Skip to content

The Sierra snowpack is California's largest single reservoir of fresh water, accounting for 1/3 of the state's water supply1. A state with a mediterranean climate, such as California, receives precipitation only during the short rain/snow season. During years of drought, when the average Californian frets about how little rain is falling, state water managers are keeping a worried eye on the amount of snow falling in the Sierra. Snow surveyors use remote sensing and field measurements to estimate the water content of the snowpack. The snow water equivalent on 1 April is used to compare snowpack water content across years.

The 2016-2017 snow year was a productive one, dumping near-record amounts of 'Sierra cement' on the mountains. (Skiers accustomed to the powder snows of Utah and Colorado often disparage the heavy snow in the Sierra, but Sierra cement carries a lot more water than powder so is much more beneficial to the state's water supply). Most of that snow eventually melts, births streams and rivers, and flows from the mountains to lower elevations. After a good snow year, though, snow fields remain at high altitudes even during high summer. That definitely is the case around Lake Tahoe.

A few days ago my husband and I hiked from Carson Pass to Big Meadow, a through hike about 8 miles long. The hike goes through some gorgeous alpine meadow, with an absolutely stunning display of wildflowers. Even in late July we had to cross several streams and saw lots of snow.

Round Top Mountain, viewed from meadow above Carson Pass
25 July 2017
© Allison J. Gong
Snow field in the high Sierra
25 July 2017
© Allison J. Gong

If you look closely at the bottom photo, you may notice some faint pink streaks on the face of the snow field. This pink snow is called 'watermelon snow' because of the color. It is a phenomenon that occurs only at high altitudes or polar regions in the summer. Here's a closer look, taken with a 70-200 mm lens that I rented for the week.

Watermelon snow
25 July 2017
© Allison J. Gong

Given the color of those streaks, you'd think the organism producing it would be a red alga of some sort, wouldn't you? I did, too, until I did some research and learned that it is a green alga! Chlamydomonas is a genus of unicellular green algae, most of which are indeed green in color because the only photosynthetic pigments they contain are chlorophylls. However, Chlamydomonas nivalis also contains reddish carotenoid pigments that serve to shield the cell's photosynthetic pigments from excess radiation, which is intense at the high altitudes where the algae live. The pigments absorb heat, which increases the melting of snow in the immediate vicinity and provides liquid water that the algae require. Watermelon snow is found in alpine regions across the globe, although it isn't known whether or not the same species of alga is responsible in all cases.

Cross-country skiers and snowshoers pass through these areas in the winter, and never report seeing watermelon snow. What happens to the cells in the winter? Do they die?

It turns out that the alga persists year-round, although in different life history stages. Given the inhospitality of their habitat, most of the life cycle involves waiting in a dormant stage, with a short burst of activity in the spring. The red form that we see in the summer is a dormant resting stage, having lost the pair of flagella possessed by swimming unicellular green algae. These spores, former zygotes resulting from fertilization, are non-motile and cannot escape to deeper snow to avoid UV radiation, so they use carotenoids to serve as sunscreens. They are not dead, though, and continue to photosynthesize all summer. They rest through the winter and germinate in the spring, stimulated into activity by increased light and nutrients, and flowing water. Germination involves the release of biflagellated cells that swim to the surface of the snow, where at least some of them function as gametes. Fertilization occurs, with the resulting zygotes soon after forming the resting spores that result in watermelon snow.

It may seem strange that this organism spends most of its time in a dormant stage, but this is not at all uncommon for things that live in hostile habitats. When conditions for life are difficult, the best strategy can be to hang out and wait until things get better. Chlamydomonas nivalis does this on a yearly basis, as do many of the marine unicellular algae. And some animals, namely tardigrades, can dry out and live for decades or perhaps even centuries in a state of suspended animation, returning to life when returned to water. As with many natural phenomena, this kind of lifestyle seems bizarre to us because it is so unlike how we do things. But if C. nivalis could observe and think about how we live, it would no doubt consider us inconceivably wasteful, expending enormous amounts of energy to remain active at times when, clearly, it would much more sensible (from C. nivalis's point of view) to sleep until better conditions return.

 


1 California Department of Water Resources

1

The marine macroalgae are, as a group, the most conspicuous organisms in the intertidal. Yet, most tidepool explorers dismiss them as "seaweeds" and move on to the next thing, which they hope is somehow more interesting. This is akin to visiting the jungles of Brazil and not paying attention to the lush foliage that defines that particular biome. I will admit that, as a zoologist whose primary interest is the marine invertebrates, I have been guilty of this offense. I've also felt guilty about the oversight and thought to myself, "I really should know the algae better." I have no formal training in phycology beyond auditing marine botany labs after I finished graduate school, but I've got the basics down and really have no excuse for the continuation of this gap in my knowledge.

So a couple of years ago I decided to start filling in that gap. I dragged out my marine botany notebook and have slowly been adding to it, building up my herbarium collection at the same time.

The red algae (Rhodophyta) are the arguably the most beautiful of the seaweeds, and inarguably are the most diverse on our coast. Some of them are easy to identify because nothing else looks like them, but many share enough morphological similarity that field IDs can be tricky if not downright impossible. For example, to ID a specimen and distinguish it from a close relative you may need to examine the number, size, and arrangement of cells in a cross-section of a blade. Some species are impossible to identify beyond genus (or even family, in some cases) unless you can look at their reproductive structures, which they might not have at the time they're collected.

One of the most ubiquitous red seaweeds, and one that is easily identified to genus, is Mazzaella. The genus name for this group of species used to be Iridea, which gives a hint as to the appearance of the thalli--many of them are iridescent, especially when wet. The species that I see most often are M. flaccida in the mid intertidal and M. splendens lower down. These species are usually not difficult to tell apart once you get used to looking at them and their respective habitats.

Mazzaella splendens at Whaler's Cove at Pigeon Point
28 June 2017
© Allison J. Gong
Mazzaella flaccida at Natural Bridges
9 July 2017
© Allison J. Gong

Mazzaella splendens is generally a solid brown with sometimes a green or purple cast. It is soft and floppy, and the blades are long (up to 50 cm) and taper to a point. The Marine Algae of California, which we call the MAC, uses the term "lanceolate" to describe this shape. Mazzaella flaccida is green or greenish-purple, sometimes more brownish along the edges; its blades are flexible but a teensy bit crisper than those of M. splendens, and its blades are described as cordate (heart-shaped) or broadly lanceolate.

Got it. That's not too bad, right?

But then you see something like this, and a whole other set of questions comes to mind.

Thalli of Mazzaella flaccida at Natural Bridges
9 July 2017
© Allison J. Gong

Based on habitat alone these are both M. flaccida. The greenish thallus on top looks like textbook M. flaccida, but the lower thallus looks more ambiguous. It has the right size and shape but is the wrong color, and what's up with all those bumps? I brought these thalli back to the lab to examine them more closely. Here are the entries from my lab notebook:

 

 

 

 

 

 

 

Now is the time to bring up the subject of life cycles in red algae. Algae such as Mazzaella alternate through three generations: male and female gametophytes, both of which are haploid; a diploid sporophyte; and a diploid carposporophyte. Here's a diagram that shows how this alternation of three generations works:

Life cycle of some red algae, showing alternation of three generations
© McGraw-Hill

It was easy to see that the bumpy thallus I collected was sexy, while the smooth green thallus was probably not reproductive. Having both thalli in hand, along with the MAC and phycology texts in the lab, I was able to determine that the bumpy brown thallus is actually two generations in one body. So cool! But how does this work? The bumps on the thallus are called cystocarps. In Mazzaella a cystocarp contains the diploid tissue of the carposporophyte surrounded by the haploid tissue of the female gametophyte. Et voilà! Two generations in a single thallus.

Now, what's inside the cystocarp? What does the carposporophyte tissue actually look like? To find out I had to do some microsurgery, first to remove a carpospore (1-1.5 mm in diameter) from the female gametophyte and then to cut it open to see what's inside. What's inside were microscopic diploid carpospores, which grow into the macroscopic sporophyte generation. Forcibly dissected out as they were, they don't look like much, just tiny round cells about 2 µm in diameter.

Carpospores of Mazzaella flaccida
12 July 2017
© Allison J. Gong

The next logical step would be to isolate some of the carpospores and try to grow them up. I wasn't thinking about that at the time and pressed both thalli. However, I do have another female gametophyte with cystocarps that I can investigate further tomorrow. It's probably a fool's errand, as I am not going to bother with sterile media and whatnot. Oh well. Nothing ventured, nothing gained, right?

This morning in the intertidal I was reminded of how often I encounter animals I wasn't looking for and almost missed seeing at all. That got me thinking about color and pattern in the intertidal, and how they can be used either to be seen or to avoid being seen. Some critters--the nudibranchs immediately come to mind--are so brightly colored that they are impossible to miss, while others are camouflaged to the point that it takes a trained eye to see them.

Truth be told, however, most of the animals in the intertidal don't have eyes, or at least eyes that can form images the way ours do. While just about any animal might be preyed upon by birds at low tide, most of the predators a creature of the tidepools might face would not be visual predators. This in turn begs the question of just how adaptive or not a species' crypticness is. The way I see it, there are three options, or hypotheses about the potential benefit of an animal's coloration and patterning:

  1. Colors and patterns that make an animal conspicuous are advantageous.
  2. Colors and patterns that make an animal cryptic or camouflaged are advantageous.
  3. Colors and patterns are neither advantageous or disadvantageous.

Today I'm going to consider hypothesis #2, as it is the most interesting one. Let's put aside for now the question of how an animal's color comes to be and consider only the its effect on visibility to Homo sapiens (specifically, me).

Example #1 (obvious): Tonicella chitons

These are the pink chitons that I find on exposed coasts. They eat encrusting coralline algae, and I suspect their color derives at least in part from their diet. Here's one that perfectly matches its food:

The chiton Tonicella lokii at Pistachio Beach
29 May 2017
© Allison J. Gong

On the other hand, Tonicella isn't always this entirely pink, nor is it always seen on coralline algae:

The chiton Tonicella lokii at Pistachio Beach
29 May 2017
© Allison J. Gong
The chiton Tonicella lokii at Monastery Beach
27 October 2015
© Allison J. Gong

The chiton I saw at Monastery Beach wasn't anywhere near coralline algae. It has obviously been eating something, probably algal films of whatever sort it comes across. Correlation is not causation, but it may not be mere coincidence that this pale version of Tonicella lokii lives on rock devoid of coralline algae.

Example #2 (obvious): Decorator crabs

Tonicella doesn't intentionally alter its appearance by eating pink food. Given the extremely rudimentary nature of a chiton's nervous system, it likely can't intentionally do much of anything. It doesn't have eyes so it cannot see, although there are light-sensing organs called aesthetes in the dorsal shell plates and light-sensitive cells in the lateral girdle. Chitons make their way through the world largely by following chemical gradients, either in the water current or on the substrate.

Crabs, on the other hand, have very complex compound eyes and can, to some extent, see what's going on around them. The compound eyes of arthropods are highly effective motion sensors, certainly much more sensitive than our eyes are, which is why it's so hard to sneak up on a fly even if you're extending your reach by using a fly swatter. Crabs certainly are aware of the visual aspects of their surroundings. They can see potential threats and typically respond in one of three ways: (1) scuttling away; (2) coming out fighting; and (3) remaining still and trying not to be noticed.

It takes energy to scuttle back and forth, and the little shore crabs (Pachygrapsus crassipes) are always on the move. They are quick to run for cover when approached, but will come out and resume their explorations if you sit still for about a minute. They are really fast and difficult to catch, perhaps not quite as challenging as the Sally Lightfoot crabs that so enraged the crew of the Western Flyer during Ed Ricketts' and John Steinbeck's excursion to the Sea of Cortez, but hard enough to be not worth my effort. Fighting is an option only for those equipped to fight. Rock crabs (for example, Romaleon antennarium) remain hidden under algae or partially buried in sand, but when exposed they come out with big claws open and ready to pinch the hell out of anything that comes close. These are the only animals that I really worry could hurt me in the intertidal.

Which leaves the hold-still-and-hope-not-to-be-seen option. This is what decorator crabs do. In terms of temperament, decorator crabs (of which there are several species) are placid and unaggressive: they will pinch when provoked and it can hurt, but they won't do the kind of damage that a rock crab would happily inflict. Decorator crabs hide in plain sight by covering their carapace and legs with little bits of the environment, usually algae. A well-decorated crab can be sporting several species of algae on its back.

This morning I saw and collected this small crab:

A small decorator crab, Pugettia richii, on a bed of Egregia menziesii at Davenport Landing
11 July 2017
© Allison J. Gong

I actually didn't see it at first. I was pawing through the thick algal growth and felt its little feet scratching my hand. I peeked under the algae and there was the crab. Its carapace is about 2.5 cm across, and its claws probably wouldn't be able to pinch human skin even if the crab tried to. Which it certainly didn't. I wanted to observe the crab more closely in and keep it for use when I teach the crustacean diversity lab this fall, so I brought it back to be examined under the dissecting scope.

A decorated Pugettia richii, observed in the lab
11 July 201
© Allison J. Gong

The crab's own color is a dark brownish red, which helps it hide amongst the red algae. It adds to the environment-as-appearance effect by attaching at least three species of red algae to its carapace. The crab does this by grabbing a piece of algae with one of its claws, then reaching up and behind its head to put it on the carapace, which has has tiny hooks that hang onto the decoration. It's a very nifty scheme, but there's one big problem. Each time the crab molts it loses its decoration and has to acquire its accessories all over again.

Example #3 (not obvious at all): Lottia digitalis

We have about a gazillion species of limpets on the California coast. Well, not really but it certainly does feel like it. To make things even more difficult I can't seem to keep the current scientific names straight. I know that many of the commonly encountered intertidal limpets have been consolidated into the genus Lottia (this includes species that I learned by another name way back when) and I'm slowly getting used to recognizing the Lottia "look". However, aside from the owl limpet (L. gigantea), which is much bigger and more conspicuous than any others, the other species are difficult to distinguish and I can never remember if species x has the deep ridges or if that's species y. Ugh.

Earlier this spring I was in the field with my friend Brenna, and she was showing me the differences between Lottia scabra and L. digitalis. Brenna studies molluscs so I know she knows what she's talking about. Lottia scabra is now easy for me to recognize, but L. digitalis is both trickier and more interesting.

Limpets Lottia scabra (upper right) and L. digitalis (left and lower right) among barnacles at Natural Bridges
25 June 2017
© Allison J. Gong

See how those all look like limpets? Now look at this:

Davenport Landing
11 July 2017
© Allison J. Gong

Do you even see the limpets?

The large animals in the photo are gooseneck barnacles, Pollicipes polymerus. They live on and amongst mussels in the mid-intertidal. This spring Brenna told me that Lottia digitalis comes in a morph that lives on and looks like Pollicipes. I'd never seen it until today. Look at the photo again. Can you see the limpets now?

Here are some more photos.

Lottia digitalis ("Pollicipes morph") at Natural Bridges
11 July 2017
© Allison J. Gong
Lottia digitalis ("Pollicipes morph") at Natural Bridges
11 July 2017
© Allison J. Gong

Isn't it remarkable how these limpets have exactly the colors and pattern as the plates of Pollicipes? And I didn't even know about them six months ago. I love having new things to learn and more reasons to pay closer attention to creatures I tend to take for granted. I think it's time for me to tackle the challenge of identifying limpets in the field. Next season, that is. Today was probably my last day in the intertidal for a few months. We won't have decent low tides during daylight hours until November.

As far as animal sizes go, we Homo sapiens are rather on the large side of things. While it's true that many animals are larger than us (we can conveniently lump these animals in the category of 'charismatic megafuauna'), the truth of the matter is that most animals are much smaller than us. We tend not to think about them much because, well, they're small and easily escape notice. Numerically, about 98% of scientifically described animal species (~1,324,402 out of ~1,382,402) are invertebrates*, the vast majority of which are arthropods. Think insects, crabs, and spiders, and you get the idea: these animals are vastly numerous, but small. We are certainly more aware of big animals because we can see them and intentionally interact with them, but my casual observation is that the average person can't see anything smaller than about 5 mm. For all intents and purposes, objects smaller than that are essentially invisible.

There is nothing good or bad about this bias towards large(r) animals; it simply is. If you think about our evolutionary history as hominids, it was much more adaptive for our ancestors to notice the large predator chasing them (or the large potential prey animal foraging in the field in front of them) than the inevitable and unescapable tiny parasites lurking in their guts or crawling on their skin.

Part of what defines an animal is multicellularity--animal bodies are made of different types of cells. The number and type of cell varies from species to species, and in some species the number of cells in the adult body is fixed, a phenomenon called 'eutely'. Given the multicellularity of animals, it is understandable to assume that we are bigger than unicellular organisms, such as bacteria and protozoans. And for the most part, this is true.

Of course, it's the exceptions to the rule that are most interesting. Yesterday I completed my contribution to Snapshot Cal Coast 2017 by collecting a plankton sample from the Santa Cruz Municipal Wharf and adding a couple dozen observations to iNaturalist. The plankton was surprisingly. . . boring. There was hardly any phytoplankton at all, and not much in the way of animal diversity. I expected more.

I did, however, see these two organisms:

  

 

 

 

 

 

They are about the same size, approximately 3 mm in diameter. But one is an animal and the other is a protozoan. Can you guess which is which?

The organism on the left is a protozoan, a predatory marine amoeba-like creature called an acantharian. As such an acantharian consists of a single cell, the protoplasm of which you can see as the darkish matter from which the skeletal spines protrude. Like all amoebae, acantharians feed by engulfing and digesting other cells. The spines, composed of strontium sulfate, are thought both to deter predation and retard sinking. For an organism that has no propulsive capability of its own, the possession of spines to increase drag is a handy way to remain in the warmer surface waters where food is more abundant. Acantharians are usually most abundant in local coastal plankton during the spring and summer. I do occasionally see them in the winter, but they are always smaller than the ones I see in the summer.

The organism on the right is an animal, the medusa of the hydrozoan Obelia. The hydroid form of this animal is very common on pilings and docks, and its medusae are present in the plankton year-round.

Life cycle of the hydroid Obelia sp.
© McGraw-Hill

These two vastly different organisms demonstrate very nicely that what's big for one group can be quite small for another. The acantharian above, measuring a whopping 3 mm in diameter (a size that would be invisible to most people), is much bigger than several multicellular animals--tardigrades, rotifers, and the larvae of many marine invertebrates come to mind. In fact, newly settled juveniles of the sea star Pisaster ochraceus are about 500 µm in diameter, or 1/6 the size of that acantharian. Of course, bigness and smallness are both relative, are they not?

Ultimate body size, whether singular or multicellular, has ramifications for physiology and ecology. Small organisms are much more strongly affected by the external environment than large ones and thus generally have more difficulty maintaining homeostasis. On the other hand, small organisms take less time to reach adulthood, have shorter generation times, and can respond more quickly to changing environmental conditions. Big organisms require more resources--space, food, etc.--and at a population level are less quick to adapt when the environment changes.

Maybe there's a lesson for us, no?

 


Reference: Brusca et al, 2016. Invertebrates, 3rd edition. Sinauer Associates, Inc.

%d bloggers like this: