Posts Tagged ‘oysters’

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.

Five Star Day on West Island

Monday, October 13th, 2008

This afternoon we explored the shoreline of West Island in Fairhaven, Massachusetts.  West Island lies on the western shore of Buzzards Bay across the water from Woods Hole, Falmouth and Naushon Island on the east side.  The weather varied from overcast to broken sunshine with temperatures in the chilly 50s and a strong easterly breeze blowing in off the bay and ocean.

West Island on Left; Buzzards Bay in Center; Falmouth & Woods Hole on Right

West Island is not normally a specimen collector’s delight with shoreline filled inches deep and yards thick with codium and eel grass, but we chanced to arrive at dead low and we decided to explore the exposed tidal pools at the southern point of the island.

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West Island Shoreline with Heavy Codium & Eel Grass Wrack

It proved a five star afternoon: seastars, that is.  We had never found seastars on West Island before, but today they seemed scattered throughout the southern tip of the island, hiding in pools of water under rocks, foraging in tidal pools and hectored by ubiquitous seagulls.

First Seastar (Asterias forbesi) on South Point of West Island

Seastars (Asterias forbesi), often popularly called starfish, have five “arms” which can regenerate.  In fact, the natural history says that a seastar needs only a segment of the central disk along with one arm to regenerate into a new seastar.  We should be so lucky!  With mostly cloudy skies, brisk winds and chilly temperatures, seastars were moving even slower than their normal sluggish pace.  But while conditions weren’t in their favor, they did present us some great opportunities to document these magnificent critters.  The following sequence from our first seastar gives an overview of the creature’s dorsal (top) and ventral (bottom) sides.

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Seastar under Rock; Dorsal (top) and Ventral (bottom) Views

Seastars have spiny skin and belong to the phylum echinodermata along with sea urchins and sand dollars.   The top or dorsal surface of a common seastar consists of numerous scattered spines. Each of these spines are, in-turn, surrounded by tiny jaws called pedicellariae. The pedicellariae remove sand and other debris and occasionally snag passing prey.  The ventral (bottom) surface of the seastar’s arms is covered with tube feet that have suctions at the bottom of each foot.  Each tube foot works in coordination with other tube feet enabling the seastar to grasp prey or move about over various surfaces.  The orange spot in the dorsal core is called the madreporite and is responsible for the movement of water into the vascular system that controls the movement of the tube feet.  The clip below shows the tube feet in action as it moves a shell along one of its arms.

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Seastar Tube Feet on Ventral (bottom) Side of Arms

Seastars are said to prefer clams, quahogs, oysters, et cetera as prey, but will consume snails in a pinch.  Tube feet on the ventral (bottom) surface act like suction cups, securing each side of a bivalve shell while the arms pull them open.  The seastar then inserts one of its two stomachs into the prey and digestion occurs inside the clam, turning the mollusk into liquid that is guided into the seastar’s mouth by cilia on its arms.  The seastar sucks up the liquified clam.

Ventral Surface with Lots of Shelled Critters Moving Along Tube Feet

The second seastar we encountered had previously regenerated one of its arms which was obviously smaller than the other four.  This ventral image below illustrates the size difference.

Seastar with One Regenerated Arm

More active than the first seastar we had discoverd, this one showed off its speed as it “dashed” along a shallow tidal pool.  I know there are some who say that observing a sailboat race is akin to watching grass grow, but it’s clear that those folks have never invested time as spectators in the ultimate sport of champions: seastar racing.  If you have time to invest, we encourage you to enjoy the next two exquisite videos, beginning with the tube-foot dash through the tidal pool.

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Seastar Glides through Tidal Pool

For those who have survived the previous experience, you are well prepared for the ever-exciting seastar sport of gymnastics; that is, tumbling 180 degrees from ventral up to dorsal up.  Judging is based on artistic content, plus degree of difficulty.  A perfect five point landing earns the highest points, especially from the Eastern European judges who are more technically oriented.

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Seastar Acrobatics

We found another seastar hugging the underside of a rock and rescued a fourth from the ravages of pestering seagulls.  The fifth and last seastar we almost missed because it looked more like a butterfly lying in a shallow pool.  It had lost three of its arms and we thought we had run across a goner. 

“Butterfly” Seastar with Only Two Arms

But a closer examination revealed that this seastar had healed from its injuries and was a lively and healthy critter, perhaps proving the point that chopping up seastars only serves to create more seastars!

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Healthy Two-Armed Seastar

A surprising day for the Turtle Journal team.  Temperature, wind, clouds and season conspired against us.  But the gods smiled and gave us quite literally a five star day.