Month: June 2014

Acid trip: ocean acidification alters marine animal behaviour

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Ocellaris clownfish, Amphiprion ocellaris
Ocellaris clownfish, Amphiprion ocellaris. Photo: Wikipedia
When assessing the impacts of ocean acidification (OA) on marine animals, peer-reviewed studies predominantly address the mortality and physiology of these organisms. However, over the past few years, it has become apparent that animal behavior can also be altered under increasingly acidifying conditions.
A recent study by Sue-Ann Watson and colleagues at James Cook University in Australia demonstrated that near-future CO2 levels can interfere with neurotransmitter functioning (i.e., chemical functioning of the brain), leading to a 50% decrease in predatory escape behavior in a species of marine gastropods, making them more susceptible to being eaten by predators in high-CO2 conditions. Studies have also suggested shifts in the behavior of various fishes, including increased anxiety in rockfish, hindered hearing behavior in clownfish, and reduced swimming behavior in dolphinfish, with the likely mechanism being hindered neurotransmitter functioning. Some of these observations in fishes have also been translated to invertebrate organisms as well. Alongside these behavioural modifications under acidic water-column conditions, some interesting research on the east coast of North America has also been suggesting that juvenile clams can change their behavior in response to increased acidification as well, except in this case, the clams respond to sediments and not the water column.
If exposed to acidic conditions for a long enough time period, the shells of living molluscs begin to dissolve and can ultimately lead to their death.
If exposed to acidic conditions for a long enough time period, the shells of living molluscs begin to dissolve and can ultimately lead to their death. Photo: J. Clements
Before they mature and dig into sediments at the bottom of the ocean in coastal areas, clams go through what is called a larval stage, where they swim around and develop in the water column (this is akin to a caterpillar and a butterfly – the caterpillar is the larvae and the butterfly is the mature). After a certain period of time, the larval clams will sink to the bottom to start their life as mature animals. However, before they dig into the sediment to start the next stage of their life, they can test the chemistry of the sediment and make a decision as to whether or not it is an appropriate place to live. So if they don’t like the initial place where they land, they can refuse to burrow into it and may be able to move to a different area.
Recent research has suggested that the acidification of these sediments may impact the behavior of these clams in their decision to dig or leave. One study conducted by Mark Green and colleagues at St. Joseph’s College in Maine, USA assessed the impact of increasing acidification within marine muds on the burrowing behavior of juvenile quahogs (Mercenaria mercenaria).
By manipulating the level of acidity in different containers of soft-sediment and watching whether or not clams burrowed into them, the scientists were able to determine that as the sediment becomes more acidic, the clams reject it and don’t burrow – the first time that acidification was found to have an impact on clam burrowing behavior.
Given this interesting result, researchers at the University of New Brunswick in New Brunswick, Canada wanted to see if this lack of burrowing actually resulted in the clams moving away. By taking the same approach as Green and colleagues, only with a different species of clam (soft-shell clam, Mya arenaria), myself and Dr. Heather Hunt (see “Publications” to download a PDF) observed the same trend of burrowing behavior that Green and colleagues did in their study – more acidic sediments had less clams burrowing. However, by adding flowing water to the experiments (a means by which soft-shell clams move), we were able to determine that when sediment was more acidic, more clams left than when sediment was not as acidic.
At high levels of acidification (low values of Ωaragonite on x-axis), fewer clams burrow into sediments (left panel), while more clams move away (right panel). Source: Clements & Hunt (2014)
At high levels of acidification (low values of Ωaragonite on x-axis), fewer clams burrow into sediments (left panel), while more clams move away (right panel). Source: Clements & Hunt (2014)
The combined results of our study and those of Green and colleagues provide evidence that the acidification of marine soft-sediments can influence the behavior and population dynamics of juvenile clams by altering their decision to burrow and subsequently their dispersion. Since acidic conditions dissolve the shells of these animals and result in death, this could be the reason why the clams decide to move away from these acidic muds. Other reasons are possible, however. For example, increased concentrations of CO2 may depress other physiological functions such as respiration, metabolism, or feeding, which would also contribute to the negative burrowing cue (recruitment cue) detected in these two studies.
Juvenile soft-shell clams used in the Clements & Hunt (2014) study. Bivalves are most susceptible to the impacts of OA in their early life stages. Photo: J.Clements
Juvenile soft-shell clams used in the Clements & Hunt (2014) study. Bivalves are most susceptible to the impacts of OA in their early life stages. Photo: J.Clements
These studies, along with others, highlight the impact of ocean acidification on the behavior of marine-dwelling animals. Changes in behavior have the potential to impact these animals in both positive and negative ways.
The bright side, at least for clams, is that if they can avoid more acidic sediments and move to better ones,  they enhance their chances of avoiding “death by dissolution” or other stressful conditions, so long as there is enough suitable mud available! However, by not burrowing immediately, the clams do put themselves at a higher risk for other mortality factors, such as predation. Ultimately, scientists have much work to do in determining how the future chemistry of our oceans could impact the behavior of marine organisms and how this could in turn influence their survival.
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Is de-extinction really a good idea?

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Given the current sequencing of its genome, the woolly mammoth (Mammuthus primigenius) is a top candidate for de-extinction.
Given the current sequencing of its genome, the woolly mammoth (Mammuthus primigenius) is a top candidate for de-extinction.
In March of 2013, a group of scientists gathered in Washington, D.C. at the TEDxDeExtinction meeting and proposed the idea of de-extinction. Yes, de-extinction is exactly what it sounds like – bringing extinct species back to life using genetic tools (biotechnology) to recreate (clone) various extinct organisms from their reassembled DNA. The idea is both exciting and interesting; however, given some of the ideas brought forward regarding such an undertaking, perplexity as to why we would bother bringing back extinct species rather than trying to preserve extant ones becomes apparent.
The concept is surely intriguing and would be one of the greatest achievements science has ever accomplished, but the idea brings forth many questions as well – particularly when it comes to ecology. For instance, how would the ‘resurrection’ of extinct species like the dodo or the woolly mammoth alter current ecosystem structure and, if we do have a grasp on how the re-introduction of these species would affect current ecosystems (which, for some, we do), will the changes be acceptable in terms of ecosystem stability and sustainability? In other words, will current ecosystems be able to sustain these organisms, given that these systems are drastically different from when such extinct organisms existed; will the current state of these systems remain stable with the introduction of these new (yet old) species? Furthermore, are we, as humans, willing to accept the associated consequences of bringing back an extinct species that simply appears “cool” or interesting?
An example of the basic concept of bringing extinct animals back to life.
An example of the basic concept of bringing extinct animals back to life.
Releasing these recreated species into the wild is easily comparable to releasing an invasive species into a novel ecosystem, and the consequences of doing so are often devastating. Of course, some of these species may have the ability to enhance biodiversity and other such metrics of ecosystem health, in which it may be beneficial to reintroduce them; but why not use these de-extinction techniques to enhance current ecosystems supporting extant organisms rather than reviving previously existing ones? Bringing back extinct species could also allow for the exploration into how these species initially became extinct, which could aid in enhancing conservation efforts for current species, whether endangered, threatened, or at risk. In artificial scenarios, these organisms could be utilized to make better predictions regarding how some extant organisms, even our own species, may be influenced by future climatic conditions or other potential extinction events. However, ethical implications then arise – do we establish populations of these organisms or just keep exposing them to conditions inducing extinction to better understand future scenarios/implications (i.e., do we keep them alive or just keep killing them)?
Stewart Brand revisiting the Conservation Pledge during his TEDTalk ‘The Dawn of De-extinction’ (photo credit: Jurvetson, Flickr).
Stewart Brand revisiting the Conservation Pledge during his TEDTalk ‘The Dawn of De-extinction’ (photo credit: Jurvetson, Flickr).
Additionally, to use the recreated organisms for this purpose, artificial ecosystems must be manufactured. Creating artificial ecosystems to bring back these organisms to life makes sense, but the historical ecosystem complexity that existed such a long time ago must be recreated with accuracy. This may not be difficult for some species, but for others it would – all this without mentioning the financial costs associated with such studies and how many species of other organisms that would have to be brought back in order to create these complex systems (many of which we don’t have the DNA for). Other questions also arise with keeping such complex populations/systems in concealment. For example, reproduction and mortality rates of revived species would have to be taken into account to sustain a confined population. If populations are to be sustained, these organisms will eventually have to be released, in which the slurry of ecological problems mentioned above then arise.
Although a ‘Jurassic Park’ scenario is not yet within our reach (nor is it likely to be), the ecological consequences of introducing genetically manufactured species which do not belong in a given ecosystem may be more detrimental than beneficial. The prospect of de-extinction is indeed interesting and stimulating, but much more thought regarding the ecological consequences of sustaining populations of such organisms must be established, and we must better understand the  beneficial or detrimental implications of such an endeavor. Clearly defining the purpose of implementing this type of technology must be well entrenched before woolly mammoths or kakapos are released into the wild along with the current flora and fauna.