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A recent college graduate and fellow marine lab denizen (Scott) and I are collaborating on a project to quantify growth rates in juvenile Pisaster orchraceus stars. This is one of the intertidal species whose populations in the field and in the lab were decimated by the most recent outbreak of sea star wasting syndrome (SSWS). We are interested in seeing how quickly the stars grow once they metamorphose and recruit to the benthos, and hope that the information will help researchers guesstimate the age of the little stars that are now being seen in the field. This would in turn tell us whether the little stars are survivors of SSWS or post-plague recruits. I keep seeing people refer to them as "babies," but they could very well be several years old. We just don't know, hence this study.

Large, healthy specimen of Pisaster ochraceus at Davenport Landing. 20 May 2015. © Allison J. Gong
Large, healthy specimen of Pisaster ochraceus at Davenport Landing. 20 May 2015.
© Allison J. Gong

But before we get to measure juvenile growth we have to get through larval development, which is perfectly fine by me because I'm always up for observing marine invertebrate larvae. Two weeks ago Scott and I ventured into the field in search of prospective parents. We brought back eight individuals from two different sites, making sure to leave many more in place than we took away. It was actually rather gratifying to see how many hand-sized-or-larger P. ochraceus there were. This morning we met at 07:30 to shoot up the stars with magic juice and then wait for them to spawn.

We have injected the stars (Pisaster ochraceus) and are waiting for them to spawn. 2 June 2015 © Allison J. Gong
We have injected the stars (Pisaster ochraceus) and are waiting for them to spawn. 2 June 2015.
© Allison J. Gong

It has been a while since I tried to induce spawning in Pisaster, and I had forgotten how much longer everything takes compared to the urchins. For one thing, the magic juice itself isn't the same stuff that we use on the urchins, and works by an entirely different mechanism. The stars' response to the magic juice takes 1.5-2 hours, whereas if the urchins aren't doing anything 30 minutes after getting shot up they either need another injection or simply don't have gametes to share.

However, despite my misgivings the animals spawned. Two large females gave us enormous quantities of eggs, and three more donated trivial amounts that we didn't end up using.

This purple individual is the one we designated Female 1. See the huge piles of salmon-pink eggs?

Large purple female Pisaster ochraceus, spawning. 2 June 2015 © Allison J. Gong
Large purple female Pisaster ochraceus, spawning. 2 June 2015.
© Allison J. Gong

and

Large orange female Pisaster ochraceus, spawning. 2 June 2015 © Allison J. Gong
Female 2, a large Pisaster ochraceus, spawning. 2 June 2015.
© Allison J. Gong

Although we had to wait for a male to spawn, we finally did get some sperm and fertilized the eggs at about 12:30. Another thing I had forgotten was that Pisaster eggs, when shed, are lumpy and strange. I was used to the urchin eggs, which are usually almost all beautifully spherical and small. The stars' eggs are about twice as big, at ~160 µm in diameter. The lumpiness doesn't seem to hamper the fertilization process, as you can see below.

Fertilized eggs of Pisaster ochraceus, 2 June 2015 © Allison J. Gong
Fertilized eggs of Pisaster ochraceus, 2 June 2015.
© Allison J. Gong

In this photo you can see the fertilization envelope surrounding most of the eggs. In stars the perivitelline space (the space between the egg surface and the fertilization envelope) is very narrow, which makes it difficult to see the envelope; in urchins the space is much larger, and as a result the envelope quite conspicuous. The rising of the fertilization envelope off the surface of the egg is referred to as the slow block to polyspermy, a mechanical barrier that keeps multiple sperms from penetrating any individual egg. There's also a fast block to polyspermy, but it happens on a molecular level milliseconds after a sperm makes contact with the egg surface; you can't see it happen in real time.

Cleavage in stars proceeds much more slowly than it does in urchins, too. In embryological terms, "cleavage" refers to the first several divisions of the zygote, during which the cell number increases as the cell size decreases. This inverse relationship between cell size and number logically has to occur because the embryo can't get any larger until it has a mouth and begins to feed, which won't happen for at least a couple of days. It took our zygotes about four hours to undergo the first cleavage division.

2-cell embryo of Pisaster ochraceus, 2 June 2015 © Allison J. Gong
2-cell embryo of Pisaster ochraceus, 2 June 2015.
© Allison J. Gong

I left the slide on the microscope to warm up and speed development a bit, and about 45 minutes later was rewarded with this mishmash of embryos at different stages. Nine hours after we started this whole process, there were 2-cell, 4-cell, and 8-cell embryos, as well as eggs that had not divided yet.

Embryos of Pisaster ochraceus, about four hours post-fertilization. 2 June 2015 © Allison J. Gong
Embryos of Pisaster ochraceus, about four hours post-fertilization, 2 June 2015.
© Allison J. Gong

This asynchrony in early development is another way that stars differ from urchins, and it takes some getting used to. I expect that development will become more synchronized as the embryos continue to cleave, and that hatching will occur for all of them at about the same time, probably before Thursday. At least it won't take another 9-hour day to see how far they've come.

 

On Monday of this week (today is Thursday) I was transferring my baby urchins into clean bowls as I always do on Mondays, and for some crazy reason decided that I needed to measure all 300+ of them. I don't remember how the details of how this decision came about, but it probably went something like this:

  • Me #1:  You know, we should probably measure these guys. We do want to see how fast they're growing, after all.
  • Me #2:  Are you kidding? Do you know how long it's going to take to measure 300 urchins under the microscope? We don't have that kind of time today!
  • Me #1:  Oh, come on, don't be so lazy. How long can it take, really? Let's do it for science!
  • Me #2:  These things always take twice as long as you think they will.
  • Me #1:  It's not as though you have anything better to do this afternoon. I mean, aside from writing a final exam and grading all those research papers you assigned.

Three-and-a-half hours later, Me #2 was soundly kicking Me #1 in the butt and we were all tired. But the urchins got measured and now I have some baseline data so I can track further growth. And, no, I don't have the urchins separated into individual containers so I won't be following individual growth, but will be able to calculate average growth rates across the cohort.

Having to look at each urchin long enough to get it lined up with the ocular micrometer in the dissecting scope gave me a chance to observe how their colors are developing. In the field, urchins of this species (Strongylocentrotus purpuratus) in this size range (mm-3 cm) are usually greenish in color; when these individuals are brought into the lab they turn purple as they continue to grow. I seem to recall that my last batch of lab-grown urchins (in Spring 2012) didn't go through that green phase as juveniles, at least not as vibrantly as what we see in the field. So while I was holding down the current batch of urchins to measure them, I noted their color.

Some of them have a definite green tinge at the base of the spines, which then fades to a mauve-y purple towards the tips. The green coloration is most evident on the younger spines:

Strongylocentrotus purpuratus juvenile, age 118 days. This individual has a test diameter of 2.7 mm. 18 May 2015. © Allison J. Gong
Strongylocentrotus purpuratus juvenile, age 118 days. This individual has a test diameter of 2.7 mm. 18 May 2015.
© Allison J. Gong

In addition to giving the urchins something more substantial than scum to eat, having them on coralline rocks gives me a chance to see some of the other critters that live on the rocks. This particular rock is inhabited by a number of spirorbid polychaete worms that build tiny circular tubes made of calcium carbonate, as well as assorted small barnacles cemented to the rock and other crustaceans crawling around.

This is a close-up shot of one of the spirorbid worms. The tube is entirely covered by pink coralline alga, but the worm's orange tentacular crown and trumpet-shaped operculum (used to close the tube when the worm withdraws) are extended as the worm filter-feeds:

Spirorbid polychaete worm on coralline rock, 18 May 2015. © Allison J. Gong
Spirorbid polychaete worm on coralline rock, 18 May 2015.
© Allison J. Gong

Another photogenic animal that I happened to find was a very small chiton. By the time I found it after measuring all the urchins I didn't have the brain energy to try and key it out; if I can find it again once I've finished grading final exams I'll give it a shot. It is extremely cute, with its bright blue spots, and was very slowly creeping around on the rock when one of the urchins barged in and ran right over it:

The chiton is probably about 4 mm long, just a bit longer than the urchin's test diameter. To the urchin, walking over a chiton isn't much different from walking over a rock; and while the chiton probably doesn't like being walked on it isn't significantly affected by the incident unless the urchin starts gnawing on it. Chitons are the masters of just hunkering down and waiting for things to get better, whether that means the tide coming back or an uncouth urchin moving along and minding its own business.

4

Answer:  When it's a snail! Yes, there are snails that secrete and live in white calcareous tubes that look very similar to those of serpulid polychaete worms. Here, see for yourself:

Serpula columbiana, a serpulid polychaete worm, at Point Piños, 9 May 2015. © Allison J. Gong
Serpula columbiana, a serpulid polychaete worm, at Point Pinos, 9 May 2015.
© Allison J. Gong

The worms secrete calcareous tubes that snake over whatever surface they're attached to. When the worm is relaxed, it extends its delicate pinnate feeding tentacles and uses them to capture small particles to eat; they are what we call suspension feeders.

Serpula columbiana polychaete worms, Seymour Marine Discovery Center, 11 May 2015. © Allison J. Gong
Serpula columbiana polychaete worms, Seymour Marine Discovery Center, 11 May 2015.
© Allison J. Gong

But there are gastropods that secrete calcareous tubes, too. They are the vermetid snails, the local species of which is Thylacodes squamigerus. This is one of my favorite animals in the low intertidal, probably because it is so delightfully un-snail-like.

There are three individuals of T. squamigerus in this photo:

The vermetid snail Serpulorbis squamigerus at Point Piños, 9 May 2015. © Allison J. Gong
The vermetid snail Thylacodes squamigerus at Point Pinos, 9 May 2015.
© Allison J. Gong
Serpulorbis squamigerus at Point Piños, 9 May 2015. © Allison J. Gong
Thylacodes squamigerus at Point Pinos, 9 May 2015.
© Allison J. Gong

Thylacodes is also a suspension feeder, but it gathers food in a very different way. When submerged, it spins out some sticky mucus threads that catch suspended particles, then reels in the threads and eats them.

So how would you tell these animals apart if you see them? Here's a hint:  Look at the tubes themselves.

I invite you to use the comments section to tell me how you'd distinguish between Serpula and Thylacodes.

This morning I took a small group of Seymour Center volunteers on a tidepooling trip to Point Piños (see red arrow in the photo below). Point Piños is a very interesting site. It marks the boundary between Monterey Bay to the right (east) of the point and the mighty Pacific Ocean to the left (west).

Map of Monterey Bay. Red arrow indicates Point Pinos.
Map of Monterey Bay. Red arrow indicates Point Piños.
Point Pinos, 9 May 2015. © Allison J. Gong
Point Piños, 9 May 2015.
© Allison J. Gong

As is my usual habit, we began our exploration on the Pacific side of the point. Almost immediately, Victoria found an octopus! And a couple of meters away, she found another one!

Octopus rubescens at Point Pinos, 9 May 2015. © Allison J. Gong
Octopus rubescens at Point Piños, 9 May 2015.
© Allison J. Gong

As we approach the summer solstice, the algae and seagrasses are at their most lush. Point Piños is a fantastic site for algal diversity; every time I come here I want to take some back with me so I can study it at the lab. Alas, collecting at Point Piños is not allowed even for someone (like me) who holds a valid scientific collecting permit.

Beds of Phyllospadix scouleri at Point Pinos, 9 May 2015. © Allison J. Gong
Beds of Phyllospadix scouleri (surf grass) at Point Piños, 9 May 2015.
© Allison J. Gong
Macroalgae at Point Pinos, 9 May 2015. © Allison J. Gong
Macroalgae at Point Piños, 9 May 2015.
© Allison J. Gong

And yes, that log-like object towards the upper-left corner is a harbor seal (Phoca vitulina). A handful of seals were hauled out on the rocks.

However, I was much more interested in the invertebrates. I wasn't looking for anything specific, but in the back of my mind I was keeping track of certain nudibranchs and looking for small stars.

We did see many Patiria miniata (bat stars) in the 1-2 cm size range. Most of them were a bright orange-red color, but some were beige, yellow, or blotchy. There was one large (bigger than my outstretched hand) Pisaster ochraceus that was intensely orange. And Point Piños is always a good spot to see many of the six-armed stars in the genus Leptasterias.

Patiria miniata (bat star), about 1.5 cm in diameter, 9 May 2015. © Allison J. Gong
Patiria miniata (bat star), about 1.5 cm in diameter, at Point Piños, 9 May 2015.
© Allison J. Gong
Large healthy Pisaster ochraceus (ochre star), 9 May 2015. © Allison J. Gong
Large healthy Pisaster ochraceus (ochre star) at Point Piños, 9 May 2015.
© Allison J. Gong
Leptasterias sp., one of the six-armed stars, 9 May 2015. © Allison J. Gong
Leptasterias sp., one of the six-armed stars, at Point Piños,  9 May 2015.
© Allison J. Gong

In terms of nudibranchs there were many Doriopsilla albopunctata, a yellow dorid with tiny white spots. We saw quite a few of them crawling around on the emersed surf grass, as well as in pools. And of course Okenia rosacea (Hopkins' rose) was there, although not in the huge numbers I was expecting.

Doriopsilla albopunctata at Point Piños, 9 May 2015. © Allison J. Gong
Doriopsilla albopunctata at Point Piños, 9 May 2015.
© Allison J. Gong
Okenia rosasea (Hopkins' rose nudibranch) at Point Piños, 9 May 2015. © Allison J. Gong
Okenia rosasea (Hopkins' rose nudibranch) at Point Piños, 9 May 2015.
© Allison J. Gong

In the low zone I saw a few thalli of the intertidal form of Macrocystis pyrifera, the giant kelp that forms the forests that the California coast is famous for. I'd seen this intertidal form named Macrocystis integrifolia, but it appears that now the two forms (intertidal and subtidal) are both considered to be M. pyrifera. To my eye, the intertidal form differs morphologically by having rounder pneumatocysts (floats) and a holdfast that is less dense than the subtidal form.

Macrocystis pyrifera (giant kelp) growing intertidally at Point Piños, 9 May 2015. © Allison J. Gong
Macrocystis pyrifera (giant kelp) growing intertidally at Point Piños, 9 May 2015.
© Allison J. Gong

Hermit crabs are diverse and abundant at Point Piños. Here's an example of Pagurus samuelis, the blue-banded hermit crab; even when you can't see the blue bands on the legs, the bright red antennae are a major clue to this crab's identity.

Pagurus samuelis (blue-banded hermit crab) at Point Piños, 9 May 2015. © Allison J. Gong
Pagurus samuelis (blue-banded hermit crab) at Point Piños, 9 May 2015.
© Allison J. Gong

When we climbed over the point to the Monterey Bay side, I found two of these little gastropod molluscs, which I didn't recognize. They are about 1 cm long, with a brown lumpy mantle that can covers the shell, which is pinkish in color. After putting it out on Facebook that I needed help with the ID, a bunch of friends and friends of friends chimed in (thanks John, Rebecca, Barry, and David!) and I was able to determine that these little guys are Hespererato vitellina:

Hespererato vitellina (appleseed Erato snail) crawling on Phyllospadix scouleri (surf grass) at Point Piños, 9 May 2015. © Allison J. Gong
Hespererato vitellina (appleseed Erato snail) crawling on Phyllospadix scouleri (surf grass) at Point Piños, 9 May 2015.
© Allison J. Gong

On our way back up the beach we noticed long windrows of Velella velella, the by-the-wind sailors, washed up. While most of them were faded and desiccated, there were enough freshly dead ones that were still blue, which may have washed up on the previous high tide.

Windrows of Velella velella (by-the-wind sailor) washed up on the beach at Point Piños, 9 May 2015. © Allison J. Gong
Windrows of Velella velella (by-the-wind sailor) washed up on the beach at Point Piños, 9 May 2015.
© Allison J. Gong

All in all, a very satisfactory morning. I saw things I expected to see, some things I didn't quite expect but wasn't surprised to see, and some things I'd never seen before. That Hespererato vitellina was completely new to me, which is always exciting.

Next up:  What kinds of things live in white calcareous tubes?

2

This morning I went here (see arrow):

Natural Bridges State Beach, viewed from Long Marine Lab, 4 May 2015. © Allison J. Gong
Natural Bridges State Beach, viewed from Long Marine Lab, 4 May 2015.
© Allison J. Gong

See how it's covered in water? I took this picture at about 13:00, probably right at high tide. And of course when I was out there this morning at 06:00, it was low tide. It wasn't the greatest of low tides but it allowed me to see what I needed to see and have a front-row seat watching the early morning surfers going up and down on the big swell that's blowing in.

Obviously, visits to the intertidal need to be timed with the tide cycle. At this time of the year we get our lowest spring tides in the morning every two weeks or so, which is great for me because I am a creature of the morning. I can get up hours before the sun rises, but don't ask me to do anything that requires any intense brain activity after about 21:30.

Low tide this morning was at 05:29, when it was still almost full dark. There was plenty of light to see by the time I got out to the rocks. The tide wasn't very low and the swell was big, a combination that makes for some pretty spectacular wave watching. Here's a view towards the marine lab from my intertidal bench; look at all that frothy water!

View of Terrace Point from Natural Bridges State Beach, 4 May 2015. © Allison J. Gong
View of Terrace Point from Natural Bridges State Beach, 4 May 2015.
© Allison J. Gong

So the water was big and the tide was mediocre, but it was still a glorious morning. Where I was the bench looked like this:

Looking seaward, Natural Bridges State Beach, 4 May 2015. © Allison J. Gong
Looking seaward, Natural Bridges State Beach, 4 May 2015.
© Allison J. Gong

What a difference seven hours can make! See that tiny black dot in the ocean? That's a surfer. While I was out there none of the three surfers I was watching did any actual surfing.

I can't seem to stop taking pictures of anemones:

A baby Anthopleura sola, measuring about 1.5 cm in diameter, 4 May 2015. © Allison J. Gong
A small Anthopleura sola, measuring about 1.5 cm in diameter, 4 May 2015.
© Allison J. Gong
Anthopleura xanthogrammica, 4 May 2015. © Allison J. Gong
Anthopleura xanthogrammica, 4 May 2015.
© Allison J. Gong
Anthopleura sola adult, 4 May 2015. © Allison J. Gong
Anthopleura sola adult, 4 May 2015.
© Allison J. Gong

My prize of the day appeared as I was walking back. I happened to look down at the right time and saw this little guy:

Little octopus in tide pool at Natural Bridges State Beach, 4 May 2015. © Allison J. Gong
Little octopus in tide pool at Natural Bridges State Beach, 4 May 2015.
© Allison J. Gong

I was able to watch the octopus for a couple of minutes. Its mantle was about 3 cm tall, and I'd guess that all spread out the animal was perhaps a bit larger than the palm of my hand. When I got up to move around to the other side of the pool for a different camera angle, the octopus oozed underneath the mussels and just disappeared.

Before it vanished I was able to catch it in the act of breathing.

Although it looks like a head, given the position of the animal's eyes, the part of the animal that's pulsating is the mantle. The visceral mass and gills are contained in the space enclosed by the mantle; not surprisingly, this space is called the mantle cavity. The octopus flushes water in and out of the mantle cavity to irrigate its gills. When it wants to swim it closes off the opening to the mantle and forces water out through a funnel which can be rotated 360° so it can jet off in any direction. But this time the octopus didn't use jet propulsion. It just oozed away.

1

Today was a big day for me. I got to graduate some of my baby urchins from glass slides onto coralline rocks. They were growing very quickly on the slides, chowing down on scum faster than I can grow it, so now it's time for the biggest ones to really put their Aristotle's lanterns to the test and chew up some rocks.

Coralline algae are red algae that have calcified cell walls, giving them a crunchy texture. They come in two morphs--erect branching forms and as encrusting sheets--and are pink in color. The corallines that I'm using for urchin food are growing as sheets on rocks. In the field it is not uncommon to see little urchins on coralline rocks, and their teeth are more than capable of grinding up the calcified algae.

So today I used my trusty frayed paintbrush to scoop up a total of ~90 urchins from their slides and dropped them onto rocks. I should have taken a picture of this valuable tool of mine, so you can see just how low-tech (and cheap!) my type of marine biology is.

Juvenile sea urchins (Strongylocentrotus purpuratus), age 97 days, 27 April 2015. © Allison J. Gong
Juvenile sea urchins (Strongylocentrotus purpuratus), age 97 days, 27 April 2015.
© Allison J. Gong

The largest urchin on this rock has a test diameter of ~2800 µm. Almost 3 mm now!

Here's a closer view of three of the urchins in the photo above:

Close-up of three urchins (S. purpuratus) on coralline rock, 27 April 2015. © Allison J. Gong
Close-up of three urchins (S. purpuratus) on coralline rock, 27 April 2015.
© Allison J. Gong

It didn't take long for the little urchins to start crawling around on their new substrate. I think they'll be happy with this more natural surface to explore and food to eat.

In the meantime, the remaining babies will stay in their jars or on their slides, eating scum. I will continue graduating urchins to rocks as they get too big for slides, feeling more nostalgic each time.

Just think, only 97 days ago these urchins were zygotes! It's not often that you can say that you've known an organism for its entire life, from the moment of fertilization. I am grateful for the privilege of having the opportunity to undertake such an intimate study of these animals' lives. Although I try at least once every year, this is my first successful urchin spawning since 2012. Those animals, by the way, are what I call my most perfect urchins because, well, they just are. I had originally thought I could use them for dissection, but after caring for them as larvae and the three years since they've metamorphosed, I just can't bring myself to sacrifice them. They are simply perfect.

I don't think I could ever get tired of this.

1

We humans use the term "hitting the wall" when we find ourselves in situations in which progress is elusive despite extreme effort. For endurance athletes or anyone doing any serious physical training it can mean not being able to break one's personal best time for a race, or not being able to continue getting measurably stronger. For me, it felt as though much of graduate school involved hitting various hard walls and coming up with a headache. Maybe it's like that for everyone, but from the perspective inside my own head it sure did seem that I was struggling harder than most.

Sometimes the wall is literal rather than figurative. And for small animals, a surface that we might be able to break through without any effort at all (or without even perceiving it as a surface) can be an impenetrable barrier. The biggest of my baby sea urchins has a test diameter of ~2700 µm now; including spines it probably measures a bit bigger than 3 mm across. While tiny urchins can use the surface tension at the air-water interface to crawl, this big guy is too heavy now to stick to the underside and would fall off of it.

However, I thought this urchin might be able to use the surface tension of a water bubble to grab onto and right itself. A hypothesis like this requires empirical data, so I picked up the little urchin and plopped it, oral side up (so, upside-down), in a bubble of water on a depression slide. As I expected, the urchin crawled over to the edge of the bubble and I could see its tube feet attaching to the underside of the surface tension. Watch here:

I watched continuously for about a minute, and the urchin never did figure out how to turn itself over. I think there may be two reasons for this:

  1. The water bubble at the edge of the depression in the slide was very shallow, probably not deep enough to cover the whole animal for the few seconds that it would be positioned on its edge. If, to the animal, the surface tension proved to be impenetrable, then a comparable situation would be for me to pin you, lying on your side sandwiched between a solid wall in front of you and a hard board against your back, then telling you to roll over. You wouldn't be able to do it, either.
  2. The surface tension of the bubble may simply not have been firm enough for the urchin to grab it and pull. Urchins use their tube feet to pull against hard objects, and adults can actually generate enough leverage to push bricks around. Obviously, it's easier to pull (or push) hard against a solid surface (say, a rock or the side of a glass bowl) than a malleable one such as the inner surface of a bubble.

Now, I'm not by any means an expert in biomechanics, but it seems pretty clear to me that the surface tension is either too hard or too soft to be used by an urchin this size to right itself. Smaller urchins would just crawl on the underside of the surface tension until they reached the side or bottom of the container, and larger urchins would push right through it to reach for whatever was on the other side. I may need to do some more experiments with these urchins and bubbles of various sizes.

Just for fun I took another video of the same animal, this time situated upright. It was much happier this way.

See?  It has pedicellariae in addition to spines and tube feet. It's also getting easier to distinguish the ambulacral and interambulacral areas. These urchins are already starting to develop some purple coloration. Typically they go through a greenish stage before turning purple; maybe that will come later. We'll have to see.

My baby urchins have become scum-eating machines! They are 88 days old now and I am beginning to wonder if I can generate scum fast enough to keep up with them. I did a head count this morning and have three bowls, each of which holds a population of ~100 urchins, and a bowl that contains another 33. The first three bowls are going through food very quickly, and I change their scum slide every 2-3 days. And, since eating results in pooping I change the water every day.

Hungry urchins looking for food:

Juvenile sea urchins (Strongylocentrotus purpuratus), 18 April 2015 © Allison J. Gong
Juvenile sea urchins (Strongylocentrotus purpuratus), 18 April 2015
© Allison J. Gong

After they eat through the food on the upper surface of the slide, the urchins migrate to the lower side and begin munching there. Once most of the food is gone they go on the prowl, and I'll find them on the sides of the bowl looking for something to eat. In the photo, can you tell which urchins are on the underside of the slide? Most of them are, actually. They're the ones where you see a darkish ring around the center; that ring is the peristomial membrane that surrounds the mouth. That's what "peristomial" means, by the way, but you didn't need me to tell you that, did you?

Changing the slide involves using a paintbrush to pick up each urchin and drop it into the new bowl. It's rather tedious but is also the most convenient time to count them. And they do seem happy every time they find themselves in a new bowl with plenty to eat.

Baby urchins with lots of food to eat now:

Juvenile sea urchins (Strongylocentrotus purpuratus), 18 April 2015 © Allison J. Gong
Juvenile sea urchins (Strongylocentrotus purpuratus), 18 April 2015
© Allison J. Gong

Using the clue I gave you up the page, can you find the single urchin on the underside of the slide?

Having pentaradial symmetry means that the urchins don't have forward-backward or left-right axes, and they can and do move in any direction on the horizontal plane. They do, however, have a strong oral-aboral axis, and they definitely have a preference for how their bodies should be oriented with respect to gravity. The normal position is to have the mouth (oral surface) facing downward, with the opposite side (aboral surface) facing up. And for this species, at least, even in the field you don't see them sticking upside-down on overhanging surfaces, unless they have a vertical surface to hang onto as well. These little guys can hang onto the underside of the slide because they're not very heavy yet. Once they get bigger, it'll be a lot more difficult for them.

Setting an urchin down on its aboral surface, with its mouth facing up, will keep it from crawling away very quickly, but sooner or later it will right itself and take off. Even my little babies don't like to be flipped upside-down. This guy was pretty stubborn at first and spent a minute waving its tube feet at me while I looked at it through the microscope, but then took another minute or so to get down to the business of turning over. Don't worry, I cut out the boring first minute so this clip shows only the action sequence.

Quite clearly, urchins don't care about forward-backward or left-right, but they do care about up-down. Like most animals that live in essentially two dimensions, adult urchins prioritize knowing the orientation of one's body with respect to gravity. But remember those bilateral larvae? They swim in any direction in their pelagic, three-dimensional world, although the body always moves through the water in a particular orientation (arm tips first). It seems this is another aspect of metamorphosis that gets overlooked: the transition from a bilateral body that swims in both the horizontal and vertical planes (three body axes, weak response to gravity), to a body with pentaradial symmetry that walks only in the horizontal plane (one body axis, strong response to gravity). Hmm. I'm going to have to think about that for a bit.

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Everybody knows that climate change is a hot--pun intended!--topic in both science and politics these days. Here along the northern California coast it seems that sea surface temperature (SST) has been elevated for at least a year now. I remember a time, not too many years ago, when I would put my hands into my seawater table and they'd go numb after several minutes. This told me that the water temperature was in the 11-12 ºC range. But that hasn't happened for a while, and recently I'd put my hands in the water and it didn't even really feel cold. My trusty not-fancy thermometer has been telling me that the temps have been hovering at around 14ºC.

The other day it occurred to me that I have a 20-year record of water temperatures from my seawater table, which is a pretty fair proxy for SST in the area. The numbers may not jive exactly with SST data produced by oceanographic instruments, but the trends should be very similar. If you click on the figure you'll be able to see a larger version of it.

Temperature in my seawater table at Long Marine Lab, July 1994-March 2015. © Allison J. Gong
Temperature in my seawater table at Long Marine Lab, July 1994-March 2015.
© Allison J. Gong

There are a couple of notable trends in these data. I was pleased to see a strong signal for the 1997-1998 El Niño event, visible as a prolonged period of elevated temperatures in the fall and winter. This was followed by a La Niña in 1998-1999, when temperatures were lower than average for a few months. Aside from those events, SST fluctuates between about 16º in the summer-fall and 11-12º in the winter-spring.

One more thing. Take a look at the far right end of the graph. Notice what appears to be a cooling trend so far in the spring of 2015?

Here are the data from March and the first three days of April:

Temperature in my seawater table at Long Marine Lab, March-early April 2015. © Allison J. Gong
Temperature in my seawater table at Long Marine Lab, March-early April 2015.
© Allison J. Gong

So there's definitely a cooling trend in the past few days. The interesting question is:  Why is this happening now, when it hasn't happened for about two years?

The answer, in a nutshell, is the wind. For the past week or so, we've had screaming afternoon winds at the marine lab, coming from the northwest. Northwest winds blowing down the coast drive the process of coastal upwelling, which results in cold water rising to the surface; it usually takes 3-4 days of sustained winds to start upwelling. This upwelled water, in addition to being cold, also contains a lot of nutrients, which are used as fertilizers by the primary producers of the marine ecosystem, the phytoplankton. Most of the phytoplankton are photosynthetic unicellular algae (NOT plants) that harvest the energy from sunlight and use it to fix carbon dioxide into organic molecules. The fixed carbon in turn feeds grazers such as copepods, which are then eaten by small predators, which are eaten by larger predators and so on up the food chain.

What this all means is that we may, for the first spring in two years, be getting some productive upwelling. I don't think I'm the only marine biologist in the area who is looking forward to seeing whether this apparent upwelling continues. If it does, then we should see the biota respond accordingly. Mind you, a four-day streak does not indicate a long-term return to typical spring upwelling conditions, and it may be merely a blip in the warmer conditions that are the new normal for us, but it is a stronger signal than we've seen in a few years. In any case, I will be keeping an eye on both the water temperature and the critters living in it.

Until recently I hadn't closely observed what it looks like when a leather star (Dermasterias imbricata) succumbs to wasting syndrome. When I had the outbreak of plague in my table almost 18 months ago now, my only leather star was fine one day and decomposing the next, so I didn't get to see what actually happened as it was dying.

(Un)fortunately, one of the leather stars at the marine lab started wasting a bit more than two weeks ago, and this time I was able to catch it at the beginning. This animal wasn't in my care so I didn't check on it as frequently as I would if it had been living in one of my tables, but one of the aquarists pointed it out to me when it began getting sick.

The first symptom was a lesion on the aboral surface. I say "lesion" but it's more of an open wound.

Dermasterias imbricata with aboral lesion, 2 February 2015. ©Allison J. Gong
Dermasterias imbricata with aboral lesion, 2 February 2015.
© Allison J. Gong

You can see that the animal's insides are exposed to the external environment. In the photo above the whitish milky-looking stuff is gonad (I'm pretty sure this animal was a male) and the beige ribbon bits are pyloric caeca, essentially branches of the stomach that extend into the arms. What typically happens along with the development of lesions like this is an overall deflating of the star as the water vascular system and other coelomic systems become increasingly compromised, and the tendency for the animal to start tearing off its arms.

Which results in this, a week later:

Wasting Dermasterias imbricata, autotomizing its arm, 9 February 2015. ©Allison J. Gong
Wasting Dermasterias imbricata, autotomizing its arm, 9 February 2015.
© Allison J. Gong

This poor animal had torn its arm off, and continued to live for a while. I find it fascinating that the lack of a centralized nervous system means that this animal literally didn't know it was dead. It was finally declared officially dead two days later. Compared to how quickly wasting syndrome kills the forcipulates that I've seen (Pisaster, Pycnopodia, and Orthasterias), the leather stars take a long time to die--several days from start to finish, opposed to a matter of hours as I saw with my stars. The leathers didn't seem to be hit as hard by the first wave of the disease outbreak, either. Is Dermasterias somehow able to fight off the infection a bit longer? It would be interesting to know, wouldn't it?

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