Just in time for Easter -- lots of eggs!

  

We went out to the rocky shore early this morning to start some surveys.  Right away Eric noticed that the tidepools looked unusual.  All of them appeared cloudy or milky.  We were aware recent ocean conditions might trigger spawning in some marine invertebrates, and sure enough, this was a massive spawning event of California Mussels (Mytilus californianus), probably the largest we've encountered.

In the photo above, the orange coloration is eggs released by female mussels.  Here's another example, with clusters of eggs concentrated along the edge of a pool:

 

 

In other pools, the color was white or gray, clouded by vast quantities of sperm released by male mussels:

 

 

Nearly every tidepool we observed on Bodega Head appeared to have mussels spawning, so the extent of this synchronous mass spawning event was truly remarkable.  Even the largest pools were visibly cloudy:

 

 

 

The ocean temperature went up from 11°C (52°F) to 13°C (55°F) yesterday, and there was a phytoplankton bloom nearshore — both environmental cues that are thought to trigger spawning in some invertebrates.

Amazing!  Let us know (and send photos) if you notice local marine invertebrates spawning, too!

Tool chest?

  

We had to do some field work in Monterey County yesterday, but we arrived a little early, so had a few minutes to observe a few sea otters while eating lunch in Pacific Grove.  

The first sea otters we saw were actively munching on sea urchins -- above, and next two photos:

 

 

 

But then our attention was drawn to a hard slapping sound, and we turned to see an otter trying to crack open a large mussel against a rock that was balanced on the otter's chest:

 

 

 

Several times we watched this otter dive down, bring up a rock and a mussel (or clump of mussels)...and then use the rock like an anvil -- hammering the mussel against the rock.

 

Sea otters are known to do this, but I hadn't photographed it before, so here are a few more images.  (Tool-use by mammals aside from humans is rare.)  In each picture, look for a rock resting on the otter's chest and a mussel between the otter's paws.
 

 

 

 

 

 

 

 

 

We were reading up on this behavior at the end of the day and came across an interesting research paper about tool use by sea otters just published in May 2024.

 

It turns out that using rocks as tools to access hard-shelled prey might be especially important for female otters in areas where their preferred and easier-to-process prey (e.g., abalone and urchins) aren't as common.  And using the rocks to open hard-shelled prey can prevent tooth damage and give the otters access to an alternative food source that otherwise wouldn't be available by biting alone.

Law et al. 2024. Tool use increases mechanical foraging success and tooth health in southern sea otters (Enhydra lutris nereis).  Science 384: 798-802.

 

Shell colors

  

Close-up of the inside of a California Mussel (Mytilus californianus).

A long way to grow!

  

Close-up of barnacles on a Californa Mussel (Mytilus californianus) shell, photographed on 29 April 2024.

There are at least two age classes of barnacles here — the larger Little Brown Barnacle (Chthamalus dalli) adults and the very tiny newly-settled recruits.  The recruits were so small they were actually hard to see in the field — just small specks scattered across the mussel shell.  They have a long way to grow!  :)

In the zones

  

This morning (24 April 2023) we were finishing some surveys at a site with lots of wave splash.  In this case that means the intertidal zonation is clearly demarcated and the zones extend very high on the rocks.  

For example, on the left, the brownish coloration is made up of seaweeds (primarily Pyropia and Pelvetiopsis), the dark blue areas are California Mussels (Mytilus californianus), and below that is a band of surfgrass (Phyllospadix scouleri) and coralline algae (some of it is bleached, likely by warm or desiccating conditions, so it's paler than usual).

In this view there was also a nice flock of Surfbirds (Calidris virgata) foraging in the zone above the mussels.

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).

At home

  

Black Oystercatcher (Haematopus bachmani) and California Mussels (Mytilus californianus).  Photographed at sunset on 17 January 2022.

Combination of factors

  

One morning last week when we were headed out to do field work, we noticed an odd smell in the area and later we found the source — some small patches of California Mussels (Mytilus californianus) that had died recently.

Although it's been warm inland, I didn't recall noticeably high air temperatures at the coast, so at first I was a bit puzzled.  But then I thought about how calm the ocean has been (hardly any large swell) and that this site is quite high on the rocks.  It's likely that the mussels growing here are used to getting splashed by waves, and if they didn't experience any wave action during a warm day, it could be a problem for them.

So we did a little sleuthing regarding the conditions that might have caused this mussel die-off.  Questions we wondered about included: 

 - Were there any higher air temperatures in Bodega Bay recently?  We looked back at some temperature records and noted a couple of days in early August when the air temperatures reached ~67°F (~19°C).  That was the warmest we found, so the air didn't get that hot.

- But we know that mussels and the rocks they grow on reach warmer temperatures than the air.  So how hot was the rock at the time?  Luckily, Eric had some data loggers on the rocks near mussels and so he looked back and found that rock temperatures reached ~98-100°F (~37-38°C) on those warmer afternoons.  That's warm enough to impact mussels, and if exposed long enough, it might kill them, but it would depend on other conditions at the time. So...

- What was the timing and height of the tides on those days?  Interestingly, this was during a neap tide series. Compared to tide heights during a spring tide series (around full moons and new moons)  the high tide heights during neap tides are relatively low.  For example, the morning high tide on August 1st was only 3.7 feet (higher high tides in our area are often over 6 feet).  And the low tide on August 1st was 2.7 feet at ~12 p.m.  This combination of a very low high tide in the morning followed by a low tide in the middle of the day is potentially dangerous for a marine organism living in the high intertidal zone, especially if the wave conditions are extremely calm and the air is relatively warm.  It basically means that mussels growing at that site (at about 5 feet elevation) were exposed to warm air/rock temperatures and no wave splash for the entire day — especially from late morning through late afternoon (the hottest part of the day).  On 1-3 August 2021, these mussels might have reached temperatures >86°F (>30°C) for 4.5-6 hours each day and they might not have experienced any wave splash for that entire time.  [I think it's even possible they didn't get splashed during the night-time high tide (which on August 1st was 5.6 feet at 7 p.m.)]

So questions remain about this die-off, but rather than being caused by extreme warm air temperatures alone, in this case I'm guessing it was a convergence of factors, including (1) these mussels lived very high in the intertidal zone at a very splashy site; (2) there was a low high tide in the morning (the mussels weren't submerged during high tide); (3) there was a low tide in the middle of the day (the mussels were exposed to warm air for many daylight hours); (4) there were warm air temperatures (this might not have happened if air temperatures had been cooler); and (5) this occurred during very calm sea conditions (the mussels weren't cooled down by wave splash).

This mussel die-off was restricted to a very high intertidal splash zone site.  Most of the mussels in the rest of the intertidal zone were fine.  But seeing this event was insightful for considering combinations of factors that could be lethal for mussels.

One more photo for the record:

 

 

Coastal colors

 

  

Colors on the inside of a California Mussel (Mytilus californianus) shell. 

 

Would you have guessed?  :)

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!

 

Surfbird photo journal

Yesterday (20 January 2020), I spent a little time watching Surfbirds (Calidris virgata, formerly Aphriza virgata) along the rocky outer coast.  Here's a bit of a photo journal of Surfbird behavior:

 

Resting on the rocks after a large wave splash.

 

Feeding on a juvenile mussel. 

Bathing in a tidepool. 

 

Aggressive behavior, during which the two birds were very vocal.

I'm curious about this aggressive behavior.  The birds were bathing along the edge of a very large tidepool.  There was plenty of space for all of the birds in the flock, but aggressive interactions between Surfbirds seem fairly frequent in these situations (while the birds are bathing).  I wonder if the intense interactions could be more about social organization and relationships, rather than competition for space?

The birds splash, call loudly, spread their wings, raise their tails, rise up, or lean over, open their bills, jab at each other, and sometimes even grab each other's bills (Ouch!). 

 

 

Check out the serrations along the edge of the bill in the photo below.  The sharp edges are probably useful for grasping prey, but perhaps they're also helpful in these interactions:

 

 

Even though Surfbirds are generally seen walking on rocks in our area, this pool was deep enough that sometimes the Surfbirds would swim across it.  A different perspective!

 

I felt grateful for the opportunity to spend some time observing these Surfbirds.  There's always something to learn!

 

Too hot -- Part 3

 

Remember the mussel mortality event that I mentioned last week?  (See posts called "Too hot" and "Too hot -- Part 2")  

Eric Simons wrote an informative article about this event for Bay Nature magazine.  You can read the article online here.

The photo above was taken on 18 June 2019 and the photo below was taken on 19 June 2019.  

In the first photo you'll notice that some mussels are empty, but others still have their adductor muscles — the white muscle that holds the two shells together.  In the photo below, the majority of mussels are empty, but in a few you can see the orange internal tissue (before it washed away or was eaten by other animals).  At low tide, healthy mussels are normally closed up tightly, so you can't see the internal tissue or the inside of the shells.

 

 

Too hot -- Part 2

For the record, I'm sharing a few more photos of the California Mussel mortality event in the intertidal zone that I mentioned last night.  We think this is the most significant mussel mortality we've seen on Bodega Head during the last 15 years (in terms of number of individuals and the amount of area impacted).

In these patches (photographed on 19 June 2019) you can see that most of the mussels in the top layer of the mussel bed have died.  The light blue color is the inside of the dead, gaping shells.  

Although it's hard to estimate percent mortality throughout the entire mussel bed, many areas across the intertidal zone look like this right now, with some shells gaping wider than others.

 

 

Too hot

Last week's record warm air temperatures (for the date) seem to have impacted some of the local rocky intertidal zone species.  Unfortunately, the high air temperatures coincided with midday low tides.  Sometimes it takes a little while for the effects to show up.  

While doing field work this morning (18 June 2019), we observed quite a bit of bleached algae in the mid-to-high zone (see below).  These seaweeds are usually darker green and brown — the whites and reds are abnormal for these species.  [In this photo, much of the white algae in the foreground is Mazzaella sp., while the reddish looking species is Dwarf Rockweed (Pelvetiopsis limitata).]

 

There has also been a significant die-off of California Mussels (Mytilus californianus).  A large percentage of the mussels were open and gaping, some were empty and some still had tissue inside.  Here's one example:

 

We're curious about how widespread this mussel die-off was.  If you see large patches of open, gaping, dead mussels in the intertidal zone and you'd be willing to share a photo, I'd be interested in hearing about your observations.

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!

Mussels, mussels, mussels

Okay, I'll admit it.  There probably aren't too many people in the world with a quest to capture an aesthetically pleasing and meaningful picture of mussels.  But I can't help it.  I want a photo that shows how abundant they can be on rocky shores, how dense they can be...an image that highlights their interesting shapes and rich colors and the complex three-dimensional structure they create...a picture that encourages the viewer to think about how mussels change the habitat beneath themselves, making it darker and moister and cooler for so many other species.

This may be a lifelong quest!  I find mussels very difficult to photograph.  Here are a few of my most recent attempts (taken on 8 January 2012) -- three different views of California Mussels (Mytilus californianus):