marine

Seven Spooky Species

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Leading up to Halloween night, I recently embarked on a #scicomm project via social media (Facebook and Twitter), sharing information about #SevenSpookySpecies from the ocean. The project was fairly successful in engaging people on Facebook (95 likes, 19 interactive comments, and 3 shared posts), and Twitter (26 likes and 23 retweets). I was able to spark interest in followers by introducing people to the the biology of skeleton shrimps, vampire squids from hell, ghostly shrimps, humpbacked anglerfish, creepy crawly spider crabs, giant isopods, and alien amphipods. I very much enjoyed delivering this series of fun (and maybe a little bit creepy) marine species. In fact, I plan to make this an annual series leading up to Halloween. Nonetheless, I wanted to make it accessible for those who may have missed my posts.

So without further ado, here are my picks for this year’s #SevenSpookySpecies!

#7. Skeleton shrimp, Caprella mutica 

Japanese skeleton shrimp (Caprella mutica)
Japanese skeleton shrimp (Caprella mutica)

Commonly known as the Japanese skeleton shrimp, Caprella mutica is native to eastern Asia and is considered an invasive species in Atlantic Canada, first reported in the Bay of Fundy in the 1990s (although it’s ecological impacts as an invader are not well understood). These guys can often be found in high densities on ropes, buoys, mussel socks, and other man-made structures. They are quite small, with males reaching a maximum size ~3.5 cm and females reaching a maximum size ~1.5 cm. The males’ neck and claws are super hairy and the males also have a segmented neck (2 segments).

#6. Ghost shrimp, Neotrypaea californiensis

Ghost shrimps (Neotrypaea californiensis) are an intertidal species found on the Pacific coast of North America. These shrimps are fairly pale in appearance and can reach a maximum size of just under 12 cm body length. Neotrypaea californiensis live underneath the sediment surface in U-shaped burrows that reach to the surface of the sediment – as such, they’re referred to as “infaunal” species (species living within the sediment). These burrows have many branches or arms and support a diverse array of other species, including snapping shrimps, copepods, crabs, and clams.

Bay ghost shrimp (Neotrypaea californiensis)
Bay ghost shrimp (Neotrypaea californiensis)

In Canada, they can be found in soft-sediment intertidal habitats (mud- and sandflats) of British Columbia where they residewith other infaunal shrimps (mud shrimps, Upogebia pugettensis). Together with mud shrimps, ghost shrimps can often be found in high densities, which can result in significant amounts of bioturbation (i.e. sediment disturbance). Because they are such efficient bioturbators, it is thought that ghost shrimps (and mud shrimps) positively affect their surrounding ecosystem increasing primary and secondary productivity, and by reducing the system’s susceptibility to eutrophication (nutrient loading). However, this bioturbation can have negative effects on the production of oyster beds and they’re often considered pests. As such, mudflats with high densities of mud and ghost shrimps are often sprayed with insecticides to remove the “pests”. These shrimps are also often used by fishermen as bait.

The adults of this species display claw dimorphism (or claw asymmetry) – meaning that one claw is bigger than the other. This feature is more pronounced in males, where the large claw can account for as much as 25% of the male’s body mass (see image below) – imagine one of your hands occupying 25% of your weight! The larger claw in males is thought to be used when two individuals are competing for a mate and is thus likely an evolutionary product of sexual selection.

#5. Spider crab, Macrocheira kaempferi

Japanese Spider Crab (Macrocheira kaempferi)
Japanese Spider Crab (Macrocheira kaempferi)

Having the largest leg span of any living arthropod, the Japanese Spider Crab (Macrocheira kaempferi) resides in the waters off of Japan. This species can have a leg span of up to 18 feet (5.5 meters) from claw to claw and is thought to live up to 100 years (although ageing crustaceans has proven difficult). M. kaempferi can weigh up to >40 lbs, making it the second heaviest living arthropod, (second to the American Lobster).

Japanese Spider Crab (Macrocheira kaempferi)
Japanese Spider Crab (Macrocheira kaempferi)

Japanese Spider Crabs use their thick and durable exoskeleton to protect themselves from predators. However,they also utilize camouflage to avoid being detected by their predators, as their carapace blends well with the sea bottom. Even more, these crabs use a super cool behaviour called decorating to disguise themselves, whereby they cover their shells in algae, sponges, and other plants and animals to enhance its cryptic appearance on the ocean floor.

Japanese Spider Crabs are omnivorous. They can use their claws to gather seaweed and algae from the ocean floor, or to pry open the shells of shellfish. Additionally, these crabs are also known to scavenge on the carcasses of dead animals on the sea floor. A small fishery for this species exists in Japan. However, population declines have meant that fishermen need to fish deeper waters to catch this species and have initiated considerable conservation efforts to protect their populations. Nonetheless, these crabs aren’t an easy catch, as they are very fast and can cause considerable damage to humans with their strong claws and long reach!

#4. Vampire squid (from Hell), Vampyroteuthis infernalis

Not an octopus, not a squid, and residing in deep temperate and tropical seas, Vampyroteuthis infernalis (which translates to “vampire squid from Hell”) is a small cephalopod reaching a maximum body length of ~30 cm. This animal is unique in that it contains the features of two other groups of cephalopods: octopuses and squids! The vampire squid has 8 arms (like an octopus) which support a web of tissue. Concealed behind this web of tissue are two “retractile sensory filaments” – sensory structures akin to squid tentacles that retract into pockets of tissue that are used to detect predators and prey (and other environmental attributes). As such, the vampire squid is placed in its own Order taxonomically – the Vampyromorphida. Because the Vampyromorphida have the features of both octopuses and squids, it is thought that this group of animals may represent a common ancestor to modern octopuses and squids. Interestingly, Vampyroteuthis infernalis is the only extant (still living) species of Vampyromorphida (as far as we know; we still have a lot to learn about the deep sea).

Vampire squid (Vampyroteuthis infernalis)
Vampire squid (Vampyroteuthis infernalis)

Behaviourally, when these animals are threatened, they use a defense response known as the “pumpkin” or “pineapple” posture. When a vampire squid is threatened by a predator or superior combatant, it throws its arms back over its body and the web of tissue acts as a “cape”. When the cape covers the body, it displays intimidating (but completely harmless; they’re simply constructed of soft tissue) spines, or “fangs”; hence the vampire reference. In addition, the animal uses bioluminesence when in the “pumpkin” or “pineapple” posture, where the tips of its arms flash light and trick a predator into biting the tips of its arms, rather than biting vital structures. Luckily, if a predator does dismember a vampire squid’s arms, they can regenerate.

A vampire squid from Hell that displays a pumpkin posture – definitely a spooky species!

#3. Humpback anglerfish, Melanocetus johnsonii

Chosen as species #3for its Quasimodo-esque name (of course, any anglerfish would suffice as a spooky species), Melanocetus johnsonii is a species of anglerfish belonging to the family Melanocetidae, which are more commonly known as “the black seadevils”. This species lives in the deep sea and can reach depths of up to 4500 m below the surface. M. jonsonii is considered fairly ubiquitous, having been found in tropical and temperate waters of all five oceans.

As in other anglerfishes, female M. johnsonii (max. size of 18 cm) are much larger than the males (< 3 cm). It is black in colour and has a broad, deep head with

Humpback anglerfish (Melanocetus johnsonii)
Humpback anglerfish (Melanocetus johnsonii)

very small eyes. Like other anglers, the humpback anglerfish possesses an illicium (or esca) – a “fishing lure” – on its head. This lure dangles near the angler’s mouth and uses bioluminescence to attract prey (remember Finding Nemo?). These predators can consume fairly large prey items – indeed a 5 cm female is recorded to with 3 fish >10 cm body length in its stomach!

While it is certainly most difficult to study anglerfish behaviour, their reproductive strategies are fairly well known. In many anglerfishes, when a male finds a female mate, he attaches himself to her permanently and acts as a parasite, releasing sperm and mating with the same female for the duration of their existence (i.e., males are often monogamous). However, while male M. johnsonii do attach to females for mating, they do not attach permanently, release from the female once she has been inseminated, and will seek other mates.

#2. Giant isopod, Bathynomus giganteus

Giant isopod (Bathynomus giganteus)
Giant isopod (Bathynomus giganteus)

If you’ve ever turned over an old log, you may have noticed a number of small, grey “bugs” that are commonly referred to as woodlice or pill bugs. These actually aren’t insects, but belong to a group of arthropods known as the Isopoda! While the thought of those little woodlice may have your skin crawling, they pale in comparison to their deep-sea relatives, the giant isopods!

Giant isopods belong to the genus Bathynomus, of which there are approximately 18 species. Within this genus, Bathynomus giganteus – first described in 1879 – is often considered the largest isopod in the world with a maximum length of 76 cm and a maximum weight of just under 4 lbs. It is likely, however, that other Bathynomus species likely reach comparable sizes. Given their overwhelming size, giant isopods are a great example of deep sea gigantism (the tendency of deep sea species to be far larger than their shallow-water counterparts).

Giant isopod (Bathynomus giganteus)
Giant isopod (Bathynomus giganteus)

The morphology of giant isopods is highly similar to their terrestrial relatives (woodlice) except for the obvious difference – their size! B. giganteus are scavengers on the sea floor and can be found at considerable depths of >2,000 meters (but also at shallower depths of approximately 170 m)! As such, B. giganteus must be able to withstand incredible pressure and extremely low temperatures (which is one potential explanation for deep sea gigantism).

These isopods are primarily carnivorous scavengers, feeding on pelagic animals that perish and sink to the sea floor. They may also act as predators, eating live animals on the sea bottom. Because food is scarce in the deep sea (another potential explanation for deep sea gigantism), however, giant isopods will essentially eat whatever they come across. When they do find food, they often gorge themselves to the point that they can no longer move (kind of like after a big Thanksgiving turkey). They are also thought to be fairly aggressive animals, as they’ve been documented attacking trawl cages and live fish – one was once filmed attacking a shark by latching onto and eating the shark’s face! While that might sound a bit unnerving, you might consider doing the same thing if you had to go upwards of 5 years without eating (as I said, food is scarce in the deep sea)!

#1. Alien amphipod, Phronima sedentaria

Phronima sedentaria is a deep sea amphipod that can be found at depths of up to1,000 m. The females of this species can reach lengths of >4 cm and are larger than males, which only reach up to 1.5 cm. P. sedentaria resides in temperate, subtropical, and tropical waters and can be found in all five of the world’s oceans. While it can reach extreme depths of up to 1,000 m, it is most commonly found in midwater pelagic habitats and can even be found at the surface.

Alien amphipod (Phronima sedentaria)
Alien amphipod (Phronima sedentaria)

So you may be wondering why the hell I chose this species as my most favorite spooky species – this little guy doesn’t seem so scary at all! That is until you realize that the queen Xenomorph in “Alien” is likely based on this tiny deep sea amphipod. While much smaller than the alien queen, the outward appearance is highly similar. For a super detailed comparison between the two, check out this killer post from Michael Bok at Southern Friend Science published back in 2010.

Not only do these amphipods look like Xenomorphs, but P. sedentaria also exploits a host organism to reproduce – just like Xenomorphs! Females will hunt for salps, consume all of their living tissue to hollow them out, and essentially live inside the hollowed-out salp “barrel”. The female amphipods then use their specialized appendages (known as pleopods) to propel the barrel through the water in search of more prey, and can even do somersaults to quickly change direction. So they essentially kill, eat, and hollow out these salps, and use them as a vehicle to cruise around the deep sea in. Then, when they’re ready, the females will lay their eggs inside the barrel, where the eggs will develop and eventually hatch. Once the larval amphipods hatch, they use the salp barrel as food. When they inevitably grow up into adult amphipods, P. sedentaria become carnivorous predators, feeding predominantly on zooplankton, krill, and arrowworms – they can even take down prey more than twice their own size!

On the need to incorporate carbonate variability parameters in predicting the biological impacts of ocean acidification

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This post is published as an excerpt of a “Quo Vadimus” essay to be submitted to a special issue of the ICES Journal of Marine Science. I highly appreciate any criticisms and/or feedback on the article.

 
     Ocean acidification is expected to yield negative implications for a wide array of marine organisms in the near future, as average oceanic pH levels are projected to drop by 0.3-0.4 units by the end of the century (e.g. Orr et al. 2005, IPCC 2014). However, as with other processes affected by global climate change, variability in oceanic carbonate chemistry can also be expected to increase. For example, precipitation and temperature are expected to become more variable in the future, while the frequency and magnitude of extreme weather is expected to increase (Easterling et al. 2007, IPCC 2014). Consequently, environmental conditions within marine habitats may become more variable, including more pronounced fluctuations in marine carbonate chemistry.
     Although we can expect the variability of marine carbonate chemistry to increase in the future, oceanic pH is already highly variable both spatially and temporally, with coastal areas being the most dynamic of these systems. This variability can be primarily attributed to differences in ecosystem processes across systems. Although some studies suggest that interannual and seasonal surface ocean [CO32-] variability is negligible, except in higher latitudes (temporal and arctic regions) (Orr et al. 2005), others report fairly substantial variability. For example, a study by Dore et al. (2009) utilizing 20 years of time-series measurements suggested substantial interannual and seasonal variability, coupled with a long-term decrease in pH in the north Pacific, with seasonal trends driven primarily by changes in temperature, mixing, and the net assimilation of photosynthetic CO2.  Biological processes have also been suggested to drive seasonal variation in CaCO3 saturation states in the Arctic Ocean (Bates et al. 2009), while highly variable carbonate parameters have been recorded in California current systems (Hauri et al. 2009, Lienweber & Gruber 2013). The degree of variability in marine carbonate chemistry also varies within and among systems. For example, in the North Sea, it has been reported that a low degree of pH variability exists in biologically inactive areas (< 0.2), but a high degree of variability exists in coastal areas, particularly those around the mouths of rivers (Hinga 2002, Blackford & Gilbert 2005). Likewise, in Australia, degrees of pH variability have been shown to vary temporally and spatially, but specific trends are not always evident (Gagliano et al. 2010), while substantial variation in carbonate saturation has been reported from a Great Barrier Reef flat, although the impacts of such variability on coral calcification are unknown (Shaw et al. 2012). Sediments are also known to be highly variable with respect to carbonate geochemistry, varying by different degrees both spatially and temporally (Figure 1, Wenzhöfer 1999, Yates & Halley 2006). Annual patterns in carbonate geochemical variability have also been documented to correlate with cyclical trends in the abundance of benthic organisms (i.e., foraminiferans; Green et al. 1993). Rainfall can also impose drastic changes and substantial variability in sediments (Figure 1) and coastal systems (Doney et al. 2007), with negative relationships observed between rainfall and pH (i.e., increased rainfall, lower pH).
Figure 1. Daily (A) and bi-weekly (B) variability in surface sediment pH at three mudflats on the Bay of Fundy in southwest New Brunswick, Canada. Red arrow indicates significant rainfall event (>20 mm). Data source: Clements, unpublished data.
Figure 1. Daily (A) and bi-weekly (B) variability in surface sediment pH at three mudflats on the Bay of Fundy in southwest New Brunswick, Canada. Red arrow indicates significant rainfall event (>20 mm). Data source: Clements, unpublished data.
     Studies have provided a solid basis for understanding the complexities of marine carbonate variability. However, the ways in which these temporal and spatial trends (or lack thereof in some areas) will impact marine organisms at the various levels of biological organization are still unknown. Some studies have started to incorporate variability parameters into assessing the biological impacts of ocean acidification, suggesting that the effects of fluctuating carbonate chemistry are species specific, allowing organisms to adapt and persist or become more vulnerable in an acidifying ocean. A study conducted by Alenius & Munguia (2012) suggested that the intertidal isopod, Paradella dianae, although adapted to a high degree of variability because it lives in the intertidal zone, experiences behavioural and physiological changes under variable pH conditions compared to a stable, low pH environment, with variable conditions (low pH) yielding negative impacts on survival, oxygen consumption, and behaviour (significantly depressed swimming time and increased resting time). Cornwall et al. (2013) also observed significantly lower growth rates of coralline macroalgae under variable pH conditions relative to static conditions. On the positive side, Default et al. (2012) have reported beneficial effects of fluctuating pCO2, reporting increases in growth and survival of coral recruits under naturally-fluctuating levels of pCO2. Similarly, when assessing the impacts of static and variable pH (O2 was also assessed, but ignored here), Frieder et al. (2014) reported that low pH treatments incorporating variability resulted in quicker transitions from trochophore to veliger larvae and larger (and less variable) larval shells compared to static low pH conditions for two species of mussels (Mytilus galloprovincialis and M. californianus). Although they did not directly test the impacts of variability on animals, Shaw et al (2013b) have outlined to importance of carbonate variability on the exposure time of marine organisms to conditions either above or below current and projected means.
Figure 2. Relative percentages of studies assessing the biological impacts of ocean acidification (n=414) incorporating only static means in carbonate parameters, and those incorporating variability in carbonate parameters. Data were obtained from a preliminary ISI Web of Science search using the keyword “ocean acidification”.
Figure 2. Relative percentages of studies assessing the biological impacts of ocean acidification (n=414) incorporating only static means in carbonate parameters, and those incorporating variability in carbonate parameters. Data were obtained from a preliminary ISI Web of Science search using the keyword “ocean acidification”.
     The vast majority of studies assessing the biological consequences of ocean acidification focus their efforts on organisms raised under or exposed to static conditions based on mean predicted near-future acidification scenarios (Figure 2). Furthermore, although research has started to shift toward assessing the biological impacts of near-future OA conditions in the context of other environmental factors (e.g., multiple factors; temperature, salinity, oxygen, etc.), they have yet to focus on understanding the impact of acidification on marine fauna in the context of current and future marine carbonate variability. Because carbonate variability can modulate an organism’s duration of exposure to carbonate conditions above, at, or below current and projected means, as well as increase the extremes that the organism experiences, variability may offset the negative effects of ocean acidification, or amplify them. Since the time spent in conditions yielding biological effects is likely increase over time, along with the extremes of these conditions (Figure 3, Shaw et al. 2013a), it would be expected that future marine carbonate variability would result in more pronounced biological effects. Of the four studies directly relating carbonate variability to biological effects, two suggested that variability will act to modulate the impacts of ocean acidification (Default et al. 2012, Frieder et al. 2014). However, it is important to recognize these studies use current degrees of variability as the basis for future variability, which may be inaccurate. As such, the duration and extremes of the conditions that the animals in those two studies were exposed to could have confounded their results, as the tested duration and extremes of conditions may not have accurately depicted those of actual future scenarios (Figure 3). As such, an accurate understanding of how carbonate variability will transpire in the future, along with how marine organisms will respond to current and near-future acidification is of utmost importance for understanding the true biological impacts of ocean acidification.
Figure 3. Potential degrees of current and projected variability in diurnal oceanic pCO2 where variability increases over time (A) and where variability remains consistent over time (B). Distance between dashed lines indicate the relative amount of time organisms would be expected to spend above thresholds where they would be impacted by ocean acidification. Patterns of variability across ecosystems will differ as a result of differing types and magnitudes of various processes across systems. Adopted from Shaw et al. 2013.
Figure 3. Potential degrees of current and projected variability in diurnal oceanic pCO2 where variability increases over time (A) and where variability remains consistent over time (B). Distance between dashed lines indicate the relative amount of time organisms would be expected to spend above thresholds where they would be impacted by ocean acidification. Patterns of variability across ecosystems will differ as a result of differing types and magnitudes of various processes across systems. Adopted from Shaw et al. 2013.
Figure 4. Percentages of positive and negative biological effects of carbonate variability in ocean acidification studies incorporating variability around mean carbonate conditions (n=4).
Figure 4. Percentages of positive and negative biological effects of carbonate variability in ocean acidification studies incorporating variability around mean carbonate conditions (n=4).
     Although the current data on how variability around current and future carbonate geochemical means suggest that marine carbonate variability will have differential effects on different species (Figure 4) and that the magnitude of the effects of ocean acidification may be more or less pronounced under variable conditions (in comparison to static conditions), the number of studies that have attempted to address variability parameters in biological ocean acidification studies is negligible and insufficient to draw any generalizations. As such, it is critical that ocean acidification research, in the context of biological impacts, begins to understand current and projected localized and broad-scale variability in marine carbonate systems to accurately predict how organisms will respond under future acidification scenarios. It is also apparent that studies focusing on the biological impacts of ocean acidification need to begin understanding how the degree of marine carbonate variability is going to change with an increasingly acidifying ocean in the myriad of systems that will be impacted by ocean acidification. Understanding whether or not the variability in the marine carbonate system is going to increase, decrease, or remain the same under future climate change scenarios is imperative for predicting how marine organisms will respond to an acidifying and warming ocean. Ultimately, because ocean acidification studies focus on stable conditions under near-future predictions, our current understanding of how acidification will impact marine organisms is very limited, rendering it critical to begin understanding how acidification will affect these organisms in the context of variability around the projected means, as well as in the context of other environmental factors and their associated variabilities.

References

Alenius B & Munguia P 2009. Effects of pH variability on the intertidal isopod, Paradella dianae. Mar Freshw Beh Phy, 45, 245-259. doi: 10.1080/10236244.2012.727235.

Bates NR et al. 2009. Ocean acidification and biologically induced seasonality of carbonate mineral saturation states in the western Arctic Ocean. J Geophys Res, 114, C11007. doi: 10.1029/2008JC004862.

Blackford & Gilbert 2005. pH variability and CO2 induced acidification in the North Sea. J Mar Sys, 64, 229-241. doi:10.1016/j.jmarsys.2006.03.016.

Cornwall CE et al. 2013. Diurnal fluctuations in seawater pH influence the response of a calcifying macroalga to ocean acidification. Proc R Soc B, 280, 20132201. doi: 10.1098/rspb.2013.2201

Default AM et al. 2012. Effects of diurnally oscillating pCO2 on the calcification and survival of coral recruits. Proc R Soc B, 279, 2951-2958. doi: 10.1098/rspb.2011.2545

Doney SC et al. 2007. Impact of anthropogenic atmospheric nitrogen and sulfur deposition on ocean acidification and the inorganic carbon system. Proc Nat Acad Sci, 104, 14580-14585. doi: 10.1073/pnas.0702218104.

Dore JE et al. 2009. Physical and biogeochemical modulation of ocean acidification in the central North Pacific. Proc Nat Acad Sci, 106, 12235-12240. doi: 10.1073/pnas.0906044106.

Easterling WE et al. 2007. Food, fibre and forest products. In: Climate change 2007: Impacts, adaptation and vulnerability (eds. Parry ML et al.), pp. 273–313. Cambridge University Press, Cambridge.

Frieder CA et al. 2014. Can variable pH and low oxygen moderate ocean acidification outcomes for mussel larvae? Glob Change Biol, 20, 754-764. doi: 10.1111/gcb.12485

Gagliano M et al. 2010. The basics of acidification: baseline variability of pH on Australian coral reefs. Mar Biol, 157, 1849-1856. doi: 10.1007/s00227-010-1456-y.

Green et al. 1993. Carbonate dissolution and temporal abundances of Foraminifera in Long Island Sound sediments. Limnol Oceanogr, 38, 331-345.

Hauri C et al. 2009. Ocean acidification in the California current system. Oceanogr 22, 60-7. doi: 10.5670/oceanog.2009.97

Hinga RH 2002. Effects of pH on coastal marine phytoplankton. Mar Ecol Prog Ser, 238, 281-300.

IPCC 2014. Climate change 2014: impacts, adaptation and vulnerability. Contribution of Working Group II to the fifth assessment report of the Intergovernmental Panel on Climate Change. Cambridge University Press.

Lienweber A & Gruber N 2013. Variability and trends of ocean acidification in the Southern California Current System: A time series from Santa Monica Bay. J Geophys Res, 118, 3622-3633. doi: 10.1002/jgrc.20259.

Orr JC et al. 2005. Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature, 437, 681-686. doi: 10.1038/nature04095.

Shaw EC et al. 2012. Impacts of ocean acidification in naturally variable coral reef flat ecosystems. J Geophys Res, 117, C03038. doi: 10.1029/2011JC007655.

Shaw EC et al. 2013. The role of CO2 variability and exposure time for biological impacts of ocean acidification. Geophys Res Lett, 40, 4685-4688. doi:10.1002/grl.50883.

Wenzhöfer F 1999. Biogeochemical processes at the sediment water interface and quantification of metabolically driven calcite dissolution in deep sea sediments. PhD dissertation, University of Bremen, Germany

Yates KK & Halley RB 2006. Diurnal variation in rates of calcification and carbonate sediment dissolution in Florida Bay. Estuar Coast, 29, 24-39.

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.

Shallow secrets of ocean acidification: Current coastal consequences

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The close relationship between atmospheric CO2 and oceanic CO2 and the ensuing drop in pH at Mauna Loa, Hawaii, suggest that increasing atmospheric CO2 is driving the acidification of our oceans.
The close relationship between atmospheric CO2 and oceanic CO2 and the ensuing drop in pH suggest that increasing CO2 is driving the acidification of our oceans. Source: Doney et al. 2009.
Known as “the other CO2 problem”, ocean acidification (OA) has crept onto the scene as one of the most menacing and destructive aspects of human-induced climate change. Basically, OA refers to the dissolving of atmospheric carbon dioxide (CO2) into the oceans, making them more acidic and spelling trouble for many marine organisms, particularly those with calcium carbonate (CaCO3) skeletons (e.g., pteropods, clams, snails, corals). Since the Industrial Revolution, the pH of the oceans has dropped from ~8.2 to ~8.1, corresponding to a 30% increase in ocean acidity, with a projected 0.3-0.4 further decrease by 2100 (120-150% increase in acidity). Ultimately, OA could result in major losses to marine biodiversity, threatened food sources for a myriad of organisms (including humans), diminished coastal protection, altered food webs and ecosystem structuring, and an interrupted carbonate system (Hardt & Safina 2008). However, OA is typically attributed to the burning of fossil fuels and the human contribution to atmospheric CO2. As a result, this can be misleading when reporting the effects that ocean acidification is having in coastal waters and those that it could have in the near future.
Recently, open-ocean acidification has been distinguished from that of coastal waters on the basis that acidification in coastal regions is functionally much different than that of the open ocean (Duarte et al. 2012). As a consequence, the pH decrease in coastal waters (particularly in estuaries) is much more pronounced than that of the open-ocean, and the variability of pH ranges is much wider. Furthermore, although atmospheric CO2 is the primary driver in open-ocean acidification, it plays less of a role in coastal systems. Instead, coastal upwelling, terrestrial and freshwater runoff, organic decomposition, and other processes not occurring in the open-ocean can act as the primary drivers of acidification in coastal systems to varying degrees. As such, organisms residing within coastal waters are subjected to extremely stressful conditions for the majority of their life.

Historically, OA studies have manipulated seawater conditions to mimic future open-ocean acidification scenarios and measured the response of various organisms to these future conditions. However, to the surprise of scientists and shellfish growers alike, the changes in seawater chemistry in coastal areas (particularly the west coast of North America) and resultant biological and economical consequences are happening right now! Shellfish hatcheries on the west coast of North America have already felt the effects of OA. In 2005-2006, shellfish growers on the west coast of the United States were experiencing mass mortality of larvae in their tanks and couldn’t figure out why. When scientists equipped the tanks with pH meters and saw that it was critically low, they were able to come up with solution strategies that worked and, in essence, saved the shellfish industry in parts of the Pacific US. More recently, the loss of approximately 10 million scallops in British Columbia at Island Scallops in 2013 and a financial loss of $10 million (and the forced lay-offs of numerous staff has been attributed to a change in pH from 8.1 in 1953 to a low of 7.3 in 2001. Furthermore, a recent study published in the journal Proceedings of the Royal Society B has reported that 53% of pteropods on the US Pacific coast had severe dissolution of their shells (Bednaršek et al. 2014).
Shell dissolution in larval oysters raised at hatcheries on the Pacific coast of North America has resulted in mass mortality events over the past 10 years. Photo courtesy of Taylor Shellfish from OSU.
Shell dissolution in larval oysters raised at hatcheries on the Pacific coast of North America has resulted in mass mortality events over the past 10 years. Image courtesy of Taylor Shellfish from OSU.
Given the magnitude and obvious immediacy of OA, understanding how this process is currently impacting coastal waters is critical. Alongside the anthropogenic sources of acidification in coastal zones mentioned above, natural causes of acidification and other physical changes (e.g., temperature, salinity, oxygen concentration, etc.) must also be taken into account when addressing acidification in coastal areas. The complex interactions between all of these factors make the task of predicting their effects on coastal ecosystems magnificently daunting. What is apparent, however, is that the pronounced acidification of coastal waters is having and will have significant consequences, not just for the organisms living in these ecosystems, but for humans as well. The overwhelming majority of the global human population depends on coastal ecosystems for survival. With coastal acidification affecting marine organisms both directly and indirectly (indeed acidification will affect more than CaCO3-bearing organisms; e.g., food web shifts and trophic cascades affecting fishes and mammals), a major source of food for billions of people is in jeopardy. Ultimately, scientific studies addressing the impacts of OA need to take the plethora of physical into account in order to sufficiently predict how coastal ecosystems are going to react to the changes that humans are imposing on them. Furthermore, studies need to start focusing more on the current impacts of OA rather than the biological impacts of future scenarios. More importantly, the general public needs to know about the implications of acidification in coastal areas to put the brakes on coastal acidification before things become drastically worse.

References:

Bednaršek, N. et al. 2014. Limacina helicina shell dissolution as an indicator of declining habitat suitability due to ocean acidification in the California Current Ecosystem. Proceedings of the Royal Society B 20140123.
Doney, SC. et al. 2009. Ocean acidification: A critical emerging problem for the ocean sciences. Oceanography 22: 16-25.
Duarte, CM. 2013. Is ocean acidification an open-ocean syndrome? Understanding anthropogenic impacts on seawater pH. Estuaries and Coasts 10.1007.
Hardt, M. & Safina, C. 2008. Covering ocean acidification: Chemistry and considerations. [online]. The Yale Forum on Climate Change and the Media. Accessed 07 May 2014 from http://www.yaleclimatemediaforum.org/2008/06/covering-ocean-acidification-chemistry-and-considerations/.