Ocean

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!

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My first offshore cruise in the Northwest Atlantic

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Click on the images to view larger versions.

For the past 6 days, I have been quite fortunate to experience my first offshore cruise in the Northwest Atlantic Ocean aboard the CCGS M. Perley – a Canadian Coast Guard research vessel. This is not my first time away from land – I’ve conducted research from fishing vessels in the Bay of Fundy and from zodiac in the Bras d’Or lakes. Even as a kid growing up in a small fishing community I was exposed to the sea, frequenting fishing vessels owned by friends’ parents. However, this was my first time venturing a substantial distance offshore on a large research vessel to sample the benthic diversity associated with the NW Atlantic.

As a recently hired biologist at Fisheries and Oceans Canada in Moncton, New Brunswick, I was offered the chance to assist in an annual (but temporary) scallop survey off the northern coast of New Brunswick. The five-year-long survey has been established since 2012, with this year being the last year of the survey. A bottom trawl is used to collect benthic samples. We trawled for 2 minutes at each site and organisms brought up were sorted, identified, counted, weighed, and measured on deck in between drags. This made for intensive 12 hour days, but the data alone provided enough currency and motivation to keep me going.

Sunsets are better at sea.
Sunsets are better at sea.

While the cruises are dedicated to assessing scallop populations off the coast of New Brunswick, data on a slew of other benthic species are collected. Indeed abundances and biomass of all collected species are recorded, along with other basic morphometrics of other key species (e.g. carapace morphometry of crabs and lobsters, and lengths of fishes). We also had a CTD on board, equipped with probes to measure depth, conductivity, temperature, salinity, dissolved oxygen, and pH.

Rock crabs (Cancer irroratus) were present in almost every drag.
Atlantic rock crab (Cancer irroratus).

The experience was nothing short of spectacular. I’ve come to note that sunrises and sunsets are much more appealing from sea. The diversity of animals was astounding and unpredictable from trawl to trawl – crustacaens, cnidarians, echinoderms, molluscs, poriferans, and fishes were all apparent in multiple trawls. The most common species were crustaceans. Shrimps (Argis dentata, Pandalus borealis, Pandalus montagui, and Sclerocrangon borea) and rock crabs (Cancer irroratus) really dominated the trawls.

Shrimps: Sclerocrangon boreas (A), Pandalus montagui (B) and Argis dentata (C). Pregnant Argis dentata (D) – note the bright teal eggs!
Shrimps: (A) Sclerocrangon boreas , (B) Pandalus montagui  (C) Argis dentata, (D) Pregnant Argis dentata – note the bright teal eggs!
We also recorded quite a few Acadian hermit crabs (Pagurus acadianus).
Acadian hermit crab Pagurus acadianus).

Closer to shore, lobsters (Homarus americanus) were quite abundant as well, while an abundance of snow crabs (Chionoecetes opilio) and toad crabs (Hyas araneus and Hyas coaractatus) were frequent at more offshore sites – in one trawl we hauled up >80 snow crabs! We also recorded quite a few Acadian hermit crabs (Pagurus acadianus).

 

Echinderms: (A) Strongylocentrotus droebachiensis, (B) Henrica sanguinolenta, (C) Solaster endeca, (D) Crossaster papposus.
Echinderms: (A) Strongylocentrotus droebachiensis, (B) Henrica sanguinolenta, (C) Solaster endeca, (D) Crossaster papposus.
Sand dollar (Echinarachinus parma)
Sand dollar (Echinarachinus parma)

In some of the trawls, a vast array of other species were evident. Echinoderms  were also abundant. Sea cukes (Cucumaria frondosa, Psolus fabricii), urchins (Strongylo- centrotus droebachiensis), sand dollars (Echinarachinus parma), sea stars (Asterias spp., Crossaster papposus, Henricia sanguinolenta, Leptasterias polaris, Solaster end- eca), and brittle stars (Ophiopholis aculeata) were quite abundant in many trawls – we even saw a couple of large basket stars (Gorgonocephalus arcticus)!

A number of bivalves were also present, including clams (Arctica islandica, Cyclocardia borealis, Cyrtodaria silique, Mactromeris polynyma, Serripes groenlandicus, and Yolida sp.,), scallops (Chlamys islandica, Placopectin magellanicus), and horse mussels (Modiolus modiolus). Similarly to bivalves, brachiopods were abundant at a number of sites. We also observed a number of gastropods (Buccinum undatum, Neptunea decemcostata, Colus stimpsoni, Aporrhais occidentalis, Lunatia heros) and chitons were abundant at a number of stations. Less common were sponges, jellyfishes, and sponges. Tube worms (Polychaeata) dominated the deeper muddy zones (>50 m depth).

Yolida sp. (clam)
Yolida clam (Yolida sp.)
Cyclocardia borealis (clam)
Heart shell (Cyclocardia borealis)
Placopecten magellanicus edge
Giant sea scallop (Placopecten magellanicus)
Serripes groenlandicus (clam)
Greenland cockle (Serripes groenlandicus)

Fishes were also present in a number of trawls. Species observed included American plaice (Hippoglossoides platessoides), Arctic alligatorfish (Ulcina olrikii), Atlantic poacher (Leptagonus decagonus), cunner (Tautogolabrus adspersus), fourline snakeblenny (Eumesogrammus praecisus), yellowtail flounder (Limanda ferruginea), winter flounder (Pseudopleuronectes americanus), longhorn sculpin (Myoxocephalus octodecemspinosus) shorthorn sculpin (Myoxocephalus scorpius), grubby (Myoxocephalus aenaeus), lumpfish (Cyclopterus lumpus), ocean pout (Zoarces americanus), sea raven (Hemitripterus americanus), and sand lance (Ammodytes sp.)

Yellowtail flounder ()
American plaice (Hippoglossoides platessoides)
Fourline snakeblenny
Fourline snakeblenny (Eumesogrammus praecisus)
Atlantic poacher (Leptagonus decagonus)
Atlantic poacher (Leptagonus decagonus)
ocean pout (Zoarces americanus)
Ocean pout (Zoarces americanus)

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Of course other species have been observed on trawls that I have not attended. The above list is nowhere near exhaustive, but is an overview of the species that I observed during my time on the M. Perley. The experience was fantastic, and I look forward to the next opportunity to get back to a place with a flat horizon.

Until then, it’s back to manuscripts and grant proposals…

Finding Nemo in an acidified ocean

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Nemo
Figure 1. Nemo, from Disney-Pixar’s “Finding Nemo”. Source: pixar.wikia.com.

It’s a story that many of us know well; a charismatic, touching and often hilarious tale of a father’s relentless pursuit to find his lost son. In Disney-Pixar’s 2003 blockbuster, “Finding Nemo”, a young clownfish by the name of Nemo ventures off into the open ocean, is unfortunately captured by humans, and is sent off to reside in a dentist office fish tank in Sydney, Australia. As a result, Nemo’s father, Marlin, with the company of his newfound pal, Dory, sets off across the big blue ocean to find his son and bring him home, while Nemo frantically plans his escape from the dentist office fish tank. After much hullabaloo, including Marlin and Dory encountering a hungry shark and a humpback whale, Nemo eventually escapes the dentist’s office and catches up with his dad (who unfortunately thinks Nemo is dead) and together with Dory they head for home – a touching story indeed. Though the ending is certainly of the feel-good genre, would the story have turned out the same in an acidified ocean?

Ocean acidification is a process whereby increasing atmospheric CO2 dissolves into the oceans, lowering their pH and making them more acidic. Though calcifying organisms are thought to be among the most negatively impacted, research has also suggested that an increasingly acidifying ocean can impair the behaviour of various marine fishes, with coral reef fish being the most intensively studied. Furthermore, among the coral reef fishes that have been studied, clownfish (Amphiprion percula) have been a fairly popular species of interest.

 Figure 1. Data reported in A) Dixson et al (2009), B) Simpson et al. (2011), and C) Munday et al. (2009), for predator avoidance (A, B) and homing ability (C).

Figure 2. Data reported in A) Dixson et al. (2009), B) Simpson et al. (2011), and C) Munday et al. (2009), depicting the impacts of elevated CO2 on the predator avoidance (A, B) and homing (C) behaviour in juvenile clownfish.

In 2010, Danielle Dixson and colleagues reported the results of their research comparing the ability of juvenile clownfish to avoid their predators under both ambient (present day) and elevated (2100 projection) CO2 conditions. What Dixson et al. (2010) found was that, in comparison to fish raised in present day CO2, juvenile clownfish reared under elevated CO2 were unable to distinguish between predators and non-predators, spending equal amounts of time hanging around both (though newly-hatched larvae were unaffected; Figure 2A). Likewise, Simpson et al. (2011) reported that clownfish lost their ability to avoid the sounds of their predators when raised under elevated CO2 conditions (Figure 2B). Additionally, negative impacts on the homing ability of clownfish have also been reported. Munday et al. (2009) found that baby clownfish raised under elevated CO2 conditions lost the ability to choose their preferred and optimal habitat and were also unable to distinguish their parents from other clownfish (Figure 2C).

These negative changes in clownfish behaviour are likely induced by a change in their biochemistry when reared under elevated CO2 conditions. Studies have suggested that high levels of CO2 interfere with one particular chemical in the brains of fishes (and other animals as well) – GABA (chief inhibitory neurotransmitter vertebrate central nervous systems; e.g. Nilsson et al. 2012). Since the GABAA receptor has a specific conductance for Chlorine (Cl) and bicarbonate (HCO3) – the two ions most likely to be impacted under elevated CO2 conditions – this explanation seems probable.

Figure 3. Marlin and Dory swim away from a hungry shark in Disney-Pixar’s “Finding Nemo”. In an acidified ocean, things may have turned out much different. Source: lyrics.wikia.com

So how would this have impacted Finding Nemo? Well, if we revisit the plot of the movie, there are two ways in which acidification may have changed the outcome of Finding Nemo. Firstly, in the original movie, Marlin and Dory swim away when they come across a predatory shark (though shark odour tracking may also be hindered in a more acidified ocean; see Dixson et al. 2014). However, in a more acidified ocean, as research has suggested, they may have done exactly the opposite and would likely have become dinner for the shark. Secondly, at the end of the movie, Nemo pops out of a sewer pipe and swims along, eventually finding his dad and Dory. Unfortunately, in a more acidified ocean, research suggests that Nemo likely wouldn’t be able to find his father.

Though I like to think that adult behaviour may not be altered and Marlin would have eventually found the dazed and confused Nemo (though other inaccuracies in the movie, if corrected for, would have led to Marlin and Dory’s demise, let alone a much more incestual tale), it is likely that the feel-good ending that we’ve all come to love would have been anything but feel-good. So we need to find ways of mitigating ocean acidification and saving our precious ecosystems from the myriad of destructive consequences that they will face if we continue our ways – not only for our own sake, but so that the Nemos of the future will have a chance to swim away from their predators or find their way home if they ever decide to venture away from their anemonemone.

REFERENCES:

Munday, PL et al. 2009. Ocean acidification impairs olfactory discrimination and homing ability of a marine fish. PNAS, 106: 1848-1852.

Dixson, DL et al. 2010. Ocean acidification disrupts the innate ability of fish to detect predator olfactory cues. Ecology Letters, 13: 68-75.

Simpson, SD et al. 2011. Ocean acidification erodes crucial auditory behaviour in a marine fish. Biology Letters, doi:10.1098/rsbl.2011.0293.

Nilsson, GE et al. 2012. Near-future carbon dioxide levels alter fish behaviour by interfering with neurotransmitter function. Nature Climate Change, 2: 201-204.

Dixson, DL et al. 2014. Odor tracking in sharks is reduced under future ocean acidification conditions. Global Change Biology, doi: 10.1111/gcb.12678.

Canada lagging behind in ocean acidification research and action

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scallop
The year was 2011, and Rob Saunders, CEO of Island Scallops, had some grim news to report from his scallop hatchery in Qualicum Bay, BC – every scallop the company had put in the water over the past 3 years had died. The likely culprit? – ocean acidification (OA). Seawater pH levels reaching 7.2 had been reported from the area, where typical seawater hovers around a pH of 8. Consequently, Island Scallops was forced to dramatically scale back production, shutting down its processing plant and laying off 1/3 of its employees.
Although often considered a future problem, OA is already impacting coastal systems on the Pacific coast of North America. Aside from the shellfish crises in the Northwest United States, and British Columbia, Feely et al. (2008) reported undersaturated seawater (with respect to aragonite; a mineral form of calcium carbonate) upwelling along the continental shelf of the Pacific coast of North America from Canada to Mexico. More recently, it has been suggested that these chemical changes in the same area are already resulting in negative biological implications at the base of the food web (Bednaršek et al. 2014). As a result of these immediate threats of OA, various committees and national projects have been formed to address and monitor OA in the United States, such as the NOAA Ocean Acidification Program (NOAA OAP), while documents outlining strategic plans for research, monitoring, and tackling the problem of OA in the US  have been published in recent years (e.g. OCBP 2009, NRC 2010, IWGOA 2014) (Europe is also leading the way in this area, but I will stick to North America for the purposes of this post; for a glimpse at the European Project on Ocean Acidification, EPOCA, see here). In fact, the United States federal government, through NOAA initiatives, has a total of 16 buoys/moorings monitoring OA in their national waters (10 on the Pacific coast, 6 on the Atlantic coast) (Figure 1).
Figure 1. Allocation of buoys/moorings monitoring ocean acidification in countries of the Pacific and Atlantic coasts of North America.
Figure 1. Allocation of buoys/moorings monitoring ocean acidification in countries of the Pacific and Atlantic coasts of North America.
While the US Federal government appears to be sufficiently concerned about OA, the Canadian Federal government seems much more disinterested. In their 2012 State of the Oceans report, Fisheries and Oceans Canada (DFO) reported that, due to its age, Pacific sub-surface water already contains a high concentration of CO2 and periodic episodes of undersaturated (pH<7.7) surface waters already occur on the Pacific coast of Canada (DFO 2012). In the report, DFO also stated that on the Atlantic coast of Canada, bottom waters in the St. Lawrence Estuary have dropped 0.2-0.3 units over the past 70 years (in comparison to the global average decrease of 0.1 units) resulting in biological implications for bottom-dwelling animals, and suggested that water from Arctic outflow moving through the Canadian Arctic Archipelago is bringing more acidic waters to the east coast of Canada, potentially making it more susceptible to future changes (DFO 2012). Although the report clearly outlines that ocean acidification is already a problem on both Canadian coasts and suggests that future conditions will get worse, the Canadian Federal government is doing very little to address OA in Canada, simply stating in the report that “Continued scientific research into ocean acidification is necessary to identify its impacts and drivers, which vary by location, with a view to developing a coherent response to the issue”. While 16 buoys are monitoring OA in US waters, Canada has a total of 1 (Pacific coast), which is itself a collaborative project with NOAA in the US (Figure 1). Canada has, however, been involved in the AMAP project which has contributed to monitoring Arctic OA, but the only other governmental OA research program in Canada is just getting off of the ground at a DFO lab in St. Andrews, New Brunswick; however, this program is very primitive and requires much more time, effort, and funding to appropriately establish an OA monitoring program on Canada’s east coast. When it comes to policy, OA isn’t even on the radar in Canada. Although, the President of the United States committed to protecting marine ecosystems of the US and tackling the problem of OA in June of 2014 (not to mention the myriad regional initiatives aimed at addressing the problem in the United States), the Canadian government has yet to mention the prospect of trying to mitigate the implications of OA in our country. While the United States have multiple, detailed documents outlining OA and potential adaptation strategies, the latest formal report outlining Canada’s action on climate change designates less than a page to OA (Warren & Lemmen 2014). Furthermore, although the Canadian government is abundantly proud of its ecoENERGY program (i.e., investing money into oil and natural gas exploration), the ecoACTION program (i.e., actively taking action against ecological problems such as climate change and ocean acidification) has been dismantled. Finally, although government agencies such as NOAA in the US and EPOCA in Europe have devoted a substantial amount of time into public outreach and education, government scientists studying OA in Canada are still struggling to speak outside of their offices.
The latest report from the Government of Canada outlining Canada's actions towards climate change restrict ocean acidification to less than a single page.
The latest report from the Government of Canada outlining Canada’s actions towards climate change restrict ocean acidification to less than a single page.
For the past decade or more, OA has been on the radars of scientists around the world. With its imminent threat to marine organisms around the world, from individual species to global biodiversity, acidification has been a hot topic, peaking the interest of scientists and (some) policy makers alike. Although disparately necessary, a global policy to address the threat of OA is lacking. Consequently, a disconnect exists between regions around the world, with some taking notice and action more than others. Although the United States has begun to lead the way in OA research and mitigation (along with numerous countries in Europe), it is quite clear that the Canadian Federal Government and associated policy makers are drastically lagging when it comes to acting on OA, a detrimental environmental issue the requires immediate attention. As a result, research into OA in Canada is drastically hindered and negative instances such as those at Island Scallops aren’t likely to be prevented for quite some time to come.

References:

Feely RA et al. 2008. Evidence for upwelling of corrosive “acidified” water onto the continental shelf. Nature, 320, 1490-1492.

Ocean Carbon and Biogeochemistry Program 2009. ocean acidification: Recommended strategy for a U.S. national research program [online]. Accessed 01/12/2014 from http://www.us-ocb.org/publications/OCB_OA_Whitepaper.pdf.

National Research Council 2010. Ocean acidification: A national strategy to meet the challenges of a changing ocean [online]. Accessed 01/12/2014 from http://hofmannlab.msi.ucsb. edu/resources/OA_A%20National%20Strategy%20to%20Meet%20the%20Challenges%20of%20a%20Changing%20Ocean.pdf.

Bednaršek N et al. 2014. Limacina helicina shell dissolution as an indicator of declining habitat suitability owing to ocean acidification in the California Current Ecosystem. Proc R Soc B, 281, DOI: 10.1098/rspb.2014.0123.

Fisheries and Oceans Canada 2014. Canada’s state of the oceans report, 2012 [online]. Accessed 01/12/2014 from http://www.dfo-mpo.gc.ca/science/coe-cde/soto/report-rapport-2012/index-eng.asp#a2.

Interagency Working Group on Ocean Acidification 2014. Strategic plan for federal research and monitoring of ocean acidification [online]. Accessed 01/12/2014 from http://www.whitehouse. gov/sites/default/files/microsites/ostp/NSTC/iwg-oa_strategic_plan_march_2014.pdf.

Warren FJ & Lemmen DS 2014. Canada in a changing climate: Sector perspectives on impacts and adaptation. Government of Canada, Ottawa, 286pp.

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.

When history meets ecology: Connecting European exploration and biodiversity in the northwest Atlantic

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Hediste diversicolor (top; E. Kristensen, marinespecies.org) and Corophium volutator (bottom; M. Storey, bioimages.org.uk)
Hediste diversicolor (top; E. Kristensen, marinespecies.org) and Corophium volutator (bottom; M. Storey, bioimages.org.uk)
Although it doesn’t happen often, the intersection of academic fields (such as history and science) can lead to exciting and important discoveries. For example, historical records of human migration and modes of transportation can provide insight into the broad-scale distribution of various organisms, ultimately telling us how and when certain animals arrived where they are today. In fact, the above-mentioned example has recently provided insight into where some species of marine organisms in the northwest Atlantic Ocean originated from, along with when and how they likely got there.
Using genetic techniques, Tony Einfeldt, a Ph.D. student in Dr. Jason Addison’s lab at the University of New Brunswick in Fredericton, NB, Canada, and his colleagues  have discovered that benthic marine worms and amphipods, which reside within mudflats of the northwest Atlantic coast, likely arrived there in the ship ballast of early European explorers. Einfeldt et al. compared the genetic structure of various populations of ragworms (Hediste diversicolor) and amphipods (Corophium volutator) residing within the Bay of Fundy and the Gulf of Maine to those along the Atlantic coast of Europe. Similarities in the genetic identity between North American and European populations are highly suggestive that the northwest Atlantic populations originated from the European coast. As Einfeldt states, “We can tell where they came from because the genetic identity of both species in the Bay of Fundy matches that of those in Europe.” Furthermore, with such precise technology and methodology, Einfeldt et al. were able to isolate two separate introductions of these species from Europe, with Bay of Fundy populations likely originating from the Bay of Biscay in France and Gulf of Maine populations coming from more northerly European nations (Norway, Denmark, Germany, etc.).
But how did they get there? To answer this question, Einfeldt et al. attempted to match the movement of these benthic invertebrates with human movement throughout history. Of course, one mode of the intercontinental dispersal of marine organisms is through the ballast water of ships, as ships empty and refill their ballast when they dock, allowing species from one coast to enter the ship through refilling and be introduced to another coast through emptying. But the species studied by Einfeldt et al. are not among those found in modern ballast water, likely because they are infaunal organisms, meaning that they reside within bottom sediment of marine intertidal areas (i.e., mudflats). However, historically, not all ballast was in the form of water. Early European explorers, including those to first cross the Atlantic, most often used rocks for ballast, along with (you guessed it) mud! In fact, the earliest known European ships to have used mud and rocks for ballast are those of Samuel de Champlain and Henry Hudson in the 1600’s, although dry ballast was used up until the 1800’s, making the point of introduction quite difficult to identify.
Some marine species in the northwest Atlantic, such as H. diversicolor and C. volutator, may have arrived here through the ballast of early European explorers. Source: Wikipedia
Some marine species in the northwest Atlantic, such as H. diversicolor and C. volutator, may have arrived here through the ballast of early European explorers. Source: Wikipedia
Although the time window of introduction is quite wide (~200 years), the results of Einfeldt et al. provide strong evidence that the presence of H. diversicolor and C. volutator along the Atlantic coast of North America is a result of European exploration and migration to North America. What’s more is that these two species are important drivers of their respective ecosystems, particularly in the Bay of Fundy. Many species of fish feed on these benthic invertebrates, while migrating shorebirds often depend on the abundance of these species in Bay of Fundy mudflats for food during annual migrations. Ultimately, if these species were never introduced to the northwest Atlantic coast, the diversity of animals that reside there, either permanently or temporarily, may be very different than it is today.

Acknowledgements

I’d like to thank Tony Einfeldt of UNB Fredericton for taking the time to chat and provide input into this post. I also want to thank Shane Fowler, CBC correspondent, for sparking my interest in publishing this post and for his dedication to the promotion of science in New Brunswick.
For those interested, the peer-reviewed publication in Invertebrate Biology can be found here.

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.