Fluorescent Life in Seaweed

Seaweed floating along shore, Quisset Harbor, MA

On a recent trip to Cape Cod I grabbed a random sample of seaweed floating by the shore in Quisset Harbor. Just enough to not overfill a plastic take-out food container. I took it back to my stereo microscope fitted with our fluorescence adapter. Wow! The diversity of life was phenomenal for this tiny little slice of the ocean. And of course I focused on the fluorescent life in the sample. I spent just a few hours collecting images but could have spent days. Here is a selection of the results.

First of all, what the heck is this?

I have no idea. Looks like a little piece of not-very-much in white light but stunning in fluorescence. If you have an idea what this is please let us know.


This is the free-swimming medusoid stage of an animal of the class Hydrozoa. The other part of its life cycle is spent as a stalked bottom dweller. I was scanning over the sample when this little guy (about 4mm) came gliding by. A gorgeous green-fluorescent swimmer. It was hard to photograph because it was constantly moving, so after getting a few blurry shots I transferred it to a dish with too little water to move around in.


Ostracods are bivalve crustaceans. This one was just a couple of millimeters long.


Chlorophyll has a characteristic red fluorescence, and you can see that in some of these images. The bright yellow comes from phycoerythrin, a photosynthetic accessory pigment in the red algae. In a healthy plant phycoerythrin absorbs light and transfers the energy to chlorophyll with high efficiency, so there is not much fluorescence from the phycoerythrin itself. When the plant starts to break down such as with this uprooted, floating seaweed the connection to chlorophyll also breaks down. The absorbed energy is no longer used for photosynthesis and some of it is emitted as this intense yellow fluorescence.

It is very rare that we grab a random sample of something and don’t see some fascinating fluorescence. This world of spectral beauty is all around us, just waiting for more discovery and images. Explore!