring females). The crab on the left is a mature female. The developing, orange-colored gonads are visible through the female’s thin carapace. Since mature females never leave the their host oyster, their carapaces (shells) are very soft and thin. This makes them very… squishy and pea-like.

You might have had the surprise of finding an oyster pea crab (Zaops ostreus) while shucking an oyster yourself. These small crabs live inside oysters and are a type of kleptoparasite, meaning they steal food from their hosts. An oyster gathers food by filtering water over its gills, trapping edible particles on its gills, and carrying those particles to its mouth using cilia (tiny hairs). Pea crabs sit on the gills and pick out some of the food the oyster traps before the oyster can consume it. By scurrying around inside oysters, pea crabs can also damage the gills mechanically. The pea crabs, like most parasites, don’t kill their hosts, but they can certainly affect the oysters’ overall health.

pea crabs 2

A gravid (egg-bearing) female pea crab next to the oyster spat in which she was living. The female, like most crabs, carries her eggs until they hatch, and then releases her larvae into the water. The baby crabs, when ready, will locate a new oyster host by smell.

As I was processing the oyster spat from all of our experimental sites (Florida to North Carolina) for survivorship, growth, and condition, I began to notice a surprising number of pea crabs living inside them and started to keep track. What’s interesting was not so much that the oysters had pea crabs, but that the percentage of oysters infected with pea crabs varied geographically. For instance, only about 25% had pea crabs in St. Augustine, Florida, whereas over 70% were infected at Skidaway Island, Georgia. Keep in mind that these spat all came from the same source and the same hatchery, so they all had the same starting condition. What’s more, I found that spat in Georgia which had naturally recruited to the tiles from the surrounding waters (of which there were quite a lot, and for which I also processed condition) rarely had pea crabs. Only about 5% of the recruits had pea crabs at Skidaway Island, Georgia. Why is there this huge difference in infection rate? Do the local oysters know something that the transplants don’t? How do these patterns in pea crab infection relate to other geographic patterns we’re finding? How does pea crab infection affect oyster condition? These and many more questions await to be addressed in further analyses and future experiments.

In the Grass, On the Reef, A World Away

Dr. Randall Hughes FSU Coastal & Marine Lab

IGOR chip- biogeographic 150IGOR chip- habitat 150David and I are in Sydney, Australia, on visiting research appointments with the University of Technology Sydney. We arrived the first of the year, and after recovering from jet lag and getting our bearings, we embarked this week on setting up a couple of new experiments.  We have great local “guides” – Dr. Peter Macreadie (UTS), Dr. Paul York (UTS), Dr. Paul Gribben (UTS), and Dr. Melanie Bishop (Macquarie University) – to introduce us to the field systems and collaborate with us on these projects.

lake_macquarie

Our seagrass and razor clam experiment is set up at Point Wolstoncroft in Lake Macquarie (north of Sydney).

Continue reading

Photo feature: Oyster Love

From the FSU Coastal & Marine Lab

IGOR chip- human appreciation 150What’s not to love about oysters? They clean the water, they’re delicious, and they have surprising economic value. Members of the Kimbro Lab found this unique oyster, which itself seems very loving, on one of their study sites. “Now I’ve seen a lot of weird-shaped oysters,” says lab tech Tanya Rogers,” but never one quite this perfect. I took it on a photoshoot this evening for some nice background and lighting.”

A long time in the making

Dr. Randall Hughes FSU Coastal & Marine Lab

IGOR chip- biodiversity 150

As I mentioned in my last update, we have been working to set up a new marsh experiment in St. Joe Bay. The goal of the experiment is to see whether the genetic diversity of marsh cordgrass (Spartina alterniflora) affects how quickly or abundantly the plants grow, or influences the number of fiddler crabs, grasshoppers, snails, and other critters (like Ibis??) that call the plants home. But what is genetic diversity, exactly, and why do we think it may be important?

IMG_1812

A flock of Ibis resting among our experimental marsh plots.

Spartina is a clonal plant, which means that a single “individual” or clone made up of many stems can dominate a large area (low diversity), or there can be lots of different individuals mixed together (high diversity). In our surveys of marshes in the northern Gulf of Mexico, we find that there can be as few as 1 and as many as 10 clones in an area of marsh about the size of a hula-hoop. You may notice that our experimental plots are about that same size, though we used irrigation tubing rather than actual hula-hoops (not as fun, but more practical and less expensive!). We’re testing whether the differences in genetic diversity (1 vs. 10 clones) that we see in natural marshes has any influence on the marsh community.

A single experimental plot of Spartina that is 1m in diameter.

But why genetic diversity? We know from experiments by other researchers that Spartina clones grown individually differ in height, how many stems they have, and other characteristics. These same plant traits affect the critters that live in and among the plants – for example, periwinkle snails preferentially climb on the tallest plants. Because different animals may be looking for different plant traits, then having greater diversity (genetic and trait) may lead to a greater number of animal species that live in that patch of marsh. Or, a single clone may be the “best”, leading to higher numbers of animals in lower diversity areas.

IMG_2389

A view of the existing marsh behind our experiment.

As my title alludes, this experiment has taken a long time to come to fruition, in large part because it’s impossible to look at any 2 stems in a marsh and know for certain whether they’re the same individual or not. Unlike some clonal plants such as strawberries, where there are multiple berries connected by a single above-ground “runner”, Spartina has runners (aka, rhizomes) that connect stems of the same genetic individual under the ground, making it difficult to tell which stems are connected to which. We have 2 ways to get around this problem: (1) we use small snippets of DNA (analyzed in the lab) to tell clones apart, and (2) we start with single stems that we know are different clones and then grow them separately in the greenhouse until we have lots of stems of each different clone. It’s this latter part that has delayed this experiment – it has taken much tender loving care from Robyn over the last 2 years to get our Spartina clones to grow in the greenhouse to the point that we have enough of each clone (36 small flowerpots of each, to be exact) to plant in our experiment.

IMG_2394

Emily and Robyn work to remove existing rhizome material from around the plot edges.

But plant we finally did! With lots of help from members of the Hughes and Kimbro labs, we got all the sand in the experimental plots sieved (to remove any existing root material) and all the plants in the ground the Thursday and Friday before Thanksgiving.

IMG_2383

Team Hug-bro (Hughes and Kimbro) helping sieve sand!

 

IMG_2386

Meagan and Randall get the easy job - planting the plants.

Now we get to wait and see (and take data) whether Spartina genetic diversity matters for the marsh plant or animal community. There won’t be any quick answers – the experiment will run for at least 2 years – but we’ll be sure to keep you up-to-date!

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

Spat on a Platter

Tanya Rogers FSU Coastal & Marine Lab

IGOR chip_ predators_NCE 150“Spat tiles” are a tool our lab commonly uses to measure the growth and survivorship of juvenile oysters under different conditions, and we’ve used them with varying degrees of success in many of the experiments chronicled in this blog. What these are essentially (in their final form, after a good degree of troubleshooting), are little oysters glued to a tile, which is glued to a brick, which is glued to a mesh backing, which is zip tied vertically to a post. Rob and I have put together a couple interesting slideshows chronicling the growth of these spat over time from two of those experiments. Ever wonder how fast oysters grow? Observe…

This is a time series from our first spat tile experiment, which you can read about in this post. As you may recall, this experiment was largely a failure because the adhesive we used to adhere the spat was inadequate. However, we decided to keep the fully caged tiles out on the reefs to see how they fared over time in different locations. I photographed the tiles every 6 weeks or so, so that we now have a series showing their growth over time. The slideshow shows one of the tiles from Jacksonville. It starts in October of 2010. You’ll notice that not much growth occurs though the late fall and winter, but the spat start to grow noticeably from April-June 2011. From June-September the spat grow explosively and many new spat settle on the tile from the water column and grow equally rapidly. Just as plants (and algae) have a summer growing season, so too do the oysters that feed on them, when conditions are warm and there is abundant phytoplankton in the water to eat.

Next is a series of images from our caging experiment last summer, which you can read about here. Our large cages contained either:

bivalves-2box

no predators (bivalves only),

consumers-2box

spat-consuming mud crabs and oyster drills (consumers),

predators-2box

or mud crabs and oyster drills plus blue crabs and toadfish (predators).

The spat tiles within the larger cages were placed either exposed to potential predators or protected from them in a smaller subcage. Here are typical examples of what tiles looked like at the end of the experiment (about 2 months after starting). You can see how all the spat on the unprotected tiles were wiped out in the consumer treatments, but a good number survived in the treatments with no predators, as we would predict. In the predator treatments, most of the spat on unprotected tiles were removed, but not as fully or quickly as in the consumer treatments, which we would predict if the predators are inhibiting consumption of spat by the mud crabs and drills through consumptive or non-consumptive effects. You’ll see one tiny spat holding on in the predator tile shown. On the protected tiles, most of the spat survived in all treatments, as expected. We plan to further analyze the photographs from the protected tiles though, to see whether spat growth rates differed between them. We may find that protected spat in the consumer treatments grew slower than in the other treatments because of non-consumptive predator effects.

Currently, we’ve recovered most of our arsenal of spat tiles from the field, and I say we have probably amassed enough bricks to pave an entire driveway! Good thing we can reuse them!

The Biogeographic Oyster Study is funded by the National Science Foundation.