Kerstin Wiklander

Aerobic scope fails to explain the detrimental effects on growth resulting from warming and elevated CO2 in Atlantic halibut

As a consequence of increasing atmospheric CO2, the worlds oceans are becoming warmer and more acidic. Whilst the ecological effects of these changes are poorly understood, it has been suggested that fish performance including growth will be reduced mainly as a result of limitations in oxygen transport capacity. Contrary to the predictions given by the oxygen- and capacity-limited thermal tolerance hypothesis, we show that aerobic scope and cardiac performance of Atlantic halibut (Hippoglossus hippoglossus) increase following 14–16 weeks exposure to elevated temperatures and even more so in combination with CO2-acidified seawater. However, the increase does not translate into improved growth, demonstrating that oxygen uptake is not the limiting factor for growth performance at high temperatures. Instead, long-term exposure to CO2-acidified seawater reduces growth at temperatures that are frequently encountered by this species in nature, indicating that elevated atmospheric CO2 levels may have serious implications on fish populations in the future.

Browsing damage on broadleaved trees in semi-natural temperate forest in Sweden, with a focus on oak regeneration

Absence of, or poor, oak (Quercus spp.) regeneration is a problem in uneven-aged, mixed closed-canopy broadleaved forests. Browsing by ungulates on small trees may contribute to poor oak regeneration in such forests. This possibility was investigated in 25 Swedish stands, and browsing damage was analysed in relation to landscape and stand factors. The proportion of browsed small (<20 cm tall) oak seedlings and other seedlings was low, and apparently a minor mortality factor. For saplings (20–130 cm tall), accumulated browsing damage was generally higher on oak than on five major competing tree species: Fraxinus excelsior, Corylus avellana, Tilia cordata, Acer platanoides and Sorbus aucuparia. Leaf removal was rare in late summer, except for rowan. The amount of cover (shelter) for ungulates near plots was positively correlated with oak browsing intensity; within plots, a high density of ash saplings may reduce browsing on oak saplings. In these forests, browsing probably retards growth of oak saplings relative to competing trees. Oak may persist as a minor stand component, but monitoring is needed to study future changes.

The impact of temperature on the metabolome and endocrine metabolic signals in Atlantic salmon (Salmo salar)

The aim was to elucidate the effects of elevated temperature on growth performance, growth- and appetite-regulating hormones and metabolism in Atlantic salmon, Salmo salar. Post-smolts in seawater (average mass 175g) that had been reared at 12°C were kept at three temperatures (8, 12 and 18°C) and sampled after one and three months. After three months, the fish kept in 18°C had decreased growth rate and condition factor, and elevated plasma levels of growth hormone (GH) and leptin, compared with fish kept at the lower temperatures. Food conversion efficiency was also decreased at 18°C, while at the same time protein uptake was improved and thus was not a limiting mechanism for growth. Redistribution of energy stores in fish at the highest temperature is evident as a preference of maintaining length growth during times of limited energy availability. NMR-based metabolomics analyses of plasma revealed that several metabolites involved in energy metabolism were negatively affected by temperature in the upper temperature range of Atlantic salmon. Specifically, the high temperature induced a decline of several amino acids (glutamine, tyrosine and phenylalanine) and a shift in lipid metabolism. It appears likely that the decreased food intake at the highest temperature is linked to an anorexigenic function of leptin, but also that the decreased food intake, feed conversion efficiency and condition factor can be linked to changes in GH endocrinology.

Response to ‘How and how not to investigate the oxygen and capacity limitation of thermal tolerance (OCLTT) and aerobic scope – remarks on the article by Gräns et al.’

We appreciate the on-going discussion and healthy evaluation of the hypothesis of oxygen and capacity limitation of thermal tolerance (OCLTT). However, we think it is unfortunate that Portner (Portner, 2104) sees little value in our study ([Grans et al., 2014][1]), which currently represents the

Metabolic Scope and Interspecific Competition in Sculpins of Greenland Are Influenced by Increased Temperatures Due to Climate Change

Ongoing climate change has led to an increase in sea surface temperatures of 2–4°C on the west coast of Greenland. Since fish are ectothermic, metabolic rate increases with ambient temperature. This makes these animals particularly sensitive to changes in temperature; subsequently any change may influence their metabolic scope, i.e. the physiological capacity to undertake aerobically challenging activities. Any temperature increase may thus disrupt species-specific temperature adaptations, at both the molecular level as well as in behavior, and concomitant species differences in the temperature sensitivity may shift the competitive balance among coexisting species. We investigated the influence of temperature on metabolic scope and competitive ability in three species of marine sculpin that coexist in Greenland coastal waters. Since these species have different distribution ranges, we hypothesized that there should be a difference in their physiological response to temperature; hence we compared their metabolic scope at three temperatures (4, 9 and 14°C). Their competitive ability at the ambient temperature of 9°C was also tested in an attempt to link physiological capacity with behaviour. The Arctic staghorn sculpin, the species with the northernmost distribution range, had a lower metabolic scope in the higher temperature range compared to the other two species, which had similar metabolic scope at the three temperatures. The Arctic staghorn sculpin also had reduced competitive ability at 9°C and may thus already be negatively affected by the current ocean warming. Our results suggest that climate change can have effects on fish physiology and interspecific competition, which may alter the species composition of the Arctic fish fauna.

A comparison of two estimators of dispersion effects

The applications of this paper is thought to be in screening designs with the purpose of identifying important factors in unreplicated experiments. The primary objective is to study which of the factors that affect the variance of the response when the levels are changed, that is, to study the dispersion effects. Unbiased estimators of dispersion effects are constructed which are unaffected by location effects. This is done by combining the ordinary estimators of the location interactions. Transforming the original variables into these linear combinations, covariances can be expressed by the dispersion effects and derived using Hadamard products. In some special cases, the distribution of the estimators are derived. The estimators are compared using simulations.

Simultaneous estimation of location and dispersion in two-level fractional factorial designs

The reduction of variation is one of the obvious goals in quality improvement. The identification of factors aff ecting the dispersion is a step towards this goal. In this paper, the problem of estimating location effects and dispersion eff ects simultaneously in unreplicated factorial experiments is considered. By making a one-to-one transformation of the response variables, the study of the quadratic functions becomes clearer. The transformation also gives a natural motivation to the model of the variances of the original variables. The covariances of the transformed responses appear as parameters in the variances of the original variables. Results of Hadamard products are used for deriving these covariances. The method of estimating dispersion effects is shown in two illustrations. In a 24 factorial design, the essential covariance matrix of the transformed variables is also presented. The method is also illustrated in a 25-1 fractional design with a model which is saturated in this context.