Rings around the boulders

We were on our way to do field work in the rocky intertidal zone early this morning, when we noticed this:

 

Can you see the orange coloration along the lower part of the wall and forming rings around the boulders?

Here's a closer view (below).  The boulder is about 2.5 feet across (~76 cm).  Any guess about what's causing the orange color?

 

There are orange sponges in this area that could look like this from a distance, but it didn't seem quite right, so we got down for an even closer view:

 

Spirorbid tubeworms!  Wow, neither of us had seen such dense and expansive aggregations before.  

The next photo is helpful because some of the tubeworms are underwater with their bright orange tentacles expanded, and others are out of the water with their tentacles withdrawn so it's easier to see their white tubes (with just a hint of orange at the entrance).

 

Most spirorbid tubeworms are brooders (brooding their larvae) and once released their larvae have very short planktonic durations — swimming in the water column for a very short time before they settle onto a rock (or other suitable surface).  

Perhaps the surge channel we walked by is a good setting for high retention, where many larvae are released and then settle in close proximity to each other instead of being swept away by waves and currents?

If you're interested in seeing microscope views of these fascinating tubeworms, review the post from 6 February 2012.

Small wonders

Time for another mystery close-up.  This is a tough one!

 

These pictures were taken at very high magnification under a microscope.  I'll zoom out a little more for a slightly broader view:

 

And here's another picture that's very similar, but from a slightly different angle (below).  

Any guesses yet?  The long feathery structures (tentacles) may be a helpful clue.

 

I can also tell you that both the tentacles and the unusual funnel-shaped pod that's filled with tiny objects with red spots can be withdrawn into a calcareous tube (visible as a white blur in the background).

The next image will give the answer away, so only look further if you're ready.

 

These are small spirorbid tubeworms.  Their feathery tentacles are fanned outward when feeding (capturing plankton from the water).  Spirorbid worms have a funnel-shaped operculum that seals the opening to their tubes when the worm pulls in.  In some species, including this one, the operculum doubles as a brood chamber for their embryos!

The tiny objects in the operculum with red spots are developing embryos.  The red spots are eyespots (two per embryo).  The embryos will develop in the operculum for ~2-4 weeks (depending on the species and water temperature), and then will hatch as larvae and swim briefly before settling down to form their own tubes.

Here's another example of a tubeworm with extended feeding tentacles and an operculum filled with embryos.

 

If you've spent some time near the shore, you've probably seen spirorbids, but you may have walked by them without a second glance because of their small size (only a few millimeters across).  But they're quite common on rocks and seaweeds (or hard-shelled animals such as mussels and snails) and sometimes occur in dense patches:

 

On 6 February 2012, I showed pictures of a different species of spirorbid from Bodega Head (see those images here).  I'm still trying to work out the identification of spirorbids that live in this region, so we'll have to update you as we learn more.  For now I hope you enjoyed learning a bit about their life history!

All aboard!

A couple of days ago, on 26 October 2013, an unusual object on the beach caught my eye:

 

This is what it looked like when I flipped it over (next image).  It was ~11 inches long.

 

It was a little wooden boat!

It was puzzling to wonder where it had come from.  All of the parts were wooden except for four metal hooks on the upper deck (one was missing) and a few small metal nails or tacks along the keel.  It looked like there used to be a mast in the center.  The boat had been painted, and at some point it had been burned (see charred markings).

I was also very curious about the animals that were aboard.  They were small, but if you looked closely you could see quite a few animals living in the grooves of the boat:

Because of their size, I decided to look at the animals under a microscope.  It was a whole different world, and after doing a mini-survey, this is what I found:

 

Two species of acorn barnacles (larger one on the left with orange on the inside of the opercular plates, and smaller ones on the right).

 

One species of gooseneck barnacle (possibly Pollicipes sp.?) — it's the small stalked barnacle at the upper edge of the photo.

 

A spirorbid tube worm (white tube between the barnacles).

 

A teeny-tiny brown limpet (very magnified in the image above).

 

Long byssal threads that indicate mussels used to live on the boat, too.

 

And finally, a mystery critter!  My first thought was bryozoan, but then I questioned that and wondered about tunicate (or sea squirt).  I haven't seen many of them this small.  If you're more familiar with them at this size, perhaps you can help with an identification?  Below is another view, showing that this animal is stalked and branched.

 

It was an intriguing assortment of life aboard a little wooden boat!

Orange and pink

 

Sunset from Bodega Head, 14 November 2012

The oranges and pinks in the sunset photo reminded me of this nudibranch crawling on coralline algae photographed the day before (13 November 2012).

 

This is a Spotted Triopha (Triopha maculata).  Note the dark brown background color, bright orange projections on the head and back, and bright orange gills (ruffled structure about 2/3 of the way back from the head).

This nudibranch was ~3 cm long.  Smaller individuals may appear dominantly orange and larger individuals are often yellow, but all of them show the spots.  Interestingly, Morris, Abbott and Haderlie (1980) note that the color pattern resembles orange/brown kelp blades with white bryozoan colonies.  (Spotted Triophas are often found on kelp and they eat bryozoans.)

I don't have a photo of kelp with bryozoans, but I do have one of kelp with white spirorbid tube worms (next photo).  To my eye, the nudibranch spots also resemble these coiled worm tubes!

 

Here's a different individual, this one was discovered at Duxbury Reef in Bolinas in November 2007.  (The image below is posed; we placed the nudibranch in an empty mussel shell filled with seawater for the photo.)

In the tube

Spirorbids are small polychaete worms characterized by coiled calcareous tubes.  They are quite common along rocky shores and you may notice their tiny white spiral tubes on rocks, algae, or shells.  The tubes measure only a few millimeters across, and the tube openings are often less than 1 mm in diameter.

Many people haven't had the opportunity to see spirorbids under water.  These beautiful worms are filter feeders, using long tentacles on their heads to capture small particles from the water.  Ciliary movement along the tentacles causes water to flow from underneath and up through the tentacles.  Once captured, the particles are then transferred along grooves towards the mouth at the center of the tentacles.

Many marine invertebrates are broadcast spawners (releasing eggs into the water), but spirorbids are brooders.  Some species brood embryos on the inside of their tubes, but others have special opercular brood chambers.  

The operculum is a trumpet-shaped structure that seals the end of tube when the worm is withdrawn — see upper left corner in photo below: the operculum is disc-shaped with some whitish coloration and is being tilted to allow the tentacles to emerge.

 

Although I'm not positive, the operculum of the worm in the center of the photo may contain eggs or embryos!  Look for the dark reddish spherical structures inside the orange chamber on the worm's lower right side.