Monthly Archives: March 2012

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.

At the Buffer Preserve, Rare Plants Are “In the Grass”

Rob Diaz de Villegas WFSU-TV
dimensions, March 21 at 7:30 PM/ ET on WFSU-TV: our latest EcoAdventure explores the Buffer Preserve in search of rare plants and one woman’s quest to learn the fire history of the area.
Explore our map!  Click enlarge on a photo to read additional information about each plant.

IGOR chip- human appreciation 150I want to apologize in advance to anyone who watches tomorrow’s EcoAdventure on dimensions and gets excited about seeing the Chapman’s rhododendron.  Aside from naturally occurring in only three North Florida counties, its peek blooming only lasts about two weeks.  This peek usually starts at the end of March and goes into April, so we had planned on shooting then.  This year’s mild winter changed our plans.  A couple of weeks ago, at the beginning of March, Dr. Jean Huffman wrote to tell me that they had exploded.  In fact, the first bush we saw once we got out there was already starting to whither.  We did find a group of bushes in full bloom, and it was worth the hike.  By the time our footage airs, those flowers might very well be gone.

The carnivorous chapman's butterwort is listed as a threatened plant. Dr. Alvin Chapman, an 19th century Apalachicola botanist, discovered many of the plant species you can see in the Buffer.

That’s the bad news.  The good news is, many of the other rare flowering plants in the Saint Joseph Bay State Buffer Preserve will start blooming soon.  In a lot of ways, finding and photographing rare plants is as difficult as finding and photographing rare birds.  Especially when our seasons go screwy.  And unlike the Chapman’s rhododendron, many of the rare plants in the Buffer are hiding in tall grasses.  The Buffer is home to 21 rare plant species, and it’s the only place where the Chapman’s rhododendron is protected on public land (Correction: there is a small population at Camp Blanding, north of Gainesville).

I thought I’d share some photos of the plants we saw.  If you look at the map above, you can see an approximation of where we saw each of them.  You can see in the satellite image that the photos of the rare plants are located where the tree cover is lighter.  This goes back to, once again, controlled burning and its role in clearing out woody growth between longleaf pines.  When those shrubs get pushed back to where lightning-caused fire had once naturally confined them, grasses and herbaceous plants sprout up (and the animals that eat them return to the flatwoods).  If you’re in the Buffer, look for where the trees are spaced apart and grasses fill the ground.  It’s in those grasses that you’ll find some interesting characters.

I also included some photos of the bay section of the Preserve.  This is how I first encountered the Buffer, shooting salt marsh footage in conjunction with Randall Hughes’ research in SJB (click up in the Salt Marsh menu for more info on that).  There are plenty of birds, crabs, and predatory snails to see if you wade out into the sand flats and marshes by the visitor center.

Thanks to my production assistant, Alex Saunders, who brought his nice camera and took the plant photos in the map.

Sounds of the Oyster Reef

Rob Diaz de Villegas WFSU-TV

IGOR chip_ predators_NCE 150Imagine you’re watching a slasher movie starring mud crabs as the protagonists.  A mud crab leaves the party in the muck under the oyster reef, where the other crabs are chomping down juvenile oysters.  As he pokes his head out from between a couple of shells, you hear a drumming sound and you shout at the screen “Don’t go out there!”

It’s fun to anthropomorphize some of the freaky looking residents of an oyster reef.  But these are the realities of living within the ecology of fear.  Predator cues have a definitive impact on how the smaller, intermediate consumers such as mud crabs behave.  That’s what David Kimbro, Randall Hughes & co. are studying in Alligator Harbor and at their sites across the southeast.  Large predators send certain cues to their prey- perhaps a certain way they move in the water, perhaps.  When the prey species sense that the predators are near, they cease activity- including the eating of juvenile oysters.  That is how large predators help maintain a healthy oyster reef- they make intermediate consumers (mud crabs) eat less of the basal species (oysters, the foundation of the oyster reef habitat). Continue reading