08 Jun 2015
It's the Little Things That Count
In the Ocean (and everywhere else) It's the Little Things That Count
With the approach of World Ocean Day, I’ve been thinking a lot about the
rich variety of species big and small that fill the ocean with life. A recent article by Claude Gascon
at the Global Environment Facility (GEF) and colleagues from 12 major
conservation organizations explored how important species are as the functional
units of all ecosystems and as sources of extraordinary ecosystem benefits to
people. Their celebration of biodiversity
should inspire awareness and care in all human activities on land or sea.
Species have even been on my mind during walks with my dog, Sam, as the air on these late-May evenings has exploded with tiny mysteries of life. I work remotely from my office in Bar Harbor, Maine, so these are rural walks.
To me the perfumed air says ‘Lilacs, Lily of the Valley, Chokecherry.’ Tracking along with his nose just above the ground, Sam may not notice those fragrances, but he is exquisitely sensitive to scents of Deer, Fox, Otter, Coyote, Meadow Vole, and of course the scents of local dogs .
Sound takes over as we near the pond. The quacking of wood frogs underlies piercing trills of
spring peepers. The volume is deafening. The foghorn croak of a bullfrog
penetrates the din, along with a puzzling creaky growl, later identified from
my phone recording by local naturalists as the call of a Pickerel Frog. See and
hear some of them here.
But sound isn’t the only thing filling the night air. Countless particles dance in my head lamp’s beam, drifting past with each puff of breeze. Some feel moist, but it isn’t foggy: the sky is clear and starry. No, the air is filled with life of some kind. What are these tiny dots? Some seem large enough to be gnats or miniscule flies or moths, but the rest? Still tinier insects? Spores? Pollen? Excrement of leaf eating bugs? Moisture droplets exuded by trees? Identifying all these particles could be done, but it would be a challenge and I didn’t have time for it now.
Marine biologists confront an even more daunting challenge
Early in my career I remember swimming at night in the waters off Woods
Hole, Massachusetts, where my dive light’s beam showed the water to be
similarly aswarm with tiny unknown particles. Many remained when I turned the light off, winking and
sparkling with their own luminescence like a galaxy of stars whenever I
moved. This time I determined to
find out what some of them were, and with my graduate school colleague, Mahlon
Kelly, I spent the summer
isolating individual cells, testing to see whether they were bioluminescent,
and drawing and identifying them.
It was clear to me even then that although although coral reefs, fish, whales, dolphins, sharks, turtles, polar bears, penguins and other large animals usually steal the show, ocean water teems with innumerable specks of living and non-living matter that are often beautiful, always interesting and much more important than you might guess from their tiny size.
‘Plankton’ refers to any organism that drifts or floats in water with only very limited power of horizontal movement (though many species carry our significant daily or seasonal vertical movements. Larger size classes of marine plankton include tens of thousands of species of animals representing 16 phyla of single-celled or multicellular animals and an estimated 3,444-4,375 species of single-celled planktonic algae. These range in size from as large as 1 meter in diameter for some jellyfish down to 2 millionths of a meter (2 micrometers = 2 microns = 2 µm).
Fine-meshed nets can capture most of the larger animal and plant
plankton, though delicate species such as jellyfish and other jellylike species
may be broken or crushed in the process. Moreover, everything that the net
catches gets mixed up together, so the natural spatial relationships among the
species are obscured.
Sound and light
Sound and light provide minimally invasive ways to show spatial
relationships among plankton and microbial species. Sound beams (sonar) used in
electronic fish finders can also locate schools of plankton, such as krill or
copepods, or even smaller organisms if higher frequencies are used. Woods Hole Oceanographic Institution’s
towed instrument BIOMAPPER II
can sample, count and identify plankton, including phytoplankton, over large
areas using 10 sonar beams, a videoplankton recorder and instruments that
measure water temperature, salinity, oxygen, chlorophyll, and light
holography can identify larger plankton organisms and visualize their
three-dimensional locations without disturbing them, but it is expensive,
technically difficult and cannot show the ocean’s very smallest life forms.
Tiniest of the tiny
The number of species of microbes (bacteria and viruses) is only beginning
to be known. The Census of Marine Life’s International Census of Marine
Microbes found that a liter of
ocean water contains 38,000 kinds of bacteria, but no oceanwide species
count exists yet.
An inventory of viruses currently in progress suggests that perhaps up
to 10,000 different kinds might exist in the ocean, though forms living in deep
water and in the sediments have not been adequately sampled yet.
Small game hunting
It’s hard to catch such tiny particles: most bacteria and nearly all
viruses slip right through even the finest nets and can only be caught by
drawing water through filters with pores sizes only a few nanometers wide. Once
that is done, some can be observed using electron microscopy. But even that technique can’t capture
Another method, flow cytometry, draws water into an apparatus where it passes through an electric field and is illuminated with lasers. Depending on their size, shape and composition, the different particles fluoresce and disturb the electric field in different ways, allowing the machine to make cumulative counts of the different types of particles present, some of which can be identified separately by visual analysis. Sutter (2007) describes those and other sampling techniques.
First of all, there are lots of tiny organisms (microbes) in the
ocean—more than anyone ever imagined—and they appear to have huge ecological
importance. The biggest of the smallest
are protistans (ciliates, amoebas and other single-celled organisms that range
from 1 µm (about 0.00004 inch) to 200 mm (about 0.008
inch). Bacteria, typically about 1 µm, include
species that require carbon to live as well as photosynthetic forms (cyanobacteria)
that manufacture their own carbon from carbon dioxide and sunlight. Smallest of
all are viruses, which are usually about 0.2 µm (=200
Taken together, these microbes contain over 90% of the biological carbon in the entire ocean. What’s more, cyanobacteria fix more carbon by photosynthesis (26-70 billion tons per year) than ocean phytoplankton do (49.3 billion tons per year) (Wilhelm and Suttle 1999). Together, in addition to forming the base of the food web, they provide about half of all the oxygen in the atmosphere.
There are about 10 times more viruses than bacteria with about one
billion to 10 billion virus particles per liter of seawater, so they win the
prize as the ocean’s most abundant organisms, making up 94 percent of all nucleic-acid-containing
particles. Though numerous, they are
so small that they only make up about 5 percent of the ocean’s biomass---yet
even that is equal to the weight of 75 million blue whales (Zimmer 2011)! Equally astounding, there are enough of
them in the ocean (about 1030) so that if lined up end to end these
tiny particles would form a line extending beyond the 60 galaxies closest to
Earth! (Zimmer 2011),
million light years!
Bacteria, though ten times less numerous, weigh 20 times more than that,
equivalent perhaps to 1.5 billion blue whales and comprising more than 90
percent of ocean biomass. Did you
ever imagine that the ocean’s bacteria would outweigh all other marine life
The ocean’s abundant and busy viruses can only reproduce by infecting and often killing plankton plants, animals, protists and bacteria as well as higher organisms. They attach to a cell membrane, inject their own DNA (or RNA) into the host cell where it is incorporated into the host’s DNA. It may immediately co-opt the host’s metabolism to begin produce new virus particles; or it may remain latent in the DNA for long periods (lysogenesis) before becoming active. Besides making new virus particles, infection can alter the host’s metabolism, including temporarily increasing the rate of photosynthesis and carbon fixation. When a virus kills (lyses) its host cell, dozens of new virus particles are released as well as the cell’s contents, contributing carbon, nitrogen, phosphorus and trace elements such as iron that fuel growth of local microbe populations (Wilhelm and Suttle 1999). Viral acceleration of bacterial or phytoplankton population turnover and nutrient cycling is known as ‘viral priming.’
So the ubiquitous viruses may be the ocean’s busiest carbon recyclers, possibly turning over as much as 150 gigatons of carbon per year—more than 30 times the amount of carbon contained in marine plankton at any one time (Suttle 2007). But how do scientists find, count and identify these nearly invisible particles?
DNA to the rescue
None of the usual methods work for identifying the ocean’s tiniest and
most poorly known components. Unlike blooming shrubs or frogs in our pond, they
are way too small to make detectible, identifiable scents or sounds. They
usually can’t be directly identified by size, shape, behavior, phenology,
geographic distribution or other typical methods, because they are too small to
see or photograph in situ and there are no museum specimens for comparison. Fortunately, genetic technology has
come to the rescue.
Using DNA to identify individuals is common. We see it all the time in TV crime shows: The scene opens. The camera pans to a victim, dead on the floor. Police photograph the victim, gather clues about the perpetrator, method and motive--- blood, hair and fingerprints just like Sherlock Holmes did a century ago, but also samples for DNA analysis.
In recent years DNA sampling has also become part of the tool kit for identifying species, primarily by revealing the magnitude of genetic difference between groups that appear to be related. Genetic differences are also used to detail the ‘evolutionary tree of life’ by verifying, quantifying and sometimes contradicting, the presumed relationships assigned to species on the basis of traditional tools (embryology, morphology, ecology and others). Few would doubt that we humans share 98 percent of our genes with chimpanzees, but would you have guessed that that more that 7,077 of a sea urchin’s 23,300 genes are also found in humans, and about 70 percent of its genes have a human counterpart (Brynner 2006; Sea Urchin Genome Sequencing Consortium 2006).
The Tara Oceans Expedition
Recently DNA and other genetic technology went to work in the ocean in
a new way, helping scientists search for organisms so small that they leave
almost no other trace of their existence. From 2009 through 2013 the 36 m (110 foot) schooner Tara and her crew carried out a 62,000 nautical mile expedition that obtained
nearly 28,000 samples of the ocean’s smallest inhabitants (2 mm or less), including
microplankton, protistans, bacteria and viruses. The expedition involved nearly
200 scientists, journalists and artists, and the results were published in a special
issue of Science on May 22, 2015.
Tara scientists identified 5,467
different types of viruses, only 39 of which had previously been known from
laboratory cultures, so almost all of the forms were new to science. The
viruses were identified only by differences in specific portions of their DNA,
so they aren’t yet known by size, shape or other physical characteristics. Most don’t have typical species names
either, but are known only by descriptions of the sequence of nucleotide base
pairs in certain portions of their DNA and the depth and location where they
The research team concluded that the ocean contains many localized communities of viruses that exist and evolve within local ecological conditions and communities of potential hosts, but that ocean currents passively disperse them to other areas around the ocean where further evolution may occur.
What is a virus anyway? Are these short strings of DNA alive? What was the role of viruses in the evolution of life? Are viruses species? These questions have fascinated scientists and philosophers for nearly a century. The more that is learned about them, the more qualified the answers become. If you are interested in these tiny, ancient, ubiquitous, versatile entities that exist at the border between biochemistry and life, you will enjoy reading Shannon and Greene (2013), Villarreal (2008) and Arnold (2014). For more information on microbes, viruses and their ecological importance, the reference list contains links to useful articles.
The bottom line
Usually we hear about bacteria and viruses in the doctor’s office
or in news reports about outbreaks of serious diseases such as E. coli, Salmonella, or Lyme Disease; or Ebola, HIV-AIDS or
Similar kinds of diseases, some very serious, affect plants and animals in natural communities on land and in the ocean, and occasionally receive publicity, such as papilloma tumors in green sea turtles, yellow-band and black-band disease in corals, or the viral epidemic that killed more than 1,000 bottlenose dolphins along the U.S. East coast in winter 2013
Beyond the harm that such forms cause, what receives less publicity, though, is how protists, bacteria and viruses also make ecosystems function and thrive. That is not their purpose. They just do what they do for their own sake and some of it is messy business. However, through opportunism and probably some co-evolution, both they and the rest of the system co-adapt in ways that may have ultimate benefits despite the underlying death, decay and chaos. It is a little like the creative destruction of capitalism, maybe not the best way to do things, and with unequal distribution of costs and benefits, but a system that has so far managed to keep itself going.
In the end, the coral reefs, fish, whales, dolphins, sharks, turtles, polar bears and penguins, as well as the frogs, flowers, deer, foxes, otters, coyotes, voles, and dogs all depend on life’s miniscule participants, as do we.
References and Further Reading
C. 2014. Hints of life’s start found in a giant virus. Quanta Magazine. July
Armbrust, E.V. and S. R. Palumbi. Uncovering hidden worlds of ocean biodiversity. 2015. Science 348, 865 (2015); DOI: 10.1126/science.aaa7378
Bork, P., C. Bowler, C. de Vargas et al. 2015. Tara Oceans studies plankton at planetary scale. Science 348(6237): 873. DOI: 10.1126/science.aac5605. 22 May 2015.
Brum, J.R., J.C. Ignacio-Espinoza, S. Roux et al. 2015. Patterns and ecological drivers of ocean viral communities. Science 348(6237): 22 May 2015. DOI: 10.1126/science.1261498
Brynner, J. 2006. Surprise! Your cousin’s a sea urchin. LiveScience November 9, 2006.
Gascon, C., T.M. Brooks, T. Contreras-MacBeath et al. 2015. The importance and benefits of species. Current Biology 25, R431-438. May 18, 2015.
Greene, S.E. and A. Reid. 2013. Viruses Throughout Life & Time: Friends, Foes, Change Agents A Report on an American Academy of Microbiology Colloquium. San Francisco. 25 pp. July 2013
Mora, C., D.P. Tittensor, S. Adl, A.G.B. Simpson and B. Worm. 2011. How many species are there on earth and in the ocean? PLoS Biol 9, e1001127.
Sea Urchin Genome Sequencing Consortium. 2006. The genome of the Sea Urchin Strongylocentrotus purpuratus. Science 314 10 November 2006, pp. 941-952.
Sournia, A., M.-J. Chrdtiennot-Dinet and M. Ricard. 1990. Marine phytoplankton: how many species in the world ocean? J. Plankton Res. (1991) 13 (5): 1093-1099. doi: 10.1093/plankt/13.5.1093
Sun, H., P.W. Benzie, N. Burns et al. 2008. Underwater digital holography for studies of marine plankton Philosophical Transactions A, The Royal Society. DOI: 10.1098/rsta.2007.2187 Published 28 May 2008
Suttle, C.A. 2007. Marine viruses — major players in the global ecosystem. Nature reviews. Microbiology 5:801-811. October, 2007.
Villarreal, L.P. 2008. Are Viruses Alive? Scientific American December 2004. Published online August 8, 2008
Weitz, J.S. and S.W. Wilhelm . 2013. An ocean of viruses. The Scientist. Published online July 1, 2013.
Wilhelm, S.W. and C.A. Suttle. 1999. Viruses and nutrient cycles in the sea. BioScience 49(10):781-788.
Zimmer, C. 2011. A Planet of Viruses. University of Chicago Press.
Zimmer, C. 2015. Scientists map 5,000 new ocean viruses. Quanta Magazine, published online May 21, 2015.
This organisms discussed in this article are of general
importance to ocean health and relate to a number of goals assessed in the
Ocean Health Index, including Biodiversity (Species) and Clean Waters
(Pathogens). However, they are not directly evaluated in the calculation of the
Index’s score. Thanks to Lindsay
Mosher and Lily Huffman for helpful editorial suggestions and to all of the
scientists and organizational who granted permission for use of their photographs.