It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Wednesday, July 03, 2024
Australian bushfire ash is deadly for aquatic life
While the impact of wildfires on terrestrial life has been well studied, only recently has research started to examine the effects of wildfire ash on aquatic organisms. New research reveals that wildfire ash can have lethal consequences on Australian water ecosystems.
Wildfires are becoming more prevalent due to the warming and drying effects of climate change, with Australia becoming especially vulnerable to dangerous bushfires. “Therefore, many Australian species may be threatened by fires,” says Miss Jenelle McCuaig, a Masters student at the University of Alberta, Canada. “This is putting them at greater risk of endangerment and possible extinction.”
Wildfires release ash into the air, which can enter aquatic environments directly or be washed into bodies of water by rainfall. “Once in the water, ash may leach metals and organic combustion products, where they can affect organisms, acquired by ingestion through intestines or respiration through gills,” says Miss McCuaig. There are also serious consequences for humans, as we rely on healthy freshwater ecosystems for water and food.
Miss McCuaig and her team focused their research on two common Australian crustacean species, a crayfish (Cherax destructor) and a shrimp (Macrobrachium australiense).
To examine the effects of wildfire ash on the crustaceans, each species was exposed to a range of ash concentrations to determine their sensitivity and likelihood of survival. Miss McCuaig then measured their oxygen consumption using a respirometry system and took tissue samples to look at their metabolic activity.
After exposure to just 5g of ash per litre of water, Miss McCuaig found that no shrimps could survive – but it took 8 times as much ash to reach complete crayfish mortality. “The huge difference in sensitivity between the two species was much greater than I expected,” says Miss McCuaig.
This research shows that even between similar species, there can be a big difference in survival response to environmental stressors such as wildfire ash. “Differences in body shape and gill structure, as well as habitat preferences, has allowed them to fulfil different niches,” says Miss McCuaig. “Crayfish demonstrated greater resilience to the ash exposure compared to the shrimp.”
For the surviving crayfish and shrimp, the individuals exposed to the highest concentrations of ash had the highest metabolic rates, suggesting a high level of physiological stress. “This is particularly concerning during ash exposure, because increased ventilation means that the animals will be taking up more of the ash particles and leached contaminants from the water, further affecting their body systems.”
“This research will allow us to identify the species that are most threatened by fires and help to inform the development of breeding programs or relocation efforts,” says Miss McCuaig. “When it comes to wildfires, resources are limited, so we must prioritise response actions.”
Miss McCuaig adds that even though many wildfires occur naturally, humans still have a responsibility to protect the living world: “Species conservation begins with wildfire prevention in the first place - it is incredibly important to be educated about, and to implement, fire-safety into our lives to mitigate human-caused wildfires”.
This research was made possible by funding from The Company of Biologists, Natural Sciences and Engineering Research Council of Canada, and the Society for Experimental Biology, as well as collaboration of the Blewett Lab and Franklin Eco-Laboratory.
This research is being presented at the Society for Experimental Biology Annual Conference in Prague on the 2-5th July 2024.
Shark hatching success drops from 82% to 11% in climate change scenario
New experimental research shows that the combined effects of ocean warming and acidification could lead to a catastrophic decrease in embryonic shark survival by the year 2100. This research is also the first to demonstrate that monthly temperature variation plays a prominent role in shark embryo mortality.
Oceanic warming and acidification are caused by greater concentrations of CO2 dissolving into marine environments, resulting in rising water temperatures and falling pH levels. “The embryos of egg-laying species are especially sensitive to environmental conditions,” says Noémie Coulon, a PhD student at the Laboratoire de Biologie des Organismes et des Écosystèmes Aquatiques, France. “The hatching success of embryos is a crucial factor for population dynamics. In the case of skates and sharks, which have a slow pace of life, low hatching rates could be critical for population renewal.”
Small-spotted catsharks (Scyliorhinus canicula) are one of the most abundant shark species in Europe. “The small-spotted catshark is already experiencing habitat loss in coastal areas, particularly during the summer months when egg-laying is at its peak,” says Ms Coulon.
Ms Coulon and her team compared small-spotted catshark embryo survival in three environmental scenarios: one control scenario using baseline temperature and pH data from the years 1995 to 2014, and two using predicted climate scenarios for the year 2100 called the Shared Socioeconomic Pathways (SSPs) as outlined in the United Nations’ Intergovernmental Panel on Climate Change’s Sixth Assessment Report released in 2021.
SSP2, known as the “Middle of the Road” scenario, represents a future where slow and non-uniform progress towards tackling climate change is present but net-zero is not reached, and predicts a temperature rise of 2.7°C and drop in pH of 0.2 by the year 2100.
SSP5, known as the “Fossil-fueled Development” scenario, represents a future where fossil fuel resources continue to be more rapidly exploited across the world, and predicts a temperature rise of 4.4°C and drop in pH of 0.4 by the year 2100.
To assess the impact of these different scenarios, Ms Coulon and her team measured embryo growth and yolk consumption within small-spotted catshark eggs every week over a 4-month period, while recording hatching success and growth of surviving baby sharks for 6 months post-hatching.
While the team found a high survival rate for both the control and SSP2 scenarios (81% and 83% respectively), there was a much lower chance of survival for the SSP5 scenario. “We were shocked by the low survival rate observed in the SSP5 scenario, with only 11% of embryos hatching,” says Ms Coulon. The team indicated that the mortality was linked with lower yolk consumption rates, lower growth rates and failure to transition to internal gills.
This research also highlights the importance of seasonal temperature variation, which can significantly increase mortality during critical egg laying periods. “This mortality was most pronounced in August, coinciding with the highest temperatures (reaching 23.1°C), and during a stage of development where embryos undergo gill reabsorption,” explains Ms Coulon.
Ms Coulon and her team noticed that the surviving 11% did not exhibit the typical growth pattern of the other sharks, which may have contributed to their resistance to environmental change: “What makes these individuals special remains unclear, but by acknowledging the inter-individual variation among young marine organisms, we could better evaluate the future ecological success of species.”
This research offers both a serious caution and a beacon of hope for marine species. “Firstly, it serves as a warning about the responses of other species that may be even more sensitive to environmental change,” explains Ms Coulon. “Secondly, our findings demonstrate that the more moderate SSP2 scenario can limit the damage inflicted on species like the small-spotted catshark, which gives us a positive incentive to reduce our greenhouse gas emissions.”
This project has received funding support from the Save Our Seas Foundation. More information can be found here: https://saveourseas.com/project/bringing-up-baby-shark-embryos-and-our-warming-oceans.
This research is being presented at the Society for Experimental Biology Annual Conference in Prague on the 2-5th July 2024.
New research finds that artificial light at night (ALAN) attracts larval fish away from naturally lit habitats, while dramatically lowering their chances of survival in an “ecological trap”, with serious consequences for fish conservation and fishing stock management.
“Light pollution is a huge ongoing subject with many aspects that are still not well understood by scientists,” says Mr Jules Schligler, a PhD student at CRIOBE Laboratory (Centre de Recherches Insulaires et Observatoire de l’Environnement) in Moorea, French Polynesia.
ALAN is the product of human-related activities such as the use of electrical lights along roads, factories, residences and resorts near bodies of water. “ALAN is everywhere and marine wildlife is not exempt to its effects,” says Mr Schligler. “A quarter of the world coastline is impacted and this level is increasing every year.”
Mr Schligler and his team set out to investigate the effects of ALAN on larval recruitment in tropical fish. Larval recruitment is the number of fish that settle in their habitat and survive their juvenile years before becoming an adult. “Larval recruitment is a key life history trait for fish that impacts on stock replenishment and adult fitness,” he says. “Larval fish are also very dependent on the natural light cycle.”
To investigate these effects, Mr Schligler used 48 corals that were split into two treatments: control corals with only natural light exposure, and ALAN corals that were exposed to light pollution at night of a similar intensity that beach resorts and streetlights produce. They focused on two dominant coral reef damselfish native to French Polynesia, the yellowtail dascyllus (Dascyllus flavicaudus) and the blue-green chromis (Chromis viridis).
“First, we monitored fish settlement to the corals to see if they preferred natural or artificial light conditions,” says Mr Schligler. “The fish were then subjected to a range of experiments to better understand the impact of ALAN after they had settled.” These experiments measured various aspects of development and survival such as growth, metabolic rate and risk of predation.
This research finds that many young fish actually prefer environments with artificial light, recruiting 2-3 times as many fish than naturally lit environments.
The study also reveals the harmful effects of ALAN on fish growth, metabolic rate and overall survival. “ALAN has produced an ecological trap where these fish, misled by human activity, now prefer habitats where their fitness will be lower,” says Mr Schligler. “In other words, ALAN has the potential to attract organisms to a less suitable environment, generating a peculiar anthropogenic stressor."
These results have implications for fish conservation and harvesting policies. “Marine protected areas have only started to consider light pollution in their management policy very recently,” says Mr Schligler. “To better understand fish stock replenishment and conservation, it is crucial to take into account as many factors as we can, such as the rarely considered effects of light pollution.”
This research is being presented at the Society for Experimental Biology Annual Conference in Prague on the 2-5th July 2024.
Experimental coral.
CREDIT
Jules Schligler
Pregnant fish can also get “baby brain”, but not the way that mammals do
SOCIETY FOR EXPERIMENTAL BIOLOGY
IMAGE:
BRAIN STAINING OF PREGNANT FISH. ON THE LEFT IS THE NISSL STAINING USE TO DETERMINE NEURON MORPHOLOGY AND ON THE RIGHT IS KI67 STAINING WHICH STAINS FOR CELL PROLIFERATION.
New research reveals that pregnancy-related brain impairment is present in live-bearing fish, but instead of affecting learning and memory as expected from similar research on mammals, it appears to have a stronger impact on decision-making and sensory reception.
There have been many studies into the detrimental impact of pregnancy on mammalian brains, sometimes called “baby brain” or “momnesia” in humans, revealing how the disruption of neurological processes like neurogenesis, or the creation of new neurons, can affect learning and memory - but this is the first study to examine this phenomenon in fish.
While most fish reproduce by laying eggs, some species are live-bearing, or viviparous, and carry their offspring internally before producing live young. Viviparous species include popular aquarium fish from the family Poeciliidae, such as guppy, molly and platy.
“We wanted to see if these pregnancy-related changes in cognition and neurogenesis occur in other live-bearing evolutionary lineages, particularly in a species which lacks a placenta,” says Tiffany Ernst, a PhD candidate in the field of developmental and reproductive biology at Wageningen University, Netherlands. “In mammals, the placenta is thought to help regulate pregnancy-related changes to the mother’s brain.”
“The species of fish that I work with, Poeciliopsis gracilis, is especially interesting as they are superfetatious, meaning they can be pregnant with multiple temporally overlapping broods of offspring simultaneously,” says Ms Ernst. “Essentially, my fish are almost constantly pregnant in adulthood - so any detrimental impact on cognition might be more evident in this species.”
“We hoped to learn how pregnancy might induce changes to the maternal brain in a non-mammalian live-bearing species,” says Ms Ernst. “This could help us to understand whether the evolution of a live-bearing reproductive strategy requires neurological trade-offs to adequately adapt for a healthy pregnancy.”
To examine the impact of pregnancy on cognition, pregnant and virgin fish were trained to associate a green disk with the location of food, and then perform a spatial learning task when presented with two seemingly identical disks in different locations. “Then we tested their cognitive flexibility by swapping the locations of the rewarded and non-rewarded disks to see how the fish adjusted to the new location of the food reward,” says Ms Ernst.
To assess the effect on fish neurology, Ms Ernst and the team removed the brains of the pregnant and virgin females and used cell staining to identify areas of new cell proliferation - an indicator of which areas of the brain were producing new cells.This study is the first to map the areas of brain cell proliferation in this species in a “brain atlas”.
Ms Ernst and her team found that while both pregnant and virgin fish were equally successful in both cognitive tasks, pregnant fish were much more hesitant when choosing which disk to approach.
“We also found no difference in cell proliferation in the regions of the brain most responsible for learning and memory,” says Ms Ernst. “However, we were surprised to see that pregnant females exhibited decreased cell proliferation in the regions which contribute to maternal olfactory reception.”
This surprising result suggests that pregnancy compromises the fish’s ability to interpret scent in the water, which may contribute to their choice-aversion in the cognitive tests. “For P. gracilis, reduced choice-propensity during pregnancy might be an adaptive strategy wherein females do not take the risk of foraging for food when the reward is not guaranteed, thus conserving energy for reproduction,” says Ms Ernst.
“Our research indicates that pregnancy may impact maternal cognition and alters brain cell proliferation, but not in the same ways as we would expect from mammals,” says Ms Ernst. “This implies that pregnancy across different evolutionary lineages has an impact on the maternal brain which in turn, affects how mothers cognitively and physiologically adapt to the burdens of live-bearing reproduction.”
This research is being presented at the Society for Experimental Biology Annual Conference in Prague on the 2-5 th July 2024.
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