Over the holiday weekend I was in Morro Bay for a surprise 80th birthday party--not mine! The party on Friday evening was a huge success (none of the guests let the cat out of the bag), the birthday girl was completely taken by surprise, and a good time was had by all. The weather was cold and sporadically stormy the entire weekend, but the clear spells between storm squalls were gorgeous and almost a little warm.
Since it wasn't raining on Saturday morning, we went out to Morro Rock to look for peregrine falcons. There are two (I think) pairs of falcons nesting on the Rock, one of which nests on the side of the rock that is visible to people. This is nesting season, and Morro Rock has a lot of ledges that make good nesting platforms. Peregrines don't make a nest, really. They lay eggs and incubate them on ledge high up on structures--rock cliffs, buildings, bridges--that dominate the landscape. We did see one peregrine way up on the rock, identifiable through binoculars but far enough away that I couldn't get a decent photo. This is the best I could do:
So not much success with the falcons, although I could at least document that they were there. Turning away from the Rock I was able to watch a great blue heron (Ardea herodias) go after and catch and eat a juvenile rockfish! The photos tell the story, so I'll just post them.
And finally, down the hatch it goes:
And there you have it! On a day when it was too blustery for human fishers to venture out of the bay, one avian predator had a successful morning. Way to go, bird!
Combine the words "gold" and "California" and you automatically come up with the Gold Rush, don't you? After all, California is the Golden State. And while that nickname may be to honor the golden hills of summer or the poppies that are the state flower, it may also be a tribute to the discovery of gold in 1848. For better or worse, the Gold Rush initiated rapid development of this area, and California eventually became the 31st state in 1850.
For me, and I suspect for many people, gold is one of the quintessential colors of autumn. Yet here we are in the middle of winter heading towards spring, and I saw a lot of gold in the forest the other day. I had taken my Ecology students to Rancho del Oso for the first field trip of the semester and set them loose to saunter through the woods and practice noticing (and recording) patterns in nature. Incidentally, I have adopted the word 'saunter' as a replacement for 'hike' for most of my own outdoor adventures. I have always been a slow hiker, and felt that in order to keep up with other people I had to miss seeing what was going on around me. Not to mention the fact that I'm always stopping to take pictures or examine some weird thing on the ground, or in the trees, or wherever. By giving myself permission to saunter along at the pace at which nature occurs, I have time to slow down and observe more carefully, and come away with a much better understanding of the world I've passed through. It certainly doesn't work for everybody, but I've learned that the journey is as important as the final destination, and that has made hiking sauntering much more enjoyable for me.
So, back to the gold. One of the very first thing I noticed when we hit the trail was this brilliant yellow-orange slime mold growing on twigs on the forest floor. This area is a mixed forest of hardwoods (mostly oaks) and various pines. I can't be certain what these sticks hosting the slime mold are, but they may be some kind of pine.
Slime molds are very strange organisms that don't fit into any of the major eukaryotic kingdoms of life (Animalia, Plantae, or Fungi). The current taxonomic position of slime molds is up for debate and far from settled, so I won't go into it here. Like fungi, slime molds feed on dead and decaying plant matter and are part of the decomposer niche of organisms. Also like fungi, most of a slime mold's life is microscopic. In the case of fungi most of the body, called a mycelium, is a network of extremely thin threads called hyphae. The mycelium for most fungi is underground and thus invisible to the casual observer. What we call a mushroom is only the reproductive fruiting body, which pushes to the surface so that spores can be released into the air.
For most of the time, or at least as long as food is plentiful, a slime mold exists as single amoeba-like or flagellated cells that feed on bacteria. These cells are haploid, containing only one set of chromosomes. Sexual reproduction (labelled SYNGAMY in the figure below) occurs when an amoeba-like cell encounters a compatible flagellated cell. I would also be willing to bet that the amoeboid and flagellated cells are triggered to find each other and initiate syngamy when food is scarce, as is the case with many animals.
The result of syngamy in a slime mold is a zygote which develops into a macroscopic stage called the plasmodium. The plasmodium undergoes nuclear division multiple times but cytokinesis doesn't occur, resulting in a large cell bounded by a single plasma membrane and containing many nuclei. In animal tissues we describe this condition as syncytial; I don't know if the same word is used by slime mold specialists, but the concept applies.
One of the things that makes slime molds truly bizarre is their method of locomotion. Using time-lapse videography, you can actually see how the contents of the cell swash back and forth in a process called cytoplasmic streaming. The net result of all this cytoplasmic streaming is the physical movement of the plasmodium into new territory. It's a process much easier to understand if you can see it, so here's a video from KQED's Deep Look series:
As with many fungi, slime molds are difficult to identify if you don't see the fruiting body. The slime mold that we encountered the other day was an immature plasmodium that hadn't yet produced fruiting bodies. The experts who took a look at my observation on iNaturalist agreed that it is likely Leocarpus fragilis, based on location and time of year, but they cannot be certain.
Continuing with our theme of gold, we saw several small blotches of golden jelly growing on tree trunks. These were the Tremella fungi. There are two species of golden Tremella in our region, T. mesenterica and T. aurantia. It seems that differentiation between the species depends on examination of microscopic structures, so I am unable to tell which species this little blob is. However, I will point out that the species epithet aurantia means 'gold', so I really hope that's the name for this blob.
Saving the best for last! Moving away from the creek and into the more enclosed forest we entered the realm of everybody's favorite terrestrial pulmonate gastropod, the banana slug. They were out in full force, chowing down on mushrooms and sliming up the foliage. One of my students picked up a banana slug and let it crawl on her hand for a while, but to my knowledge nobody licked one. All of the banana slugs that I saw were bright yellow with no brown or gray blotches, so I conclude that they were either Ariolimax californicus (the so-called Peninsula banana slug) or A. dolichophallus (the Santa Cruz banana slug, also the school mascot for UC Santa Cruz).
But this is where things get interesting. According to their mitochondrial DNA these two species, A. californicus and A. dolichophallus, do not have overlapping ranges. And the dividing line between them is Rancho del Oso, with A. californicus occurring to the north and A. dolichophallus occurring to the south. So, if Rancho del Oso is the magic line defining the ranges of these two species, what species are the slugs at Rancho del Oso? I think that answering this question will require a much finer scale study. For now, I'm just going to call them Ariolimax sp., because that seems to be the safest option until things get sorted out.
I've written about banana slugs before, but I've never had a chance to photograph them doing the actual nasty. Luckily for me and the students, banana slugs have no shame. I think the entire class got to get a close look and photos of this copulating pair:
This perfect yin-yang symbol is the result of how banana slugs align themselves during copulation. Each hermaphroditic slug has a genital open behind the head on the right side of the body. There's a lot of kinky stuff that happens during banana slug sex, including the chewing off of one partner's penis, but suffice to say that one animal's penis is inserted into the vagina of the other and, well, we don't know how quickly sperm is transferred, but the animals remain locked together for several hours. Yes, HOURS. Ahem. The penis chewing thing doesn't happen every time slugs mate, and biologists are still trying to figure out the function for this unusual behavior.
We have another several weeks (hopefully!) of rainy weather, so there will be lots of time to explore the world of fungi, slime molds, and banana slugs. The combination of rain and lengthening days creates great conditions to revel in the gold of a California winter in the forest.
The spring semester started this week, which means that every Friday I'll be taking my Ecology students on field trips. Yesterday's field trip, the first of the class, was to Rancho del Oso and Waddell Beach. Every year I've taken the students to these sites to visit two different habitats: forest and beach. And all we have to do to get from one to the other is cross the highway. The beauty of this particular field trip is that it is almost entirely unstructured. My goal is to give the students a chance to spend time outdoors and slow down enough to really observe what's going on around them. They get to crack open their brand new notebooks and work on their first entries, which can be a little intimidating for them. One suggestion I made was to find a spot to sit quietly, close their eyes, and observe the world using their other senses. Since we humans are such visual creatures, people are always surprised to discover how much they can perceive with their eyes closed.
Getting to do yesterday's field trip at all wasn't something to be taken for granted. There are some storm systems working their way through the area. They're nothing like the polar vortex that has been subjecting the midwest and now the east coast to well-below-freezing temperatures, but are projected to dump a lot of rain and blow like crazy. I'd been keeping an eye on the weather forecast all week, hoping that the rain on Friday would at least hold off until the afternoon so we could do the forest part of our field trip. I figured that if we got to any of the beach stuff after lunch that would be gravy.
Here we are, in the midst of winter, and already there are signs of spring. The willows are starting to leaf out and there was a lot of poison oak putting out leaves, all shiny and dangerous. Fortunately the poison oak is easy to recognize--and avoid--when it has leaves, and hopefully nobody who is allergic was exposed to it.
Of course, one of the best things about the forest in winter is the mycoflora. Rancho del Oso is a good place to see mushrooms and slime molds, and yesterday I saw things that I'd never seen before. Now, I'm not a mycologist by any stretch of the imagination. But I did my best, with the help of Mushrooms of the Redwood Coast and iNaturalist, to identify the ones I saw and managed to take decent photos of. And some remain unidentified. I simply don't know enough to make more than a very rough guess, which isn't at all likely to be correct.
When people think of the genus Amanita they think of things like the death cap mushroom (A. phalloides) or A. muscaria, with its iconic white-spotted red cap. But Amanita is a large genus, with many species categorized into several sections. Not all of the Amanita mushrooms are poisonous, and some are edible if prepared properly. This one is a rather nondescript brown, but based on photos in MotRC, Amanita fruiting bodies come in various shades of white, gray, yellow, brown, and russet. It's going to take me a lot of time and practice to begin getting these mushrooms straight!
I've always been drawn to the various shelf or bracket fungi because their morphology is so un-mushroomlike. Most of the bracket fungi we have here are polypores, meaning that the fruiting body releases spores through holes on the bottom surface rather than the more familiar gills you see on mushrooms. The very common and variable turkey tail (Trametes versicolor) grows on many host species is a polypore. Its congener, T. betulina, however, has gills. The rather paradoxical common name of T. betulina is gilled polypore, which of course doesn't really make sense.
Of course, I forgot to look at the bottom surface of this bracket fungus, so I don't know which species of Trametes it is. Naturalist fail!
This bizarre mushroom, which looks like a miniature bok choy that is black instead of green, is an elfin saddle in the genus Helvella.
According to MotRC there are two species of Helvella that co-occur in this area and can be difficult to distinguish without genetic analysis. Helvella vespertina (western black elfin saddle) is associated with coniferous trees and fruits in autumn and winter. Helvella dryophila (oak-loving elfin saddle) is usually found in with oaks and produces fruiting bodies in winter and spring. Because we saw this mushroom in a mixed forest in the middle of winter, I'm going to play it safe and stick with Helvella sp.
These red-capped mushrooms are a species of Russula, I think. It looks like they've been munched on, perhaps by banana slugs. More on that in the next post!
There are some very bizarre fungi out there! Some of them have fantastic fruiting bodies, and some are much more blobby. The jelly fungi are very aptly named, and are the blobbiest. We saw lots of little bright orange blobs growing on hardwoods. These are called witch's butter, known to mycologists as Tremella aurantia:
Despite the common name, T. aurantia is edible but apparently not appealing. So eating it won't make you sick, but you may still wish you hadn't eaten it. When it comes to mushrooms, that's definitely not the worst possible outcome. Given my own lack of expertise with mushrooms I'm one of the last people to tell you which ones to eat. But I do know enough not to eat anything that I find in the field. Some day I hope to go mushroom foraging with someone who really knows what he or she is doing, and whose judgment I trust. Until then, I'll continue to enjoy mushrooms where they grow and not concern myself with issues of edibility. The mushrooms certainly do deserve to be appreciated for their appearance and the ecological relationships they form with the plants and animals of the forest.
Among photographers and those who watch the sky, last night's lunar eclipse was an event to stay up late for. In much of California the latest storm left the sky cloudy, but I was lucky to have pretty good viewing for most of the eclipse. The moon was behind clouds at the beginning of the eclipse and for most of the period of totality, though, so I didn't get any pictures of those times.
I did, however, take a series of photos of what I could see. Here they are, in chronological order. All photos were taken with my new camera, a Nikon D750 combined with the Nikkor 300mm f/4 prime lens.
21:36 Pacific Standard Time:
21:41 Pacific Standard Time:
21:51 Pacific Standard Time:
22:33 Pacific Standard Time:
22:48 Pacific Standard Time:
At this point the clouds came back and it started to rain. I didn't wait for the eclipse to end, as I wouldn't have been able to see it anyway. When I got up this morning the skies had cleared, and since the moon would still be full I sat on the front porch in my pajamas and bathrobe and took this final shot.
05:53 Pacific Standard Time:
And there you have it--my series of eclipse photos! I learned a lot while shooting and processing these. I am embarrassed at how long it took me to figure out how to create this montage:
People who moved here from other states often say that California doesn't really have seasons. I think what they mean is that in general we don't oscillate between frigid winters and hot, humid summers. The Pacific Ocean moderates weather conditions through most of the state, giving us our Mediterranean climate characterized by a short rainy season and a long dry summer. However, California is a very large state with many different climate zones. Here on the coast our summers are cool and foggy, while in the interior of the state summers can be quite hot, upwards of 38° C for weeks at a time. Snow falls in the Sierra Nevada, providing much of the state's annual water budget, but the rest of the state usually remains snow-free for most of the winter.
That said, California does of course have seasons, even though they may not be as in-your-face as what you'd see in, say, New England. One of the ways to experience the seasons is to observe the comings and goings of migratory wildlife, especially birds. In fact, bird migration patterns make up a significant part of phenology, the study of the timing of biological events in the natural world. California's position along the Pacific Flyway provides fantastic bird watching opportunities throughout the year. There are many locations within California that are pit stops for birds migrating up and down the coast and overwintering oases for birds that breed much farther north.
The San Luis National Wildlife Refuge (NWR) in Merced County is one such place. Located in the Central Valley, it represents some of the original habitat in this part of the state. The San Joaquin River winds through the Reserve, providing riparian habitat, although the river is currently a mere ghost of its former glory. Since 2009, federal and state entities have worked to restore the San Joaquin, increasing water flows and cleaning up the surrounding lands. While it would be marvelous to see chinook salmon once again migrating from San Francisco Bay up the San Joaquin, it hasn't happened yet. The re-establishment of salmon runs up to just below Friant Dam would indicate a healthy San Joaquin River, and I really hope to see it in my lifetime.
Before the era of modern agriculture, much of the Central Valley flooded with the winter rains and spring snowmelt. Only a tiny fraction of these wetlands remain; most have been drained for agriculture and further deprived of water by state and federal water diversion projects. In areas such as these, small pools form during the wet season. These vernal pools--so called because they are often at their deepest during the spring--are ephemeral habitats. They almost always disappear during the long dry summer, but during their short existence they provide living space for a unique biota. A few vernal pools occur in most of the flat areas of California, although there are far fewer of them than before, and they differ biologically throughout the state. It is not uncommon for each vernal pool in a given area to have its own combination of flora and fauna, all of which have adapted to thrive in both desiccated and flooded conditions.
On our way back to the coast after spending Christmas with my family, we stopped at the San Luis NWR to do some wildlife watching. The visitor center was closed because of the federal government shutdown, but the roads were open. The Refuge has two auto tour routes, one to the tule elk reserve and the other to see resident and visiting aquatic birds. We chose to drive the bird route, because winter is a good time to see birds that spend the rest of the year at much higher latitudes.
Coots (Fulica americana) are ubiquitous in California's wetland habitats, and because of that they are easily overlooked. When I was little we called them 'mudhens' and smirked at them because they weren't ducks. Of course I now realize that that thinking is entirely unfair, and have come to appreciate coots because they aren't ducks.
In addition to the coots, which weren't much of a surprise because we expected to see them, we saw large numbers of several species that we weren't as familiar with. There were ducks and geese, which took us some time to ID because they weren't mallards and Canada geese. Fortunately I keep a bird field guide and binoculars in the car! My favorite bird ID book is the National Geographic Field Guide to the Birds of North America; we keep one of the later editions at home, but my beloved and well battered third edition lives in the glove compartment.
The ducks turned out to be northern shovelers, which I've seen at Elkhorn Slough. True to the typical avian way of doing things, the males are strikingly colored, with brilliant green heads, while the females are a dark streaky brown. In the photo below, a female swims with two males.
The geese were entirely new to us. We first saw them flying overhead in the V-shaped formations that you expect from a gaggle of geese in the air. But they didn't honk like Canada geese so we knew right away that they were something different.
I wasn't able to ID these until we got home and I looked at my photos on the computer. iNaturalist helpfully gave me a tentative ID of greater white-fronted goose (Anser albifrons), which I was happy to go along with.
In North America, greater white-fronted geese nest in the Arctic of western Canada and through most of Alaska, including out along the Aleutians. They migrate south to spend the winter along the Gulf coast and along the eastern coast of the Sea of Cortez. The winter wetlands of the Sacramento and San Joaquin Valleys host many of these geese, and smaller numbers overwinter in coastal Oregon and Washington.
Living in California, I don't usually expect to encounter any species whose common name includes the word 'tundra', but tundra swans do indeed spend their winters here! They nest in the very high Arctic on tundra, a habitat that is threatened by climate change, and winter is the only time we would see them in the lower 48, when large flocks venture south to overwinter near lakes and estuaries. I'll keep an eye out for them next time I'm at Elkhorn Slough or Moss Landing.
We saw hundreds of these swans hanging out with the shovelers. Only a few were within photograph range, as I don't have a very long telephoto lens (yet!), but there were lots of large white blobs floating, foraging, preening, and sleeping. They were fun to watch through the binoculars. We had hoped to see some sandhill cranes in the Refuge, too. We had seen them off in the distance, much too far to be photographed, but it wasn't until we were on the last leg of the auto tour that we saw them up close. They were not mingling with the swans and geese, and as far as we could tell tended to gather in single-species flocks. They seemed to be more skittish, too, and would startle and fly away when they heard human noises. I had to move slowly and quietly to get this close to them. Even the sound of the camera shutter caught their attention and made them wary.
The Central Valley is Ground Zero for sandhill cranes in California, where they can be seen only in the winter. They don't breed here, of course, but there is a small population of ~460 pairs of sandhill cranes breeding in far northeastern California. There are locations in the Central Valley that are known for hosting large crane populations in the winter, and one of my goals is to witness a big 'fly-in' event, when huge flocks come in to roost in the evening. I've seen pictures, and it looks like a spectacular sight. I want to see it with my own eyes.
All this is to say that we do indeed have seasons in California. The shifts between summer and winter are perhaps more subtle here than in other states, but an observant eye keeps track of changes in the natural world. And you don't have to be a trained scientist to track seasonal changes wherever you live, either. We tend to use temperature to tell us which season we're in, but in reality light is a much more reliable indicator. Just think of how dramatically temperature can fluctuate in a few days, and how much more extreme these fluctuations seem to be in recent years, due to climate change. Day length cycles, however, remain constant over geologic time, as we humans haven't yet figured out a way to mess with the tilt of the earth's axis. Everyone notices how the amount and quality of light change with the seasons. It takes just a little more effort to notice the ways that life responds to those changes.
For a number of reasons--a lingering injury to my bum knee, scheduling difficulties, and ongoing postconcussion syndrome--I missed the autumn return of the minus tides. At this time of year the lowest tides are in the afternoon, and at the end of the day I just didn't have the energy to deal with field work. It took until today, the winter solstice, for me to find my way back to the intertidal. An additional motivating factor was a request from both the Seymour Center and Seacliff State Beach for critters to populate their displays. So off I went!
Over the past day or so a storm system blew through the area. It didn't drop any rain on us in Santa Cruz, but earlier this week the National Weather service issued a small craft advisory and suggested that people stay off the beach, due to a combination of big swell and high tides. Usually when I go collecting at Davenport I go to the reef on the north end of the beach, which has more varied vertical topography and a similar, but generally richer, biota than the gently sloping benches to the south. However, the big swell had washed away a lot of the sand, leaving the beach steeper than it would be in the summer, and even the -1.0 ft tide didn't make the reef safely available to someone not clad in a wet suit.
So I trudged across the beach and went to the south instead. It gave me an excuse to poke at the stuff that had been washed up onto the beach and look for nice pieces of algae to take to the Seymour Center. Algal pickings are rather slim in the winter, but I did find several decent small clumps that will do nicely in the touch table. One noteworthy find was a dead gumboot chiton (Cryptochiton stelleri). There were four such corpses washed up on the beach, in varying states of decay and stench.
Cryptochitonstelleri is the largest of the chitons, routinely growing to length of 20 cm. It's a hefty beast, too. The chitons as a group have their greatest diversity in the intertidal, but Cryptochiton is a subtidal creature. Unlike the intertidal residents, Cryptochiton's sticking power is pretty weak. Living below the worst of the pounding of the waves, it generally doesn't have to cling tightly to rocks. However, because it doesn't stick very well, Cryptochiton often gets dislodged by strong surge, especially during spring tides. Then they get tumbled by the waves and wash up dead on the beach. I don't think I've ever seen a live Cryptochiton washed up.
The reef to the south of the beach consists of flat benches that slope down to the ocean. There are some channels and a few pools, but otherwise there is no real topography. Of course, for creatures living in the intertidal, there is topography--the nooks and crannies, as well as vertical faces, provide a variety of microhabitats.
Mopalia lignosa is one of the intertidal chitons that I'm always delighted to find because it's not as common as some of the others, and it's a beautiful animal. The species epithet lignosa means 'wood' and refers to the patterning on the dorsal shell plates.
As usual, there were spectacular anemones to be seen. And I saw something new! Anthopleura sola, the sunburst anemone, is one of the large aclonal anemones that is very common. At Natural Bridges there is a brilliant fluorescent A. sola in a pool on one of the benches I visit. I've been keeping an eye on this animal for a couple of years now, just to reassure myself that it's still there and doing well. The animal is hardly hidden, but it feels like a little insiders' secret that not everybody knows about.
For the first time, I saw fluorescent A. sola at Davenport Landing. Three of them, in fact! And boy, were they all bright!
The third fluorescent anemone was closed up. There were just enough partial tentacles visible to see that it is indeed a fluorescent specimen.
Now, I don't spend as much time at the south end of the beach as I do on the north side, but until today I had never noticed these fluorescent animals. Could I have missed them all this time? It's kind of hard to miss a neon green animal the size of a cereal bowl! At any rate, now that I know they exist and hopefully remember where they are, I'll be able to keep an eye on them, too.
A few years ago I had a student, Brett, who had played baseball while he was in high school. One day in lab the students and I were chatting about nothing in particular when the conversation turned to the difficulty of memorizing the scientific names of all the animals they were studying. We got into one of those debates about the usefulness of common names as opposed to scientific names, and I got on my soapbox to deliver my usual sermon: common names are fine, if you are talking with non-scientists and as long as the names are unambiguous, but for scientific communication and to avoid confusion and ambiguity you need to use an organism's scientific name. Also, taxa that have been well studied for decades or centuries, such as birds and flowers, often have common names that are widely accepted and used by both scientists and naturalists. This evolved into a discussion of bird-watching and how birders have developed a sort of shorthand for birds' common names; RTHA for red-tailed hawk (Buteo jamaicensis), for example.
At this point Brett chimed in with a bit of wisdom imparted by one of his high school baseball coaches, who said, "All you need to know to identify birds is whether or not it has webbed feet. If it has webbed feet, it's a duck! And if it doesn't have webbed feet, it's a pigeon!" I must say, as far as methods for distinguishing different groups of birds, I have heard worse. The possession of webbed feet at least has a functional significance, and it's usually easy enough to see a bird's feet, or at least to infer the presence or absence of webbing by observing the bird in its habitat.
My own proficiency at IDing birds is sketchy at best. I'm pretty good with the birds that I see all the time in my backyard and canyon, and I can get most other sightings down to major group, but there are some types that I will probably always find difficult. Gulls and the wading shorebirds, for example. Gulls are notoriously problematic because there are many species and they go through three or four juvenile stages before attaining adult plumage. Wading shorebirds (sanderlings, and whatnot) all look alike to me, and absolute size differences are hard to discern when dozens or hundreds of birds running up and down the beach are about the same size.
One bird that I can easily identify based on its silhouette, is a cormorant. They are related to pelicans and have the same gular pouch under the throat that they use to catch fish, but are their bodies are much more streamlined. Unlike pelicans, which dive from the air to catch fish, cormorants are pursuit divers, using their webbed feet to swim after fish below the surface. These webbed feet are located at the posterior end of the body, where they are well positioned for propulsion under water (think about where a submarine's propeller is located). Having their feet at the back end of the body gives cormorants a more upright stance on land compared to pelicans, whose feet are positioned towards the middle of the body and thus carry themselves along a more horizontal axis.
Clearly, despite their webbed feet, cormorants are not ducks. However, like ducks they do spend most of their time on or in the water. Cormorants are unusual for aquatic birds in that they don't have oil in their feathers. You've heard the phrase "Like water off a duck's back", right? It means not being affected by external events, instead letting them roll off and away the way that water beads and falls off a duck's plumage. The saying is true because ducks and other waterfowl do indeed have a coat of oil in their feathers. In fact, most birds have feathers that are water-repellent to some degree. The oil keeps water from penetrating through the feathers and chilling the body. It also provides additional buoyancy. When you see a bird preening, part of what it is doing is distributing the oils over the feathers in an even coat.
Not having oiled feathers, cormorants soon become waterlogged, which enables them to stay underwater and swim efficiently below the surface. Unfortunately, getting soaked to the skin means the cormorants are susceptible to hypothermia. When they have finished feeding, they need prepare their feathers before they can make any prolonged flights. You will often see cormorants perched on rocks or cliff ledges, basking with their backs to the sun and wings outstretched. They have to do this to dry their wings and warm up their bodies before they can fly. Their dark coloration absorbs heat quickly and speeds up the drying process.
Even though they don't have oiled feathers, cormorants do spend a lot of time preening. They use their beak to smooth feathers and make sure they lie properly on the body. Usually they pay special attention to the wing feathers, as the proper condition and alignment of these feathers makes flight possible.
Another characteristic that makes cormorants different from ducks is their solid bones. Almost all of the flying birds have hollow bones, to lighten the load they have to carry through the air. Flight is a very energetically expensive endeavor, and over millennia the hollow skeleton has evolved to make it slightly less so. Penguins, of course, do not fly in air, but their swimming motion is essentially underwater flight. They have solid bones, to provide weight and counteract the positive buoyancy generated by their blubber and oiled feathers. Like their flightless tuxedo-wearing relatives, cormorants also have solid bones, to help keep them underwater as they pursue fish.
The hitch in this plan for cormorants, however, is that they do fly. Cormorants travel through the air and hunt for prey in cold water. They certainly aren't the only birds with this combination of habits; there are tern species, for example, that migrate thousands of miles and feed by plunge diving. But cormorants, being pursuit divers, spend more time underwater than most other flying birds. They have had to evolve a combination of adaptations for flight (flight feathers, wings long enough to enable flying) and adaptations for swimming underwater (legs at the back of the body, lack of oil in feathers, and dense bones). Natural selection is often about just this sort of compromise. An organism doesn't have to be perfect to be fit for its environment, but it does have to be good enough. And when an animal spends time in both air and water, it has to be good enough in two environments. Cormorants, traveling through air and hunting in water, manage to be successful at both and thus persist.
The other day I joined the Cabrillo College Natural History Club (NHC) on a natural journal walk through Natural Bridges State Park and Antonelli Pond here in Santa Cruz. The NHC is a student club at the college where I teach, and I attended one of their meetings early in the semester. It's a very active club, and although I'm not currently one of the official faculty sponsors I hope to become one in the future. I had a prior commitment and couldn't meet them when they started their walk, but since they were traveling at what club president described as "a nature journaling pace" I was able to catch up with them.
Monarch butterflies (Danaus plexippus) overwinter at Natural Bridges. On warm sunny days they flit about, feeding and warming their bodies in the sun. When it's cold or raining they huddle together in long, drooping aggregations from the eucalyptus trees. It hasn't been cold yet this year, but in November of 2017 I went out on a chilly morning and was able to photograph monarchs clustered together.
These two photographs are the same clump. Notice that the butterflies' wings look very different when they are closed up. The insects roost with their wings held together over the back, showing the paler, dusty undersides. I think this posture minimizes risk of damage to the fragile wings as the butterflies huddle close together to retain as much warmth as possible. As the sun warms their bodies the butterflies begin opening and closing their wings to generate additional heat for their flight muscles. The brilliant orange color of the top side of the wings is the hallmark of a monarch butterfly.
The monarchs hanging out at Natural Bridges in 2018 are the great- great- grandchildren of the butterflies that were here last year. It takes four generations to complete one migration cycle. The butterflies in Santa Cruz today emerged from chrysalises up in the Pacific Northwest or on the west slope of the Rocky Mountains, and flew thousands of miles to get here. They'll be here through the winter, departing in February to search for milkweed on the western slope of the Sierra Nevada. The eggs they lay there will hatch into caterpillars and eventually metamorphose into the butterflies of Generation 1 in March and April. Generation 1 butterflies migrate further north and east, lay eggs on milkweed, and die after a post-larval life of a few weeks. Generation 2 butterflies, emerging in May and June, continue the northeast migration, lay eggs on milkweed, and die. Their offspring, the Generation 3 butterflies, emerge in July and August and disperse throughout the Pacific Northwest and eastward to the Rockies; they lay eggs on milkweed and die. Generation 4 butterflies emerge in September and October, and almost immediately begin migrating south to where their great- great- grandparents overwintered the previous year. Of the four generations, 1-3 are short-lived, lasting only a few weeks before dying. Only Generation 4 butterflies live long, and their job is to escape the winter and survive elsewhere in a milder climate.
This truly is an extraordinary migration. Given that each individual travels only part of the migration route, how do they all know where they're supposed to go? Each individual is heading for a location that hasn't been encountered for four generations. Day length cycles are probably the primary migration trigger for each generation. I imagine that since each generation is born at a different latitude from the others and at different times of the year, day length signals may be generation-specific, at least enough so to tell the butterflies where they should go.
One of the students asked a great question: Other than the fact that they make the long leg of the migration and live longer, are there any differences between Generation 4 butterflies and the others? I don't know the answer to that. I suspect that there may not be obvious morphological differences, but there certainly are physiological differences. The Generation 4 butterflies have much greater physical stamina than Generations 1-3, and have to fuel flight muscles to travel over 1000 miles. That's quite a feat for an animal that looks so delicate! Appearances can be deceiving.
When I teach sponge biology to students of invertebrate zoology, I spend a lot of time describing them as phenomenal filter feeders, and suspect that most other professors do the same. There really are no animals that come close to possessing sponges' ability to remove very small particles from the water. Sponges have this ability despite the fact that their bodies are extraordinarily simple. I can draw pictures on the board to diagram the variety of sponge body types, but I've always wanted to show students how these bodies actually work.
Thing is, from the outside sponges just aren't that interesting. Some grow into large, conspicuous tube or vase shapes, but most occur as crusts of varying thickness and color. For example:
Not much to write home about, is it?
But as with most things invertebrate, sponges are more complex than they appear to be at first glance. And of course their complexity can be best appreciated when you observe sponges under the microscope. That's what I've been doing over the past few weeks: making wet mounts of living sponge and looking at them under the compound microscope. I'm still figuring out the best way to take photos through the scope, and trying to find the magic combination of lighting, magnification, and depth of field to obtain the clearest images.
Let's take a step back and review some basic sponge fundamentals. Sponges are animals in the phylum Porifera. Their bodies are characterized by a lack of true tissues; in other words, a sponge's body consists of various types of cells that do not form permanent connections. The different types of cells have different functions, but most of the cells retain the characteristic of totipotency, the ability to differentiate into another cell type as needed.
The sponge cells that do the filtering are called choanocytes. They form the lining of the sponge's body cavity. Choanocytes consist of a cell body and a collar region of microvilli that form a ring. From the center of the ring protrudes a single flagellum, whose undulations travel from base to tip. The choanocytes are arranged so that the flagella face into the body cavity, and their collective beating draws water through the body. The flagella also capture food particles, which are phagocytosed by the cell.
In its simplest tubular form, a sponge can be visualized as a miniature vase, with a single body cavity called a spongocoel ('sponge cavity') which is lined with choanocytes. Water enters the sponge through many microscopic pores on the outer skin of the body, is filtered by the choanocytes, and exits through a single opening called the osculum. This system works, but the efficiency of filtering is limited by the surface area of the choanocyte layer lining the spongocoel, and very few sponges have this body type.
Now if you imagine making invaginations into the choanocyte layer and continue the choanocytes into the channels you create, you could increase the filtering surface area of a sponge without having to increase its overall body size. Continue this maneuver to its logical end and you'd end up with something that resembles a cluster of grapes. The skin of the grapes would represent the layer of choanocytes, all oriented so that their flagella face the hollow interior of the grape, which would correspond to what we call a choanocyte chamber. This type of body plan has a vastly expanded surface area to volume ratio compared to the tubular form, and these sponges achieve the largest sizes. Incidentally, natural selection has used this exact same strategy to maximize the respiratory exchange surface area of your lungs: gas exchange occurs in the alveoli, which are tiny thin-walled sacs where oxygen diffuses into and carbon dioxide diffuses out of capillaries. The total respiratory surface area of your lungs is about 70 m2--i.e., roughly equivalent to one side of a standard tennis court, without the doubles lanes--all tucked neatly into the volume of your thoracic cavity.
The canals leading into and out of each choanocyte chamber are smaller than the chamber itself, and this arrangement takes advantage of some fundamental fluid dynamics: a given volume of water flows faster through a tube with a narrow diameter and slower through a tube with a wider diameter. Water travels relatively fast through the narrow canals on either end of a choanocyte chamber and slows down significantly within the chamber proper. This gives the choanocytes time to capture all of the food particles in the water stream, and speeds the water to the outside of the body once it has been filtered.
Now we can get back to the animals themselves. Their external appearance may not look like much, but sponges are very interesting when viewed under a microscope. I've been taking samples and squashing them under coverslips for a close look.
Here's a view under darkfield lighting:
The clear-ish objects that look like the back roads of a map are spicules. They provide a bit of skeletal support for the sponge's body and help to deter predators--who would want to bite a mouthful of glass splinters?
When I switched to higher magnification and phase-contrast lighting I could see hollow spherical structures that vaguely resembled blackberries. I felt a thrill of excitement to realize that these were probably choanocyte chambers, and I was looking at the choanocytes themselves!
Here's another view at the same magnification, which shows more clearly the cells of the chamber:
The chambers themselves closely resemble the blastula stage of early animal embryology. Like a blastula, a choanocyte chamber is a hollow ball of cells; unlike a blastula, which has a ciliated outer surface, a choanocyte chamber consists of flagellated cells with the flagella oriented towards the inner hollow space. At a bit less than 40 µm in diameter, the chambers are about half the size of my sea urchin blastulae.
Remember how I said that the structure of the choanocyte chambers is similar to that of our alveoli? You may not be able to visualize the alveoli in your lungs, but this photo shows how the chambers resemble a cluster of grapes.
Because it's impossible to see the three-dimensional structure of the chambers from the single plane of focus you get with a photograph, I shot some video while focusing up and down through the sample on the slide.
This semester I am teaching a lab for a General Biology course for non-majors. I polled my students on the first day of lab, and their academic plans are quite varied: several want to major in psychology (always a popular major), some want to go into business, a few said they hope to go into politics or public policy, and some haven't yet selected a field of study. I think only one or two are even considering a STEM field. Which is all just to say that I have a group of students whose academic goals don't have much in common except to study something other than science. Several of them are the first in their families to go to college, which is very exciting for them and for me.
Most of the activities we do in this class are lab studies. Last week, for example, the students extracted DNA from a strawberry (100% success rate for my class, thank you very much) and then used puzzles and 3-dimensional models to understand the structure of DNA. We do have a couple of field trips scheduled, though, which are the days that students really look forward to. Outside the classroom is where most of the fun stuff happens.
Today I took my class to the beach! We were there to do some monitoring for LiMPETS (Long term Monitoring Program and Experiential Training for Students). For the past few years I've taken my Ecology students out to the intertidal to do the rocky intertidal monitoring. The General Bio students don't have the background needed for the intertidal monitoring and I don't have the classroom time to train them, so we take them to do sand crab monitoring instead. This is a simpler activity for the students, although the clean-up on my end is a lot more intensive even though I get them to help me.
Emerita analoga is a small anomuran crab, more closely related to hermit and porcelain crabs than to the more typical brachyuran crabs such as kelp and rock crabs. It lives in the swash zone on sandy beaches and migrates up and down the beach with the tide. Its ovoid body is perfectly shaped to burrow into the sand, which this crab does with much alacrity. The crabs use their big thoracic legs to push sand forward and burrow backwards into the sand until they are entirely covered. They feed on outgoing waves, sticking out their long second antennae (which can be almost as long as the entire body) and swivel them around to capture suspended particles.
We went out to Seacliff State Beach to count, measure, and sex sand crabs. The protocol is to lay out a 50 m transect along the beach, roughly parallel to the shore where the sand remains wet but isn't constantly covered by waves. Students draw random numbers to determine their position along the horizontal transect and venture out into the ocean, measuring the distance between the transect and the point where they are getting wet to the knees. Then they divide that distance by 9 to yield a total of 10 evenly spaced sampling points along a line running perpendicular to the transect.
The corer is a PVC tube with a handle. It is submerged into the sand to a specified depth and collects a plug of sand that is dumped into a mesh bag. Sand is rinsed out of the bag and the crabs remain behind. Students then have to measure and sex each of the crabs.
Each crab is classified as either a recruit (carapace length ≤9 mm) or a juvenile/adult (carapace length >9 mm). Students get to use calipers to measure carapace length, which they enjoy. Adult crabs are sexed, and females are examined for the presence of eggs.
A sand crab's sex is determined by the presence or absence of pleopods, abdominal appendages that females use to hold onto eggs. If a female is gravid, the eggs are visible as either bright orange or dull tannish masses tucked underneath the telson (see below):
The pointed structure in the photo above is the telson. You can see the tan eggs beneath the telson. They look like they would fall off, but they adhere together in a sticky mass until they are ready to be released. Adult females have pleopods whether or not they are gravid, making it easy to sex the crabs even when they are not reproductive.
Most of the larger crabs today were gravid females and could be sexed with a quick glance at the ventral surface. Sexing the smaller individuals requires a lot more effort. The crab's telson has to be gently pulled back to expose the abdomen, which isn't easy because the crab doesn't like having its parts messed with. In fact, one of the ways to determine whether or not a crab playing dead is really dead is to pry up its telson--a dead crab will let you without making a fuss, while a live one will start thrashing about.
It was a good day to spend time at the beach. The weather got better as we worked and the water wasn't very cold. The students had a good time splashing around in the waves, and they all fell in love with the crabs. There were a few sad moments when crabs got chopped in half by the edge of the corer, but the vast majority were released back to the ocean unharmed. From a teaching perspective, I was happy to give the students an opportunity to do some outdoor learning. After all, the world is our biggest and best classroom. Most students learn best when they get to actually 'do' science, and even though most of this group will not go on to complete a science major, they hopefully have a better appreciation of what it is like to collect real data as citizen scientists.