Invasive SpeciesDasysiphonia

Dasysiphonia japonica
FOUND by RedRiots
Cape Elizabeth
ID Confirmed
Quality checked by 18 students in Marine Biology and a teacher
Peer reviewed by 18 students in Marine Biology and a teacher
Field Notes
Our Marine Biology class went to Crescent Beach on a grey, but mild morning in search of at least twelve different species of seaweeds. We are studying macroalgae and getting to know the local seaweeds. We limited our search to specimens that had washed up on the beach, in order to minimize disturbances to intertidal communities. Since we collected drift seaweed, we cannot determine exactly where these algae were growing. We know that seaweeds need a surface for attachment. Since our species were not bleached, we thought they got torn off of the surrounding ledges during some recent rough seas. We were wondering if we might find some southern species due to the warm ocean temperatures we experienced this summer and into the fall. We collected red, brown, and green samples, some familiar and some unknown, which we brought back to the classroom to press and identify.
Supporting Evidence
Photo of my evidence.
We examined the cells of our specimen and found that the main axis had rows of rectangular cells, similar to Polysiphonia, but the side branches were one-cell thick. We haven't seen this in any of the Polysiphonia species that we know. The main axis, or branch, seems to be 3-4 cells wide in our specimens. These cells do not seem as narrow as those found in Seirospora, although their size varied a bit among our specimens.
Photo of my evidence.
The clusters of branches made us question whether or not this was a native species. None of the other reds in our local guides showed two branches curving inward with many smaller, seemingly newer branches inside. We saw this again and again at various stages of growth, some just starting to appear. We noticed that the shape of the cells changed towards the tip of some branches, too. The branch in the upper-right side of the photo shows an example of this. We even found a pointed, banded tip, called an apex in some red species, that might be the early stages of these circular cells. Seirospora interrupta, in its reproductive state, possesses seirospores in rows, and photos on show both rectangular and circular cells on S. interrupta. S. interrupta is uncommon north of Cape Cod and is often found in warm bays and estuaries. Since the water off of Crescent beach was so warm this summer, we kept focusing on S. interrupta and other local reds, but none showed the branching clusters that we saw repeatedly on our seaweed. We examined photos of Heterosiphonia on alagebase and they included specimens with very similar growth patterns.
Photo of my evidence.
Many of us were drawn to this species by its bright red, almost pink, color. This seaweed is soft and delicate, not stiff and wiry like some reds. Once we read reports of this species in Cape Elizabeth, we began to examine more images online, since none of our guides included Heterosiphonia. This is an invasive species that has taken over regions in other parts of New England. This concerns us, since we found multiple specimens. We've been able to collect addition samples on return trips to Crescent beach, indicating that there might be an abundance of this species growing here. Ten out of seventeen students found this species during our trip to Crescent Beach. Other students may have the species, but they opted not to identify it for their project.
Species Observation: Species Looked For
Did you find it?: 
I think I found it
Scientific name:
Dasysiphonia japonica
Common name:
Sampling method: 
Just looking around
Photo of our sampling method.
Place Studied
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Map this species
N 43.563669 °
W -70.219614 °
Observation Site Information
A photo of our study site.
Coastal - Beach or dune
Trip Information
Crescent Beach
Trip date: 
Fri, 2012-10-19 07:40
Town or city: 
Cape Elizabeth
Type of investigation: 
Species Survey
Time of low tide: 
Fri, 2012-10-19 08:12


This is good stuff! It's great that you guys were thorough enough that other experts can jump right in and have enough info to agree with your finding. This is a big deal. I also like the thought of you guys being the front lines for ongoing research about this stuff, and looking for it in other places now that you know what to look for! VITAL SIGNS! Connecting those who know, with those who want to know, and with other people that may or may not know,..... you know?


To follow up on Carol's and Kathy Ann's comments, this is clearly Heterosiphonia, and our divers recently found it growing in situ in subtidal SCUBA surveys around Cape Elizabeth, including Fort Williams State Park, Two Lights State Park, and Kettle Cove.

On Tuesday, December 4, 2012 we went to Dyer Cove, Trundy Point, and Pond Cove, all in Cape Elizabeth. We searched each beach to see if we could identify Heterosiphonia by sight. We took samples from the three locations back to our classroom. Today, Thursday, each student examined two specimens from each site. 100% of the students positively identified Heterosiphonia. We were able to distinguish this filamentous red species from other filamentous reds in the field, and we confirmed its identity in the lab. We might go to Willard Beach and Mackworth Island to see if Heterosiphonia is present there.

Speaking for a Vital Signs Trained group of 5-6th graders at school on Mackworth Island, we'd love to either join you if you come out to look for Heterosiphonia OR if you give us clear instruction for field identification we'd be a happy to check around for you. Let us know. Collaboration is our middle name!

We think that you will be able to identify this seaweed. We will be posting more pictures next week. Take a look and let us know if you want to plan a joint trip or try it on your own. We can schedule an outing to Mackworth, if you want immediate feedback and/or instruction.

Did you ever get to posting more pics? Could you send a link? I THINK we can ID it but more pics and key characteristics to use in the field would be super helpful.


Did you search this spring? To complicate matters, a number of "spring" reds were all over the beach this season. They have the same color as Heterosiphonia, but not the same structure under the microscope. Still, all are beautiful to examine and you can tell them apart with close examination.

Hello Macworth! My name is Keirstan and I am one of the students that helped to ID Heterosiphonia. If you are interested, I could come for a visit and help you guys with your ID-ing.

Wonderful. Looking forward to more pics, and tips on key characteristics to look for. Happy to help.

We have a bunch of pictures in a Powerpoint, which we can share. People planning a visit can bring some actual samples, if we all promise not to be vectors contributing to the seaweed's spread.

Now that everyone is trained, I'd be especially interested in whether Heterosiphonia is showing up in the drift further Downeast. Any chance you could take students to mid-coast Maine? Or even farther afield? If not now, maybe we can organize something for next summer. I would be especially keen to use citizen and student scientists to highlight potential locations where H. japonica is washing up on the beach so that our teams of divers can then target those locations for subtidal surveys to verify abundance where it is actually growing on underwater rocky reefs.

Based on where you've looked underwater so far, where would you like to see the RedRiots and others look next for Heterosiphonia? The Vital Signs network in Maine is strong and definitely up for a challenge!

I agree with Kathy Van Alstyne- this is definitely Heterosiphonia japonica. My lab at U. Rhode Island, and Matt Bracken's lab at Northeastern U., are working on Heterosiphonia extensively. Thank you for this observation.
-Carol Thornber

I teach at Shoals Marine Lab and observed this species there for the first time in July 2011.

Your photo clearly showed the polysiphonous main axes and monosiphonous laterals of the invasive weed known as "Heterosiphonia" japonica. The generic status of this seaweed is not clear. -- but your specimen is clearly the invasive species.

This observation is incredible. How did you get those microscope photos? Those are amazing. I really hope this isn't the invasive red algae, but it looks like you have been really thorough.

And thanks for sharing info like - "We've been able to collect addition samples on return trips to Crescent beach, indicating that there might be an abundance of this species growing here. Ten out of seventeen students found this species during our trip to Crescent Beach. Other students may have the species, but they opted not to identify it for their project."

That seems like it could be really handy in terms of getting a sense of abundance.