Arne J. Jensen

Present and future needs for algae and algal products

A review of the present needs, mainly for production of phycocolloids and food condiments, is given. Supply and demand vary from balanced, in some, to disproportionate in other fields. World-wide shortage of agarophytes contrasts with huge, unexploited beds of brown seaweeds.

Sex-dependent dominance at a single locus maintains variation in age at maturity in salmon

Males and females share many traits that have a common genetic basis; however, selection on these traits often differs between the sexes, leading to sexual conflict. Under such sexual antagonism, theory predicts the evolution of genetic architectures that resolve this sexual conflict. Yet, despite intense theoretical and empirical interest, the specific loci underlying sexually antagonistic phenotypes have rarely been identified, limiting our understanding of how sexual conflict impacts genome evolution and the maintenance of genetic diversity. Here we identify a large effect locus controlling age at maturity in Atlantic salmon (Salmo salar), an important fitness trait in which selection favours earlier maturation in males than females, and show it is a clear example of sex-dependent dominance that reduces intralocus sexual conflict and maintains adaptive variation in wild populations. Using high-density single nucleotide polymorphism data across 57 wild populations and whole genome re-sequencing, we find that the vestigial-like family member 3 gene (VGLL3) exhibits sex-dependent dominance in salmon, promoting earlier and later maturation in males and females, respectively. VGLL3, an adiposity regulator associated with size and age at maturity in humans, explained 39% of phenotypic variation, an unexpectedly large proportion for what is usually considered a highly polygenic trait. Such large effects are predicted under balancing selection from either sexually antagonistic or spatially varying selection. Our results provide the first empirical example of dominance reversal allowing greater optimization of phenotypes within each sex, contributing to the resolution of sexual conflict in a major and widespread evolutionary trade-off between age and size at maturity. They also provide key empirical evidence for how variation in reproductive strategies can be maintained over large geographical scales. We anticipate these findings will have a substantial impact on population management in a range of harvested species where trends towards earlier maturation have been observed.

Interactions between wild and cultured atlantic salmon: a review of the Norwegian experience

Abstract Most Norwegian salmon populations are characterized by small numbers of fish. The proportion of cultured salmon in these populations has increased together with the rapid growth of the Norwegian salmon farming industry. In several spawning populations, fish of cultured origin now exceed the number of wild fish. The cultured salmon occurring in Norwegian streams are largely dominated by escapees from fish farms, although some are released for stock enhancement and ocean ranching purposes. Life history characters in cultured salmon—for instance, age and size at spawning, time of spawning and migratory behavior—often differ from those of the local stock of wild salmon. Possible ecological effects of interactions in the freshwater stages are discussed. The most serious effects so far have been the introductions to wild populations of lethal parasites and diseases with cultured fish. In recent years, more than 30 populations of salmon have been completely wiped out by the monogean parasite Gyrodactylus salaris . High mortality of adult salmon has also been observed as a result of furunculosis in some streams. In biochemically detectable loci, small but statistically significant differences in allele frequencies exist between populations within and between rivers. Possible long-term effects of genetic interbreeding and erosion of local adaptations are discussed. Increased numbers of cultured salmon may also increase the fishing intensity on wild salmon. Suggestions to reduce negative effects of interactions from cultured fish are proposed.

Heavy metal tolerance of marine phytoplankton. III. Combined effects of copper and zinc ions on cultures of four common species

Abstract The combined effects of copper and zinc ions on the growth of three marine diatoms and one dinoflagellate in culture have been studied. The two metals were found to act synergistically to all algae except Phaeodactylum tricornutum Bohlin. With this species an antagonistic effect was observed. Addition of zinc ions reduced the inhibition of growth caused by the more toxic copper ions. Zinc toxicity to this alga increased at low concentration of magnesium, indicating a common route for divalent metal ions in general.

Growth of young migratory brown trout Salmo trutta correlated with water temperature in Norwegian rivers

(1) The objective is to test the generality of Elliotts (1975a) growth model developed on brown trout, Salmo trutta, fed on maximum rations, and the data are observed growth rates of parr of anadromous brown trout from twelve Norwegian rivers. (2) The mean annual instantaneous growth rates of the twelve Norwegian brown trout populations in their second year of life (1 +) varied between 1-14 and 1 94. In five of the rivers, the annual growth rates were not significantly different from those computed from the model, whereas values in four rivers were significantly higher than those computed. Values in three rivers were significantly lower than those computed. The mean growth rates on a 1-year basis varied between 76 and 136% of the computed maximum for that temperature regime. In thirty-eight of the fifty-four comparisons, recorded growth rates were not significantly different from those computed from the model, but ten were significantly higher and six significantly lower than model predictions. (3) In three rivers brown trout were sampled twice annually, once just after the ice break in late April or early May, and again in early August. The daily growth rates in early summer in all three rivers were higher than the corresponding growth rates computed from Elliotts model. In late summer the observed compared to the computed growth rates were usually lower than in early summer, and in some cases no growth was observed after early August. (4) The growth rates of brown trout in some Norwegian rivers exceeded the established rates for trout fed on maximum rations. This indicates genotypic differences in the growth rates of Norwegian populations and the experimental fish in England, or higher food intake in wild trout exposed to diel fluctuating temperatures than among experimental fish held at constant temperatures.

Heavy metal tolerance of marine phytoplankton. IV. Combined effect of zinc and cadmium on growth and uptake in some marine diatoms

Abstract Combinations of zinc and cadmium ions acted synergistically on the growth of the marine diatoms Thalassiosira pseudonana (Huds.) Hasle and Skeletonema costatum (Grev.) Cleve, clone Skel-5. Mixtures of the metals behaved less than additively on Phaeodactylum tricornutum Bohlin, and antagonistically on Skeletonema costatum , clone Skel-0. Sorption studies supported the hypothesis that the two latter algae gained their relative resistance to heavy metal ions from competition for uptake sites by the zinc and cadmium species involved. In the more resistant alga, Phaeodactylum tricornutum , the sorption of cadmium and zinc was also dependent on the magnesium concentration of the medium, in a way which indicated a common uptake route for several divalent cations in this species. Cadmium was found to be more toxic than zinc to Skeletonema costatum , clone Skel-0 and to Thalassiosira pseudonana , while zinc was slightly more toxic than cadmium to Phaeodactylum tricornutum and Skeletonema costatum , Skel-5.

Exposure of phytoplankton to ekofisk crude oil

Abstract Solutions of Ekofisk crude oil in sea water were prepared by slow stirring for 21h in a closed system. Headspace and GC/MS techniques were applied to establish dose composition and levels. The standardized test medium produced in a closed system contained approximately 14 mg oil per litre and was dominated by low molecular weight aromatic hydrocarbons and phenols. The toxicity of the standarized oil-containing medium to three marine diatoms was studied in a cage culture turbidostat and by conventional batch culture technique. The three algal species differed in sensitivity to the oil compounds, but showed identical ranking in both test systems. Standardized test medium diluted to 50% with respect to oil content stopped the growth of the most sensitive alga, Skeletonema costatum . For comparison naphthalene was applied and gave 50 % growth reduction at a concentration of 400 μg litre −1 . The growth of Chaetoceros ceratosporum was only slighty affected by the full strength standard test medium, which had no influence on the growth of Phaeodactylum tricornutum , the least sensitive organism. The presence of an oil layer on the surface of the standard test medium during the growth test greatly increased its toxicity and blocked completely the photosynthesis even of P. tricornutum after 4 days.

Quantitative studies on brown algal phenols. III. Light-mediated exudation of polyphenols from Ascophyllum nodosum (L.) Le Jol

Abstract When freshly collected thalli of Ascophyllum nodosum (L.) Le Jol. were allowed to stand in batches of filtered sea water for 1 to 4 h at 10 ± 2° C , polyphenolic substances were released into the contact media. Polyphenol release during photosynthesis far exceeded dark-release, and rates of release were greater during the initial period of the experiment (whether light or dark) than during subsequent light or dark periods, respectively. The release could be ‘turned on’ and ‘turned off’ by successive irradiation and darkening of a single sample, demonstrating that much of the release is exudation in the strict sense, not merely a symptom of stress, shock or injury. No light intensity threshold for polyphenol exudation could be detected, and an apparent ‘saturation’ was seen at intensities above 9 × 10 2 W m −2 . Rates of light-mediated release of polyphenols under these protected laboratory conditions were 9.2 ± 3.6 μg · g −1 dry matter·h −1 .

Thermal growth performance of juvenile brown trout Salmo trutta: no support for thermal adaptation hypotheses

Using thermal growth data from eight populations of anadromous and lake-feeding brown trout Salmo trutta, hypotheses of adaptation to local optima and countergradient variation in growth were tested. The adaptation to local optima hypothesis suggests that natural selection can shift optimal performance temperatures to match the prevailing temperature in a new or changed thermal niche. In contradiction, the countergradient variation hypothesis suggests that populations from hostile environments perform better than conspecifics from benign environments at all temperatures. In this study, growth capacity varied between populations but there was no significant correlation between any of the estimated thermal performance parameters (e.g. lower and upper thermal growth limits, optimal temperature for growth and maximum growth capacity) and natural climatic conditions among populations. Hence, S. trutta growth response to temperature lends no support for either of the two suggested thermal adaptation hypotheses. Instead, growth capacity among populations tended to correlate positively with female size at maturity.

Influence of size and nutritional value of Artemia franciscana on growth and quality of halibut larvae (Hippoglossus hippoglossus) during the live feed period

Abstract In a first feeding experiment, halibut larvae were offered either short term enriched (ST) 1-day old Artemia franciscana or A. franciscana of successively increasing size (ST, 2-, 3- and 4-day old juveniles), from day 0 to day 60. No differences, either in growth (approximately 6.5% daily weight increase, DWI) or in survival (ca. 25%) between the two treatments were observed, but both were satisfactory. However, feeding increasing sizes of A. franciscana increased the number of completely pigmented and metamorphosed larvae from 4 to 20%. Protein/lipid ratio in the feed seems to be important for pigmentation and metamorphosis, provided the levels of essential fatty acids (esp. DHA) are sufficient. Juvenile A. franciscana may therefore be a better live feed than ST A. franciscana for halibut larvae. The fact that a relatively high load of bacteria was introduced by 4-day old A. franciscana , may have had a negative influence on the growth of the larvae. Tests indicated that a great part of the bacteria exhibited hemolytic activity, and many of the bacteria were apparently Vibrios . Strict microbial control in the production of live feed is very likely just as important as control of the nutritional composition of the larval feed. This is a challenge for further work.