Invasive SpeciesDasysiphonia

Dasysiphonia japonica
NOT FOUND by srichman
South Portland
ID Confirmed
Quality checked by SRichman
Peer reviewed by Marine Biology Class
Field Notes
Today, May 19, 2015, I went to Spring Point Marina early in the morning to get some plankton samples. As I walked along the docks, I noticed a lot of filamentous red seaweed growing on the cement walls. I often find filamentous reds attached to the underside of the docks, but this species seemed to be really abundant. I was concerned that it might be the invasive species, Heterosiphonia japonica, now called Dasysiphonia japonica, taking over the area. I collected a sample for us to examine under the microscope at school. Everyone in the class examined this seaweed, but there was disagreement about its identity. Ten out of sixteen people combined their observations for this entry.
Supporting Evidence
Photo of my evidence.
We know the red seaweed is not Heterosiphonia japonica because the branches of the seaweed we examined are multiple cells thick, while H. Japonica has side, or smaller, branches that are one cell thick. Therefore these are two different species of red algae. In most of our samples, all branches are the same thickness or appear to be. Using more scientific terms, in Heterosiphonia, the main branch is polysiphonous, and the smaller side branches are monosiphonous.
Photo of my evidence.
Our seaweed has sections of rounded cells, or little bulbs, inside the branches. This is something not found in the rectangular cells of H. Japonica. The seaweed in question is not H. Japonica. These might be reproductive structures
Photo of my evidence.
Heterosiphonia growth is axial, not dichotomous. Our specimen grew dichotomously, or split into twos. Because of the two different growth patterns, they cannot be the same species. Plus, there aren’t irregular side branches that appear “hair like” and narrowing like those of Heterosiphonia. The side branches of our seaweed appear thick
Species Observation: Species Looked For
Did you find it?: 
I think I did not find 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 43.649568 °
W -70.230900 °
Observation Site Information
A photo of our study site.
Coastal - Dock
Trip Information
Spring Point Marina
Trip date: 
Tue, 2015-05-19 06:35
Town or city: 
South Portland
Type of investigation: 
Species Survey
Time of low tide: 
Tue, 2015-05-19 06:36


What a great observation and dialogue! With the incredible photos, great evidence to rule out Heterosiphonia/Dasysiphonia, and field notes to boot, I've submitted this as a Best of Vital Signs candidate to the VS team. Many hands do make great work it seems.


This looks like a Polysiphonia species to me.

We believe this species is Polysiphonia denudata. Polysiphonia denudata branches are three to four cells thick in the lower axis. The sample we looked at had three to four cells as well. Other Polysiphonia species like Polysiphonia nigra and Polysiphonia fucoides have many more cells in its branches ranging from 6-9.