Tiny shells and spines

Well, I'm running out of time tonight, but I thought it would be fun to share this photo:

 

While doing intertidal surveys this past weekend, we noticed quite a few Sandcastle Worm (Phragmatopoma californica) tubes that were built primarily out of Foraminifera (informally called "forams") shells and small sea urchin spines.  [Forams are single-celled amoeba-like protists.]

More often, these worm tubes are made of darker colored sand grains (see the post "A close call" for examples of the more typical tubes).  But the tubes we saw this weekend really stood out — beautiful white foram shells cemented together with green and purple urchin spines and skeleton pieces.

I'm not sure if the forams are more common right now for some reason, but the worms sure did a good job at finding them and using them to build their tubes!

Meet Noctiluca

A couple of days ago I posted some pictures of the bright orange Noctiluca concentrations along the coast.  On the way to work today, Eric noticed a few orange patches along the shoreline of Bodega Harbor.  We scooped some up and later took photos under a microscope to share what the actual organisms look like.

Here's the first view.  Remember that these are single-celled organisms called dinoflagellates.  Each individual is ~1-1.5 mm across.

 

You can see that they're rounded and shaped somewhat like balloons.  The outer surface of the cell is soft.

With a closer look, and when viewed at the right angle, you'll notice that there is a strong ventral groove giving Noctiluca a pinched or kidney-shaped appearance (someone else said it reminded them of a lily pad).

Within the ventral groove there is a tiny flagellum (not visible in these images), a small tooth (also not visible), and a large striated tentacle.  The tentacle is easy to see on several individuals in the next two images.  

 

 

Inside each individual you can see the cytoplasm concentrated in thin, interconnecting strands that extend to the edge of the cell.  These strands are visible in all of the photos, but are more distinct under greater magnification (see below). 

 

At the top of the image above, you can also see one individual undergoing binary fission  — it's splitting into two.

Noctiluca uses its long tentacle to capture food and sweep it into a slit within the ventral groove.  They engulf their food (e.g., diatoms and other dinoflagellates) and store it in temporary compartments called vacuoles.  If you scan these images, you'll see food particles stored inside the cells.  Most of them look pink in these images (the color depends on what Noctiluca has eaten). 

Noctiluca itself is mostly clear, so you may be wondering why the dense patches observed in the ocean are so orange.  The color of the patches probably comes from the pigments (e.g., carotenoids) contained within the food that Noctiluca ingests!

 

The Smithsonian's National Museum of Natural History has summarized  information about Noctiluca and provides several helpful photographs and illustrations.  Go to their marine dinoflagellates web page and then click on the link at the top where it says "Plate 30, Figs. 1-4."

Orange by day, sparkling by night

 

Looking out at the ocean today from Bodega Head, there were bright, almost glowing, orange bands everywhere you looked.  

Here's a view to the north along the Sonoma Coast (below).  Some of the patches were quite concentrated, while others were more diffuse.

 

The color was so intense that it was sometimes hard to believe.  The next two photos show waves approaching Salmon Creek Beach.

 

 

And here's a close-up of the color in a wave approaching the outer coast of Bodega Head.  (Although I used a polarizer, I didn't enhance the color in any way.)

 

These are accumulations of Noctiluca, a dinoflagellate.  Dinoflagellates are protists, single-celled animal-like organisms that are often motile.  Noctiluca is heterotrophic — they can't make their own food like algae or plants can, but instead eat other organisms (such as diatoms, other dinoflagellates, and bacteria).

You might see these events referred to as "red tides," although in this case I'm not sure it's the most accurate term. It's not really red, and it's not really related to tides.  

 

It's important to remember that not all of these events are toxic.  I've read that Noctiluca does not produce toxins...although at times the dense concentrations might produce anoxic conditions or high levels of ammonia.

Some species of Noctiluca are famous for their bioluminescence at night.  Noctiluca means "night light" and is commonly called "sea sparkle."  I'd be very interested in hearing about any signs of bioluminescence at local beaches!  [ADDENDUM (4 October 2012): I've since learned that Noctiluca might not be bioluminescent in the Northeast Pacific Ocean.]

While taking these photographs, I noticed a few Gray Whales among the patches.  I wondered if the whales would avoid the Noctiluca, or if they would be attracted to it or other animals feeding on or associated with it?  Sometimes they surfaced right in the middle of the patches.

 

 

Noctiluca is microscopic, but may reach 1-1.5 mm in length.  If you'd like to see what the actual organism looks like, there's a nice illustration here (top three drawings).