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This week was my spring break, and although I have more than enough work to catch up on, I decided that each day I would spend a few hours doing something fun before or after getting stuck in with adult responsibilities. I didn't set up formal plans, but knew I wanted to collect a plankton sample early in the week. Monday 21 March 2022 was the vernal equinox, which seemed as good a time as any to see what was going on in the plankton.

And the plankton was quite lively! I was very pleased to see a lot of diatoms in the sample. Diatoms are early season bloomers, able to take advantage of nutrient inputs due to coastal upwelling. They are usually the most abundant phytoplankters from about March through July.

Mixed marine plankton
Mixed plankton sample, collected from the Santa Cruz Municipal Wharf
© Allison J. Gong

All of those button-like round objects are centric diatoms in the genus Coscinodiscus. They can be large cells, getting up to 500 μm in diameter. Coscinodiscus is in some ways the quintessential centric diatom, as you will see below.

Take a look at these objects:

Clearly, one is a circle and one is a rectangle, right? Well, yes, but these two objects are the same type of thing—they are both cells of Coscinodiscus. The easiest way to understand diatom anatomy is to think of the frustule (the outer skeleton of the cell) of Coscinodiscus as being constructed like a petri dish. Because that's actually what it is: an outer casing of silica with two halves, one of which fits over the other exactly the way a petri dish lid fits over the bottom of the petri dish. If you place a petri dish on a table and look down on it, you will see a circle. But if you pick up the petri dish and look at it from a side view, you will see a rectangle. If you don't believe me, go ahead and try it with any canned food item in your pantry. Coscinodiscus is the same. If it lands on the microscope slide lying flat, it will look like a circle; this is called the valve view because you are looking down on the surface of one of the two valves of the frustule. Most of time when we see Coscinodiscus we see it in valve view. Sometimes you get lucky and a cell remains "standing up" even after you drop a cover slip on top of your sample, and you see the cell as a rectangle. This is called the girdle view. So in the photo above, what you see on the left is a Coscinodiscus cell in valve view, and what you see on the right is the same type of cell in girdle view. Same object, two perspectives, and two shapes. By the way, this is the answer to the question posed in the previous post.

And this is what a valve view of Coscinodiscus looks like when you zoom in:

Circular object with golden-brown spots
Coscinodiscus sp. under brightfield lighting, showing true colors
© Allison J. Gong

You can see some of the sculpturing on the frustule, and the beautiful golden-brown color of diatoms. The diatoms are related to the brown algae and share the same overall set of photosynthetic pigments, which explains why diatoms are often the same colors as kelps.

Another of the common diatoms around here are those in the genus Chaetoceros. The prefix 'chaet-' means 'bristle', and the cells of Chaetoceros have long bristles. Unlike Coscinodiscus, Chaetoceros forms chains. Some species form straight chains, others form spiraling chains, and still others form a sort of meandering chain that is embedded in a tiny blob of mucilage. The cells below are forming a straight chain.

Chain of rectangular boxes, each containing amorphous golden blobs. Long bifurcating bristles protrude from the corners of the boxes.
Chaetoceros sp.
© Allison J. Gong

In addition to all of the diatoms, there were more dinoflagellates than I expected to see. Ceratium was very well represented, often in chains of two cells.

A golden cell with two points at one end and a single point at the other. Three golden ovoid cells in a chain.
Dinoflagellate (Ceratium lineatum, top) and an unidentified diatom
© Allison J. Gong

I was even able to capture some video of Ceratium cells swimming in the thin film of water under the coverslip. Dinoflagellates have two flagella: one wrapped in that groove, or "waistline", and one that trails free. Usually it's the trailing flagellum that's easier to see, and if you watch you'll be able to see it in each of the cells.

Protoperidinium was another common dinoflagellate in the sample. Unlike the diatoms and photoautotrophic dinoflagellates, which have that sort of golden-brown color, Protoperidinium is a heterotroph. It eats other unicellular protists by extruding its cytoplasm out of the holes in its cellulose skeletal plates and engulfing prey, similar to the way an amoeba feeds. Because it does not rely on photosynthesis for obtaining fixed carbon, Protoperidinium comes in colors that we typically don't associate with photoautotrophs. Pink, red, and grayish brown are common colors. This time I saw several that were bright red.

A disc-shaped object with a single point on one side and two points on the other side. Object contains small red blotches.
Protoperidinium, a heterotrophic dinoflagellate
© Allison J. Gong

So that's a glimpse of springtime in the ocean. Now let's look up!

Legend has it that the swallows return to San Juan Capistrano every year on March 19, which is St. Joseph's day. I don't pay attention to St. Joseph's day, but I do pay attention to the vernal equinox every year and keep an eye out for the return of our swallows to the marine lab. We get both cliff swallows (Petrochelidon pyrrhonota) and barn swallows (Hirundo rustica) building mud nests on our buildings. Last year (2021) the cliff swallows showed up first, with the barn swallows arriving a few weeks later; I remember being worried that they might not show up at all.

This year the swallows returned right on schedule. I saw my first barn swallows on the day of the vernal equinox, 21 March 2022.

Barn swallow (Hirundo rustica)
© Allison J. Gong

They are so pretty! I haven't seen any nest-building yet, but did witness what might have been a territorial spat. The bird in the photo above is the one on the left that is retreating in the photo below

Bird perched on a sign
Two barn swallows (Hirundo rustica) expressing a difference of opinion
© Allison J. Gong

Look at that gorgeous outspread tail! Barn swallows migrate to North America from southern Mexico and Central America. The cliff swallows come all the way from South America; no wonder they're a little late arriving in California! I think they'll show up any day now, and both they and the barn swallows will begin daubing mud above doorways and under the eaves.

Somehow, no matter what else is going on and what the calendar says, it never feels like spring until the swallows are zooming around again. Spring is my favorite season, as there's so much going on, and I begin to feel energized again with the longer days. I have a busy spring teaching schedule and don't know how much time I'll have to do fun things like look at plankton for the hell of it, but will try to slow down often enough to take note of what's happening around me.


For the second year in a row (that I am aware of, anyway), the Brandt's cormorants (Urile penicillatus) have claimed the last remaining arch at Natural Bridges as a breeding rookery. I remember being so excited at "discovering" them in 2021. Anyway, they're back again, building piles of algae into nests.

Rock with dozens of black birds, some sitting on nests of algae
Brandt's cormorants (Urile penicillatus) on top of the arch at Natural Bridges
© Allison J. Gong

BTW, if you're keeping score at home, the genus name for the North Pacific cormorants has been changed from Phalacrocorax to Urile. A 2014 study showed this North Pacific group to be a sister clade to those in the genus Phalacrocorax, and in 2021 the International Ornithologists' Union formally adopted the genus Urile for them.

Adult cormorants with white breeding plumes on neck and back
Brandt's cormorant (Urile penicillatus)
© Allison J. Gong

During the breeding season the Brandt's cormorants develop long, wispy white plumes on the cheeks and in two smaller tufts over the shoulder blades. In my head I've been calling them Einstein plumes because although they probably do have a real name, I don't know what it is. When you see a face portrait of one of these birds, you'll know what I mean.

Male cormorant bringing algae to mate on top of rock
Brandt's cormorants (Urile penicillatus)
© Allison J. Gong

The color blue also features in the breeding phenotype of Brandt's cormorants. Cormorants are related to pelicans, which of course have that huge gular pouch that can hold gallons of water. The gular pouch of cormorants isn't nearly as large. For the Brandt's cormorants, the blue gular pouch indicates sexual maturity. And can you see the color of the eye of the bird that is bowing? The eye of a sexually mature bird turns a brilliant cobalt blue during the breeding season. Brandt's cormorants nest on rocks or cliffs, with the male gathering most of the nesting material. At Natural Bridges, the nests are made up mostly of algae, but I've seen a few birds flying by with surfgrass in their mouths. This male above has brought back a nice clump of red algae (a species of Cryptopleura, maybe?) to an appreciative mate.

So those are the Brandt's cormorants.

This year there is a second species of cormorant hanging out on the sides of the rock. These are pelagic cormorants (Urile pelagicus).

Three cormorants on rock cliff
Pelagic cormorants (Urile pelagicus) at Natural Bridges
© Allison J. Gong

I first noticed the pelagic cormorants early in March. I saw those white patches on the flanks and thought, "But that's not the right body shape for a pigeon guillemot!" I came home, looked them up, and sure enough, they are pelagic cormorants. The pelagic is a little smaller and more slender than the Brandt's, and has a red face and glossy black-green plumage with the white rump patches during the breeding season. These three pelagic cormorants are on small ledges on the side of the same rock where the Brandt's cormorants are nesting, providing a nice demonstration of resource partitioning.

So, are these pelagic cormorants really the new kids on the rock? Going by my photographs from 2021, I'd say yes. I looked back through the photos I took when I discovered the Brandt's cormorants, and did not see pelagic cormorants in any of them. Of course, absence of evidence is not necessarily evidence of absence, and it could very well be that the pelagics have been there all along with the Brandt's and I simply never noticed them. Given that my area of expertise is absolutely not birds, I'm quite prepared to learn that I am wrong about this. But the pelagic cormorants are new to me, and that's reason enough to be delighted by them.

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