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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 .

Sam and I appreciate species in very different ways!  

Photo credit: Susan Lerner

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).

Copepods and other marine plankton from a net haul. 

Photo Credit: National Marine Fisheries Service (NMFS)

Marine diatoms through the microscope. 

Photo credit: Prof. Gordon T. Taylor, Stony Brook University. NOAA Corps Collection. Licensed under Public Domain via Wikimedia Commons 

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 intensity. Laser 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.

In situ plankton imaging of eHoloCam. (a) Fragilespecies (Larvacea or Appendicularia) surrounding a self-built ‘house’ (circledin white); (b) semi-transparent species (not identified); (c) behaviour of aCtenophora-type plankton with its stretched tentacles capturing food; (d) anopaque Cirriped larva; (e) a copepod with bolded antennae in the middle and aphytoplankton chain at the bottom; (f) transparent jellyfish larva; (g) asingle marine diatom cell (Thalassiosira-type); (h) Exuvia of (d) type. 

Credit: Figure 7 from Sun et al. 2008

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.  

Photograph of some marine bacteria, eachapproximately 1 µm long.    

Photo credit: Julie Huber, NOAA.

Marine viruses isolated from phytoplanktoncollected during the Tara Oceans Expedition. Note that scale marker is 100nanometers (nm). 1 nm = one-thousandth of a µm.  Linedup end to end, it would take about 250 of these viruses to reach across a humanhair.    

Photo credit: Dr. Jennifer Brum, Tucson Marine Phage Laboratory, University of Arizona.  Also see Encyclopedia of Earth

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 everything. 

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.  

Why bother?  

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 nm).    

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.  

Virus nation    

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), approximately 6 million light years!

Seawater that has been stained with a fluorescentDNA dye SYBR Green I that reveals DNA containing bacteria (larger dots) and viruses(smaller dots). The bacteria are about 0.5 µm. 

Photo and information courtesy of Dr. Jed Fuhrman, University of Southern California, Los Angeles

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 combined?  

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 under sail on her 3 yearglobal expedition to study the ocean’s smallest residents: microplankton,protisans bacteria and viruses.  

Photo credit: F. Latreille courtesy of Tara Expeditions.

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 were found.   

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. 

Viral mysteries    

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 Hepatitis-C. 

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 

Arnold, C. 2014. Hints of life’s start found in a giant virus. Quanta Magazine. July 10, 2014

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.