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In April and May of 2020, a large phytoplankton bloom composed primarily of the dinoflagellate Lingulodinium polyedra reached historic levels in geographic expanse, duration, and density along the coast of southern California, United States, and Baja California Norte, Mexico. Here, we report the water quality parameters of dissolved oxygen and pH over the course of the red tide, as measured by multiple sensors deployed in various locations along San Diego County, and document the extent of mass organism mortality using field surveys and community science observations. We found that dissolved oxygen and pH corresponded with bloom dynamics, with extreme hypoxic and hyperoxic conditions occurring at multiple locations along the coast, most notably within select estuaries where dissolved oxygen reached 0 mg L−1 and hypoxia occurred for up to 254 consecutive hours, as well as along the inner shelf of the open coast where dissolved oxygen dropped as low as 0.05 mg L−1. Similarly, pH ranged widely (6.90–8.79) across the bloom over both space and time, largely corresponding with dissolved oxygen level. Extreme changes in dissolved oxygen and pH, in addition to changes to other water parameters that affect organismal health, ultimately led to documented mortalities of thousands of demersal and benthic fishes and invertebrates (primarily within estuarine and inner-shelf environments), and long-term surveys within one lagoon showed protracted changes to benthic infaunal density and species composition. In addition to field observations, we also quantified water quality parameters and organism mortalities from four local aquarium facilities, with varying levels of filtration and artificial oxygenation, and documented the morphological changes in the gills of captive-held Pacific sardine in response to the red tide. We show that multiple factors contributed to organismal stress, with hypoxia likely being the most widespread, but not the only, cause of mortality.

ABSTRACT The invasive Diadema setosum (Leske, 1778) long‐spined sea urchin has been in the Mediterranean Sea since 2006, and then, it has been known that its population density has reached high values on the southern Aegean coasts of Türkiye. This study aimed to report the mass mortality event of D. setosum with the determined agent on the Aegean coast of Türkiye. In addition, it was targeted to provide information on the current status of its density based on seasonal SCUBA diving observations for the period between January 2023 and November 2023. The results showed that the mass mortality of D. setosum was determined in Muğla, Aegean Sea, in August 2023. Spine loss, the mucoid layer at the bottom of the appendages, and the outer body surface were observed as the clinical symptoms of the diseased samples. Bacterial growth was detected on Vibrio‐selected TCBS agar plates, while no other parasitic agents were determined in the coelomic fluid of sea urchins. The results of the biochemical (API 20E) and molecular tests confirmed the isolated bacteria as Vibrio spp. The density of D. setosum showed statistically significant temporal changes, and the highest and lowest mean density values were recorded in autumn and spring, respectively. Environmental stressors, such as increasing sea temperature levels, affect the marine ecosystem and lead to opportunistic pathogens. Long‐term monitoring of disease outbreaks is necessary to understand the interactions between species and the ecosystem. [ABSTRACT FROM AUTHOR]

Abstract Maternal investment theory is the study of how breeding females allocate resources between offspring size and brood size to achieve reproductive success. In classical trade-off models, r/K-selection and bet-hedging selection, the primary predictors of maternal investments in offspring are population density and resource stability. In crowded, stable environments, K-selected females invest in large offspring at an equivalent cost in brood size. In uncrowded, unstable environments, r-selected females invest in large broods at an equivalent cost in offspring size. In unpredictable resource environments, bet-hedging females invest moderately in brood size and offspring size. The maternal risk-management model represents a profound departure from classical trade-off models. Maternal investments in offspring size, brood size, and brood number are shaped independently by autonomous risk factors: the duration of gaps in resources during seasonal cycles, rates of predation, and unpredictable catastrophic events. To date, no single model has risen to a position of preeminence. Here in sharks, we show that maternal investments within and across species do not agree with the predictions of trade-off models and instead agree with the predictions of the maternal risk-management model. Within and across shark species, offspring size and brood size were independent maternal investment strategies. The risk of starvation favored investments in larger offspring. The risk of predation favored investments in larger broods. If empirical studies continue to confirm its predictions, maternal-risk management may yet emerge as a unifying model of diverse reproductive adaptations by means of natural selection.

Mass oyster mortality occurred at an oyster farm in the Setiu Lagoon on the east coast of Peninsular Malaysia in December 2023. According to interviews with aquaculture farmers, heavy rains that occurred from 20 November to early December caused flooding in the surrounding area, leaving it exposed to low-salinity water for a long period. Mass mortality occurred at oyster farms in early December, with farmers estimating that the dead oysters had a shell length of 1–5 cm and mortality rate of over 90%, and that approximately 50,000 oysters had died. An analysis of meteorological data indicated that a monthly rainfall value of more than 1200 mm/month, which is more than double the normal amount, was observed in November in the same region. During the same period, the seawater temperature in the South China Sea was 1°C higher than normal, and the northeast monsoon caused winds from the northeast to transport moist air to the eastern coast of Peninsular Malaysia, causing heavy rain. Currently, only one waterway, approximately 200 m wide, connects the lagoon to the sea. Until approximately 2012, two waterways were connected to the sea. We concluded that by increasing the number of channels to two, the decrease in salinity in the lagoon during the rainy season could be reduced by enhancing phytoplankton occurrence.

Maternal investment theory is the study of how breeding females allocate resources between offspring size and brood size to achieve reproductive success. In classical trade-off models, r/K-selection and bet-hedging selection, the primary predictors of maternal investments in offspring are population density and resource stability. In crowded, stable environments, K-selected females invest in large offspring at an equivalent cost in brood size. In uncrowded, unstable environments, r-selected females invest in large broods at an equivalent cost in offspring size. In unpredictable resource environments, bet-hedging females invest moderately in brood size and offspring size. The maternal risk-management model represents a profound departure from classical trade-off models. Maternal investments in offspring size, brood size, and brood number are shaped independently by autonomous risk factors: the duration of gaps in resources during seasonal cycles, rates of predation, and unpredictable catastrophic events. To date, no single model has risen to a position of preeminence. Here in sharks, we show that maternal investments within and across species do not agree with the predictions of trade-off models and instead agree with the predictions of the maternal risk-management model. Within and across shark species, offspring size and brood size were independent maternal investment strategies. The risk of starvation favored investments in larger offspring. The risk of predation favored investments in larger broods. If empirical studies continue to confirm its predictions, maternal-risk management may yet emerge as a unifying model of diverse reproductive adaptations by means of natural selection. [ABSTRACT FROM AUTHOR]

Thylacocephalans are enigmatic fossil marine euarthropods, often associated with pancrustaceans. Known from at least the Silurian to the Cretaceous, they have a patchy fossil record stratigraphically. They were particularly diversified during the Triassic, which is considered as the period with their highest taxonomic richness. Unknown until recently in the fossil record of Slovenia, many specimens of thylacocephalans have been collected from the Middle Triassic beds (Anisian) of the Velika planina member and Strelovec Formation in the Kamnik-Savinja Alps, as well as in the Upper Triassic beds (Carnian) of the Martuljek Formation in the Julian Alps. In this study, we report eight thylacocephalan taxa, including three new species. Atropicaris lintveri sp. nov. is described from the Velika planina member and represents the oldest mention of Atropicaris. In the Strelovec Formation, common Middle and Late Triassic taxa, including the oldest mention of Microcaris, are documented (Microcaris sp., Atropicaris aff. lintveri) and two new morphotypes are also identified, including Kamnikaris cemazevkaensis gen. et sp. nov. Finally, Austriocaris sp., Atropicaris sp. and Microcaris ajdovskae sp. nov. are described from the Martuljek Limestone Formation, in which accumulations of specimens probably resulting from numerous mass mortality of swarm of thylacocephalans are observed. Based on those new findings, we compile diversity data for Triassic thylacocephalans and investigate their diversification. We show that the thylacocephalan diversity is relatively high as early as the Early Triassic. [ABSTRACT FROM AUTHOR]

To the best of our knowledge, this study is the first to track and demonstrate the mortality event in Diadema setosum (Leske, 1778) along the Egyptian Red Sea coasts. The diadematid is a group of echinoid echinodermates that play an important ecological role in marine ecosystems. However, the current global mass mortality events in Diadema setosum have the potential to significantly change the fundamental structure of the ecosystem. This report was based on the 2023-summer observations of a D. setosum die-off during an ecological investigation in the northern Red Sea, Egypt. To determine the entirety of the event, a group from the Red Sea protectorates carried out an extensive survey simultaneously. The current survey covered the coastal regions of the Elba protectorate in the south, the Wadi El Gemal protected area in the middle, and Hurghada in the north. A diverse population of D. setosum was found dead on the bottom during both snorkeling and scuba diving. Representative photographs were taken at each explored site. Several features were noticed in the dead D. setosum, including a frail body, sand-covered body parts, spines distributed on the bottom, and inactive tube feet. The current findings, therefore, recommend crucially the performance of regular monitoring for the status of D. setosum. In addition, biological and ecological investigations are needed as soon as possible to interpret the causative and potential factors responsible for D. setosum loss. [ABSTRACT FROM AUTHOR]

The cage method for the cultivation of the seaside scallop Mizuhopecten yessoensis is the most developed and popular method at sea farms in Primorsky Krai (Sea of Japan). However, this method of mollusk cultivation requires the careful planning of farming activities. Recently, mariculture farms in different countries have often encountered the mass mortality of cultured hydrobionts. The causes of such diseases are not quite clear, and often their identification requires a large amount of time and financial expenditure. Therefore, the use of predictive mechanisms based on biomarkers can help identify hidden threats in cultured scallop organisms that lead to mass mortality. In this study, we propose a rapid diagnostic method for predicting the distant mass mortality of M. yessoensis cultured in cages using biomarkers. The assessment of the pathological state of cultured mollusks at earlier developmental stages using the DNA comet method and oxidative stress markers (malondialdehyde) will allow the diagnosis and prediction of significant losses of marketable individuals in marine farms. In this study, we evaluated different age groups of mollusks cultured in the different water areas of Peter the Great Bay (Sea of Japan). During the study, we found that the death of cultured mollusks increased with increasing DNA damage and the active accumulation of malondialdehyde in tissues. It was observed that in scallops aged 1+ cultured in Severnaya Bay, high levels of DNA molecule damage and malondialdehyde were registered in the digestive glands and gills, which subsequently led to the death of almost all marketable individuals aged 3+. Therefore, the work is of significant value in assisting the aquaculture industry in solving the emerging problems of scallop farming and preserving marketable products. The proposed markers effectively reflect the condition of molluscs under extreme conditions caused by various factors, making them highly suitable for monitoring studies and forecasts on aquaculture farms. [ABSTRACT FROM AUTHOR]

Introduction: The black coral Leiopathes glaberrima is a key component of deep-sea animal forests of the Western Mediterranean and North-Atlantic hard bottoms. Due to its ecological role, biological characteristics and sensitivity to fishing activities, it has been included in the Annex II of the Barcelona Convention, listed as an endangered species in IUCN Red Lists, and recognized as an indicator of Vulnerable Marine Ecosystems by the FAO. Methods: During a survey conducted in the Strait of Sicily, 140 ROV transects were carried out allowing the characterization of environmental preferences, associated fauna and population structure of L. glaberrima in the study area. Results and discussion: 1020 colonies were distributed between 165 and 672 meters and arranged in 17 patches and isolated colonies. The average height was determined to be 40.9 ± 1.0 cm, with the range spanning from a minimum of 5 cm up to nearby 200 cm. Pristine colonies accounted for 62.9%, mainly constituted by small-sized individuals densely aggregated (up to 14.5/m2 in a single frame) in the eastern part of the area. 24.5% of the specimens were dead and localized in the western margin where we reported a rare case of mass mortality in the deep-sea environment and the first ever described for black corals, opening new scenarios regarding the possibility that these events can occur in environments previously considered safe from danger. The triggering causes of these events in inaccessible environments are actually only hypothesized, but it is not to be excluded that, sooner or later, a similar effect could potentially result from anthropogenic climate changes. [ABSTRACT FROM AUTHOR]

The bivalve mollusc Pinna nobilis, endemic to the Mediterranean Sea, has been vanishing since 2016 from the whole basin because of an infection by multiple pathogens that caused mass mortality events. In the Eastern Mediterranean, some small populations seem to be resistant to the infection. These individuals could represent the only possibility for the species to recolonize desert habitats. Thus, according to the recommendations of IUCN, looking for living specimens of P. nobilis is a priority. With this goal in mind, we carried out surveys in different areas of Southern Italy, and in 2018, we launched a Citizen Science campaign to involve recreational and professional divers in this challenge. As a result of a monitoring activity carried out in 2022–2024, along the Ionian coast of Apulia, in Southern Italy, we can say that there are no more living specimens there but only empty shells. Concurrent to the vanishing of the queen P. nobilis, its congeneric P. rudis, resistant to the infection, seems to be taking advantage, becoming more common and colonizing habitats once exclusive to P. nobilis. In fact, from different areas of the Mediterranean, sightings of the new possible queen, P. rudis, are increasing, together with the discovery of individuals exhibiting morphological traits that are a mixture of the two species. In some cases, these morphological features are not easy to detect; nevertheless, the presence of these hybrids, resistant to the infection, is important for the conservation of the species. [ABSTRACT FROM AUTHOR]

Freshwater bivalves play key ecological roles in lakes and rivers, largely contributing to healthy ecosystems. The freshwater pearl mussel, Margaritifera margaritifera, is found in Europe and on the East coast of North America. Once common in oxygenated streams, M. margaritifera is rapidly declining and consequently assessed as a threatened species worldwide. Deterioration of water quality has been considered the main factor for the mass mortality events affecting this species. Yet, the role of parasitic infections has not been investigated. Here, we report the discovery of three novel protist lineages found in Swedish populations of M. margaritifera belonging to one of the terrestrial groups of gregarines (Eugregarinorida, Apicomplexa). These lineages are closely related–but clearly separated–from the tadpole parasite Nematopsis temporariae. In one lineage, which is specifically associated with mortality events of M. margaritifera, we found cysts containing single vermiform zoites in the gills and other organs of diseased individuals using microscopy and in situ hybridization. This represents the first report of a parasitic infection in M. margaritifera that may be linked to the decline of this mussel species. We propose a tentative life cycle with the distribution of different developmental stages and potential exit from the host into the environment. [ABSTRACT FROM AUTHOR]

The Akoya pearl oyster (Pinctada fucata (Gould)) is the most important species for pearl cultivation in Japan. Mass mortality of 0-year-old juvenile oysters and anomalies in adults, known as summer atrophy, have been observed in major pearl farming areas during the season when seawater temperatures exceed about 20 _C since 2019. In this study, we identified a novel birnavirus as the pathogen of summer atrophy and named it Pinctada birnavirus (PiBV). PiBV was first presumed to be the causative agent when it was detected specifically and frequently in the infected oysters in a comparative metatranscriptomics of experimentally infected and healthy pearl oysters. Subsequently, the symptoms of summer atrophy were reproduced by infection tests using purified PiBV. Infection of juvenile oysters with PiBV resulted in an increase in the PiBV genome followed by the atrophy of soft body and subsequent mortality. Immunostaining with a mouse antiserum against a recombinant PiBV protein showed that the virus antigen was localized mainly in the epithelial cells on the outer surface of the mantle. Although the phylogenetic analysis using maximum likelihood method placed PiBV at the root of the genus Entomobirnavirus, the identity of the bi-segmented, genomic RNA to that of known birnaviruses at the full-length amino acid level was low, suggesting that PiBV forms a new genus. The discovery of PiBV will be the basis for research to control this emerging disease. [ABSTRACT FROM AUTHOR]

Bioinvasions constitute both a direct and an indirect threat to ecosystems. Direct threats include pressures on local trophic chains, while indirect threats might take the form of an invasion of a microorganism alongside its host. The marine dinoflagellate Hematodinium perezi, parasitizing blue crabs (Callinectes sapidus), has a worldwide distribution alongside its host. In Greece, fluctuations in the blue crab population are attributed to overexploitation and the effects of climate change. The hypothesis of the present study was that blue crab population reductions cannot only be due to these factors, and that particular pathogens may also be responsible for the fluctuations. To investigate this hypothesis, both lethargic and healthy blue crab specimens were collected from three different fishing sites in order to assess the health status of this important species. Together with the lethargic responses, the hemolymph of the infested crabs presented a milky hue, indicating the first signs of parasitic infestation with H. perezi. The histopathological results and molecular identification demonstrated the effect of the presence of H. perezi in the internal organs and their important role in the mortality of blue crabs. Specifically, H. perezi, in three different tissues examined (heart, gills, hepatopancreas), affected the hemocytes of the species, resulting in alterations in tissue structure. Apart from this dinoflagellate parasite, the epibiotic peritrich ciliate Epistylis sp. was also identified, infecting the gills. This study represents the first detection of H. perezi in the eastern Mediterranean, demonstrating that this is the main causative agent of blue crab mortality on Greek coastlines. [ABSTRACT FROM AUTHOR]

IntroductionThe black coral Leiopathes glaberrima is a key component of deep-sea animal forests of the Western Mediterranean and North-Atlantic hard bottoms. Due to its ecological role, biological characteristics and sensitivity to fishing activities, it has been included in the Annex II of the Barcelona Convention, listed as an endangered species in IUCN Red Lists, and recognized as an indicator of Vulnerable Marine Ecosystems by the FAO.MethodsDuring a survey conducted in the Strait of Sicily, 140 ROV transects were carried out allowing the characterization of environmental preferences, associated fauna and population structure of L. glaberrima in the study area.Results and discussion1020 colonies were distributed between 165 and 672 meters and arranged in 17 patches and isolated colonies. The average height was determined to be 40.9 ± 1.0 cm, with the range spanning from a minimum of 5 cm up to nearby 200 cm. Pristine colonies accounted for 62.9%, mainly constituted by small-sized individuals densely aggregated (up to 14.5/m2 in a single frame) in the eastern part of the area. 24.5% of the specimens were dead and localized in the western margin where we reported a rare case of mass mortality in the deep-sea environment and the first ever described for black corals, opening new scenarios regarding the possibility that these events can occur in environments previously considered safe from danger. The triggering causes of these events in inaccessible environments are actually only hypothesized, but it is not to be excluded that, sooner or later, a similar effect could potentially result from anthropogenic climate changes.

Theoretically, species' characteristics should allow estimation of dispersal potential and, in turn, explain levels of population genetic differentiation. However, a mismatch between traits and genetic patterns is often reported for marine species, and interpreted as evidence that life-history traits do not influence dispersal. Here, we couple ecological and genomic methods to test the hypothesis that species with attributes favouring greater dispersal potential-e.g., longer pelagic duration, higher fecundity and larger population size-have greater realized dispersal overall. We used a natural experiment created by a large-scale and multispecies mortality event which created a "clean slate" on which to study recruitment dynamics, thus simplifying a usually complex problem. We surveyed four species of differing dispersal potential to quantify the abundance and distribution of recruits and to genetically assign these recruits to probable parental sources. Species with higher dispersal potential recolonized a broader extent of the impacted range, did so more quickly and recovered more genetic diversity than species with lower dispersal potential. Moreover, populations of taxa with higher dispersal potential exhibited more immigration (71%-92% of recruits) than taxa with lower dispersal potential (17%-44% of recruits). By linking ecological with genomic perspectives, we demonstrate that a suite of interacting life-history and demographic attributes do influence species' realized dispersal and genetic neighbourhoods. To better understand species' resilience and recovery in this time of global change, integrative eco-evolutionary approaches are needed to more rigorously evaluate the effect of dispersal-linked attributes on realized dispersal and population genetic differentiation.

This article discusses the mass disappearance of intertidal mussels in eastern Canada after an unusual winter cold snap in February 2023. The decline in mussel abundance is concerning due to its impact on coastal biodiversity. The cold snap, which saw temperatures drop below -20°C, is believed to be the main driver of the mass disappearance. Other factors such as predation, ice scour, and wave action were ruled out as causes. The article highlights the potential implications of climate change on the future of coastal ecosystems and emphasizes the need to study the frequency of extreme weather events. [Extracted from the article]

Pervasive epizootic events have had a significant impact on marine invertebrates throughout the Caribbean, leading to severe population declines and consequential ecological implications. One such event was the regional collapse of herbivory, partly caused by the Diadema antillarum mortality event in 1983-84, resulting in a trophic cascade and altering the structure of reef communities. Consequently, there was a notable decrease in coral recruitment and an increase in the coverage of macroalgae. Nearly four decades later, in early 2022, the Caribbean basin experienced another widespread mass mortality event, further reducing the populations of D. antillarum. To assess the effects of this recent mortality event on the current demographics of D. antillarum, we surveyed eight populations along the eastern, northeastern, northern, and northwestern coast of Puerto Rico from May to July 2022, estimating their population density, size distribution, and disease prevalence. Additionally, the study compared these population parameters with data from four sites previously surveyed in 2012 and 2017 to understand the impact of the recent mortality event. The survey conducted in 2022 showed varying population densities at the surveyed reefs. Some populations exhibited mean densities of nearly one individual per square meter, while others had extremely low or no living individuals per square meter. The four populations with the highest density showed no evidence of disease, whereas the four populations with the lowest D. antillarum densities exhibited moderate to high disease prevalence. However, when considering all sites, the estimated disease prevalence remained below 5%. Nevertheless, the comparison with data from 2012 and 2017 indicated that the recent mortality event had a negative impact on D. antillarum demographics at multiple sites, as the densities in 2022 were reduced by 60.19% compared to those from the previous years. However, it is still too early to determine the severity of this new mortality event compared to the 1983-84 mortality event. Therefore, it is imperative to continue monitoring these populations. [ABSTRACT FROM AUTHOR]

Marine sponges are prominent organisms of the benthic coral reef fauna, providing important ecosystem services. While there have been increasing reports that sponges are becoming one of the dominant benthic organisms in some locations and ecoregions (e.g. Caribbean), they can be impacted by changing environmental conditions. This study presents the first documentation of a mass mortality event of the barrel sponge Xestospongia sp. in the lower Gulf of Thailand and its consequences on population dynamics and size distribution. Two anthropogenic impacted reefs (Haad Khom and Mae Haad) of the island Koh Phangan and two anthropogenic non-impacted reefs of the islands Koh Yippon and Hin Yippon within the Mu Ko Ang Thong Marine National Park were surveyed in the years 2015 and 2016. The results showed a strong shift in population densities at Koh Phangan. Fatal "bleaching" ending up in mass mortality was observed for these reefs in 2015. Xestospongia sp. abundance decreased from 2015 to 2016 by 80.6% at Haad Khom and by 98.4% at Mae Haad. Sponges of all sizes were affected, and mortality occurred regardless of the survey depth (4 and 6 m). However, Xestospongia population densities in the Marine Park were at a constant level during the surveys. The abundances in 2015 were 65% higher at the Marine Park than at Koh Phangan and 92% higher in 2016. The most likely causes of the mass mortality event was a local harmful algal bloom event, pathogens, undetected local higher water temperatures, or a combination of these factors, whereas sea surface temperature analyses showed no marine heatwave during the observed mass mortality event in 2015. Considering the ecological importance of sponges such as Xestospongia sp., long-term monitoring of reefs and their environmental parameters should be implemented to prevent such mass die-offs. [ABSTRACT FROM AUTHOR]

The cage method for the cultivation of the seaside scallop Mizuhopecten yessoensis is the most developed and popular method at sea farms in Primorsky Krai (Sea of Japan). However, this method of mollusk cultivation requires the careful planning of farming activities. Recently, mariculture farms in different countries have often encountered the mass mortality of cultured hydrobionts. The causes of such diseases are not quite clear, and often their identification requires a large amount of time and financial expenditure. Therefore, the use of predictive mechanisms based on biomarkers can help identify hidden threats in cultured scallop organisms that lead to mass mortality. In this study, we propose a rapid diagnostic method for predicting the distant mass mortality of M. yessoensis cultured in cages using biomarkers. The assessment of the pathological state of cultured mollusks at earlier developmental stages using the DNA comet method and oxidative stress markers (malondialdehyde) will allow the diagnosis and prediction of significant losses of marketable individuals in marine farms. In this study, we evaluated different age groups of mollusks cultured in the different water areas of Peter the Great Bay (Sea of Japan). During the study, we found that the death of cultured mollusks increased with increasing DNA damage and the active accumulation of malondialdehyde in tissues. It was observed that in scallops aged 1+ cultured in Severnaya Bay, high levels of DNA molecule damage and malondialdehyde were registered in the digestive glands and gills, which subsequently led to the death of almost all marketable individuals aged 3+. Therefore, the work is of significant value in assisting the aquaculture industry in solving the emerging problems of scallop farming and preserving marketable products. The proposed markers effectively reflect the condition of molluscs under extreme conditions caused by various factors, making them highly suitable for monitoring studies and forecasts on aquaculture farms.

The bivalve mollusc Pinna nobilis, endemic to the Mediterranean Sea, has been vanishing since 2016 from the whole basin because of an infection by multiple pathogens that caused mass mortality events. In the Eastern Mediterranean, some small populations seem to be resistant to the infection. These individuals could represent the only possibility for the species to recolonize desert habitats. Thus, according to the recommendations of IUCN, looking for living specimens of P. nobilis is a priority. With this goal in mind, we carried out surveys in different areas of Southern Italy, and in 2018, we launched a Citizen Science campaign to involve recreational and professional divers in this challenge. As a result of a monitoring activity carried out in 2022–2024, along the Ionian coast of Apulia, in Southern Italy, we can say that there are no more living specimens there but only empty shells. Concurrent to the vanishing of the queen P. nobilis, its congeneric P. rudis, resistant to the infection, seems to be taking advantage, becoming more common and colonizing habitats once exclusive to P. nobilis. In fact, from different areas of the Mediterranean, sightings of the new possible queen, P. rudis, are increasing, together with the discovery of individuals exhibiting morphological traits that are a mixture of the two species. In some cases, these morphological features are not easy to detect; nevertheless, the presence of these hybrids, resistant to the infection, is important for the conservation of the species.

Pervasive epizootic events have had a significant impact on marine invertebrates throughout the Caribbean, leading to severe population declines and consequential ecological implications. One such event was the regional collapse of herbivory, partly caused by the Diadema antillarum mortality event in 1983–84, resulting in a trophic cascade and altering the structure of reef communities. Consequently, there was a notable decrease in coral recruitment and an increase in the coverage of macroalgae. Nearly four decades later, in early 2022, the Caribbean basin experienced another widespread mass mortality event, further reducing the populations of D. antillarum. To assess the effects of this recent mortality event on the current demographics of D. antillarum, we surveyed eight populations along the eastern, northeastern, northern, and northwestern coast of Puerto Rico from May to July 2022, estimating their population density, size distribution, and disease prevalence. Additionally, the study compared these population parameters with data from four sites previously surveyed in 2012 and 2017 to understand the impact of the recent mortality event. The survey conducted in 2022 showed varying population densities at the surveyed reefs. Some populations exhibited mean densities of nearly one individual per square meter, while others had extremely low or no living individuals per square meter. The four populations with the highest density showed no evidence of disease, whereas the four populations with the lowest D. antillarum densities exhibited moderate to high disease prevalence. However, when considering all sites, the estimated disease prevalence remained below 5%. Nevertheless, the comparison with data from 2012 and 2017 indicated that the recent mortality event had a negative impact on D. antillarum demographics at multiple sites, as the densities in 2022 were reduced by 60.19% compared to those from the previous years. However, it is still too early to determine the severity of this new mortality event compared to the 1983–84 mortality event. Therefore, it is imperative to continue monitoring these populations.

IntroductionThe widespread mass mortality of the noble pen shell (Pinna nobilis) has occurred in several Mediterranean countries in the past 7 years. Single-stranded RNA viruses affecting immune cells and leading to immune dysfunction have been widely reported in human and animal species. Here, we present data linking P. nobilis mass mortality events (MMEs) to hemocyte picornavirus (PV) infection. This study was performed on specimens from wild and captive populations.MethodsWe sampled P. nobilis from two regions of Spain [Catalonia (24 animals) and Murcia (four animals)] and one region in Italy [Venice (6 animals)]. Each of them were analyzed using transmission electron microscopy (TEM) to describe the morphology and self-assembly of virions. Illumina sequencing coupled to qPCR was performed to describe the identified virus and part of its genome.Results and discussionIn 100% of our samples, ultrastructure revealed the presence of a virus (20 nm diameter) capable of replicating within granulocytes and hyalinocytes, leading to the accumulation of complex vesicles of different dimensions within the cytoplasm. As the PV infection progressed, dead hemocytes, infectious exosomes, and budding of extracellular vesicles were visible, along with endocytic vesicles entering other cells. The THC (total hemocyte count) values observed in both captive (eight animals) (3.5 × 104–1.60 × 105 ml−1 cells) and wild animals (14 samples) (1.90–2.42 × 105 ml−1 cells) were lower than those reported before MMEs. Sequencing of P. nobilis (six animals) hemocyte cDNA libraries revealed the presence of two main sequences of Picornavirales, family Marnaviridae. The highest number of reads belonged to animals that exhibited active replication phases and abundant viral particles from transmission electron microscopy (TEM) observations. These sequences correspond to the genus Sogarnavirus—a picornavirus identified in the marine diatom Chaetoceros tenuissimus (named C. tenuissimus RNA virus type II). Real-time PCR performed on the two most abundant RNA viruses previously identified by in silico analysis revealed positive results only for sequences similar to the C. tenuissimus RNA virus. These results may not conclusively identify picornavirus in noble pen shell hemocytes; therefore, further study is required. Our findings suggest that picornavirus infection likely causes immunosuppression, making individuals prone to opportunistic infections, which is a potential cause for the MMEs observed in the Mediterranean.

Marine sponges are prominent organisms of the benthic coral reef fauna, providing important ecosystem services. While there have been increasing reports that sponges are becoming one of the dominant benthic organisms in some locations and ecoregions (e.g. Caribbean), they can be impacted by changing environmental conditions. This study presents the first documentation of a mass mortality event of the barrel sponge Xestospongia sp. in the lower Gulf of Thailand and its consequences on population dynamics and size distribution. Two anthropogenic impacted reefs (Haad Khom and Mae Haad) of the island Koh Phangan and two anthropogenic non-impacted reefs of the islands Koh Yippon and Hin Yippon within the Mu Ko Ang Thong Marine National Park were surveyed in the years 2015 and 2016. The results showed a strong shift in population densities at Koh Phangan. Fatal “bleaching” ending up in mass mortality was observed for these reefs in 2015. Xestospongia sp. abundance decreased from 2015 to 2016 by 80.6% at Haad Khom and by 98.4% at Mae Haad. Sponges of all sizes were affected, and mortality occurred regardless of the survey depth (4 and 6 m). However, Xestospongia population densities in the Marine Park were at a constant level during the surveys. The abundances in 2015 were 65% higher at the Marine Park than at Koh Phangan and 92% higher in 2016. The most likely causes of the mass mortality event was a local harmful algal bloom event, pathogens, undetected local higher water temperatures, or a combination of these factors, whereas sea surface temperature analyses showed no marine heatwave during the observed mass mortality event in 2015. Considering the ecological importance of sponges such as Xestospongia sp., long-term monitoring of reefs and their environmental parameters should be implemented to prevent such mass die-offs.

To investigate the mass mortality of the macrobenthos community, primarily asari clams, triggered by upwelling-driven hypoxia, we conducted continuous observations of temperature, salinity, and DO, and monthly macrobenthos monitoring on the Rokujo tidal flat in Mikawa Bay, central Japan, from 2014 to 2016. Additionally, laboratory experiments were conducted using sediments on a tidal flat containing macrobenthos to examine the possibility of hydrogen sulfide formation in tidal flats. The bottom layer at the offshore station was intermittently hypoxic, and the station of the tidal flat was occasionally hypoxic in August and September for three years. Hypoxia was mostly observed on the tidal flat when constant easterly winds were recorded offshore. The biomass of asari clams decreased considerably from September to October 2016 when hypoxia was intermittent. Hypoxia persisted for approximately one week from 20 September, which was associated with the calm weather and stagnation of tidal currents owing to the neap tide. Conversely, the hydrogen sulfide concentration in the water directly above the sediment exceeded 30 mg L−1 after 3 days of incubation in the laboratory experiment. Therefore, the possibility of oxygen consumption on tidal flats due to hydrogen sulfide formed by biological die-offs was considered in the long-term persistence of hypoxia. [ABSTRACT FROM AUTHOR]

Oysters are a major commercial and ecological fishery resource. Recently, the oyster industry has experienced mass mortality in summer due to environmental factors. Generally, the survival of oysters in aquatic environments is mainly impacted by environmental stressors such as elevated sea temperatures and reduced salinity; however, the stressors impacting tidal flat oysters that are repeatedly exposed to air remain poorly understood. Hence, we studied the relationship between environmental factors and the survival of tidal flat pacific oysters in Incheon, South Korea, where mass mortality is common. Principal component analysis and Bayesian networks revealed that air temperature (in spring and summer) and sea temperature (in summer) are related to oyster production. In habitats of the tidal flat oysters during the summer, high temperatures of 34.7–35.4°C (maximum 47.6°C) were observed for average durations of 0.8–1.9 hours (maximum 3.6 hours). Furthermore, heat waves occurred for up to 12 consecutive days. Results from the multiple stress test showed that when exposed to 45°C (air temperature) for 4 hours per day, the survival rate of oysters was 42.5% after only 2 days and 0% after 6 days. The findings stemming from the field observations and stress tests suggest that high temperatures during emersion may contribute to mass mortality of oysters in summer, indicating a potential threat to oysters due to climate change. To understand the effects of future thermal stress on oysters more accurately, simultaneous long-term trend analyses and field-based observations are required.

Freshwater mussels (Unionida) are globally imperiled, in part due to largely unexplained mass mortality events (MMEs). While recent studies have begun to investigate the possibility that mussel MMEs in the Eastern USA may be caused by infectious diseases, mussels in the Western USA have received relatively little attention in this regard. We conducted a two-year epidemiologic investigation of the role of viruses in ongoing MMEs of the Western pearlshell (Margaritifera falcata) and the Western ridged mussel (Gonidea angulata) in the Chehalis River and Columbia River watersheds in the Western USA. We characterized viromes of mussel hemolymph from 5 locations in 2018 and 2020 using metagenomic methods and identified 557 viruses based on assembled contiguous sequences, most of which are novel. We also characterized the distribution and diversity of a previously identified mussel Gammarhabdovirus related to pathogenic finfish viruses. Overall, we found few consistent associations between viruses and mussel health status. Variation in mussel viromes was most strongly driven by location, with little influence from date, species, or health status, though these variables together only explained ~1/3 of variation in virome composition. Our results demonstrate that Western freshwater mussels host remarkably diverse viromes, but no single virus or combination of viruses appears to be associated with morbidity or mortality during MMEs. Our findings have implications for the conservation of imperiled freshwater mussels, including efforts to enhance natural populations through captive propagation. [ABSTRACT FROM AUTHOR]

Mass-mortality events are seldom reported in sea cucumbers (Echinodermata: Holothuria), but here we document a localized mass die-off of giant California sea cucumbers (Apostichopus californicus) in Western Canada from August to October 2021. We recruited volunteer divers to count wasting and healthy sea cucumbers, resulting in observations spanning 500 km of coastline. Reports of dead and wasting sea cucumbers were restricted to Nanoose Bay, BC (Snaw-naw-as First Nation territory, 49°17'N, 124°08'W), with the exception of a single report from Hornby Island, some 55 km away. In Nanoose Bay in 2021, up to 94% of observed sea cucumbers were affected, with healthy sea cucumbers generally observed below 16 m. Following reports of wasting sea cucumbers, population abundance declined sharply. We returned in September 2022 to survey a subset of sites and observed similarly spatially isolated but less severe wasting symptoms. Although the mass-die off in 2021 occurred after an unprecedented summer heatwave, the cause of this event remains uncertain. This case study shows that mass illness events in echinoderms can be geographically isolated and negatively impact local populations. [ABSTRACT FROM AUTHOR]

A colonial ascidian of the genus Distaplia caused a mass mortality of the pen shell Atrina maura (Sowerby, 1835) during June 2016 in the southwest of the Gulf of California (Mexico), with a significant socioeconomic cost. Tentatively identified in previous works as Distaplia cf. stylifera, a precise taxonomic determination was still lacking. In the present work, based on a detailed morphological study, it is confirmed that this aggressive species is Distaplia stylifera (Kowalevsky, 1874). Originally described from the Red Sea, the species currently has a wide circumtropical distribution (with the exception of the Eastern Pacific to date) and is reported as introduced in parts of its range. The present account thus represents an important range extension of this species. However, when revising the original description and later observations, the reported variability of several characters makes it likely that the binomen is in fact a complex of species, as is common in other ascidians with wide distributions. A complete morphological and genetic study including populations from the entire range of distribution would be necessary to settle the status of D. stylifera. Taxonomic uncertainties hinder a correct interpretation of biogeographical patterns and inference on the origin of the studied population. Nevertheless, the known introduction potential of the species, coupled with an explosive growth in an anthropized environment, and the lack of any previous reports in the Eastern Pacific, strongly suggest that the investigated population represents yet another instance of ascidian introduction. From the point of view of management, its invasive behavior is cause for great concern and warrants mitigation measures. [ABSTRACT FROM AUTHOR]

In 1983 to 1984, a mass mortality event caused a Caribbean-wide, >95% population reduction of the echinoid grazer, Diadema antillarum. This led to blooms of algae contributing to the devastation of scleractinian coral populations. Since then, D. antillarum exhibited only limited and patchy population recovery in shallow water, and in 2022 was struck by a second mass mortality reported over many reef localities in the Caribbean. Half-a-century time-series analyses of populations of this sea urchin from St. John, US Virgin Islands, reveal that the 2022 event has reduced population densities by 98.00% compared to 2021, and by 99.96% compared to 1983. In 2021, coral cover throughout the Caribbean was approaching the lowest values recorded in modern times. However, prior to 2022, locations with small aggregations of D. antillarum produced grazing halos in which weedy corals were able to successfully recruit and become the dominant coral taxa. The 2022 mortality has eliminated these algal-free halos on St. John and perhaps many other regions, thereby increasing the risk that these reefs will further transition into coral-free communities. [ABSTRACT FROM AUTHOR]

Bioinvasions constitute both a direct and an indirect threat to ecosystems. Direct threats include pressures on local trophic chains, while indirect threats might take the form of an invasion of a microorganism alongside its host. The marine dinoflagellate Hematodinium perezi, parasitizing blue crabs (Callinectes sapidus), has a worldwide distribution alongside its host. In Greece, fluctuations in the blue crab population are attributed to overexploitation and the effects of climate change. The hypothesis of the present study was that blue crab population reductions cannot only be due to these factors, and that particular pathogens may also be responsible for the fluctuations. To investigate this hypothesis, both lethargic and healthy blue crab specimens were collected from three different fishing sites in order to assess the health status of this important species. Together with the lethargic responses, the hemolymph of the infested crabs presented a milky hue, indicating the first signs of parasitic infestation with H. perezi. The histopathological results and molecular identification demonstrated the effect of the presence of H. perezi in the internal organs and their important role in the mortality of blue crabs. Specifically, H. perezi, in three different tissues examined (heart, gills, hepatopancreas), affected the hemocytes of the species, resulting in alterations in tissue structure. Apart from this dinoflagellate parasite, the epibiotic peritrich ciliate Epistylis sp. was also identified, infecting the gills. This study represents the first detection of H. perezi in the eastern Mediterranean, demonstrating that this is the main causative agent of blue crab mortality on Greek coastlines.

[Display omitted] • Composting broiler carcasses and litter is feasible during mass depopulation events. • After 30 days of composting, Newcastle and Avian flu were reduced below detection. • Salmonella survived composting at 40 °C both under aerobic and anaerobic conditions. • Biomass losses was substantially higher under aerobic and mesophilic conditions. • Wet culling methods can lead to issues of excess water within composting sleeves. Composting poultry carcasses and the infected litter is considered feasible during mass depopulation events in response to disease outbreaks. We demonstrate the effect of temperature (40, 50, 60 °C) and aerobic/anaerobic conditions on the degradation of broiler carcasses and broiler litter (BL) and the elimination of pre-inoculated Avian flu and Newcastle viruses and Salmonella Infantis (3.3 × 105.6 EID 50 , 7 × 106.0 EID 50 and 2 × 107 CFU g-dry matter (DM)−1, respectively). Six broiler carcasses and BL were inoculated and treated with a water-based foam, simulating a common culling method. After 30 days of composting, both viruses were eliminated under all conditions, while Salmonella persisted at 40 °C under aerobic and anaerobic conditions (7.4 × 105 and 4.4 × 103 CFU g-DM−1, respectively). Mass losses were 42–44, 24–26, and 18–22% (aerobic) and 18–27, 21–23, and 0–7% (anaerobic) at 40, 50, and 60 °C, respectively. In the end, the associated odors were not typical of carcasses (aerobic), or they were strong and offensive (anaerobic). Considering the observed mass losses and biomass water holding capacity, we present a sensitivity analysis of the water balance expected in composting sleeves if they are utilized on mass depopulation events. Composting of the carcasses and the BL in enclosed sleeves with forced aeration, following culling by means of water-based foam will generate excess water, depending on sleeve volumes, aeration conditions, and co-addition of absorbing materials like sawdust. No excessive moisture is expected if dry culling methods are used. [ABSTRACT FROM AUTHOR]

A new genus and species of freshwater isopod is described from Pliocene volcanic sedimentary ashes found in an ancient lake basin in the Santa Rosa Dam region, Amatitlán, Jalisco, West-central Mexico. The new isopod is represented by a few corpses and molts. Due to the relatively poor preservation, no further morphological details can be offered to the moment, but the observed features are sufficient to distinguish this isopod from any living or fossil freshwater Sphaeromatidae species. This contribution extends the stratigraphic and geographic record of fossil isopod bearing localities in Mexico, being this the youngest fossil Peracarida recorded from this country. [ABSTRACT FROM AUTHOR]

Summary: The current catastrophic decline in African vultures is caused mainly by poisoning, and killing for consumption and belief-based use (traditional medicine). To find out more about the key threats to vultures in West Africa, we assessed the main anthropogenic causes of vulture mortality in Burkina Faso. We analysed incidents of mass vulture mortality, based on interviews conducted in 2016 with local butchers, veterinarians, foresters, and abattoir watchmen at 44 sites across the country. A total of 730 interviews revealed that poisoning was the main cause of mortality of vultures in Burkina Faso (20 of the 23 mass mortality incidents described by respondents were caused by poisoning). Poisoning was also the most lethal threat to vultures (779 out of 879 known vulture deaths were due to poisoning). According to the survey, intentional poisoning of vultures with poisoned baits (which comprised 15 out of 23 mass mortality incidents) produced the highest number of victims (577 out of 879 dead vultures). The number of vultures killed by poisoned baits was higher closer to the borders than elsewhere in Burkina Faso and we believe these recent intentional vulture poisoning events in Burkina Faso were intended to meet the growing demand for vulture body parts in West Africa. The survey showed that unintentional poisoning was the second main cause of vulture mass mortality (5 out of 23 mass mortality incidents comprising 202 of 879 dead vultures). Other important anthropogenic causes of vulture mortality included electrocution at electricity poles and motor vehicle collisions. Our results highlight the need for awareness campaigns, improved policy and legislation, and stronger commitment from governments in West Africa, to halt the trade in vultures and prevent their extirpation. [ABSTRACT FROM AUTHOR]

Freshwater mussels (Unionida) are among the world's most imperiled taxa, but the relationship between freshwater mussel mortality events and infectious disease is largely unstudied. We surveyed viromes of a widespread and abundant species (mucket, Actinonaias ligamentina; syn: Ortmanniana ligamentina) experiencing a mortality event of unknown etiology in the Huron River, Michigan, in 2019–2020 and compared them to viromes from mucket in a healthy population in the St. Croix River, Wisconsin and a population from the Clinch River, Virginia and Tennessee, where a mortality event was affecting the congeneric pheasantshell (Actinonaias pectorosa; syn: Ortmanniana pectorosa) population. We identified 38 viruses, most of which were associated with mussels collected during the Huron River mortality event. Viral richness and cumulative viral read depths were significantly higher in moribund mussels from the Huron River than in healthy controls from each of the three populations. Our results demonstrate significant increases in the number and intensity of viral infections for freshwater mussels experiencing mortality events, whereas individuals from healthy populations have a substantially reduced virome comprising a limited number of species at low viral read depths. [ABSTRACT FROM AUTHOR]

Numerous outbreaks of high-pathogenicity avian influenza (HPAI) were reported during 2020–2021. In Africa, H5Nx has been detected in Benin, Burkina Faso, Nigeria, Senegal, Lesotho, Namibia and South Africa in both wild birds and poultry. Botswana reported its first outbreak of HPAI to the World Organisation for Animal Health (WOAH) in 2021. An H5N1 virus was detected in a fish eagle, doves, and chickens. Full genome sequence analysis revealed that the virus belonged to clade 2.3.4.4b and showed high identity within haemagglutinin (HA) and neuraminidase proteins (NA) for viruses identified across a geographically broad range of locations. The detection of H5N1 in Botswana has important implications for disease management, wild bird conservation, tourism, public health, economic empowerment of vulnerable communities and food security in the region. [ABSTRACT FROM AUTHOR]

We describe a mass mortality event at a school in Medford, Oregon in which the remains of over 5600 Vaux's Swifts (Chaetura vauxi) were found at the bottom of a chimney. The use of operating chimneys by migratory aggregations of this species poses the risk of significant mortality. We offer suggestions to reduce the risk of Vaux's Swift mortality caused by operating chimneys and illustrate how community involvement can contribute to mortality reduction. [ABSTRACT FROM AUTHOR]

Seismic activity, erosion, sedimentation, and extreme temperatures can cause compounding large-scale disturbances to marine organisms, like large intertidal foundational seaweeds. In November 2016, a 7.8 Mw earthquake uplifted 130 km of coastline by 0.5–6 m near Kaikōura, New Zealand and thereby increased intertidal desiccation, aerial temperatures, reef erosion, and water turbidity. Furthermore, stress on uplifted intertidal species was compounded by unprecedented marine heatwaves over the summer of 2017/18. Here we documented altered dominances of large foundational seaweed and possible flow-on effects on seaweed-associated flora and fauna, following the uplift and heatwaves. These compounding disturbances caused instant high canopy loss of the dominant primary foundation species - the large perennial canopy-forming southern bull kelp Durvillaea antarctica – and no post-disturbance recovery, suggesting a maintenance threshold has been exceeded. After canopy loss of the primary foundation species, alternative foundation species – i.e., subordinate competitors under pre-disturbance conditions (the perennial canopy-forming fucoids Carpophyllum maschalocarpum , Cystophora scalaris, and Hormosira banksii) increased in abundance. Furthermore, field observations of attachment interaction networks demonstrated that the primary and alternative foundation species facilitated different sessile and mobile taxa. For example, the smaller and more morphologically complex C. maschalocarpum , H. banksii, and C. scalaris, supported more novel attachment associations, whereas the larger Durvillaea supported longer attachment chains. Overall, our results highlight abrupt and potentially long-lasting ecological changes after compounding disturbances, which altered dominance hierarchies. Alternative foundation species are now more common than the pre-disturbance primary foundation species, with flow-on effects on wider communities that depend on biogenic habitats. • Compounding disturbances: Earthquake-induced coastal uplift and extreme marine heatwaves caused severe seaweed canopy loss. • No recovery of primary intertidal foundation species (Durvillaea antarctica) observed five years post-disturbance. • Shift in dominance: Alternative foundation species increased in abundance. • Attachment networks reveal distinct community facilitation by primary vs. alternative foundation species. • Long-lasting ecological changes alter dominance hierarchies with broader community impacts. [ABSTRACT FROM AUTHOR]

Pacific oyster mortality syndrome (POMS) in Pacific oysters Crassostrea gigas is defined by mass mortality with Ostreid herpesvirus I (OsHV-1). In this study the association of Vibrio species with oysters before, during and after POMS events was investigated at population level to clarify their involvement with OsHV-1 in mass mortality events in the Georges and Hawkesbury River estuaries, Australia. In the POMS affected Georges River estuary, three patterns were observed concurrently at different sites: i) Vibrio counts and OsHV-1 DNA concentrations increased in adults and spat as mortalities started then decreased as mortalities stopped ii) bacterial counts increased in spat but not in adults associated with mortalities due to OsHV-1 iii) bacterial counts increased in the absence of mass mortality or high concentrations of OsHV-1 DNA. Although almost half of the 120 bacterial isolates were identified as an unknown Vibrio species belonging to the Splendidus clade with two predominant biotypes (A and H), there was no association between biotype and mortality. Concurrently in the Hawkesbury River estuary, neither mortality nor OsHV-1 were found, Vibrio counts fluctuated significantly and of 84 isolates identified, V. alginolyticus, V. parahaemolyticus and unidentified Vibrio sp. dominated; only five Splendidus clade isolates were identified. However, when POMS emerged in the Hawkesbury River estuary, the Splendidus-clade isolate became the dominant bacterial species. Mortality also occurred there without OsHV-1 and the dominant bacteria then were V. alginolyticus and V. harveyi, but the Splendidus-clade isolate was not detected. None of the bacterial species were specifically associated with POMS, although the Splendidus clade isolate increased in prevalence after POMS emerged in the Hawkesbury River estuary. V. aestuarianus was not detected in this study. While the findings suggest that bacterial proliferation follows infection with OsHV-1 in POMS, this was not a consistent feature. The number and diversity of bacteria within oyster tissues varied over time, between estuaries, between sites within an estuary and were associated with flooding, growing height, the age of oysters, mortality and OsHV-1. • Cultivable bacterial and vibrio counts varied over time. • None of the vibrio species identified were specifically associated with POMS. • An unknown Vibrio species in the Splendidus clade became dominant after OsHV-1 mortality. • The environment had a strong effect on bacterial populations in oyster tissues. [ABSTRACT FROM AUTHOR]

To investigate the mass mortality of the macrobenthos community, primarily asari clams, triggered by upwelling-driven hypoxia, we conducted continuous observations of temperature, salinity, and DO, and monthly macrobenthos monitoring on the Rokujo tidal flat in Mikawa Bay, central Japan, from 2014 to 2016. Additionally, laboratory experiments were conducted using sediments on a tidal flat containing macrobenthos to examine the possibility of hydrogen sulfide formation in tidal flats. The bottom layer at the offshore station was intermittently hypoxic, and the station of the tidal flat was occasionally hypoxic in August and September for three years. Hypoxia was mostly observed on the tidal flat when constant easterly winds were recorded offshore. The biomass of asari clams decreased considerably from September to October 2016 when hypoxia was intermittent. Hypoxia persisted for approximately one week from 20 September, which was associated with the calm weather and stagnation of tidal currents owing to the neap tide. Conversely, the hydrogen sulfide concentration in the water directly above the sediment exceeded 30 mg L−1 after 3 days of incubation in the laboratory experiment. Therefore, the possibility of oxygen consumption on tidal flats due to hydrogen sulfide formed by biological die-offs was considered in the long-term persistence of hypoxia.

The 1983-1984 die-off of the long-spined sea urchin Diadema antillarum stands out as a catastrophic marine event because of its detrimental effects on Caribbean coral reefs. Without the grazing activities of this key herbivore, turf and macroalgae became the dominant benthic group, inhibiting coral recruitment and compromising coral reef recovery from other disturbances. In the decades that followed, recovery of D. antillarum populations was slow to non-existent. In late January 2022, a new mass mortality of D. antillarum was first observed in the U.S. Virgin Islands. We documented the spread and extent of this new die-off using an online survey. Infected individuals were closely monitored in the lab to record signs of illness, while a large population on Saba, Dutch Caribbean, was surveyed weekly before and during mortality to determine the lethality of this event. Within four months the die-off was distributed over 1,300 km from north to south and 2,500 km east to west. Whereas the 1983-1984 die-off advanced mostly with the currents, the 2022 event has appeared far more quickly in geographically distant areas. First die-off observations in each jurisdiction were often close to harbor areas, which, together with their rapid appearance, suggests that anthropogenic factors may have contributed to the spread of the causative agent. The signs of illness in sick D. antillarum were very similar to those recorded during the 1983-1984 die-off: lack of tube feet control, slow spine reaction followed by their loss, and necrosis of the epidermis were observed in both lab and wild urchins. Affected populations succumbed fast; within a month of the first signs of illness, a closely monitored population at Saba, Dutch Caribbean, had decreased from 4.05 individuals per m2 to 0.05 individuals per m2. Lethality can therefore be as high as 99%. The full extent of the 2022 D. antillarum die-off event is not currently known. The slower spread in the summer of 2022 might indicate that the die-off is coming to a (temporary) standstill. If this is the case, some populations will remain unaffected and potentially supply larvae to downstream areas and augment natural recovery processes. In addition, several D. antillarum rehabilitation approaches have been developed in the past decade and some are ready for large scale implementation. However, active conservation and restoration should not distract from the primary goal of identifying a cause and, if possible, implementing actions to decrease the likelihood of future D. antillarum die-off events.

Standing genetic variation enables or restricts a population's capacity to respond to changing conditions, including the extreme disturbances expected to increase in frequency and intensity with continuing anthropogenic climate change. However, we know little about how populations might respond to extreme events with rapid genetic shifts, or how population dynamics may influence and be influenced by population genomic change. We use a range-wide epizootic, sea star wasting disease, that onset in mid-2013 and caused mass mortality in Pisaster ochraceus to explore how a keystone marine species responded to an extreme perturbation. We integrated field surveys with restriction site-associated DNA sequencing data to (i) describe the population dynamics of mortality and recovery, and (ii) compare allele frequencies in mature P. ochraceus before the disease outbreak with allele frequencies in adults and new juveniles after the outbreak, to identify whether selection may have occurred. We found P. ochraceus suffered 81% mortality in the study region between 2012 and 2015, and experienced a concurrent 74-fold increase in recruitment beginning in late 2013. Comparison of pre- and postoutbreak adults revealed significant allele frequency changes at three loci, which showed consistent changes across the large majority of locations. Allele frequency shifts in juvenile P. ochraceus (spawned from premortality adults) were consistent with those seen in adult survivors. Such parallel shifts suggest detectable signals of selection and highlight the potential for persistence of this change in subsequent generations, which may influence the resilience of this keystone species to future outbreaks.

The population of ecologically important Pinna nobilis (Linneaus, 1758), the largest bivalve species of the Mediterranean, has been under serious threat since 2016 as a result of both anthropogenic effects and the epidemic caused by Haplosporidium pinnae. In addition, in recent years P. nobilis mortalities caused by Vibrio sp. infections in the North Aegean Sea have been reported. In this study, the effects of the mass mortalities of P. nobilis observed in the Mediterranean were investigated in the populations in the Dardanelles. For this purpose, P. nobilis populations in 30 different stations were observed and counted along transects between June 2020 and September 2021. Underwater observations were carried out either by scuba diving or free diving depending on the underwater characteristics of the region. Observations based on a total of 2183 minutes of bottom time indicated that mortality rate of pen shells increased to 94.67% in 2021 as compared to 81.15% in 2021. In addition, in a period 1 year, the number of stations with 100% mortality increased from 11 to 14 and the number of stations with no presence of pen shells increased from 3 to 5. The decrease in the total number of live pen shells from 1108 to 207 and the consequent reduction of pen shell density (individual/100 m2) from 13.15 to 9.2 in a period of one year indicate the imminent threat of extinction for P. nobilis in this region. In addition to monitoring studies, aquaculture of pen shells and their transplantation to affected areas should be carried out to mitigate the effects of mass mortalities observed in this region.

A mass mortality event involving cultured blood cockles (Tegillarca granosa) occurred in the Welu estuary in Chanthaburi Province, Thailand, during July and early August of 2013. We collected surviving blood cockles (n = 30) shortly after the mortality event in mid-August and evaluated the physiological conditions of the specimens by performing histological observations of various organs. We found that most specimens of both sexes were at the peak of spawning. Histological observations revealed an absence of food in their digestive ducts and flattened epithelial cells in their midgut glands. The specimens had been experiencing low food availability and nutrient uptake. In addition, rainfall data for Chanthaburi Province revealed that the rainfall in July 2013 was more than twice the average amount received in previous years, and surface salinity data from around the aquaculture site revealed that salinity was < 10 Practical Salinity Unit for longer than a month. Therefore, we concluded that prolonged low-salinity conditions were a major cause of this mass mortality event.

Unprecedented large-scale algal blooms were observed during autumn 2021 around the Katsurakoi fishing port, Kushiro, eastern Hokkaido, Japan. Monitoring of shoreline water showed that chlorophyll a (Chl a) concentrations and the cell density of Karenia spp., dominated by Karenia selliformis, repeatedly increased synchronously between September and November 2021. These increases were associated with a southerly wind-driven current, which transported offshore water on the shelf towards the shoreline at the sea surface. The blooms were prolonged as a result of algal accumulation in the semi-closed fishing port. The maximum Chl a concentration and cell density exceeded 50 µg Chl a/L and 104 cells/mL, respectively. During the autumn bloom of Karenia spp., the nitrate + nitrite and phosphate concentrations in the water were lower than those in 2019 and 2020, and the silicate concentration was comparable. The ammonium concentration during the bloom was notably higher than before the bloom period, reaching 15 µM. Mass mortality of several fish species and echinoderms that were cultured using rearing water intake from the same shoreline occurred synchronously with the increase in Karenia spp. [ABSTRACT FROM AUTHOR]

Study of the impacts of the 2019-2020 Black Summer bushfires on flying-foxes has mainly focused on the effects of burnt habitat on food availability. It has previously only been assumed that flying-foxes probably died directly from these bushfires. We report an eyewitness account of numbers of grey-headed flying-foxes (Pteropus poliocephalus ) being killed as they attempted to escape a bushfire engulfing a flying-fox camp in Jeremadra, New South Wales. Once in the air, most of the flying-foxes dropped to the ground, scattering carcasses throughout the vicinity. This observation represents the only eyewitness report of flying-fox mortalities occurring directly from these bushfires. Given the substantial proportion of the grey-headed flying-fox range affected by these bushfires, we infer that such mortalities likely occurred in other locations. [ABSTRACT FROM AUTHOR]

Climate change is increasing the frequency and intensity of transient extreme climate events that can be catastrophic for ecological communities. We studied the 2014-2022 period along the northern coasts of Sicily (Western Mediterranean Sea), evaluating the ecological impacts on three macroalgae (Ericaria amentacea, Jania rubens, and Padina pavonica) and one complex of species (Laurencia complex) inhabiting the vermetid bioconstructions. All climatological metrics indicate that desiccation conditions occurred in the intertidal zones for many consecutive days during 2022, compared to previous years. These extreme conditions have led to a drastic algal biomass reduction, especially for E. amentacea, P. pavonica, and Laurencia complex species. Consistently, the analysis of mollusc communities associated with macroalgae highlighted a sharp collapse, with a general inverse relationship between community composition and structure versus air temperature values. This worrying evidence indicates that anomalous desiccation conditions could have serious short-term impacts on the fragile and neglected vermetid ecosystem., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)