November 2012 Archives

I'm crushed with teaching at the moment, so this post is getting less attention than it deserves, but I wanted to get this out anyway.  Since 2005, I've been involved in a scientific skirmish about the degree to which pelagic marine ecosystems are structured from the bottom-up or from the top-down.  The latest round in this debate is now available in a pair of short communications in Fisheries Oceanography (1 and 2).

The top-down view is championed by Ken Frank from BIO.  Beginning with a 2005 Science paper, he has had a series of high profile papers presenting an argument that the Eastern Scotian Shelf ecosystem has experienced a trophic cascade caused by the removal of groundfish--principally, cod.  The hallmark of a trophic cascade is a flip-flop pattern as you move down the food chain.  So, according to his view, when the cod collapsed in the late 1980s, it led to an increase in shrimp, a decrease in large zooplankton, and an increase in phytoplankton, and a decrease in nutrients.

The bottom-up side has been led by Chuck Greene from Cornell, with contributions from me and a host of others.  Our view, outlined in a series of less high profile papers (3 and 4) has been that the changes in the NW Atlantic Shelf ecosystems are ultimately tied to physical forcing.  We documented a decrease in salinity in the Gulf of Maine in the 1990s, increased phytoplankton, increased small copepods, decreased large copepods (i.e. Calanus), and increased small pelagic fish (herring).  Implicit in our view is that changes in groundfish have a limited impact on the pelagic food web. 

As with many scientific debates, the debaters (debatees?  debatants?) are not always comparing apples to apples.  As Frank points out in his note, our work has focused heavily on the Gulf of Maine while his has focused on the Eastern Scotian Shelf.  Never mind that I looked at the plankton changes in the Eastern Scotian Shelf along with several other regions along the shelf in my 2010 JPR paper--that's OK, Chuck forgets about that paper, too.  There is probably a resolution here, but that's not the point of this post.  No, the purpose of this post is to show how some of the best evidence of bottom-up forcing of NW Shelf ecosystem is in Frank's original 2005 paper. 

Frank's 2005 paper hinges on a figure that shows the trophic flip-flops.  However, there are two physical time series that he presents, but quickly dismisses.  For example, on the left are his groundfish time series plotted on top of his time series of bottom temperatures (I pulled the time series from a PDF of his paper using Illustrator):
On the right,  I've shifted the bottom temperature forward by six years.  The rise and fall of groundfish is strongly correlated with temperature.  Temperature leads fish, as you would expect from a bottom-up effect, and the six year time lag is a reasonable generation time for larger groundfish.  I have not done the statistics, but this correlation is stronger than any in his paper (that's a low bar to cross though, since no statistics appear in the paper).

But wait, there's more!  Close readers will quickly note that even if temperature was driving the changes in cod, the cod could still be driving the train.  Here is Frank's phytoplankton time series plotted on top of the stratification index that appears in his paper:
Higher phytoplankton levels are associated with increased stratification, consistent with the hypothesis Chuck and I put out in our 2007 paper.  Again, I haven't done the stats, but I'm confident that this relationship is stronger than any in the paper.  

This debate is both academically interesting and practically important.  On the practical side, understanding how fish populations influence marine food webs is vital for understanding the impact of fishing.  Understanding the impact of physical forcing is vital for understanding how these ecosystems will respond to climate change.  On the academic side, you can view this as a debate between ecology and oceanography.  Ecology has a long tradition of documenting the importance of predators--think about Paine's classic work in the intertidal or Estes' work in kelp forests.  Oceanography has tended to emphasize the connection between physics and biology.  Clearly both predation and physics are important, the real question is where, when, and why one process dominates over another.  I've always considered myself an ecologist (my Ph. D. is in Ecology and Evolutionary Biology) who happens to work in the ocean, and Chuck recently reminded me that Robert Paine was on his committee.  I'd like to think I'm open to the possibility of strong top down forcing in the ocean; however, I think the weight of evidence suggests that physics has a stronger influence on plankton than fish.

The weirdness of 2012 continued

This has been a bizarre year in the Gulf of Maine. A short time ago, Andy wrote an entry on the warm water anomaly in the Atlantic that has occurred this year.  It has been a basin-scale event that we'll probably be analyzing for many years to come. As I compose this entry, people are seeing all kinds of strange things up and down the coast of Maine.

In early November, there were reports of seahorses washed ashore and caught in traps in southern Maine. These charming fish are quite rare in the Gulf of Maine, with only a few reports off the Scotian Shelf. Initially, I suspected a connection with hurricane Sandy, or perhaps a warm-core ring. Earlier this week, however, I heard reports of seahorse sightings throughout the summer in midcoast Maine.

In October, I was out sampling with a group of Bowdoin students.  I had hoped to show them the wonders of copepods--an important lesson for all aspiring oceanographers.  However, our zooplankton samples were mysteriously devoid of them.  We even ran some 10-micron-filtered samples through a FlowCAM, and didn't see a single nauplius.  Instead, net after net came to the surface with voluminous orb-shaped ctenophores.


This beroe sp. was almost as large as my fist. The ecosystem we observed, with its large ctenophores and inscrutable lack of copepods, was quite different from what I had expected. Recently, I have heard reports of these large ctenophores throughout Casco Bay all autumn.

The question remains as to how significant these anomalies are.  Gelatinous species, like ctenophores, can bloom suddenly then vanish.  They can also settle in for the long term and dramatically reshape the ecosystem, as Mnemiopsis leidyi famously did in the Black Sea. Some ecologists have even forecast a "jelly ocean" following the collapse of global fisheries.  The basic idea is that gelatinous species out-compete fish for crustacean prey.

The "jelly-ocean" prediction is a debated one, as there are huge gaps in our knowledge of gelatinous species. They are undersampled, and there is much we don't know about them. Most models don't account for them, and they even thwart some the underlying assumptions in ocean ecosystem theory, such as the nice trophic size structure of marine ecosysems (that is, large eats small). For example, as you can see in the image below, ctenophores like beroe can be prey for tiny crustaceans.  We are even still discovering new families in the Gulf of Maine (see Pages et al. 2006, Scientia Marina). 


These changes often occur more quickly than we can understand or even sample them.  Keep your ears peeled for other strange happenings, and unexpected visitors.  And we encourage you to let us know what you happen upon.  We'll need many eyes on the sea if we hope to solve this puzzle.
-Nick Record, signing off

Celebrating 10 years of Québec-Océan

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I'm writing from a conference hall in a hotel downtown Montréal.
There the oceanographer's community from the province of Québec (eastern Canada) is celebrating 10 years of achievements for the inter-institutionnal group in oceanographic research, Québec-Océan: numerous institutions from the academic and the government, 64 researchers, several federal research and excellence Chairs, above 200 students that graduated with a Masters or a PhD for the last 10 years. This group is supported by the provincial funding agency (FRQ-NT) and strengthened a long tradition of concerted research in all the disciplines of oceanography in Québec. When you are small, you need to school together to be successful, something well known in biological oceanography!

For my part, I'm proudly presenting the fruits of our research with Andy and Nick (Québec's neighbours down in Maine), for the glory of science and also in hope that it will help me land a position in one of these nice institution here!
My talk is about the adaptations of copepods thriving in highly seasonal environments, meaning environments alternating regularly between good and bad conditions for growth and reproduction. A key adaptation is dormancy, which consists of staying quiet for months at depth while the environment is bad. Pelagic copepods do just that with tremendous success. But to be successful, the dormancy strategy requires the ability (1) to accumulate reserves during good times and (2) to save this capital during bad times. Point (1) is well documented now and it's mainly about the large relative amount of lipids copepods can store, but point (2) is surprisingly less known. Hence I reviewed the metabolic requirements during dormancy published for 15 species. The punch of my talk is the prediction of dormancy duration for pelagic copepod as a function of their initial body mass and ambient temperature, and how that interacts with the growth(metabolism)-development tradeoff in copepods in order to shape life-cycle strategies, biogeography and biodiversity.

Isolines of the dormancy duration (days) were computed according to the average metabolism of dormant copepods we reviewed from the literature, the ambient temperature during dormancy and the body mass of copepods at initiation of dormancy. Dormancy is assumed to stop when a copepod reaches 30% of its body mass at onset of dormancy. Black triangles: observed position within the in situ temperature/mass space of the active individuals. Coloured circles: idem for dormant individuals. Colour scale reflects estimated dormancy duration based on species-specific metabolic values.


This figure presents the modeled mass-stage structure of copepods developing in constant temperature and non-limiting food conditions, based on parameters from our literature review. Isolines, triangles and circles same as preceding figure.

This work has a lot of implications and helps answer several critical questions:
  • Practical: in which environment can copepods use successfully a dormancy strategy to thrive in highly seasonal environments?
  • Theoretical: how come that some copepods not only spend months dormant relying on internal reserves but also produce a large number of eggs out of it?
  • Predictive: how will environmental changes influence the biogeography and biodiversity of pelagic copepods?

Data vs. Intuition or How the Election is Like Climate Change

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elections.001.jpgWe live in a data rich world.  With a few minutes on google, I can look up the current wave height in the Gulf of Maine, whether the waters in the equatorial Pacific suggest an El Nino is coming, or the percentage of time a pro football team converts a 4th and 5.  Ostensibly, the purpose of all of this data is to help us make smarter decisions--whether we're deciding if it's a good weekend to go surfing, how to manage water resources in California, or if it's better to go for it on fourth down or settle for a field goal. In reality, though, many of the decisions that we make are based on intuition.  How many times have you heard a football coach talk about how their gut or their heart informed their bold call that won the game?

The conflict between data and intuition is at the heart of much of the opposition to climate change and evolution.  Our intuition about how climate is changing is informed by our daily experience with weather.  Because weather conditions are so variable, it is hard for us to detect the trends that the climate data says are there.  Many people conclude that climate is always changing (true) and that these changes are unpredictable (not true). You can also get people concluding the right thing for the wrong reasons.  Many people interpreted Superstorm Sandy as evidence for climate change.  (BTW, I've decided that when I finally form my band, it will be named "Superstorm").  I think the jury is still out on the degree to which climate change (warmer oceans, more water vapor, less ice) helped contribute to Sandy.  This summer's drought and ocean heat wave are much better evidence for climate change.

In my opinion, the most exciting fight over data versus intuition is playing out in the media coverage of the presidential election.  The news media, even "high-information" sources like the New York Times and National Public Radio are reporting that the election is a toss-up.  While the polls are very tight, the data point to a very strong advantage for President Obama.  My favorite website is Nate Silver's FiveThirtyEightblog. This is the ultimate data-nerd view of the US elections.  He has built a rigorous statistical model, which he described in detail throughout the campaign, that blends information from state and national polls, demographic data, and economic indicators and provides a probabilistic forecast for the presidential election.  His take is that there is only a 15% chance that Mitt Romney will win on Tuesday. 
Many pundits have accused Nate of being biased.  His data-driven interpretation of the election runs counter to their intuition about the election and their preconceived ideas about the mood of the country. As with climate change, many of them have a vested interest in portraying the race as close--if your career is based on your ability to interpret the news and possibly sway voters, then it's in your best interest to make it seem like things are close. The criticism of his model has a similar flavor to many of the criticisms leveled at climate models, especially when the predictions run counter to what our gut tells us. At least election modelers will have a definitive test of their predictions tomorrow.

Election morning update: Nate Silver has the odds of an Obama victory at 91.6%.  He had a great discussion with Stephen Colbert about gut instincts vs. polls:

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This page is an archive of entries from November 2012 listed from newest to oldest.

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