Revisiting The Birds?

  

Do you remember the scenes from Alfred Hitchcock's movie The Birds when the gulls are attacking?  Well, nearly 60 years later, they're still at it!  This morning (10 March 2022) they were mobbing a Bald Eagle on the tidal flats in Bodega Harbor.  The eagle wasn't that happy about it:

 

 

 

 

 

Mystery on the tidal flats

Last week Eric and I were exploring the tidal flats in Bodega Harbor when we noticed these patches of orange and white in shallow pools on the surface of the mud:

 

 

 

When we looked closer, we could tell that something had been spawning — releasing eggs (orange) or sperm (white) — but we weren't sure what type of animal was responsible.

 

Here are two close-ups showing the vast number of eggs:

 

 

 

 

 

 

 

We kept wondering who was releasing these eggs/sperm, and eventually we came across an animal in the act of spawning:

 

 

 

This is a fairly large polychaete worm.  We're not sure which species it is, but after consulting with some experts, it's possible it's in the family Amphinomidae.  [I'll update this post if we learn more.]

Many marine invertebrates reproduce by broadcast spawning — releasing gametes into water.  The strategy involves some luck in that the sperm need to encounter the eggs.  In the situation below, you can see how that might happen (with the sperm drifting over the eggs), but if they were farther apart, it might be less likely:

 

 

Although many marine invertebrates spawn in this manner, you don't get to see it that often in the field.  Because larval forms can sometimes be useful for species identification, we decided to mix some eggs and sperm together to see if they'd develop into planktonic larvae in the lab.  A week later, here's what we found under the microscope!

 

 

 

This is a larval form called a trochophore.  Those long spines (or chaetae) are likely used to defend the larva against predators and might also slow sinking in the water (they can spread the spines out to the side).  Many worms might spend weeks developing and growing in the plankton before undergoing metamorphosis into a juvenile worm that will burrow in the mudflats.

 

Many thanks to Eric for this wonderful photo of a fascinating trochophore larva!

 

P.S.  For a couple of other examples of broadcast spawning, see the posts called "Fortuitous" on 28 June 2013 (sea anemones) and "Broadcast news" on 2 May 2019 (sea stars).

 

Tsunami surges

To document evidence of the tsunami yesterday, I took a few photos from the shoreline of Bodega Harbor.  Below I'll share a short time series, but before I do that I wanted to explain what you'll be seeing.  

I learned a lot from seeing the Tohoku tsunami in 2011.  It's easier to think about these effects not as one larger wave, but instead as a series of water level changes.  The water surges above the predicted tide height and then recedes below the predicted tide height, and this happens over and over and over again.  (In 2011 the effects were visible for at least 7 days.)  These changes in water level happen relatively quickly – e.g., rather than taking 6 hours to go from high tide to low tide, during the tsunami events we've experienced in 2011 and 2022 some of the water levels changed from the equivalent of high tide to low tide within 30 minutes!

So if the estimate for the Bodega Bay area was for the water level to change by 1.5 feet, then the water level would surge 1.5 feet above the predicted tide height and then recede 1.5 feet below the predicted tide height, and then the flow direction would change and the water would come in again and then go out again.  (In general, the water level deviations are greatest within the first day and then get smaller during the following days.)

Because waves in this area are large (often in the 5-8 foot range), it's actually harder to see the effects of a 1.5 foot water level change on the outer coast.  (Although there can be dangerous surges on sandy beaches.)  But the effects of the tsunami are much easier to see in Bodega Harbor during low tides because you can see the water flooding over the tidal flats and then receding and then flooding in again.  I'll admit, after spending most of my life around tides, it has felt somewhat surreal to me to see this happening!

So here's a time series of photos taken from the same site along Westshore Road.  There is a pink arrow pointing to a clump of algae for a visual landmark to judge the height of the water.  (Note that in these images the water flows in from the left and then recedes to the left.)

The first image was taken at 1:02 p.m. when the water level was relatively high:

 

Then the water receded and was very low within 15 minutes, the time of the second image at 1:17 p.m.:

 

Then suddenly the water started surging back in and it returned to the relatively high level within 7 minutes, by 1:24 p.m.:

After that the water receded again and stayed out for while (but it eventually came back in ~2:30 p.m. after I had left):

 

 

To make this a little easier to visualize, I've also annotated the water level graph from the tide gauge at Point Reyes.  The red line shows all of the water level changes above and below the predicted tide height associated with the tsunami.  I've put in pink arrows at the times that match the photos shown above:

 

 

Amazing to see the effects of the Tonga tsunami reaching Bodega Bay, ~5200 miles (8500 km) away.

P.S.  You can click on the images above and then move through the images faster to see the water level receding, flooding, and receding again.

Swirls above the sand

 

Yesterday I was helping Maddy and Eric look for ribbon worms on the tidal flats in Bodega Harbor.  I know, I was supposed to be looking for ribbons worms (and I did find some!), but I always get distracted when there are phoronids around.  Crowns of tentacles (lophophores) of Phoronopsis harmeri, Bodega Harbor, 20 July 2020.  [You can click on the image for a larger version.]

Above and below

 

Looking south over the tidal flats in Bodega Harbor on 9 March 2020.  Sometimes it's worth working late!

 

Bedraggled

 

We were trying to do a shorebird survey this afternoon (5 December 2019) when I looked towards Doran Beach and noticed a very large bird on the tidal flats.  It was a bit bedraggled by the weather — rain showers and southeast winds — but it was fun to see this Bald Eagle (Haliaeetus leucocephalus) in Bodega Harbor.

Mottled like sand

 

Arrow Goby (Clevelandia ios), Bodega Harbor, 18 July 2019

I was looking for Ghost Shrimp on the tidal flats today and noticed a few Arrow Gobies.  Fun to see them up close!

Their common name describes their long slender bodies (and ios is Greek for "arrow").

 

Their genus, Clevelandia, was named after Mark Cleveland, a co-founder of the San Diego Society of Natural History.

Arrow Gobies are small — this one was ~2 inches (6.3 cm) long.  They live in the burrows of other invertebrates, such as Ghost Shrimp (Neotrypaea californiensis), Blue Mud Shrimp (Upogebia pugettensis), and Innkeeper Worms (Urechis caupo).  Check out the beautiful colors and patterns on their eyes and face:

 

 

Out on the flats

Last September I posted about an interesting "sap-sucking sea slug" called Aplysiopsis enteromorphae.  The photographs accompanying that post were taken in the lab, but recently I encountered this species in the field, so here's a picture from the Bodega Harbor tidal flats:

 

This sea slug was ~20 mm long.  To learn more about this local species, check out the post called "One cell at a time" from 23 September 2017. 

P.S.  Related to last night's post, there are a couple of very small phoronids in the photo above (bottom center and top right).  I didn't notice them when I was trying to photograph Aplysiopsis traveling across the sand.  But when I was reviewing the photos, I saw these tiny phoronids emerging from the sand.  Fun!

A fan of phoronids

It's getting late, but here are a couple of quick photos of phoronids (Phoronopsis harmeri) from pools on the tidal flats in Bodega Harbor this week:

 

 

I've always been impressed by the elegant feeding tentacles (lophophores) of these fascinating animals.  For more information about phoronids, you can review the post called "Ebb and flow" on 26 July 2017.

P.S.  Hi, Amy!

Green eyes and green tentacles

A few photos from the tidal flats in Bodega Harbor (20 February 2012).

 

View from Doran Beach looking towards the town of Bodega Bay.  Mount Roscoe is in center background.

Can you find the animals in the picture below?

There's a small fish (~4 cm long) camouflaged against the sand (probably a sculpin).  Here's a closer view.  Look at those eyes!

There are also a couple of phoronids (Phoronopsis harmeri, formerly P. viridis) above the fish.  Phoronids are worm-like animals in their own phylum.  There are only 14 species in the world, so we're fortunate to have 2 species on Bodega Head!  

Here are two more photos that show phoronids with their lophophores (crown of tentacles) expanded.  The largest lophophore is ~5 mm across.  These U-shaped, spiraled feeding structures are very distinctive.  If you want to find phoronids, look closely for the small green lophophores in shallow pools on the tidal flats.

P.S.  The other species of phoronid on Bodega Head (Phoronis vancouverensis) is shown in the post from 27 November 2011.  It has white lophophores and is found on outer coast rocky shores.