Archive for August 2010
Edit: Republished at the American Society for Microbiology blog, Small Things Considered
“When I think of the floor of the deep sea…I see always the steady, unremitting, downward drift of materials from above, flake upon flake, layer upon layer…the most stupendous “snowfall” the earth has ever seen.”
-Rachel Carson, The Sea Around Us (1951)
Marine snow: does the phrase make you think of fish wearing ice skates, seahorses in knit caps, and crabs building snow-fish? If so, I can’t entirely blame you: the stuff looks like snow, hence its name. But marine snow is not composed of frozen water, each flake unique and beautiful. It is, in fact, made up entirely of dead organisms, poop, and random junk floating in the ocean. (Still fancy a marine snowball fight?)
To undergo photosynthesis, marine phytoplankton (the “wandering plants” in Greek) can only live in the sunlit areas (the photic zone) of the ocean, which rarely reaches a depth greater than 200 meters. The phytoplankton do their thing, you know, generate nearly half of the planet’s primary production (no big deal?!), until they are either eaten or die. And when you’re living at the top of a miles-deep ocean, the only way to go is down. And thus we have marine snow.
Marine snow is complicated stuff. While initially it is mostly composed of dead material, slowly drifting downward, overtime it is affected by many processes that create an indescribable mass of fluff and particles and organisms stuck together. But along the way, it continues to sink, until eventually it reaches the seafloor, often miles down. And it needs to reach that destination, as it is a primary source of carbon for deep sea organisms who have no light by which to photosynthesize.
A floater or a sinker?
But how does a clump of algae or cells manage to sink for miles? By straight physics alone, a particle in still seawater would take years to reach the seafloor. Add to that waves, currents, water stratification, and you have some particles that aren’t going anywhere. Many studies have provided evidence that most movement takes place when the phytoplankton have been ingested and egested as fecal pellets (i.e. poop).
An environmentally sobering study done in 1987 and published in Nature presents strong evidence for the increased sinking rates of fecal pellets. After the Chernobyl Disaster in 1986, when a nuclear power plant blew out and released radioactive fallout, scientists studying vertical transport in the ocean decided to make the best of the tragedy. Several days after the disaster on April 26, 1986, rain fell on the ocean, delivering the radioactivity to the surface of the water. The scientists had already set up particle traps at 200 meters depth and, upon review, found that radioactivity was found in the traps just 7 days after the rainfall, with an average sinking rate of 29 m/day. Physics predicted that radioactive particles would take years to reach this depth! To explain this discrepancy, the authors identified the particles as fecal pellets and – lo and behold! – the high sinking rate was explained by the repackaging of these radioactive particles through ingestion and then egestion by zooplankton. The fecal pellets were larger in size and more dense, and thus able to sink more rapidly through the water column.
But not all fecal pellets are created equal; many factors contribute to their size and density, which in turn determines how fast they will sink and quickly they will deliver carbon and nutrients to deeper waters. Different “types” of feeders, for example, have different efficiencies of repackaging as particles. Carnivores tend to eat larger food and make it smaller, while grazers such as filter feeding mollusks or some zooplankton species collect tiny, slow-sinking particles and collect them into a larger fecal pellet, greatly increasing the sinking rate of those particular particles.
In the below figure, from a 2001 Bioscience paper entitled “Feces in Aquatic Ecosystems,” data on sinking rates of various taxa are shown. However, these data need to be taken with a grain of salt. These are sinking rates from individual studies taken in different years in different parts of the ocean. Fecal pellet sinking rate is determined not only by repackaging efficiency by species, but also by the organisms’ diets, water turbulence at the surface, water stratification, season, and even time of day. But what it does show is how variable sinking rates are, even for something as simple as a little speck of poop.
But the wild trip isn’t over for organic carbon bound up in fecal pellets. As they sink, they get stuck in larger pieces of marine snow. They start to degrade from friction alone, but also from grazing organisms or microbes that are living on them*, creating more drag and slowing their sinking rate. And then, inevitably, a fish or a zooplankter comes along and eats them, transporting the carbon back up to the surface or down deeper until they are re-released as a fresh pellet, and the cycle begins again.
It seems like such a long and hard way to travel: passively drifting for miles, eaten and pooped out over and over again. How does marine snow ever make it to the seafloor? We had photographs of marine snow at the seafloor, but its existence did not seem to make sense. Paper after paper reported that marine snow in the water column decreases with depth due to much grazing in the euphotic and mesopegalic (where light reaches, but not enough for photosynthesis) zones. Most papers rely on sediment traps: essentially a huge funnel to collect small particles. A 1993 Nature paper evaluated this method itself, and suggested that it severely underestimates the volume of marine snow in the water column. But there had been no detailed studies yet quantifying marine snow volume in multiple locations and depths.
That is… until this May (PNAS, 2010), when the marine snow veterans Alexander Bochdansky, Hendrik van Aken, and Gerhard Herndl decided to try a new method: quantification through photographic analysis and optical backscatter.
On a research vessel, the team traversed a 4000 km horizontal transect across the Atlantic, including area over the Romanche Fracture Zone, which at 6000 meters is the deepest section of the mid-Atlantic Ridge. The researchers threw lights at sections of water at particular angles, and the light reflected back by particles was visible in photographs (>500 um). They additionally used a Seapoint Turbidity Meter, which quantifies light reflected off of very small particles in the water through voltage. By running these tests at 17 points along their transects, and at these points, from the surface to the ocean floor, the researchers were able to visualize a bigger picture for particulate and marine snow suspension in the ocean.
The figure above shows this picture. In the upper 2000 meters of the ocean, marine snow abundance is high, gradually decreasing with depth, with microscopic particles more abundant than macroscopic ones. But below 2000 meters, there is an increase in marine snow overall, and there are greater numbers of macroscopic particles than microscopic. The researchers also looked at oxygen rates in each frame they selected, and found a significant negative cross-correlation between oxygen values and particle volume, or more particles meant less oxygen. This suggests that there is greater oxygen consumption at particles, indicating microbial respiration.
The authors suggest that, at greater depths, the marine snow particles and fecal pellets form larger aggregates, which slows their sinking rate due to increased drag and decreased density. These are larger particles that are sinking very slowly or are neutrally buoyant, and are thus not caught in sediment traps. The particles that are able to escape the highly grazed areas of the mesopelagic clump together in the deep, but are less rapidly consumed because there are simply fewer organisms around to consume them. Slowly but surely they sink down, providing carbon to the depths and forming “hotspots of biological activity.”
In light of recent research: ecosystem effects of decreased phytoplankton
Marine phytoplankton have been hot in the news lately: Daniel Boyce and Boris Worm published a study in Nature (covered well by others) reporting that over the last century, marine phytoplankton biomass has decreased by 1% per year. You read right: the organisms that produce nearly half of our oxygen and absorb a significant amount of carbon dioxide are disappearing at an alarming rate.
Much of the coverage has focused on the climate change aspect of this study. Phytoplankton are a huge carbon sink, and it was assumed that increased temperatures through climate change would actually increase their growth. But – alas! – the decrease in phytoplankton biomass actually correlated with increased sea surface temperatures. So the exact opposite of what we predicted would happen is occurring, according to this study.
But I’m an ecologist: what does this decrease in phytoplankton mean for the marine ecosystem? As I’ve explained throughout this post, phytoplankton are the primary energy source for the ocean. They themselves convert sunlight to energy, are eaten by other organisms, and then this poop slowly sinks to the deep-sea to provide food for organisms living on the seafloor. In his 2002 review, Jefferson Turner argues that seasonal mass sinks of phytoplankton and algae biomass are vital for survival for deep-sea organisms.
While we probably haven’t lost enough phytoplankton to cause great loss in the deep, it’s something we should be thinking about. A tenet of ecology is that a change in the abundance of one organism can have cascading effects through an ecosystem, in turn affecting the abundances of many others. The thought of losing a primary carbon sink is unsettling; but the thought of removing a crucial food source for most of the ocean is far more horrifying. It seems unlikely enough that a fecal pellet would reach the deep on its own even with the relative abundance of phytoplankton that exists now. Losing a significant amount of phytoplankton could have grave impacts through the entire ocean ecosystem. I don’t think we want to know the end of that story.
* Fecal pellets as microhabitats or even islands is a fascinating subject. A 1978 Science paper found that there is greater taxonomic diversity on pellets than in the open water, and that the species living in and on pellets is significantly different that those in the water. Also, organisms that survive gut passage (microbes and invertebrates) are often released, live, in fecal pellets. For more on this, see this recent paper on applying island biogeography to fecal pellets.
Fecal pellet sinking rates figure:
(1) Turner JT. 1977. Sinking rates of fecal pellets from the marine copepod Potella meadii. Marine Biology 40: 249–259.
(2) Alldredge AL, Gotschalk CC, MacIntyre S. 1987. Evidence for sustained residence of macrocrustacean fecal pellets in surface waters off Southern California. Deep-Sea Research Part A: Oceanographic Research Papers 34: 1641–1652.
(3) Smayda TJ. 1969. Some measurements of the sinking rate of fecal pellets. Limnology and Oceanography 14: 621–625.
(4) Deibel D. 1990. Still-water sinking velocity of fecal material from the pelagic tunicate Dolioletta gegenbauri. Marine Ecology Progress Series 62: 55–60.
(5) Ladle M, Welton JS, Bell MC.1987. Sinking rates and physical properties of faecal pellets of freshwater invertebrates of the genera Simulium and Gammarus. Archiv für Hydrobiologie 108: 411–424.
(6) Fowler SW, Small LF. 1972.Sinking rates of euphausiid fecal pellets. Limnology and Oceanography 17: 293–296.
(7) Ladle M, Welton JS, Bell MC.1987. Sinking rates and physical properties of faecal pellets of freshwater invertebrates of the genera Simulium and Gammarus. Archiv für Hydrobiologie 108: 411–424.
(8) Yoon WD, Marty JC, Sylvain D, Nival P. 1996.Degradation of faecal pellets in Pegea confoederata (Salpidae,Thaliacea) and its implications in the vertical flux of organic matter. Journal of Experimental Marine Biology and Ecology 203: 147–177.
(9) Taghon GL, Nowell ARM, Jumars PA. 1984. Transport and breakdown of fe- cal pellets: Biological and sedimentological consequences. Limnology and Oceanography 29: 64–72.
Bochdansky, A., van Aken, H., & Herndl, G. (2010). Role of macroscopic particles in deep-sea oxygen consumption Proceedings of the National Academy of Sciences, 107 (18), 8287-8291 DOI: 10.1073/pnas.0913744107
Boyce, D., Lewis, M., & Worm, B. (2010). Global phytoplankton decline over the past century Nature, 466 (7306), 591-596 DOI: 10.1038/nature09268
Fowler, S., Buat-Menard, P., Yokoyama, Y., Ballestra, S., Holm, E., & Nguyen, H. (1987). Rapid removal of Chernobyl fallout from Mediterranean surface waters by biological activity Nature, 329 (6134), 56-58 DOI: 10.1038/329056a0
Goldthwait, S., Carlson, C., Henderson, G., & Alldredge, A. (2005). Effects of physical fragmentation on remineralization of marine snow Marine Ecology Progress Series, 305, 59-65 DOI: 10.3354/meps305059
Iseki, K. (1981). Particulate Organic Matter Transport to the Deep Sea by Salp Fecal Pellets Marine Ecology Progress Series, 5, 55-60 DOI: 10.3354/meps005055
Lampitt, R., Hillier, W., & Challenor, P. (1993). Seasonal and diel variation in the open ocean concentration of marine snow aggregates Nature, 362 (6422), 737-739 DOI: 10.1038/362737a0
SILVER, M., SHANKS, A., & TRENT, J. (1978). Marine Snow: Microplankton Habitat and Source of Small-Scale Patchiness in Pelagic Populations Science, 201 (4353), 371-373 DOI: 10.1126/science.201.4353.371
Turner, J. (2002). Zooplankton fecal pellets, marine snow and sinking phytoplankton blooms Aquatic Microbial Ecology, 27, 57-102 DOI: 10.3354/ame027057
WOTTON, R., & MALMQVIST, B. (2001). Feces in Aquatic Ecosystems BioScience, 51 (7) DOI: 10.1641/0006-3568(2001)051[0537:FIAE]2.0.CO;2
Good morning, folks,
Just writing this self-promotional post to inform you that T. Delene Beeland did a little Q&A section with me in the Charlotte Observer for Blog of the Week. So if you want to read my answers to 3 questions, click here. (Also there is a picture of me with my stuffed shark I got in Alabama. His name is El Sanguino, i.e. The Bloody One. My very own bastardization of Spanish, thank you very much.)
Good day, y’all!
Many of you may be familiar with Ed Yong’s post on the Origin of Science Writers, in which he invited writers to post their stories, their travels and travails to get to their current status. (There are over 100 comments at this point.) As I read through the contributions, I realized that something was missing: young or new science writers (with one or two exceptions).
Although encouraged by a seasoned blogger to contribute myself, I felt uncomfortable with the idea. After all, almost all the other writers have higher degrees, have been writing for many years, have published books, etc. Who am I to add myself to the list? I, a mere 23-year old with her bachelor’s degree, a science writer by self-definition more than anything else – do I dare to add myself to their ranks?
The science writing world is changing, and not just because of the ScienceBlogs exodus (Bora’s must-read farewell here). We no longer need credentials to write about science: I can just sign up for a wordpress page and do it! I can risk irrevocable embarrassment and failure on the internet, dooming my dreams of becoming a “real” science writer!
Joking aside, I can see why some people would be hesitant about the emergence of younger, less-experienced science writers on the scene. I don’t know everything about science. I haven’t received my grad school drilling in identifying faulty methods. I haven’t been trained in journalism or ethics. So I care a lot about science and education – does that alone make me qualified to spout off on various topics that I’ve only learned about in the past week?
The potential problem with inexperienced writers is a greater likelihood of making mistakes. I admittedly use this blog as a learning tool for myself. It’s an incentive to read and do research, and then regurgitate it in a fluid way so that I can get a sense of how the research fits together and, in the process, make it useful to other people. While some of my recently graduated friends comment on how their learning has dropped in this year since college, I would say that I’ve actually learned more, in great part due to this blog.
My awareness of my relative inexperience and thus potential for spreading misinformation makes me work really hard to not blather on about things I don’t know anything about. This is one of the reasons I can’t write a blog post every day (or week): for every post I write, I first fact-check, read review articles, and generally make sure I know what I’m talking about. My lack of expertise forces me to do my research well (resulting in mini-epic blog posts). This also helps me toward my goal of creating posts that provide a lot of background, so that I’m providing more than just a small piece of the puzzle when I write about a topic.
But mistakes happen to everyone – not just inexperienced writers – and the internet community should respond to error in a constructive way. Several times I have been torn up in the comments by other scientists (sometimes with unfounded anger) in a way that doesn’t help correct an error, but simply to make me feel like an idiot and doubt myself. That doesn’t do good for anyone: it doesn’t provide a correction, makes me want to disappear, and only serves to make the commenter feel good about her/himself. (As if showing intellectual dominance through mockery should make anyone feel good… bullies.) Mistakes should be corrected through polite questioning and suggestion, increasing information quality without discouraging the writer.
But these potential mistakes don’t mean that we young bloggers don’t belong. We are kids who have normal jobs. We don’t have time scheduled into our workday to read papers, but do it when we get home instead of going out drinking. Our worldviews are not yet jaded by academia. And I think this shines through in our writing – excitement, a certain humbleness, an ability to admit that we don’t know everything.
Well, now I’ve blogged about blogging. If that doesn’t make me a science writer, I don’t know what does.
And with that: several weeks ago Bora (aka the blogfather) of A Blog Around the Clock tagged me in the Blogging with Substance meme, and I’d like to dedicate mine to a few young bloggers that are doing really great work
1. Sum up your blogging motivation, philosophy and experience in exactly 10 words.
That’s a hard one – 10 words is incredibly restrictive. I guess I’ll write a haiku!
Teaching and learning;
Never limit oneself;
Share always the cool
2. Pass it on to 10 other bloggers with substance
I’m going to tag other young bloggers with substance – just because we don’t have PhD’s doesn’t mean we don’t have something to say!
Never thought I’d actually get around to a Pt. 2, eh? Well, I’ve shown you! Here’s the first part: Inevitability and Oil, Pt. 1: the inherent risk for accidents in complex technology
For decades now economists and scientists have predicted the “end of oil:” the day when we use up our oil reserves, potentially resulting in economic collapse, starvation, chaos, you know, the apocalypse, whatever. It’s a strange science – part speculative geology (if you can imagine such a thing!), part economic theory, and at least 2 parts anxiety.
Why is the “end of oil” such a problem? It is well summarized in Wolfgang Haber’s 2007 leading article in Environmental Science and Pollution Research: our dependence on fossil fuels is an “ecological trap.” While it is easy to consider our species as above competition, as we now dominate the planet, we have reached this state as simple organisms trying to out-compete others and maintain (and expand) our own population.
How did we do this so successfully? First of all, we are the only organism (as far as I know) that obtains energy from an external source: that is, through fire. Our ability to burn various substrates (initially wood, moving onto fossil fuels such as coal and oil later) allowed us to expand our range and create accessibility to new food sources through cooking. Thus the first ecological trap: to maintain our current population, we need to have something to burn. Forests and wood are sustainable to a point, but with our current population, we’d go through our reserves pretty quickly.
According to Haber, the second major “ecological trap” is farming. The switch from hunting and gathering to agriculture created a human dependence on soil (easily nutrient-depleted by farming itself) as well as space devoted to farming. Once again, the advent of large-scale agriculture allowed our population to boom, and created a niche for people who don’t need to work – such as scholars – but now we are wholly dependent upon outside food. Could you forage for yourself if needed?
And thus, while our species has outcompeted all others, we are trapped in a sense: bound to fuel for fire, and bound to soil which is not easily replenished at the rate of its use.
Traditionally, drilling for oil and mining have not held too many moral questions. The main question has been, “what are we going to do when we run out?” After all, these fossil fuels are not being used by other species, and their removal doesn’t seem to have any effects on ecosystems. But after the BP oil spill (as with the 1989 Exxon-Valdez spill and suggestions of drilling in the Alaska National Wildlife Refuge), there has been an outcry to reduce our dependence on oil not for our species’s own survival, but rather because of the damage we do to other species. That while drilling in and of itself may not be harmful, its effects can be.
From here I will overview some of the typical outlooks on what will happen at the end of oil, and then provide some reflection on conservation as an argument for reducing drilling.
Anthropocentrism: the viewpoints on the end of oil (briefly)
In his 2007 article in the South Atlantic Quarterly, Imre Szeman asks whether or not the “end of oil” is truly a disaster – a disaster for humankind, or just the status quo of our society. He outlines the 3 central ways that people think about the end of oil.
- Strategic Realism. This viewpoint is held by those deeply invested in maintaining the current economic and political spheres of our species. The questions asked are more about how the political structure of the world will change with the “end of oil,” and finding solutions to keep the current powers and countries of the world in balance. To quote Szeman, “Those who employ [this viewpoint] – and it is a discourse employed widely by government and the media alike – suspend or minimize concerns about the cumulative environmental disaster of oil or the fact that oil is disappearing altogether, and focus instead on the potential political and economic tensions that will inevitably arise as countries pursue their individual energy security in an era of scarcity.”
- Techno-utopianism. Techno-utopianism and strategic realism often go hand in hand: it is the discourse of dreamers who believe that science and technology will provide new access to oil and new technologies, which will enable us to maintain the capitalist economy. Our lifestyles will not change, but rather we will simply replace oil with a new form of energy, such as nuclear or hydrogen. It relies heavily on the idea that scientific innovation is just around the corner – that our solutions will arrive in time.
- Apocalyptic environmentalism. The apocalyptic environmentalists follow a different train of thought: that the “end of oil” will change everything. That social and political change will not only come, but will be necessary – that the carrying capacity of the planet will fall, standard of living will fall, and there is nothing to be done about it. The difference between this viewpoint and the others is that it serves a pedagogical purpose, as Szeman explains: that we need to change our actions now, moving towards a “simpler, non-affluent way of life.”
The role of Homo sapiens in conservation
These viewpoints, all of which you’ve probably witnessed, are all anthropocentric in nature. And this makes sense – we are a species trying to compete, and right now a resource we’re dependent upon is threatened. We need to think about how we, Homo sapiens, are going to survive this.
While economists often like to talk about the “end of oil,” I don’t have a good feel for the public mindset on the topic. While the “sustainability movement” is picking up speed, it often feels to be, frankly, bullshit sold at Whole Foods wrapped in 10 layers of plastic packaging to make people feel better about themselves. I can tell you this: I hadn’t noticed so much attention aimed toward ending our oil dependence until we saw pictures of pelicans covered in oil right in our own backyard, our own fishing grounds, affecting our own people in the BP oil spill.
While a competitive species should be concerned about this for their own sake, this recent rise in “oil awareness” is instead due to the harm we’re causing other species.
I’ve had many discussions lately about the anthropocentrism of our species, and how that affects the ways we view our environment. Some argue that conservation, while seeming altruistic, is actually the wrong way to think about the environment. That species have gone extinct for millennia; that invasive species do not exist; that the preservation of our environment is based on how we view “nature” and not how it functions itself. (See this comic for a simple representation.) That our care for nature or animals is selfish in itself, as they are symbols for how we view nature and places that we value aesthetically. Some even suggest that we give up on conservation efforts altogether and let evolution and nature take their course, even if it means our own extinction.
The response to the oil spill has shown that this empathy for other organisms (a sense which we evolved, I might add) may have more motivating power than our own survival. That our desire to assist those in struggle – whether they be oiled birds or starving people – creates a greater response than the thought that, sometime in the future, we may have to drastically change our lifestyles. This may be due to its immediacy, as we can save a bird RIGHT NOW but adjusting our carbon footprint or energy use will not have effects in the short-term. After all, as I said earlier, we are a competitive species: while ideally we all agree that preserving the status quo for our children is a good idea, we still are selfish and need to succeed the best we can now, so those good intentions are often left to the wayside.
While I do agree that we cannot save every species and that natural selection must take its course, I also consider that we evolved empathy. Homo sapiens have an instinct to try and help each other, other organisms, and “nature” generally, even if it doesn’t seem to make sense competitively. I, however, think it makes perfect sense: we need these resources in order to survive. We need a sense of the importance of “nature” and a drive to conserve it for our own good. The fact that we can “feel their pain” gives us an incentive to save them, and thus preserve our own resources.
So to those who look down on empathizing with nature? I say: haters gonna hate. We need a reason to reduce oil dependency, encourage technological innovation, rethink our society in order to continue to compete as a species. Clearly the thought of the “environmental apocalypse” isn’t a good enough motivator. If our empathy with hurt animals or disgust at our own species for ruining “perfect nature” is the cause, so be it. We need a reason, any reason. I say let’s follow our instincts and try to make change, if not for ourselves, then for the pelicans.
Haber, W. (2007). Energy, food, and land — The ecological traps of humankind Environmental Science and Pollution Research – International, 14 (6), 359-365 DOI: 10.1065/espr2007.09.449
Kerr, R. (1998). GEOLOGY:The Next Oil Crisis Looms Large–and Perhaps Close Science, 281 (5380), 1128-1131 DOI: 10.1126/science.281.5380.1128
Szeman, I. (2007). System Failure: Oil, Futurity, and the Anticipation of Disaster South Atlantic Quarterly, 106 (4), 805-823 DOI: 10.1215/00382876-2007-047