Biology subjects

Spatharis, S.

Publications and source records attributed to Spatharis, S..

5 recordsLinked to original sources

bioRxiv2023

High resolution longitudinal molecular and morphological tracking of planktonic threats to salmon aquaculture.

Marine-phase salmonid aquaculture is a major component of the coastal economies of Northern Europe, North America and Chile and is under threat from numerous challenges to gill health, many of which originate from the phyto- and zooplankton. Associated losses are growing as a proportion of production year on year. A first step towards mitigating losses is to characterize the biological drivers of poor gill health. Numerous planktonic species have been implicated, including toxic and siliceous microalgae, hydrozoans and scyphozoans; however, rigorous longitudinal surveys of planktonic diversity and gill health have been lacking. In the current study, we present and assess an exhaustive identification approach combining both morphological and molecular methods (environmental DNA metabarcoding) approaches in combination with robust statistical models to identify the planktonic drivers of complex gill disease (CGD) and fish mortality. We undertook longitudinal molecular and microscopic evaluation at two marine aquaculture facilities on the west coast of Scotland using daily data collected during the 2021 growing season (March-October). Examining these two different sites, one sheltered and one exposed to the open sea, we identified new, important, and unexpected planktonic drivers (e.g. doliolids and appendicularians) of CGD and mortality and confirmed the significance of some established threats (e.g. hydrozoans and diatoms). We also explored delayed or lagged effects of planktonic abundances on gill health and undertook a comparison of environmental DNA metabarcoding and microscopy in their ability to identify and quantify planktonic species. Our data highlight the diversity of planktonic threats to salmonid aquaculture as well as the importance of using both molecular and morphological approaches to detect those. Despite our study relying on two farm sites only, our results evidence the role of the different planktonic players on salmon gill disease; there is now an urgent need to expand systematic longitudinal molecular and morphological approach across multiple sites and over multiple years. The resultant catalogue of main biological drivers will enable early warning systems, new treatments and, ultimately, a sustainable platform for future salmonid aquaculture in the marine environment.

zoology↗

bioRxiv2023

The effects of artificial light at night (ALAN) on the gaping activity and feeding of mussels

Artificial light at night (ALAN) is one of the most widespread forms of environmental pollution. Studies on terrestrial organisms have shown that the effects of ALAN can be pervasive, and importantly, can depend on the colour (i.e., wavelength) of light. ALAN also affects marine environments as it is present in more than 22% of the worlds coastlines and can reach depths of up to 100m. However, the impact of different colour ALAN on coastal marine organisms is under-investigated. In this study, we tested the effects of different ALAN colours on Mytilus edulis, a widespread coastal bivalve known for its high phytoplankton clearance capacity amongst other valuable ecosystem services. Using a lab-based valvometry system, we recorded the impact of red, green, and white ALAN on gaping activity patterns and phytoplankton clearance capacity of individual mussels and compared these to dark night control. Mussels exhibited a semi-diel activity pattern in both proportion of time open and gaping frequency. Although ALAN did not have significant effects on the proportion of time open it did significantly affect the gaping frequency. This effect was colour-specific with red and white ALAN resulting in lower activity compared to the dark night control but there were no effects on the phytoplankton consumption. Under green light, however, mussels showed a higher gaping frequency and reduced phytoplankton consumption with increasing time spent open compared to the other ALAN treatments and the dark control. Our findings suggest that ALAN does have colour-specific effects on mussels and indicate the importance of further investigating the physiological mechanisms behind these patterns, and their potential ecological consequences.

ecology↗

bioRxiv2022

Dispersal provides trophic-level dependent insurance against a heatwave in freshwater ecosystems

Climate change-related heatwaves are major recent threats to biodiversity and ecosystem functioning. However, our current understanding of the mechanisms governing community resilience (resistance and recovery) to extreme temperature events is still rudimentary. The spatial insurance hypothesis postulates that diverse regional species pools can buffer ecosystem functioning against local disturbances through immigration of better adapted taxa. However, experimental evidence for such predictions from multi-trophic communities and pulse-type disturbances, like heatwaves, are largely missing. We performed an experimental mesocosm study with alpine lake plankton to test whether a dispersal event from natural lakes prior to a simulated heatwave could increase resistance and recovery of local communities. As the buffering effect of dispersal may differ among trophic groups, we independently manipulated dispersal of organisms from lower (microorganisms) and higher (zooplankton) trophic levels. The experimental heatwave suppressed total community biomass by having a strong negative effect on zooplankton biomass, probably due to a heat-induced increase in metabolic costs that in turn caused mortality. Heating thus resulted in weaker top-down control and a subsequent shift to bottom-heavy food webs. While zooplankton dispersal did not alleviate the negative heatwave effects on zooplankton biomass, dispersal of microorganism enhanced biomass recovery at the level of phytoplankton, thereby providing evidence for spatial insurance. The different response of trophic groups may be related to the timing of dispersal, which happened under strongly monopolized resource conditions by zooplankton, creating limited opportunity for competitors to establish. At the same time, the heatwave released phytoplankton from grazing pressure and increased nutrient recycling, which may have facilitated the establishment of new phytoplankton taxa. Our findings clearly show that even a short heatwave can strongly alter energy flow in aquatic ecosystems. Although dispersal can enhance community resilience, the strength of its buffering effects depends on the trophic level.

ecology↗

bioRxiv2021

Wavelength-dependent effects of artificial light at night on phytoplankton growth and community structure

Artificial light at night (ALAN) is increasingly recognised as a disruptive form of environmental pollution, impacting many physiological and behavioural processes that may scale up to population and community-level effects. Mounting evidence from animal studies show that the severity and type of the impact depends on the wavelength and intensity of ALAN. This knowledge has been instrumental for informing policy-making and planning for wildlife-friendly illumination. However, most of this evidence comes from terrestrial habitats, while research testing alternative wavelength illumination in marine environments is lagging behind. In this study we investigated the effect of such alternative ALAN colours on marine primary producers. Specifically, we tested the effect of green, red, and natural white LED illumination at night, compared to a dark control, on the growth of a green microalgae as well as the biomass, diversity and composition of a phytoplankton assemblage. Our findings show that green ALAN boosted chlorophyll production at the exponential growth stage, resulting in higher biomass production in the green algae Tetraselmis suesica. All ALAN wavelengths affected the biomass and diversity of the assemblage with the red and green ALAN having the stronger effects, leading to higher overall abundance and selective dominance of specific diatom species compared to white ALAN and the dark control. SynthesisOur work indicates that the wavelength of artificial light sources in marine areas should be carefully considered in management and conservation plans. In particular, green and red light should be used with caution in coastal areas, where there might be a need to strike a balance between the strong effects of green and red light on marine primary producers with the benefit they bring to other organisms.

ecology↗

bioRxiv2017

Environmental DNA: a new low-cost monitoring tool for pathogens in salmonid aquaculture.

Sequencing of environmental DNA (eDNA-seq) is an emergent new monitoring tool that promises to facilitate the accurate and cost effective detection of species in environmental samples. eDNA monitoring is likely to have a major impact on the ability of salmonid aquaculture industry producers and their regulators to detect the presence and abundance of pathogens and other biological threats in the surrounding environment. However, for eDNA-seq to develop into a useful bio-monitoring tool it is necessary to (a) validate that sequence datasets derived from amplification of meta-barcoding markers reflect the true species identity and abundances in biological samples, and (b) establish a low-cost sequencing method to enable the bulk processing of environmental samples. In this study, we employed an elaborate experimental design whereby different combinations of five biological agents were crossed at three abundance levels and exposed to pre-filtered and normal seawater, prior to coarse filtering and then eDNA ultrafiltration of the resultant material. We then benchmarked the low-cost, scalable, Ion Torrent sequencing method against the current gold-standard Illumina platform for eDNAseq detection in aquaculture. Based on amplicon-seq of the 18S SSU rDNA v9 region, we found that Illumina and Ion Torrent were equally good in identifying the two parasite species (Lepeophtheirus salmonis and Paramoeba perurans), whereas the microalgae species Prymnesium parvum, Pseudo-nitzschia seriata and P. delicatissima could be assigned correctly only to the genus level. Illumina and Ion Torrent were also equally able to reflect community composition in our samples, whereas Ion Torrent was more sensitive in detecting species richness when the medium was unfiltered seawater. Both methods were able to reflect the correct abundances of 4 out of 5 species in samples from unfiltered seawater, despite the significant amount of background noise from both bacteria and eukaryotes. Our findings indicate that eDNA-seq offers significant potential in the monitoring of species harmful to aquaculture and for this purpose, the low-cost Ion Torrent sequencing is equally as accurate as Illumina.

genetics↗