Havermans, Charlotte
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Havermans, Charlotte
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Havermans, Charlotte
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Item-typ:Veröffentlichung, Optical observations and distribution modeling of gelatinous zooplankton in the Arctic Ocean(2023-11-16); ; ; One of the most understudied components of the rapidly changing Arctic ecosystems is the gelatinous zooplankton, comprising cnidarian medusae (Hydrozoa and Scyphozoa), ctenophores, pelagic tunicates, and sometimes also including chaetognaths. Although these organisms play important roles in marine ecosystems, occupying multiple trophic levels, they have been historically neglected due to the difficulties associated with sampling them and the paradigm of them representing a "dead end" in food webs. However, representatives of the different groups were recently shown to serve as a food component for commercially important fish species, act as versatile predators, and contribute significantly to the biological carbon pump. The hypothesis of an ocean "jellification", i.e., a worldwide increase in gelatinous zooplankton biomass, proposed more than a decade ago, is still debated today. For the Arctic Ocean, the questions whether gelatinous zooplankton will increase in abundance, and whether biogeographic shifts in their distributions will take place, have remained largely unanswered. In order to understand the likelihood of such distributional shifts, reliable data are needed on species diversity and abundances and to identify the key physical and biological factors that determine the distribution of gelatinous zooplankton in the Arctic at the local, meso- and pan-Arctic scale. To do so, I leveraged an extensive dataset of historical biological data and analyzed newly collected optical data from recent expeditions to study the diversity, distribution, and abundance of gelatinous zooplankton in several types of ecosystems of the Arctic Ocean. I employed species distribution modeling techniques on both large-scale datasets and regional optical datasets, to evaluate changes in species distributions in space and time, under various climate change scenarios. For addressing these questions on the Pan-Arctic scale, I compiled extensive datasets for gelatinous zooplankton taxa from four public databases: the Ocean Biodiversity Information System (OBIS), the Global Biodiversity Information Facility (GBIF), the Jellyfish Database Initiative (JeDI), and PANGAEA, spanning six decades and comprising over 24,000 observations. Rigorous data cleaning and taxonomic examination narrowed the focus to eight dominant gelatinous zooplankton taxa with solid identification bases, including two Hydrozoa (Aglantha digitale and Sminthea arctica), two Appendicularia (Oikopleura vanhoeffeni and Fritillaria borealis), two Scyphozoa (Cyanea capillata and Periphylla periphylla), and two Ctenophora (Mertensia ovum, Beroe spp.). Three-dimensional species distribution models were applied to these datasets, revealing a pan-Arctic trend of polar shifts in the distribution of gelatinous zooplankton. The projections indicated for most studied species an expansion of suitable habitat, with the largest one for the scyphozoan Cyanea capillata (180% increase of its niche from 1950-2014 to 2050-2099). The largest niche contraction was found for the hydrozoan Sminthea arctica (15% decrease). I further focused in-depth on different ecosystems that are at the core of the ongoing Atlantification, the open waters of the Fram Strait, the shelf system of the southern Barents Sea, and the western fjords of the Svalbard archipelago. In situ observations of gelatinous zooplankton were collected by conducting depth transects with the Pelagic In situ Observation System (PELAGIOS, for which I annotated over 3200 gelatinous zooplankton observations). For the Fram Strait, I assessed the diversity of the water column from 20 to 2,400m, revealing seasonal migration patterns of gelatinous zooplankton communities, providing major additions to our understanding of the regional bathypelagic diversity. A significant population of Sminthea arctica was observed in the bathypelagic layers of Fram Strait, indicating its important, but so far neglected role, and I recorded the southernmost observation for the hydrozoan species Bathykorus bouilloni. Based on the optical datasets of Fram Strait, I carried out a community distribution modeling approach that was used to model gelatinous zooplankton species abundance and community richness. It was projected that environmental changes in Fram Strait will result in less diverse but more abundant gelatinous zooplankton communities. In terms of species-specific responses, the abundance of the hydrozoan Aglantha digitale is projected to increase by 2% in the water column by 2050, the hydrozoan Sminthea arctica is projected to experience a decline in abundance of up to 60%. The analysis of optical surveys also allowed me to document large aggregations of ctenophore species. In the southwestern part of the Barents Sea, I recorded one of the largest aggregations of adults of Bolinopsis infundibulum. This aggregation was most likely a seasonal phenomenon, supported by a large phytoplankton bloom, and may have extended over several tens of kilometers. Similarly, in a western fjord of Svalbard, Van Mijenfjorden, I found the largest number of individuals ever recorded for the species Beroe sp. and could be linked with oxygen-rich waters. These findings indicate the interplay of physical and biological factors for influencing small-scale distribution patterns of gelatinous zooplankton. A general trend in gelatinous zooplankton community structure was found shared between the results of the in- situ observational studies in Fram Strait and in the Svalbard fjords: Atlantic and transformed Atlantic waters were more abundant in gelatinous zooplankton, whereas the highest taxonomic richness was found in the intermediate and Arctic water masses. These findings hint towards a potential jellification with progressing Atlantification in some Arctic regions. With an overall trend toward niche expansions for most of the arcto-boreal and cosmopolitan species modeled, I anticipate major shifts in the distribution of gelatinous zooplankton in the Arctic regions. These changes are likely to have profound impacts on ecosystem dynamics, affecting fish stocks, biogeochemical cycles and the efficiency of the biological carbon pump.Dissertation262 146 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Trophic ecology of Arctic gelatinous zooplankton(2024-07-24); ; ; The overarching goal of this dissertation is to reject the hypothesis of gelatinous zooplankton (GZP) as a trophic dead end for the Arctic and sub-Arctic seas. To do so, I investigated the role of GZP in the diet of different invertebrate and fish species, during different seasons and at different locations. To do so, I used DNA metabarcoding of the stomach contents of bentho-pelagic amphipods and demersal and bathypelagic fish species. I also, aimed to prove the usefulness of DNA metabarcoding in diet studies and the detection of GZP, which are rapidly digested and due to that often overlooked with traditional methods. Furthermore, I aimed to investigate the role of GZP species in the marine food web, which was investigated using stable isotope analysis, to determine the trophic level of GZP and fish species in Porsangerfjorden. Overall, I was able to show that GZP was consumed regularly by many predators in the Arctic and sub-Arctic seas during different seasons. Furthermore, I showed that GZP should be considered as different groups in food web models rather than being pooled into one term.Dissertation115 82 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Applying environmental DNA metabarcoding to investigate patterns of Arctic marine biodiversity with a focus on gelatinous zooplanktonThe Arctic is warming at least four times faster than the global average, as a result of anthropogenic climate change. Sea and air temperatures are rising, and perennial sea ice coverage has declined over the last four decades, with ice-free summers predicted to occur before 2050. Furthermore, in the Arctic gateway, Fram Strait, an increasing influence of warm Atlantic water is driving the ‘Atlantification’ of both environmental and biological processes. These changes affect habitat and resource availability for marine species in the region, causing shifts in species distributions and assemblages. There has been an intensification in research targeting the impacts of these changes over the last decades, however, important gaps in baseline knowledge of the current state of Arctic marine biodiversity still remain. The development of environmental DNA (eDNA) metabarcoding techniques has given rise to cost-effective and non-invasive methods for biodiversity assessments. One major advantage of eDNA is that it has the potential to detect delicate or elusive taxa that are typically overlooked or damaged by traditional net sampling, such as gelatinous zooplankton (GZP). This highly diverse group plays major roles across Arctic marine ecosystems. However, gaps in basic ecological data persist, including information on species assemblages and distribution. Thus, the overarching aim of this thesis was to apply eDNA metabarcoding to increase our knowledge of Arctic marine biodiversity, with a focus on GZP ecology. Environmental DNA signals elucidated well-known vertical structuring of pelagic diversity and community composition in the open ocean (Chapter Two) and in the marginal ice zone (Chapter Three) of Fram Strait. Distinct community assemblages were linked to environmental conditions, which represented different water masses (Chapter Two) and different sea ice and meltwater dynamics (Chapter Three). Finally, significant structuring in community composition was revealed across the inner section of a Svalbard fjord (Chapter Four), based on seawater- and sediment-derived eDNA. These findings demonstrate that eDNA metabarcoding is a valuable tool for investigating the spatial patterns and abiotic drivers of marine biodiversity in the Arctic. It also proved to be a sensitive and accurate method for investigating biodiversity across different spatial scales, habitats, seasons and environmental conditions. It was applied across a large area of the open ocean in Fram Strait during summer, in a sampling scheme that encompassed depths from surface waters down to the bathypelagic (Chapter Two). It was also used to detect fine-scale patterns in the upper meters of the sub-ice water column in the marginal ice zone, during the late summer (Chapter Three). Lastly, it was implemented during the polar night period, in the central section of a semi-enclosed fjord system with high levels of glacier input and water turbidity (Chapter Four). Additionally, this thesis was able to demonstrate that eDNA metabarcoding is a valuable method for investigating the diversity of GZP in the Arctic Ocean. Comparisons between eDNA and non-DNA-based survey methods (Chapters Two and Four) showed that eDNA recovered the highest numbers of species. It was also evident that each technique had inherent biases, with different GZP communities detected depending on the survey method used. Thus, we were able to confirm that eDNA greatly improves our repertoire for sampling GZP in the Arctic, but a combination of sampling methods should be employed to gain a more accurate picture of the diversity present. Finally, multi-marker analyses were applied (Chapters Three and Five) to further investigate the accuracy of two commonly used universal metabarcoding markers and their associated primers for amplifying common Arctic GZP taxa. The COI gene showed higher taxonomic resolution (e.g., species-level) but was affected by primer mismatches for some groups. The 18S gene was able to amplify more GZP groups, but genus and species-level assignments were not accurate. Therefore, it was evident that both are useful for investigating GZP diversity, but which one to prioritize should be determined by the research question at hand. Finally, it was evident that gaps in reference databases persist for both genes and that filling these with GZP samples from the Arctic should be a priority for future research. Overall, the research presented in this thesis supports the use of eDNA metabarcoding as a non-invasive and sensitive method for improving our understanding of Arctic marine biodiversity. It shows the utility of eDNA metabarcoding to go beyond presence data and to investigate abiotic drivers of eukaryotic biodiversity in different marine habitats and conditions. Moreover, it highlights the benefits of incorporating eDNA methods into GZP research to better understand how this important, yet understudied group will be affected by ongoing climate change in the Arctic. Finally, this thesis contributes valuable baseline data to our current understanding of marine eukaryotic biodiversity in the Atlantic sector of the Arctic.Dissertation148 126