Beginning in 2017, I am now publishing short, lay summaries for each of my peer-reviewed publications in an attempt to increase public outreach and education. Below, you can find general summaries for each paper published after January 01, 2017. I will upload summaries for prior papers in the near future.
Wanted dead or alive: Polydora websteri recruit to both live oysters and empty shells of the eastern oyster, Crassostrea virginica
Jeff C Clements, Daniel Bourque, Janelle McLaughlin, Mary Stephenson & Luc A Comeau
As highlighted in a previous publication summary on this page, Polydora worms are shell parasites of shellfish and can result in negative implications for commercially important oysters. Although it is well documented that Polydora worms use the shells of live oysters as a resource, whether or not these shell parasites use empty shells of dead oysters remains a mystery. If the worms do recruit to empty shells, however, an accumulation of dead shells near live oyster beds or aquaculture operations may impact the prevalence of Polydora worms in the live oysters.
To test whether or not Polydora actively recruit to and use empty oyster shells as a resource, we ran a field experiment in collaboration with some oyster growers in New Brunswick that have experienced Polydora outbreaks in the past. In a nutshell, we put empty oyster shells and live oysters in cages and deployed them at an oyster lease for 50 days during a time that we knew Polydora worms were active. After the 50 day period, we collected the shells and live oysters, took them back to the lab, and counted the number of Polydora worms that were present in them.
When we were finished counting the worms, our analysis of the data suggested that Polydora worms most definitely recruited to empty oyster shells. Moreover, the analysis showed that the number of Polydora in the empty shells was essentially the same as the number in the shells of live oysters! Pretty cool!
So, our results suggest that these Polydora worms actively use both live oysters and empty shells as a resource – but why does that matter? Well, as mentioned above, if there is a large amount of empty shells accumulated near a wild oyster bed or near oyster cages, it could potentially affect the prevalence of parasitic worms in live oysters that an oyster harvester might try to fish and sell. So, if there is an outbreak of Polydora worms near a live oyster lease, having a bunch of empty shells for those worms to use might reduce the number of worms that try to use live oysters. In contrast, adding a bunch of empty shells might increase the number of worms that survive during an outbreak and could make things even worse for live oysters! We thus suggest that future studies need to assess the potential relationship between discarded oyster shells and the prevalence of Polydora worms in live oysters – such studies could aid in understanding Polydora dynamics and would provide important information for oyster harvesters and growers.
Elevated seawater temperature, not pCO₂, negatively affects post-spawning adult mussels (Mytilus edulis) under food limitation
Jeff C Clements, Carla Hicks, Réjan Tremblay & Luc A Comeau
We can probably all agree that, in general, ocean acidification (OA) is bad. BUT… it’s important to remember that OA isn’t the only thing that’s affecting our oceans; a bunch of other so-called “global change stressors” are also evident, including ocean warming (OW) and deoxygenation (decreasing ocean oxygen content). So, what happens to mussels when they are faced with multiple stressors? That’s EXACTLY what we set out to test in our latest paper!
In this study, we used fully-grown mussels from Prince Edward Island. In case you’re unaware, mussels are SUPER important to the island’s economy and to Canadian mussel production. We wanted to test how mussels responded when they were exposed to a combination of OA and OW during a period of their life when they are vulnerable – after they spawned (i.e., released their eggs and sperm to make baby mussels)! For about 3 months, we exposed the mussels to three different OA scenarios (current pH conditions, pH predicted for the year 2100, and pH predicted for the year 2300) at two different temperatures: 16°C and 22°C. We then measured a bunch of stuff including how many mussels died and how healthy they were (their condition index), byssal attachment strength after 1 month and 2 months (mussels use sticky strings called byssus to attach to hard things like rocks), and their energy content.
We found the OA had absolutely no effect on the mussels – they just dealt with it! So that was pretty cool… Worryingly, though, OW reduced glycogen content in the mussels (glycogen is the main energy reserve for these animals) and that led to mussel health, a reduced ability to stick to hard things, and increased the number of mussels that died.
So, while these mussels seem to be able to deal with OA, they can’t handle the heat! This is concerning because waters around PEI are warming fast, and the number of days that nearshore waters are above 20°C are increasing.
What can we do about this, and what should we do about it? Well, we can try and make the mussels more comfortable by putting them in artificially-cooled water, but there are just too many mussels produced on PEI for this to be feasible. Plus, this would just be a temporary Band-Aid on a much larger issue that is the root cause of these global change stressors in the ocean – the burning of fossil fuels.
Ultimately, we need to reduce our carbon emissions to try and halt OA and OW – and other global changes – or else delicious PEI mussels on your dinner plate may someday be a thing of the past; and that, my friends, starts with you…
Didemnum vexillum: invasion potential via harvesting and processing
of the Pacific oyster (Crassostrea gigas) in British Columbia, Canada
Louis F Ferguson, John DP Davidson, Thomas Landry, Jeff C Clements & Thomas W Therriault
Shellfish aquaculture provides food and jobs for thousands of Canadians on the east and west coasts. When ready, oysters are harvested and often transferred to different areas to be processed, which can pose a number of risks. One such risk is the movement of invasive species (which are bad because they have negative effects on native species and biodiversity), like tunicates, into new areas, since moving shellfish from an area where an invasive species exists to an area where the invasive does not exist can result in the spread on the invasive species. Because of this, it is important to document and understand the degree of threat that transferring product between oyster farms poses in terms of spreading invasive species.
To better understand the risk of tunicate spread associated with the transfer of oysters between areas, we conducted a study to quantify how the physical process of oyster harvesting altered the coverage of invasive tunicates on oyster product in British Columbia. We isolated three main stages of the oyster farming process – harvesting, transportation, and processing – and quantified the % coverage of the “pancake batter tunicate” at each of the three stages on oysters from two aquaculture sites in BC.
We found that the physical act of processing reduced the amount of tunicates on the product from both aquaculture sites (although sites did differ). The percent coverage of invasive tunicates, on average, was about 48% immediately after harvesting. After the transfer process, the percent coverage decreased to 30%, and decreased further to 17% after shucking. Thus, on average, each stage of the process reduced the amount of invasive tunicates by about 15%. However, 15% of the final shucked oysters still had invasive tunicates on them!
Given that the final shucked oysters still had a substantial amount of invasive tunicates covering them, we concluded that even after physical processing, the threat of introducing the invasive “pancake batter tunicate” is high. However, mitigation techniques can be implemented at each stage of the processing regime to reduce the risk of spreading the invasive tunicate.
Testing for sediment acidification effects on within-season variability in juvenile soft-shell clam (Mya arenaria) abundance on the northern shore of the Bay of Fundy
Jeff C Clements & Heather L Hunt
Much of the work I conducted for my PhD was experimental, where I manipulated sediment pH conditions in the lab (while holding other conditions constant) and tested whether or not pH affected clam burrowing behaviour and movement. But what do experiments mean if they can’t reflect what’s really happening in nature? I’d argue not much, and that’s why I also conducted a field study for my PhD, to try and detect whether or not sediment pH can actually affect the recruitment of baby clams in the field.
For this part of my thesis, I studied four different mudflats in the Bay of Fundy from May to November in 2012 (when baby clams are most abundant). At each mudflat, I took a bunch of sediment pH across the mudflat and counted the number of baby clams that were found in in each of the areas that I measured pH. Based on my experiments, I predicted that I would find fewer clams in areas that had low sediment pH than I would in areas with high sediment pH.
Our results confirmed correlations between sediment pH and baby clam abundance, and the mudflats that had lower average pH levels also had the lowest clam abundances. Interestingly, at the sites with low pH and low clam abundance, the size of sediment grains was also much smaller, and the sites were characterized by thick, muddy sediment; the sites with higher pH had larger grains of sediment and were sandier. Because the water above the sediment has a higher pH than the porewater in the sediment (i.e., the water that fills the space between the tiny sediment grains), we concluded that larger sediment grains probably let more water from above the sediment into the spaces between the sediment grains. This allows sites with bigger grain sizes to have a higher pH and, as a result, allows more baby clams to settle and live there. But previous studies also suggest that the sediment grain size in and of itself can also affect clam burrowing, so we don’t know for sure whether the pH or the grain size affected the number of baby clams I counted. Most probably it is a combination of both.
Extreme ocean acidification reduces the susceptibility of eastern oyster shells to a polydorid parasite
Jeff C Clements, Daniel Bourque, Janelle McLaughlin, Mary Stephenson & Luc A Comeau
Ocean acidification (OA) is expected to impact marine organisms in the future. In particular, OA is thought to have negative effects on many calcifying animals, such as shellfish. Although there is much research documenting the effects of OA on individual organisms, there is a drastic lack of knowledge about how OA affects parasite-host interactions – an important aspect of ecology. As mentioned in previous summaries, mudworms are shell parasites of marine molluscs, burrowing and living inside the shells of their molluscan hosts. These mudworms can result in unsightly mud blisters in oysters, which can reduce product quality and increase oyster vulnerability to illness and environmental stress. So understanding potential factors that can contribute to mudworm infestations in oysters is important. While siltation could be one of them (see “Siltation increases the susceptibility of…” below), OA could also influence oyster susceptibility to mudworm infestation, as weaker shells could increase oyster vulnerability to these shell parasites.
To test this idea, we conducted a field experiment in the Fall of 2015. We exposed empty oyster shells (of about the same size) to three different pH levels (8.0, 7.5, and 7.0) for 3-5 weeks. We then deployed those oyster shells for 50 days during the mudworm recruitment season at an aquaculture farm that reported an outbreak of mudworms two years earlier (in 2013). After the 50 days, we took the shells back to the lab and extracted and counted the worms from each shell.
To our surprise, our original hypothesis was completely overturned! Rather than oyster shells under low pH conditions being more susceptible to mudworm recruitment, the ones raised under low pH were less susceptible! This was a really neat finding, and we think that the low pH conditions likely dissolved the softest parts of the oysters shells, leaving behind the harder parts of the shell and making it more difficult for the mudworms to burrow into (although this is just a hypothesis; there are a number of other things that could be at play). While this work suggests that oyster shells raised under lower pH conditions may be less susceptible to mudworms, we used empty shells. Future work looking at the effects of OA on mudworm recruitment to live oysters and the subsequent response of those oysters under low pH conditions are needed to adequately understand the effects of OA on this parasite-host system.
The Dusky Cockroach in the Canadian Maritimes: establishment, persistence, and ecology
Jeff C Clements, David B McCorquodale, Denis A Doucet, Jeffrey B Ogden
This lay summary starts off with a story:
One day during my PhD, I was enjoying a walk at Rockwood Park in Saint John, New Brunswick when I noticed an interesting insect sitting on a leaf. I’d never seen this kind of insect before and was curious. Because I’m a nerd and a scientist, I usually have my camera and some pill bottles to photograph and collect insects while I’m wandering around in nature. So I snapped a few shots of the insect so that I could identify it when I got home. After doing a bit of searching and getting confirmation from some local naturalists online, I had determined that this insect was a Dusky Cockroach (scientific name: Ectobius lapponicus) – a non-native species of cockroach that was introduced to eastern North America in New Hampshire in the late 1980s.
Interestingly, some of the local naturalists that I was talking to informed me that this was the first record of the species in the province of New Brunswick, and one of only a few records for the Maritime Provinces. So together with some colleagues who had collected a few specimens of this species elsewhere in the Maritime Provinces, we wrote a paper documenting the establishment of the Dusky Cockroach in the Canadian Maritimes.
Soon after the publication of that paper, records of the species started pouring in! People from all across the Maritimes were sending me photos and specimens of what they thought were Ducky Cockroaches – and they were right! Given the drastic increase in reported Ducky Cockroach sightings, my colleagues and I decided to publish an update paper on the species in the Maritimes.
We collected all of the reported Dusky Cockroach sightings in Maritime Provinces and documented the year and month of the sighting, the sex and life stage of the individual cockroach, and the location that it was seen; we also documented the habitat in which the individual was found and the person who found it. We also searched online for reports of this species in Maine, USA, which is adjacent to New Brunswick and what we thought was the likely entry point of the cockroaches into the Maritimes. We also searched for other records of this species across Canada. To be included in the study, all records had to be accompanied by a specimen and/or a clear photo that would allow us to confidently identify it as a Dusky Cockroach.
With this information, we were able to show that Dusky Cockroaches have been observed in the Maritimes almost every year since 2004, and, to date, a total of 119 individuals have been reported in the Maritimes (45 from New Brunswick, 38 from Nova Scotia, and 36 from Prince Edward Island). Interestingly, we also found that 78% of the records occurred in tourist destinations (parks and campgrounds). Coupled with an abundance of this species in Maine, it is likely that this cockroach entered the Maritimes from the eastern United States, likely by hitching a ride with tourists. This species also appears well established in Ontario. Luckily, however, the vast majority of individuals have been observed outdoors in disturbed habitats near forest edges (although some indoor records exist). Finally, given the months in which the records occurred, it seems that this species is active from June–September, which is in accordance with typical periods of activity in its native continent of Europe.
While this species is non-native, it is unlikely that its introduction has resulted (or will result) in any ecological damage. We suggest that detailed studies focused on this species are now needed to determine the whole range and number of this species in eastern Canada. We also think that experimental studies of this cockroach’s diet and behavior will aid in understanding the ecological role of this non-native species in North America.
Elevated temperature has adverse effects on GABA-mediated avoidance behaviour to sediment acidification in a wide-ranging marine bivalve
Jeff C Clements, Melanie M Bishop, Heather L Hunt
Early on in my PhD, I was able to show that if I added CO2 to sediments (which made them more acidic), clams decided to not burrow into those sediments and moved away (see here and here). While not burrowing can reduce a clam’s chances of survival under normal conditions, not burrowing into CO2 acidified sediments is likely a good thing, because more acidic sediment can dissolve clams’ shells and kill them (this avoidance behaviour to conditions that are bad for the clams is what we call an adaptive behavioural response)!
Although my early work showed that clams don’t burrow into acidic sediments, there were still some unanswered questions. First, as a global change biologist, I was interested to understand how future climate change conditions (ocean warming) might impact the clams’ ability to avoid acidic sediments, since previous research suggested that temperature can influence clams’ burrowing behaviour. Second, as a researcher interested in animal behaviour, I wanted to know what part of the clams’ biology allowed them to engage in this adaptive behaviour (i.e., avoiding acidic sediments). So, we (my honours student Melanie Bishop and my PhD supervisor Heather Hunt) conducted two separate experiments to answer precisely those two questions.
To answer the first question, we raised juvenile clams in 18ºC water and 21ºC – 18ºC was chosen based on intertidal temperatures during the time of the experiment (early September) and 21ºC was chosen based on near-future ocean warming predictions (+3ºC). We then exposed the clams to sediments with pH condition that most often occurs in the Bay of Fundy (based on my own observations; pH~7.30) and with pH conditions that are at the lower end of those that I observed in the Bay of Fundy (pH~6.50).
To answer the second question, we raised all juvenile clams in 16ºC water for 2 weeks and then exposed them to the same two kinds of sediment pH (i.e., ~7.30 and ~6.50). Before the clams were exposed to the different pH sediments, however, we drugged them with a drug called gabazine. This drug closes a particular neuroreceptor in the clams’ “brain” (they don’t actually have a brain like you and I have, but they have nerve cells in their tissues) – the GABAA neuroreceptor. We did this because previous studies with fish have shown that CO2 induced ocean acidification alters the behaviour of fish by interfering with the GABAA neuroreceptor in the fish’s brains. So, if interference with the GABAA neurotransmitter was causing the adaptive behaviour in the clams, we would expect to see about the same number of drugged clams burrow into high and low pH sediments, but we would expect to see drastically fewer undrugged clams burrow into low pH sediments (compared to the high pH sediments).
In the first experiment, we found that more clams burrowed when they were raised in 21ºC than when they were raised in 18ºC but that fewer clams burrowed into low pH sediments, regardless of the temperature. However, when we included the clams from the second experiment (the one with gabazine) at 16ºC, we found that elevated temperature negatively affected the clams’ ability to avoid low pH sediment, because fewer clams managed to avoid low pH sediment at higher temperatures (see Fig. 1).
In the second experiment, we found that a similar number of clams burrowed into high and low pH sediments when they were drugged with gabazine, but that far fewer clams burrowed into low pH sediments when they were not drugged (see Fig. 2). This was exactly what we hypothesized if GABAA interference was responsible for the adaptive behaviour in these clams!
From these experiments, we concluded two things:
- Elevated temperature consistent with ocean warming predictions has a negative impact on an adaptive behaviour in these clams. That is, ocean warming reduces these clams’ ability to avoid acidic sediments, which can kill them!
- The behavioural response of these clams to avoid acidic sediments is likely driven, biologically, by CO2 interfering with GABAA neuroreceptors, that are found in the nerve cells of the clams’ feet (a clam’s foot is what some people think of as a clam’s tongue).
This research is important, because it’s the first to show that the effects of CO2 on GABAA neuroreptors can actually benefit animals – all other research to date suggests that ocean acidification effects on GABAA neuroreceptors result in negative behavioural effects. This provides insight into the evolution of GABAA neuroreception and how it might impact animals under future ocean conditions (high CO2).This also provides insight into the proximate (causal) physiological mechanisms underpinning bivalve burrowing behaviour. Finally, the research is also important because burrowing animals like these clams are critical in connecting the areas above and below the sediment surface (a process known as benthic-pelagic coupling), and if their burrowing is reduced or increased in the future, it can influence entire ecosystems at the bottom of the ocean.
Siltation increases the susceptibility of surface-cultured eastern oysters (Crassostrea virginica) to parasitism by the mudworm, Polydora websteri
Jeff C Clements, Daniel Bourque, Janelle McLaughlin, Mary Stephenson & Luc A Comeau
Mudworms can result in unsightly mud blisters in oysters (see images below). These blisters can reduce product quality and increase oyster vulnerability to illness and environmental stress. It’s thus important to understand factors that can contribute to mudworm infestations in oysters.
LEFT: An adult mudworm, Polydora websteri. RIGHT: Eastern oyster shells from the study site that
are not impacted (a), mildly impacted (b) and severely impacted (c) with mud blisters. Blisters are outlined in red.
One factor that could impact mudworm parasitism in oysters is siltation. Heavier loads of silt on oysters are reported to increase mudworm infestations, but studies report mixed effects to this regard. In 2013, however, oyster growers at a farm in New Brunswick reported an abnormal mudworm outbreak; they also reported that their oysters were dirtier than usual when they were washing them. As such, we conducted a field experiment to test for the effects of siltation on mudworm parasitism in eastern oysters.
The experiment took place at an oyster farm in New Brunswick, Canada where a mudworm outbreak happened in 2013. We collected 60 oysters from this site and gently washed 30 of them to remove silt and didn’t wash the others (so that silt remained). We also collected 30 additional oysters at the beginning of the experiment to make sure that washing didn’t affect the number of mudworms that were present prior to collecting and washing oysters (the gentle washing we employed had no effect on initial mudworm numbers). This gave us two silt treatments: high & low. The high treatment contained approx. 2× more silt. Oysters were then deployed at the oyster farm for 50 days to accumulate mudworms.
We found that oysters from the high silt treatment contained, on average, approx. 1.5× more mudworms than low silt oysters. This result remained the same when we standardized for oyster size.
Our results suggest that increased siltation on eastern oysters can result in increased rates of mudworm parasitism. In the future, increased coastal erosion from sea level rise could exacerbate these mudworm outbreaks. Enhanced washing may help alleviate mudworm parasitism in these oysters, although other mitigation strategies exist. More research is now needed to determine the mechanism for increased parasitism under heavier loads of silt.
Effects of CO2-driven sediment acidification on infaunal marine bivalves: a synthesis
Jeff C Clements & Heather L Hunt
Ocean acidification describes the process whereby increasing amounts of carbon dioxide (CO2) dissolving into the oceans is resulting in a decrease in seawater pH. This process and associated chemical changes in the ocean are documented to have negative effects on a wide range of marine animals. However, CO2 concentrations and pH in sediment porewater (the water that fills spaces between grains of sediment) at the bottom of the ocean far exceed projected conditions under ocean acidification.
Ocean acidification effects on marine organisms are well documented. But the impacts of sediment acidification on animals that live below the sediment in the sea (such as clams and worms) are relatively understudied. However, a recent increase in such studies has occurred and warrants a review of sediment acidification effects. As such, we reviewed peer-reviewed literature and synthesized the effects of sediment acidification effects on marine bivalves that live below the sediment surface.
Based on the literature review, we were able to conclude that more acidic sediments can lead to increased shell dissolution, lesions, and mortality in these bivalves.Some studies reported sediment acidification effects on the uptake of heavy metals in marine bivalves, but these effects appear appear complex and uncertain. Studies (including my thesis) unanimously suggest that these bivalves reduce burrowing and increased dispersal in more acidic sediments. This is likely an adaptive behaviour to avoid the negative effects described above (although it also makes the bivalves vulnerable to other mortality factors like predation). While the decreased burrowing and increased dispersal is likely a good thing, elevated temperatures consistent with ocean warming predictions can compromise this avoidance behaviour, and cause clams to burrow into acidic sediments.
While our literature review elucidated a number of effects of sediment acidification, studies in this area are limited. More work is needed to determine how future climate change might influence the impacts reported in our review, as well as how these impacts affect ecosystem processes.
Open access articles receive more citations in hybrid marine ecology journals
Jeff C Clements
Scholarly open access publishing — making published scholarly articles freely available for anyone on the internet to access — has been adopted in attempt to remove barriers to accessing scholarly information. However, open access costs can be quite substantial for authors and the benefits for authors to publish open access in many disciplines are unknown.
In this paper, I presented the results of a study assessing how often open access (freely accessible) and non-open access (restricted access) articles, published in three marine ecology journals with an open access option, are cited in other scholarly articles. I collected citation data from articles in three hybrid marine ecology journals with similar impact factors as a microcosm to test for open access effects on citations: ICES Journal of Marine Science (Oxford Press), Marine Ecology Progress Series (Inter-Research), and Marine Biology (Springer). I also controlled for a number of other factors that could potentially influence citation rates, including self-citations, article type, time since publication, the number of authors, and the year that the article was published.
I found that open access articles received, on average, 57%, 38%, and 24% more citations than closed access articles for ICES Journal of Marine Science, Marine Ecology Progress Series, & Marine Biology, respectively.
This study suggests that publishing open access can benefit scholarly authors since the reputation of researchers is most often a reflection of the number of times their works have been cited, and can ultimately benefit the broader research community by making scholarly works free and accessible by all. Although the trend observed in my study could be driven by authors’ self-selection to publish only their best work as open access, the results are in line with numerous other studies showing a citation advantage for open access articles.