Belgium

Coastal habitats are among the most productive ecosystems on Earth, acting as biodiversity hotspots and essential nursery grounds for marine life. In Scandinavia, seagrass Zostera marina habitats provide food and shelter for many fishes. However, these meadows are typically confined to shallow areas due to water turbidity and eutrophication. As global warming intensifies the severity, frequency, and duration of heat waves, eelgrass-associated fishes are increasingly at risk of thermal stress. Yet, the extent of species-specific thermal limits and their plasticity for acclimation remains poorly understood. To address this gap, we investigated the effects of warming on wild eelgrass-associated fish during summer, when their thermal history is highest and temperature extremes are most impactful. We exposed twelve species from six families to a control temperature (19°C) or a simulated heatwave (23°C) for five days. We then studied their thermal tolerance using the Critical Thermal Maximum (CTmax) test and measured the temperature at loss of equilibrium. Our results showed differences in upper thermal limits across species, partly influenced by phylogenetic history. Most species exhibited an acclimation response to warming, reflected by an increase in CTmax, though some species acclimated faster than others. Our findings emphasize the importance of considering species-specific thermal responses when assessing the ecological impacts of heatwaves on coastal fish communities.

SEB Conference 2025

Capacity for rapid thermal acclimation differs across eelgrass-associated fishes

seagrass fauna

thermal sensitivity

climate warming

ectotherm

plasticity

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Pacific salmonids are anadromous and generally migrate to the Bering Sea in summer to forage. Chum salmon (Oncorhynchus keta), one of the most abundant Pacific salmonids in the summer Bering Sea, spends a significant portion of its life at sea. However, due to its migratory nature, little is known about its foraging migration ecology. This study investigated the open-ocean migratory behavior of chum salmon using satellite pop-up archival tags (PSATs). A chum salmon, captured in the central Bering Sea (56.0°N, 175.0°W) on 30th July 2024, was tagged with a PSAT (miniPAT-348) and released. The PSAT surfaced as scheduled 75 days later in the North Pacific Ocean near the waters off Amchitka Island, Aleutians (50.8°N, 179.3°E). Over the next seven days, the PSAT transmitted depth, water temperature, and activity data, with 50.4% of the recorded data successfully retrieved. From 60 days after release until three days before surfacing, the PSAT recorded sea surface temperatures above 20 °C, suggesting predation by an endothermic fish. The estimated migration path, excluding the predation period, indicated a generally southward movement from the release site but remained in the Bering Sea. The salmon primarily used the surface (above 20 m) but occasionally dived below the thermocline (below 40 m). The fish did not exhibit diel vertical movement; however, it tended to increased activity around sunrise and sunset. This study provides insights for the open-ocean migratory behaviour of chum salmon but further study is required to explore this in more detail.

Ocean Migration Behaviour of Chum Salmon in the Summer Bering Sea Using Pop-up Satellite Archival Tag　

Environmental temperature is a key determinant of fitness in insects, influencing survival, reproduction, and behaviour. With climate change increasing the frequency and intensity of extreme thermal events, it is crucial to understand the adaptational capacity of insects to this new thermal reality. While the impacts of acute thermal stress on physiological traits are well-documented, less is known about the developmental effects of such extreme events, particularly regarding environmental buffering mechanisms like parental care behaviours. In this study, we investigated how exposure to a heatwave during the larval stage ofNicrophorus vespilloidesinfluenced reproductive success and parental care in adulthood. Larvae were exposed to either a heatwave (26°C for 72 hours) or kept at control conditions (20°C) and assessed for reproductive and behavioural outcomes in the adult focal individuals and their offspring. We found that heatwave exposure significantly reduced survival to eclosion in the focal larvae. However, there was no significant impact of the heatwave on either the parental behaviour or the duration of care exhibited. Similarly, no developmental effects of thermal stress were observed on adult reproductive traits or for offspring fitness. These results suggest that extreme thermal events early in life do not necessarily have long-term detrimental effects, contrary to recent findings on ontogenetic sensitivity in insects. This highlights the complex interactions between temperature and insects’ life history and underscores the need for further research to more accurately assess resilience in a rapidly changing world.

Exploring developmental effects of acute thermal stress on reproductive and parental care abilities in burying beetles

Light pollution is the most common and fastest-growing form of urban pollution worldwide. While urbanization is recognized as one of the primary drivers of the global decline of amphibians, little attention has been paid to the impact of artificial light at night (ALAN) on this particularly threatened group of vertebrates. In this study, we investigate the direct effects of two types of LED lights (5 lux warm-2700K and 5 lux cold-6000K) on the metabolic rate of larvae of the crested newt species,Triturus ivanburschi. We also examined the delayed effects of ALAN. Metabolic activity was investigated in juvenile individuals three weeks after their development under ALAN. The oxygen uptake of individuals at rest was measured as a proxy for the standard metabolic rate at both life stages. Our findings showed that larvae developed under both cold and warm LED lights had higher metabolic rates compared to the control group. However, in juveniles, alterations were observed only in individuals that have been exposed to cold LED lights; these individuals exhibited lower metabolic activity than both the control and warm LED groups. Overall, the results suggest that ALAN affects the metabolic activity of crested newt larvae, with possible delayed effects in subsequent life stages. These changes may have long-term negative impacts on the fitness of newt populations, which is crucial for biodiversity conservation in a world plagued by light pollution.

How exposure to artificial light at night affects the metabolic rate of crested newts during early life stages

Artificial light at night (ALAN) is a widespread pollutant that impacts wildlife at various levels. However, our understanding of the effects of ALAN on amphibians, particularly tailed amphibians, is limited. In this study, we examined how ALAN affects the development, growth rate, and activity of larvae from two species of crested newts:Triturus macedonicusandT. ivanbureschi, as well as their hybrids. Given that responses to ALAN can vary based on light intensity, spectral composition, and duration of exposure, we compared the effects of warm (2700K) LED light and cold (6000K) LED light. Larvae were exposed to two light intensities (5 lux and 30 lux) from hatching until they reached developmental stage 62. Our results indicated that while both types of light can alter development, body size, and movement activity, cold LED light at higher intensity resulted in more significant effects. Comparing the species, we found thatT. ivanbureschiand theT. macedonicus-mothered hybrids showed a greater response to ALAN. Specifically, these larvae experienced prolonged development, lower growth rates, and reduced activity when exposed to 30 lux of cold light. This type of light is generally considered to be more harmful to organisms. Our research highlights the complex effects of ALAN on amphibians and emphasizes the difficulty in generalizing its impact across different species.

Effects of two types of LED lights at night on the development, body growth, and behavior of larvae of two crested newts species and their hybrids

As ectothermic animals, fish are particularly vulnerable to the impacts of rising temperatures, with many populations approaching their thermal limits. A holistic understanding of the vulnerability of fish populations is thus vital to mitigate environmental and societal impacts under climate warming. While early life stages have been suggested to be more vulnerable to thermal stress than juveniles and adults, existing methods for measuring heat tolerance are inconsistent between fish life stages. These methodological inconsistencies have fuelled debates about the increased sensitivity of embryos to thermal stress and have limited our ability to predict the impacts of climate change on fish populations. Fortunately, alternative approaches to measuring thermal tolerance now allows us to standardise assessments across life stages. I propose to conduct a distributed experiment—uniting researchers across the world to collect data on embryonic thermal tolerance using standardised methods. These experiments will be simple, replicated across various species and regions, and all contributors will be co-authors on the resulting publication. By identifying the developmental stage most sensitive to heat stress, this project will yield crucial knowledge to predict the impacts of climate change on fish populations.

A call for distributed experiments on fish embryonic thermal tolerance

Koala populations in Australia have declined by 54% in the last three decades. Millions of dollars are spent annually on protecting koalas, focussing on safeguarding habitat and treating disease. Yet, two thirds of all koala deaths occur when they are moving along the ground, due to vehicle strikes and dog attacks. Despite decades of research, little is known about how koalas move on the ground. Traditional GPS tracking provides limited insight into these movements, as they generally record locations only once or twice a day. To address this gap, we use accelerometers—bio-loggers that record three-dimensional movement at hundreds of points per second—to determine the orientation and movement of koalas during specific behaviours. We collared 10 koalas in the wild with accelerometers and high-resolution GPS devices for an average of 8 days. From these data, we quantified (1) the frequency and duration of ground visits, (2) the speed and distance moved, and (3) the locomotion style used on the ground (e.g., walking, bounding). We found that koalas visited the ground three times per day on average, totalling only 45 minutes. Koalas travelled on average 260 metres per ground visit, mainly walking at 1.7 km/h with occasional bounding at 10.4 km/h. Combining accelerometer and GPS data, we identified the specific trees koalas moved between. This is the first comprehensive analysis of koala movement in the wild, revealing new insights into their ground behaviour. Understanding these movement patterns is crucial for protecting koalas where they are most vulnerable.

Monitoring the 'Mundane': What Do Koalas Do When They're NOT Sleeping?

The king penguin is one of the champion avian divers, surpassed only by its larger relative, the emperor penguin. The foraging ecology of king penguins is typically studied during the austral summer, when foraging trips are relatively short (weeks). Consequently, little is known about the fall/winter period, when birds undertake long foraging trips (months) and the descent of their preferred prey to greater depth might challenge their dive capacity. Investigating the dive behaviour of 7 king penguins from the Crozet Islands during fall/winter, we found that birds conducted deeper and longer dives during this period. Most birds exceeded the previous depth and duration records but the deepest (424.5 m) and longest (10 min) dives were conducted by the same individual. These dives are the deepest and longest yet reported for king penguins and illustrate their ability to respond to seasonal changes by enhancing their dive capacity, likely through gradual acclimatization.

Exploring new depths: king penguins break dive records during the austral winter

Supervised machine learning is widely used to detect fine-scale animal behaviour from accelerometer data. However, there is currently no standardised protocol for verifying the accuracy of this technique, and the risks associated with common machine learning verification pitfalls have yet to be widely recognised. One such pitfall is model overfitting, which occurs when a model becomes too closely aligned with the training data, memorising noise rather than capturing generalisable patterns. As a result, while the model may show high performance on the training set, its ability to generalise to new, unseen data is compromised. This limitation can be detected with the application of robust time-series specific validation techniques. We conducted a systematic review of 119 accelerometer-based behaviour classification supervised machine learning papers to see what proportion of existing literature conducted appropriate time-series validation. We found that 79% (94 papers) did not validate their models sufficiently well to identify potential overfitting. Although this does not inherently imply that these models are overfit, the absence of independent test sets limits the interpretability of their results. To address these challenges, we provide a theoretical overview of overfitting in the context of time-series accelerometer data and propose succinct, ecologist-accessible guidelines for optimal time-series validation techniques. Our aim is to equip ecologists with the tools necessary to adapt general machine learning theory to the specific requirements of time-series biologging, facilitating reliable overfitting detection and continuing to advance the field.

Practical Guidelines for Supervised Machine Learning Model Validation in Accelerometer-based Animal Behaviour Classification

Background: There is individual variability in the response of core body temperature (CBT) during exposure to heat load. Ewes classified as having high rectal temperatures on hot days before breeding had smaller lambs, with those lambs having lower survival rate than the lambs from ewes that had a lower rectal temperature on hot days before breeding. The ability to classify animals as having either a high or low body temperature suggests the possibility that a thermal phenotype may exist in CBT.
Aims: Rumen temperature (Trumen ) was recorded as a proxy for CBT in ewes during summer to determine whether a repeatable thermal phenotype could be identified within individuals.
Methods: Trumen  was recorded every five minutes over 34 days during the hottest period of summer in 43 ewes kept in a paddock with no access to shade, while data from a weather station were used to calculate the average daily temperature-humidity index. On each day, each ewe was ranked based on its 95th  percentile Trumen  for that day. The consistency of the ranking was assessed across days by correlating each ewe’s ranking on a given day with its ranking on every other day during summer.
 Results: The individual ranking of Trumen  was stable over time, with the correlation coefficient between days ranging between 0.25 and 0.75.
 Conclusion and Implications: Ewes have a thermal phenotype in CBT during summer. This thermal phenotype may impact animal performance and welfare.

Identifying a thermal phenotype from field measurement of the core temperature of ewes

In the Mediterranean, populations of the spider crab, Maja squinado, are drastically declining. As a necessary step for successful restoration programs, this study focuses on ontogenetic changes in M. squinado (from larvae to adults), and takes into account intrinsic factors such as energy balance, size, molt and gender. For this purpose, individual routine metabolic rates were collected from reared larvae and juveniles and wild-caught adults. Results revealed distinct metabolic variations throughout development.
Zoea 1, the first planktonic larval stage, has higher metabolic rates than zoea 2, likely due to an increase in inactive material and reliance on egg reserves, while zoea 2 depends on external food. As development progresses to megalopa and benthic juvenile stages, metabolic rates rise exponentially, reflecting increased activity and organ development, making essential self-maintenance processes more energy dependent. From 7-month-old juveniles to adults, metabolic rates decline, likely due to extended intermolt periods and reduced growth, along with different survival strategies and behaviors. In reproductive adults, males have twice the metabolic rate of females, possibly due to territorial competition and reproductive efforts. Metabolic rate inversely correlates with size: individuals under 20 g consume oxygen at twice the rate of those over 80 g. Molting significantly impacts metabolism, with lower rates in post-molt individuals compared to pre-molt stages.
The successful rearing of M. squinado and the significant physiological insights gained into the different developmental stages enhance our understanding of the species' ecosystem interactions, and pave the way for further analyses before the implementation of restoration trials.

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Ocean Migration Behaviour of Chum Salmon in the Summer Bering Sea Using Pop-up Satellite Archival Tag

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Capacity for rapid thermal acclimation differs between life stage and species in fish

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