Monday, October 21, 2019

Algae: The Simple Is Complex

Writer Ruth Kassinger praises algae unstintingly in her new book, Slime:  How Algae Created Us, Plague Us, and Just Might Save Us (2019).  They are, she asserts, “the most powerful organisms on the planet” and, to them, we owe our existence.

Though we humans are here due to the work of a host of other entities and a long series of fortuitous events as well, I will grant Kassinger her point.  In perhaps their most signal contribution to the planet, algae, through the chemical magic of photosynthesis, added oxygen to an atmosphere that, heretofore, had been inimical to multicellular life.  And their crucial gifts go well beyond oxygen.  There’s the production of soil, without which the colonization of land by plants was a non-starter.  Plants, themselves, evolved from the charophytes (a taxon of green microalgae).  Take algae out of the food chain and animal life is done for.  The development of the large Homo sapiens brain can be attributed in part, Kassinger argues, to algae.  Early hominins living along shorelines had diets rich in “brain-selective nutrients,” those minerals and fatty acids critical for brain development.  Central to this diet was probably seaweed.  Of increasing importance, there’s the sequestration of carbon dioxide in their bodies that accumulate in untold numbers on the ocean floors.  Coral reefs?  Not without algae.  The list goes on.

So, what are algae?  This turns out to be a complicated question to which there is no consensus answer.  Kassinger fudges this:  “Algae (and the singular alga) is a catchall term, a name for a group of diverse organisms.”  (p.xii)  She notes that all do (or did) photosynthesize, though they are not plants.  Paleontologist Steven M. Stanley in Earth System History (2nd edition, 2005) places algae in the Kingdom Protista.  The catchall nature of the label stems from the fact that the different algal taxa did not evolve from a common ancestor.  Kassinger describes three main groups:  single-celled blue-green algae or cyanobacteria; single-celled microalgae; and multicellular macroalgae (the seaweeds).

She tells of the good, the bad, and the ugly of algae.  I’ve already cited many of their positive natural contributions, but, as Slime documents, there are a host efforts underway to harness the power of algae to address multiple needs of the planet and its inhabitants.  These range from enlisting algae in cleaning polluted waters, to developing more eco-friendly plastic polymers, to producing algae oil (growing the algae needed for this would take carbon dioxide out of the atmosphere), to introducing more algae-based food stuffs into our and other animals’ diets.

As powerful as algae are for good, their capacity to wreak havoc must enter into the equation.  When these organisms “bloom” or run wild, often sparked by the excess nutrients we are putting into our bodies of water, they can create massive dead zones, killing or driving away other living creatures, releasing toxins, and ruining scenic beaches.  It’s not a pretty picture.

Kassinger’s book is a forceful statement on behalf of algae’s centrality to life on Earth, though she is less persuasive in asserting that they “just might save us” from the existential threats arising from climate change.

I wish I could endorse the book whole heartedly.  Kassinger certainly can distill complex topics, presenting them in ways that the lay person can understand and appreciate.  Her topic has deep appeal and the reader comes away having learned a great deal.  My primary complaint is that she has succumbed to the temptation facing (and undoing) many writers of popular science:  making themselves heroes of their stories, forcing their subject matter to share and, at times, relinquish the spotlight.

In Slime, the personal anecdotes of her journey in pursuit of information about algae finally wore thin for this reader.  I really wasn’t interested in, say, her scuba diving lessons or the challenges of staying warm on board a boat traveling over open water.  Beyond that, I think her editor failed her because, when some issue emerges as important for her research, Kassinger will use the same or similar language to explain to the reader why she’s now in some other part of the world:  “In search of answers, I find myself,  . . . .”  (p. 63) or “Nova Scotia is where I’ve come to investigate . . . .” (p. 106) or the phrase “which is why . . . .” (this last turns up at least four times – at pages 35, 81, 171, and 196 – to introduce a new location and some more personal anecdotes).

Yet, Kassinger probably achieves her aim.  Having read the book, I certainly am much more aware of algae and what they have done, and are doing, for me.  I’ve responded to the book in some small ways.  For instance, seaweed has a bit more of a role in my diet.

The book’s strongest impact on me came from the chapters that Kassinger devotes to lichens.  She introduced me to these surprising entities, marvelous in their composition and their impact on the planet.  Their range of structures and color is remarkable.  The label “lichen” applies not to organisms grouped by structure or color, but by a symbiotic relationship, a way of life, that has married algae and fungi.  The algae, often termed a “photobiont” in this association, uses its photosynthetic power to manufacture sugars and other carbohydrates, much of which are absorbed by the fungi with which they reside.  The fungi, in turn, provide the algae an environment replete with critical moisture, shields against harmful ultraviolet rays, and toxins that ward off predatory animals.  Though there is no typical arrangement of algae and fungi in lichens, the illustration below of the interior of a simplified foliose lichen (one of the main groupings of these organisms) captures some of the essence of the lichen structure.  This illustration is my own but was guided by those that appear in Joe Walewski’s Lichens of the North Woods (2007, a useful volume though limited in scope to the “North Woods,” an area surrounding Lakes Superior and Huron).  This illustration is of a view I have not seen in person though I tried to do so (my microscopes and dissecting equipment were not up to the task).
Lichens are organized into several groups:  crustose lichens which lie very flat against the substrate on which they are affixed; foliose lichens which are much more three-dimensional with lobed growths and some separation from the substrate on which live (two examples of such lichens are discussed shortly); fruticose lichens which, as Kassinger notes, “often resemble miniature tumbleweeds and attach to a substrate as a single point.”  (p. 37)  In the massive and gorgeously illustrated Lichens of North America (2001), Irwin M. Brodo and his co-authors identify a fourth group of lichens, the squamulose which are “intermediate between foliose and crustose growth forms.”  (p. 17)

To call a relationship symbiotic suggests (to me, at least) a relative balance in the partnership, one that appears to be somewhat lacking in lichens.  Yes, the different kinds of organisms involved benefit, but there are aspects that clearly favor the fungi.  Quite frequently in this relationship, according Brodo et al., the fungi is killing the enveloped algae.  Thankfully, that murderous impulse is somewhat more than offset by the algae’s rate of reproduction.

Which raises the question of reproduction in such an entity made up of two different kinds of organisms with different reproductive strategies.  As a result, it’s not surprising that lichens engage in a variety of ways of reproducing.  One approach is to paper over the reproductive differences altogether.  Kassinger observes, that “many lichens stake out new territory asexually.  When a fragment detaches and blows away, if it lands in a similar location, it attaches and starts growing as a new individual.”  (p. 37-38)  For other lichen species, asexual reproduction is more deliberate and complicated.  These species create little balls (called soredia), each consisting of a single algae surrounded by fungi filaments.  If these reproductive spheres are detached from the lichen and come to rest in a hospitable environment, a new lichen can grow.  The challenges of asexual reproduction pale when compared to the sexual reproductive strategy some lichen species pursue.  The fungi in most of these lichens produce spores which begin as sex cells (gametes) and then, after fusing with other sex cells, are released.  But these spores, cast to the winds, will create a new lichen only if they happen to land on an alga of a specific, requisite species.  Here the fungi appear to be playing against long odds, though producing countless spores in the process helps shift the odds a bit.

Lichens literally are everywhere.  They are extremophiles.  Brodo and his colleagues write, “They are found from the poles to the tropics, from the intertidal zones to the peaks of mountains, and on every kind of surface from soil, rock, and tree bark to the backs of living insects!”  (p. 3)  To call them an evolutionary success story is to undersell their accomplishment.  There are nearly 14,000 different species covering some six percent of Earth’s surface.  Lichens are the sine qua non for soil.  Without them, plants could not have invaded land.  Those lichens that employ rock as a substrate engage in a slow, very slow process of eroding the rock into soil.  Their anchoring filaments penetrate cracks in the rocks and, as the weather alternatively moistens the lichens, expanding their anchoring filaments, and then dries them out, the substrate is broken up.  Despite the seeming inefficiency of this method of creating soil, Kassinger counters that “rocks covered by lichens disintegrate ten times faster than they would otherwise.”  (p. 32)

Lichens are affected profoundly by air quality.  The diversity of species in a location is a gauge of how polluted its atmosphere is.  Urban areas host very few species, and my suburban neighborhood outside of Washington, D.C., seems to be home to only a handful of lichen species.  That said, I am only beginning to search for lichens and, as I’ve noted previously on this blog, the success of any quest in nature depends largely on having internalized appropriate “search images.”  Too often, the neophyte can be staring at the object of his or her quest and miss it entirely.  So, I suspect there are more lichen species here than I have noticed.  Just the other day, I spotted a lichen species new to me living on the ledge outside my second floor bathroom window.

The two species described below are ones that I found on twigs that had fallen from deciduous trees.

The first I’ve identified as the foliose lichen Parmotrema crinitum, the salted ruffle lichen.  The first picture shows the entire specimen.  The subsequent images are closeups of different areas of the specimen.  I continue to be amazed at the microworld that unfolds as the exterior of a lichen is magnified.

If I’m wrong in this identification, then my defense is that I was misled by the lichen’s gray-green color, lobed shape, brown underside near the lobe edges, and, most importantly, the cilia, those hair-like filaments that come out of the edges of the lichen’s lobes in abundance.

This next lichen is another foliose, tree-dwelling species, Physcia millegrana, the mealy rosette lichen.

 I have to admit that this identification relies mostly on gazing at the pictures in Brodo’s lichen bible.  The pale gray color and the thin lobes favor this ID.  I do not know what the green circular patches are.  Clearly, I am a neophyte at this but I am avoiding the beginner’s tendency to assume that any find is exceptional.  P. millegrana is, according to Brodo, “among the most common bark-dwelling lichens in eastern North America, even occurring close to urban areas on cultivated as well as wild deciduous trees.”  (p. 555)

Lichens, a complex world beckons.

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