Whales!

Big Sur is one of my absolute favorite places. I don’t visit frequently enough. Being there rejuvenates my passion for exploration and for wilderness. And though it has perhaps become more crowded over the years, one can still find relative quiet and a chance to be absorbed by the immensity of this rugged and beautiful place.

With my two youngest kids I took a day off work to camp and tidepool over an extended weekend. Long sunny days and cool temperatures – the weather was perfect.

We camped at Plaskett Creek, a small US Forest Service campsite just east of California highway 1 in the southern stretch of Big Sur. Given that the low tide was very early the next morning, it made for convenient tidepooling at nearby Sand Dollar Beach. The site is a wide sandy cove, buttressed along the whole shoreline by bluffs, except for a single point of access via a stairwell at the southern third of the cove. There are rocky intertidal areas at the northern and southern ends of the sandy beach.

Sand Dollar Beach

The encrusting sponge,
Haliclona.

On any visit to the coastal rocks my eye is trained for seaweeds, but my most significant impression of the intertidal biota on this visit was the abundance of Phragmatopoma californica, an annelid worm that constructs intricate dwellings of sand at the edge of intertidal rocks much like a marine beehive. The colonies seemed to be quite abundant, challenging my memory of whether they were so common on my visit to this same site years ago.

Returning to the plants, steel grey-green Porphyra were common on rocks in the high intertidal zone and from the mid-intertidal down there were rich coverings of seaweeds. Small individuals of giant kelp, Macrocystis pyrifera, were frequent in the lower intertidal and I also found about three small bull kelp sporophytes.

Bands of the light brown Phragmatopoma colonies lining intertidal rocks.

One of the treats of the long drive along the Big Sur coast was spotting 4 grey whales – three near Willow Creek (a beach access point near the outpost of Gorda) and one farther north. The group of three swam together close to the rocky shore for quite some time, surfacing briefly perhaps every minute or so. Their dark grey mottled backs would appear at the surface, or sometimes a lone flipper would poke into the air. They frequently swam close together, at some points appearing a pair appeared to be nestled together.

Grey whales, now mostly only a northeast Pacific species, migrate annually between Baja California and Alaska. These animals, the loitering in Big Sur aside (I can’t blame them), were probably on their way north. Today there are perhaps about 20,000 animals along the west coast of North America, so the chance to observe several on our trip was fantastic. 

A trio of grey whales surfacing together.

We also saw sundry other marine mammals.

Macrocystis pyrifera, giant kelp.

Fucus distichus, Silvetia compressa and various red seaweeds on intertidal rocks.

Middle Fork American River

Sometimes gems lie close to home. I’ve passed through the town of Auburn, California quite a few times, but rarely have ventured off to explore the area with its distinctive red soils. Auburn is just northeast of Sacramento, a gateway to the low elevation foothills of the Sierra Nevada.

Yesterday for a rare day off work, I went hiking in the Auburn State Recreation Area with a close friend. We hiked and scrambled among rocks along the middle fork of the American River, an untamed Sierra river of rapids, sand and gravel bars, and crisp cool waters flowing through steep forested hills. Given the worsening drought in California, I imagine the flow may have been low compared to historic levels.

Bedrock, boulders and cobbles of various sizes were littered among the river basin, much of the bedrock having a greenish serpentine hue and smooth undulations from centuries of erosive forces. Milky white quartz could be found as smooth stones in the river bed or as white veins that sharply interrupted the darker bedrock. At a shady spot at the edge of a river - a lunchspot - a large yellow-brown banana slug slowly meandered up a huge vertical rock face. With no vegetation nearby, it seemed off course for finding a food or mate.

The steep south-facing hill slopes along the river were covered in abundant flowers, especially blue lupines and California poppies, their brilliant orange petals consistently smaller here than in other grasslands or gardens. I found milkweeds and a white species of Castilleja too. Butterflies were abundant and included a large yellow but black-striped species, and a black shimmering species. They wouldn't sit still long enough to be photographed except at a large blooming tree where they congregated in abundance.

Ctenophores

A beach-stranded ctenophore (perhaps Pleurobrachia)
found near the mouth of Humboldt Bay, CA, 2007.

Most people, many biologists included, get excited about mammals, birds, or other such furries and fuzzies. I’ve long been attracted to much more obscure groups of creatures. I think cyanobacteria are amazing; I love ferns and gymnosperms; I can’t get enough of kelps or red seaweeds. In college I was very interested in invertebrates, and thought for a time that I would do research on marine inverts once I started graduate school. In my professional work since I’ve steered towards photosynthetic organisms, but I still have a fondness for the inverts. One of the smallest phyla of invertebrates is the Ctenophora, also known as comb jellies or sea gooseberries. There are approximately 150 species globally. As a group they live completely in the ocean, with no freshwater representatives (Brusca and Brusca 1990).

Most comb jellies are pelagic organisms in the open ocean. As members of the plankton, ctenophores are largely passive drifters. However, they are also capable of some locomotion, powered by eight rows of fused cilia that line the outside of their gelatinous bodies. These rows of cilia, called ctenes, are one of the distinctive characteristics of the phylum. If your local aquarium has ctenophores on display, you are likely to be able to see the beautiful shimmering iridescence of the beating comb rows as the animals swim. A few ctenophores are benthic (bottom-dwelling).

One of my favorite ctenophores is Pleurobrachia, also known as the sea gooseberry. It is one of the model ctenophores that are introduced in invertebrate zoology courses. It has 8 rows of fused cilia like other members of its phylum. The body is nearly spherical and has an attractive radial symmetry (technically bi-lateral symmetry).

All ctenophores are believed to be predators, preying for example on marine zooplankton. In Pleurobrachia, there are two long tentacles emerging from its nearly spherical body. Specialized cells called colloblasts line the tentacles and are involved in prey capture. In essence, these cells burst and release adhesive materials on contact with the prey. The captured organisms are then drawn to the vicinity of the mouth when the tentacles retract towards the body. Some ctenophores also just passively capture food once it is caught in mucus on the outside of the body (talk about a free lunch!). 

Most ctenophores are hermaphrodites, producing eggs and sperm in the same individual. They have relatively simple life histories compared to many other invertebrates or marine algae. Fertilized eggs divide into an embryo and then into a larval phase known as a cidippid. The larval stage looks like Pleurobrachia. Like other “simple” organisms, ctenophores can also grow asexually – replacing even large portions of the body if damaged.

Beroid ctenophore. Credit: NURP, NOAA, archived here.

With translucent bodies and quasi-radial symmetry, many comb jellies resemble true jellyfish, but the latter are classified in class Scyphozoa of the phylum Cnidaria, and are a distinct evolutionary lineage of animals. Cnidaria possess stinging cells (pneumatocysts) with which they capture prey, but these specialized cells are lacking in the ctenophores. Though comb jellies and true jellies also both have simple nervous systems – usually characterized as a “nerve net” – recent research suggests their nervous systems are fairly distinct. The evolutionary relationships of ctenophores to other simple animal groups such as sponges (Porifera) and cnidarians has been a prominent research topic lately.

In late 2013, a team led by NIH researchers published the genome sequence of Mnemiopsis leidyi, an Atlantic Ocean ctenophore that is infamous for invading several Eurasian bodies of water and negatively impacting native food webs. Using DNA sequences from Mnemiopsis, Ryan et al. (2013) found evidence that ctenophores were the most ancient of major animal groups, branching from the animal tree of life before sponges, cnidarians and other animals. For a long time, sponges – which lack nerve cells and differentiated tissue layers – were believed to be the most primitive animal group. Last year, in another high-profile study, a large team of researchers compared the genome of Pleurobrachia and the transcriptome of additional ctenophores species with other animal groups (Moroz et al. 2014). Like Ryan et el. (2013), their findings also suggested that ctenophores are the most primitive major group of invertebrates.

Currently hypothesized relationships among animal groups including the ctenophores. Image from Figure 1f in Moroz et al. 2014, Copyright 2014 Macmillan Publishers Limited, under CC BY-NC-SA 3.0 license.

Both studies discussed the implications of this new understanding of ctenophore phylogeny for the evolution of nervous systems in animals as a whole. Because ctenophores have nerve and muscle cells (and sponges lack them), the question emerges about how many times nervous systems have evolved in animals. Moroz et al. (2014) found that ctenophore nervous systems are missing (or silence) many of the neurotransmitter molecules that are found in other animal groups, so they proposed that nervous systems may have evolved twice during the course of animal evolution: once for ctenophores, and once for cnidarians and more complex animals. The alternative hypothesis is that the animal nervous system evolved once in the common ancestor of all animals, but then was lost in sponges and another amoeboid-like group of invertebrates group known as the Placozoa. While this evolutionary question is far from settled (e.g., Ryan 2014), these are intriguing ideas pertinent to the early evolution of animal life some 600 million years ago. What is exciting is that biology continues to acquire new tools (in this case large-scale nucleic acid sequencing) to help address questions about the diversity of life that have been around for a long time!

Bibliography and citations

- Brusca RC and Brusca GJ. 1990. Invertebrates. Sinauer Associates, Inc., Sunderland, MA, 922 pp.

- Moroz LL et al. 2014. The ctenophore genome and the evolutionary origins of neural systems. Nature 510:109-114.

- Ryan JF et al. 2013. The genome of the ctenophore Mnemiopsis leidyi and its implications for cell type evolution. Science 342:1242591-1 to 8.

- Ryan JF. 2014. Did the ctenophore nervous system evolve independently? Zoology 117:225-226.

Spring in the Snow Mountain Wilderness

Oak woodland.

It has been perfect spring weather in northern California, concerning only because it is scarcely past mid February and spring has already arrived. Yesterday I visited the SE corner of the Snow Mountain Wilderness which sits in the coast range of northern California. At only about 2000 ft, I visited one of the lowest elevations in the wilderness, which includes East Snow Mountain peak that exceeds 7000 ft elevation. Geographic names notwithstanding, there was not a trace of snow on the trail or on any mountains in the distance.

The region of the Bath House Trail that I explored included oak and pine woodland and chaparral. Some of the deciduous oaks were just beginning to produce new leaves, showing the brilliant tender green color of new foliage. Other species included manzanita, pines, poison oak and some scattered western redbud. The oak woodland had a carpet of green grass, Galium and several flowering species: purple onions, yellow buttercups, pink beak-shaped Dodecatheon and an interesting forb bearing bluish flowers that reminded me of a milkweed.

Unknown forb with blue flowers. The white hoods on the petals that
form a ring at the center of the flower remind me of a milkweed flower.

Fritillaria recurva.

On one north-east facing hillslope, I found scarlet fritillary, a lily-like herb with bright orange flowers. According to the Calflora website, Fritillaria recurva typically blooms from April to June, but flowers were already on full display during my visit. This species is also apparently associated with serpentine soils. Serpentine rocks can be greenish in color, and their soils are relatively low in calcium and high in magnesium, creating conditions that host quite a few endemic plant species. I would like to learn much more about the serpentine flora of the west coast.

Incredible plants: Nereocystis

I wrote previously about a fascinating intertidal kelp, the sea palm, found in the northeastern Pacific Ocean. A very close relative of this species is the bull kelp, Nereocystis luetkeana. This very large marine seaweed is a favorite beach find of kids (and more playful adults) since the flexible stipes of the plant make excellent ropes or whips during beach adventures.

Bull kelp forest at Deception Pass State Park, northern Washington, July 2013.

Despite the genetic similarity between Postelsia and Nereocystis, the bull kelp occupies a different habitat than Postelsia and has a rather different morphology. Nereocystis is principally a subtidal species with morphological features that are adapted for maximizing photosynthesis in deeper water. At the ocean bottom, plants are attached to a hard substratum with conical holdfasts that support long, thin, flexible stipes. Each stipe gradually expands into a semi-spherical pneumatocyst, the air bladder of the species. Several smooth strap-shaped blades emerge from the pneumatocyst at the top of each plant. Filled with mostly carbon monoxide (yes, the poison!), the function of the pneumatocyst is to help the blades stay afloat near the water surface.

A Nereocystis blade with sori (dark brown
patches) at Trinidad, Humboldt County,
California, August 2002.

Like all kelp species, the large plants seen along the coast actually only represent half of the kelp life cycle. The macroscopic plants are called sporophytes. The other, microscopic stage of the life cycle begins with the production of spores in tissues (called sori) that develop in the center of the blades of the sporophytes. The sori fall to the sea floor and release spores which develop into gametophytes - multicellular, but microscopic, filaments of cells on rock surfaces (Druehl 2000). Separate male and female gametophytes produce eggs and sperm and after fertilization of the egg, a new sporophyte generation is born.

 Nereocystis is one of only a few kelps worldwide that grows large enough to form subtidal kelp forests. Ecologically, such species are known as “foundation species” (Dayton 1972) because they literally provide the habitat structure upon which an entire ecosystem is built. Kelp forests are home to other numerous other species of macroalgae, invertebrates, fish and marine mammals. In the northern Pacific Ocean (the global hotspot of kelp diversity), other kelp species that are large enough to form forests include Macrocystis (giant kelp), Pelagophycus (elk kelp), and to some degree, Eualaria fistulosa and Egregia menziesii. Nereocystis is the main canopy-forming kelp species north of about Santa Cruz, California. From about Santa Cruz south to Baja California, Macrocystis is the main forest-forming species. In certain areas of the central California coastline, such as Big Sur, Macrocystis and Nereocystis can co-occur.

An intertidal bull kelp sporophyte with Costaria costata, Egregia
menziesii and other seaweeds, Carmel, Monterey County,
California, May 1999.

Like its relative Postelsia, Nereocystis is usually an annual species (Abbott and Hollenberg 1976). Most adult plants last no more than one growing season. With such a short life span and the capacity to attain a length of up to 36 meters, the bull kelp sporophyte has prodigious growth rates – estimated to be as much as 6-17 cm per day (Druehl 2000, Springer et al. 2010)! Though usually subtidal, bull kelps also occasionally grow in the intertidal and can be seen on a calm day at low tide. I love finding small sporophytes anywhere from a few inches to a few feet long during a low tide excursion.

To dive in a Nereocystis kelp forest is a delightful experience. One of my most memorable dives occurred during college at the Big Creek Ecological Reserve south of Monterey on the rugged Big Sur coast. There, in the frigid water I was able to observe the graceful stipes of bull kelps rising like kites up in the sea. The bull kelp is a stout but graceful plant, perfectly depicting the dual beauty and wildness of the Pacific coast.

References

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

Dayton PK. 1972. Toward an understanding of community resilience and the potential effects of enrichment to the benthos at McMurdo Sound, Antarctica. In: Proceedings of the Colloquium on Conservation Problems in Antarctica.

Druehl LD. 2000. Pacific Seaweeds. Harbour Publishing.

Springer Y et al. 2010. Ecosystem based management of Nereocystis. Oceanography and Marine Biology: An Annual Review.

Ten Mile State Marine Reserve

Intertidal and offshore pinnacle at Ten Mile State
Marine Reserve, Mendocino County, CA, Jan 2015.

Friday was a bright sunny winter day on the northern California coast. I went tidepooling at Ten Mile State Marine Reserve a few miles north of Fort Bragg in Mendocino County. I discovered this site years ago and named it site 71.70 from the mile marker for nearby state highway 1. In 2012, this area was incorporated into a state marine reserve. Access to the intertidal is down a hundred foot coastal bluff which is impossible in most places except for a steep thin trail that leads down loose soil and rocks. It isn’t the easiest trail, but it isn’t particularly harrowing either if one is careful.

There are abundant intertidal gardens and tide pools here among dark boulders of various sizes. Numerous pinnacles and rocks off shore provide some protection to the immediate coastline, which is a fairly narrow beach consisting of coarse sand, cobbles and bedrock. The swells were relatively calm. January is about the least optimal time to observe the glory of marine algae in the northeast Pacific, but there were perennial kelps, rockweeds and red seaweeds present on the rocks. Photos from my last visit during summer 2008 indicated that patches of the sea palm Postelsia palmaeformis were present on intertidal rocks at this site, but there was no sign of that species today. Perhaps new sporophytes (adult plants) of this species will appear this coming spring.

Left: Intertidal Postelsia population in summer 2008. Right: Jewel top snail, 2015.

One of the most striking plants I observed today was Codium setchellii, a dark green (almost black), seaweed of velvet texture that spreads over rocks in the lower to mid-intertidal zone. It is sister to another green seaweed, Codium fragile, that has the popular name of “dead-man’s fingers” because of its cylindrical dark green branches. Instead of morbid appendages hanging pendant on the rocks, however, C. setchellii grasps the substrate with crenulations that aren’t too dissimilar to a human brain. I think therefore, in honor of its relative, an appropriate common name for this plant is “dead man’s brains”.

Codium setchellii, aka "dead man's brains"!

This tidepooling trip was also the maiden voyage for a new “action” video camera I purchased. I’ll need to practice the underwater techniques in the future, but I’ve included a short video of some tidepool footage. 

Looking north at Ten Mile State Marine Reserve from the coastal bluffs, Jan 2015.

Carmel tidepools

Costaria costata, 2014.

The Monterey Bay area is one of the coastal gems of California: strikingly beautiful marine life, diverse and easily accessible tide pools, and a rich tradition of marine research and education. Ever since my undergraduate days at UC Santa Cruz, I've loved to explore tidepools from the San Mateo County coastline south to Monterey and Big Sur. Spring-time low tides are an ideal period to visit the rocky intertidal, though that often necessitates an early rise of 5 or 6 AM to catch the action.

Carmel Point is one of my favorite places to tidepool. It is a few minutes south of the Monterey Peninsula by car. The town of Carmel is probably one of the most affluent coastal communities in California, but it is small and has a laid back feel. Carmel Point is a short stretch of rocky coastline that interrupts two more-or-less crescent shaped coves of sandy beach to the north and south. Offshore kelp forests run right into the low intertidal, so at the right times one can literally walk through a grove of giant kelp by just getting wet up to the knees.

Panorama at Carmel Point. Tidepools extend to the south. The Monterey peninsula is in the distance at center and right.

Corallina officinalis, 2014.

Carmel Point is an incredible spot for seaweed lovers like myself. There are interesting finds in all of the three major phyla of marine seaweeds. Green seaweeds are represented by alluring plants like "dead man's fingers" (Codium fragile) and the delicate Bryopsis. Reds appear in their varied hues, including the rich blades of Chondracanthus and Erythrophyllum delesserioides. There are various species of branching coralline algae in the lower to mid intertidal, lending a vibrant pink to the mosiac of benthic organisms on the rocks. 

Low intertidal Macrocystis pyrifera, 2007.

And, of course the large and conspicious brown algae are very diverse here. In addition to long strands of giant kelp (Macrocystis pyrifera) in the intertidal, there is bull kelp (Nereocystis), low intertidal groves of Laminaria setchellii and occurrences of feather boa kelp (Egregia menziesii) and Alaria marginata. The higher rocks host several species of rockweeds: Fucus distichus, Pelvetiopsis limitata, Silvetia compressa and Hesperophycus californicus.

Chondracanthus exasperatus, 2014.

I've made a half dozen or so trips to this site over the years, so I'm starting to have a few places I can check for favorite seaweed species. For instance, I've observed during intermittent visits a mid-intertidal population of the sea palm, Postelsia palmaeformis. The population this year grew on only a single rock, and plants looked a little tattered. One of my all time favorite kelp species, Costaria costata, appeared to be pretty common this spring. I found it in a usual pool just south of the Postelsia rock and in a high density at another low intertidal spot.

The nudibranch Triopha maculata on an opaque tunicate, 2014.

While tidepooling, my attention is usually taken with the seaweeds, but occasionally I notice some showy invertebrates too. This spring I found three species of colorful nudibranchs. On a previous visit I found a really cool green shrimp, its body colored perhaps from ingesting green algae.

Super cool green shrimp, 2009.

A small bull kelp, Nereocystis luetkeana,
submerged in a tidepool, 2010.

One thing I thought of during my visit this spring to Carmel was the intellectual challenge of understanding the ecology of these diverse rocky intertidal communities. There are literally hundreds of species of benthic algae and invertebrates packed tightly into the complex amalgam of bedrock, boulders and sand. Sure, there is the obvious vertical zonation of species that is driven heavily by the tides, but there is also so much three dimensional habitat structure creating seemingly infinite combinations of light, wave energy, sand scour and temperature. Add to these physical gradients the host of possible biological interactions (competition, herbivory, facilitation) among the dozens of co-existing species, and the unique life history patterns of immense phylogenetic diversity, and comprehension of the grand picture can seem unattainable. So, an observation here or experiment there that lends insight into these incredible ecosystems is a tremendous intellectual reward.

The strawberry anemone, Corynactis californica, growing underwater in the low intertidal, 2014. 

This is a small red alga, Pterosiphonia dendroidea, that I captured with my macro lens growing in a sandy area at Carmel Point in 2009. Most fronds of this plant are only a few cm in length. I love how individual cells can be seen on this plant!

Salmon-Huckleberry Wilderness

Salmon River

Western Oregon is so green, especially from the perspective of a naturalist who moved back to California recently. Last week I returned to the northwest for two weeks of professional meetings and field work, but I was able to explore a bit on my days off during the Memorial day weekend. Yesterday, I headed east from Portland towards Mt. Hood. On a clear day this beautiful white peak presents a marvelous site from Portland. The Mt. Hood area is home to three wildernesses: Mt. Hood Wilderness encompassing the mountain's summit and its slopes to the east and west, Badger Creek to the east, and Salmon-Huckleberry to the southwest. I spent one night backpacking into the green coniferous forest of Salmon-Huckleberry and its lush green understory. Here are some photos from the wilderness and surrounding Mt. Hood National Forest.

The diminutive Cornus unalaschkensis.

This is an incredible spider that I encountered. Its brown body was not more than a centimeter long but each of the needle-like black legs were a few inches long!

Two of the three Maianthemum species present in the area: M. stellatum (left) and M. racemosum (right).

Oregon tidal wetlands and climate change (pt. 4)

In the previous post, I discussed our attempt to understand how salinity and flooding affect tidal wetland plant growth. A final question I’ll describe in this series of posts was the effect of salinity on seed germination and the first days of seedling growth. Climate effects, whether manifest as higher temperatures, increasing salinity, or greater flooding could impact young seedlings, not just adult plants. Such effects on seed germination could impact the population sizes of species in wetland habitats.

Plantago maritima seeds in a germination experiment.

To address this question, we planned a simple series of experiments in the lab. Using one to several species per experiment, we put seeds collected from the field into lab dishes moistened at a series of salinity levels. Our treatments ranged from freshwater conditions (0 ppt) to 20 ppt, a level about 2/3 the salt strength of full seawater. From our measurements of soil salinities in the region’s tidal wetlands, we found that wet season salinities really didn't exceed about 20 ppt, even in the saltiest marshes. 

It is very well established that salt is physiologically stressful for vascular plants. It presents a challenge for intracellular osmotic balance, requiring plants to expend energy to maintain acceptable levels of ions in their tissues. Species living in salt marshes have various mechanisms for handling salt much better than most other plants. These "salt-lovers" are known as halophytes. Most plants cannot live in salty environments and are known as glaucophytes. To cope, halophytes may extrude salt from their leaves, store salt internally, or have other means of dealing with these unneeded ions.

We collected seeds in the field from perhaps some two dozen species and ultimately worked with 13 species that showed promise of germination under lab conditions. The species in our tests included grasses, some annual and perennial forbs, a rush, and a shrub (twinberry, Lonicera involucrata) that forms scrub-shrub wetland in some parts of Oregon estuaries. Unfortunately, we found that sedges did not germinate well under our basic lab conditions, so we were unable to examine salinity effects in this important group of wetland plants. With species from a variety of tidal marsh habitats and taxonomic groups, we were able to see which plants were more or less tolerant of high salinity at their earliest life history stage.

The lab tests we conducted generally confirmed what is already known about many estuarine species: though often tolerant of elevated salinity, most species germinated most readily in freshwater. These species are thus not really true "salt-lovers", but rather salt-tolerators. Also, unsurprisingly, we found that species varied in their tolerance of higher salinity conditions. Two species - pickleweed (Sarcocornia perennis) and Douglas' aster (Symphyotrichum subspicatum) - appeared to act the most like true halophytes. These results alone did not shed any profound light on seed germination biology, but did provide valuable data for plants found in the Pacific Northwest.

Germination responses (means and SE) for three Oregon tidal wetland species across a range of salinities.

 In the final part of our study, however, we tried to take our work one step further. We asked how salinity effects on germination matched, or failed to match, patterns of plant distribution in the field. To explore this, we returned to the data set described in parts 1 and 2 of this series of blog posts. We looked at the full range of summer soil salinities found in our research (~1 to 44 ppt) and assessed how each species was distributed along this gradient.

For about half of the species we looked at, the answer seemed to be that adult distributions didn't match predictions based on seed tolerance. In this group of species, seed germination was usually greatly reduced at salinities of 10 or 20 ppt, but they were commonly found in soils with salinities of 30 (even up to 44 ppt) as adults in the field. Because we didn't conduct additional experiments, we could not account for the reasons underlying this mismatch in these species, but one idea is that their seeds may be adapted to germinate under conditions of low salinity. These periods of low salinity are most likely to occur in late winter or spring when the Pacific Northwest is very rainy. As plants continue growing into the summer, they presumably become more tolerant of elevated salinities during dryer summer months in the Pacific Northwest.

Our germination study was relatively simple, but it highlighted the fact that we still have much to learn about even common species in our coastal habitats. Each species might be affected by salinity, temperature, changing carbon dioxide concentrations and other environmental factors differently. Moreover, each life stage of each species could have different responses to these factors. Add in the fact that species interact with other species, and the complexity of community ecology grows exponentially. With dozens of plant species in coastal marshes and swamps, there is much to learn about species relationships with the coastal environment and how these may be altered with climate change.

Reference

Janousek CN, Folger CL. 2013. Inter-specific variation in salinity effects on germination in Pacific Northwest tidal wetland plants. Aquatic Botany 111:104-111.

Oregon tidal wetlands and climate change (pt. 3)

Our survey work in Oregon's coastal wetlands showed patterns of species distribution suggesting how and which species might be vulnerable to climate change on the Pacific Northwest coast.  In previous posts, I discussed some of our findings relative to wetland algae and plants. However it was important to extend our knowledge of climate impacts by conducting controlled experiments too. During the summer of 2012 I was fortunate to work with an enthusiastic summer intern who participated in an EPA program that gives undergraduate students from smaller liberal arts colleges opportunities to work in federal research labs.

Seedlings.

The project we conducted was a short-term experiment to assess the dual effects of salinity and flooding on wetland plant productivity. We used seven species that were easily grown from seed; most are commonly found in Oregon tidal marshes. The species we used also differed in apparent tolerance to salinity and flooding based on their field distributions. We grew several hundred seedlings at the lab starting in the spring.

Some of the experimental pots placed at three tidal
elevations at one of our sites. A blue salinity sensor
can be seen at bottom center; a tall white stilling well
with a water level sensor is at the right.

To conduct the experiment with a range of salinities, we planned to work at three sites in the Yaquina estuary - one near the mouth of the estuary and two farther inland. We placed salinity/temperature sensors in the field track conditions over the course of the experiment and the data time confirmed that our sites had quite different salinity profiles.

To create differences in flooding intensity among treatments, we planned to set out plants at three tidal elevations at each site. We used mean higher high water (MHHW) as our baseline, which is about a mid-marsh elevation on the Oregon coast. We placed other plants at 25 and 50 cm below this elevation. We synchronized positions in the tidal frame across the three sites (to within about 5 cm) with high accuracy GPS. Our approach followed efforts in marshes in other parts of the US that have used "organ pipe" arrays to vary flooding intensity. However, instead of actually building an apparatus to hold plants at different elevations, we simply used the sides of tidal channels in the marshes to provide the needed elevations for the study.

In mid June, with some welcome help from another summer intern, we excavated terraces from the channel banks to place several hundred potted seedlings into the field. It was two long and very muddy days of field work!

Our plants grew under different salinities and flooding levels for five weeks. This was a relatively short length of time - constrained by the limited period of the internship - but long enough to assess treatment effects on the seedlings. We checked on the plants about every week and some were lost to the vagaries of field experimentation. (I think a few were uprooted by birds.) During our checks we noted which plants browned, probably due to physiological intolerance of environmental conditions.

Above ground dry mass (means and SE) of Grindelia stricta seedlings grown at 3 tidal elevations in low, moderate and high salinity wetlands. Like Grindelia, most species we investigated had lower above- and below- ground growth with greater flooding and/or greater salinity.

By mid summer, the experimental results were pretty unequivocal. All species, including one that we expected to be most tolerant of flooding and salinity stress based on its field distribution, grew less with higher salinity and/or greater flooding. Species seemed to differ in terms of their sensitivity to one experimental factor or the other, but all showed the same trend.

One concept we explored in the study was idea that "salinity exposure" - the combined effects of both flooding and salinity - could account for differences in plant productivity. In other words, we tested whether plants exposed to low salinity for long periods of time might be stressed as much as plants exposed to higher salinity for shorter periods of time. We created a simple index to quantify this total exposure and found that it correlated reasonably well with plant biomass for a number of species in the study.

Change in shoot dry mass in Plantago maritima seedlings with increasing salinity exposure. Our salinity index combined the length of exposure to flooding with absolute levels of local salinity. The index would be 0 in wetlands that are never flooded by salt water and ~33 for at a site continuously submerged in full seawater. Intermediate values could be due to long exposure to low salinity water or brief flooding by higher salinity water.

In terms of future sea-level rise, the overall results seemed pretty clear: for the species we investigated, if vertical marsh growth cannot match sea-level rise, plant production is expected to decline. Of course any increase in flooding or salinity at a given site would occur over the scale of decades, not the short time scale of our study. Yet declines in plant production in future wetlands might result in less food for marsh consumers and less detritus for the formation of new wetland soils.

I really enjoyed conducting this study. I was nervous about whether our seedlings would grow in the lab or whether they would quickly get destroyed once transplanted in the field. But the plants were hardy enough (or we had enough luck) to give us a good data set. Conducting this research, I had an opportunity to think about plant physiology and environmental stress. I read about some basic ideas in plant ecology such as how plants may trade off allocation of resources to above (shoot) or below-ground (root) production.

Though exciting, manipulative field experiments are challenging! The goal is to isolate factors to determine cause and effect, but at the same time maintain conditions that are as realistic as possible. Also, ecologists often want to be able to derive broad conclusions about such experiments, but various constraints often mean it is necessary to work at a single site, with a limited number of species, or only for a limited period of time. After conducting experiments such as these, it is important to ask: would different species or locations or seasons give different results? Extracting generalities from such complex ecosystems is a rewarding, but heavy intellectual challenge.

Reference

Janousek CN, Mayo C. 2013. Plant responses to increased inundation and salt exposure: interactive effects on tidal marsh productivity. Plant Ecology 214:917-928.  

Oregon tidal wetlands and climate change (pt. 2)

Which factors affect the distribution of tidal wetland
plants? Will these gradients shift with climate change?

In the last post, I began to describe some of the work I conducted as an ecologist with the EPA. Our initial investigation was a regional survey to quantify plants, algae and environmental characteristics in wetlands scattered throughout four estuaries along the Oregon coast. After working through the algae, a second goal of the regional survey was to relate vascular plant species abundance, composition and diversity to the major environmental gradients present in these wetlands (link to the paper). Salinity and elevation relative to tides (this determines when and how long plants are flooded) were of particular interest. With future sea-level rise, both flooding and salinity exposure are expected to increase.

It is already well known that factors like elevation and salinity impact wetland vegetation in a general sense (e.g., Watson and Byrne 2009), but the specific relationships between plant communities and their local environment are less well known in the Pacific Northwest. Additionally, it is useful to know which environmental factors have the greatest effect on plant communities.

A first step was to look at different environmental factors as relative predictors of plant occurrence. From the plant surveys we had a simple dataset showing whether each species was present or absent at each location we sampled. We also had quantitative data at each location for five gradients of potential importance to plant distribution: tidal elevation, soil salinity, soil nitrogen content, soil grain size, and a hydrologic index that quantified the degree of marine versus river dominance for the estuary from which the data were collected. The plant and environmental data were put into logistic regression models for many of the common species. The exciting next step - which I learned about after encountering a study on butterfly habitat use - was to apply a technique called hierarchical partitioning. This statistical technique enables a researcher to assess the relative strengths of effects (independently and jointly with other factors) of different variables in a statistical model. Like all statistical methods, it has its limitations (for instance, it doesn’t perform well with non-linear relationships between dependent and independent variables), but it seemed like a promising technique to quantify the relative importance of selected environmental factors on plant distribution.

I ran the analyses for 20 of the more commonly-occurring species and obtained some interesting results. First, for quite a few species, soil salinity was the most important variable in explaining the presence or absence of the species in the wetlands. In the figure below, for instance, salinity was positively related to the presence of perennial pickleweed (Sarcocornia perennis). Pickleweed occurrence was also positively correlated with tidal elevation, estuarine river-dominance, and soil clay content, though less strongly. (The positive correlation with river flow seems somewhat counter-intuitive for this salt-loving species, but may be due to its high frequency of occurrence from low marsh at our most river-dominated site.)

Relative strength of abiotic factor effects on the occurrence of pickleweed (Sarcocornia perennis) in Oregon tidal wetlands. All factors had statistically significant effects, but soil salinity appeared to have the greatest effect in the statistical model.

Elevation turned out to be the most important variable predicting the presence or absence of some other species. And, more rarely, soil nitrogen stood out as a key environmental gradient. Grain size (percent clay) of the soils generally only weakly correlated with species presence and absence.

The logistic regression models enabled a species-by-species look at environmental correlates of plant occurrence, but wetland plant communities in the Pacific Northwest are very diverse and species associations occur in complex patterns. We used another exciting statistical technique, non-metric multidimensional scaling (NMDS), to investigate overall plant composition in our dataset. In a nutshell, NMDS is a computational technique that aims to represent all of the differences between pairs of samples in a simple 2 or 3 dimensional graphical display. Its value lies in its ability to take a complex multi-dimensional dataset and summarize that information in a visually-intuitive manner from which patterns can be deduced.

The plot below shows the results of our NMDS analysis based on the abundance of 20 common plant species. Points closer to each other are more similar in terms of species composition. In the figure, the samples are colored based on their tidal elevation. Brownish points are plots from lower wetlands (e.g., below mean higher high water, MHHW) and greenish points are plant assemblages from high tidal marsh that is less frequently flooded. The analysis shows that plant communities separate out on an elevation gradient, similar to the patterns of vertical zonation one would see with invertebrates and algae on a typical rocky shoreline.

Non-metric multidimensional scaling plot of vascular plant communities in Oregon tidal wetlands. Plots are colored according to their height above or below local mean higher high water (m). Plot stress = 0.11.

Below I’ve shown the same NMDS plot, but with points coded by summer-time soil salinity. Plant composition differs between more saline and fresher wetlands, but there is a gradual gradient as with elevation.

An observational study like this is valuable for generating hypotheses about which environmental factors affect the distribution of different wetland species. However, we know that species are affected my more than environment itself – interactions with other species matter too. To more clearly determine causality, and not just patterns in the data, controlled experiments are needed. With dozens of species in the tidal wetland flora of Oregon and many potential abiotic and biological factors of importance, comprehensive study of this question would be a massive undertaking! In the next two posts, I’ll discuss some limited experimentation we performed to assess the effects of a few abiotic factors on plant growth and germination.

References

Janousek CN and Folger CL. 2014. Variation in tidal wetland plant diversity and composition within and among coastal estuaries: assessing the relative importance of environmental gradients. J. Vegetation Science 25:534-545.

Watson EB and Byrne R. 2009. Abundance and diversity of tidal marsh plants along the salinity gradient of the San Francisco Estuary: implications for global change ecology. Plant Ecology 205:113-128.