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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Climate change and marine biology: questioning our understanding

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Copyright © Joachim S. Müller, Creative Commons
Copyright © Joachim S. Müller, Creative Commons

At some point or another, you’ve probably read or heard the common headline:

“Climate change threatens ____________ (insert your favorite species).”

But once you’ve digested the doom-and-gloom story, have you ever wondered how we know how climate change impacts various marine species? What is it that scientists do that leads to such claims? Are these claims legitimate? How accurate are they?

When assessing the impacts of climate change on living organisms, most studies employ controlled experiments, where researchers can tinker with one or a number of relevant variables to mimic predicted future conditions and observe how organisms respond to these conditions. There are substantial problems with this approach, however. First, biological responses are typically assessed in the context of only one or two environmental stressors, while we know that a multitude of factors (e.g., temperature, acidification, eutrophication, hypoxia, salinity, etc.) will have independent and/or synergistic biological impacts. Second, over the duration of such experiments, conditions are often kept constant, mimicking average future conditions. Finally, studies typically assess species in isolation, which doesn’t adequately address the community and/or ecosystem consequences of climate change, nor how individual species will respond when residing in their natural habitats. Consequently, I argue that the biological effects of a changing climate are, at present, poorly understood.

Table 1. Summary of studies assessing the behavioural impacts of ocean acidification in the context of co-occurring environmental parameters expected to occur under future climate change scenarios.
Table 1. Summary of studies assessing the behavioural impacts of ocean acidification in the context of co-occurring environmental parameters expected to occur under future climate change scenarios.

The ways in which organisms respond to a given environmental stressor do not solely depend on that single stressor. The interactive effects of multiple environmental stressors can elicit drastically different biological responses. For example, it is increasingly recognized that food availability can modulate the magnitude of effect when assessing the biological impacts of climate change in the ocean, suggesting that, at least physiologically, many species can tolerate a warming and acidifying ocean as long as they have enough energy to do so. In a recent literature review of the behavioural impacts of ocean acidification (Clements & Hunt, in review), we found that 7/8 publications incorporating the independent and synergistic effects multiple environmental stressors (Table 1) in experiments derived different conclusions than when acidification was tested in isolation. Furthermore, the outcomes were all over the board, with additional stressors attenuating, amplifying, or not affecting the behavioural endpoint in question. The problem is that only 8/57 studies actually addressed the effects of multiple environmental stressors – a problem that transfers other biological responses to climate change as well.

It doesn’t take a rocket scientist to know that nature is far from stable. Growing up in the Maritime Provinces of Canada, I know that a look out the window from one moment to the next can yield drastically different weather observations. While the term “weather” applies to environmental phenomena over small temporal scales (hours, day, weeks, months, etc.), “climate” refers to the average of those weather conditions over long periods of time (years, decades, centuries, millennia, etc.). Since climate is a function of weather, understanding the impacts of climate change requires incorporating an understanding of the weather that derives the climate. The variability (i.e., the weather) around projected climatic means can modulate the amount of time that an organism experiences environmental conditions above or below a threshold whereby the organism is affected (Figure 1). Unfortunately, few studies take variability into consideration. In the same literature review mentioned above (Clements & Hunt, in review), only 1/57 studies took variability into consideration, reporting a negative effect of acidification + variability, while acidification alone elicited no effect.  Furthermore, studies incorporating multiple environmental stressors and their associated variability are virtually non-existent. Ultimately, a strong understanding of how climate change influences biology requires embracing variability, not dismissing it – otherwise our understanding remains flawed.

Figure 1. 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.
Figure 1. Potential degrees of current and projected variability in diurnal oceanic pCO2 where variability increases over time (A), where variability remains consistent over time (B), and where variability decreases over time (C). Distance between vertical 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.

Species interactions can also elicit different responses to climate change. For example, the presence of marine plants and their density/abundance within a given marine system can, to an extent, buffer oceanic pH and mitigate the impacts of ocean acidification to other organisms residing within that system. As such, understanding the impacts of climate change in terms of community- and ecosystem-wide consequences not only provides a broader understanding of the biological and ecological impacts of climate change, but can provide a more accurate understanding of how individual organisms will be impacted by shifting environmental conditions within their natural habitats.

So does this all mean that we shouldn’t worry about climate change? – ABSOLUTELY NOT! Climate change is currently, and will continue to be a huge problem for humans and a plethora of other organisms. However, I do think that the degree to which climate change will be a biological problem is poorly understood. On the bright side, scientists are beginning to recognize these shortcomings and are now working toward a better understanding of how climate change will affect marine organisms. Furthermore, not all studies simply employ highly controlled laboratory experiments; there is field evidence that provides sound information regarding the biological effects of climate change for some species. Ultimately, stamp collecting gets us nowhere – experimental approaches need to incorporate multiple shifting stressors and their associated variability, as well as numerous species (optimally mimicking communities or ecosystems) in order to adequately understand the biological implications of a changing climate. Until then, we will likely remain naive about the ways in which climate change will impact marine species.

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/.