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Late yesterday afternoon I met my friend Brenna at the harbor to go on a slug hunt. Brenna is working on the taxonomy of a group of nudibranchs for her dissertation, and we've gone collecting out in the intertidal together a few times. I knew I'd need some harbor therapy after teaching a microscope class in the afternoon so when she suggested a slug hunt I didn't have to think twice about saying "Yes!"

I arrived at the harbor before Brenna did, and spent some time lying on the docks taking pictures of the fouling community that lives there. The late summer afternoon light was perfect for picture taking, and I got some great shots.

Mussel (Mytilus sp.) at the Santa Cruz Yacht Harbor, 29 August 2015. © Allison J. Gong
Mussel (Mytilus sp.) at the Santa Cruz Yacht Harbor, 29 August 2015.
© Allison J. Gong

This is one of my favorites. It's a view into the posterior end of a live mussel (Mytilus sp.). Mussels live inside a pair of shells and open up only the posterior end to suck in water for respiration and filter feeding. They shut the shells very quickly when disturbed, so I had to sneak up on this individual and take a picture before it knew I was there. Looking through the opening you can see a blurry pale structure running from left to right; I think this is the mussel's gill. The elaborately fringed dark structure that looks like a pair of curtains extending towards each other is the edge of the mantle. Because most of the mussel's body is enclosed within the shells, the mantle edge contains most of the animal's sensory organs. Mantles are exquisitely sensitive to touch, light, and certain chemicals; scallops, another type of bivalve mollusk, often have actual eyes on the mantle edge.

In addition to spying on mussels, I also tried to catch polychaete worms off-guard. There are several different types of tube-dwelling polychaetes living at the harbor. Most of the ones I saw yesterday were serpulids living in meandering calcareous tubes. Like these:

Serpulid polychaete worm at the Santa Cruz Yacht Harbor, 29 August 2015. © Allison J. Gong
Two examples of Serpula columbiana, a tube-dwelling polychaete worm, at the Santa Cruz Yacht Harbor, 29 August 2015.
© Allison J. Gong

Polychaete worm tubes come in many different materials and morphologies. These serpulids live in calcareous tubes that snake over surfaces. Because the tubes are mineralized, they can extend upwards from a surface, too. The worm spends its entire post-larval life in the tube that it secretes, extending only its "head", visible as a tentacular crown, for filter-feeding. Like the mussels, serpulid polychaetes are very quick to respond to anything they perceive as a threat. Even a mere shadow passing over them can cause a rapid retreat into the tube finalized by sealing off the tube with the trumpet-shaped operculum.

One of the most conspicuous animals at the harbor is an invasive encrusting bryozoan, Watersipora subtorquata. This animal is one of the first to colonize new real estate. Nothing else looks like it, so it is easy to identify.

Watersipora subtorquata, an introduced bryozoan at the Santa Cruz Yacht Harbor, 29 August 2015. © Allison J. Gong
Watersipora subtorquata, an introduced bryozoan at the Santa Cruz Yacht Harbor, 29 August 2015.
© Allison J. Gong

Watersipora grows as a crust on surfaces such as mussel shells and floating docks, but when two colonies meet they use each other as surfaces, forming these curling sheets. The faint fuzziness that you see sort of hovering above the surface of the sheets is due to the lophophores extending from the zooids. Here's a closer shot:

Watersipora subtorquata, an introduced bryozoan at the Santa Cruz Yacht Harbor, 29 August 2015. © Allison J. Gong
Watersipora subtorquata, an introduced bryozoan at the Santa Cruz Yacht Harbor, 29 August 2015.
© Allison J. Gong

Another of the common introduced species at the harbor is the colonial sea squirt Botrylloides violaceus. This animal comes in a wide range of oranges and even purple. Here's a colony that seems to understand the visual impact of pairing high-contrast colors:

Colony of the colonial sea squirt Botrylloides violaceus growing over mussel shells at the Santa Cruz Yacht Harbor, 29 August 2015. © Allison J. Gong
Colony of the colonial sea squirt Botrylloides violaceus growing over mussel shells at the Santa Cruz Yacht Harbor, 29 August 2015.
© Allison J. Gong

What looks like a mass of pale orange doughnuts is actually a strictly organized colony. Each of the doughnuts is a zooid, and the hole of the doughnut is the incurrent siphon through which the zooid draws water in. Each zooid has its own incurrent siphon. In this photo you can see several larger holes; these are excurrent siphons, shared by several zooids, through which waste water is expelled. It's difficult to see in the photo, but the excurrent siphons are raised up above the level of the colony, so water that has already been filtered doesn't get sucked in again. This is exactly the reason that human structures such as smokestacks and chimneys are tall.

Oh, and since you asked, Brenna did indeed find slugs! And she taught me some field characteristics to help me ID slugs that I find. We both got what we needed on our little jaunt to the harbor.

Day 3 of wasting in Leptasterias

The saga continues. When I checked on my ailing stars yesterday I saw, as expected, that most of what I had called Leptasterias #1 (the pink star that had ripped itself into pieces the day before) had disintegrated into small piles of mush. There was no sign of life in any of the small fragments so I threw them away. The largest piece, consisting of two adjacent arms attached to what looks like most of the central disc, was still walking around so I kept it. Today I was surprised to see that it hasn't died yet. In fact, it looks a little better, with both of the arms active and the central disc appearing to be somewhat more contracted and less sloppy.

Remnant of wasting Leptasterias star, 30 August 2015. © Allison J. Gong
Remnant of wasting Leptasterias star, 30 August 2015.
© Allison J. Gong

The two arms appear to be working together, rather than trying to walk away from each other. I think this is a good sign, although it's too early tell how much longer this fragment of a star will survive.


The star I had designated Leptasterias #2, which had the very large lesion on Friday, had died and dissolved into a mass of amorphous tissue and skeletal ossicles when I looked at it yesterday.


On the other hand, Leptasterias #3, the larger of the two gray stars, seems to be holding its own, or at least not getting any worse. On Day 1 of the outbreak this star had a small fluffy lesion on its aboral surface. Today the wound appears to have grown a bit but its edges look a little cleaner:

Leptasterias star affected by wasting syndrome, 30 August 2015. © Allison J. Gong
Leptasterias star affected by wasting syndrome, 30 August 2015.
© Allison J. Gong

This star was particularly active this morning. I didn't want to disturb it or give it any incentive to autotomize its arms, so I left it in its screened container to take pictures and video. It was zooming around and acting, for all intents and purposes, like a normal healthy star.

Fingers crossed that this one makes it!

Sometimes the only word that will do is a bad word. I generally try not to use a lot of bad language because on the occasions when I do swear I want my f-bombs to really mean something. Late this afternoon I was on my way out of the lab when I made a quick last trip through the wet lab just to make sure everybody would be okay for the night, when out of the corner of my eye I saw a few odd pink bits in one of my screened containers.

This container held three small six-armed stars of the genus Leptasterias. I had collected them earlier this summer with the goal of showing them to my students when we do the echinoderm diversity lab at the end of the semester. Stars in this genus are interesting because their normal arm number is six and they brood their babies instead of broadcasting gametes into the sea to meet, fertilize, and develop on their own. Plus, like all their echinoderm kin, they are pretty animals. Lastly, enamored as I am of oddballs and out-of-the-ordinary things, I am charmed by Leptasterias's six arms because most stars have only five.

So when I opened up the screened container and saw that one of my Leptasterias stars had torn itself into pieces, I let fly with a few f-bombs and other choice expletives. I removed the star pieces into a bowl for a better view.

Leptasterias star dismembered due to wasting syndrome, 28 August 2015. © Allison J. Gong
Leptasterias star dismembered due to wasting syndrome, 28 August 2015.
© Allison J. Gong

Seeing a star that had ripped its own arms off is every bit as horrifying when the star has six arms as when it has five. This act of self-mutilation had probably occurred today, as the star looked fine when I checked on it yesterday. All of the pieces were still alive and crawling around:

Actually, if you examined each of the pieces independently and didn't know that it was only part of a greater whole, you'd think that they were entirely viable. I put these pieces aside in a separate bowl, although honestly I don't know why. I'm almost certain they'll be dead when I check on things at the lab tomorrow morning, and even if they aren't they'll be decomposing while still sort of alive, which is even worse. I must be a glutton for punishment.

For a while I held out a teensy glimmer of hope that the other two stars might be okay, but that didn't last long. It took only a glance to see a big aboral lesion on the center of one of them:

Leptasterias star with large aboral lesion, 28 August 2015. © Allison J. Gong
Leptasterias star with large aboral lesion, 28 August 2015.
© Allison J. Gong

Examination under higher magnification shows just how deep and intrusive these lesions are. The body wall is entirely compromised, resulting in the exposure of internal organs to the outside environment.

Lesion on aboral surface of Leptasterias star, 28 August 2015. © Allison J. Gong
Large lesion on aboral surface of Leptasterias star, 28 August 2015.
© Allison J. Gong

It turns out that none of these Leptasterias is unaffected. The third star in my container has a small aboral lesion:

Small aboral lesion on Leptasterias, 28 August 2015. © Allison J. Gong
Small aboral lesion on Leptasterias star, 28 August 2015.
© Allison J. Gong

Whether or not this third individual will survive is up for grabs, but I wouldn't bet on it. From my experience with wasting syndrome in Pisaster and Pycnopodia, the disorder progresses extremely rapidly once the animal starts showing signs of illness. And all of these animals appeared just fine yesterday. The small pink star is essentially dead already, it just hasn't realized it yet. The gray star with the large lesion may very well be dead tomorrow, too. The star with the small lesion might still be alive tomorrow, and this is the only one for which I have a bit of hope for survival.

About a week ago the seawater temperature dropped to 16°C for a few days, but then started creeping back up; today it topped out at 19°C. Correlation is not causation, but I do wonder if another spike in the 19-20° range, on top of stress caused by the ongoing period of warm water, is the proverbial straw that broke the camel's back. These poor stars have gone through hell lately, and there's no indication that the water will cool off any time soon. I'd throw up my hands and ask, "What's next?" but I have a sneaking suspicion that I'll find out soon enough.

Early next week (31 August - 2 September), PBS and the BBC are going to present a huge "live" media event. I say "live" because although the event will be aired in the evenings, all the preview footage I've seen has been shot in during daylight hours. Anyway, you can read all about it in the press release.

Big Blue Live, as it is called, is a collaboration among the Monterey Bay Aquarium, NOAA, and both media networks. I can guarantee that there will be some spectacular footage of wildlife within the Monterey Bay. You know, whales, dolphins, seals and sea lions, and perhaps the odd bird or two. This is the stuff of wildlife, the so-called charismatic megafauna, that have warm bodies and look at you with big eyes.

My concern, as a perennial fan of the overlooked and underappreciated, is that the whole media event will focus only on these large mammals (and maybe a bird and possibly even a fish), and neglect or give short shrift to the countless fascinating and ecologically crucial critters that form the lower trophic levels. In other words, the invertebrates. Not to mention the organisms that ultimately produce all of the food in the marine trophic system, the phytoplankton. I expect that there might be lip service paid to the phytoplankton, krill, and baitfish which are the reason that the whales and such come to Monterey Bay, but I will be pleasantly astonished if more than a few seconds of air time are devoted to them. Somehow it's just not easy to make diatoms sexy to lay people, even those who say they love marine biology.

Thus, anticipating that my beloved invertebrates won't get much mention, I'm going to post some of my favorite pictures of them here, as I photographed them in the field. And as you're watching Big Blue Live, keep in mind that there's more to (wild)life than charismatic megafauna.

Pisaster ochraceus in tidepool at Natural Bridges State Beach, 17 June 2014. © Allison J. Gong
Pisaster ochraceus in tidepool at Natural Bridges State Beach, 17 June 2014.
© Allison J. Gong
The vermetid snail Thylacodes squamigerus at Pistachio Beach, 18 January 2015. © Allison J. Gong
The vermetid snail Thylacodes squamigerus at Pistachio Beach, 18 January 2015.
© Allison J. Gong
Juvenile sea star at Davenport Landing, 19 January 2015. © Allison J. Gong
Juvenile sea star at Davenport Landing, 19 January 2015.
© Allison J. Gong
Octopus rubescens in a tidepool at Natural Bridges State Beach, 4 May 2015. © Allison J. Gong
Octopus rubescens in a tidepool at Natural Bridges State Beach, 4 May 2015.
© Allison J. Gong
Henricia sp. at Point Pinos, 9 May 2015. © Allison J. Gong
Henricia sp. at Point Pinos, 9 May 2015.
© Allison J. Gong
Hespererato vitellina, the appleseed erato snail, at Point Pinos, 9 May 2015. © Allison J. Gong
Appleseed erato snail (Hespererato vitellina), at Point Pinos, 9 May 2015.
© Allison J. Gong
Kelp crab (Pugettia producta) on the beach at Franklin Point, 31 July 2015. © Allison J. Gong
Kelp crab (Pugettia producta) on the beach at Franklin Point, 31 July 2015.
© Allison J. Gong
Mouth of Anthopleura sola at Natural Bridges State Beach, 6 April 2015. © Allison J. Gong
Mouth of Anthopleura sola at Natural Bridges State Beach, 6 April 2015.
© Allison J. Gong
The brittle star Ophiothrix spiculata at Franklin Point, 31 July 2015. © Allison J. Gong
The brittle star Ophiothrix spiculata at Franklin Point, 31 July 2015.
© Allison J. Gong
The anemone Anthopleura artemisia at Davenport Landing, 2 August 2015. © Allison J. Gong
The anemone Anthopleura artemisia at Davenport Landing, 2 August 2015.
© Allison J. Gong

1

Having read multiple news accounts of domoic acid (DA) events up and down the Pacific coast of the U.S., I decided to do my own informal survey of the culprit that makes DA. Domoic acid is a naturally occurring toxin that is produced by some (but not all) species of the diatom Pseudo-nitzschia during a plankton bloom. It is ingested by filter-feeding animals such as mussels and anchovies and gets passed to higher trophic levels as these animals are themselves preyed upon. The filter feeders are thought to be unaffected by the DA they ingest, but due to bioaccumulation the toxin occurs in higher concentrations in the tissues of the predators. Humans can be affected by DA also, when they eat contaminated shellfish, for example. This is why coastal states advise seafood foragers not to collect and eat bivalves (clams, mussels, oysters) when DA is detected in the water. When humans are sickened by domoic acid, the affliction is called Amnesic Shellfish Poisoning (ASP).

I had originally hoped to collect a sample from a boat over deeper water, but when those plans failed to materialize I did the best I could on my own:  I went out to the end of the Santa Cruz Municipal Wharf and threw the net from there. As soon as I hauled the net back up I could smell the diatoms. Yes, diatoms have a smell, as does just about anything when you concentrate it enough. The diatom smell is rich and organic, but not at all unpleasant.

This is what the sample looked like:

All those clear needle-like things are chains of Pseudo-nitzschia cells. When they are reproducing quickly (a.k.a. "blooming") the cells remain connected by their tips (see below). Longer chains indicate favorable conditions for asexual reproduction in diatoms; I saw some chains that were 12+ cells long. The small whitish things zooming around are barnacle nauplii. Obviously barnacles are having lots of sex right now.

Pseudo-nitzschia is a pennate diatom, which simply means that the cells are pen- or boat-shaped. Some of the pennate diatoms have a raphe, or slit-like opening on the frustule through which a tiny bit of protoplasm can be extruded. These diatoms, of which Pseudo-nitzschia is one, don't swim but can actually scoot around on surfaces. Don't believe me? Then watch this long chain of Pseudos move back and forth like a train on tracks.

Here's a still shot at higher magnification:

Cells of the pennate diatom Pseudo-nitzschia sp. 21 August 2015. © Allison J. Gong
Cells of the pennate diatom Pseudo-nitzschia sp. 21 August 2015.
© Allison J. Gong

See how the individual cells remain connected to each other by their overlapping tips? Each of the cells is about 75 µm long and contains two roughly rectangular chloroplasts that are golden brown in color.

Pseudo-nitzschia wasn't the only diatom in the sample, either. I saw surprising numbers of Coscinodiscus, a genus of centric diatoms, ranging in size from 160-250 µm in diameter. Coscinodiscus frustules are beautifully sculptured, making the cells look like fancy buttons.

Cells of the centric diatom Coscinodiscus sp. 21 August 2015. © Allison J. Gong
Cells of the centric diatom Coscinodiscus sp. 21 August 2015.
© Allison J. Gong

That little bleb at about 10:00 on the larger diatom is a dinoflagellate, Peridinium or Protoperidinium, that came along for the ride. There is also a chain of Pseudos making a cameo appearance in the bottom of the photo.

The other unusual diatom in the sample was Chaetoceros. This diatom has a name that hints at the morphology of the cells:  "chaet-" is Greek for "spine" or "bristle". Indeed, the cells of Chaetoceros are box-shaped and have four long spines that link adjacent cells together to form chains.

Cells of the centric diatom Chaetoceros sp. 21 August 2015. © Allison J. Gong
Cells of the centric diatom Chaetoceros sp. 21 August 2015.
© Allison J. Gong

The intriguing question that came to my mind was "Why now?" Around here I've grown accustomed to a typical succession of phytoplankton in Monterey Bay, with diatoms (especially Chaetoceros) blooming in the spring and early summer, corresponding to our usual upwelling season, then giving way to dinoflagellates in the late summer and fall when upwelling abates. And yes, we did have a major Pseudo-nitzschia bloom back in April and May. Diatoms bloom in response to high levels of nutrients, especially nitrate, that occur when upwelling returns nutrients to surface waters. We did have a few weeks of decent upwelling in the spring. Then El Niño started to build and we went through several weeks of warm, clear water when diatoms were pretty much absent and we saw phytoplankters such as silicoflagellates and coccolithophores, which can thrive in waters that are too nutrient-depleted for diatoms.

And now the diatoms are back. Chlorophyll levels in nearshore waters are high right now all along the central California coast. These data are from CeNCOOS, an ocean observing system:

Chlorophyll concentrations along the central California coast, 17-19 August 2015. © CenCOOS
Chlorophyll concentrations (µg/L) along the central California coast, 17-19 August 2015.
© CeNCOOS

Assuming that the chlorophyll being measured is in the cells of Pseudo-nitzschia and other diatoms, it appears that we're having a return to springtime conditions. Bait fish are back in the Bay, and following them are dolphins and birds. I would dearly love to do some whale watching this fall; we may have another spectacular season for humpback whales. Whatever the cause for this apparent late-season rebirth, this autumn is shaping up to be interesting.

5

Next week classes for the Fall semester begin, and this will be my fourth term teaching a marine invertebrate zoology class at this particular institution. I have built this class on a foundation of comparative anatomy and functional morphology; lab activities include dissections (to observe how bodies are put together) and diversity labs (to examine the morphological diversity within major taxa). This year I wanted to include a lab with a broader ecological context. So back in April I hung a box of glass slides from one of the boat slips at the harbor. The idea is that the students in the invert zoo class will examine the slides after they'd been marinating in the ocean for several months and have to figure out what's growing on them.

The organisms that have and will continue to colonize the slides are members of what is rather disparagingly referred to as a "fouling community." To be fair, they can be nuisances, fouling docks and pilings, boat hulls, water intake and outflow pipes, and pretty much anything that is left in the water for any significant amount of time. In fact, my friend Adam has a job scraping fouling organisms off the bottoms of boats at the harbor; boat owners either pay to have this done or do it themselves every so often. But to me, these animals and algae form a fascinating ecological community that illustrates many of the principles I teach to my students.

Harbors are some of the places where exotic (i.e., non-native) species are first detected. It is not uncommon for many of the species in a fouling community to have evolved elsewhere and been transported (usually, but not always, unintentionally) to a new location, where they grow swiftly and often out-compete the native species. Obviously, not all species introductions "take" and it's anybody's guess how many species were dumped in a new site and failed to stick around. The ones that do take, though, tend to become very prominent.

So, back to my slide box. It was still there, hanging from a string about 2.5 meters below the bottom of the dock. As I pulled it up, I was relieved to see different colors and textures:

Slide box hanging from a floating dock at the harbor. 20 August 2015. © Allison J. Gong
Slide box hanging from a floating dock at the harbor. 20 August 2015.
© Allison J. Gong

Up close, it looked even more promising:

Slide box hanging from a dock at the harbor. 20 August 2015. © Allison J. Gong
Slide box hanging from a dock at the harbor. 20 August 2015.
© Allison J. Gong

Even without knowing what all the differently colored blotches are, you can tell that there's a lot of stuff growing. I'm not going to dismantle the box until we use it in lab in early November, but I thought it might be worth a closer look. It just so happened that I had both a clean bucket in my car and the foresight to bring it with me onto the dock. This photo shows that the slides themselves are covered with growth:

Slide box hanging from a floating dock at the harbor. 20 August 2015. © Allison J. Gong
Slide box hanging from a floating dock at the harbor. 20 August 2015.
© Allison J. Gong

The red encrusting sheet is the bryozoan Watersipora, probable species subtorquata, an invasive species that is found in harbors all along the California coast. The pale orange blobs are colonies of sea squirts; it is difficult to identify them to species without examination under a microscope. There is also quite a bit of a brown upright branching bryozoan that I think belongs to the genus Bugula.

As an unabashed aficionado of all things hydroid, I'm always very pleased to see certain species of 'droids at the harbor. They are simply so beautiful that I love looking at them. This is the hydroid Ectopleura crocea. It is common but sporadic and patchy at the harbor, and usually isn't one of the first species to colonize an area. Its congener, E. marina, occurs in the intertidal; I can find it fairly reliably in a particular pool at Davenport Landing and have occasionally seen it elsewhere.

Ectopleura crocea growing out of a colony of Watersipora subtorquata. 20 August 2015. © Allison J. Gong
The hydroid Ectopleura crocea growing out of a colony of Watersipora subtorquata. 20 August 2015.
© Allison J. Gong

Having reassured myself that my slide box was doing well I took some time to check out other bits of real estate in that area of the dock. I played around with the super-macro setting on my camera, with mixed results. I do now know, though, that it works underwater:

Tentacular array of a serpulid polychaete worm. 20 August 2015. © Allison J. Gong
Tentacular array of a serpulid polychaete worm, with bryozoans in the background. 20 August 2015.
© Allison J. Gong

I found a cooperative barnacle and took some video footage of feeding behavior. Barnacles are strange crustaceans that lie on their backs and kick their modified thoracic appendages through the water to capture small particles. What a weird way to make a living. But the animal is always right, and barnacles can be quite efficient at clearing water.

And, finally, does anybody know the source for the title of this post? Answer in the comments section, please!

Today Scott and I gathered all of our tiny Pisaster stars and assigned them to food treatments. We're not doing a feeding experiment per se but have the goal of getting these juveniles to grow, and to do that we need to figure out what they eat when they're this small. Nobody knows, or at least we haven't been able to find any literature on the subject, so we're trying a shotgun approach and offering them several different items.

One of the food items is the bryozoan Membranipora membranacea, which I wrote about yesterday. Scott picked up some fresh kelp yesterday afternoon and several of the blades were encrusted with Membranipora. We thought these new colonies might be a more appetizing meal for the stars. We knew we'd have to remove any of the Corambe slugs that might be feasting on the bryozoan, so I put a piece under the scope. And. . . whoa. . .

So lively! The bryozoan colony was unbelievably gorgeous. All of the zooids were active and reactive, with lophophores extended and tentacles flicking. This video is taken in real-time. Note how the zooids act independently, but REact as a group. They share enough neural apparatus that stimuli are perceived almost instantaneously by all the zooids in a region.

One of the things I love about colonial and clonal animals is that they upend our preconceived notions of what an individual is. In an animal like a bryozoan, what is the individual? Is it the zooid, possessing its own feeding apparatus that it employs independently from the other zooids to which it is genetically identical? Or is it the colony, consisting of many zooids? And what role does genetic identity play in the definition of individual? How much integration among units is required before they collectively form what we call a body? So many fascinating questions to ponder!

Anyway, Scott had the brilliant idea of gut-loading the bryozoans before feeding them to the stars, so I fetched a couple mL of the green alga Dunaliella tertiolecta that we have growing in pure culture and gave them a few drops, just to see what the zooids would do.

Wow.

This video is also shot in real-time. The zooids are kind of just doing their thing, but when I add the drop of algae about halfway through the video they kick into high gear and go hyper. I didn't expect such an energetic response.

It is difficult to convey just how mesmerizing these bryozoans are. They are a fantastic example of animals that are completely overlooked even by many biologists because to understand and appreciate them you need to look at them under a microscope. Without magnification they really don't look like much, just whitish gray crusts growing on kelp blades. But the microscope opens up a view into their lives and shows us how complex and beautiful they are. Sometimes the most amazing and gorgeous things are the ones you can't see with the naked eye. And that is exactly what I love about them.

1

I came of age, in an academic sense, working as a technician in a lab where the research focused on colonial hydroids. The other tech in the lab, Brenda, and I would get sent out to collect hydroids, then spend another day or so picking the predatory nudibranchs off the colonies. The PI of the lab called nudibranchs "the enemies of the state" and they really did have a way of showing up out of nowhere and then eating a hydroid colony down to nothing. It was rather amazing, actually. Brenda and I would swear we'd picked off all the nudibranchs, and more would show up the next day. This same PI had another saying:  "For every hydroid there's a nudibranch that lives on it, eats it, and looks just like it."

Case in point. Today Scott and I were examining not hydroids, but bryozoans, which are a completely unrelated type of colonial animal. We want to see if our tiny juvenile Pisaster stars will eat the bryozoan. It didn't take long to see this:

The nudibranch Corambe sp. on the encrusting bryozoan Membranipora membranacea. 13 August 2015. © Allison J. Gong
The nudibranch Corambe sp. on the encrusting bryozoan Membranipora membranacea. 13 August 2015.
© Allison J. Gong

A bryozoan colony consists of many units, called zooids, that are connected in some way to form a functioning larger body. The brick-like white structures in the above photo are the zooecia, or "houses" of the bryozoan zooids. The round object near the center of the photo with wavy white lines is the nudibranch Corambe. The white lines on the back of the slug make it blend in very nicely with the bryozoan on which it feeds, and break up the outline of the body to disguise its size; how can you determine how big something is if you can't see its edges? This slug is probably 2-3 mm long. As with most creatures this size and so effectively cryptic, it is very easy to overlook the slugs and never see them; however, once you have a good search image they become much more conspicuous and you find them everywhere. Search images are great things.

It's also easier to see something if it's moving, and it turns out that this slug can move pretty fast:

The voice that you hear is Scott's.

Corambe lives primarily on Membranipora and eats it. Membranipora responds to this predation by forming spines along the edges of the colony; the spines make it more difficult for the nudibranch to crawl around. This kind of response is called an inducible defense. The same thing occurs when plants begin to produce noxious chemicals after being munched on by an insect herbivore. Scott and I will set up some feeding treatments for our juvenile stars and Membranipora will be one of the courses served, so we were both glad to see that despite all the slugs we picked off there were still lots of viable zooids remaining.

Here's what a bryozoan is all about. Each zooecium forms the outer casing of one zooid. The zooecium itself is non-living but contains the living part. In Membranipora all of the zooids in the colony are the same, and each one possesses a ciliated tentacular crown called a lophophore. The cilia on the tentacles produce a current that directs food particles to the mouth, which is located at the base of the lophophore. In this video you can see particles moving in the current, and one zooid accidentally sucks in a glom of stuff that is too big. Watch how it tries to get rid of the piece it doesn't want.

See how the individual tentacles sort of bend and then straighten up? I call that tentacle flicking.


If you spend a couple of hours looking at something through a microscope it's inevitable that you'll see something different and new. In one of the bryozoan pieces I saw two little pink blobs in an otherwise empty zooecium. It looked like they were moving, so I zoomed in and saw that they looked like shmoos. "Shmoo" has become my term for any undifferentiated, unsegmented, worm-like thing that I can't identify. These pink shmoos were definitely moving, and here's the video to prove it:

That little squeal at the end of the video? That's me. I was delighted to see that the shmoos have two eyes and turn somersaults. I still have no idea what they are, and I'm totally okay with that. It's enough to know that they exist.

1

This past weekend I attended a family reunion at South Lake Tahoe. It had been several years since the previous reunion for this side of the family, and it was wonderful seeing almost all of my cousins and their various offspring, plus aunts and uncles, in a glorious setting. All good things must come to an end, though, and finally we all left Tahoe to return to our regular lives.

On our way back I stopped at the Taylor Creek Visitor Center and did a short hike. The Rainbow Trail is a 1/2-mile loop that winds through forest, meadow, and riparian habitats and includes the stream profile chamber, which shows a bit of the natural creek where kokanee salmon migrate in the fall. It's a beautiful spot to walk around a bit and get a last nature fix before dealing with traffic and the drive home. Some day I'll time a visit to coincide with the salmon run. "Salmon run? What salmon run?" you may wonder. Well, read on.

Taylor Creek flows northward about 3.5 km from Fallen Leaf Lake into Lake Tahoe. It forms part of the wetland that protects Tahoe from runoff and silt, helping to maintain the clarity of the lake. As with most of the land in the Tahoe basin, Taylor Creek has been modified by human activity:  the streambed itself has been altered by road development, and the introduction of non-native species such as bullfrogs threatens populations of native species. Still, it is a remarkably beautiful place.

Meadow at Taylor Creek, South Lake Tahoe. 9 August 2015. © Allison J. Gong
Meadow at Taylor Creek, South Lake Tahoe. 9 August 2015.
© Allison J. Gong
Taylor Creek, South Lake Tahoe. 9 August 2015. © Allison J. Gong
Taylor Creek, South Lake Tahoe. 9 August 2015.
© Allison J. Gong

Beavers are also continually changing the course of the creek. They fell trees and construct dams that redirect water flow and create still ponds upstream of the dam. In the summer it is not uncommon to see dams and other evidence of beaver activity. Of course, the dams impede the movement of most fish up and down the creek.

Beaver dam on Taylor Creek, South Lake Tahoe. 9 August 2015. © Allison J. Gong
Beaver dam on Taylor Creek, South Lake Tahoe. 9 August 2015.
© Allison J. Gong
Tree almost felled by beavers at Taylor Creek, South Lake Tahoe. 9 August 2015. © Allison J. Gong
Beaver-gnawed tree at Taylor Creek, South Lake Tahoe. 9 August 2015.
© Allison J. Gong

One of the more noteworthy fish living in Taylor Creek is the kokanee salmon, a landlocked version of the sockeye (Oncorhynchus nerka) that is one of five species of salmon in the northeastern Pacific Ocean. Whereas most eastern Pacific salmon are anadromous, living their adult lives at sea but returning to freshwater rivers to reproduce, the kokanee spend their entire lives in freshwater. Kokanee were introduced into Lake Tahoe in the 1940s and have since become a popular game fish. In the fall, they migrate from Lake Tahoe into Taylor Creek to spawn. Beaver dams would block the kokanee's return to their spawning grounds, so every year the U.S. Fish and Wildlife Service demolishes the dams to allow the salmon access to the creek; this action also increases runoff into Lake Tahoe and decreases the total area of wetlands in the region, both of which have a detrimental effect on the lake's clarity. The net result is spawning habitat for a non-native species, the kokanee, at the cost of decreased lake clarity and (arguably) damage to a native species, the beaver. We humans seem to be unrelentingly amenable to making such trade-offs. I wonder where that will get us in the long run.

For most visitors, the highlight of the Rainbow Trail is the stream profile chamber. This little chamber has displays about the life cycle of the kokanee salmon, the seasons of Taylor Creek, and a window into the stream itself. At this time of year the only fish inhabitants were Lahontan redsides (Richardsonius egregius), minnow-like fishes about the length of my hand or a bit shorter. The kokanee, wearing their brilliant mating costumes, will pass through the stream in October.

I did take some video footage of the redsides swimming in the chamber, bathed in the sunlight that filters through the upper layers of water. The bird and other animal sounds you hear are recordings that are played in the chamber.

Returning to the outdoors, I hiked through more meadows and forest, stopping frequently to look and listen for birds. This summer, despite drought conditions throughout California, the Tahoe region has gotten enough rain for wildflowers (and mosquitos) to persist; I walked through fields of goldenrod, blooming skunk cabbage, lupine, and Queen Anne's lace. The aspen trees (Populus tremuloides) haven't started changing color yet, but walking through them I could hear the rustle of their leaves, which is one of the characteristic sounds of northern California high-altitude Sierra Nevada forests.

Aspen grove at Taylor Creek, South Lake Tahoe. 9 August 2015. © Allison J. Gong
Aspen grove at Taylor Creek, South Lake Tahoe. 9 August 2015.
© Allison J. Gong

In the autumn the aspens will change color and blanket the high Sierra in golds and oranges--yet another reason to return to the Tahoe area in the fall!

2

Two months ago now I gave my juvenile sea urchins a job. It's the kind of job they're perfectly suited for:  eating algae. I measured them all and randomly divvied them up into three food treatments. One group remains on the pink coralline alga they'd all been eating once they graduated from a diet of scum, one group gets to eat the soft green alga Ulva sp., and the third group is eating the kelp Macrocystis pyrifera. I fully expected that the urchins on coralline algae would grow much more slowly and experience higher mortality than the other groups. And now I have data to validate my intuition!

Test diameter of juvenile sea urchins (Strongylocentrotus purpuratus) as a function of diet. 3 August 2015. © Allison J. Gong
Test diameter of juvenile sea urchins (Strongylocentrotus purpuratus) as a function of diet. 3 August 2015.
© Allison J. Gong

It has been clear from the get-go that the Ulva and Macrocystis urchins are growing faster than the poor guys relegated to coralline algae. The coralline urchins are hanging in there, though, and are even growing a bit. They are also dying, a lot.

Population sizes of juvenile sea urchins (Strongylocentrotus purpuratus) as a function of diet. 3 August 2015. © Allison J. Gong
Population sizes of juvenile sea urchins (Strongylocentrotus purpuratus) as a function of diet. 3 August 2015.
© Allison J. Gong

During the first month of the experiment I was surprised to see the high attrition rate of urchins eating Macrocystis. I think these early deaths were due to the fact that Macrocystis, once it starts to go bad, goes bad fast. Even with daily water changes to rinse out the poop, the Macrocystis bowl tended to get dirty faster than the others, so poor water quality may have killed the urchins. The copious slime from the Macrocystis itself doesn't help, either. Eventually I will be able to graduate the urchins to containers that will allow flow-through water, but for now most of them are too small to be kept in screened containers because they would escape through the mesh.

Overall, the Ulva urchins seem to be the happiest. I haven't lost any this past month and they eat and poop a lot. These individuals have the good fortune that Ulva doesn't foul the water as quickly as Macrocystis does. They are extraordinarily beautiful, too, and are becoming much more colorful:

Juvenile sea urchin (Strongylocentrotus purpuratus), age 196 days. 3 August 2015. © Allison J. Gong
Juvenile sea urchin (Strongylocentrotus purpuratus), age 196 days. 3 August 2015.
© Allison J. Gong

I've always wondered about the biochemical magic that allows this species of sea urchin to eat algae (primarily kelps, but also some red and green algae) and end up so unabashedly purple as they grow to adulthood. I know from experience in the intertidal that juveniles of S. purpuratus usually go through a green stage when they're in the 1-2 cm size range, before they become purple. And once they're purple, they stay purple. Part of the reason I wanted to do this feeding experiment is to see how the juvenile diet affects color of the animal. These urchins are all from the same mating, so they are full siblings. Presumably there would be some color variation even among a cohort of full-sibs, but if I can distinguish differences between urchins eating Ulva and urchins eating Macrocystis, then perhaps these would be at least partly due to diet?

The difficulty is in photographing individual urchins under the same lighting and background conditions so that color can be somewhat objectively registered. I'm going to have to become a much better photographer, and the urchins are going to have to be more willing to sit still and pose for me. In the meantime, it is easier to compare overall color between the two groups, rather than individual urchins. Looking at the two bowls side-by-side, I get a better feel for the gestalt of each group; can you see the difference? Before you read the caption, can you guess which is the Ulva group and which is the Macrocystis group?

Juvenile sea urchins (Strongylocentrotus purpuratus), age 196 days. Urchins on the left are eating the green alga Ulva; urchins on the right are eating the kelp Macrocystis. 3 August 2015. © Allison J. Gong
Juvenile sea urchins (Strongylocentrotus purpuratus), age 196 days. Urchins on the left are eating the green alga Ulva; urchins on the right are eating the kelp Macrocystis. 3 August 2015.
© Allison J. Gong

To my admittedly very subjective eye, the urchins on the left have more dark pigment and the ones on the right have a more overall golden color. The golden color makes sense because Macrocystis is golden in color (even though taxonomically it is considered a brown alga). But the darker purple in the urchins eating green algae? That makes less sense to me. In any case, I'll have to wait and see how the color develops in both groups of urchins. I suspect that in the long run they'll all end up purple, because that's what they do in the field, but they may take different routes getting there. Stay tuned!

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