What Does The Future Hold For ‘Low Trophic’ Sea Life?

Challenged by concerns over environmental and animal welfare issues, “seafood” providers may soon start to shift their focus from fish aquaculture to farming more “environmentally-friendly” and “simple” animals. Low trophic species — marine animals much lower on the food chain within corresponding ecosystems — are the buzz nowadays. These animals, mainly various bivalves ranging from mussels to clams or oysters and echinoderms including sea urchins and cucumbers, vary from being strict herbivores to opportunistic omnivores (e.g. urchins and cucumbers don’t shy away from aquatic invertebrates who come across their way).

“Advantages” that such aquaculture boasts include that mussel and oyster farming typically does not involve dredging, thus no other sentient animals are killed or displaced in the process. Furthermore, filter feeders clean the water while being farmed, creating safer habitats for other animals in areas of farming. However, it has already been shown that some bivalve species can become invasive. In terms of animal welfare, bivalves’ capacity to experience pain is at best a precautionary statement as things stand. However, due to their generally immobile nature, it is proposed that they would experience less pain and stress in captivity compared to other, more active animals. Be that as it may, here we will go through some of the species that may soon be exposed to more intense farming and see how they react to their surroundings. 

Bivalves In A Nutshell

Clams and scallops, the two types of bivalves that exhibit motion beyond larval stage, initiate escape swimming when a threat is detected. They also have simple eyes and chemosensory organs, suggesting that some integration of information and basic decision making thus must occur. Bivalves have simple nervous systems consisting of two pairs of nerve cords and three pairs of ganglia. They show nociceptive responses (i.e. react to noxious stimuli) such as withdrawing their siphons when prodded. Theoretically, some form of “pain” might exist although very different from how we experience it, but we are far from being sure of this. Even if there was “pain” being transmitted by the nerves, the brainless animals couldn’t possibly be aware of it and suffer. At least as far as we know it, bivalves may be lucky enough to lead pain-free lives.

There are no published descriptions of behavioral or neurophysiological responses to tissue injury in these animals. Usually, animals who experience pain tend to their wounds and act differently until healed. Bivalve pain perception opponents often claim that there are no adaptive reasons for animals who cannot effectively escape to develop the capacity to sense pain. Nevertheless, researchers highlight that across the board, evidence suggests that at least nociceptive processes are highly conserved across a diverse range of animal taxa. Although nociception is a definitive possibility, since our understanding of pain revolves around subjective experience, it is practically impossible to detect and measure it in animals very different from us, thus certain conclusions about their possible capacity to feel pain may elude us forever.

A recent Faunalytics summary has revealed that oysters sense various sounds typical for their marine environment, ranging from thunderclaps, noises made by potential predators, and the noise of our many cargo ships zigzagging the oceans. For such species that cannot relocate once disturbed by noise, the consequences can be dire and include disturbed feeding and breeding patterns, and difficulties in detecting approaching predators. And although the pandemic has potentially reduced the amount of noise-making we expose our oceans to, the trend is expected to reverse and noise levels will most likely increase with time. On a more positive note, in order to counter our incessant oceanic expansion, Canadian researchers looked into how noise pollution could be effectively reduced and regulated on a national level, inspiring optimism in animal advocates.

Noise pollution is not the only type of environmental disturbance that marine animals are exposed to. Back in 2009, researchers found that mussels and oysters in Thailand had ingested polychlorinated biphenyls (PCBs). These chemicals were widely used as additives in paints and plastics in the past. More recently, a summary highlighted that oysters nowadays ingest microplastics, too.

Another recent article summary points to human-driven speciation — the formation of new and distinct species, as a key contributor to invertebrate extinction. In fact, the study suggests that mollusks may be disproportionately affected by us – out of 359 invertebrates gone extinct, they made up 81%. The animals face threats in confinement, too. Apparently, disease outbreaks keep hitting the European oyster industry. There, the farmers resort to importing oysters from other ecosystems, in turn endangering local mollusks, as well as the coastal environment via invasive hitch-hikers that come with the brought oysters.

Pain or no pain, do bivalves truly sense their environment and actively react to changes? One study found that low water salinity leads to poorer immune function in mussels. Similarly, the animals altered their breathing patterns after being manhandled. Another scientific article reported that bivalves experienced negative impacts at biochemical, physiological and behavioral levels both at low and high water salinity conditions. Similarly, other researchers found that both biochemical stress indicators and metabolic status respond when the animals are exposed to extreme temperatures. This may have animal welfare implications as bivalves are typically transported and stored out of water, in ice and handled roughly due to their perceived strength, being within a shell and all. In the wild, extended exposure to such sub-optimal conditions, be it due to fishing activities or climate change, is expected to reduce species’ resilience and induce organism vulnerability to pollutants and other environmental externalities. 

Even more fascinating bivalvian capabilities have been revealed. The researchers found that blue mussels change their behavior when in the presence of injured mussels and potential predators. It was shown that small mussels seemed to be most distressed. In addition, researchers observed that mussels closed their shells much faster when under threat of predation. However, the animals reacted differently to various predators, indicating that such responses are graded and complex. The variations could imply that animal-based trade-off assessments between feeding and being attacked take place. Further highlighting the impressive anti-predatory behavior of mussels, another study adds that mussels within a group remained closed less time compared to their solitary counterparts – a behavior consistent with lower individual vulnerability to predation in group-living settings. Interestingly, the researchers also found that individuals showed consistency in how they close up, suggesting that they might comply with behavioral syndrome theory – a principle used to explain why some individuals of the same species are generally more bold or active. In either case, it is clear that mussels put their defenses up when needed, and are up for a fight.

Very little research is available on the nociceptive capacities of oysters. Unfortunately, there are many research groups that focus on how we can effectively farm the animals, instead. Out of the few that did study how the animals behave, one study found that oysters grew larger, heavier, and stronger shells when growing up in environments with potential crab predators. Here, too, the animals reacted differently to different types of predators, hinting to species-based trade-offs, but changing their shell morphology was effective against predation. Regardless of being immobile as adults, mussels and oysters are still nothing like plants — they need to actively react to their environment to protect themselves and carry out biological functions vital for their survival.

The Spiking Interest In Echinoderms

Echinoderms such as sea urchins, cucumbers and starfishes have unusually-structured nervous systems, with clusters of neurons in each limb. Very little research has been done on studying nociception in these animals. Interpretations made based on the very limited body of relevant data in mollusks and echinoderms are uncertain by definition and often prone to anthropocentrism.

Some research has found that urchins use their spines to see and that they move purposefully. Interestingly, their motion was highly consistent, challenging claims that echinoderms are randomly acting automata. The researchers suggest that the vision may help urchins seek shelter and avoid large predators. Other research has found that sea urchins react strongly to predatory fish, potential prey and injured fellow urchins in vicinity, albeit via chemosensing. Finally, other observations show that temperature, water pollution, and injuries affect the animals on cellular and biochemical levels. 

Despite their derogatory names, sea cucumbers also are motile animals, observed to contract and retreat from danger. Researchers found that their response often starts with local contraction and crawling, bending of the body, and, ultimately, culminating with active swimming. Potential welfare issues arise when fishermen are transporting and storing the caught sea cucumbers. They are often stored dry on boat hulls or stacked crowded in bins with insufficient seawater. Research has recently shown that desiccation is extremely stressful for most sea animals, including sea cucumbers. They conclude that, depending on the temperature, 6hrs in air leads to irreparable physiological and immunological damage.

One study by a leading expert in all things sea cucumber, highlights that most sea cucumber fisheries worldwide are ineffectively managed and animal stocks are declining. The researcher points out that gaps in fisheries biology knowledge of even the most commonly targeted species lead to population collapses and with an estimated 3 million sea cucumber fishers worldwide – that’s quite a risk. Regulatory enforcement should be ensured in low‐income countries, where the level of biodiversity loss is particularly high.

Moving onto strictly carnivorous echinoderms, starfish, although not in contention for being next in line for commercial farming in aquaculture, also actively react to their surroundings. Upon injury or exposure to caustic chemicals, they retreat quickly and if positioned on a perpendicular surface, they detach and fall to the bottom of the water to escape. They are also light-sensitive and research has actually shown back in the 60s that at least some starfish can learn to associate food with a light stimulus. Other research has concluded that low temperatures, low water salinity and parasitic infection influenced the immune responses of starfishes. However, the researchers highlighted high variability across individuals, suggesting that nutritional or health status may be behind this.

Decision Time

Although seemingly less intelligent than their fellow mollusks at the top of the class – sea hares and octopuses — bivalves and echinoderms are animals nonetheless. Be it motile or immobile, they have nervous systems and react actively to changes in their environment. The key question for animal advocates here is on what basis should we decide whether these animals deserve protection and to what extent? Should we take the precautionary approach and say “Hey, they MIGHT feel pain!” or advocate for their right to live and be free based on other physiological capabilities? Or should we take on a kingdomist approach altogether, and deem all animals worthy of protection merely because we all belong to the same animal kingdom? As of yet, there is no scientific evidence that their sensory capacities go beyond automatic reflexes to nociception, they do not tend to their injuries and not much data backs higher cognitive capacity such as associative learning.

Some may argue that beyond taking pain, suffering, and sentience into consideration, we may soon resort to protecting plants, too. The major difference between the defense mechanisms employed by plants and, for instance, bivalves are their activity. Essentially, it boils down to whether the particular lifeform moves. The venus flytrap plant also reacts to stimuli and moves, but it would not be beneficial for it to feel pain as it cannot avoid it, rather – its motility is targeted at nutrient acquisition instead of defense. Animal advocates and biologists aside, bivalves, echinoderms and plants are often thought of similarly, with widespread use of terms such as “collecting oysters”, “growing sea urchins”, “bivalve seeds (here referring to the young used in farming)” and “harvesting sea cucumbers” promoting the misconception further. 

The question is definitely not an easy one – these ethical waters are murkier for most than other types of animal consumption. We as a society need to decide which and whether certain capabilities can deem beings worthy of being included in our circle of moral consideration. Protection means welfare factors need to be identified and enforced in potential farming applications. But beyond that, looking at the bigger picture, should animal product consumption be shifted towards low trophic animal aquaculture, can we expect a lower total of sentient beings killed? The predicted low environmental impact and no mortality of sentient beings in bivalve farming adds complexity to the equation, even when comparing to the impacts of strictly plant-based diets. Which shall we choose, promoting the shift towards and allowing animals who may not feel pain to be farmed, or trying to prevent it, and continuing our efforts towards the protection of the well-being of other aquatic animals currently farmed at increasing rates? Which would be more effective and reduce the overall suffering of non-human animals?