Weight-to-weight conversion factors for benthic macrofauna: recent measurements from the Baltic and the North seas

The availability of standardised biomass data is essential for studying population dynamics, energy flows, fisheries and food web interactions. To make the estimates of biomass consistent, weight-to-weight conversion factors are often used, for example to translate more widely available measurements of wet weights into required dry weights and ash-free dry weight metrics. However, for many species and groups the widely applicable freely available conversion factors have until now remained very rough approximations with high degree of taxonomic generalisation. To close up this gap, here for the first time we publish the most detailed and statically robust list of ratios of wet weight (WW), dry weight (DW) and ash-free dry weight (AFDW). The dataset includes over 17 000 records of single measurements for 497 taxa. Along with aggregated calculations, enclosed reference information with sampling dates and geographical coordinates the dataset provides a broad opportunity for reuse and repurposing. It empowers the future user to do targeted sub-selections of data to best combine them with their own local data, instead of only having a single value of conversion factor per region. The dataset can thereby be used to quantify natural variability and uncertainty. The dataset is available via an unrestricted repository from https://doi.org/10.12754/data-2021-0002-01 (Gogina et al., 2021).

Macroinvertebrate community responses to mammal control - Evidence for top-down trophic effects

<p>New Zealand’s invertebrates are characterised by extraordinary levels of endemism and a tendency toward gigantism, flightlessness and longevity. These characteristics have resulted in a high vulnerability to introduced mammals (i.e. possums, rats, mice, and stoats) which are not only a serious threat to these invertebrates, but have also altered food web interactions over the past two-hundred years. The establishment of fenced reserves and the aerial application of 1080 toxin are two methods of mammal control used in New Zealand to exclude and reduce introduced mammals, respectively. Responses of ground-dwelling invertebrates to mammal control, including a consideration of trophic cascades and their interactions, remain unclear. However, in this thesis, I aimed to investigate how changes in mammal communities inside and outside a fenced reserve (ZEALANDIA, Wellington) and before-and-after the application of 1080 in Aorangi Forest, influence the taxonomic and trophic abundance, body size and other traits of ground-dwelling invertebrates on the mainland of New Zealand. I also tested for effects of habitat variables (i.e. vegetation and elevation), fluctuations in predator populations (i.e. mice, rats and birds) and environmental variables (i.e. temperature). Additionally, I investigated how squid-bait suspended over pitfall traps influenced the sampling of ground weta and other invertebrates in Aorangi and Remutaka Forests. Contrary to my expectations, there were no differences in abundance or body size of invertebrates within ZEALANDIA (which excludes introduced mammals except mice) relative to the outside, except for Staphylinidae which were more abundant outside the fence. Differences in the agents of predation pressure from mainly mammals, outside the reserve, to mostly birds within ZEALANDIA, but potentially little change in net predation pressure, may explain this apparent similarity in ground-invertebrates. No differences in invertebrate communities were also recorded in the 1080-treated area (Aorangi Forest) after one year of the aerial application of 1080. It could imply that the use of this toxin does not produce any apparent detriment to invertebrates at a population level. The application of 1080 usually leads to changes in insectivorous predator (birds and introduced mammals) dynamics in the short-term mainly due to meso-predator release, which may affect invertebrate communities as a result. Temporal and spatial variation of different components of the ecosystem appear to be more significant drivers of invertebrate dynamics, than 1080 mammal control. For example, rats (Rattus spp.) limited the abundance and body size of large invertebrates (i.e. ground weta, cave weta and spiders) in Aorangi and Remutaka Forests. Smaller invertebrates such as gastropods, weevils and springtails were affected directly by spatial factors such as vegetation, while dung beetles responded to an increase in mouse density. Based on a comparison of pitfall trapping methods, I suggest the use of squid baiting as an effective method for sampling ground weta (Hemiandrus spp.) in New Zealand, as they responded positively to these baits. Finally, I propose ground weta and spiders as suitable indicators of rat predation, as they are abundant in forests and easily recognised by non-specialists, and they respond negatively to rat densities. This thesis underlines the importance of studying the effect of introduced mammal dynamics derived from mammal control in an ecosystem approach, to achieve conservation goals both in the short- and long-term, especially considering the New Zealand Government’s ambitious goal of eradicating three of the most prevalent mammal predators (rats, possums and stoats) by 2050.</p>

Macroinvertebrate community responses to mammal control - Evidence for top-down trophic effects

<p>New Zealand’s invertebrates are characterised by extraordinary levels of endemism and a tendency toward gigantism, flightlessness and longevity. These characteristics have resulted in a high vulnerability to introduced mammals (i.e. possums, rats, mice, and stoats) which are not only a serious threat to these invertebrates, but have also altered food web interactions over the past two-hundred years. The establishment of fenced reserves and the aerial application of 1080 toxin are two methods of mammal control used in New Zealand to exclude and reduce introduced mammals, respectively. Responses of ground-dwelling invertebrates to mammal control, including a consideration of trophic cascades and their interactions, remain unclear. However, in this thesis, I aimed to investigate how changes in mammal communities inside and outside a fenced reserve (ZEALANDIA, Wellington) and before-and-after the application of 1080 in Aorangi Forest, influence the taxonomic and trophic abundance, body size and other traits of ground-dwelling invertebrates on the mainland of New Zealand. I also tested for effects of habitat variables (i.e. vegetation and elevation), fluctuations in predator populations (i.e. mice, rats and birds) and environmental variables (i.e. temperature). Additionally, I investigated how squid-bait suspended over pitfall traps influenced the sampling of ground weta and other invertebrates in Aorangi and Remutaka Forests. Contrary to my expectations, there were no differences in abundance or body size of invertebrates within ZEALANDIA (which excludes introduced mammals except mice) relative to the outside, except for Staphylinidae which were more abundant outside the fence. Differences in the agents of predation pressure from mainly mammals, outside the reserve, to mostly birds within ZEALANDIA, but potentially little change in net predation pressure, may explain this apparent similarity in ground-invertebrates. No differences in invertebrate communities were also recorded in the 1080-treated area (Aorangi Forest) after one year of the aerial application of 1080. It could imply that the use of this toxin does not produce any apparent detriment to invertebrates at a population level. The application of 1080 usually leads to changes in insectivorous predator (birds and introduced mammals) dynamics in the short-term mainly due to meso-predator release, which may affect invertebrate communities as a result. Temporal and spatial variation of different components of the ecosystem appear to be more significant drivers of invertebrate dynamics, than 1080 mammal control. For example, rats (Rattus spp.) limited the abundance and body size of large invertebrates (i.e. ground weta, cave weta and spiders) in Aorangi and Remutaka Forests. Smaller invertebrates such as gastropods, weevils and springtails were affected directly by spatial factors such as vegetation, while dung beetles responded to an increase in mouse density. Based on a comparison of pitfall trapping methods, I suggest the use of squid baiting as an effective method for sampling ground weta (Hemiandrus spp.) in New Zealand, as they responded positively to these baits. Finally, I propose ground weta and spiders as suitable indicators of rat predation, as they are abundant in forests and easily recognised by non-specialists, and they respond negatively to rat densities. This thesis underlines the importance of studying the effect of introduced mammal dynamics derived from mammal control in an ecosystem approach, to achieve conservation goals both in the short- and long-term, especially considering the New Zealand Government’s ambitious goal of eradicating three of the most prevalent mammal predators (rats, possums and stoats) by 2050.</p>

Microfluidic chips provide visual access to in situ soil ecology

Microbes govern most soil functions, but investigation of these processes at the scale of their cells has been difficult to accomplish. Here we incubate microfabricated, transparent ‘soil chips’ with soil, or bury them directly in the field. Both soil microbes and minerals enter the chips, which enables us to investigate diverse community interdependences, such as inter-kingdom and food-web interactions, and feedbacks between microbes and the pore space microstructures. The presence of hyphae (‘fungal highways’) strongly and frequently increases the dispersal range and abundance of water-dwelling organisms such as bacteria and protists across air pockets. Physical forces such as water movements, but also organisms and especially fungi form new microhabitats by altering the pore space architecture and distribution of soil minerals in the chip. We show that soil chips hold a large potential for studying in-situ microbial interactions and soil functions, and to interconnect field microbial ecology with laboratory experiments.

Positive species interactions strengthen in a high-CO 2 ocean

Negative interactions among species are a major force shaping natural communities and are predicted to strengthen as climate change intensifies. Similarly, positive interactions are anticipated to intensify and could buffer the consequences of climate-driven disturbances. We used in situ experiments at volcanic CO 2 vents within a temperate rocky reef to show that ocean acidification can drive community reorganization through indirect and direct positive pathways. A keystone species, the algal-farming damselfish Parma alboscapularis, enhanced primary productivity through its weeding of algae whose productivity was also boosted by elevated CO 2 . The accelerated primary productivity was associated with increased densities of primary consumers (herbivorous invertebrates), which indirectly supported increased secondary consumers densities (predatory fish) (i.e. strengthening of bottom-up fuelling). However, this keystone species also reduced predatory fish densities through behavioural interference, releasing invertebrate prey from predation pressure and enabling a further boost in prey densities (i.e. weakening of top-down control). We uncover a novel mechanism where a keystone herbivore mediates bottom-up and top-down processes simultaneously to boost populations of a coexisting herbivore, resulting in altered food web interactions and predator populations under future ocean acidification.

Metal(loid) speciation and transformation by aerobic methanotrophs

Manufacturing and resource industries are the key drivers for economic growth with a huge environmental cost (e.g. discharge of industrial effluents and post-mining substrates). Pollutants from waste streams, either organic or inorganic (e.g. heavy metals), are prone to interact with their physical environment that not only affects the ecosystem health but also the livelihood of local communities. Unlike organic pollutants, heavy metals or trace metals (e.g. chromium, mercury) are non-biodegradable, bioaccumulate through food-web interactions and are likely to have a long-term impact on ecosystem health. Microorganisms provide varied ecosystem services including climate regulation, purification of groundwater, rehabilitation of contaminated sites by detoxifying pollutants. Recent studies have highlighted the potential of methanotrophs, a group of bacteria that can use methane as a sole carbon and energy source, to transform toxic metal (loids) such as chromium, mercury and selenium. In this review, we synthesise recent advances in the role of essential metals (e.g. copper) for methanotroph activity, uptake mechanisms alongside their potential to transform toxic heavy metal (loids). Case studies are presented on chromium, selenium and mercury pollution from the tanneries, coal burning and artisanal gold mining, respectively, which are particular problems in the developing economy that we propose may be suitable for remediation by methanotrophs.

Summertime Amino Acid and Carbohydrate Patterns in Particulate and Dissolved Organic Carbon Across Fram Strait

Amino acids (AA) and carbohydrates (CHO) are important components of the marine organic carbon cycle. Produced mainly by phytoplankton as part of the particulate organic carbon (POC) fraction, these compounds can be released into the outer medium where they become part of the dissolved organic carbon (DOC) pool and are rapidly taken up by heterotrophs (e.g., bacteria). We investigated the quantity and quality of POC and DOC, AA and CHO composition in both pools in three different water masses in the Fram Strait (Arctic Ocean) in summer 2017. Polar Waters and Atlantic Waters showed similar concentrations of particulate and dissolved AA and CHO, despite Polar Waters showing the highest DOC concentrations. In Mixed Waters, where the two water masses mix with each other and with melting sea ice, the concentrations of particulate and dissolved AA and CHO were highest. AA and CHO composition differed substantially between the particulate and dissolved fractions. The particulate fraction (&gt;0.7 μm) was enriched in essential AA and the CHO galactose, xylose/mannose, and muramic acid. In the dissolved fraction non-essential AA, several neutral CHO, and acidic and amino CHO were enriched. We further investigated different size fractions of the particulate matter using a separate size fractionation approach (0.2–0.7 μm, 0.7–10 μm and &gt;10 μm). The chemical composition of the 0.2–0.7 μm size-fraction had a higher contribution of non-essential AA and acidic and amino sugars, setting them apart from the 0.7–10 μm and &gt;10 μm fractions, which showed the same composition. We suggest that the relative differences observed between different size fractions and DOC with regards to AA and CHO composition can be used to evaluate the state of organic matter processing and evaluate the contribution of autotrophic phytoplankton or more heterotrophic biomass. In the future, changing conditions in the Central Arctic Ocean (Atlantification, warming, decreasing ice concentrations) may increase primary production and consequently degradation. The AA and CHO signatures left behind after production and/or degradation processes occurred, could be used as tracers after the fact to infer changes in microbial loop processes and food web interactions.

The Role of Food Web Interactions in Multispecies Fisheries Management: Bio-economic Analysis of Salmon, Herring and Grey Seal in the Northern Baltic Sea

Multispecies bio-economic models are useful tools to give insights into ecosystem thinking and ecosystem-based management. This paper developed an age-structured multispecies bio-economic model that includes the food web relations of the grey seal, salmon, and herring, along with salmon and herring fisheries in the Baltic Sea. The results show that the increasing seal population influences salmon fisheries and stock, but the impacts on the harvest are stronger than on the stock if the targeted management policies are obeyed. If seal population growth and a low herring stock occur simultaneously, the salmon harvest could face a serious threat. In addition, scenarios of the multispecies management approach in this paper reveal a benefit that our model can evaluate the performance of different fisheries with identical or different management strategies simultaneously. The results show the most profitable scenario is that both fisheries pursuit aggregated profits and reveal a trade-off between herring fisheries and salmon fisheries. Our model indicates that the herring harvest level and the approaches to managing herring fisheries can influence the performance of salmon fisheries. The study also demonstrates a way to develop a multispecies bio-economic model that includes both migratory fish and mammalian predators.

Weight-to-weight conversion factors for benthic macrofauna: recent measurements from the Baltic and the North Seas

Estimates of biomass often involve the use of weight-to-weight conversion factors for rapid assessment of dry-weights based metrics from more widely available measurements of wet weights. Availability of standardized biomass data is essential amid research on population dynamics, energy flow, fishery and food web interactions. However, for many species and groups the widely-applicable freely available conversion factors until now remained very rough approximations with high degree of taxonomic generalization. To close up this gap, here for the first time we publish the most detailed and statically robust list of ratios of wet weight (WW), dry weight (DW) and ash-free dry weight (AFDW). The dataset includes over 17000 records of single measurements for 497 taxa. Along with aggregated calculations, enclosed reference information with sampling dates and geographical coordinates provides the broad opportunity for reuse and repurposing. It empowers the future user to do targeted sub selections of data to best combine them with own local data, instead of only having a single value of conversion factor per region. Data can help to quantify natural variability and uncertainty, and assist to refine current ecological theory. The dataset is available via an unrestricted repository from: http://doi.io-warnemuende.de/10.12754/data-2021-0002 (Gogina et al., 2021).