Peter Thor - Academia.edu (original) (raw)

Papers by Peter Thor

Ocean acidification is expected to have dramatic impacts on oceanic ecosystems, yet surprisingly ... more Ocean acidification is expected to have dramatic impacts on oceanic ecosystems, yet surprisingly few studies currently examine long-term adaptive and plastic responses of marine invertebrates to pCO 2 stress. Here, we exposed populations of the common copepod Pseudocalanus acuspes to three pCO 2 regimes (400, 900, and 1550 latm) for two generations, after which we conducted a reciprocal transplant experiment. A de novo transcriptome was assembled, annotated, and gene expression data revealed that genes involved in RNA transcription were strongly down-regulated in populations with long-term exposure to a high pCO 2 environment, even after transplantation back to control levels. In addition, 747 000 SNPs were identified, out of which 1513 showed consistent changes in nucleotide frequency between replicates of control and high pCO 2 populations. Functions involving RNA transcription and ribosomal function, as well as ion transport and oxidative phosphorylation, were highly overrepresented. We thus conclude that pCO 2 stress appears to impose selection in copepods on RNA synthesis and translation, possibly modulated by helicase expression. Using a physiological hypothesis-testing strategy to mine gene expression data, we herein increase the power to detect cellular targets of ocean acidification. This novel approach seems promising for future studies of effects of environmental changes in ecologically important nonmodel organisms.

Search: onr:"swepub:oai:services.scigloo.org:112474" > DOC flux mediated b... ... Th... more Search: onr:"swepub:oai:services.scigloo.org:112474" > DOC flux mediated b... ... Thor, Peter, 1965-(author) Göteborgs universitet, Institutionen för marin ekologi Møller, Eva Friis (author) Nielsen, Torkel Gissel (author) University of Gothenburg Faculty of Sciences. ...

Marine Ecology Progress Series

Using 14 C-labeled phytoplankton as tracer, we investigated 2 mechanisms of immediate dissolved o... more Using 14 C-labeled phytoplankton as tracer, we investigated 2 mechanisms of immediate dissolved organic carbon (DOC) release during grazing activity of Calanus spp. -sloppy feeding and leakage from newly expelled fecal pellets. Half of the carbon cleared by Calanus spp. was released as DOC through sloppy feeding. Freshly expelled fecal pellets lost more than 20% of their carbon content within the first hour, corresponding to 6% of the carbon cleared. Thus, copepods should not only be considered as an essential link to higher trophic levels, but also as a feedback link to the microbial food web.

This file provides the excel sheet for the calculations of normal distributions and their fits to... more This file provides the excel sheet for the calculations of normal distributions and their fits to particle counter outputs. Ready to use!

In the present study, six laboratory populations of the calanoid copepod Pseudocalanus acuspes we... more In the present study, six laboratory populations of the calanoid copepod Pseudocalanus acuspes were established at three different CO2 partial pressures (pCO2 of 400, 900 and 1550 µatm) and grown for two generations at these conditions. Our results show evidence of buffering of OA effects as a result of transgenerational transmission. Second generation adults showed a 29% decrease in fecundity at 900 µatm CO2 compared to 400 µatm CO2 accompanied by a 10% increase in metabolic rate indicative of metabolic stress. Reciprocal transplant tests demonstrated that this effect was reversible and the expression of phenotypic plasticity. Furthermore, these tests showed that at a pCO2 exceeding the natural range experienced by P. acuspes (1550 µatm), fecundity would have decreased by as much as 67% compared to at 400 µatm CO2 as a result of this plasticity. However, transgenerational buffering partly reduced OA effects so that the loss of fecundity remained at a level comparable to that at 900...

Våra utsläpp av koldioxid ökar i en oroväckande takt. Vi vet att en konsekvens är global uppvärmn... more Våra utsläpp av koldioxid ökar i en oroväckande takt. Vi vet att en konsekvens är global uppvärmning, men det som an-tagligen är mindre känt är vad marina kemister kallar " det andra koldioxidproblemet " . En tredjedel av den koldioxid som släpps ut absorberas av världens hav. I havet reagerar den med kalcium och vatten och bildar kolsyra. Detta gör att pH i oceanerna sjunker, och vi får en försurning. En två millimeter lång hona av hoppkräftan Pseudocalanus acuspes med ägg. Våra studier visar att både ämnesomsättningen och äggproduktionen minskade hos hopp-kräftor som utsattes för försurade miljöer. u nder de senaste trehundra miljoner åren har pH-värdet i havets ytvatten varit någor-lunda stabilt, med ett genom-snitt på cirka 8,2. Idag är det runt 8,1, en minskning som motsvarar en ökning i surhet med 25 procent under de senas-te två århundradena. oceanerna absorbe-rar för närvarande cirka 22 miljoner ton koldioxid per dag. Prognoser baserade på dessa siffror visar att i...

Crustaceana

We measured ingestion rate (IR), egg production rate (EPR) and egg hatching success (EHS) at incr... more We measured ingestion rate (IR), egg production rate (EPR) and egg hatching success (EHS) at increasing prey concentrations and calculated egg production efficiency (EPE) and maintenance rate (MR) in the estuarine copepod Acartia tonsafed three different algal diets. EPR and EHS were relatively more affected by prey species than by prey concentration. EPEs were constant among carbon concentrations (C) on a diet of Rhodomonas baltica(0.202 ± 0.055, mean ± SD) and Dunaliella tertiolecta(0.034 ± 0.015), but decreased significantly from 0.371 ± 0.062 (mean of two lowest prey concentrations) to 0.200 ± 0.019 at the highest concentration of Thalassiosira weissflogii. In general it seems that other requirements than C demand limit EPE and EHS in A. tonsa. The MR (IR when EPR = 0) was significantly higher on D. tertiolecta, which also yielded the lowest EPEs, and it seems that variations in maintenance requirements may have been instrumental in evoking EPE variations as well.

Measurements of algal cell concentrations on particle counters have long been limited to monoalga... more Measurements of algal cell concentrations on particle counters have long been limited to monoalgal samples due to the difficulty of discrimination of cells with overlapping sizes. Here I suggest a simple method for enumeration of algal cells in mixes of monocultures of algae with overlapping size distributions using computer spreadsheets. The method is based on correlations of the sum of two or more normal or lognormal distributions to the outputs from a particle counter. The correlations exhibit only one local optimum and by iterating the procedure several times an optimal value for cell concentrations is reached. Tests showed that the optimal values are reached from a wide range of starting values of peak sizes, medians, and standard deviations of the fitted distributions. Often no more than 3 iterations are needed to reach the optimal values. The method was tested against direct particle counts of mixed algal samples. The values obtained by the fits were always better than those ...

Marine Ecology Progress Series, 2003

Marine Ecology Progress Series, 2006

We assessed metabolic balance, RNA content, and egg hatching success (EHS) in Acartia tonsa and A... more We assessed metabolic balance, RNA content, and egg hatching success (EHS) in Acartia tonsa and A. clausi over a wide salinity range (2 to 33 and 16 to 33, respectively). For A. tonsa, the energy partitioning between ingestion, production and respiration was relatively constant with small differences in gross growth efficiency (GGE) and cost of growth (CG). In contrast, A. clausi exhibited significantly reduced ingestion and GGE, and highly elevated CG at salinities ≤20. In both species, RNA levels mirrored egg production. EHS was generally high in both species, but decreased by 80% for A. clausi at 16. These results contribute to the understanding of distribution patterns of both species along salinity gradients. The observed responses would allow the dominance of A. tonsa at low salinities, although its higher energetic requirement and feeding activity subject it to stronger predation pressure than competing A. clausi.

Marine Ecology Progress Series, 2008

Mortality rates of the copepods Calanus hyperboreus, C. glacialis, C. finmarchicus, Pseudocalanus... more Mortality rates of the copepods Calanus hyperboreus, C. glacialis, C. finmarchicus, Pseudocalanus sp. and Oithona similis were investigated during June 2001 in Disko Bay, western Greenland. These 5 species dominated the zooplankton community in the upper 75 m, contributing 89% of the total copepod biomass. Instantaneous mortality rates of copepodites of all 5 species and nauplii of Pseudocalanus sp. and O. similis were calculated using vertical life tables on abundances and published information on stage duration times. Compared with those covering a range of boreal habitats, the mortality rates were higher, with highest rates occurring in C. finmarchicus and C. glacialis copepodite stages I to III and Pseudocalanus spp. stage III (maximum = 0.18 d -1 ). Mortality rates remained lower in all stages of O. similis. When superimposing mortality rates for all species and stages on copepod size a significant peak at 1.3 mm prosome length was evident. This peak fitted a prey size dependent functional response of predation and the high mortality rates were, therefore, most probably attributable to size-specific predation.

$Research paper thumbnail of Influence of two different green algal diets on specific dynamic action and incorporation of carbon into biochemical fractions in the copepod Acartia tonsa$

Journal of Plankton Research, 2002

Journal of Experimental Marine Biology and Ecology, 2008

Salinity variability at short time scales constitutes a severe restriction to marine life in coas... more Salinity variability at short time scales constitutes a severe restriction to marine life in coastal and estuarine ecosystems. In these environments zooplankters may experience rapid salinity variations due to diverse processes, yet lethal or sub-lethal responses to such changes have been scarcely studied. We assessed shortterm (12 h) survival and time-integrated clearance (F; mL ind − 1 h − 1 ) and ingestion rates (I, µgC ind − 1 h − 1 ) after 1, 2, 4, 8 and 12 h of two widespread and abundant coastal copepods, Acartia tonsa and A. clausi, subjected to instant salinity changes from 32 PSU to 26, 20, 14, 8 and 4 PSU (A. tonsa) and from 32 to 26, 20 and 14 PSU (A. clausi). We expected that A. tonsa, which occur naturally in environments where sharp salinity gradients are common would tolerate wider salinity changes than A. clausi, which less frequently encounter sharp gradients in nature. For A. tonsa mortality for the extreme haline shock (change from 32 to 4 PSU) was 31%, whereas A. clausi reached 22% mortality already at a change from 32 to 14 PSU; in comparison, mortality for A. tonsa at the 32/14 PSU treatment was only 3%. F and I decreased significantly at extreme treatments, and the total clearance in experimental bottles with salinity shocked animals (F tot, mL h − 1 ) was only 5% of rates measured in non-shocked control bottles for A. tonsa (32/4 PSU change) and 20% for A. clausi (32/14 PSU change); corresponding total ingestion (I tot , µgC h − 1 ) represented 9.5% of that in control bottles for A. tonsa and 24% for A. clausi. In comparison, the 32/14 PSU treatment did not affect either clearance or ingestion rates in A. tonsa. Results suggest that in the field A. tonsa is not likely to suffer significant mortalities due to sudden salinity reductions in the surrounding mediumexcept under extreme circumstances-while A. clausi cannot tolerate changes N 18 PSU. However, in both species feeding activity could be severely compromised by salinity reductions. The decreased feeding rate may have direct implications for processes ranging from energy acquisition at individual level to organic matter transfers at ecosystem level and thus deserves more attention in experimental studies and population modelling.

Aquatic Microbial Ecology, 2003

Fecal pellets were produced by Acartia tonsa fed 14 C-labeled diatom, cryptophyte, and dinoflagel... more Fecal pellets were produced by Acartia tonsa fed 14 C-labeled diatom, cryptophyte, and dinoflagellate diets, and were incubated in 1.2 µm-filtered Long Island Sound seawater. Based on the 14 C label, the decrease in fpOC (fecal pellet organic carbon), the release and fate of dissolved organic carbon (DOC) and particulate organic carbon (POC), as well as bacterial production and enzymatic activity, were followed over a 96 h period. fpOC decreased by 9, 14, and 19% d -1 in diatom, cryptophyte, and dinoflagellate pellets, respectively. There was a fast, possibly passive, leakage of DOC from pellets from all 3 diets within a few hours after egestion, which may not have been utilized by attached bacteria. Bacterial production rates were 17, 12, and 31 pg C pellet -1 h -1 , on diatom, cryptophyte, and dinoflagellate pellets, respectively. These were 5 orders of magnitude higher than production rates of free-living bacteria, indicating that copepod fecal pellets are hot spots of pelagic microbial production. The high production was caused primarily by high initial bacterial abundances. Accordingly, production and growth were entirely uncoupled in diatom pellets. There were no increases in abundance of attached bacteria on any of the 3 diets, indicating that the produced bacterial cells were released from the fecal pellets. Attached bacteria had a higher ectoenzymatic activity than free-living bacteria, but their production and ectoenzymatic activity were uncoupled and they only assimilated a minor fraction of the released DOC. DOC was therefore released favoring free-living microbes. The chitinase activity, which increased several-fold, was coupled to the production of attached bacteria; thus, chitin may play an important role in bacterial production on copepod fecal pellets.

… Meeting, Nice, France, 2009

Search: onr:"swepub:oai:services.scigloo.org:112460" > Effects of salinity... ... Th... more Search: onr:"swepub:oai:services.scigloo.org:112460" > Effects of salinity... ... Thor, Peter, 1965-(author) Göteborgs universitet, Institutionen för marin ekologi Calliari, Danilo, 1969-(author) Göteborgs universitet, Institutionen för marin ekologi Andersen Borg, M (author) ...