Cephalopodcast

Florida Surf Clams (aka, Coquina, Donax variabilis), © Jason Robertshaw

What the Shell Is That? is my series on beachcombing and tidal life. Living on the west coast of Florida, it is mostly about shells, but can also be about other flotsam, fauna and even flora.

Note:
This is a bonus, double-feature entry. You get the WSIT #5 and Cephalovlog #4 combined in one.

Florida Surf Clams (aka, Coquina, Donax variabilis)

Date: 6 April 2008
Location: Siesta Key, Sarasota, Florida, U.S.A.
All along the surf.

Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Order: Veneroida
Family: Donacidae
Genus: Donax
Coquina Clams (Donax variablis)

Report:
Surf clams, also called Coquina, are bean-sized (2 cm), colorful bivalves that make their living in one of the most challenging habitats, the surf zone. They are filter feeders, extending their siphons into the water as it washes over them. As the wave pulls back out, they are often exposed at the surface and have to quickly put their muscular foot down to scoot back beneath the sand. It seems like a very energetically expensive way to make a living and it’s surprising they get enough nutrients from just filtering bacteria and algae out of the water (but still further proof that even the tiniest mollusks are tough enough to whip any echinoderm’s hiney).

The clams, in turn, are an important food source for shorebirds. People seem to like them too, but personally I have never eaten them before. The shells of these animals also accumulate over time and mix with other sediment to form a consolidate material called Coquina rock. It is used as a building material throughout Florida.

Something else that was remarkable, and requires more investigation, was the presences of hundreds of small marine worms. You can see a close up in the video about half way through. These worms would suddenly appear in the hundreds, wriggling after a wave wash, only to disappear instantaneously beneath the sand.

Cephalovlog #4: 60 Second Surf

I borrowed the Sanyo Xacti E1 from work for a field test. This little camera is immersible to 5 meters. I did not need to send it that far down to video these little guys, as they are in the wash zone of the beach. Video was edited in iMovie and scored in Garageband. Note, this is not time-lapse footage. The clams really do dig that fast.

Donax me

References

• Ruppert, Edward and Richard Fox. Seashore Animals of the Southeast. Columbia: University of South Carolina Press, 1988. pp. 158.
• Witherington, E., Blair and Dawn Witherington. Florida’s Living Beaches. City: Pineapple Press (FL), 2007. pp. 109.

Additional Links

• YouTube: Cephalovlog #5
• Wikipedia: Donax
• Wikipedia: Coquina rock
• SeashellGuide.com: Coquina: Catching “Butterflies”
• FL Fish and Wildlife Research Institute: Coquina Clams

Mesoglea (tissue) from a sea jelly, © Jason Robertshaw

What the Shell Is That? is my series on beachcombing and tidal life. Living on the west coast of Florida, it is mostly about shells, but can also be about other flotsam, fauna and even flora.

Note: I spent a lot of the last week traveling, so did not get a chance to hit the sand. So this is a WSIT encounter from a couple of months ago.

Sea Jelly Mesoglea

Date: 1 December 2007
Location: Siesta Key, Sarasota, Florida, U.S.A.
All along the surf.

Report:
Back around Thanksgiving of last year there were reports of increased numbers of sea jellies in Sarasota Bay. On several occasions I witnessed New Pass awash with numerous drifting moon jellies and sea nettles. Local reports suggested there might be some connection with the extended drought that we were/are experiencing and that an increase in the salinity of the bay contributed to the presence of the jellies.

What I actually found on my walk that day was the eroded remains of some of these creatures. I can’t be sure which ones because there was not much left. The more delicate tentacles and tissue wear away in the intertidal, leaving the denser mesoglea in the surf. Mesoglea is the gelatinous material between the outer and inner cell layers of the sea jellies. It is made of collagen-like connective fibers and tissues. The material is actually pretty resilient, feeling more like a contact lens than like jello.

Coincidentally, the Beachhunter also has a gelatinous post up today. Check out David’s entry Man-of-War Jellyfish Video Clip & Photos.

Also, if there are any budding biologists out there who would like to answer this question, you have a few days left: Why is the mesoglea really thick in medusa and really thin in polyps?

References

• Ruppert, Edward and Richard Fox. Seashore Animals of the Southeast. Columbia: University of South Carolina Press, 1988. pp. 26.
• Witherington, E., Blair and Dawn Witherington. Florida’s Living Beaches. City: Pineapple Press (FL), 2007. pp. 39.

Additional Links

• Sarasota Herald Tribune: Jellyfish inundate Southwest Florida bays; drought may be to blame
• BeachHunter.net: Man-of-War Jellyfish Video Clip & Photos

Parchment tube from Chaetopterus mixed with thousands of dead urchins, © Jason Robertshaw

What the Shell Is That? is my semi-irregular series on beachcombing and tidal life. Living on the west coast of Florida, it is mostly about shells, but can also be about other flotsam, fauna and even flora.

Parchment Tube Worms (Chaetopterus sp.)

Date: 12 March 2008
Location: Siesta Key, Sarasota, Florida, U.S.A.
All along the wrack line.

Kingdom: Animalia
Phylum: Annelida
Class: Polychaeta
Order: Spionida
Family: Chaetopteridae

Parchment Tube Worm (Chaetopterus sp.)

Report:
We had some storms roll through recently that managed to dislodge quite a number of benthic invertebrates. All kinds of critters were washed up on the beach, some in the thousands. There were worms, sea urchins, sea shells and seaweeds of all different kinds and colors. It was good pickings for the beachcombers but even better pickings for the shore birds.

One of the castoffs that piled up in the wrack line were the casings from parchment tube worm (Chaetopterus veriopedatus). Normally these worms burrow into the sand with either end of the tube poking out (see illustration here). The worm itself has several highly modified, bell-like paddles that they beat inside the tube to maintain water circulation. One of the neatest aquarium exhibits I’ve seen was a live Chaetopterus placed inside some clear vinyl tubing. It was thereby possible to watch the rhythmic beating of its paddles. Here’s a photo of a similar set-up.

Another critter that my wife found was one that has long been on my life-list but is so obscure I did not recognize it at the time (hence the poor picture). It was a Polyonyx sp., or a commensal porcelain crab that lives almost exclusively in the tubes of parchment worms. It is rare to find them anywhere else and this one presumably was dislodged from one of the many casings on the beach. You might note how it’s claw seems oddly bent. It wasn’t broken but appeared to be shaped that way.

There were also casings from another type of worm called the decorator or plumed worm (family Onuphidae). You may have heard about the recent debunking of bug eyespots as being mimicry. Well there is a similar amazing story underwater with these creatures. Recent research from Sarah K. Berke and Sarah A. Woodin (University of South Carolina) suggests that the Onuphid’s tube decoration may not be for camouflage after all.

References

• Ruppert, Edward and Richard Fox. Seashore Animals of the Southeast. Columbia: University of South Carolina Press, 1988. 203.
• Williams, Winston. Florida’s Fabulous Seashells. City: World Publications (Tampa, FL), 1988. pp. 39
• Witherington, E., Blair and Dawn Witherington. Florida’s Living Beaches. City: Pineapple Press (FL), 2007. pp. 125.

Additional Links

• Woods Hole Marine Biological Laboratory: Chaetopterus variopedatus (Tube Worm). Includes nice pics of the worm and Polyonyx.
• Polychaet Diverstiy and Feeding: Chaetopterus
• Science Musings: Red fish, blue fish…
• Google Docs: A Study of the Life History and Habits of Chaetopterus Variopedatus, By Howard Edward Enders (Published 1906)
• Biological Bulletin Online: Tube Decoration May Not Be Cryptic for Diopatra cuprea (Polychaeta: Onuphidae) Berke and Woodin Biol Bull.2008; 214: 50-56
• National Geographic: Hawai’i’s Unearthly Worms
• ScienceDaily: Zoologists Challenge Longstanding Theory That ‘Eyespots’ Mimic The Eyes Of Predators’ Enemies

Eggcase from a skate. © J. Robertshaw

The Great Eggcase Hunt

With the coming of spring in the northern hemisphere also comes a time to hunt for eggs. But it’s not just about birds anymore. The folks over at the Shark Trust also want people to head to the beach to look out for the fecundity of fish.

Colloquially known as mermaid’s purses, eggcases are the protective capsules laid by skates and some rays**. Inside is a tiny baby skate and a big yolk sac. Typically the capsules have odd keels and horns to help them remain tangled in seaweed and camouflaged on the bottom. The young develop for several months before hatching out as miniature adults. But after hatching, the horny cases begin to breakdown and may come loose, washing up on the shore. Storms might also dislodge living ones from the bottom. If you find a lot of eggcases in an area, it may indicate that a skate nursery is located nearby. This kind of information is valuable to conservationist who are trying to protect these species.

Why does the Shark Trust want you to record eggcases? In recent decades several species of skate and ray around the…coast have dramatically declined in numbers…The identification of these critical areas will enable the Shark Trust to propose conservation measures, in order to reverse the decline of these charismatic animals.

So now’s your chance to contribute to skate and ray conservation and have a lot of fun at the same time.

They have a lot of resources for citizen scientists and for educators who want to organize a local eggcase hunt. And if you don’t live near the coast, you can still take some time this spring to create your own giant eggcases (PDF link) out of balloons and papier-mâché. Or better yet, make some chocolate ones that you can send to me!

• Great Eggcase Hunt
• A Fieldguide to Eggcases (PDF)
• **What’s the difference between a skate and a ray?

Rabbitfish Helping to Save the Reef

Continuing with my aquatic version of things vernal, there is news that rabbitfish might be helping to save the Great Barrier Reef. Many herbivorous reef fish species like parrotfish and tangs regularly graze on the fast-growing algae of the reefs. But apparently they only like to eat it when it’s young and not too weedy. This is where the rabbitfish comes in.

“Then, to our even greater surprise a fish we had never seen in this area before was observed grazing on the weed. The rabbitfish (Siganus canaliculatus), came out of nowhere and began to clear-fell the weed placed on the reef crest.”

The rabbitfish were caught on underwater videocams, in schools of up to 15 fish, grazing the crest, slopes and outer flats of the reef, and chomping away at more than ten times the rate of other weed-eaters.

• Red Orbit: Rabbitfish Helping to Save the Great Barrier Reef
• Science Daily: Rabbit Fish To The Rescue Of The Reef

sƎʇɐʞs ɹƎɥ :ɐ*

I have not gone out to the beach as much as I had hoped when I first started What the Shell. But not too far from the horse conch, we found this little fellow.

Stone Crab (Menippe sp.)

The one pictured below is probably a juvenile M. mercenaria, the Florida Stone Crab. That’s based on the range; I haven’t found anything definitive yet.

2 September 2007
New Pass, Sarasota, Florida, U.S.A.
Found crawling on a dead quahog shell.

Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Suborder: Pleocyemata
Infraorder: Brachyura
Superfamily: Xanthoidea
Family: Menippidae
Stone Crab (Menippe sp.)

Gortoning Myself

I am probably Gortoning myself with this one, but stone crab season begins today in Florida.

Only legal-sized claws (2 ¾ inches) are harvested in the stone crab fishery; crabs are returned to the water alive to generate new claws. Approximately 13 percent of commercially harvested claws are regenerated. The fishing season is open October 15 through May 15 each year, but the harvest of egg-bearing female crabs is prohibited at all times.

Most of the sources on stone crabs note that this is a “sustainable fishery,” owing to the notion that the crabs will regrow their claws. The rate of regrowth varies, taking anywhere from one to three molts before the new claw approaches the same size as the one removed. The molting rate depends on the initial size, sex and environmental conditions of the animal, among other things.

Duress of the Dungeness*

You can file this under duh, but Mark recently noted some new research that indicates crabs with claws removed have increased stress levels which could affect survival rate. As picked up by ScienceDaily:

Professor Bob Elwood, from the School of Biological Sciences studied crabs’ reaction to declawing. Crabs felt increased stress and had a lower survival rate after the removal of one claw.

Professor Elwood said: “We found a strong stress response within ten minutes of taking off one claw and this stress remained after 24 hours. The stress response was greater if the crab was declawed rather than being induced to cast off a claw. So, the stress is not due specifically to claw loss but to the manner of the claw loss.

I don’t imagine most folks will pay much mind to this news. But personally, I’ve cut back tremendously on the amount of meat I consume, mostly for ethical and environmental reasons. And this research doesn’t incline me make an exception for crustaceans, no matter how deliciously sustainable they may be.

Sources

• Blogfish: Removing claws is harmful to crabs
• ScienceDaily: Declawing Crabs May Lead To Their Death, which is a rehash of the original press release from Queen’s University, Belfast.
• NOAA FishWatch fact sheet: Gulf and Florida Stone Crabs (Menippe adina and Menippe mercenaria)
• The 2006 Stock Assessment Update for the Stone Crab, Menippe spp., Fishery in Florida
• A Proposed Evolutionary History of Stone Crabs
• Observations of the Stone Crab Commercial Fishery. From the 2006 season, with a couple of nice vignettes by Florida Wildlife Commission field crew members.
• Creative Loafing, Sarasota: ‘Tis the Season, Sandy claws are coming to town. Brian works in an jab at vegetarians in both the print and podcast versions.

*Forgive me the poetic license, I know they are different species. This also concludes my Blog Action Day report.