John Teal is an ecologist from Woods Hole Oceanographic institution in Massachusetts. He is one of the first to analyze energy flow in the salt marsh system. This study is largely dependent on the work of others. I had a hard time finding anything else on him. He is currently still working for the institution and still publishing to this day. 129 publications with over 6,000 citations, according to Research Gate.
Introduction
Food Webs
Methods
Spartina alterniflora is the main grass in the marsh and therefore one of the main producers focused on this study. The herbivores are broken into 2 categories: those that feed directly on living spartina, and those that feed on detritus.
Spartina grasses and grasshoppers had complete sampling, enough to determine production. The rest of the organisms were estimated from turnover time ( production = one maximum population per turnover period) or assuming the ratio between respiration and production for the group in question is 0.25/0.30 ( it seems this ratio was found in one of his previous studies: Teal 1958).
Primary production
Spartina was measured by harvesting and weighing these plants in monthly intervals; respiration was measured by short term harvesting so 305 kcal/m2 yr (insect consumption) needed to be added to arrive at the “true net production.” This respiration value only makes up 19% of gross production- and may fluctuate based on the seasons. The rest comes from the decomposition of the grasses by bacteria and algae, making the grass more edible to the rest of the community.
Decomposition
To find out how spartina is broken down, it was air dried and 10g of it were placed in 500ml flask with 200ml of ocean water, 1ml of marsh mud at 20 C with no light. Sampling occurred at 0,2,7,14,28,56, and 112 days. Oxygen consumption was measured and the material was analyzed for protein, fat, fiber, ash, nitrogen-free compounds, and caloric content. The results are summarized in figure 3.
Bacteria, along with algae are active in degradation process. Bacteria alone degrade 2090 kcal/m^2 yr. Average respiration which is 60 mm^3/gr hr multiplied by biomass of spartina gives us 1000 kcal/m^2 yr. Their activity accounts for 3890kcal/m^2 yr breaking down about 59% of spartina.
Community Energy Flow
Gross production is 6.1% of incident light energy and most of this is metabolized by the plants. Net production=1.4 % of incident light.
The plants are eaten by the herbivores with not much lag time and they assimilate 4.6% of potential food.
There is more lag in detritus feeders due to the fact that it must first be broken down by algae and bacteria. This seems harder to quantify and I do not see a figure in the text. see fig 4
Stability
Stability minimizes disturbances that can lead to extinctions and according to Dunbar 1960, stability in ecosystems has selective value and over time they will develop more stable configurations. According to MacArthur stability is established in one of two ways: by having many species with restricted diets or few species with broad diets. The latter is an example of the salt marsh. The reasons for this could be due to having only one dominant plant species, lacking variety and niche space. The other reason could be that biomass is restricted by tidal currents and most of it is washed away. So for this community the only way to reach stability is for the consumers to develop broad, unrestricted food habits.
Findings
55% of net production is utilized by marsh community with producers consuming the most energy, bacteria degrade only 1/7 as much energy as producers, and consumers degrade 1/7 as much as the bacteria.
Another finding is that Spatina respires over 70% of its energy, which is a huge loss in energy. Likewise the bacteria consumed and respired 45% of net primary production. Last, 45% of the net production was unaccounted for. This 45% is thought to be lost through tidal currents and washed up in estuaries where more species persist possibly due to more stability? (this was not studied in paper)
Qs
In the paper Teal talks about respiration of Spartina, why is this over 70%? It seems like a huge waste of energy, but I do not know much about plants so I could be wrong. In the texts it briefly states that this may be due to the large amounts of salt, but it does not touch on any mechanisms or other possibilities.
Does the Georgia salt marsh seem like a stable system to you?
Did Teal have enough data to support all of his claims? A lot of it seems to be extrapolated.
How well does this paper stand to todays standards?
Do you think there were species that he could have overlooked, especially microorganisms in the soil?
Was respiration the best way to test for overall production? Does this method have any faulty assumptions or leave anything important out?
I don’t really understand figure 3, why does protein increase as fat drops?
Has this study been updated to include carnivorous birds and insects?
Great seminal paper ( cited about 1118 times). The system for me was perfect to tackle question with regard to energy budgets in one ecosystem. Given the fact, that Spartina is providing much of the productivity in the study site i was thinking if the the regulation in this ecosystems might be bottom up?. Hypothetically, the elimination of Spartina might disrupt the Stability of the ecosystems?. I was amazed by the fact that this is one of the most productive ecosystem in plane earth.
ReplyDeleteVery interesting some of the conclusions made here. This system is defined as stable because it has few species that have broad diets and over the time this study was conducted there were no noticeable changes in population size of any of the important animals. I wonder if this is truly an accurate way of measuring stability…To answer Mateo’s question regarding Spartina respiring over 70%, I believe this plant respires a lot because it produces a lot. Even though net production is much less than gross production it is still high compared to other systems. Gas exchange and water vapor loss take place through the same openings in the leaves called stomata. As CO2 is sequestered from the atmosphere water is lost and in this system that is not water or nutrient limited it can assimilate and respire as much as its heart desires and still produce at a high level.
ReplyDeleteI would add on a musing about why its respiration might also be high. It might need to actively transport out some of the salt that is in its cytoplasm since it needs to maintain an internal homeostasis. That might require a lot of energy and might account for 70% of the energy going towards just functioning of the grass and not towards production of more biomass.
DeleteIn ecosystem studies today carbon rather than energy tends to be the common currency. An approximate global average C use efficiency (net/gross productivity) for forests in 45%, with 55% being respired, so by that standard the salt marsh is vegetation is not a very efficient user of photosynthate. Interesting idea on the energetic costs of salt transport.
DeleteThere seemed to be a lot of guestimation here and I don't think Teal's methods would be up to snuff today, but as one of the first complete ecosystem studies without today's technology (Li-CORs, isotopes etc.), this was pretty good. I really liked the figures and how comprehensive he tried to be - it's clear Teal really know this ecosystem.
This paper did a great job of putting numbers to a food web/energy transfer study. While previous studies have certainly made similar observations this paper actually quantifies the efficiency and energy use of each major organism in this salt marsh food web. The simplicity of this system certainly makes for an easy study system without too much complexity. I like how he relates his findings back to stability and how this system stands contrary to the diversity stability hypothesis. He uses the abiotic environment (salt and tides) to argue why this system stands as an exception for good reason. I also like that this study is one of the first to put any real emphasis on the importance of microbes, though this may have been more of a necessity here to account for energy and lack of trophic complexity.
ReplyDeleteThe abiotic factors make this a really unique ecosystem to study. As mentioned the variability seen in the salinity has a definite impact on what producers and consumers will be present. A majority of organisms found here spend their lives on the edges fewer live in the marsh itself. This may limit the diversity seen and in some ways simplify the study. Also unique to this system is the amount of production flushed out of the system, 45%. However I feel assuming that spider and birds predating insects take the same portion of prey as detritus-algae eaters might not be accurate and would warrant further investigation.
ReplyDeleteA salt marsh is an interesting system. Having spent some time paddling in a Georgia salt marsh, I can see such a system being ready made for a trophic dynamics study like this one. It is a relatively simple system although not so simple that meaningful conclusions can not be drawn. Thats not to say salt marshes lack diversity, the authors provide a sizable list of macro-fauna that play some role in the salt marsh. Moreover, I'm not sure that the salt marsh really stands contrary to the diversity stability hypothesis. Granted, there is only one major plant but here are still a lot of niches to be utilized, many are temporal (available at low or high tide) and there are lot of edge habitats to be utilized in the spartina labyrinth. Carlos mentioned the hypothetical removal of the Spartina. It seems to me that the very existence of the salt marsh relies on the grass and the elimination of Spartina would greatly disrupt the system to the point where there would be physical loss of the stinky mud that makes up the marsh substrate.
ReplyDeleteI think you are right Chris, this ecosystem is very dependent on these grasses. In 2001 there was a huge die back of the salt marshes in Georgia and Louisiana. With the grasses gone there is only mud, and the ecosystem seems to disappear, almost as a bottom up effect like Carlos mentioned. The disease seems to be caused by a multitude of factors rather than just one. Here is one of the articles that has some good info:
Deletehttp://www.altamahariverkeeper.org/oldsite/advocacy/coastal_marshland/marsh_dieoff.asp
I have the same question Mateo does regarding Figure 3 in this paper. According to Teal’s narrative, bacterial action in the flasks containing Spartina and seawater is low starting from 2 weeks on. If these are the only contents of the flasks, why does the percentage of protein appear to double from week 8 to week 16? What accounts for this?
ReplyDeleteI was happy to see that Teal’s study highlighted the importance of bacteria in making the nutrients from Spartina available to other consumers. I appreciated the energy-flow diagram (Figure 4), and how it shows the key role of bacteria in recycling energy from the higher consumers.
It seems odd that a study with an extensive discussion of stability would take place in an environment where 45% of the total energy is lost to the tides. Still, I believe Raymond Lindeman would have been glad to see his work expanded so assiduously.
Looking at the figure, I think that it could be an artifact of the total amount of calories and stuff going down and therefore the protein would become a larger part of the mixture because it is harder to break down. But I could also be way off base there. It is an interesting figure and I would love to see the data behind it.
DeleteLooking at the figure, I think that it could be an artifact of the total amount of calories and stuff going down and therefore the protein would become a larger part of the mixture because it is harder to break down. But I could also be way off base there. It is an interesting figure and I would love to see the data behind it.
DeleteI like the idea of looking at the salt marsh as a simplistic natural system and thought this was a quantitatively robust study. It makes sense that this is a simplistic system because of the high salinity and homogeneous Spartina habitat. The Georgia salt marsh system is reliant on S. alterniflora, and it is often referred to as an "environmental engineer." Because of S. alterniflora's engineering properties, it was introduced purposefully (and accidentally) into the US Pacific Coast by the Army Corps of Engineers to promote marsh habitat. Unfortunately, S. alterniflora has over taken native Spartina and become an invasive species that disrupts the natural Pacific Coast marsh habitat.
ReplyDeleteMost of these trophic studies make me wonder how these would be better informed using isotopic analysis. It seems to me that the best way (today) to get at what different animals are feeding on within a system and how much they rely on a certain food source could be through the use of stable isotopes. Of course, I am fairly new to stable isotope analysis and couldn't say for certain. This could especially be helpful in understanding insectivore diets.
ReplyDeleteLike the Davidson & Andrewartha paper, I think this paper has methodological shortcomings, but is nonetheless an important contribution as a demonstration of how food webs and ecosystems can be quantified and understood from an energetics perspective. There were a lot of assumptions and potential missing pieces (e.g. secondary consumer insects and some fauna), and I'm not sure if assimilation/net production would be accurately captured by their estimates of biomass and respiration (the methods may be better detailed elsewhere?). But what they did must have been a ton of work, and as mentioned in the intro, provided a valuable way to compare ecosystems.
ReplyDeleteThe stability argument was interesting. They didn't really provide any evidence, much less measurement, that the salt marsh ecosystem was particularly stable relative to others, but the ideas that ecosystems select for stability and "evolve" towards more stable configurations is intriguing. I wonder how much this notion has gained traction in evolutionary ecology.