Sandy claws

  

A few days ago Eric and I were walking along the beach during the Yuletide when we came across these sandy claws.  :)

Happy holidays to all!

P.S.  The claws belong to a Spiny Mole Crab (Blepharipoda occidentalis).

Sunset snack

 

 

Young Sanderling (Calidris alba) with a Mole Crab (Emerita analoga), 16 September 2021

Fueling up for a long journey

Okay, here you go, a few more Ruddy Turnstone (Arenaria interpres) photos from Dillon Beach yesterday (15 May 2021).  

First, a few while the turnstones were feeding — looking for juvenile mole crabs just beneath the surface of the sand:

 

 

 

 

 

 

 

 

Although the turnstones look bright and colorful against the sand, you can see how their varied plumage works well to camouflage them against rocky habitats mixed with sand and seaweeds:

 

 

 

 

 

 

 

And one more, just for fun — a close-up with seaweed and fog:

 

 

 

Wish them luck on their journey to the Arctic!

On the way to the tundra

  

After field work yesterday we caught a glimpse of a small group of six Ruddy Turnstones (Arenaria interpres) at Dillon Beach.  I only had a point-and-shoot camera at the time, and was disappointed not to have a larger camera and lens because the turnstones were quite striking in nearly full breeding plumage.  So I made another run to the beach early this morning (15 May 2021) to see if they were still around.  

I'll be sharing some more photos, but here's one to start.  The turnstones (and other shorebirds) were feeding on small mole crabs (Emerita analoga).  I was glad to see them before they depart for the Arctic — Ruddy Turnstones are one of the most northerly breeding shorebirds!

Point A to Point B

Last week Eric and I noticed this looping trail on the beach (below).  Immediately both of us thought of an illustration from a card we like, so we added an A and a B:

 

Here's the card:

 

This illustration has seemed relevant at various times in our lives, as the paths we find ourselves on are often unpredictable and rarely follow a straight line.  This seems to ring true right now, with the way this coronavirus has upended the world.  It's helpful to think about the big picture, though, and to visualize the entire path, right?  Although it's often hard to know exactly how we'll get there, we will get to the next point!

P.S.  Thanks to the mole crab for making the path in the sand and to PAPYRUS for the wonderful card.

 

Digging for crabs

Last night I mentioned that we encountered a River Otter (Lontra canadensis) feeding on Mole Crabs (Emerita analoga).  We spent some time watching the otter and documenting the behavior, so here's a bit of a photo journal:

Padding along in the surf zone:

 

Stopping to dig for crabs.  The otter wasn't messing around.  It would actively dig with its front legs, bulldoze through the sand with its snout, and sometimes it would bury its entire head in the sand! 

 

 

 

 

The otter seemed quite successful capturing prey.  When chewing crabs, the otter often assumed this distinctive position with its nose pointed towards the sky (making it look similar to a sea lion):

 

Sometimes the otter caught female Mole Crabs carrying eggs (note the bright orange color):

 

Between prey captures, the otter would look around:

 

And sometimes shake its wet fur:

 

The otter and Sanderlings seemed to keep an eye on each other:

 

Every time we encounter a River Otter, we learn something new and have more questions about them.  And every time, I'm grateful for a few minutes with such an endearing animal.

 

Crab opener

The recreational crab season opened today (2 November 2019).  Most fishermen were headed out after Dungeness Crab (Cancer magister), but one seemed more interested in catching Mole Crabs (Emerita analoga):

Heads in the sand

Some interesting observations of River Otters (Lontra canadensis) this morning (3 October 2018).  This group of three otters was spending some time in the swash zone on a sandy beach:

 

From their postures, it appeared they might be feeding.  Note the young otter on the far left — the nose-up position is one that you often see when otters are eating something.  And check out the mother otter on the far right with her head curved downward.  She appears to be holding something and perhaps chewing on it or manipulating a prey item in some way.

I started to wonder if they might be eating Mole Crabs (Emerita analoga).  So I took a few more pictures.  Watch the young otter in the middle of the photo — you can see it "bulldozing" its head through the sand, perhaps in pursuit of a crab:

 

 

And here's one more photo, with all three otters lined up.  It looks like the younger otter in the foreground might be using its paw to dig at something in the sand:

 

I've read about Sea Otters (Enhydra lutris) eating Mole Crabs, but I haven't seen reference to River Otters doing so.  Perhaps it's an opportunistic behavior?

 

Spiny -- Part 2

Okay, here's the mystery photo from last night:

 

This is a noticeably spiny crab claw.  Next question — which species of crab is it from?

The photo below is another hint.  (And note the sandy habitat where this crab lives.)

 

The picture above shows a distinctive crab carapace, with dramatic spines.

This species might be more familiar to those of you living south of San Francisco.  It's a Spiny Mole Crab (Blepharipoda occidentalis).  I've written about them once before; you can review previous photos from Doran Beach and Salmon Creek Beach here.

Most people are probably more familiar with the more common Mole Crab (Emerita analoga).  In contrast to Emerita, Spiny Mole Crabs can grow to be much larger; they have dramatic spines; and as the mystery photo shows, they have claws.  They use the claws to scavenge and tear apart food.  The spines on the outer edges of the claws and the carapace probably help to deter predators (such as fish).

 

I don't have a digital photo of a Spiny Mole Crab, but you can find a nice picture of the entire crab here (by Zen Faulkes) and on this EOL page.

I'm writing about Spiny Mole Crabs again because we're interested in whether anyone has found them north of Salmon Creek Beach.  

Recently, we counted many more molts than usual, so it's possible Spiny Mole Crab numbers have increased in our area, which also means there is potential for them to be found even further north than previously documented.

Below are two more examples of Spiny Mole Crab carapaces (two different sizes).  Let us know if you see a Spiny Mole Crab carapace or claw on a beach near you!

 

Mini-mole

 

It looks like it's another big year for juvenile mole crabs.  They're very abundant on beaches right now.  The photo above shows a typical adult — about 4 cm (1.5 inches) long — and a very small juvenile — only about 5 mm long.  Photographed on 1 March 2015.

See last year's post about them on 30 March 2014 here. 

Mystery below the sand

A few days ago, Eric and I were walking on Salmon Creek Beach and noticed an unusual pattern in the sand.  Most of the sand we'd been walking by had been very smooth, but this patch was marked with lots of nooks and crannies:

 

We decided to take a closer look to try to identify what was causing the pattern.  We started by swiping away the top layer of sand to see what was below.

This revealed a very high density of small animals!  Can you tell what they are?

 

To confirm their identity, Eric scooped up a small handful of sand and poured a little water over it for a better view of the animals:

 

Ah ha!  What an amazing number of juvenile Mole Crabs (Emerita analoga)!

I can't resist showing a few more pictures:

 

They burrowed into the sand very quickly.  Look for the paired dark eyes among the sand grains:

 

The next image is a little blurry, but I like it because Eric's fingers provide a sense of scale.  Each Mole Crab was ~5 mm long.

 

The entire roughened patch in the sand was about 6 meters long by 2 meters wide.  If the density of juvenile Mole Crabs was consistent across the patch, there were a lot of Mole Crabs in that area!

This made me think about the Sanderlings we observed feeding so intensively — see post from 24 March 2014.  Peter mentioned the possibility of them feeding on small Mole Crabs.  There are other options (e.g., amphipods or isopods), but it's intriguing to discover such a high density of juvenile Mole Crabs and to wonder about their vulnerability to shorebirds.

At the end of the trail

Do you have a guess about what kind of animal made this trail on the beach?

 

I almost walked by...but then I stopped and gently probed one end of the trail.  

Here's another clue.  It's an extreme closeup taken under the microscope:

 

Those black spots with gold flecks are eyes looking to the left.  (But the eyes look different at this stage than they do later in the life of this animal.)

This next image will give it away:

 

The trail was made by a tiny Mole Crab (Emerita analoga)!  There were several of them scattered along the beach on 24 February 2014.  These crabs had a carapace length of only ~4-5 mm, which means they settled out from the plankton not too long ago.

Here's one more view (below).  Watch for these meandering trails and new Mole Crab recruits at a sandy beach near you!

 

 

P.S.  For a picture of an adult Mole Crab and a little more information about them, see the post from 25 February 2012.

Spiny!

Want to take a guess about the following mystery object?  (Warning: The answer is below the image.)

 

 

Did you guess part of a crab?  If so, you're right!  Here's the entire object.

 

This is the carapace (basically the "back") of a Spiny Mole Crab (Blepharipoda occidentalis).  I found it washed up at Doran Beach on 1 November 2013.  It was ~2 inches (5 cm) long.

Most people are familiar with a more common species of Mole Crab (Emerita analoga).  They're smaller, grayer, more rounded or domed, and lack the prominent spines.  Here are the two side-by-side for comparison (see next image).

 

When you find just the carapace alone and not the entire crab, it's often a molt, which means that the animal has shed its old exoskeleton (that's what you're looking at) but has grown a new exoskeleton and is still alive.

We moved to Sonoma County in December 2004 and were excited to find Spiny Mole Crab molts at Doran Beach and Salmon Creek Beach.  When you read about the distribution of Spiny Mole Crabs in books, you may see their northern range limit described as San Francisco, Stinson Beach, or Drakes Beach.  So it's quite possible that the observations at Doran Beach and Salmon Creek Beach are the northernmost records for this species in California.

In 2005, I found a live Spiny Mole Crab at Doran Beach.  They live in the very low intertidal zone and subtidal zone, so it's harder to find them than the more familiar Emerita analoga. 

For site documentation purposes, finding a live crab is better than finding a molt because a molt could wash in from farther away.  To say that Spiny Mole Crabs regularly occur at Salmon Creek Beach, it would be good either to find live Spiny Mole Crabs there, or to locate additional molts.  

This past week I had a strange experience in that I was remembering the Spiny Mole Crab molt that Eric and I found on Salmon Creek Beach in 2004.  I haven't seen one there since.  I haven't done a purposeful search for them, but I keep my eyes open as I'm walking the beach.  

Well, after I found the molt at Doran Beach on November 1st, I went for a quick walk on Salmon Creek Beach on November 2nd, and what do you know, there was a Spiny Mole Crab molt on Salmon Creek Beach (see picture below)!

 

We still don't know if there are Spiny Mole Crabs actually living at Salmon Creek Beach, so it'll be interesting to see if we can find a live crab there some day.  (Or let me know if you or anyone else you know has found one there or even farther north!)

Probing for prey

Sanderlings (Calidris alba) are one of the more familiar shorebirds on outer coast sandy beaches.  They spend the winter here, and then fly to the high-Arctic tundra to nest during the summer.  You'll encounter them running along the edges of the waves, then following the receding water out and probing very rapidly in the sand.

 

Can you identify the type of prey captured by this Sanderling?

It's a mole crab, or sand crab (Emerita analoga).  Mole crabs are active burrowers in the swash zone.  They have smooth, rounded bodies (up to ~35 mm long) and specialized appendages for rapid digging.  Instead of claws (mole crabs are filter feeders), the terminal segment of the first leg — formally called a dactylopodite — is a large, oval, paddle-like appendage.  

Their eyes are on long stalks that are sometimes visible above the sand, even when the rest of the crab is below the surface.  Check out the eyes and the digging paddles in the photos below.  (These images were taken at Asilomar Beach in Pacific Grove, but the same species is found on Salmon Creek Beach and Doran Beach).