Algae: the world’s most important “plants”—an introduction

Abstract

Early in the history of life, algae changed the planet’s atmosphere by producing oxygen, thus paving the way for the evolution
of eukaryotic organisms. In an era in which the consumption of fossil fuels is a prime topic of concern, few people realize
that the oil we currently exploit comes mostly from Cretaceous deposits of marine algae. Moving from ancient times to the
present, the algae remain more important than most people realize. Today, the production of oxygen by algae (ca. 50% of all
oxygen production) is another reason for saying “our lives depend on algae.” Those who love seafood should thank the algae
because algae are the primary producers upon which aquatic ecosystems depend. Thanks should come from all who are vegetarians
or omnivores, because all land plants derive from a freshwater class of green algae and all land-animals—including the cows
that provide the steaks for meat-lovers—depend directly or indirectly on land plants for food and often for shelter as well.
As we use up the oil deposits provided by the ancient algae, we are turning to the modern algae for help. Given the photosynthetic
abilities of the algae, they are one of the major focuses for sustainable biofuel production and CO2 consumption. Finally, the algae that give us the air we breathe, the food we eat, and the fuel for our cars (past and, perhaps,
future), are also a source of active pharmaceutical compounds that can be used against drug-resistant bacterial strains, viruses
(including Herpes Simplex and AIDS), and cancers. Roses are pretty and oak trees are impressive, but no other groups of “plants”
have done so much, for so long, and, for so many as have the algae!

Full text

ORIGINAL ARTICLE
Algae: the world’s most important “plants”—an intr oduction
Russell Leonard Chapman
Received: 24 May 2010 / Accepted: 11 August 2010 / Published online: 1 September 2010
#
The Author(s) 2010. This article is published with open access at Springerlink.com
Abstract Early in the history of life, algae changed the planet’s atmosphere by producing
oxygen, thus paving the way for the evolution of eukaryotic organisms. In an era in which
the consumption of fossil fuels is a prime topic of concern, few people realize that the oil
we currently exploit comes mostly from Cretaceous deposits of marine algae. Moving from
ancient times to the present, the algae remain more important than most people realize.
Today, the production of oxygen by algae (ca. 50% of all oxygen production) is another
reason for saying “our lives depend on algae.” Those who love seafood should thank the
algae because algae are the primary producers upon which aquatic ecosystems depend.
Thanks should come from all who are vegetarians or omnivores, because all land plants
derive from a freshwater class of green algae and all land-animals—including the cows that
provide the steaks for meat-lovers—depend directly or indirectly on land plants for food
and often for shelter as well. As we use up the oil deposits provided by the ancient algae,
we are turning to the modern algae for help. Given the photosynthetic abilities of the algae,
they are one of the major focuses for sustainable biofuel production and CO
2
consumption.
Finally, the algae that give us the air we breathe, the food we eat, and the fuel for our cars
(past and, perhaps, future), are also a source of active pharmaceutical compounds that can
be used against drug-resistant bacterial strains, viruses (including Herpes Simplex and
AIDS), and cancers. Roses are pretty and oak trees are impressive, but no other groups of
“plants” have done so much, for so long, and, for so many as have the algae!
Keywords Algae
.
Biofuels
.
Food
.
Oxygen
.
Pharmaceuticals
.
Land plant evolution
.
Sustainable fuels
Mitig Adapt Strateg Glob Change (2013) 18:5–12
DOI 10.1007/s11027-010-9255-9
R. L. Chapman (*)
Center for Marine Biodiversity & Conservation, Scripps Institution of Oceanography (MC 0202),
University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0202, USA
e-mail: rchapman@ucsd.edu
R. L. Chapman
Department of Oceanography and Coastal Sciences, Louisiana State University, 1002-Y Energy,
Coast & Environment Building, Baton Rouge, LA 70803, USA
e-mail: chapman@lsu.edu

1 Introduction
Algae and attitude Mo st peop le are not at al l awa re of the import ance of algae. Thi s
lack of appreciati on of the world ’s most i mportant plants is not surprising, at least
among English-speaking populations. Consider the common names used for the
algae: pond scum, seaweeds, and even frog spittle! Indeed many people only
experience algae in “bad situations” such as a big problem in l ocal lakes, fishing
holes, or even personal swimming pools, or as insect-covered seaweed litter on the
beach or as contaminants in tropical fish tanks, or even worse, as red tides
poisoning o ur seafood and/or us. Perhaps there is no wonder about why more people
have never, ever taken a phycology course to understand the plants upon which their
lives tot ally dep end. Thi s arti cle wil l, one hopes, serve as a mini-phycology course
that will pr ovide j ust eno ugh backg round in format ion to gi ve the reader who has
very little awareness about al gae a basi c appreciation of what they are and how
tremendous the variation in size, habitat, and “life style” among algae is. Thus,
when one encounters the mounting mass of articles about algae and biofuels or algae
and carbon capture, etc., there will a context for understanding which algae are
being proposed to do what functions.
Now no one likes to begin an overview article on an important topic with a
controversy and I will avoid controversy by explaining I have placed the word
“plants” in the title in quotes to avoid or at least minimize controversy. Some people
would argue (strongly) that “plants” are only the land plants we all commonly think
of as plants (the bryophytes—mosses, liverworts, and hornworts, pteridophytes—
ferns and fern allies, gymnosperms—conifers and their kin, and angiosperms—the
flowering plants). Others woul d say m olecu lar evidence shows cl early that the green
algae (i.e., the Chlorophyta) and the land plants are plants, but no other algae are.
Others, also citing molecular evidence, would say that the red algae (i.e., the
Rhodophyta) are also “plants.” But to extend the term “plants” any further, beyond
the land plants, green algae , and red algae, may be very troubling (horrifying) to
some. The vexation caused might reach its peak over calling the blue–green algae
plants—in fact there is even controversy about calling them blue–gree n algae rather
than cyanobacteria (despite the fact that the former term is more colorful). Well,
often controversies rage simply because people accept different definit ions of t erms
(and actually have no real basis for quarrel at all beyond the definitions). Thus, to
avoid even a hint of controversy, the working definition of “plants” for this article is
as follows: organisms that contain chlorophyll a and perform oxygen-producing
photosynthesis (and their colorless close relatives [e.g., Astasia is thought of as a
colorless Euglena that no longer has chloroplasts]). With this defini tion the blue–green
algae can remain truly cyanobacteria but we can ca ll them plants. And we do not have to
say that the magnificent, giant, plant-like kelps are not plants. Clearly, thos e who can not
abide this working defin ition of “plants” c an simply use whatever definition they prefer
in their own writings, and f orgive me for using “plants” as a convenient term for this
article.
Plan of attack This article will begin with a simple grammar lesson, comment on
attitudes, discussion of some the major examples of the importance of algae, and a
very brief introduction to some major groups of algae. It will then return to additional
ways in which the algae are far more important to humankind than most humans
realize.
6 Mitig Adapt Strateg Glob Change (2013) 18:5–12

2 Discussion
Grammar lesson You can have one alga, or, two or more algae, but you can never have
“algas” (unless you are writing in Spanish or Portuguese that is). Despite the fact that
recognizing “alga” is singular and “algae” is plural seems fairly simple, one has only to
listen to the radio or to university lectures or read the papers to realize that seeing or hearing
expressions like “Algae is an important source of biofuels.” are probably here to stay (at
least until all editors are forced to take Latin 101).
Algae and attitudes In the English language, the common terms for algae include “pond
scum,”“seaweeds,”“rockweed,”“bladder wrack, ”“sea wrack” and, even “frog spittle.”
Thus, the poor algae start off with a negative connotation as soon as we talk about them.
Similarly, since most people do not learn about algae at all at any level of their educational
history, awareness of the algae may derive from basically bad situations, such as news clips
about poisonous red tides and shellfish poisoning, about masses of green seaweeds
threatening Olympic sailing events in China, or from algal problems in their own swimming
pool. Indeed when one hears or reads that the local fish-kill in the town lake was caused by
a massive bloom of algae, one cannot escape thinking, “Algae are bad.” In response to this
erroneous notion, the subtheme of this article is, “Algae good, people bad” (at least as far as
the environment is concerned). Though this mantra may be considered overly zealous on
behalf of the algae, one can argue that the “pond scum” and “seaweeds” need a strong
defense and the best defense is often an offence.
Olden times Some 3.5 billion years ago prokaryotic life began on the planet in the absence
of oxygen. The cyanobacteria (blue–green algae) arose and began releasing oxygen into the
atmosphere as the waste product of chlorophyll a-mediated photosynthesis. However, the
levels of oxygen did not rise significantly for about a billion years. Why? Because exposed
iron and other metals in surface rocks oxidized and consumed oxygen, and because the
massive ocean absorbed oxygen. But about 2.45 billion years ago the level of oxygen in the
atmosphere began to rise because the exposed minerals were fully oxidized and absorption
by the oxygen-enriched upper layers of the ocean abated (Kump 2008). Oxygen levels rose
and the evolution of eukaryotic organisms began, giving rise along the way to humans (for
better or worse). For changing the atmosphere and the course of evolution, the blue–green
algae deserve our thanks.
Modern times Algae in the oceans, rivers, and lakes of the world are thought to produce
about half of all the oxygen produced on the planet. Those of us who appreciate breathing
should offer the algae our thanks. Given that the total biomass of the world’s algae is but a
tenth of the biomass of all the other plants, the efficiency of the algae is impressive (and of
interest in terms of producing biofuels—but more of that later).
Conquering the land Among the various eukaryotic organisms evolving in the oceans and
lakes of the planet were various forms of algae, including the green algae (Chlorophyta). In
the Paleozooic era perhaps about 480 million years ago (Wellman et al. 2003), a grand
conquest occurred and yet this victory is not routinely celebrated by any nation on the
planet! It was the conquest of the land by green algae and the evolution of the “real plants,”
that is, the land plants (including the bryophytes, ferns and fern allies, the gymnosperms,
and the flowering plants). Since all land plants come to us via the green algae, every
vegetarian and vegan should thank the algae. Of course, those of us who enjoy steaks and
Mitig Adapt Strateg Glob Change (2013) 18:5–12 7

beef Wellington also should thank the algae because cows eat grass. While we are
discussing food, it is important to note that those who like salmon, oysters, lobster, and
every other form of seafood must offer their thanks to the algae, since the algae are the
primary producers in aquatic ecosystems—the starting point in the food chain or food web
and thus the sine qua non for the fine seafood some of us love. Man lives not by bread
alone, so although we must acknowledge that the algae, in a sense, have given us all of our
seafood and all of our “land–food,” we have to thank them also for timber and fibers, for
habitats, for beautiful flowers and beautiful forests…basically for life as we know it.
The major groups of algae Having acknowledged and thanked the algae for changing the
earth’s atmosphere and facilitating the evolution of us and other eukaryotes, for providing
much of the world’s oxygen each year, for providing all seafood and all “land food” for us
and all other animals, and for all the habitats, products, and beautiful flowers we enjoy, it is
time to introduce some major groups of algae. We will start with the big ones and then
cover the little ones.
The big algae—the seaweeds Everyone who has spent time along the ocean coasts or
around lakes and ponds, has noticed some of the big algae, or macroscopic algae and these
easily visible algae are mostly three groups with simple, colorful names. They are the green
algae, the red algae, and the brown algae (or the Chlorophyta, Rhodophyta, and Phaeophyta
respectively). Books can be, and have been, written about each group, but just a few
essential facts will serve as a quick introduction to each group.
Green algae (Chlorophyta) There are an estimated 6,000 to 8,000 species of green algae
(and one should remember the number is truly just an estimate) and ninety percent of them
are freshwater rather than marine. As mentioned above, a freshwater green algal ancestor
conquered the land and gave rise to the land plant flora, in fact the green algae are in a
monophyletic (or natural) group with the land plants. The green algae and the land plants all
share a common ancestor, and, all descendants of that common ancestor are either green
algae or land plants. Although many of the green algae are large (macroscopic) seaweeds,
they can also be tiny unicellular or colonial organisms. Some marine green algae are truly
sea “weeds” and one beautiful green alga, Caulerpa, is known as the “scourge of the
Mediterranean” where it is a highly invasive weed introduced by accident in Monaco in
1984 just beneath the Oceanographic Museum (Meinesz et al. 2001). A less beautiful green
alga, Codium (“deadman’s fingers”), has been invading the east coast of the U.S., steadily
moving northward and plaguing already plagued shellfish industries along the way. Given
these examples of invasive species, the question arises: Are these algae bad? The answer is
a resounding, “No!” Humans deliberately or accidently released these “weeds” to habitats
where they should not be. The algae did not invade on their own, they were released into or
transported to new environments by people. People created the problems, thus we must
remember the mantra “Algae good; people bad.” If you want to be a bit more kind toward
people, you can use “Algae good; people iffy” as does one of my colleagues.
Red algae (Rhodophyta) There are ca. 4,000–5,000 species of red algae and, in striking
contrast to the green algae, 90% of red algae are marine. Although there are some
unicellular red algae, most are macroscopic algae often growing abundantly on rocky
shores. Some molecular studies have indicated that the red algae are in the same
monophyletic (natural) group as the land plants and the green algae, so one can argue that
the red algae are real plants (although our working definition makes all of the algae
8 Mitig Adapt Strateg Glob Change (2013) 18:5–12

“plants”). Some red algae are coralline and make calcium carbonate structures that are often
very important components of “coral reefs” and in fact may be the major component in
some reefs (the latter might be better called “biological reefs”). The red algae are the source
of agar and carrageenans (sulfated polysaccharides used in hundreds of products including
ice creams, beer, pâtés, shampoo, soy milk, and pet foods inter alia), and thus are harvested
for commercial purposes. The red alga Porphya is also harvested as Nori and is the dark
purple–reddish wrapper used in sushi around the world. The red algae are among the most
beautiful seaweeds and many of them have been found to contain useful pharmaceutical
compounds (with antibacterial, antiviral, or anti-cancer effects).
Brown algae (Phaeophyta) The brown algae can be thought of as the “macho algae” and
include all of the giant kelps as well as smaller but equally “tough” intertidal seaweeds.
There are only 1,500 to 2,000 or so species and they are almost entirely marine (even more
so than the red algae). This group includes such famous entities as Sargassum of Sargasso
Sea fame and the giant kelp Macrocystis which forms large forests and is harvested for
alginic acid, a commercially important polysaccharide with a host of industrial uses from
thickening food products to glossy paper production to beer brewing. Like the red algae, the
browns are a source of potential pharmaceutical compounds. Like the greens and the reds,
the brown algae are often major components of the rocky intertidal zone and thus are
exposed at low tide and must withstand both desiccation and, in many cases, the full force
of major wave action as the tides come in.
The small algae, the phytoplankton—the pasturage of the seas Although the seaweeds are
often b eautiful and often very noticeable (too noticeable when there are large blooms or
when storms wash too much up on the beaches), they largely occur in coastal regions at
or near the shoreline. In contrast the phytoplankton are microscopic and some are very
beautiful. Although phytoplankton are often not noticeable at all (compared to the
seaweeds), phytoplankton can be actually very noticeable when there is a massive
bloom (such as the red tides and other Harmful Algal Blooms [HABs]). In such cases,
the phytoplankton can change the color of the ocean for miles and poison the air. These
algae are tiny, but the important thing to note is that the oceans and th e major lakes of
the world provide a vast habitat for the phytoplankton and t hey can achieve almost
unimaginable densities. Indeed the vast number of phytoplankton cells are the initial
food for marine and freshwater food webs (hence the expression “pasturage of the
seas”). It is also the phytoplankton that generate most of the annual algal oxygen
production (about half of the planet’s total annual oxygen production). There are
several interesting groups of marine and freshwater phytoplankto n not covered in this
brief introduction and there are important green algae phytoplankton—especially in
freshwater ecosystems, but this r eview will stick to the marine Big 4 or Pasturage of
the Seas, that is, the diatoms, dinoflagellates, coccolithophorids, and the blue–green
algae.
Diat oms (Bacillariophyta)—algae in glass houses Microscopic, eukaryotic (nucleus-
containing) diatoms literally make their wall (or “frustules”) from silicon dioxide, that is,
glass, and these glass walls overlap like the cover and bottom of a traditional lab Petri dish.
Despite living in glass houses, the diatoms in some cases actually move around and at
certain times even manage to have sex. But perhaps the single most important thing to note
is that diatoms are often very abundant and, thus, important members of their respective
ecosystems. The glass houses (or more scientifically, the frustules) survive for thousands of
Mitig Adapt Strateg Glob Change (2013) 18:5–12 9

years and in fact diatomaceous earth (diatomite) used in pool filter systems and in car
polishes is found in massive deposits sometimes hundreds of feet thick. There are 12,000
known species of diatoms and some estimate that there may be as many as 60,000 to
600,000 species (Hasle and Syvertsen 1997).
Dinoflagellates (Pyrrhophyta) The eukaryotic dinoflagellates are very abundant normally
and can achieve densities of 10
7
–10
8
cells per liter (Graham and Wilcox 2000) during
blooms which are often HABs associated with paralytic shellfish poisoning, amnesic
shellfish poisoning, diarrhetic shellfish poisoning, neurotoxic shelfish poisoning, and
ciguatera fish poisoning. Given the litany of obnoxious poisoning that can be caused by
dinoflagellates, one must return to the question: Are these algae bad? The answer is, of
course, a resounding “No!” People bad; algae good. First, the dinoflagellates are mostly
harmless sources of oxygen and food for other organisms. Second, whenever massive
blooms of dinoflagellates occur there is most often a human cause, most typically excessive
nutrients from anthropogenic pollution. Even if one notes that there are more HABs now
than ever before and/or they are occurring in places where they have never occurred before
and/or the blooms are worse in intensity than ever before, one must also note that human
pollution is the cause of the blooms and the fact that they are occurring in new sites is
undoubtedly due to human transport of dinoflagellates to new habitats (as, for example, via
ship ballast water). So the problem, gentle reader, is not in our algae, but in ourselves. On a
more positive note, dinoflagellates can exhibit bioluminescence and produce dreamlike
scenes of people, boats, or dolphins moving through the water at night creating glowing
trails. The dinoflagellates have a more serious role as the symbionts (or, zooxanthellae) of
corals. Unfortunately increasing levels of pollution and increasing water temperatures cause
“coral bleaching” wherein the algae abandon their coral hosts because of the unfavorable
conditions and the corals die. A large percentage of the world’s coral reefs are dead, dying,
or threatened.
Coccolithophorids These eukaryotic phytoplankton species a re fascinating in several
ways. First there is their name: Coccolithophorids or “coccolith-bearers”.Whatarethe
“coccoliths”? They are, often beautiful, calcium carbonate platelets borne on the surface
of the flagellated unicellular algae. The exact function of the coccoliths is not
understood, but there is experimental evidence that ocean acidificatio n can clearly
interfere with normal coccolith production and thus might have adverse effects on these
important phytoplankton species. Another dramatic feature of the coccolithophorids is
that they can be very abundant—so abundant in fact that they can turn the surface of
the northern Atlantic whitish for miles and miles, and clearly can be seen in satellite
photographs. T he abundance of the coccolithophorids can be made dramatically clear
when one considers that the flagellated unicells are microscopic—too small to be seen
without a good microscope. And the calcium carbonate coccoliths that they bear on
their surface are smaller still—each cell often bearing eight or more coccoliths as small
as 1–3 μm in diameter. If one keeps in mind how tiny the coccoliths are and then
considers the white cliffs of Dover and realizes that the chalk of the white cliffs of
Dover is largely composed of coccoliths, one realizes that there had to have been
billions and billions of coccolithophorids living and dying i n the ocean over millions of
years to generate such massive accumulation s.
Blue–green algae (Cyanobacteria) It seems appropriate to return to, and conclude with, the
prokaryotic blue–green algae, those hardworking photosynthesizers that changed the
10 Mitig Adapt Strateg Glob Change (2013) 18:5–12

atmosphere of the planet. Like other prokaryotes the blue–green algae are abundant and
present in almost every conceivable habitat from oceans and lakes (as expected), to ice,
snow, thermal hot springs, and deserts (perhaps not as expected). Since more than 99% of
all species ever evolved on Earth have gone extinct, it is probable that humans will (the
optimist would say “might”) be a relatively short-term component of life on Earth, but the
blue–green algae that were major players 3.5 billion years ago at the start of life as we
know it, likely will survive well after the large-brained, walking, talking animals have gone
extinct. But while we and the blue–greens co-inhabit the planet, we owe them our thanks
not only for the oxygen they produce and the vital role they play as primary producers in
the food webs, but also for nitrogen fixation. Our atmosphere is filled with nitrogen and this
inert gas prevents the oxygen in our atmosphere from igniting when we strike a match
(when the first nuclear bomb test was planned there could have been at least a bit of
concern that the buffering effects of nitrogen would not suffice and the whole planet might
have gone up in flame but luckily that was not the case!). Living organisms must have
nitrogen (hence millions of dollars spent on nitrogen-rich fertilizers around the world), but
not in the form of the inert gas (two nitrogen atoms tightly bound by three covalent bonds).
Thus, nitrogen fixation (or, the process of breaking those covalent bonds and adding other
atoms like hydrogen and oxygen to the nitrogen) is, like photosynthesis and respiration, one
of the most important physiological processes. The blue–green algae are nitrogen fixers
which explains, in some cases, why blue–green algae can grow in such hostile
environments and why we should thank the blue–green algae once again for what they
do. Like the other phytoplankton algae described, the blue–greens are very abundant and
can achieve bloom-level densities that color the water, often reddish (due to the red
phycoerythrin pigment that can mask the blue–green phycocyanin pigment). Some suggest
that Homer’s “wine-dark sea” (or, “wine-faced sea”) was “wine-dark” because of blooms of
blue–green algae (specifically, Trichodesmium erythraeum). Of course, the question of how
the blind poet Homer knew the sea was wine dark is an interesting question. (And, there are
non-algal explanations for “wine-dark” as well, but they have no place in this introduction
to the algae.)
But wait, there’s more The algae changed the atmosphere of the planet, gave rise to the land
plants, provide half of the planet’s annual oxygen supply, are directly responsible for all
seafood, and indirectly responsible for all “land food,” and they help supply fixed nitrogen
to support life on the planet. At this point our gratitude should know no bounds, but there is
indeed still more. The major gas and oil deposits that we are so rapidly depleting came
largely from Cretaceous algae deposits. Another thank you is in order. Various kinds of
algae (but especially the blue–greens, reds, greens, and browns) are sources of new
pharmaceutical compounds helpful in our battles against antibiotic-resistant bacterial strains
plaguing our hospitals, against viral infections (including Herpes and AIDS), and against
some forms of cancer. Another thank you... Lastly, we come to the latest potential major
“gift” of the algae to humankind and one that will receive more attention in this journal
issue, namely: the algae are a potential source of renewable biofuels—a source that from
many perspectives is far more tractable than land plants (like corn or even sugar cane). In
short, the algae are efficient harvesters of sunlight and do not waste much energy on
intricate structure or pretty flowers. They can grow in brackish or salt water and do not need
precious crop lands for growth. The algae can strip nutrients from polluted waters and they
do use lots of CO
2
to grow and prosper. So, as we face the end of cheap fossil fuels and the
perils of global warming, the algae might, once again, change things for the better and help
give humankind some extra time before we go the way of 99.9% of all the species that have
Mitig Adapt Strateg Glob Change (2013) 18:5–12 11

ever been. It would certainly be a grand advance if we found ourselves having to thank the
algae yet again.
3 Conclusion
The algae have benefitted humankind since the earliest days of life on the planet —when the
blue–green algae changed the planet’ s atmosphere and triggered the evolution of eukaryotic
organisms including humans. They helped us again during the Cretaceous when our major
current oil and gas deposits were generated by marine algae. They now provide about half
of the planet’s oxygen, a boon to those of us who breathe, and they directly or indirectly
give us all of our food. The fact that the algae are also a potential source of renewable
biofuels makes the world’s most important “plants” even more important. Additional
general information about the algae can be found in texts such as
Algae (Graham and
Wilcox 2000),
Phycology (Lee 2008), and Algae—An Introduction to Phycology (van den
Hoek et al. 2010). There are also many useful websites including but certainly not limited
to the Phycological Society of America http://www.psaalgae.org/ and Michael Guiry’s
Seaweed Site http://www.seaweed.ie/guiry/.
Open Access This article is distributed under the terms of the Creative Commons Attribution
Noncommercial License which permits any noncommercial use, distribution, and reproduction in any
medium, provided the original author(s) and source are credited.
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