Restless Kilauea

Halemaumau Crater inside Kilauea's caldera.

Kilauea lies on the southeastern slopes of Mauna Loa. One of five volcanoes on the Big Island, it is the most active. The caldera itself is one of the centerpieces of Hawai’i Volcanoes National Park. It is an oval depression, a few miles across, its floor paved with twisted dark grey barren lava. Calderas form as the summit of the volcano collapses. At the west side of the caldera is the steaming depression of Halemaumau, visible only from a distance. During the day steam and sulfurous gases billow up and are blown to the west by the trade winds. At night the basin glows a fiery orange.   

The caldera area is active with steaming vents, and lush forests grow up the slopes of the volcano to the rim. There are many more craters along the slopes of the volcano, some visible from Chain of Craters Road.

Repeated lava flows down the slopes of Kilauea over the decades are recorded in the mosaic of forest and barren rock across the landscape of the Park. The majority of surface rocks on Kilauea are less than 500 years old, making these among the youngest rocks on earth. The lava consists of a variety of forms, from braided twisted rock to large plates that have cracked. The Hawaiian names for two main classes of cooled lava are a’a and pahoehoe. The a’a lava is jagged rubble, lying in heaps on the landscape. The smoother pahoehoe is more common. Until these new deposits erode to form soils, there is little space for plants to colonize.

Kilauea volcano on the Big Island. Map from USGS, Hawaiian Volcano Observatory.

Halemaumau crater glowing at night.

Steaming vents in vegetation on the northern side of the Kilauea caldera. Halemaumau crater is to the left.

Lava flows down Kilauea as seen from Chain of Craters
Rd. The a'a is dark grey; pahoehoe is lighter grey. The
Pacific Ocean is visible in the distance.

Click here for a USGS thermal webcam view into the lava caldron of Halemaumau Crater.

References

Holcomb RT 1987. Eruptive history and long-term behavior of Kilauea Volcano. Chapter 12. USGS Professional Paper 1350.

National Park Service. 2008. Hawai’iVolcanoes National Park Business Plan. 

Ka Lae

The southwestern coast of the Big Island is known as the Kau district. It is sparsely populated and transitions from the forested slopes of south Kona to wind-swept grasslands at the southern tip of the island (Ka Lae) to the volcanic terrain of the National Park farther east.

A wave pounding the southern coast at Kae Lae. Padina and other seaweeds carpeted this great southern tidepool.

Ka Lae.

There is some spectacular coastline at the southern end of the island. A paved road leads from the Belt Highway to Ka Lae, which is the southern-most point in the 50 US states. A rocky shore of black lava is swept hard by the wind and pounded by surf. Tropical seaweeds line the coastal rocks and filled a few tide pools. The overcast sky present over the last few days in south Kona gave way to sun and cumulous clouds at Ka Lae. Looking south, I thought of the thousands of miles of open ocean that stood between this point and the next land to the south, not even knowing which islands would be closest.

Five kilometers to the east of the southern point is Papakolea, a green sand beach, one of only a few in the world. We hiked along the hot, dry, dusty and windy lattice of orange dirt roads that lead from a parking area near Ka Lae to the small cove with the famous green sand. It is a tourist trap of sorts, complete with a small local economy that offers cold drinks to parched hikers and truck/van rides over the rough terrain for those so desiring. Beaches with rugged black lava occurred along the trail. The upland was carpeted in grasses, dancing elegantly in the consistent warm wind.

Volcanic coastline along the route to green sand beach.

Green sand beach and the grey bluffs that form the
east rim of the old volcano.

After an hour or so, we finally reached the cove, an extra wind-swept nook with black lava to the right and a grey striated cliff to the left. At the base of the cove was a short stretch of green sand, comprised of olivine, a light green mineral. The olivine is derived from a 50,000 year old cinder cone that sits right here, a part of one of the rift zones of the massive Mauna Loa volcano to the north. I was swimming in a small relict volcano!

Polished olivine gives the sand its green hue at Papakolea.

References

https://en.wikipedia.org/wiki/Kau,_Hawaii

https://en.wikipedia.org/wiki/Papakolea_Beach

Honaunau Bay

Our first two full days on the Big Island provided a chance for beach exploration on the south Kona coast. To snorkel I originally wanted to visit Kealakekua Bay, a marine life conservation district (state marine reserve), but the only public road led to the southern part of the Bay where the swell was probably too significant for the kids to venture much into the water. Honaunau Bay to the south became an excellent alternate location, and I the reef were enjoyable enough to return for a second day.

Slate pencil urchins, Heterocentrutus mammillatus.

The Bay is located just north of a small National Historic Park and seems to be a popular tourist location. Many bobbing snorkelers notwithstanding, the fringing coral reef that hugs the shore was teeming with biological activity. Most human visitors stayed close to home base and it was easy to get away from the crowds by venturing a bit north just offshore. The reefs gradually descended offshore, to depths of probably at least 50 feet. Bright yellow tangs and many other species were abundant in shallow water, so it was easy to see quite a few fish species in only 10-20 feet deep.

Corals comprising the reefs came in various shapes, mostly as massive plates, and some were bleached. The most abundant motile invertebrates may have been urchins, or at least this was the taxonomic group that caught my eye. Pencil urchins with their brick red cumbersome spines were tucked into crevices in the complex reef, while large black urchins with full arrays of thin quill-like spines ventured out in the open, cognizant that no other reef creatures would be likely to interfere with their activities.

The fish were most impressive, occurring in abundance, busily tending to the business of reef life. Bright yellow tangs, in groups or large schools were probably most common. Other groups included butterfly fishes, flamboyant Moorish idols, triggerfish and parrotfishes. There was some chasing, but much of the activity involved feeding; many species were presumably herbivores grazing the sparse algae that happen to grow up on the reef. I enjoyed the solitary greenish blue parrotfish which tended to be shy when I tried to approach with a camera. Most species stayed close to the reef though a few ventured higher into the water column. Some thin blue fish in contrast, stayed just beneath the water’s surface, and since one tends to look down while snorkeling, it was a while before I noticed them.

A reef fish sampler. Top row, from left: moorish idol, Zanclus cornatus with orange band surgeonfish, Acanthurus olivaceus; unknown white and gold-colored butterfly fish; yellow trumpetfish.  Bottom row, from left: fourspot butterflyfish, Chaetodon quadrimaculatus; whitebar surgeonfish, Acanthurus leucopareius; unidentified parrotfish.

Thin, well camoflauged bluish fish hanging out near the water's surface.

A shallow coral escarpment with a pair of ornate butterfly fish, Chaetodon ornatissimus.

References

Mahaney C, Witte A. 1993. Hawaiian Reef Fish. Blue Kirio Publishing.

Origin of the Hawaiian Islands

Mauna Kea from the west, Nov 2015.

From a geologic perspective, Hawaii is an ephemeral and dynamic anomaly. The islands’ origins lie deep undersea where a large hotspot feeds a succession of active volcanoes underneath the center of the Pacific plate. Measured against geologic history, each island lives a very short life - they burst forth from the sea floor and then quickly drown under the forces of erosion.

Hawaiian volcanoes are the largest on earth, by height (as measured from the sea floor) and by total mass. In fact, their mass is so great that they depress the Earth’s crust in their vicinity. Whereas the typical depth of the seafloor might be 4.5 km, near Maui and the Big Island, the volcanic giants push sea floor depths to over 9 km.

The arc of the Hawaiian Islands formed as a result of the northwest-ward movement of the Pacific plate, currently estimated at a rate of 10 cm per year. New volcanoes form over the hotspot with great rapidity, taking only about 0.3 million years between their inception and the point at which they break the ocean surface. The Big Island is the youngest in the Hawaiian chain, with the oldest rocks dated to about 0.6 million years. Oahu formed about 3-4 mya, and Kaua’i and Ni’ihau have the oldest rocks at about 6 million years old.

The Hawaiian archipelago. Map from Langenbeim and Clague (1987).

To the northwest of the main Hawaiian Islands lies a series of atolls (including Kure and Midway), which are volcanic islands in their old age, hanging on to the sea surface by their reef building corals. Farther into the north Pacific, the Hawaiian Island chain bends northward and becomes the Emperor Seamounts which stretch towards Russia. The bend in the path is dated to about 43 mya, and the change in course of the Pacific plate is believed to be linked to the collision of the Indian subcontinent with Asia at that time. 

Topography of the Big Island, Hawaii, with elevations in feet. Mauna
Kea (north) and Mauna Loa (south) both exceed 13,000 ft elevation.
Map modified from USGS, "Ground Water Atlas of the United
States. Source.

Hawaiian volcanoes progress through 4 stages, starting with the preshield phase when volcanic activity begins. Stage 2 is the shield stage and is the most active period of volcanic activity when the vast majority of the volcano’s volume is created. Magma rises from the hotspot located as deep as 60-70 below the crust where it is stored in shallow reservoirs. During volcano growth, erupting lava emerges both from the summit of the volcano and from several lateral rift zones. The post-shield stage is next, and consists of additional volcanic activity for about 0.1 to 0.3 million years after the shield stage. Finally, after perhaps a quiescent period, there is the rejuvenated stage, a period of variable length where some additional volcanic activity may occur. The Big Island is the only Island in the shield stage. Landslides and erosion gradually wear down the volcanoes.

There are five volcanoes comprising the Big Island: Kohala, Mauna Kea, Hualalai, Mauna Loa, and Kilauea. Only the latter two have erupted recently. Kilauea is the most active volcano in the world. I hope to see lava flows when we visit the National Park in a few days. A bit to the southeast of the Big Island lies the submerged Loihi, which is the newest volcano in the long Hawaiian chain. Some thousands of years into the future, it may form its own island by breaking the ocean surface or it may merge with its neighbors to grow the size of the Big Island.

The five volcanoes of the Big Island. Map and key modified from Sherrod et al. (2007).

References

Clague DA, Dalrymple GB. 1987. The Hawaiian-Emperor Volcanic Chain. Part I. Geologic Evolution. USGS Professional Paper 1350.

Langenbeim VAM, Clague DA. 1987. The Hawaiian-Emperor Volcanic Chain. Part II. Stratigraphic Framework of Volcanic Rocks of the Hawaiian Islands. USGS Professional Paper 1350.

Sherrod DR. 2009. Hawaiian Islands, Geology. In: Encyclopedia of Islands, Gillespie RG and Clague DA (eds), University of California Press, Berkeley, CA, p.404-410.

Sherrod DR, Sinton JM, Watkins SE, Brunt KM. 2007. Geologic Map of the State of Hawai’i. USGS Open-File Report 2007-1089.

Signs of the western drought

As I traveled through northern California into Oregon last month, evidence of the severe drought lingering in the west was apparent. Late summer and early fall are typically dry periods in California with the grasses having long since turned golden. But there were perhaps other signs of the on-going drought: water levels at Lake Shasta were very low revealing a large band of reddish soil between the reservoir and the treeline; pines in northern California and southern Oregon appeared stressed; normally glaciated Mount Shasta, nearly the highest point in California, had just thin ribbons of snow on its southern slopes.

Low water levels at Shasta Lake (a major reservoir in northern California).

Pines in the vicinity of Mt. Shasta in northern California and
into southern Oregon looked perhaps unusually stressed with
significant amounts of dead needles.

In California the drought is now in its fourth year, and concern finally reached the level where mandatory reductions in water usage by residential consumers were put into place. Other parts of the west are also in drought. Nevada is nearly as dry as California. Oregon and Washington have had abnormally low precipitation this year. The maps of drought conditions for the United States, updated weekly by the U.S.Drought Monitor, show that the western U.S. as a whole is quite dry.

Mt. Shasta with low snow coverage.

One useful metric of drought conditions is the PalmerDrought Severity Index. The index incorporates both precipitation and temperature information to indicate drought intensity. Values ≤ -4 indicate “extreme drought”; and values between -2 and -4 indicate “moderate” or “severe” drought. Trees are also excellent sentinels of overall environmental conditions because their growth patterns integrate the various stressors they experience such as temperature, soil water content and nutrient availability. Thus tree ring data provide excellent annual historical records of environmental conditions.

On-line I located the work of a team from NOAA’s Nation ClimaticData Center that used hundreds of tree ring samples to study long-term changes in drought intensity throughout the U.S. I downloaded and plotted Palmer Index data for the last 500 years in the northern California region. Tree ring data from 26-55 samples cover this time period. I am definitely not an expert on the science of drought, but to me the data suggest that normally there is substantial year-to-year variation in drought conditions in this region. Some longer-term patterns can also be discerned from the time series. For example, from about 1915 to 1935 – a period coinciding with the dust bowl in the Midwestern US – northern California appeared to be in an extended drought.

Palmer Drought Severity Index data reconstructed for northern California from tree ring data over the last 500 years. The 
blue lines indicate annual values; the thicker red line is a ten year running mean. The time series ends in 2003, so the
current drought is not shown on the figure. Data source: NOAA NCDC.

Recent drought status in the continental U.S. as measured by the Palmer Index. Map source.

Only time will tell if California experiences a fifth year of drought. With a strong El Nino currently developing in the eastern Pacific Ocean, chances are that greater than average precipitation will fall in California this winter and some relief will come. It has also been a warmer year than ever, so more of that precipitation may come as rain rather than snow.

Crater Lake

Crater Lake National Park was the last significant stop on my recent trip to the Pacific Northwest. Located about 50 miles north of the California border, it is the only national park in Oregon. The park centers on the magnificent lake with its deep, cold, and intensely blue waters.

Crater Lake and Wizard Island (center) from the southwest side of rim drive.

Wizard Island is a small crater that formed inside Crater Lake
after the massive eruption of Mount Mazama (NPS 2013). With
its beautiful shape, it is my favorite feature of the Park.

The crater in which the lake rests was formed by a massive volcanic explosion some 7700 years ago. Prior to this cataclysmic eruption, Mount Mazama was one of the highest peaks in the Cascade Range, reaching about 12,000 feet in elevation (NPS 2013). The area has breathtaking vistas and holds fascinating lessons in geology.

I camped for a single night at Lost Creek campground, a small site among pines on the eastern slope of the mountain. It was the night of the lunar eclipse and blood moon and Crater Lake was the perfect location for sky watching. At about full eclipse in the late evening (approximately 8 PM PDT), hundreds of stars were visible in the darkened sky because of the obscured moon. Later, after the eclipse lapsed, the landscape became much more illuminated from the brilliant full moon. I drove back down the road a few miles from the campsite to the pinnacles area that I had visited just before sunset.

Pinnacles at the southeast side of the park. The discreet bands of color show
the evolving composition of volcanic material as it was erupted from Mount
Mazama 7700 years ago (NPS 2013).

I have made a few day trips to Crater Lake in the past, but saw the pinnacles for the first time on this trip. Formed during the last eruption, they stand as spires on both sides of a wide valley cut into the eastern slope of Mount Mazama. In essence, during the eruption large flows of hot ash poured down the slopes of the mountain. Heated gases rose through the ash to escape into the atmosphere over time, hardening columns of mud (called “tuff”) surrounding the gaseous vents. Finally over time, erosion removed the softer ash but not the more hardened columns of mudstone surrounding the vents, leaving a landscape of spires for us to admire today (NPS 2013).

Crater Lake from the trail at Cleetwood
Cove.

In the morning following a cold night of camping, I hiked down the only trail that leads from the rim of the crater to the lake itself. It is a short but moderately steep trail that passes through light conifer forest. The water of the lake was calm, reflecting sparkles from the sun in the east. At the end of the trail there is a boat launch (for paid tours to Wizard Island), and a small shack housing a water level measurement station. I put my feet in the cold lake in the warm morning sun.

The history of Crater Lake is one of violent geologic forces, but the placid lake and singing birds on a warm morning in early fall, and the green carpets of forest on Mount Mazama’s slopes belied its turbulent past.

Reference

National Park Service (2013). Crater Lake National Park. Geologic Resources Inventory Report. Natural Resource Report NPS/NRSS/GRD/NRR-2013/719

The pinnacles illuminated by the full moon.

The eclipse and blood moon from the Park. 

Shaw Island

The Salish Sea, including Puget Sound, was carved by glaciers during past ice ages. When sea-level began rising about 10,000 years ago, it left a maze of channels and islands in central and northern Washington. The San Juan Islands are nestled between Vancouver Island to the west and mainland Washington to the east. There is regular ferry service to four of the islands – San Juan, Orcas, Shaw and Lopez – and of these, Shaw is the least populated and developed.

I arrived yesterday morning on Shaw and made my way to Indian Cove on the south side of the Island. This county park (where I also camped last night), is about the only official place to launch a boat since the vast majority of the island is privately owned. I paddled for about two hours around the east and northeast ends of Shaw to Blind Island, a tiny rock at the north end of Blind Bay and south side of Harney Channel.

Shaw Island in northern Washington state.

Blind Island is along a “marine trail” and boaters can pitch a tent there for a modest fee. The island is mostly grass and rock and weeds (unfortunately some non-natives like English Ivy are established there), but I found about 5 tree species including madrone, douglas fir, grand fir, and apples. It was a surprise to see apple trees; perhaps a resident of Shaw tried to establish an orchard here in the past.

The return paddle was another 2-3 hours and I explored the eastern shore of Canoe Island for a time. It was between Shaw and Canoe Islands that I saw the most developed bull kelp forests of the day. With a single unbranched stipe, these annual kelps reach the waters surface where their deep brown blades spread out to gather sunlight. Along my paddling route, I saw a variety of wildlife, though it wasn’t possible to capture all on camera – a bald eagle, many other birds, curious harbor seals, river otters (!) and a dolphin. 

Skittish river otters at the edge of the water southwest of Indian Cove. From my boat it was difficult to see these
otters under the dark overhanging rocks and trees, but with my telephoto lens this shot came out great!

A great blue heron standing on a raft of bull kelps near Shaw.

Just after setting up camp yesterday evening back on the south shore of Shaw, the rains came and continued a bit into the morning. There was a so-so low tide early in the day, so I walked out to Reefnet Point on the south end of the Shaw to observe the intertidal. Only a few species of seaweeds were common, and of these, Fucus and Ulva comprised most of algal cover along the rocks. In the shallow and fairly murky water, however, I found a variety of interesting invertebrates: cancer and other crabs, shrimp, anemones and one or two species of holothuroideans (sea cucumbers).

With limited places to explore (so much of the island is private property), I’m not sure I’m likely to visit Shaw again in the near future, but being at the center of the archipelago, it is a good starting point for kayaking adventures to other islands in all directions. And, aside from the occasional noise of airplanes, ferries or other sources, the island was very quiet, a great location for solitude.

A madrone hanging over the water on the northwest shore of Shaw Island.

Sauvie Island

It was a gorgeous weekend in the Pacific Northwest, the time of year when the warmth of late summer lingers but the first signs of fall appear: yellowing maple leaves, a sky full of cumulus clouds and a few raindrops. 

The Columbia River, third largest river in the US, is one of the iconic symbols of the Northwest. Yet despite living in Oregon for four years until recently, I’ve really spent little time exploring it. I had a free afternoon on Sunday, and a boat, and was in Portland, so off to explore the Columbia it was.

Seagulls over the Columbia River. Sauvie Island in Oregon is to the left; Washington State is to the right.

The northern end of Sauvie Island with approximate
 locations where jumping fish were observed. USGS Topo.

If the signs are to be believed, Sauvie Island is the largest riverine island in the nation (Oregon seems to have a penchant for pointing out superlative natural landmarks, an example being the ‘D River’ on the central coast, which is apparently the “nation’s shortest river” or something like that). Sauvie Island is located just northwest of where the Willamette River meets the Columbia, and it is large indeed: large expanses of farms and woodland protected by levees, and miles of roads throughout the island connected to the Oregon mainland by a single bridge. The northern part of the island is a state wildlife reserve. It was there that I launched the kayak on the western bank of the river.

The afternoon was calm and virtually all of the chop to contend with in the kayak was generated by the frequent passing of motorboats. I paddled perhaps a few miles north along the river, staying close to the shore, and finally rounded the tip of the island turning south into the Multnomah Channel. The island shoreline alternated between sand and firm mud; the upland was vegetated with deciduous trees, shrubs and some late season wildflowers.

A perched blue heron.

The highlight? Definitely fish jumps. I unexpectedly caught the first, a large salmon perhaps a hundred meters away that flopped a half meter into the air to crash back into the cool river. Over the next couple hours of rowing I saw (or heard) several more splashes, the fish leaping to catch an insect meal or tease the fisherman on the river. Their infrequent leaps and splashes lasted just a second, a real challenge for anyone trying to record the action. 

This is the most luck I had catching a shot of jumping fish. 

Algae and vascular plants at the shore of Sauvie Island. The sedge at right is so cool, but I have not yet tried to identify it.

The west is ablaze

Much of the western United States has been on fire this summer. Affected landscapes range from California chaparral to temperate rainforest in the Pacific Northwest. Fire danger appears to be elevated this year because of the convergence of a few important factors. First, much of the western US (but particularly California) has been experiencing severe drought over the last few years. Second, climate change continues to steadily result in higher land temperatures year over year. And finally, western forests have been subject to a long history of fire suppression by management agencies that have left more fuel than would otherwise be present.

Fire is a natural part of some ecosystems. In fact, certain plant species are dependent on fire for establishment of juveniles or completion of their life cycle. Examples include many species of pines and the giant sequoia of the Sierra Nevada. The latter species requires high light and fires help clear out competitors that might shade young sequoias.

Stebbins Cold Canyon Reserve in spring 2014 with
pine, oak and chaparral habitat.

Unfortunately, fire management policies have exacerbated the threat of large intense fires in the west. During the early decades of the 1900s, fire was suppressed at all costs. In some cases this may have led to the excessive buildup of fuels in dense forests. Once the importance of fire to some native ecosystems began to be better understood, land management agencies such as the US Forest Service recognized the importance of allowing some fires to run their course. Despite this change in attitude about fires in western ecosystems, fires are still managed in many cases. Continued encroachment of human development deeper into forests or other wildlands increases the likelihood that a fire will need to be suppressed to protect human infrastructure instead of letting it runs its natural course.

The Wragg fire was a moderate sized fire that ignited earlier this summer and burned through chaparral and pine forest habitat along state route 128 in the coast range hills of northern California near Lake Berryessa. The fire consumed the whole area of the Stebbins Cold Canyon Reserve, a small University of California research reserve where I have been hiking several times over the last decade.

Stebbins Cold Canyon Reserve protects a north-south oriented canyon in the hills of the northern California coast range. It is an example of relatively dry coast range habitat, with a mixture of chaparral and oak and pine woodland. The valley floor has a small creek with riparian habitat and the valley slopes are spotted with oaks and pines and manzanitas.

My most recent hike at the reserve was during April 2014. Monkeyflowers, Brodiaea, Castilleja and Dichelostemma were in bloom at the time. The most striking plant I observed was the heartleaf milkweed, Asclepias cordifolia. Emerging stoutly a half meter or so from the short groundcover of grasses, it had slate green fleshy opposite leaves and bright purple flowers. The magenta petals were slightly reflexed (bent backwards) and contrasted vividly with white hoods that form little loops around the center of the flower.

Habit and flowers of Asclepias cordifolia, heartleaf milkweed, spring 2014.

Cold Canyon in late August 2015, after the Wragg fire.

The Wragg fire however, transformed the landscape dramatically this summer. Although the Reserve is currently closed to visitors, from the highway it is possible to see the scorched hillsides. The ground was blackened and trees stood like ruins on the hillside. Looking closely, I could see that not all vegetation was equally affected; many trees had at least some green in their canopies, suggesting tree damage, but not complete mortality. Of course, the soil retains a seed bank and perhaps individuals of some species escaped mortality if the fire moved quickly through an area. It will be very fascinating over the next few years to hike the trails again and observe how the ecosystem recovers.

References

- Eckenwalder JE. 2009. Conifers of the World. Timber Press, Portland.

- Forest History Society. U.S.Forest Service Fire Suppression.

- Harvey HT. 1978. The sequoias of Yosemite National Park. Yosemite Association, Yosemite National Park, CA, 36 pp.

Nudibranchs

Rocky intertidal habitats can burst with color. In Pacific tidepools, among the most colorful organisms are beautiful sea slugs, or nudibranchs. They are roughly similar in size to their shell-less cousins on land, but they are not at all drab like terrestrial slugs.

Scientifically, nudibranchs are classified in an order (Nudibranchia) within a subclass of mollusks known as the opisthobranchs. There are several other groups of opisthobranchs, including sea hares. The nudibranchs themselves are divided into a few groups. The most common are dorid nudibranchs, which have a tuft of gills on the top of the body midway, or towards the posterior end of the animal. Another group, the aeolid nudibranchs, is showy, having rows of protrusions (cerata) along the top of the body. While many molluscs have hard shells for protection (clams and limpets for example), the sea slugs do without. The nudibranchs are predators, feeding on other invertebrates and sometimes on other nudibranchs. Their bright colors may serve as a warning to potential predators that might be tempted to eat these soft-bodied morsels.

Hermissenda crassicornis, an aeolid nudibranch, from Greyhound Rock, Santa Cruz Co, CA, June 2015.

With such delicate bodies, it is a wonder that sea slugs can survive on wave-pounded coasts. Clinging to seaweeds in calm pools at low tide, within a few short hours, the rising tide will bring crashing waves and turbulence. Other intertidal invertebrates – mussels, limpets, chitons and barnacles for example – cling with great tenacity to intertidal rocks to withstand strong hydrologic forces within their environment. The marine algae have a different strategy: they typically have flexible branches or stipes that allow them to be passively whipped back and forth as waves rush over them. How do the delicate nudibranchs make it? Do they retreat into refuges among the rocks when hydrologic chaos is at its greatest?

Triopha catalinea, a dorid nudibranch, at Greyhound Rock. 

I’ve seen quite a few nudibranchs on intertidal trips this year to the central California coast. For example, during a very brief stop at Greyhound Rock in northern Santa Cruz County in June I found four different species in the low intertidal. The most colorful was a single individual of Triopha catalinae, a few centimeters long. Clinging to a strand of feather boa kelp (Egregia menziesii) right at the water’s surface, the milky white body punctuated with bright orange spots was a striking contrast with the chocolate brown kelp below.

One of the most common nudibranch species this year has been the distinctive Okenia rosacea, or Hopkin’s rose. I found close to a dozen animals in just a half hour of tidepooling at Greyhound Rock. In fact, I’ve seen this species on many of the intertidal trips I took this spring in California: Pigeon Point in San Mateo County, Glass Beach in Mendocino County, and at Sand Dollar and Mill Creek in Big Sur. Essentially a hot pink mess of slug, there is nothing quite like it on the coast and you can’t miss it!

Okenia rosacea (formerly known as Hopkinsia rosacea) from Pigeon Point,
San Mateo County, CA, October 2009.

References

Behrens DW. 1991. Pacific Coast Nudibranchs. Sea Challengers, Monterey, CA.

 ...also, check out the Sea SlugForum

Hunting heron

Duxbury Reef is a low-relief intertidal bench at the west end of Bolinas Bay in Marin County in northern California. Tidal seaweeds and invertebrates live in a matrix of cobbles and silty sand which left the water rather murky – more like an estuary than the outer California coast. It seems like the unusual substrate of this site limits algal diversity and results in a fairly unique community. Several parallel ridges of bedrock provide some rare additional relief that hosts more typical mid-intertidal species like rockweeds and mussels.

Birds were actually the highlight of my low tide visit earlier this month to the reef. Unnerved by my presence, a great blue heron hunted in the shallow water with the rising tide. I crouched and observed for some time, witnessing at least two successful hunts of intertidal fish. The bird’s patience was obvious, but they must have remarkable eyesight to see fish which are probably well hidden in the dark tidepools.