At the end of my trip through the
southwest, I shifted from National Parks and lizards and desert wildflowers to
marine life of the central California
coast. At tidepooling stops in Cambria and northern Santa Cruz County ,
I encountered two new-to-me brown seaweed species, exciting discoveries
punctuating my long-term study of natural history and biogeography along the
west coast.
The first new species was a high
intertidal species of rockweed at Cambria in San Luis Obispo County .
Rockweeds are a family of brown seaweeds in the order Fucales. Many coastal
visitors (enthusiastic about slimy seaweeds or not) have likely seen these
organisms since they tend to be common on rocky shorelines and live high in the
intertidal zone where a good low tide isn’t necessary to leave them exposed.
Until recently, five rockweed
species were recognized along the California
coast (Abbott and Hollenberg 1976; Gabrielson et al. 2004; Gabrielson et al.
2012). These species are Fucus distichus,
Silvetia compressa, Hesperphycus californicus, Pelvetiopsis limitata, and Pelvetiopsis arborescens. There have
been several changes to the scientific names of the California
rockweeds since the publication of the landmark book on California seaweeds (Marine Algae of California; Abbott and Hollenberg 1976), so I’ve
included the older Latin names in the table below.
Wandering the west coast, I have
seen all five of these species at various points, the rarest being P. arborescens which is only found in
the vicinity of Monterey .
My visit to Cambria last month was my first
encounter with the sixth rockweed species, since it was newly described in the
scientific literature in a paper earlier this year (Neiva et al. 2017). Maybe I
have seen it before without recognizing it as a distinct species.
Two common rockweed species in California: Fucus distichus (left; Carmel Pt., Monterey Co., 2014) and Silvetia compressa (right; Scott Creek, Santa Cruz Co., 2007). |
Traditionally species have been
described based on their morphology, but increasingly molecular signatures are
complementing, and even upending, traditional concepts of differences between
species. Neiva
and colleagues examined mitochondrial DNA from Pelvetiopsis
and Hesperophycus, identifying a
new species of Pelvetiopsis: P. hybrida.
Neiva et al.’s study resulted in
some other interesting findings. First, they found evidence that P. hybrida originated because of a relatively
recent hybridization event between Hesperophycus
californicus and Pelvetiopsis arborescens.
Up until this study, the authors note, this type of hybridization
(allopolyploidy) has probably never been documented before in brown seaweeds.
Polyploidy refers to chromosome multiplication inside the nucleus during a
hybridization event (for instance, a hybrid progeny has twice the number of
chromosomes as its parents). Allopolyploidy occurs when the two parents are
from different species.
Second, the researchers confirmed
that P. arborescens is a distinct
species genetically, and suggested that its restricted range indicates it is a
climatic relict. Finally, they found that the evidence didn’t favor placing Hesperophycus on its own separate branch
on the evolutionary tree. Instead this genus seemed to stem from within the Pelvetiopsis branch, meaning that it
should be renamed to be a part of that group. Hesperophycus californicus was this renamed to P. californicus in the study.
All those scientific name changes,
annoying as they can be when trying to be a diligent student of natural
history, are part of the evolution of scientific understanding and hopefully
bring us to a better picture of the true evolutionary relationships among
organisms over time. So, the current names for the (now) six species of California rockweeds are
below:
At Cambria ,
the high intertidal rocks had populations of P. hybrida where it was pretty common. I photographed the species
pretty intensely, noting that they seemed different from the usual Pelvetiopsis limitata (this species is
the most common and widespread of all the species in the genus where I tend to
tidepool), but I wasn’t confident I was really seeing the new species until I
returned home and reviewed Neiva et al’s paper. Perhaps unsurprisingly because
it is a hybrid lineage, P. hybrida is
morphologically intermediate to its parent lineages. It has some cryptostomata
(tufts of very small colorless hairs on the surface of the plant) like Hesperophycus, but its branches are
narrower, intermediate between the two parental species.
A mix of four intertidal rockweed species at Point Pinos, Monterey Co., 2016. Can you identify the four species? |
~ ~ ~ ~
My second new seaweed find got me
really excited. It was a kelp, another group of brown seaweeds in the order
Laminariales. Kelps are one of my favorite groups of marine plants and after
about two decades of tidepooling along the west coast, I think I’ve seen
virtually every species that occurs between San Diego
to Washington …except
one. That would be the elusive Laminaria ephemera.
I’ve seen L. ephemera as a herbarium specimen to be sure, but until this
spring I had never seen it in the wild. The magic location was Greyhound Rock
in northern Santa Cruz
County .
As I often do during rocky
intertidal visits, I was compiling a list of large brown seaweeds
(Laminariales, Fucales, etc.) present at the site, when I stumbled upon a few
long kelp blades in the low intertidal that didn’t immediately register as a
known species. The blades were entire (not divided), long, slender, and simple
except for a really pronounced sorus (area of spore production) at the center
of the blades. I initially thought of Laminaria
farlowii, but the blades of that species are distinctly ruffled all over
its surface. And then my mind settled on Laminaria
ephemera, a species I had long known about but had never positively
identified in the field.
The key feature to identify L. ephemera lies in the holdfast. Unlike
most other kelp species, it has a discoid holdfast that lacks haptera (spreading
branches that superficially resemble plant roots). The holdfast is essentially
a small golden brown suction cup that anchors the plant to a rock. Gently
moving aside some of the algal cover around the base of the plant, sure enough,
I could see the small smooth holdfast.
Laminaria ephemera at Greyhound Rock, Santa Cruz Co., CA, April 2017. Left: Blades. Right: close-up of discoid holdfast. |
The population of L. ephemera I discovered was of unknown
size, but it didn’t seem large from my observations. There were about 10 blades
that seemed to meet the visual criteria for the species, and I checked about
half of those to verify the presence of the correct holdfast. There were
smaller kelp blades in the low intertidal that could have been less mature
plants of the species, or possibly specimens of L. sinclairii or L.
setchellii, both of which were also present at the site. The challenge with
identification of the kelps is that the juvenile sporophytes all look terribly
similar, regardless of species.
Two blades of L. ephemera with sori (regions of a seaweed blade that produce spores) at Greyhound Rock, April 2017. |
How would a large seaweed like L. ephemera be hard to miss? A few
reasons perhaps. First, as one of the few annual kelps, L. ephemera would quickly mature and then disappear after several
months of growth. It would be an unlikely find in the fall or winter. Second,
blades might be easily confused for small plants of L. setchellii (before the blade begins to divide into individual
straps) or L. sinclairii. One would
have to check every holdfast to distinguish L.
ephemera from related kelps. Finally, L.
ephemera appears to be fairly rare along the west coast of the US . Abbott and
Hollenberg (1976) note that it is present from Alaska
to Monterey County , but also call it “infrequent”.
Reviewing herbarium records available on-line at the Macroalgal Herbarium Portal, in California this species seems to
have mainly been collected from Monterey and Humboldt Counties ,
so my finding of a small population in northern Santa Cruz County
may possibly be a new location for this species. This is a species I’d like to
study further in terms of prior collections, and … I need to check more kelp
holdfasts in the field!
References
Gabrielson PW, Widdowson TB,
Lindstrom SC. 2004. Keys to the seaweeds and seagrasses of Oregon
and California ,
north of Point Conception. Phycological Contribution No 6.
Gabrielson PW, Lindstrom SC,
O’Kelly CJ. 2012. Keys to the seaweeds and seagrasses of southeast Alaska , British Columbia ,
Washington , and Oregon . Phycological Contribution No 8.
Macroalgal Herbarium Portal. 2017.
http://macroalgae.org/portal/index/php.
Accessed 16 May 2017.
Neiva J, SerrĂ£o EA, Anderson L,
Raimondi PT, Martins N, Gouveia L,Paulino C, Coelho NC, Miller KA, Reed DC,
Ladah LB, Pearson GA. 2017. Cryptic diversity, geographical endemism and
allopolyploidy in NE Pacific seaweeds. BMC Evolutionary Biology 17:30.
Silva PC. 1990. Hesperophycus Setchell & Gardner,
nom. cons. prop., a problematic name applied to a distinct genus of Fucaceae
(Phaeophyceae). Taxon 39:1-8.
Silva PC, Pedroche FF, Chacana ME,
Aguilar-Rosas R, Aguilar-Rosas LE, Raum J. 2004. Geographic correlation of
morphological and molecular variation in Silvetia
compressa (Fucaceae, Fucales, Phaeophyceae). Phycologia 43:204-214.
This a wonderful post, Chris! I was only vaguely aware of Pelvetiopsis aborescens and Laminaria ephemera, and now I will look. My bet is that many more "hybrid" species will be found, and our understanding of speciation in algae will undergo a revolution. You were at UCSC just after I retired and I somehow missed you then. The next time you are in the intertidal in the Monterey area, let me know. It would be great to go out with you. John Pearse (pearsester@gmail.com).
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