Periwinkles Anyone?


Look what the seagrass brought up with it- Periwinkles!!! Each time I am with the Eelgrass Blitz group from North South River’s Watershed Association   something new shows up with the eelgrass.  On this almost stormy Friday morning in July, we were set up with Captain John’s boat to conduct our water quality monitoring. Another thing that I love about the eelgrass blitz is the community of kindred spirits sharing a passion for our oceans.

Isaac Mann and Patrick Scott are both studying Environmental Sciences and were both excited to be working in the field documenting eelgrass. I noticed that this year every thing went digital. There was a new app that the summer interns were responsible for, that shares data automatically. Cool!

Since 1980, 75 % of the eelgrass in Duxbury, Plymouth and Kingston Bay has been disappearing.  I have personally been out 4 times  conducting these surveys and it’s been bitter sweet.  However, each year there is a sense of hope as we begin.

We started by plotting the GPS locations of previous seagrass sites. Then we we located the sites and anchored the boat. Here, in the above photo Isaac is sending down the waterproof camera. 


Then Isaac is checking the camera to see what’s going on at the bottom. We checked for eelgrass on four corners of the boat. We were disheartened to find nothing  in almost five of the first sites we went to. Then, we noticed  a couple of blades at site six. We were overjoyed we found inklings of eelgrass!

It turned out that these two sporadic blades didn’t give us much to sample.  In the past all these sites were thriving and bustling with seagrass and life. Water quality issues( run offs) along with rising temperatures are having a drastic affect on the eelgrass population which in turn affects the food web, including fish.  John our captain, an avid fisherman in both the rivers and the bay, pulled out his fishing rods to see if he could find any fish. Nothing. It became clear why there were no fish. Without seagrass, there is no nursery or an abundance of food for the fish. 

We continued our data collection by sending down a metallic water translucency reflector plate. This basically is hoisted down until it becomes no longer visible. We measure the depth of visibility with a tape as shown below and pop in the info into the app.

Several more sites showed no eelgrass, then finally at site eleven we hit jackpot! I think everyone came and snapped a photo of our finding. This was like a pot of gold. ( Actually wouldn’t that be amazing, if we could place monetary value  to this fragile ecosystem- then everyone would be invested in growing more- I think this is another story)

So this is what a healthy seagrass meadow should look like. Next we caught some floating eelgrass blades to measure and document. Here is Patrick with his find:)

Once we had samples the measuring could begin.  The length, width and general condition of the blades were uploaded to the app with a photo. 

Back to my exciting find of the the day- Periwinkles!!! These gastropods look utterly majestic on the eelgrass blades!

They have a great curvilinear shape and an almost musical sounding name: Littorina Littorea! 

They are interesting mollusks that are also non-native to Massachusetts. They apparently came on boats with the Europeans in the 1800s. These gastropods( AKA snails) are also food for humans and are eaten in Europe and other parts of the world. Some fossil findings are dating the Canadian influx back to possibly Viking times. Fascinating! 

Cool Facts on Periwinkles(From the Smithsonian):

  • This snail reaches a mature size in one year and has a life span of at least 5 years.
  • Sexes are separate, with males slightly larger than females, and fertilization is internal
  • The egg capsules are usually suspended in the plankton and can be abundant in nearshore waters. The eggs take about 6 days to hatch into planktotrophic veligers, which remain in the plankton for 2-4 weeks. The larvae settle with shells
  • Periwinkle inhabit the middle and upper intertidal zone, primarily of rocky shores, but also extending into mudflats and marshes.
  • They like to eat benthic algae; detritus; egg capsules.
  • They are eaten by crabs, fishes, shorebirds, & humans.

More on these beautiful creatures can be found in the link below:

 Smithsonian Institution


Why am I so mesmerized by  these tiny snails? They are beautiful,  have a wonderful color variation and shade that remind me of the rings around Saturn.  They also play an important role by cleaning off the algae on the seagrass blades. So they are like natural vacuums!

I think it’s neat that people also eat them. However, before you go jumping in your kayaks to collect a bunch of Periwinkles for lunch, be sure to check your local shellfish advisory board. There are many restricted areas due to biotoxin closures. Check with local  DMF updates  (978) 282-0308

or the website here:

Back to our amazing crew, a big thank you to Captain Johnathan Dwetwiler, an avid fisher and steward of our oceans. Also thank you to Isaac and Patrick from the  North South Rivers Watershed Association for giving us this terrific opportunity  to share in the joy of our oceans.