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Tuesday, March 20, 2018

Polydora the Explorer

A few nights ago, I posted some photos of the hydrocoral, Stylantheca papillosa (See "Hello, hydrocoral!").  I also referenced a post from 2012 called "The hydrocoral and the worm."  Well, we have a friend who is interested in the worm that is associated with the hydrocoral, so we made an effort to obtain better documentation (including live video!) of this interesting spionid polychaete.  

As a reminder, here's a photo I shared from the research paper that first described Polydora alloporis:

From Light, W.J.  1970.  Polydora alloporis, new species, a commensal spionid (Annelida, Polychaeta) from a hydrocoral off Central California. Proceedings of the California Academy of Sciences 37: 459-472.

And here's your first view of a worm living in Stylantheca papillosa:

This worm is thought to live exclusively in hydrocorals.  [Note the earlier paper discovered the worm in a different species of hydrocoral, Stylaster (formerly Allopora) californica.]

You can see the "double-barreled" tube that the worm lives in.  A pair of tentaculate palps emerges from one opening, and the disc-shaped pygidium (or tail end) is sometimes visible in the other opening (see below):

The tentaculate palps are the most visible feature.  They're very active and are used to explore the surroundings and to capture food.  There is a prominent groove that runs down the middle of each palp.  When a food particle is captured either from the water or the surrounding surface the particle is moved down the food groove towards the mouth by cilia.  You can see particles in the food grooves below (white arrows):

Here's an explanatory diagram (below).  Note that the food groove is deeper in the middle of the palp and shallower near the base of the palp. 

Modified from Dauer, D.M., C.A. Maybury, and R.M. Ewing.  1981.  Feeding behavior and general ecology of several spionid polychaetes from the Chesapeake Bay.  J. Exp. Mar. Biol. Ecol. 54: 21-38.

As particles get closer to the base, they "ride up" into the shallower section of the groove and accelerate towards the mouth.  You can see this for yourself in the video below.

Watch for the following: (1) exploring palps, (2) food particles moving along the food grooves (from ~18-28 seconds and ~29-32 seconds), and (3) the posterior end appearing near the surface of the tube.

We have lots of questions about the relationship between the worm and the hydrocoral.  Does the worm steal food particles from the hydrocoral (from the surface or even from within the hydrocoral pores)?  Does the feeding activity of the worm help keep the hydrocoral free of debris?  How do the larval worms find the hydrocorals?  Do the juvenile worms take over an established hydrocoral pore?

Sunday, March 18, 2018

Blue and purple

Just a quick note about a couple of recent observations:

There were thousands of By-the-wind Sailors (Velella velella) washed up on Salmon Creek Beach on 16 March 2018.  Most were between 10-20 mm long (those are millimeter marks on the ruler in the photo), but many were smaller than that.  With a storm coming mid-week, there might be more Velella washed ashore.

We also spotted a few Purple Sea Snails (Janthina umbilicata) on 16 March 2018:

Although we haven't seen many Purple Sea Snails during 2017-2018, we remain curious about what oceanographic conditions are driving these pelagic snails onshore two years after an El Niño event (with which their appearances here are more often associated).

Saturday, March 17, 2018

Hello, hydrocoral!

I've always been drawn to our local hydrocoral, Stylantheca papillosa.    It appears as bright pink patches growing on rocks in the low intertidal zone:

Now that I have a waterproof camera, I thought it might be interesting to photograph Stylantheca under water.  During a very low tide in February, I found a patch that was submerged, plunged my camera under water, held the camera in front of the patch and took some pictures.  (Note that I couldn't really see what I was photographing at the time.) 

This was one of my first pictures.  (Each pore is ~1.5-2 mm across.)

Interesting!  And can you see those very slender thread-like things in front of the colony (especially in the lower right corner)?

I thought there might be something drifting in the water, so I moved the camera and tried again, this time a little closer:

With this view I could tell that those "threads" probably weren't random debris.  They looked like they could be tentacles associated with the colony.  At this point I realized how little I knew about this species.  Were those really tentacles?  They're so long!

I took more pictures, then the tide came in and I had to leave.  Here's another example of what I captured:

I was really puzzled about these tentacle-like structures and decided to do some reading about Stylantheca to learn what they were.  Well, it turned out this was not an easy question to answer!  I had trouble finding good descriptions of Stylantheca anatomy.  Eventually I found a couple of older papers from 1879 and 1938 that helped.

Hydrocorals (a type of hydrozoan) are colonial animals made up of different units with specialized functions, e.g., defense or feeding.  These long tentacle-like units are involved in protecting the colony and are called dactylozooids.  Note that their tips are slightly but noticeably swollen:

Since they have a defensive function, you would expect the dactylozooids to have a high concentration of stinging cells (like jellyfish or sea anemones).  To confirm this, we clipped one of the dactylozooids and looked at the tip under a high-powered microscope.

Check it out (below)!  The entire surface is packed with stinging cells (oval shapes).  At the lower right are three stinging cells dislodged from the surface.  When triggered, the cells rapidly fire tiny coiled harpoons called nematocysts, which appear as the long dark threads emanating from the battery of stinging cells.

Note that the dactylozooids are not always expanded.  Often they're retracted and look like short tentacles tucked inside the pores:

While learning about the dactylozooids, I read that the hydrocorals have feeding units (called gastrozooids) in the center of their pores.  So I went back and took more pictures, hoping I could capture an image of a gastrozooid:

And there they were!  In the center of the pores, can you see the little rounded polyp with tiny tentacles (nubs) around the perimeter?  The gastrozooids can withdraw to the bottom of the cavity, but they can also extend upward to the rim.  The gastrozooids have little mouths they'll open up to ingest food (either caught by their own tentacles, or possibly passed to them from the dactylozooids).

It took me a while to sort out all of this.  In the process, I decided to try to sketch what I was seeing and learning.  In case it's helpful, here's an example from my notebook to summarize:

For such a striking species, I was surprised how hard it was to find out more about it.  I hope this makes information about Stylantheca papillosa a little more accessible!

P.S.  I first wrote about Stylantheca in 2012 — see "The hydrocoral and the worm" on 22 May 2012.

P.P.S.  We have more stories to tell about Stylantheca and its associates, so stay tuned.  

Friday, March 16, 2018

Radiating stripes

You might remember this beautiful barnacle from 2016 or 2017.  Paraconcavus pacificus reaches its northern limit in Northern California.  I first wrote about this species in September 2016 (see the posts called "Unexpected plate appearance" and "P-pac, Part 2"), and I mentioned it again in February 2017 (see "Red-and-white revisited").

We found two of these barnacles washed up on the beach tonight (16 March 2018).  We're still interested in other observations of this southern species, so let us know if you encounter any!

Thursday, March 15, 2018

The 1 o'clock visitor

Close-up of a Baby Blue Eyes (Nemophila menziesii) flower, with aphid, 13 March 2018

Wednesday, March 14, 2018

Before the squall

I was trying to get a few things done in the field this morning, when I looked up to see this beautiful rainbow over the ocean:

I took a few pictures, including the one below, with a Gray Whale "photo-bombing" the rainbow seascape.  (The spout is on the left side just below the horizon.)

The sky became very dark and I decided I should head back before getting soaked, but I took one more shot looking to the northwest from Bodega Head, with the waves rolling into Salmon Creek Beach. 

I made it back to the office just in time.  It started pouring rain a few minutes later.  I think we recorded ~0.35 inches of rain within ~20 minutes!

Monday, March 12, 2018

Driftwood and foam

Driftwood and foam, Salmon Creek Beach, 23 February 2018