End of a long odyssey

For Eric’s summer class, we used a small plankton net to collect some plankton near the mouth of Bodega Harbor during a flooding tide last week.  The students sorted through the plankton sample in lab to see what larval forms they could find.  One of the students (Zack) spotted an amazing larval form.

This is a brachiolaria, a late-stage larva of a seastar, that appears to be the Ochre Seastar (Pisaster ochraceus).  The photo above was taken under the microscope, but the specimen is quite large for a planktonic larval stage, close to 2 mm long and visible with the naked eye. This larval form is beautiful and alien in appearance and doesn't look much like an adult seastar!   

A surprising feature of the brachiolaria larva is that the juvenile seastar begins developing within the transparent larval body.  In the photo above, the juvenile body is visible near the bottom of the larva and is shiny white in color.  With a closer view, you can see that the developing juvenile body already includes the start of calcareous ossicles that will become the internal skeleton of the juvenile and adult seastar!  In the photo below, the developing ossicles look like intricate snowflakes (white arrow).

 

This brachiolaria appeared to be nearing the completion of its planktonic larval phase, which can be a long odyssey in seastars.  Under laboratory conditions, the planktonic phase has been reported to last from ~40 to 228 days in Pisaster ochraceus, depending on temperature and food.  Pisaster spawns in the spring in California, so this larva likely spent at least several months at sea before entering Bodega Harbor.

When the brachiolaria returns to a rocky shore and finds suitable habitat, it will initially attach to the rock with a short stalk.  Remarkably, the transparent larval body is reabsorbed into the juvenile body during a dramatic metamorphosis. Soon after settlement, the juvenile sea star breaks off its stalk and crawls away as a tiny sea star. 

The larval phases of a sea star.  Illustrations compiled and modified from various sources.

Eric was able to capture some video under the microscope of this beautiful sea star larva.  In the video, notice the long ciliated larval arms used for swimming and gathering food from the plankton. You will also see a close-up of the developing juvenile body (white in color) and the snowflake-like ossicles.  (If you can't see the video player below in the e-mail message, click here to go directly to the video.)

With many thanks to Zack for spotting this planktonic wanderer!  And to Eric for his microscope camera skills and the helpful diagram.

P.S.  For more information about development in sea stars, see earlier posts on the larvae of the Bat Star (Patiria miniata) — "A new star(t)" in 2013 and "A profound change" in 2023.

P.P.S.  As a reminder, when juvenile Pisaster are first visible to human eyes in rocky shore areas, it's about 4-6 months after metamorphosis.  Here's an example of one that's about 4.5 mm across (between ¹/₈ inch and ³/₁₆ inch), photographed in November 2014.

 

Blue background

  

Last week I came across an Ochre Sea Star (Pisaster ochraceus) that was noticeably blue.  It's a little hard to tell from the photo above, but hopefully you can see the blueish background coloration among the clusters of white spines.

We've been monitoring Pisaster for over a decade and have observed thousands of individuals during that time, but I can't recall seeing a blue adult sea star until now.  The most common colors are orange, brown, and purple, but this blue individual seemed unusual, so I took a quick photo for the record.

That said, we often see juveniles with blueish coloration — see photos below from this past winter:

 

 

 

I've often wondered if the blue juveniles gradually turn purple, and perhaps some do, but the blue adult in the first photo shows that sometimes the adults can be blue, too! 

Twinkle, twinkle

  

Juvenile Short-spined Sea Star (Pisaster brevispinus) photographed in late December 2024.  This individual was only ~20 mm across (arm tip to arm tip).

Winter star

  

Juvenile Ochre Sea Star (Pisaster ochraceus), about 6 mm across, on 30 December 2024

Pinky

  

Okay, this isn't a recent photo, but I've been busy working on a presentation about sea stars...so here you go!  A young Short-spined Sea Star (Pisaster brevispinus), photographed on 23 May 2015.

Lower limits

 

 

Whew, I'm finally getting over a heel injury...and it's just in time for spring field work!  Eric and I were doing some intertidal surveys this afternoon (1 April 2023) and Eric took this nice photo of Ochre Sea Stars (Pisaster ochraceus) —  some feeding on very large California Mussels (Mytilus californianus).

So egg-citing!

  

So cool!  This is a female Ochre Sea Star (Pisaster ochraceus) spawning.

We had to work a little late tonight, but it paid off because just before we were getting ready to leave, Eric noticed that a few sea stars were spawning in one of the tanks at the lab!

It's possible they were triggered by the recent change in the weather.  When the NW winds are strong, seawater temperatures are usually cool; then when the winds calm down, seawater temperatures often rise.  Yesterday the seawater temperature was 9°C (48°F), but it increased to 13°C (55°F) today. 

Here's an even closer view where you can see a large number of eggs being released through pores in the surface of the sea star:

 

 

Some of the eggs gathered on a piece of kelp below:

 

 

 

 

We were curious about whether other animals might also be triggered to spawn, so we checked another nearby tank and...voilà!

 

 

 

This is a male Red Abalone (Haliotis rufescens) releasing sperm.  The raised pores in the shell act like little volcanoes when the abalone is spawning:

 

 

 

 

 

We don't get to see sea stars and abalone spawning that often, so it was a fun way to end the day!

 

Feet first?

  

Although you might have heard that sea stars use their tube feet to grab hold of mussels and to pull the two valves open slightly (enough to insert their stomach inside the shell), you don't always get to see the tube feet in action.  

Often the sea star is hunched up over the mussel, so it's hard to see what's going on.  In this case, the Ochre Sea Star (Pisaster ochraceus) is pulling on a very large mussel and it hasn't yet moved into a position where the tube feet are hard to see.

Here's an even closer view: 

 

 

Impressive!

 

One extra

  

Whew!  It's been a busy week.  Sorry for the lack of posts!  Here's a photo from field work this evening.  You might remember that we've been monitoring local sea star populations since 2013.  Tonight Eric spotted this juvenile Ochre Sea Star (Pisaster ochraceus) with six arms (they usually have five).  We occasionally see six-armed adults, but we haven't seen that many juveniles with this configuration.  This individual was ~2.5 cm (~1 inch) across.

 

Wishing on a star

Maybe I keep thinking about stars recently because I've been hoping and hoping that the night skies would be clear enough to see Comet NEOWISE.  Have you seen it?

No luck here yet, but below is a juvenile Ochre Sea Star (Pisaster ochraceus) photographed a couple of days ago.

 

Octoaster?

Many of you are probably familiar with the common intertidal sea star in this area, the Ochre Sea Star (Pisaster ochraceus).  Ochre Sea Stars typically have five arms (or rays).  From time to time you might come across one with six arms, but we hadn't encountered an individual with eight arms (!) until Eric spotted this one.  Because this is a rare occurrence, we thought it would be good to document it for the record.

Here's another view showing the oral side:

 

We're still puzzling over the possible paths that could have led to an eight-armed Ochre Sea Star.

 

Pisaster palette

I've been busy with field surveys recently, so here's a quick photo from the rocky intertidal zone:

 

Ochre Sea Stars (Pisaster ochraceus) — in three color forms — and Giant Green Anemones (Anthopleura xanthogrammica)

 

Broadcast news

On 28 April 2019, Barbara was exploring the rocky intertidal zone with her family.  They saw something unusual under the boulders:

 

Did you notice the bright orange patches?  

Any guesses about what it could be?

The next image will be closer and might give away part of the answer.

 

Now you can see that the bright orange patches are concentrated below upside down Ochre Sea Stars (Pisaster ochraceus).

Here's another example:

 

The bright orange patches are pools of many tiny eggs!  Ochre Sea Stars are broadcast spawners — they release their gametes into the water during the spring.  Females release eggs which tend to be orange, while males release sperm which are white.  [Unless you happen to catch a sea star spawning, you can't tell its sex from its external appearance.]  Fertilization occurs in the water and then the larvae will spend ~76-228 days in the plankton before undergoing metamorphosis and becoming juvenile sea stars.

Barbara captured some excellent footage of the sea stars shedding their gametes.  Below is a short video clip showing a female first and then a male.

Note that spawning occurs more commonly when sea stars are fully submerged under water, but Barbara documented several sea stars spawning while out of (or partially out of) water.  You don't get to see spawning sea stars very often, so I thought it would be worth including a video.  [If you're viewing this in an e-mail and can't see the video player below, click on the title of this post to go to the web page.]

Many thanks to Barbara for sharing this observation as well as her images and videos.  And thanks to Eric, also, for putting together the video clips. 

Up in arms?

 

Somehow I missed them when I was taking this picture in the field, but when I was reviewing photos, I noticed two peanut worms (Phascolosoma agassizii) extending their introverts up between the arms of this juvenile Ochre Sea Star (Pisaster ochraceus). 

The visible parts of the peanut worms are tubular and grayish with black stripes.  If you'd like to learn more about peanut worms, you can review the post called "Introducing the introvert" on 31 January 2013.

Growing up

I've been working on a few projects recently, so I ran out of time tonight, but here's a nice sea star photo from last month:

 

Juvenile Ochre Sea Stars (Pisaster ochraceus) on 13 July 2018

 

Spiny and groovy

 

Close-up of a very spiny Ochre Sea Star (Pisaster ochraceus).  The rounded white spines (or tubercles) are calcareous projections of the sea star's internal skeleton.

 

Close-up of the madreporite (or sieve plate) of an Ochre Sea Star (Pisaster ochraceus).  [I introduced madreporites back in 2013, so if you're interested in reviewing that post, check out "Take five" from 7 May 2013.]

Let the games begin

A close-up mystery photo (below).  Somehow, it reminded me of the Olympics, with everything so sparkly and glittery.  [Click on the photos for larger versions.]

 

Zoomed out a bit more:

 

And the entire animal:

 

This is a Short-spined Sea Star (Pisaster brevispinus).  They usually have five arms, but since this individual had six arms, I took a photo for the record.  Photographed on Bodega Head on 31 January 2018.

 

Rounded spines

I haven't had a chance to post this mystery close-up photo.  Do you recognize what animal this is?

 

Below is an expanded view.  Perhaps it will start to look more familiar?

 

These are close-ups of the spines of an Ochre Sea Star (Pisaster ochraceus).  The spines are made of calcium carbonate and are external projections of the sea star's internal skeleton.  Most of the time, we're used to seeing the spines from farther away, scattered across the surface of the sea star:

 

It's fun to see what the spines look like up close!

Double-wide

We've been busy with field work during the weekend.  During one of our sea star surveys, Eric noticed an Ochre Sea Star (Pisaster ochraceus) that looked a little different.  Can you see what's odd?

 

It might be a little hard to tell from a photograph, but one of the arms (the lowest one) is much wider than all of the others.  Aside from the width of the "double-wide" arm, we couldn't see anything unusual, until we looked at the other side:

 

From above (photo #1), this sea star has 5 arms (the normal number), but from below (photo #2) it has 6 arms, although two of those arms are fused, creating the extra width seen from above.

Here's an even closer look at that unusual "arm":

 

Note that the arms are completely fused throughout their length.  There are two parallel ambulacral grooves — the grooves from which the tube feet arise (they're the yellowish grooves in the image above).

I was curious about the partial gap near the tip of the arm.  By partial I mean that from above this area is completely fused, but from below there is a slight separation.  Here's a close-up of that area:

 

When we looked at the very tip of the arm, we were intrigued.  Here's the tip, curling up slightly.  Remember that a sea star has a small red eyespot at the tip of each arm.  Can you see the eyespot?

 

Okay, that was a bit of a trick question.  There are two eyespots!  Below is an even closer view of the arm tip, showing both eyespots.  They're partially hidden by the spines (white bumps), but I think you'll be able to see both of them:

 

Well, we've looked at thousands and thousands of Ochre Sea Stars, and we've never seen one like this.  Have you?

We did some research, and there are a few records of sea stars with "double ambulacral grooves," but it's very rare.  Hotchkiss (2000) listed 11 individual examples, most of which were Asterias spp., and only one was Pisaster ochraceus.  That specimen was collected over 70 years ago in southern California.

Hotchkiss proposed that this abnormality was due to an injury and abnormal regeneration of the arm.  (The other possibility is a developmental irregularity during metamorphosis.)

The sea star we encountered had no obvious signs of an injury or regenerated arms (e.g., all of the arms were similar in length, ~5 cm long).  If the unusual arm arose from an injury, perhaps the injury happened quite a while ago when the sea star was much smaller.

Interestingly, the earlier Pisaster record is slightly different.  The arms are fused almost to the tip, but then they split:

 

Image from Fisher, W.K.  1945.  Unusual abnormalities in sea-stars.  Journal of the Washington Academy of Sciences 35: 296-298.

 

Who knows if we'll encounter another sea star with a "double-wide" arm.  If we do, I'm sure it'll raise our eyebrows again while we continue to wonder about this unusual phenomenon.

 

P.S.  The reference mentioned above is: Hotchkiss, F.H.C.  2000.  Inferring the developmental basis of the sea star abnormality "double ambulacral groove" (Echinodermata: Asteroidea).  Revista Chilena de Historia Natural 73: 579-583.