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Remote sensing and spatial analysis reveal unprecedented cyanobacteria bloom dynamics associated with elephant mass mortality
Get PDFThe 2020 mass mortality of 350 African elephants (Loxodonta africana) in Botswana sparked global concern, with
cyanotoxins in watering holes (pans) being a suspected cause, though evidence remains inconclusive. Combining
remote sensing and spatial analysis, we examined the relationship between the ecohydrology of ~3000 pans and
the locations of deceased elephants. Our analysis revealed a significant difference in the spatial distribution of
fresh versus decayed carcasses (p < 0.001), indicating that the die-off deviated from typical regional elephant
mortality patterns. We identified 20 pans near fresh carcasses that experienced increased cyanobacteria bloom
events in 2020 (n = 123) compared to the previous 3 years combined (n = 23), exhibiting the highest average
phytoplankton biomass of the period 2015–2023 (Normalised Difference Chlorophyll Index >0.2). These findings
suggest a heightened risk and likelihood of cyanotoxin presence in these pans. Elephants were estimated to have walked 16.5 km (± 6.2 km) and died within 88 h (± 33 h) of exposure. Our study provides evidence that
cyanobacterial toxicity could be a contributing factor to the 2020 die-off, while also considering other potential
causes, and offers a general framework for investigation of future mortality events. We underscore the need to
integrate spatial analysis and regional ecohydrological assessments to monitor and mitigate animal mortality
events and inform conservation strategies
Observing change in pelagic animals as sampling methods shift: the case of Antarctic krill
Get PDFUnderstanding and managing the response of marine ecosystems to human pressures including climate change requires reliable large-scale and multi�decadal information on the state of key populations. These populations include the pelagic animals that support ecosystem services including carbon export and
fisheries. The use of research vessels to collect information using scientific nets and acoustics is being replaced with technologies such as autonomous moorings, gliders, and meta-genetics. Paradoxically, these newer methods sample pelagic populations at ever-smaller spatial scales, and ecological
change might go undetected in the time needed to build up large-scale, long time series. These global-scale issues are epitomised by Antarctic krill (Euphausia superba), which is concentrated in rapidly warming areas, exports substantial
quantities of carbon and supports an expanding fishery, but opinion is divided on how resilient their stocks are to climatic change. Based on a workshop of 137 krill experts we identify the challenges of observing climate change impacts with shifting sampling methods and suggest three tractable solutions. These are to: improve overlap and calibration of new with traditional methods; improve communication to harmonise, link and scale up the capacity of new but localised sampling programs; and expand opportunities from other research
platforms and data sources, including the fishing industry. Contrasting evidence for both change and stability in krill stocks illustrates how the risks of false negative and false positive diagnoses of change are related to the temporal and
spatial scale of sampling. Given the uncertainty about how krill are responding to rapid warming we recommend a shift towards a fishery management approach that prioritises monitoring of stock status and can adapt to variability and change
A machine learning model-based satellite data record of dissolved organic carbon concentration in surface waters of the global open ocean
Get PDFDissolved Organic Carbon (DOC) is the largest organic carbon pool in the ocean. Considering the biotic and abiotic factors controlling DOC processes, indirect
satellite methods for open ocean DOC estimation can be developed, using conceptual, empirical or statistical models, driven by multiple satellite products.
In this study, we infer a time series of global DOC from data of the European Space Agency’s (ESA) Ocean Colour Climate Change Initiative (OC-CCI) in combination with a global database of in situ DOC observations. We tested
empirical machine learning modelling approaches in which the available in situ data are used to train the models and to find empirical relationships between DOC and variables available from remote sensing. Of the tested methods, a random forest regression showed the best results, and the details of this model are further reported here. We present a time series of global open ocean DOC concentrations between 2010–2018 that is made freely available through the
archive of the UK Centre for Environmental Data Analysis (CEDA
Planktonic marine fungi: A review
No full textFungi in marine ecosystems play crucial roles as saprotrophs, parasites, and pathogens. The definition of marine fungi has evolved over the past century. Currently, “marine fungi” are defined as any fungi recovered repeatedly from marine habitats that are able to grow and/or sporulate in marine environments, form symbiotic relationships with other marine organisms, adapt and evolve at the genetic level, or are active metabolically in marine environments. While there are a number of recent reviews synthesizing our knowledge derived from over a century of research on marine fungi, this review article focuses on the state of knowledge on planktonic marine fungi from the coastal and open ocean, defined as fungi that are in suspension or attached to particles, substrates or in association with hosts in the pelagic zone of the ocean, and their roles in remineralization of organic matter and major biogeochemical cycles. This review differs from previous ones by focusing on biogeochemical impacts of planktonic marine fungi and methodological considerations for investigating their diversity and ecological functions. Importantly, we point out gaps in our knowledge and the potential methodological biases that might have contributed to these gaps. Finally, we highlight recommendations that will facilitate future studies of marine fungi. This article first provides a brief overview of the diversity of planktonic marine fungi, followed by a discussion of the biogeochemical impacts of planktonic marine fungi, and a wide range of methods that can be used to study marine fung
Large protistan mixotrophs in the North Atlantic Continuous Plankton Recorder time series: associated environmental conditions and trends
No full textAquatic ecologists are integrating mixotrophic plankton – here defined as microorganisms with photosynthetic and phagotrophic capacity – into their understanding of marine food webs and biogeochemical cycles. Understanding mixotroph temporal and spatial distributions, as well as the environmental conditions under which they flourish, is imperative to understanding their impact on trophic transfer and biogeochemical cycling. Mixotrophs are hypothesized to outcompete strict photoautotrophs and heterotrophs when either light or nutrients are limiting, but testing this hypothesis has been hindered by the challenge of identifying and quantifying mixotrophs in the field. Using field observations from a multi-decadal northern North Atlantic dataset, we calculated the proportion of organisms that are considered mixotrophs within individual microplankton samples. We also calculated a “trophic index” that represents the relative proportions of photoautotrophs (phytoplankton), mixotrophs, and heterotrophs (microzooplankton) in each sample. We found that the proportion of mixotrophs was positively correlated with temperature, and negatively with either light or inorganic nutrient concentration. This proportion was highest during summertime thermal stratification and nutrient limitation, and lowest during the North Atlantic spring bloom period. Between 1958 and 2015, changes in the proportion of mixotrophs coincided with changes in the Atlantic Multi-decadal Oscillation (AMO), was highest when the AMO was positive, and showed a significant uninterrupted increase in offshore regions from 1992-2015. This study provides an empirical foundation for future experimental, time series, and modeling studies of aquatic mixotrophs
Direct observational evidence of strong CO 2 uptake in the Southern Ocean
Get PDFThe Southern Ocean is the primary region for the uptake of anthropogenic carbon dioxide (CO2) and is, therefore,
crucial for Earth’s climate. However, the Southern Ocean CO2 flux estimates reveal substantial uncertainties and lack direct validation. Using seven independent and directly measured air-sea CO2 flux datasets, we identify a 25%
stronger CO2 uptake in the Southern Ocean than shipboard dataset–based flux estimates. Accounting for upper ocean temperature gradients and insufficient temporal resolution of flux products can bridge this flux gap. The gas transfer velocity parameterization is not the main reason for the flux disagreement. The profiling float data–based flux products and biogeochemistry models considerably underestimate the observed CO2 uptake, which may be due to the lack of representation of small-scale high-flux events. Our study suggests that the Southern Ocean may take up more CO2 than previously recognized, and that temperature corrections should be considered, and a higher resolution is needed in data-based bulk flux estimates
The vulnerability of sharks, skates, and rays to ocean deoxygenation: Physiological mechanisms, behavioral responses, and ecological impacts
No full textLevels of dissolved oxygen in open ocean and coastal waters are decreasing (ocean deoxygenation), with poorly understood effects on marine megafauna. All of the more than 1000 species of elasmobranchs (sharks, skates, and rays) are obligate water breathers, with a variety of life-history strategies and oxygen requirements. This review demonstrates that although many elasmobranchs typically avoid hypoxic water, they also appear capable of withstanding mild to moderate hypoxia with changes in activity, ventilatory responses, alterations to circulatory and hematological parameters, and morphological alterations to gill structures. However, such strategies may be insufficient to withstand severe, progressive, or prolonged hypoxia or anoxia where anaerobic metabolic pathways may be used for limited periods. As water temperatures increase with climate warming, ectothermic elasmobranchs will exhibit elevated metabolic rates and are likely to be less able to tolerate the effects of even mild hypoxia associated with deoxygenation. As a result, sustained hypoxic conditions in warmer coastal or surface-pelagic waters are likely to lead to shifts in elasmobranch distributions. Mass mortalities of elasmobranchs linked directly to deoxygenation have only rarely been observed but are likely underreported. One key concern is how reductions in habitat volume as a result of expanding hypoxia resulting from deoxygenation will influence interactions between elasmobranchs and industrial fisheries. Catch per unit of effort of threatened pelagic sharks by longline fisheries, for instance, has been shown to be higher above oxygen minimum zones compared to adjacent, normoxic regions, and attributed to vertical habitat compression of sharks overlapping with increased fishing effort. How a compound stressor such as marine heatwaves alters vulnerability to deoxygenation remains an open question. With over a third of elasmobranch species listed as endangered, a priority for conservation and management now lies in understanding and mitigating ocean deoxygenation effects in addition to population declines already occurring from overfishing
The genome sequence of the cuckoo wrasse, Labrus mixtus Linnaeus 1758
No full textWe present a genome assembly from an individual Labrus mixtus (the cuckoo wrasse; Chordata; Actinopteri; Labriformes; Labridae). The genome sequence has a total length of 740.60 megabases. Most of the assembly is scaffolded into 24 chromosomal pseudomolecules. The mitochondrial genome has also been assembled and is 16.49 kilobases in lengt
The first comprehensive taxonomic and ecological checklist of free–living marine nematodes in Korea (2004–2023)
No full textThis study aims to compile a comprehensive ecological checklist of free–living marine nematodes in Korea. The ecological characteristics of free–living marine nematodes, including habitat, lifestyle, and distribution, are listed from a meta–analysis of 50 publications over the period 2004–2023. A total of 323 nematode species were recorded in Korea and published in both 41 taxonomy and 9 ecology studies. In taxonomy studies, Draconematidae was most frequently recorded, and in ecology studies, the large sedimentary Chromadoridae was most often recorded. In all publications, genera Daptonema and Enoplus were recorded most frequently, and the majority of species were documented near Busan and Jeju Island, South Korea. This study provides important basic data for predicting the distribution of free–living marine nematodes in coastal benthic ecosystems in Kore
Cross-basin and cross-taxa patterns of marine community tropicalization and deborealization in warming European seas
No full textOcean warming and acidification, decreases in dissolved oxygen concentrations, and changes in primary production are causing an unprecedented global redistribution of marine life. The identification of underlying ecological processes underpinning marine species turnover, particularly the prevalence of increases of warm-water species or declines of cold-water species, has been recently debated in the context of ocean warming. Here, we track changes in the mean thermal affinity of marine communities across European seas by calculating the Community Temperature Index for 65 biodiversity time series collected over four decades and containing 1,817 species from different communities (zooplankton, coastal benthos, pelagic and demersal invertebrates and fish). We show that most communities and sites have clearly responded to ongoing ocean warming via abundance increases of warm-water species (tropicalization, 54%) and decreases of cold-water species (deborealization, 18%). Tropicalization dominated Atlantic sites compared to semi-enclosed basins such as the Mediterranean and Baltic Seas, probably due to physical barrier constraints to connectivity and species colonization. Semi-enclosed basins appeared to be particularly vulnerable to ocean warming, experiencing the fastest rates of warming and biodiversity loss through deborealizatio