Last month I spent four days in the town of Egmont, BC. My husband and I had joined a friend on his annual excursion to the stomping grounds of his youth. We trailered the friend’s boat, Scherzo, up through Oregon and Washington and into British Columbia. We took a ferry and then ditched the car in Sechelt, piled our belongings and food into Scherzo, and headed up the Sechelt Inlet to arrive in Egmont. Incidentally, Egmont is entirely reachable by road, but it was kind of cool showing up in a little boat to the dock of the house we had rented.
On our way up Sechelt Inlet I had noticed quite a bit of brown scum on the surface of the water. I couldn’t collect any on my hands and it didn’t have a detectable odor, but some of my cerebral neurons did their job and the name Noctiluca came into my head. Noctiluca scintillans is a bioluminescent dinoflagellate. It is a regular component of the plankton in Monterey Bay at this time of year. What makes it distinct from other dinoflagellates are its large size (can be greater than 1mm in diameter) and the fact that its hydrophobic theca (cell wall) causes cells to get stuck at the surface of the water. They can look like tiny bubbles floating at the surface.
There wasn’t as much Noctiluca at our dock in Egmont as we’d seen on our way up the inlet, but it was worth going out at night just to see. Dinoflagellates and other bioluminescent critters light up when disturbed. We borrowed Scherzo‘s oar to disturb the water and see what happened. We could see light when Alex drew the oar back and forth in the water, but a washing machine-like agitation was the best for getting the cells to flash.
Bioluminescence is one of those phenomena that never gets tiring. In this case, each Noctiluca cell emits one tiny flash of light when it gets bumped. These photos give you an idea of how dense the population was. Dinoflagellates tend to be late-season bloomers, becoming more abundant than the diatoms that dominate the spring and early summer phytoplankton. Many dinoflagellates, despite being considered part of the phytoplankton, are heterotrophic either in addition to or instead of being autotrophic (photosynthetic). Noctiluca is one of the heterotrophic dinoflagellates. It preys on smaller cells, including diatoms, small invertebrate larvae, and fish eggs.
If I had been at home with my lab supplies at hand I would have collected some of the cells in a scintillation vial, brought them into a dark room in the house, and shaken them up to observe the bioluminescence under controlled conditions. As it was, seeing it in the field, so to speak, was really cool.
Earlier this week I collected a plankton sample and settled down for a day of microscopy. For a variety of reasons it was my first foray into actual biology for the month of June, and I just wanted to feel like a marine biologist for a while.
As far as plankton samples go, there wasn’t a lot to write home about. The large centric diatoms that we had seen in the spring were much less abundant, although there was quite a bit of the pennate diatom Pseudonitzschia. Part of the reason I did the plankton tow was to have something to look at under the microscope and to practice taking photos. There are all sorts of gadgets that allow one to use a phone to take photos through the microscope, but I’ve found those to be either specific to one phone model or too fiddly and frustrating to get properly lined up. Besides, when I bought my microscope several years ago now I had the foresight to splurge for the trinocular head, which allows me to mount a real camera and leaves both eyepieces available to look through. Might as well take advantage of it!
So, I just took a bunch of photos.
First up was a chain diatom in the genus Chaetoceros. Phase contrast lighting might not have been the best option here, but oh well. Chaetoceros cells are box-shaped, with a spine protruding from each corner of the box. Aside: ‘chaeto’ means ‘hair’ or ‘bristle’ in Greek. The spines of adjacent cells sort of interlock and hold the cells together, forming the chain. Spines also provide some defense against predation.
Many species of Chaetoceros form straight chains like this.
Earlier in the spring there were a lot of Coscinodiscus diatoms in the local plankton. Those are the big button-like diatoms with the sculpted frustule. They aren’t nearly as common now, but I did see a few. And managed to get a nice shot of one:
The star of the show was Thalassiothrix, another diatom in which the ends of cells cells remain connected after dividing. Instead of forming chains as Chaetoceros does, Thalassiothrix makes colonies that are either zig-zag or star-shaped. It just so happens that this organism looks especially brilliant under darkfield lighting, so I was very happy.
Isn’t that a spectacular organism? I had a lot of fun developing and processing that image, and am happy at how well it turned out. Darkfield lighting is fun to play with!
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.
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:
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.
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.
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.
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.
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
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.
This past weekend I was trying to manage some concussion headache issues and stayed away from the marine lab for four days. Usually that’s not a big deal. Since I’ve been absent so much of the summer due to the head injury, the lab assistants whose job it is to make sure that everybody has air and water and food have been told to check my stuff and change water daily. They’ve been keeping things alive when my headache wouldn’t tolerate my being at the lab, and I’ve gone in when I could (usually on weekends) to take care of the big chores. And so far, under normal conditions at the lab, this has worked.
But every so often conditions stray from the norm, and we are in one of those situations now. It isn’t uncommon at this time of year for us to experience an algal bloom in Monterey Bay. This isn’t the sort of spring phytoplankton bloom we get in the upwelling season, but a massive population explosion of a single species, usually a dinoflagellate. This kind of algal bloom is referred to as a “red tide,” even though the organism that causes it isn’t so much red as golden.
I went to San Francisco yesterday afternoon, and the water was brownish like this all the way up the coast. The bloom wasn’t evenly distributed; there were large patches of brown water interspersed with areas of clear blue water. At Scott Creek and Waddell Creek the breaking waves were distinctly tea-colored, which did not keep the kite surfers out of the water.
It might be easier to see the discoloration when the water is moving:
The seawater intake for the entire marine lab is straight off the point here in the surf zone, so this mucky water is the exact same stuff that’s trickling through our labs. When I returned to the lab on Monday after a 4-day absence the first thing I noticed when I opened the door was the smell, which I recognized immediately because we get red tides like this every year or so. It’s not really a horrible smell, like the smell of dead sea things, but it gets classified in my mind as ‘bad’ because of what it connotes. And it can get really bad, if the gunk accumulates and begins to rot.
When the cell concentration is this high, filter apparatuses get clogged up fast. This applies to both mechanical and biological filters. Unlike, say, small sediment particles that get suspended in water but act more or less independently of each other, the cells of these blooming dinoflagellates are sticky. They glom together in stringy mucilaginous masses, and tend to settle out in little eddies and areas with less water movement. When this muck settles on animals’ bodies, it can clog up gills or other respiratory surfaces, making gas exchange difficult or impossible. So while the red tide persists we siphon out tanks and flush tables at least once daily.
I guess when you see the color of these masses of cells, it makes sense to call this phenomenon a red tide. Under the microscope, however, the cells are golden. Based on the guilty party of the last big red tide event we had and some sampling data from Santa Cruz and Monterey dated 7 September, I’m pretty sure the cells are Akashiwo sanguinea. The cells are fairly large by dinoflagellate standards, ~100 µm long, and have the usual pair of flagella (1 wrapped around the middle and the other trailing free) that propel the cells through the water.
The groove around the middle of the cell is called the cingulum; one of the cell’s flagella sits in this groove like a belt going around your waist. The other indentation that runs from the cingulum to the posterior end is the sulcus, and houses the other flagellum that trails free like a very skinny tail. The beating of this pair of flagella causes the cell to swim in a spiral fashion:
People always want to know if a red tide is toxic, and if they need to stay out of the water. Akashiwo sanguinea, as far as anybody knows, does not produce toxins like some other dinoflagellates do. However, it does secrete surfactants that produce foam in agitated water, and a report from 2007 correlates a mass stranding of seabirds in Monterey Bay with a large bloom of A. sanguinea. The authors hypothesize that the foam from the surfactants of A. sanguinea coated the feathers of seabirds and hindered their ability to thermoregulate.
This afternoon I am heading out to the intertidal. One of the things I’ll be looking for is signs of the bloom. I do want to take some pictures in the tidepools, so I hope the discoloration isn’t too bad. Fingers crossed!
Spending the summer trying to heal a concussion brain injury means that not much science has been happening in my life lately. Now three months post-accident, I’m finally able to do a little bit of thinking and am not quite as exhausted as I was, although extended periods of concentration are still taxing and usually result in what I’ve come to call the concussion headache. I’m very disappointed to have been on the DL (disabled list) for most of the summer intertidal season, and hope that when the afternoon minus tides return this fall I’ll be able to take advantage of them. Fortunately my condition has progressed to the point that I can drive myself out to the wharf to collect a plankton sample and spend a couple of hours looking through microscopes at what I’ve caught. That’s about the limit of what I can do these days; it’s not much, but at least it’s something.
As we approach the autumn equinox I would expect to see signs that the summer growing season is winding down. Days are noticeably shorter than they were a month ago, and the major upwelling season has passed. In terms of plankton, this should mean a reduction in phytoplankton abundance and diversity, with an overall shift in population makeup away from the strictly photosynthetic diatoms and favoring dinoflagellates, many of which are at least sometimes heterotrophic.
The water at the wharf is remarkably clear right now. Visibility would be fantastic for anyone who wanted to dive under the wharf. September and October tend to be the best months for SCUBA diving in Monterey Bay because the natural cessation of coastal upwelling results in clearer and warmer surface water. I didn’t have a Secchi disk or any other way to measure turbidity, but judging by how far below the surface I could see the plankton net as it sank I’d guesstimate that visibility was about 7.5 meters. For people used to diving in the oligotrophic waters of the tropics this level of visibility is downright awful, but for those who dive in productive areas this is not bad.
As expected, when I pulled up the net there wasn’t much phytoplankton in the net, and none of the diatom smell I get in spring plankton tows. The net came up pretty clear and rinsed easily into my jar. There was, however, a lot of zooplankton. When I got back to the lab I started looking through small aliquots to see what was there.
The usual suspects were quite plentiful. These included:
copepods, in both larval and adult stages
polychaete worms
veliger larvae, of both gastropod and bivalve types
medusae from the hydroid Obelia sp.
tintinnids, a type of protozoan that lives in a goblet-shaped glass shell
echinopluteus larvae, probably of the sand dollar Dendraster excentricus
Especially beautiful in today’s sample were the acantharians:
Acantharians are large single-celled protozoans; I’ve seen some that are 3 mm in diameter. They build spines of strontium sulfate, which are arranged in precise geometric formations. The protoplasm of the cell extends partway along the spines, which are thought both to deter predation and provide buoyancy. Acantharians are predatory, feeding on smaller unicellular organisms, but also form symbiotic relationships with unicellular algae. The algae are given safe harbor within the cell of the acantharian, and in return provide fixed carbon to the protozoan. Although the players are different, this is pretty much the exact same symbiosis as occurs between reef-building corals and zooxanthellae in the tropics (and also between some of our temperate sea anemones and zooxanthellae).
Here’s a puzzle for you. Take a look at this pair of animals:
Both consist of a roundish body and a tail. The one on the left is much larger, about 5 mm long, and more opaque. The one on the right is about 2 mm long and is very transparent.
Question: Do you think these animals are the same thing?
Answer: It can often be a mistake to assume any close evolutionary relationship between animals that appear to share a morphological similarity, but in this case shape does result from genetic relatedness. Both of these animals are chordates, my (and your!) closest invertebrate relatives. Yes, we share a closer kinship to these critters than we do to any other invertebrates. We also share with them the following morphological characteristics: pharyngeal gill slits, a dorsal hollow nerve cord, a notochord, and a post-anal tail. Of course, for us the gill slits, notochord, and tail are gone long before we are born, but if you look at pictures of human embryos you can see them. Once we are born the only chordate characteristic remaining to us is the dorsal hollow nerve cord, which runs up through our vertebral column.
The animal on the left is called a tadpole larva, probably of one of the benthic solitary or colonial tunicates. Tadpole larvae are short-lived and lecithotrophic (i.e., non-feeding); the opacity of the body is an indicator of energy reserves stored in body tissues. Tadpole larvae have a short larval life. They typically don’t disperse far from the parent, and within a few hours metamorphose into new tunicates.
The animal on the right is a larvacean. It bears a superficial resemblance to the tadpole larva, but is an adult. Larvaceans are entirely planktonic and have one of the most interesting lifestyles imaginable. They live in a house of snot. The house is secreted from an area on the back of the animal, and is inflated as the animal pumps its tail up and down in a rhythmic sinusoidal fashion. The mucus house actually consists of two distinct meshes: the outer mesh is coarse and serves to keep large particles from clogging up the finer feeding mesh. The feeding mesh collects very small particles, which are transported in a mucus thread to the animal’s mouth.
Larvacean in its mucus house.
Larvaceans are prodigious mucus makers. As any filter does, the house eventually clogs up. Instead of trying to backflush and clean out its house, the larvacean wiggles out of it and secretes a new one. They can build up to three houses a day when the water is full of plankton! The discarded houses of countless larvaceans slowly sink from the surface and are a major source of food to animals in the deep sea.
Larvaceans caught in a plankton net are almost always dislodged from their houses. In a dish or a drop of water on a microscope slide, they thrash about in a characteristic larvacean sort of way. Only once have I caught a larvacean and then been able to watch it build a new house in my dish of water. What I saw today is much more typical.
This poor animal was trapped under a cover slip so it can’t move freely, but the tail still thrashes about. You can also see its little heart beating like mad.
The tadpole larva, on the other hand, is a much more sedentary creature. It doesn’t disperse far so its tail remains still, and its heart rate is much slower than that of its pelagic cousin:
To shift to a completely different taxon there were, as usual, many crustaceans. In addition to the larval and adult copepods, today I saw several examples of Podon, a type of crustacean called a cladoceran. The most familiar cladocerans are the freshwater Daphnia species, but in Monterey Bay we see Podon on a fairly regular basis. Cladocerans reproduce via parthenogenesis, in which unfertilized eggs develop into daughters, and in the springtime most of the Podon I catch are gravid. At this time of year, however, they are not reproducing, at least not parthenogenetically.
The most striking feature of Podon is its large compound eye, which causes problems. For many creatures living up in the water column, the only way to hide is to be transparent. This invisibility would be interrupted by any pigment in or on the body. Unfortunately for Podon and other animals that try to hide in plain view, eyes are, at bare minimum, a collection of pigmented cells that detect light. For them, eyes are both a useful sensory structure and a big “Here I am!” signal for predators.
The best thing I saw in today’s sample, aside from the acantharians, was a small ciliated blob with little ciliated flaps. This cute little creature is the Müller’s larva of a polyclad flatworm. It’s hard to appreciate the cuteness of Müller’s larva in a 2-dimensional still shot, so here’s a video:
Okay, so maybe it’s not the cutest larva in the plankton. It was swimming really fast and I had to squash it a bit under a cover slip to slow it down enough that I could keep up with it. But I don’t come across them very often, so it’s always a pleasure when they show up. You’ll have to take my word that they’re cute.
Oh, and by the way, I kept the tadpole larva and a couple of other shmoo-like larvae in a dish of seawater to see what they will turn into. Tomorrow I may have new things to look at. I dumped the rest of the plankton into a tank of filter-feeders, where they will resume their place in the food chain.
This week it has been very windy on the coast. As in hope-the-next-gust-doesn’t-arrive-while-I-am-still-holding-onto-the-door windy. Seriously, the other day I almost wrenched my shoulder when the wind caught a door I was walking through just as I opened it. I should have braced myself before opening that door. The wind also blows around dust and pollen, exacerbating everybody’s spring allergies.
Despite all that, the wind is a good thing because it is the driving force behind coastal upwelling, the oceanographic phenomenon that brings cold, nutrient-rich water from depth to the surface. Upwelled water provides the nutrients that primary producers such as phytoplankton require for photosynthesis. The simple equation is: Sunlight + nutrients = photosynthesis. With the days getting longer as we head toward the summer solstice, this is the perfect time of year to be a phytoplankter. (Note: a phyto- or zooplankter is any creature that lives as plankton)
It takes several days of sustained winds from the north to start upwelling along the coast. I record the temperature in one of my seawater tables every day and keep an eye out for decreases that might indicate upwelling. Given that it’s been crazy windy since Sunday (today is Wednesday) I thought today would be a good day to collect a plankton sample and see what’s going on.
What did I find? Lots of phytoplankton, right on schedule!
Most of these critters are diatoms, of which there were several different types. Diatoms are unicellular algae whose cells are encased in a fancy silica shell called a frustule. More on that later. In Monterey Bay, the first phytoplankters to bloom in the spring are usually diatoms; they can take advantage of upwelled nutrients to fuel rapid asexual division so their populations grow quickly. Photosynthetic creatures from diatoms to redwood trees can perform the biochemical magic of capturing light energy and converting it to chemical energy held in molecules containing fixed carbon (e.g., glucose). Diatom blooms provide food for grazing zooplankters such as copepods and krill. These small animals become food for any number of larger animals, and so on up the food chain, so in every sense possible the phytoplankton are the foundation upon which the entire marine food web is based. Interested in saving the whales? Then you should focus your energies on saving the phytoplankton. Seriously.
The largest object in the photo above is a large protozoan ciliate called a tintinnid. They also live in glass shells, only theirs is called a lorica (L: “body armor”). The tintinnids I see most frequently in tows from the Wharf have a clear goblet-shaped lorica that is entirely transparent. These tintinnids are big, for single-celled creatures, up to over 1 mm in length. That’s a lot bigger than some multicellular animals!
Tintinnids are frantic little swimmers. They are heavily ciliated, which means they can swim really fast. The one in the photo was tangled up in the phytoplankton and squashed under a cover slip, which conveniently retarded its motion, but in this video you can see its little cilia beating. I added a few seconds of a different tintinnid swimming solo to the end of the video clip, which will give you a better idea of how they swim.
Here are some other plankters from today’s sample:
Photo #1 – Diatoms. The large cell with the spines on both ends is Ditylum brightwellii, one of my favorite scientific names. Chaetoceros cells each have long spines at the corners of the cells. The spines link adjacent cells together, forming chains.
Photo #4 – Assorted phytoplankton. In this photo the five roundish cells are the dinoflagellate Protoperidinium. They have two flagella, one in a groove that wraps around the cell and one that trails free. The two button-like cells near the center of the picture are (I think) the diatom Thalassiosira. There are two chains of Chaetoceros debilis and several other chain diatoms. That big opaque vaguely bullet-shaped object to the right of center? That’s a fecal pellet, probably from a copepod.
Speaking of copepods, as usual they were very abundant, both as adults and as larvae. In terms of numbers of individuals, copepods are likely the most abundant animals in the sea. Copepods are small crustaceans that feed on phytoplankton and are in turn eaten by many larger animals. In life they have beautifully transparent bodies, allowing us to see the beating heart. See for yourself:
And, finally, about those diatom frustules. As I mentioned above, a diatom’s frustule is a sculpted shell made of silica (SiO2). It comes in two parts, an epitheca and a hypotheca, that fit together like the two halves of a petri dish. In fact, I use a petri dish as a frustule model for my marine biology students; it is made of roughly the same substance and demonstrates the size relationship between the epitheca and hypotheca.
The large round centric diatoms best show the structure of the frustule. Here’s the best photo I was able to take today of one of the very large centrics, Coscinodiscus:
I hope that later in the season I can take some better photos of these diatoms. They are so beautiful that I really to do them justice. So much diversity early in the season makes me hope for a good productive season. We’ll see!
Friday 1 April was the last day of my spring break, and tomorrow I go back to teaching. Spring break felt very short this year, and I was busy the entire week. I decided to spend my last day of freedom doing my favorite lab-related things: looking through microscopes at tiny organisms. I had already planned on spending a few hours dealing with my two batches of larvae, and figured I might as well make a day of it and collect a plankton sample on my way in.
Alas, as gorgeous as the outdoor scenery was, I couldn’t linger long once I’d collected the plankton sample so I headed to the lab. If you’ve ever wondered what a marine biologist’s desk looks like, here’s mine:
The dissecting scope on the left belongs to me, as it was a graduation gift I bought for myself when I finished graduate school. The compound scope on the right belongs to the lab, but I’m the person who uses it most frequently. I find that, when looking at something like plankton, it’s easiest to start by looking at a bit of the sample in a small dish under the dissecting scope; then, when I find interesting critters I can pipet them out and put them on a microscope slide for observation under the compound scope. It may seem a little awkward, but this switching back and forth between “forest” and “tree” views works for me. And honestly, any field biologist worth her salt should be able to switch focus from “big picture” to “small detail” fairly easily. How else would she be able to develop a solid understanding of the system(s) she studies?
Now back to the plankton. Right off the bat I could see with the naked eye some big (by plankton standards) crustaceans zooming around. It wasn’t easy chasing them down with the pipet, but after a while I caught one and dumped it on a depression slide. It was a mysid shrimp.
Those big compound eyes are stereotypical of many crustaceans–think crabs, lobsters, large shrimps, etc. Looking carefully at the tail of this particular individual, can you see two small circular structures? Those are statocysts, the organs that give the animal information about its orientation with respect to gravity. The presence of two statocysts in the uropods (the appendages on the most posterior segment of the body) tell me that this animal is a mysid, rather than one of the gazillion other shrimplike crustaceans living in the sea. I saw at least half a dozen mysids in this plankton sample.
Overall, this wasn’t the most interesting plankton sample I’ve ever collected. When my students and I collected and examined a sample a week earlier, we saw much more animal diversity than I saw the other day. We had some strong winds on Monday-Thursday of last week (I’m writing this on Sunday) and the surface water temperature dropped to 12°C; I thought this would be the start of the spring upwelling season. If it was, then the phytoplankers hadn’t responded when I collected this plankton sample on Friday. In any case, it appears that the spring phytoplankton bloom hadn’t yet begun. I expect that in another week or two I’ll find more diatoms in the plankton.
After lunch it was time to tend and observe my larvae. There’s not much to report about the Dermasterias (leather star) larvae. If you remember, I’ve split these larvae into three different food treatments: (1) Dunaliella only; (2) a combination of Dunaliella and Isochrysis; and (3) Isochrysis only. At this point, 38 days into development, there is no discernable difference between treatments 1 and 2. The larvae in treatment 3, however, don’t look so good. They are stunted and appear to be regressing to earlier developmental stages.
On the other hand, the Dendraster (sand dollar) plutei continue to astound and fascinate me. They are stunning!
They are happy and healthy and seem to be doing well. Their posterodorsal arms have grown and their pre-oral arms (the fourth and last pair to form) are poking out. The larvae are eating all the food I’m giving them and are putting it to good use. At this rate I expect to see their rudiments developing soon.
You may have heard that earlier this month the California Department of Fish and Wildlife postponed the scheduled opening of the commercial Dungeness crab season. Gasps of dismay were heard all over the state from Californians whose Thanksgiving traditions include cracked crab, as well as from the folks who make a living fishing for them. The closure is due to the detection of domoic acid (DA) in the crabs. DA is a naturally occurring toxin produced by some species of diatoms in the genus Pseudo-nitzschia. DA is ingested by filter-feeding animals such as mussels, and due to the process of bioaccumulation occurs in higher concentrations in the tissues of animals that feed at higher trophic levels. Humans can be affected by DA also, which is why state officials warn people not to collect and eat mussels when DA levels are high enough to be concerning.
Since the crab fishery closure I’ve been wanting to do my own informal assessment of Pseudo-nitzschia in the water, but with one thing and another I didn’t have the time or opportunity until today. This morning I collected a plankton sample and gave myself a few hours to play with it before I had to start grading papers. Pseudo-nitzschia was present but not incredibly abundant, especially compared to what I saw this past August. Today’s Pseudos were in chains of 3-4 cells, instead of the 12 cells that were common in the summer.
But it turns out that Pseudo-nitzschia wasn’t the most interesting thing I found in the plankton today. Just about at the time that I was supposed to stop playing and start grading, I saw one of these:
This was a big cell, measuring 250 µm long and 80 µm wide. Right away it had a diatom look about it: the visible protoplasm was golden-brown, the color of diatoms; it didn’t have any cilia or flagella; and it was scooting along very slowly, the way a pennate diatom does. But it wasn’t anything that I recognized, which made it all the more intriguing. I made an executive decision to investigate further, even if it meant not getting my papers graded. Damn the consequences, science was calling!
I did some poking around, searching through photo databases of local diatom species, not having much success. Since this was a new (to me, at least) critter, it warranted not just a photo and video but an entry in my real lab notebook:
Besides, spending time with a microscope, notebook, and pencil feels more like doing science than when I take pictures. And it has been a while since I’ve been entirely stumped, so I was having fun.
It turns out that this diatom isn’t all that uncommon in Monterey Bay. I happened across a report of a diatom named Tropidoneis antarctica that had been detected in a plankton tow off our very own Santa Cruz Wharf about a week ago. BINGO! I had a name for my mystery critter, learned something new, and got to play for a morning. And notice that I spelled the genus name wrong in my notebook? Oops.
And, by the way, the papers did all get graded. I am (un)fortunately far too responsible to have let them not get graded. I’m working on that, though. Give me another 50 years or so and I’ll be as flaky and unreliable as the next guy.
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.
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.
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.
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:
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.
