Posts Tagged ‘Predators’

European Invaders: Periwinkles

Saturday, October 18th, 2008

As we explore the intertidal zone, that area between low and high tide where land and sea are locked in eternal battle, where life must confront pounding surf one moment alternating with barren exposure to rasping winds the next, where creatures are attacked by water predators half the time and land predators the rest of the day, where everything is drowned in brine at high tide and then soaked in rain at low, a harsh clime of extreme contrasts that change as quickly as New England’s weather; as we search this region we find one of its more common residents, the languid and familiar periwinkle (Littorina littorea).  Some scientist sure wanted us to remember where this critter came from with both genus and species derived from the Latin littoralis (or litoralis) meaning “of the shore.”

Periwinkles and Barnacles

My earliest memories of Cape Cod sealife are of periwinkles dotting the rocky sidewalls of the canal where my mom and dad brought me each Sunday to fish.  Back then fishing was less commercial, yet not purely recreational, either.  Yes, it was a break from the intense six-day, back-straining work week, but no excurision was successful unless you brought home food that would supplement household resources, especially for meatless Fridays.  And while fish were plentiful and Sunday after Sunday yielded flounder or cod or tautog or bass for the family table, there were days when the fish just “weren’t biting” and we had to look elsewhere on the food chain to meet our needs.

Blue Mussels

Next down our list were blue mussels that grew in large colonies on the old mud flats near the railroad bridge.  Back in those days few people ate mussels.  So, it’s amusing five decades later that you can’t read a seafood menu without mussels marinara or mussels something.  But if the tide was too high and our access to the flats was cut off, there was always one last food source to exploit: periwinkles.  They may have been small, but they were plentiful, very plentiful.  And no one, no one ate or even thought of eating periwinkles.  Yet, mom sauteed them in butter and garlic, then tossed them into her fresh spaghetti sauce for flavoring instead of pork or beef on meatless Fridays.  Many years later when I visited my parents and brought them out to dinner at a fancy Boston restaurant, I suggested to mom that she try the escargot, sauteed in garlic and butter, as an appetizer.  She looked at me as though she had raised a barbarian.  “Snails!  You want me to eat snails!”  I smiled, apologized and suggested the mussels marinara.

Periwinkle (Littorina littorea)

While an extremely common critter along our rocky shores, jetties, dock pilings and tidal pools, periwinkles are not native to North America.  They are an invasive species introduced into the Northeast perhaps sometime in the 19th century.  First documented in Nova Scotia in the mid-1800s, periwinkles can now be found in plentiful numbers up and down the Eastern Seaboard.  Whether they were brought to our shores deliberately as a favorite food of European settlers or they hitchhiked across from Europe in ballast water or clinging to creases in ship plankings, the method of their arrival is clouded in history.  They are consumed extensively in Europe today and are increasingly being harvested from New England shorelines.

The main body of this small, shell-covered snail is comprised of a large foot, head and mantle, covered with a protective operculum (see image above).  The operculum, a tough, horny “door” snaps the snail’s soft, vulnerable body into the shell during dry spells such as low tides. 


Periwinkle Anatomy


Two antennae (chemosensory organs) peek out from a fleshy foot.  In the image above you can see one eye near the stem of the higher antenna and the snout between the two antennae.  The sole of the foot is the curved white surface behind (below) the operculum.  The muscular, mucus laden foot enables the periwinkle to move along rocky boulders and transverse rocky and sandy shores in search of food.  Periwinkles are herbivores.  They graze copious amounts of algae such as the the macro algae sea lettuce (Ulva lactuca) and much smaller diatoms (phytoplankton).



Periwinkle in Action


Factoid:  Periwinkles have a serrated, rasping, knife-like tongue called the radula.  The radula scrapes algae from rocks.  (In other snail species, the radula bores through hard shells like quahogs, oysters, et cetera.)  For periwinkles, the algae is mixed with mucus and then passed into the digestive track.

Predators include crabs, seastars, birds and now a voracious worldwide human population.

As Arrival of Fall Speeds Up, Turtles Slow Down in the Great White North

Thursday, September 18th, 2008

Raw, blustery September has gripped terrapin nesting sites on the Outer Cape.  As temperatures plunge, hatchlings hunker down in their underground hide-aways, snoozing in the warm darkness, hoping and waiting for a sunny respite to heat up the sand and their bodies for the sprint from nest to safety in the abutting nursery habitat.

Temperatures Begin to Plunge Below 55F Activity Threshold

Yet, while they wait with quiet patience, predators act.  Mammals and insects sniff the odor of organic material issuing from the pipped eggshells.  These predators take advantage of the hatchlings’ stupor to snatch an easy meal.

Lethargic Hatchling and Potentially Viable Egg

Nest 996 fell victim to secretive plant and insect predators.  As we excavated the nest in the morning chill, we encountered egg after egg that had been attacked by roots, stilting embryo development and piercing the shell.  Once the egg is cracked, insects stream in and consume the organic material.  Near the bottom of the nest, we found a seemingly lifeless hatchling wrapped in an eggshell that we would have instantly discarded as non-viable.  Peeling the shell away, we found a healthy, if motionless hatchling.  And at the bottom of the nest, we removed one potentially viable egg that has been carefully transplanted to the “second chance” bucket where eggs go to finish incubation and hopefully achieve their full potential.

Excavating Six Sluggish Hatchlings

A few feet away we discovered a concavity in the sand that indicated that a pipped nest might lie beneath.  About four inches under the surface we found a half dozen hatchlings, some pipped but still inside eggshells, but others just snoozing the chill away.  Check out these sluggish babies once they are excavated as they lie about like cordwood, waiting for sunshine to warm their bodies before dashing to freedom.

September weather in the Great White North can be cruel for tiny hatchlings.  But a saving hand can make a world of difference for this threatened species by dramatically increasing the number of live hatchlings that enter the ecosystem each year.

Rescuing Live Hatchlings from Maggot Infested Nests

Wednesday, September 10th, 2008

No, it’s not a pretty thought.  It’s not a pretty sight and it’s certainly not a pleasant experience.  But it is the real world of terrapin conservation and so for the serious naturalist, it’s a necessary learning moment.  Be thankful that the pictures are two dimensional and that there is no smell-vision key on the video clip.

Research from September 2000 revealed for the first time that a significant percentage of diamondback terrapins nests in the Wellfleet Bay system were being destroyed  by fly maggots.  The infestation appears to begin at pipping when hatchlings poke openings in their eggshells allowing the odor of organic material to escape and to attract flies.  Since Outer Cape hatchlings remain in their shells and underground for several days after pipping, maggots have the opportunity to attack an extremely vulnerable prey as the maggots work their way through the cracked shell to devour the exposed hatchling.

Pipped and Vulnerable (Upside-Down) Terrapin Hatchling

In most cases, the maggots begin with the umbilicus and enter the main body of the living hatchling through the yolk sac, hollowing out the baby from within.  Thus, hatchlings and whole nests are destroyed by these insidious predators underground without ever being exposed for counting by researchers like nests preyed upon by more obvious predators.

Maggots Attacking Helpless Hatchling (Rescued)

Observations over the last nine seasons confirm the 2000 discovery and underscore the severe constraint this predation places on the number of live hatchlings that emerge on the Outer Cape each year.  This season (2008) alone has seen more than half of all nests in the critical habitat of Lieutenant Island infested with maggots.

Maggots Consume Hatchling Embryo

Thankfully, the aggressive conservation protocols developed after the 2000 discovery have rescued more and more hatchlings each year from this infestation.  By checking nests as they begin to pip and harvesting them at the first sign of maggots, our efforts have significantly increased the number of live hatchlings entering the system since the turn of the millennium.  Even after the infestation has begun, our actions can save most hatchlings from the most heavily infested nests.  We harvest the pipped eggs and remove all maggots before re-burying premature hatchlings in clean, moist soil to finalize the incubation process.  These efforts have rescued thousands of hatchlings that would never have seen the light of day.

Hatchlings Rescued from Maggot Infested Nest

This particular nest on Turtle Point gave away its location by a concavity on the surface.  As hatchlings pip and squirm around inside the egg chamber, sand gets displaced and this underground activity shows itself as ripples of the surface sand to the most seasoned turtle researcher.  We were able to rescue 10 baby hatchlings from the devouring horde of maggots in this nest, hand-picking tiny maggots from limb cavities and off yolk sacs, then bathing the hatchlings in clean, fresh water for rehydration before release.  So, a good day in the Land of Ooze where we saved an order of magnitude better than our goal of one turtle at a time.

Two-Ton Vehicle Versus Quarter Ounce Hatchling

Sunday, September 7th, 2008

Due to human development and associated pressures, some of the best remaining nesting sites for diamondback terrapins on the Outer Cape are one-lane dirt roads that abut salt marsh nursery ecosystems for hatchlings. Obviously, roadways are extremely dangerous for the female as she spends more than 30 minutes digging her nest, depositing her eggs and covering it once again.  Because these compacted roadways are so hard, and her nest sculpting creates a natural arch to spread the load of vehicular traffic, the eggs appear to do fine through June, July and August as they incubate under the summer sun.

Female Terrapin Nesting in Middle of Dirt Road

But when hatchlings begin to pip and squirm about in the nest, and when one or more begins to tunnel to the surface leaving an emergence hole in the road, then the architectural integrity that served so well during incubation is compromised.  Weight no longer is evenly distributed, and the egg chamber compresses and begins to collapse under the stress. 

Emergence Hole in Middle of Marsh Road on Lieutenant Island

I discovered this little (3 gram) hatchling wedged under the lip of the nest that had been collapsing under the day’s traffic.  Two of its siblings had already been crushed in the center of the egg chamber.

Premie Hatchling Distorted by Road Traffic

In addition to problems with its distorted shape, its eggshell had been invaded by fly maggots that were trying to find a vulnerable orifice to invade.  I had to hand-pick these nasty predators from the tiny hatchling.  Based on experience, I know that this critter will now do quite well.  With a little time, some warm hydration and a bit of TLC, its shell will resume a normal shape and it should be ready to be released into the wild within a few days to a week.

Emerged Terrapin Hatchling Run Over on Marsh Road

I wish the same could be said for another sibling (above) that I found a foot outside the nest and squished in the south tire track of the dirt road.  It’s a dangerous world for a turtle hatchling.  Few survive to tell the tale of their harrowing youth.  But with a little luck and a guardian angel or two, one turtle at a time can be saved and the whole world along with it.

Close-Up of Rescued Distorted Hatchling