Glowing green

When the winds let up during the summer, sometimes you can find gelatinous animals washed up on the beach — e.g., jellyfish, hydromedusae, siphonophores, ctenophores (also known as comb jellies), and salps.  (I'll show some examples of these animals during the next week.)  

Several days ago I noticed quite a few gelatinous animals, and I was especially curious about some of the comb jellies.  This particular comb jelly (Beroe sp.) doesn't look like much once it ends up on the beach.  It could even just look like a thin patch of slime with a pinkish hue:

 

But if you look closely, you can see long parallel lines running from one end to the other — that's your first clue that it's a comb jelly (rather than a jellyfish).

I was looking at these lines (called comb rows) when I thought I saw some green coloration:

 

In my experience, it's unusual for the comb rows to appear green, so I zoomed in for a closer view:

 

Definitely green!  So what's going on?

Most (but not all) species of comb jellies are bioluminescent.  That means they can emit light via an internal chemical reaction.  Bioluminescence is often more visible in the dark, so I was a little confused about what I was seeing...and I still am.

On this web page about bioluminescence, I read that "there are strong antioxidant properties to luminescent reactions (i.e., they mop up oxygen radicals) so there may be light produced internally during protective reactions."

Could this be what has happening with the comb jellies washed up on the beach?  I'll have to ask around, but I thought you might like to see the photos, and perhaps you have some ideas about the green color in these comb jellies:

 

P.S.  Several years ago I showed pictures of this species of comb jelly swimming.  If you'd like to see those pictures, check out the post called "The Pink Predator — Part 2" from 3 November 2014.