California's marine biogeographic break

Felimeda macfarlandi, a chromodorid nudibranch at Cambria.

This month I’m repeating my spring road trip through the southwest, but oppostite of my general course last year, I’m first heading down the California coast. My focus is on marine life for a few days and then I head to the deserts and mountain ranges inland. Cambria was my first stop on Thursday morning on the central coast just south of Big Sur.

At Cambria, fleshy red seaweeds, surfgrass, kelps, and invertebrates filled out the rocky sandstone boulders and bedrock. I again saw a healthy population of the rockweed Pelvetiopsis hybrida, a seaweed I first encountered and wrote about last year. There were adorable small sporophytes of bull kelp in a handful of small patches in the low intertidal. One new find was a beautiful purple chromodorid nudibranch, gliding among leafy red algae.

Young sporophytes of Nereocystis luetkeana (bull kelp)
in the low intertidal at Cambria. Egregia menziesii is in
the background.

Friday morning I was at the Palos Verdes Peninsula in Los Angeles. Remarkably I have never been tidepooling in LA County despite growing up in the region and attending graduate school in San Diego. Pt. Fermin was my planned destination, but when I arrived there in the morning, all access was officially blocked off. Skirting around a barrier would have been no problem, but it didn’t seem advisable. Instead I drove a little farther north to White Pt.

Relatively strong surf pounded some high relief rocks in the intertidal just off the southern parking lot. I explored a section of coastline south of there, almost to White Pt. itself. The site was comprised of sandstone benches, boulders, and cobbles, a drab yellow color.

The changed character of the biota between central California and Los Angeles was immediately evident. I was struck with the incredible abundance of barnacles in the upper intertidal at White Pt. – a desert as far as macroalgae were concerned. Red fleshy seaweeds were essentially non-existent, and the large seaweeds (a few species of kelps and large brown algae) were generally limited to the low intertidal zone.

I had crossed a well-known biogeographic barrier by entering southern California, and the marine flora in particular indicated this dramatic change in biotic composition. Point Conception north of Santa Barbara is often regarded as the break; this is where the mainly north-south coastline of northern and central California bends toward the east to form the southern California Bight. North of Point Conception, water temperatures are cooler and there are pockets of coastal upwelling that bring nutrient-rich cool water to shallow depths for photosynthetic organisms to enjoy. The north-to-south California Current dominates the near-shore. South of the point, waters are warmer and the south-to-north Davidson Current is present. Hot and dry Santa Ana winds that blow from the northeast can bake the southern California coast.

A wave crashing into sandstone benches just north of White Pt., Los Angeles Co.

A cowrie at White Pt.

Desiccation stress, always a concern for aquatic organisms which are periodically exposed to air, may be more intense in southern California than in more northerly parts of the state. More intense sun, less rainfall, and warmer temperatures in southern California probably exacerbate desiccation stress in southern California.

I found the abundance of small barnacles in the high intertidal curious. These organisms must be hardy against desiccation – they are exposed to air most of the time after all – but I wonder how being clamped tightly shut most of the time affects their ability to capture food. They must open up and sweep the water in order to catch food particles.

Except for the low intertidal which is submerged often, tidepools were the other microhabitat at White Pt. where larger seaweeds were likely to be seen. Relative to the central coast, however, these were not particularly large, consisting of branching coralline algae, Gelidiales, and others. Small fish darted to hiding spots when they sensed me nearby.

Common low intertidal kelps north and south of Pt. Conception. Left: Laminaria setchellii at Cambria. Right: Eisenia arborea at White Pt.

One of the interesting kelps of southern California that is not seen farther north is Eisenia arborea. Its species name suggests “tree”, and that is not an inaccurate moniker. Eisenia is a small kelp species, born on a stiff stipe from which two sets of blades droop down in a sort of disheveled brown mess. At White Pt. it was almost exclusively in the low intertidal, with some stragglers a little higher up where pools were present. Eisenia also occurs in Japan. In central and northern California Laminaria setchellii takes its place in both overall form (though it is not such a mess) and in ecological niche. I’m curious to know if these species overlap in distribution at all, or where one begins exactly and the other ends. Some exploration of Santa Barbara and the northern Channel Islands holds the answer to that question I think.

Juvenile spiny lobster (Panulirus interruptus) in a tide
pool at La Jolla. It's carapace was about 3-4 cm long.

Today I was in La Jolla. The flora was different yet again, but more similar in overall growth form to White Pt. than Cambria. Eisenia was present, but so too was a small kelp, Laminaria farlowii, that I didn’t see in Los Angeles. These plants are simple ruffled blades, aggregating or growing as singlets in the low intertidal. La Jolla also had a remarkable contingent of brown seaweeds of the order Dictyotales. This group tends to favor tropical and subtropical regions globally.

At La Jolla I explored the area around Nicholson Pt., a series of sandstone benches between the posh homes and the Pacific. Ravines, and even an arch, were cut into the sandstone. In the mid and high intertidal were also pools of various depth and diameter – all providing a variety of microhabitats for marine organisms. The beautiful marine plants notwithstanding, today’s best find was probably a tiny lobster in the warm water of a pool in the mid-intertidal! I’m tempted to tidepool once more tomorrow morning, though I originally planned to leave early for Arizona. We shall see!

Zonaria farlowii (Dictyotales) was very common in low elevation
sandy tide pools at Nicholson Pt., La Jolla. This species grows in
elegant rosettes.

Pigeon Point intertidal

Pigeon Point in San Mateo County, CA is one of my favorite tidepooling
locations and I have visited this area for many years. In late March I returned
to the south side of the point. Here waves crash into rocks with a population of
the sea palm, Postelesia palmaeformis. The Pigeon Pt. lighthouse is in the
background.

Many of the palms exhibited desiccation stress, perhaps due to a combination
of mid-day low tides, warm sun, and wind. 

Another of my favorite kelp species on the California coast is this species,
Dictyoneurum californicum. It occurs as clusters of blades on rocks in
the low intertidal. I love the color and texture of the blades. 

At least two species of seagrasses in the genus Phyllospadix appear
to be present at Pigeon Pt. Here is P. scouleri underwater. It
occupied the low intertidal, often in channels between higher rocks.

Red seaweeds (Rhodophyta) are the stars of the show at Pigeon Pt. since they are in such high abundance relative to other seaweeds. Here is a sampling of species. From left to right is Osmundea spectabilis, Sarcodiotheca gaudichaudii (with some small epiphytic Microcladia coulteri), and a coralline alga - the most unusual "rhodolith" I've ever seen!

"Leafy" red seaweeds were relatively common in the low intertidal too. I
think this is one of the Botryoglossum species (Delesseriaceae).

Out on the rocks near the sea palms there were a few deeper tide pools
that had anemones, and high concentrations of purple urchins. 

I found a sculpin in one of these pools as well.

Finding this tube worm, Serpula columbiana, and photographing it underwater
was a treat. The colorful plume is used to catch food and accomplish gas change.
The operculum can be seen behind the the plume at top right. It is used to seal up
the tube when the animal retracts. Hat tip to my friend Allison Gong for the
species name. 

Incredible plants: Stenogramma

In some respects, red seaweeds (Phylum Rhodophyta) are the most interesting of the three major groups of marine algae inhabiting coastal shorelines. They are the most diverse seaweed group in temperate regions like the western US, they have fascinatingly complex life histories (that topic alone warrants its own post some day), and they occur in a tremendous diversity of growth forms and colors. They can be pink, brown, cherry red, or even greenish!

Generally red seaweeds are smaller and less ostentatious than the large brown seaweeds like kelps that sometimes dominate the intertidal shores of rocky temperate coastlines. But look under mats of surfgrass or in rocky crevices that are seemingly a little too dark for plant life – here you are likely to some of the more intriguing smaller red seaweeds. I came across one such species, Stenogramma californicum, in relative abundance during my exploration of Pfieffer Beach in Big Sur last month. This species has long been one of my favorite reds.

Stenogramma californicum underwater at Pfeiffer Beach, Big Sur, CA, Feb 2018.

The first thing to note about Stenogramma is that is has dichotomous branching. This means that each axis of the plant splits in two at a branching point, with each branch of equal length. Many red seaweeds have dichotomous branches, but Stenogramma has one other feature that makes it almost immediately jump out as distinct from other similar-looking species: in some plants it has thin white longitudinal lines that run down the center of each branch. These lines are actually present on female plants and are the locations where spores (carpospores to be precise) are produced after female eggs are fertilized. There are several orders of branching.

Stenogramma californicum is typically 6 to 20 cm in length. The flat dichotomous branches are up to 1 cm wide and have broadly rounded tips. According to Abbott and Hollenberg (1976) it is a relatively common plant in the northeast Pacific, occurring from British Columbia to Baja California. Related species also occur in British Columbia, Europe, South America, and Australia. In my experience it is not all that frequent along the NE Pacific coast, but there may be some good reasons I have overlooked it in the past: it is a smaller plant, it grows in the low intertidal to subtidal where it may be more challenging to find, and one can easily overlook species one is not specifically hunting for.

Herbarium specimens of Stenogramma in the UC Berkeley University Herbarium.
Left: a female plant, bar = 2 cm long. Right: a tetrasporophyte from Jalama Beach, Santa Barbara
County, CA, bar = 5 mm long.

On the north shore of Pfieffer Beach where I explored last month, it grew in the low intertidal, with or without the cover of surfgrass. The female plants were relatively common. I suspect there are many unanswered questions about the natural history of Stenogramma and smaller seaweed species like it. How long do plants typically live? Which herbivores graze on them? Does Stenogramma produce anti-herbivore compounds? How far do spores travel? How quickly do newly settled spores grow on a rocky substrate? What is the ideal amount of light? How much gene flow occurs between populations that may be separated by kilometers? 

Another plant underwater with articulated coralline algae at Pfeiffer Beach, Feb. 2018.

For smaller species like Stenogramma that may not have immediate economic value, or which don’t play major structural roles in coastal ecosystems (e.g., kelps), it may be hard to find the funding to study many questions about their natural history and ecology. Yet these smaller species, like all others, hold tremendous natural history value. They are each literally a wealth of millions of years of evolutionary innovation, holding some stories that will be forever lost to time, and revealing other stories that will enrich those who seek to know them better.

References

Abbott IA, Hollenberg GJ. 1976. Marine Algae of California. Stanford University Press, Stanford, CA.

Gabrielson PW, Lindstrom SC, O’Kelly CJ. 2012. Keys to the seaweeds and seagrasses of southeast Alaska, British Columbia, Washington, and Oregon. Phycological Contribution Number 8.

Jade Cove

Monday 26 Feb 2018: Big Sur revealed its different faces today as a morning overcast sky gave way to drizzle, rain by early afternoon, and finally brilliant winter sun and crisp wind. Tonight clouds pass over a nearly full moon rising before sunset from the east, the short storm having now moved on. The bright stars of the Big Dipper are visible to the northeast. It is quiet in southern Big Sur, the temporary end of highway 1 just a few miles more to the south. The road closure and winter perhaps isolate this area a bit more than usual.

Jade Cove and the southern Big Sur coastline.

The low intertidal kelp, Laminaria setchellii with surfgrass,
Phyllospadix, in the background.

The low tide this afternoon was good, uncovering the kelps, surfgrass, coralline algae, and invertebrates of the rocky coastline of Big Sur. I was wet due to rain from above and surges of surf from below, but excited as a climbed over boulders to explore a new site. This was the area of Jade Cove – picked over by divers for the heavy nephrite jade – though I was there principally for the seaweed gems. The little cove was accessed by a steep and unstable trail from the bluffs south of Sand Dollar Beach.

At the lower tides, a cluster of large rocks towards the center of the cove were accessible by hopping like steppingstones across several slippery boulders covered in emerald surfgrass. Inshore of these rocks in an area somewhat protected from the full impacts of the incoming surf, there was a small population of a large brown seaweed Stephanocystis osmundacea (not a kelp, but typically growing with them) inhabiting the low intertidal and shallow subtidal zones. Despite the relentless pounding of surf here, some of these rocks were jagged and sharp with deep crevices, sort of like a geologically young mountain range thrust boldly into the sky, ignorant of erosive forces that will eventually smooth them.

Black abalone.

In these crevices I found several dozen black abalone, their smooth dark shells pressed against the rocks protecting a soft body beneath. They were wedged as far away from surf or predators as possible. The abs were of various sizes from a few centimeters long to about the size of my hand. There was also a lone red abalone of similar cryptic disposition in the low intertidal.

Across the cove, the kelps Laminaria setchellii and Egregia menziesii were the dominant large brown algae of the low intertidal, the blades of former species like little golden brown flags drooping from short flagpoles. Patches of purple sea urchins (Strongylocentrotus purpuratus) and the general dominance of pink coralline algae in the low intertidal suggested a harsh world for the fleshy red seaweeds which can otherwise dominate the low intertidal at other sites in central and northern California. There were some specimens of Chondracanthus corymbiferus and Prionitis but the lacy red seaweeds of the Delesseriaceae seemed generally missing from the algal community.

Offshore some large floats of bull kelp (Nereocystis luetkeana) rolled with each incoming well. These plants are last year’s stragglers since this species is usually an annual. Farther offshore still, signaling perhaps the presence of a shallow reef hundreds of meters from shore, was evidence of a canopy of giant kelp, Macrocystis pyrifera. I counted perhaps 10 individuals of this same species in the low intertidal and shallow subtidal along the shore, separated from their offshore family.

Some sea caves in Jade Cove. Stooping, I walked through the one on the right.

As the rain of the early afternoon let up and the sky began to clear, there was a band of puffy white cumulus clouds bunched together low on the horizon over the sea. The sun broke through with the rising tide and being quite wet and very cold I was decidedly done exploring the intertidal. I had enough coordination left to climb the steep muddy trail back up to the bluff some 200 feet above. I walked around the bluffs for a time slowly warming in the sun. The wind kept up all afternoon and was especially strong at the crest of the bluffs which afford the most incredible views of a majestic unrepentantly wild coastline. 

An early California spring

The last week has been rather warm in California, and today was exceptionally so. I admit that the warmth is very pleasant, but it is way too early for 70°F highs in northern California. Indications are that this warmth may persist for some time with California and the rest of the Southwest remaining quite dry for the month.

Weather of course is not climate, but as spring conditions trend towards occurring earlier year over year, this is a strong indicator of climate change in action. Out here in the western US, the exceptional warmth coupled with low rainfall may exacerbate drought conditions. California traditionally has highly variable rain patterns (of all states in the US it has the greatest year-to-year variation in precipitation), so swings from last winter (when precipitation was well above average) to this year (where we are rather below average) are to be expected.

I wanted to take advantage of the pleasant weekend and went on a short hike today to the Stebbins Cold Canyon Reserve in the coast range near Winters, California. Unsurprisingly a lot of other people had the same idea. Few plants were in bloom yet, but ferns and shrubs were thriving. A little ways up the trail into the canyon, there was a small amount of cool water in the creek, perhaps soon to dry up if February remains dry. I photographed water striders which posed on the surface tension of the water, active in the warm sun, leaving oversized shadows on the smooth rocks in the creek bed. 

Water strider shadows in the shallow creek.  

One of my newest favorite trees, the California bay laurel (Umbellularia californica) was in bloom along the trail! At the base of its spatulate leaves there were small clusters of yellow flowers. The flowers had a pleasant smell, different from the equally pleasant smell one obtains by rubbing the leaves of the plant through one’s fingers.

Blooming bay laurel.

It remains to be seen if an early spring is really here in California. If so perhaps we will begin to see blooms in short order on the almonds, peaches and other stone fruits prevalent in orchards of the central valley. Typically almonds will begin to bloom in mid February, shortly before my birthday, followed by other Prunus species. In the foothills, an assortment of wildflowers may soon be on display.

This coming April I’m hoping to take a road trip through the southwest, another version of the really memorable trip I completed in April of 2017 that took me to some exceptional national parks and monuments. If conditions are much drier this coming spring than last year, it will be interesting to see if the effect is noticeable. For example, last year I recalled seeing snow on the transverse ranges through central eastern Nevada, and a greener than expected landscape in that state. I experienced rain showers as I camped in Moab, Utah and backpacked in the Petrified Forest in eastern Arizona. 

One of the few blooming species at the reserve.
It superficially resembles a paintbrush, but I'm not sure
what this species is.

The breakwater forest

Giant kelp beneath the kayak near the Monterey
Breakwater.

A good series of low tides often falls around the turn of the new year and so was the case for the beginning of 2018. Winter days are short, but in California the spring low tides of the winter often occur in the afternoon, enabling a good trip if weather and swells are favorable. A trip to the coast was in order and for two days I had excellent tidepooling excursions to rocky shores near Pistachio Beach in San Mateo County and at Carmel Pt. south of Monterey.

My past several visits to Monterey over the course of the year taunted me with seemingly calm conditions on the eastern side of the Monterey Peninsula because I had failed to bring the kayak. Not to be stymied again, for this trip to the coast I determined I would bring the boat along. Approaching the peninsula yesterday morning, conditions seemed promising again. On New Year’s Day morning during a high tide I launched from the thin strand of sandy beach at the Monterey Breakwater, more officially known as San Carlos Beach.

The Breakwater is well known to me, as well as many other SCUBA divers, because it is a frequently-visited location for recreational diving, including beginning courses. There is marine life on the breakwater rocks, a subtidal eelgrass meadow, sandy bottoms, and a giant kelp forest (Macrocystis pyrifera) offshore of Cannery Row. It is part of the Ed Rickett's State Marine Conservation Area.

A curious sea otter.

The waves were manageable yesterday so I launched from the beach, though there was more chop and wind than would have been ideal. I didn’t venture far, but circled around the kelp forest, paddling intermittently to maintain position. Few kayakers or divers were out. My kayak is more suited for calm riverine or estuarine paddling, but can handle milder ocean conditions.

Five, perhaps six, sea otters occupied the same kelp forest that I spent time in. The animals generally kept their distance, but peered curiously at me during breaks from their routine of diving below the surface to hunt for food. Some black cormorants flew low over the water.

I was reminded of the difficulty of photography while kayaking. The constant motion of the kayak precluded having much time to compose thoughtful shots. The otters were too far away for any excellent above-water photos with the waterproof camera. Below the surface, the main subjects were kelp and Chrysaora, a purple jellyfish that has been abundant at the breakwater on my last two visits to Monterey. As the kayak lumbered over swells and drifted in currents and wind, I plunged the camera into the water over the side of the kayak and took stabs in the dark, so to speak, of kelp and jellies at various angles. Remarkably, a few shots turned out fairly well! 

Jellies of the genus Chrysaora at the water's surface.

Macrocystis pyrifera is the dominant canopy-forming species
in most kelp forests in central and southern California.

Incredible plants: giant sequoia

General Grant tree in the Grant Grove, Kings
Canyon National Park, 2014.

California is a land of superlatives, and especially so botanically. Trees are at the top of the list for California’s record breaking plants: the state is home to the world’s oldest trees (the bristlecone pines, Pinus longaeva), the world’s tallest trees (coast redwood, Sequoia sempervirens), and the world’s largest trees by volume (the giant sequoia, Sequoiadendron giganteum). Each of these record-setting trees occurs in different geographic areas and environments among California’s diverse set of geologies and climates. They are all conifers, a widespread group of gymnosperms (gymnosperms are seed-bearing, but flowerless, vascular plants).

The giant sequoia has a narrow geographic range, found solely on the western slopes of the Sierra Nevada range in central California. It occurs across a fairly broad range of elevations (825-2700 m), though most populations of the species lie between about 1800 and 2100 m above sea-level (Yu et al. 2017). Upper and lower elevations of the species may be limited by low temperatures and low precipitation respectively. The coast redwood is distributed in the coast ranges from central California to southwest Oregon. It typically grows at much lower elevations than the giant sequoia and generally in close proximity to the coast with its cool and foggy maritime air.

The coast redwood is believed to be the closet living relative of the giant sequoia. Both species are classified in the conifer family Cupressaceae which includes cedars, junipers, and cypresses. Metasequoia glyptostroboides (the dawn redwood), which occurs in China and was only discovered within the last century, is a cousin to the two California redwood species. Fossil evidence suggests that redwood-like trees were formerly much more widespread in distribution across the Northern hemisphere. Sequoiadendron for example, may have been distributed in the past in North America, Europe, and New Zealand. Thus, these three redwood species might be considered relict species with greatly constricted modern distributions relative to the past. Perhaps glacial cycles (increased northern latitude ice cover implicated in the case of Metasequoia) and other factors over time have led to the range constriction of this group of conifers.

Hypothesized evolutionary relationships among giant sequoia (Sequoiadendron giganteum), coast redwoods (Sequoia sempervirens), the dawn redwood (Metasequoia glyptostroboides) and other Cupressaceae. Tree after Kusumi et al. 2000. 

The giant sequoia is a behemoth, estimated to be greater in volume than any other tree species in the world. The largest individuals have an imposing presence in the mixed conifer forests in which they occur. The base of the trunk in the largest individuals can often reach up to 11 m in diameter and 90 m in height (a little shorter than the coast redwood). The giant sequoia has reddish fibrous bark like the coast redwood, with deep furrows evident in older, larger trees. Old growth individuals may live several millennia.

Needles and cones in the giant sequoia and coast redwood are different enough to enable easy identification (in addition to differences in native range between the species). The giant sequoia has short pointed leaves that emerge from stems in a radial fashion, whereas most leaves on the coast redwood are pinnate sprays of leaves flattened in one plane. (An interesting exception is the leaves at the very top of a coast redwood which look quite similar to giant sequoia leaves in overall form.) Giant sequoia trees have both male and female cones on the same individual. Female (seed-bearing) cones of Sequoiadendron and Sequoia are both egg shaped and similar in morphology, but cones of the giant sequoia are about twice as large, almost the size of a chicken egg. Female cones of the giant sequoia are produced in clusters high in the foliage and bear small papery seeds a few centimeters in size.

Foliage of giant sequoia (left) and coast redwood (right). Photos from Bearskin Grove, Sequoia National Forest (2014) and Ventana Wilderness, Los Padres National Forest, Big Sur (2015).

Female cones and seedling of giant sequoia, Tuolumne Grove, Yosemite National Park, 2017.

Several giant sequoias with other conifers in the
Tuolumne Grove, 2017.

Fire is a necessary ecological disturbance for the persistence of the species. Unlike coast redwoods which can grow semi-clonally (e.g., from burs), sequoias generally only produce new individuals from seed, though new shoots can develop from injured stumps in younger trees. Mature trees are resistant to fires of low to moderate intensity which remove understory plants and favor sequoia seed germination by exposing bare soils for germination and increasing light levels reaching the forest floor. When occurring in mixed conifer species forests, sequoias are often found with sugar pines (Pinus lambertiana) and white firs (Abies concolor). Lack of fire will promote white fir relative to giant sequoias.

Controlled fire is used today by some agencies to manage sequoia groves. Reducing woody biomass in the forest understory is a means of protecting groves from more intense large scale-fires made more likely by decades of fire suppression practices in the western US. 

With its immense size, the giant sequoia was a prized timber species in the 19^th century. Many of the 67 groves of living giant sequoia are currently protected on state or federal land. This includes three groves in Yosemite National Park and many groves in Sequoia and Kings Canyon National Parks. Additional groves within Sequoia National Forest were protected from commercial logging (which occurred up until the 1980s) with the creation of Sequoia National Monument in 2000. The groves vary greatly in size, old-growth forest extent, and logging history. The smallest of all groves is also the most northerly grove in Placer County west of Lake Tahoe. It has only 6 trees.

Panorama of the Muir Grove in Sequoia National Park, 2014. The sequoias are clustered at top center and can be distinguished from other conifer species by their slightly yellow-brown color and bushy crowns.

Sequoias are vulnerable to root disturbance and intense fires. Climate change might also present challenges to the species persistence, possibly through increasing drought impacts in the future in the Sierra. For instance, recent work by Yu et al. (2017) suggests that drought impacts may be more severe in sequoia groves than in nearby forests dominated by other tree species. However, Willard (2000) suggests that groves have been doing well recently, with many recovering from historic logging and some expanding in size.

References

Baldwin BG, Goldman DH, Keil DJ, Patterson R, Rosatti TJ, Wilken DH. 2012. The Jepson Manual. Vascular Plants of California. 2^nd ed. University of California Press, Berkeley, CA.

Eckenwalder JE. 2009. Conifers of the World. The Complete Reference. Timber Press, Portland OR.

Kusumi J, Tsumura Y, Yoshimaru H, Tachida H. 2000. Phylogenetic relationships in Taxodiaceae and Cupressaceae sensu stricto based on matK gene, chlL gene, trnL-trnF IGS region, and trnL intron sequences. American Journal of Botany 87:1480-1488.

Su Y et al. 2017. Emerging stress and relative resiliency of Giant Sequoia groves experiencing multi-year dry periods in a warming climate. Journal of Geophysical Research: Biogeosciences 122:3063-3075. Preprint link.

Weatherspoon CP. 1986. Silvics of giant sequoia. In Weatherspoon et al. Proceedings of the workshop on management of giant sequoia; May 24-25, 1985; Reedley, California. USFS General Technical Report PSW-95.

Willard D. 2000. A Guide to the Sequoia Groves of California.Yosemite Association, Yosemite National Park, CA.

Sequoias in the Muir Grove, 2014.

Cluster of female cones (left) and close-up of trunk (right), Tuolumne Grove, 2017.

The value of biodiversity

A controversial opinion piece on extinction and biodiversity conservation was published Thanksgiving week in the Washington Post by an evolutionary biologist. In the last few days, scathing assessments of the op-ed came across my Twitter feed, but I avoided the article until today. I finally dove in, and here are a few thoughts that emerged during the time I could muster on a Sunday evening.

Diverse assemblage of flowering plants in the understory
of a montane forest in the John Muir Wilderness,
California, summer 2017.

In the op-ed R. Alexander Pyron argues that “extinction is the engine of evolution”, states that almost all species that have ever lived on Earth have already become extinct, and notes that extinctions are inevitable for all currently living species. He argues that despite the loss of a species “the world will be none the poorer from it”. From this assortment of assertions (some obviously true like the inevitability of eventual extinction of all species), he then goes on to build a case that conservation is only prudent in-so-far as it benefits humankind.

In taking a rather extreme view of the role of conservation, the visceral reaction of many biologists to publication of this op-ed in a major media outlet is understandable. But does the author miss the mark? I think so on several major fronts:

1. The author paints an incomplete and superficial view of evolution and the production of biodiversity. Succinctly put, extinction is not the “engine” of evolution as the author claims. Rather, natural selection is the mechanism of evolutionary change, and as another evolutionary biologist S. Claramunt points out in a rebuttal, natural selection operates at the population level, not at the species level that Pyron discusses. Natural selection is one of the key processes of microevolution, which involves the generation of genetic variation within a species (novel genotypes and phenotypes) and its subsequent persistence or demise in the next generation by selection. This initial step in microevolution – the generation of genetic variability such as by mutation or genetic drift – is inherently a creative process, albeit a mostly random and inefficient one. In this light, the two major steps of microevolution (generation of variability and environmental selection) are both productive and destructive. Claramunt and Caroline Tucker address other controversial statements by Pyron here and here.

Where Pyron may be partially correct about extinction is its role in producing biodiversity at the macroevolutionary level. As one example, he cites the radiation of mammals and birds following the global mass extinction that wiped out the dinosaurs. However, while extinction may be an occasionally helpful mechanism for promoting radiations of new lineages over geologic time, it is certainly not necessary to generate new species. Speciation, on the other hand, is requisite for the creation of new biodiversity, and it can proceed easily enough in the absence of extinction through allopatric or sympatric mechanisms. A report just this week suggests the very rapid evolution of a new finch species in the Galapagos stemming from a hybridization event. Many species form from others without the parent lineage going extinct, increasing biodiversity. Moreover, when one surveys the history of life on Earth, despite messy fluctuations over geologic history, there may be more biodiversity today than during any geologic era of the past. For a net increase in global diversity to occur over the long term, long-term speciation rates have been greater than extinction rates. If anything speciation is the “engine” of evolution.

2. Though Pyron advocates for conservation if it serves a direct human need, the extent of species he seems willing to advocate for probably falls far short of the number really needed, even from simply a utilitarian point of view. The problem here is obvious: any argument about selective conservation of a smaller fraction of species fails to recognize the unknown inter-dependency of species in all ecosystems. What of the undiscovered connections and dependencies in the global web of life of which we are still woefully ignorant as ecologists? What of species that hold future drug discoveries, or that will only in the future be discovered to be critical to the persistence of other species or even the functioning of whole ecosystems? Even if impending extinction provokes difficult conservation decisions about which species to save in the future, those decisions need to be informed by understanding the ecological roles of the species and the relative loss of services that could result from extinction. I posit that we presently know very little about the ecological roles of the vast majority of species to be able to effectively triage our conservation efforts.

This notion of the interdependency of life is not just the poetry and song of nature lovers. Rigorous empirical research manipulating biodiversity levels at smaller spatial scales over the last two decades demonstrates that biodiversity often matters in order to sustain ecosystem productivity, stability, or other services upon which humankind depends (Cardinale et al. 2012, Lefcheck et al. 2015). Put simply, a grassland with two or three species is not the same as one with several dozen species; that extra plant biodiversity has measurable effects on the functioning of the grassland ecosystem. The importance of biodiversity for ecological functioning extends to genetic diversity within a species (Hughes & Stachowicz 2004), and by extrapolation (though we cannot experiment on continental or global scales) also reasonably extends to the whole biosphere: global diversity sustains a global suite of diverse ecosystem functions. A prudent, precautionary approach is to conserve as much global biodiversity as possible.

3. Finally, the op-ed fails on the ethical front. I won’t argue from a particular religious or philosophical point of view here, but rather simply from a humanistic one. To appreciate, conserve, and cultivate biodiversity is an inherently human experience. We need look no further than zoos and gardens to understand our intrinsic desire to connect with other species. As much as Homo sapiens is a destructive, warlike, compulsive, and competitive species, we are also inherently caring, empathetic, altruistic, and prudent. Biodiversity enriches our human experience, spiritually and aesthetically. And conservation of a mere fraction of Earth’s species upon which we are most dependent for food and shelter will not satisfy that enduring need for connection to the biosphere. Pyron’s anthropocentric arguments about conservation were taken to an extreme in the op-ed, and in so doing that viewpoint paradoxically harms our species by artificially disconnecting us from our deep human need for biodiversity.

The global, bipartisan efforts we put towards conservation, towards preservation of wilderness, towards city and national parks attest to the value we place on the conservation of other species. We cannot escape the deep connection (the “biophilia” of E.O. Wilson) that we have as humans to other forms of life. Though they lived long before the term “biodiversity” was coined, naturalists such as Humboldt, Haeckel, and Muir intuitively assessed the interconnected nature of life through observation of the natural world (Wulf 2015). Muir understood this dependency of all species on each other and asked a powerful ethical question useful as an antidote to an overly anthropocentric view of the value of biodiversity: “Why ought man to value himself as more than an infinitely small unit of the one great unit of creation?”

References

Cardinale et al. 2012. Biodiversity loss and its impact on humanity. Nature 486:59-67.

Hughes AR,  Stachowicz JJ. 2004. Genetic diversity enhances the resistance of a seagrass ecosystem to disturbance. Proceedings of the National Academy of Sciences 101:8998-9002.

Lefcheck et al. 2015. Biodiversity enhances ecosystem multifunctionality across trophic levels and habitats. Nature Communications 6:6936.

Wulf A. 2015. The Invention of Nature. Vintage Books, New York.

Yosemite VI: Wapama Falls at Hetch Hetchy

Our final Yosemite destination last weekend was Hetch Hetchy, my second visit to this remarkable and controversial valley at the northern end of Yosemite National Park. The valley is beautiful despite the reduction in its dimensions and grandeur by the controversial decision to build a dam and flood the valley a century ago. I cannot help but feel some sadness over that outcome, one that John Muir vigorously opposed in his last days. Only he and others of that era saw the valley before it was drown to satiate San Francisco’s thirst for water. I can only hope that the valley will be restored someday, with the water supply and hydroelectric energy the dam provides being provided elsewhere, though that presently doesn’t seem politically or legally likely.

Farther up the valley, beyond the reach of the dam lies an area of the park known as the “Grand Rapids of the Tuolumne River”, a backpacking destination that I hope I can visit someday. Backcountry wilderness trails crisscross the area to the north and south of Hetch Hetchy.

Crossing over the dam and through a tunnel blast into rock, a trail starts at the northern end of the reservoir heading along the west rim of the valley. The vegetation along the slopes is as much chaparral and shrub as forest, with manzanita, bay laurels, and oaks in abundance. At the four km point from the parking lot one reaches Wapama Falls which crashes down a steep granite face at the northern end of the valley. There are some pools near the base of the falls before it descends a bit further to reach the reservoir. Though not many plants are in bloom at this season in Yosemite, the rocky wetland gardens where the trail crosses the falls had a population of small attractive bright yellow flowers of the monkey flower genus Mimulus.

Wapama Falls on the north side of the Hetch Hetchy valley in the spring of 2011 (left) and fall of 2017 (right).

Flowers of Mimulus floribundus near
pools at the base of Wapama Falls.

Hetch Hetchy has been described as a companion valley to the much more famous and visited Yosemite Valley to the south. John Muir described it thus: “…it is a wonderfully exact counterpart of the great Yosemite, not only in its crystal river and sublime rocks and waterfalls, but in the gardens, groves, and meadows of its flowery, park-like floor”.

Views of the Hetch Hetchy Valley today from the north rim of the valley. At right
in center of photo is Kolana Rock.

Presently it is hard to gauge the original dimensions of the valley, but historical photos of the valley show its former glory. About 100 meters of water cover the valley floor currently. Taber’s historical photo from 1908 shows meadows (some perhaps actively grazed), wetlands, and a meandering Tuolumne River on the valley floor. Another photo taken a few years later farther up stream depicts the beautiful canyon and its forested and rocky slopes.

The Hetch Hetchy Valley in 1908 before dam construction. Wapama Falls can be seen at
center right in. Photo by Isaiah Taber, published in the Sierra Club Bulletin. Source.

Historical photo of the Grand Canyon of the Tuolumne River by F. Matthes of the USGS
in about 1914. The photo faces west towards the valley with Kolana Rock at center. Source.

Crossing over the dam to the north side of the reservoir, none of the information placards I viewed that are placed to inform the public show any such historical photos of what Hetch Hetchy looked like before its burial, something I note with some cynicism. With its swelling population and capricious annual precipitation, a reliable water supply is critical for California. However, there are alternatives to a dam at Hetch Hetchy, but like so many issues in conservation, the choice comes down to priorities and values. At a minimum we can strive to ensure that another decision like Hetch Hetchy is never made again in our most cherished national landscapes.

References

Wenk E. 2015. Wildflowers of the High Sierra and John Muir Trail. Wilderness Press, Birmingham, AL.

Worster D. 2008. A Passion for Nature. The Life of John Muir. Oxford University Press, New York, NY.

The O'Shaughnessy Dam as seen from the southwest
on the drive towards Hetch Hetchy Valley.