The Case for Vegans Eating Oysters, Mussels, & Other Invertebrates?

Nope, Here’s Some Science. 

Update: See Part II for a continuation on this topic and further discussion on sentience and environmental impacts.

Part III on NOT eating Oysters

                           

This topic has come up numerous times in the last few days. After reading the comments on a few discussion groups, I realized that a lack of understanding of simple science and biology is being used to justify the addition of bivalves into the vegan food chain. 

Some of the misinformation is in part spread by the most quoted blog post written by a psychologist that calls herself the Sentientist. On her blog, she tries to make the ethical case for eating some bivalve species. Unfortunately, the rest of the unsupported argument is being spread by readers of the blog that don't realize there really isn't much there based on any reliable evidence. I believe I only found one reference to a published paper when I checked the sources earlier this week. 

To counter this misinformation and bring accurate science into the discussion, below, I attempt to set the science straight and provide examples that tear down most one of the Sentientist's points in support of eating these bivalves. I am purposely copying and pasting portions of actual scientific literature to clearly show that my statements are not based on ideology and made up or non-existent data. I also do not try to make the case (or not) for sentience because it just doesn't make sense...You'll see what I mean. 

I also mostly directly quote research studies and use the Sentientist's own sources to show how cherry-picking data that you may not understand makes for bad arguments. I begin, however, by addressing some of the most erroneous statements surrounding conversations that I've witnesses on discussions surrounding this topic.

Classification

Proponents of eating bivalves seem to believe that classification of living beings is based on archaic methods from the 18^th century, as one of them put it. However, in current times, classification of living beings is based on morphology and molecular data, which are used to establish evolutionary relationships between them. And guess what? Mollusks, including bivalves, are still in the Animal Kingdom. I'm not aware of any connection to plants when it comes to the phylogenetic tree of mollusks, including bivalves. You can read all about mollusk phylogeny and evolutionary asociations here: http://www.nature.com/nature/journal/v477/n7365/full/nature10382.html 

Spoiler alert: You're not going to find anything about plants. 

Image: Photo of a comment  in a facebook group discussion trying to justify eating mussels and oysters as a vegan.

Image: http://tolweb.org/Animals/2374

Bivalves Are Not Plants

"Are they plants of the sea?" "Aren’t they just like plants?" These are the types of questions and statements that I continue to find in threads that discuss whether vegans should eat bivalves. 

Image: Photo of a comment in a facebook group discussion asking for more information on the ethics of eating bivalves.

No. Bivalves, as we established above, are animals. They are not, I repeat, are not plants. And where does someone get that they have roots? Perhaps they meant a byssus? However, byssus are not roots and are nothing like plant roots.

For some reason, bivalve eating supporters have this idea that oysters and mussels are basically plants or have more in common with plants, but let’s look at that image again: 

Image: http://tolweb.org/Animals/2374

Still not plants; otherwise, they would be classified as such...I'm going to go with the experts on this one.

Regardless, the Sentientist (by providing a link to wikipedia about general plant responses) alludes that the closing and opening mechanism in sessile bivalves is as simple an action as that in carnivorous plants. However, conveniently, she does not go further into the topic. Here is why that statement is false...and just shows a lack of basic understanding of biology, as well as, animal and plant physiology. 

As we discussed above, plants are in the plant kingdom while bivalves are in the animal kingdom. By now, it should be common knowledge that plants have absolutely NO nervous system - at all. Bivalves DO have a nervous system regardless of how simply it may be. There are many species of carnivorous plants that don't have a closing mechanism, but I will assume that the plant that is being discussed is the venus flytrap. Volkov et al. (2008) stated that, "Plants can react to mechanical stimuli (Ksenzhek and Volkov, 1998; Braam, 2005) with the use of mechanosensitive channels... Mechanosensory ion channels in plants are activated by mechanical stress and transduce the sensed information into electrical signals (Volkov and Haack, 1995)....Touching trigger hairs protruding from the upper leaf epidermis of the Venus flytrap activates mechanosensitive ion channels and generates receptor potentials, which induce an action potential (AP; Burdon-Sanderson, 1874, 1882; Burdon-Sanderson and Page, 1876; Stuhlman and Darden, 1950; Jacobson, 1965; Sibaoka, 1966; Volkov et al., 2007)." It's basically a spring-like mechanism caused by electrical signals.

Meanwhile, to explain it as simply as possible, in mollusks, closing of the shell is done by muscles. In blue mussels, the nerve fibers in the nerve within the anterior byssus retractor muscle control the opening and closing of the shell via the release of seratonin (Schmidt-Nielsen 1997). 

This is not the same thing at all. Again, plants have NO nervous system while bivalves, such as mussels and oysters DO have a nervous system. One closing mechanism is done by electrical signals triggered by hairs on the plant (no nerves or muscles) while the others one is guided by nerves/nerve fibers and muscles. Most importantly, mussels need to engage their muscles actively to keep the shells closed. 

Also, it has been documented that mussels will close their shells " by contraction of “quick” muscles in response to perceived danger. This reaction is supported by the literature, which documents that mussels rapidly close their valves when threatened (Ruppert etal.2004)." (Robson, Wilson, and Leaniz 2007)... 

This (contraction due to the perceived danger of a predator) is NOT the same in anyway to a simple response (guided by membrane proteins responding to mechanical stress, i.e. hairs being pushed down on to cause a reaction) that a venus fly trap will have by the simple action of sensory touch to a minimum of 3 of it's protruding modified leaf hairs simply because an insect (or any thing else that can cause pressure on the leaves) happens to fly by. 

Image: An excerpt from the Sentientist's Article "The ethical case for eating oysters and mussels"

Now that we’ve established a few things…

The Sentientist and other supporters of bivalve eating in the vegan community claim that mussels and oysters are not sentient because they do not have “brains.” No, mussels and oyster do not have a brain. However, they do have ganglia. Ganglia, in simple terms, is basically their form of a brain – how they get their systems to function and respond when they need to. Yes, invertebrates have much simpler nervous systems than vertebrates, but they still have nervous systems. How developed their nervous system is depends on the species.

More specifically, mussels, for example, have “sensory systems such as pallial tentacles with primary ciliary receptor cells as mechanoreceptors (Ruppert etal.2004), pallial eyes (ocelli), cerebral eyes(cephalic eyes) and chemoreceptors, possibly including osphradia [olfactory organ in mollusks] (Ruppert etal.2004; Leonard 1999), which may be used to assess environmental quality so it is appropriate that these animals display an appropriately complex behavioural response.” (from Robson, Wilson, and Garcia de Leaniz 2007) <- I didn’t make that up based on made-up ideology. Experts in the field made that statement.

Mobility, Evolution, and Pain

In the case of oysters and mussels, the Sentientist attempts to establish that, because of their lack of mobility, they did not develop the ability for pain. However, she then edits her article to admit that freshwater mussels do move and that “these facts make [her] less confident in the motility argument,” which is a pretty huge chunk of her whole argument that fails right from the start.

Image: An excerpt from the Sentientist's Article "The ethical case for eating oysters and mussels"

Evolution has nothing to do with motility or with an individual. Evolution is not dependent on whether an organism feels pain or not. It has to do with a whole species and what is the cheapest means to reproduce efficiently. "Sessile macrofauna probably developed originally as en adaptive condition to unstable and scattered substrata, under the influence of unpredictable physico-chemical factors and followed a generalist (r-selected), opportunistic strategy" (Sara 1984). Evolution would, therefore, favor that a sessile or slower moving lifestyle conserve energy and produce large quantities of offspring. However, reproduction, and whether they move or not does not establish that well, "they must just not be capable of reacting to any stimuli, which must mean no pain." Even if you are a fully sessile organism, stress responses are vital to survival. What happens if a siphon gets clogged or an influx of food comes by – it would be necessary for negative stimuli to arise so the animal, in this case an oyster or mussel, responds to and deals with the clogged siphon or whatever other issue arises. Without any stimuli, why would blue mussels move or do anything else?

Well, guess what, “Most, if not all, invertebrates have the capacity to detect and respond to noxious or aversive stimuli. That is, like vertebrates, they are capable of ‘nociception” (Smith 1991).  Responses to negative stimuli, such as pain, which is very subjective depending on the individual, can indicate that something more than a simple nociceptive reflex is involved. Together, they may help the animal to recover from damage caused by the painful event and avoid being harmed in the future” (Smith 1991). While invertebrates probably do not feel pain in the same way humans do, Smith states that, the issue isn’t closed. He further states that, “Mather (1989) suggests, we should simply accept that these animals ‘are different from us, and wait for more data.’ 

It would be ridiculous to apply the same guidelines of pain that we apply to ourselves and other vertebrates to species that are completely different to us. Smith (1991) warns that, "pain might incorrectly be denied in certain invertebrates simply because they are so different from us and because we cannot imagine pain experienced in anything other than the vertebrate or, specifically, human sense.”

Unfortunately, “reports are notably lacking in sessile molluscs, primarily due to the difficulty of quantification of behaviours that occur in these generally small animals whose behaviour is characterized by minimal movement carried out over comparatively long time periods. Such movement may, however, be critical in survival and its quantification may provide insights into strategies and environmental conditions of consequence for this important animal group (Robson, Wilson, and Garcia de Leaniz 2007).

If they were nothing but barely living filtering rocks without the ability to respond to, well, anything, as the Sentientist wants you to believe, why do mussels have a need to detect and respond to predators, or even respond to stress at all? The Sentientist claims mussels and oysters cannot respond to stimuli simply because their reaction to it doesn't stem from a central nervous system while ignoring the fact that they do have a nervous system.

Images: Excerpts from the Sentientist's Article "The ethical case for eating oysters and mussels"

Gartner & Litvaikis (2013) found that blue mussels “selectively alter byssal thread production and movement in the presence of injured conspecifics and potential predators.” In addition, Robson, Wilson, and Garcia de Leaniz (2007) found that “mussel response to predation is graded and complex and may well indicate animal-based assessments of the trade-off between effective feeding and the likelihood of predation." <-- isn't this a form of decision-making?

Opioid receptors have also been observed and studied in mussels (Aiello 1986; Cadet and Stefano 1999) AND to quote the Sentientist herself, “Many animals have opiate receptors, indicating they are making painkillers and regulating pain within their own nervous system.

Well, “investigations have shown that similar opiate systems may have a functional role in invertebrate nociception (Fiorito, 1986; Kavaliers, 1988). In addition, “Opiate binding sites, with properties similar to those of mammalian opiate receptors, have been shown to be present in the neural tissue of the marine mollusk Mytilus edulis (Kavaliers et al., 1985)”

 – M. edulis is a species of mussel!

Image: An excerpt from the Sentientist's Article "The ethical case for eating oysters and mussels"

Yet AGAIN, the Sentientist admits that she's not even confident in her statements! And she really shouldn't be because they are based on pretty much no reliable evidence. 

Unfortunately, the Sentientist actually misunderstands her own quote, which she tries to use to convince the reader that bivalves are not capable of response to pain. Cronk & Walters (2011) state, “to our knowledge there are no published descriptions of  behavioral or neurophysiological responses to tissue injury in bivalves.” That certainly does NOT mean, as she states, “previous studies have not shown this kind of response in bivalves.” What they say is that there are no published studies, as in, no studies have been published. Therefore, at the time of publication of their paper, no publications existed that had established neurophysiological or behavioral responses to tissue injury in bivalves. They just did not exist, so they could not determine whether they react or not to tissue injury with pain. If previous studies had determined a lack of response, the authors would have stated something like, “previous studies have determined a lack of response to tissue injury in bivalves.” How else does one know no studies exist(ed)? Because the authors do not cite any research at the end of the statement. They are simply saying the research hasn't/had not been published.

Image: An excerpt from the Sentientist's Article "The ethical case for eating oysters and mussels"

The same article quoted by the Sentientist above as proof that some bivalves are OK to eat as vegans, concludes, ironically, that, “Scientifically accepted definitions of pain and nociception neatly distinguish these concepts (e.g., Merskey and Bogduk 1994), but drawing a line between the two can be difficult in practice. Furthermore, no experimental observation of nonverbal animals (nonhumans) can demonstrate conclusively whether a subject experiences conscious pain (Allen 2004). Suggestive evidence for painlike experiences in some animals is available, and nociceptive responses measured at the neural and behavioral levels in molluscs have provided evidence that is both consistent and inconsistent with painlike states and functions. Unfortunately, inferences drawn from the relatively small body of relevant data in molluscs are limited and prone to anthropocentrism. Identifying signs of pain becomes increasingly difficult as the behavior and associated neural structures and physiology diverge from familiar mammalian patterns of behavior, physiology, and anatomy, making interpretation of responses in molluscs particularly difficult." This does not only refer to cephalopods though. This is a general statement inclusive of all mollusks.

A “disembodied finger,” which the Sentientist describes akin to oysters and mussels, doesn’t have any reaction to anything because it's basically dead. As I have cited, we have studies that show the opposite of what the Sentientist claims. Mussels have responses to stimuli (Stephano 2002), including stress (Anestis et al. 2008), and as we have seen, may make decisions based on threats of predation ((Gartner & Litvaikis (2013); Robson, Wilson, and Garcia de Leaniz (2007)). 

Last time I checked, a disembodied finger doesn’t respond to stimuli or display any behavior at all.

Image: An excerpt from the Sentientist's Article "The ethical case for eating oysters and mussels"

Sentience in Veganism

Veganism is a lifestyle that stands up against the exploitation of nonhuman animals. Exploitation and Animals are the key words when it comes to a vegan lifestyle. Nowhere does the definition include a lack of sentience as a determining factor in which to exploit an animal species or not. Are oysters, mussels, and other species sentient in the way that we are? I have no idea, but there isn’t a single published study that will establish that they are not sentient or that will full out tell you they don’t have the ability to respond to their environment or react in a non-automatic way. Research is still on going. Read more in Part II of this topic.

A lack of research and VERY vague ideology based on

unsupported statements does NOT justify adding an 

animal species to the vegan food chain.

Sources – where is your proof?

I keep reading about all that research that has been done, but no one seems to be able to provide me with all these studies that have determined oysters and mussels are basically rocks with plant-like features mistakenly classified as animals. Who classified these animals as the lowest sentient beings? The only multi-cellular animal without a nervous system are sponges, not any of the bivalves.

The key issue that continues to surface is sentience based on unsupported comments like “No brain, no pain,” as someone claimed, but where is the conclusive data?

WHERE ARE YOUR SOURCES?

Image: Photo comment used by someone on a facebook group discussion to justify the Sentientist's article "The ethical case for eating oysters and mussels"

Also, mushrooms are the fruiting bodies of fungi; therefore, mushrooms are not comparable to animals or even plants in any shape or form. 

Environmental impacts

I’m not going to go very much into this because as an ethical vegan, an environmental stance is not above direct harm to a living being. However, fecal matter accumulation from mussel farms can lead to problems of sedimentation for species not adapted to dealing with low oxygen levels caused by sedimentation and large quantities of waste products. This is one example of a negative impact that such farming can have: http://icesjms.oxfordjournals.org/content/58/2/411.full.pdf 

What would farming mussels and oysters look like for 7 billion people? 

The Sentientist made assumptions that such farming may be more beneficial, but made no calculations or further looked into it to provide any credible evidence. She also did not take into account the negative impacts that have already been recorded from such farming practices.

"There is a considerable body of research on the environmental effects of mussel farming within and outside New Zealand, reviewed in detail elsewhere (Morrisey & Swales 1997; Kaiser et al. 1998; Inglis et al. 2000; Sinner 2000; Cole 2001; Kaiser 2001; Broekhuizen et al. 2002). Environmental effects may arise from mussel feeding habits, farm structures or activities associated with mussel cultivation. Documented environmental effects include: phytoplankton depletion, modifying the benthic environment and species assemblages, altering local hydrodynamics, increasing marine litter, and facilitating the spread of unwanted organisms. The severity and extent of environmental effects is influenced by many factors including size and age of the farm, stocking densities, water depth and flow regimes, season and climatic conditions." http://www.doc.govt.nz/Documents/science-and-technical/musselfarms04.pdf 

Sorry, but what was that about no negative impacts? The above is for rope-cultured mussels, by the way. 

It would be naive to assume that because species like phytoplankton (most likely categorized as non-sentient and therefore, unimportant...?) are some of the species affected that an impact on them would not affect macrospecies in anyway. This is particularly true because phytoplankton form the basis for many, if not most, marine and fresh water food chains. However, I can only guess what "non-sentient" species the Sentientist was talking about since she didn't bother to say.

Read more about this topic in Part II.

Image: An excerpt from the Sentientist's Article "The ethical case for eating oysters and mussels"

In Essence…

I'm a scientist, and I believe in showing evidence to back my claims and actually doing research before making statements that can't even be determined and might lead a whole group of species to even more exploitation and death.  

Saying vegans don't eat any species of animal has nothing to do with being a purist; the fact remains that ALL bivalves are animals and regardless of being "less developed" than us, vegans don't eat animals. If you want to eat animals and plants, as science has established, you are an omnivore. 

Sentiency for non-invertebrates is something that, as I've explained above, is a concept that may not be applicable to species that are physiologically completely different to us in the same way because we, living life as vertebrates, can't understand how they would process it or how it would manifest in a completely different life form.   

The Sentientist, hailed as an authority on the ethics of eating bivalves fails to make a case for eating mussels and other bivalves since her stance is riddled with errors, unsupportive statements, misinterpretation of theories and misunderstanding of published reports. She does a poor job of providing any evidence for all of her arguments. Her disembodied finger comment does not help the case either since bivalves are living animals while a dead finger is just a dead finger.

Linking to definitions in text books, blog posts from slate, or quoting philosophers, doesn't a sound argument make...I checked her citations/links, and they include wikipedia definitions, text book descriptions of terms, blogs, and more that are not considered reliable evidence for the statements that she makes.

Image: An excerpt from the Sentientist's Article "The ethical case for eating oysters and mussels"

Some of her sources/footnotes are also somewhat confusing. I don't understand what many of them have to do with her arguments and still lack evidence/reliability. I find it particularly confusing when she includes a random quote about tunicates to make a failing case about brains not being biologically expansive (what does this have anything to do with tunicates - why didn't she discuss it as it relates to them if it is so vital to her argument?). 

When making an argument, which would impact an animal species so greatly, one should always be able to back their position with science literature and other reliable evidence and sources. 

It's also important to note that non-exploitation and animals are keywords in veganism.

Qualifications

The author of this post has a B.S. in Biological Sciences with an emphasis in Marine Science and a M.Sc. in Conservation & Ecology with an emphasis in research. Other experiences include, but are not limited to, aquaculture, molecular biology, fungal and plant symbiosis, and invasive species ecology. The author is also vegan, which means the author does not consume or consciously exploits any species of animal. 

References (that are not linked above, please let me know if I missed something!)

Aiello, Hager, Akiwumi & Stefano (1986), An Opioid Mechanism Modulates Central and Not Peripheral Dopaminergic Control of Ciliary Activity in the Marine Mussel Mytilus Edulis, Cellular and Molecular Neurobiology, Volume 6, Issue 1, 17-30.

Anestis, Pörtner, Lazou1 & Michaelidis (2008), Metabolic and molecular stress responses of sublittoral bearded horse mussel Modiolus barbatus to warming sea water: implications for vertical zonation, Journal of Experimental Biology 211, 2889-2898.

Croock & Walters (2011), Nociceptive behavior and physiology of molluscs: Animal welfare implications, ILAR J, 52(2):185-95.

Gartner & Litvaikis (2013), Effects of injured conspecifics and predators on byssogenesis, attachment strength and movement in the blue mussel, Mytilus edulis, Journal of Experimental Marine Biology and Ecology, Volume 448, October 2013, Pages 136-140.

Robson, Wilson, & Garcia de Leaniz(2007), Mussels flexing their muscles: a new method for quantifying bivalve behaviour, Mar Biol., 151:1195–1204. 

Sara (1984) Reproductive strategies in sessile macrofauna, Boll. ZOO. 51: 213-248.

Schmidt-Nielsen (1997), Animal Physiology: Adaptation and Environment, Cambridge University Press, Apr 10,  pp 421-423 (Note: I have this book from university, so I had to summarize the information instead of quoting it directly into the text)

Smith (1991), A Question of Pain in Invertebrates, ILAR J,  33 (1-2): 25-31.

Stefano , Cadet, Zhu, Rialas, Mantione, Benz,  Fuentes, Casares, Fricchione, Fulop, & Slingsby (2002), The blueprint for stress can be found in invertebrates, Neuro Endocrinol Lett., 23(2):85-93.

Volkov, Adesina, Vladislav, Markin, & Jovanov (2008), Kinetics and Mechanism of Dionaea muscipula Trap Closing, Plant Physiology, February, vol. 146 no. 2 694-702.

"Invertebrates are not ‘simple animals’, but they are indeed masters of economy: their small nervous systems contain many fewer nerve cells than those of even the tiniest vertebrates, yet these animals solve all of the same survival problems, can live in highly organized societies and can communicate complex messages. The goal of this article is to outline general features of the nervous systems of invertebrates, and to begin to ask how these tiny information-processing systems drive such diverse behaviour." 

- Thomas Matheson, University of Cambridge, on invertebrate nervous systems

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