Western Norwegian Fjord Research Articles

Seasonal temperature regulates network connectivity of salmon louse

Abstract Chronically high infestation of salmon louse (Lepeophtheirus salmonis) questions the sustainability of the Norwegian Atlantic salmon (Salmo salar) aquaculture industry. The confinement of millions of hosts, within hundreds of farms with overlapping larval dispersal kernels create the structure for extremely persistent parasite meta-populations. However, the processes regulating the temporal variation in cross-contamination of pelagic salmon louse stages among farms (i.e. connectivity), a vital process driving louse population dynamics, are not well described. Here, we employ a data driven biophysical dispersal model that reproduces three-and-a-half years of production histories of 132 salmon farms in western Norway and quantifies the connectivity of infective pelagic lice stages among the farms with the ocean currents. We show that although the complex geography of western Norwegian fjords governs the long-term topology of the connectivity network, there was a strong seasonal component to network fragmentation. The main de-structuring agent was the delayed infectivity of the pelagic lice stages at cooler temperatures increasing dispersal distances, enhanced by occasional large scale wind forcing events. Coordinated fallowing strategies and de-lousing treatments only played a marginal role in network fragmentation, suggesting that novel lice restraining strategies that consider the environmentally sensitive transport distances must be developed to successfully break up the connectivity network.

Aragonite saturation states and pH in western Norwegian fjords: seasonal cycles and controlling factors, 2005–2009

Abstract. The uptake of anthropogenic carbon dioxide (CO2) by the ocean leads to a process known as ocean acidification (OA), which lowers the aragonite saturation state (ΩAr) and pH, and this is poorly documented in coastal environments including fjords due to lack of appropriate observations.Here we use weekly underway data from the Voluntary Observing Ships (VOS) program covering the period 2005–2009 combined with data from research cruises to estimate ΩAr and pH values in several adjacent western Norwegian fjords, and to evaluate how seawater CO2 chemistry drives their variations in response to physical and biological factors.The OA parameters in the surface waters of the fjords are subject to strong seasonal and spatially coherent variations. These changes are governed by the seasonal changes in temperature, salinity, formation and decay of organic matter, and vertical mixing with deeper, carbon-rich coastal water. Annual mean pH and ΩAr values were 8.13 and 2.21, respectively. The former varies from minimum values ( ≈ 8.05) in late December – early January to maximum values of around 8.2 during early spring (March–April) as a consequence of the phytoplankton spring bloom, which reduces dissolved inorganic carbon (DIC). In the following months, pH decreases in response to warming. This thermodynamic decrease in pH is reinforced by the deepening of the mixed layer, which enables carbon-rich coastal water to reach the surface, and this trend continues until the low winter values of pH are reached again. ΩAr, on the other hand, reaches its seasonal maximum (> 2.5) in mid- to late summer (July–September), when the spring bloom is over and pH is decreasing. The lowest ΩAr values ( ≈ 1.3–1.6) occur during winter (January–March), when both pH and sea surface temperature (SST) are low and DIC is its highest. Consequently, seasonal ΩAr variations align with those of SST and salinity normalized DIC (nDIC).We demonstrate that underway measurements of fugacity of CO2 in seawater (fCO2) and SST from VOS lines combined with high frequency observations of the complete carbonate system at strategically placed fixed stations provide an approach to interpolate OA parameters over large areas in the fjords of western Norway.

Specific Metabolites in a Phaeodactylum tricornutum Strain Isolated from Western Norwegian Fjord Water.

We have searched for special characteristics in growth, protein expression, fatty acids and volatile organic compounds (VOCs) in a local Phaeodactylum tricornutum Bohlin strain (Bergen Marine Biobank), by comparing it with a common accession strain (CCAP). Differences in growth and expressed proteins were detected between the BMB strain and the CCAP strain, and the BMB strain reached the highest cell densities under the given growth conditions. Fatty acid (FA) analyses showed highest relative eicosapentaenoic acid (EPA) levels in the exponential phase (25.73% and 28.31%), and highest levels of palmitoleic acid (16:1 n-7) in the stationary phase (46.36% and 43.66%) in the BMB and CCAP strain, respectively. The most striking finding of the VOCs analyses was the relatively high levels of ectocarpene, 6-((1E)-butenyl)-1,4-cycloheptadiene, hormosirene, and desmarestene and structurally related compounds, which were exclusively detected in the BMB strain. Many of the VOCs detected in the CCAP and, in particular, in the BMB strain have been reported as antimicrobial agents. We suggest that the array of pheromones and antimicrobial substances could be part of an allelopathic strategy of the BMB strain, dominated by oval cells, thus reflecting the benthic life stage of this morphological form. These findings show the potential for bioactive metabolites in the BMB strain.

Norwegian seiches from the giant 2011 Tohoku earthquake

AbstractSeismic waves of the giant 2011 Tohoku earthquake triggered seiches in western Norwegian fjords. The seiching began a half hour after the earthquake origin time. The oscillations were noted by eyewitnesses and recorded by surveillance and cell phone cameras. The observations show maximum trough‐to‐peak amplitudes of 1.0–1.5 m and periods of 67–100 s. The water waves were not triggered from the arrival of the surface waves, the timing inferred for other seiches. Instead, the seiching began during the passage of horizontal S waves. We reproduced the S wave trigger by means of a shallow‐water wave model calibrated previously to Norwegian tides and storm surges. The simulations, which used the observed earthquake motion as forcing, show water waves with periods and amplitudes similar to those in the film clips. However, the strongest horizontal ground oscillations with shorter periods (20–30 s) did not contribute much to the formation of the seiches.

Dynamics of phytoplankton distribution and photosynthetic capacity in a western Norwegian fjord during coastal upwelling: Effects on optical properties

The present study describes the coupling between optical properties and the dynamics of phytoplankton distribution and photosynthetic capacity in the Lysefjord during an exceptional coastal upwelling. At the mouth of the fjord, transparent Coastal water was “piled up” against the sill, while more turbid Fjord water from the outer fjord system was flowing over the sill, creating the intermediate layer which extended further into the fjord. This was reflected by high spectral attenuation coefficients in the upper 10 m of the fjord. Outside the sill, clear water with low spectral attenuation coefficients were found below sill depth down to at least 30 m, while the attenuation coefficients inside the sill were significantly higher between 10 and 20 m. About 4–7 km outwards from the head of the fjord clearer deep basin water was entering the upper layer due to the upwelling which could be traced up to 7 m, bounded by the 7.5 °C and the 31 salinity isolines. In the outer part of the fjord waters with a high chl a content and photosynthetic capacity were observed below the outflowing surface layer containing “old water” from the inner part of the fjord, which was characterized by low nutrient and chl a concentrations. Maximum quantum efficiencies (0.5) were encountered within this subsurface layer. Quantum efficiencies exceeded 0.3 when nitrate and silicate concentrations increased above 2 mmol m −3 . About 50% of the PAR light attenuation (0–30 m) was caused by chl a , and the 1% light depth varied between 27 and 35 m along the transect. Due to the influence of freshwater outlets, non-pigmented particles were more abundant in the inner part of the fjord than in the outer part. Colored dissolved organic matter (CDOM) contributed strongly to absorption within the upper 10 m at wavelengths below 470 nm while scattering was the major attenuation contributor for wavelengths above 600 nm. With respect to possible climate change effects on the growth of phytoplankton in Norwegian fjords, our results indicate that the alteration of coastal wind patterns due to its impact on coastal – fjord water exchanges, is probably more important than increased temperature and/or increased precipitation.

Horizontal movements of simulated escaped farmed Atlantic salmon (Salmo salar) in a western Norwegian fjord

Abstract Skilbrei, O. T., Holst, J. C., Asplin, L., and Mortensen, S. 2010. Horizontal movements of simulated escaped farmed Atlantic salmon (Salmo salar) in a western Norwegian fjord. – ICES Journal of Marine Science, 67: 1206–1215. The dispersal of simulated escaped farmed Atlantic salmon (Salmo salar) in Hardangerfjord in western Norway was studied by telemetry. Tagged fish were released from fish farms on five different dates in the course of 1 year. Irrespective of the time of year, the fish dispersed rapidly, with a mean displacement from the release site of 5–7 km after 1 d, and 9–12 km after 2 d. Individual rates of movement varied, but were much higher than the rate of displacement from the release site, as fish moved around in the fjord basin in all directions. As a result, the fish were spread over an area of more than 500 km2 after 1 week. The number of released fish recorded in the fjord gradually declined after each release from ∼40% remaining in the fjord after 3 weeks to few or none after 7 weeks. In all, 38% moved out of the fjord, and 36 and 2% were reported as captured inside and outside the fjord, respectively. Their rapid dispersal suggests that concentrating efforts to recapture escaped salmon in the proximity of an escape site will probably not be successful, at least from locations of this type. In fact, the recaptures demonstrate that it is both necessary and possible to expand the fishing effort to cover a large area and to sustain it for several weeks to attain high rates of recapture. The wide dispersal of escaped fish potentially acting as vectors within the fjord basin also has implications for the spread of disease and parasites.

Vertical movements of “escaped” farmed Atlantic salmon (Salmo salar L.)—a simulation study in a western Norwegian fjord

Abstract Skilbrei, O. T., Holst, J. C., Asplin, L., and Holm, M. 2009. Vertical movements of “escaped” farmed Atlantic salmon (Salmo salar L.)—a simulation study in a western Norwegian fjord. – ICES Journal of Marine Science, 66: 278–288. To study the vertical distribution of fish that had been allowed to escape, farmed Atlantic salmon were tagged with acoustic tags equipped with depth sensors, and then released on five different dates in the course of a year from two fish farms in the Hardanger Fjord in western Norway. Release stimulated the fish to dive to deeper than 15 m during the first hours or days post-release, often down to 50–80 m. However, during the following 4 weeks, most of the escapees spent most of their time above the pycnocline at depths of 0–4 m. The fish were more widely distributed in the water column after release during winter, but still spent most of the time in the cold surface layers. There was a wide range in the vertical distribution of individual fish, and the proportion of detections below 14-m depth ranged from 0 to 90%. There was a significant diurnal cycle in all seasons except midsummer, when the fish were less abundant in the upper layer during daylight, especially on brighter days. The results suggest that salmon diving activity following escape may complicate the recapture of escaped fish at the farm site but that the subsequent tendency of most fish to stay near the surface, virtually irrespective of the time of year, may facilitate recapture.

Effects of organic effluents from a salmon farm on a fjord system. III. Linking deposition rates of organic matter and benthic productivity

The vertical flux of organic matter and infauna production, biomass and abundance at six stations along a gradient away from a salmon farm, located in a western Norwegian fjord at a depth of 230 m and which produced 2910 tonnes of fish in 19 months, was measured repeatedly during an entire on-growth cycle. The study showed that large increases in benthic secondary production can result from the loading of organic waste in nutrient-poor systems like fjords and a strong correlation between annual sedimentation rates of particulate organic matter (carbon and nitrogen) and annual benthic secondary production was found. At the stations that received the bulk of the waste matter (stations situated within 250 m from the mooring point of the farm) infauna production followed feeding regimes at the farm and in 2004 annual benthic secondary production was 40 g ash-free dry weight m − 2 , 50 times as high as the production 550 to 3000 m away from the farm. Production close to the farm was mainly due to the polychaete Heteromastus filiformis and the bivalve Abra nitida in periods with moderate loadings of organic matter, and by the polychaete Capitella capitata in periods with high loadings. The results of the study further indicate that the threshold for increased infauna production in this deep benthic ecosystem had been reached at an annual flux of 500 g C m − 2 and that continuous loadings at this magnitude over time might cause overloading of fish farm localities.

Seasonal abundance and vertical distribution of siphonophores in western Norwegian fjords

Seasonal abundance of siphonophores in Korsfjord and Fanafjord was studied by net sampling. Nanomia cara, Lensia conoidea and Dimophyes arctica were dominant species present throughout the year. Abundance of N. cara colonies peaked in late May and early June. Low numbers of relatively large colonies and high numbers of siphonulae were observed during winter. Dimophyes arctica and L. conoidea had a generation shift in March, when large over-wintering and small young polygastric colonies co-existed briefly before the former disappeared. Abundances were lowest during winter, and eudoxids were consistently more numerous than polygastric colonies for both species. Maximum abundances of polygastric D. arctica and L. conoidea occurred in early May and late June, respectively. Lensia conoidea may have more than one annual generation in Korsfjord. Vertical distributions of siphonophores were studied with an remotely operated vehicle in nine fjords. The distributions of agalmatid physonects, probably mostly N. cara, differed significantly between the fjords, with the weighted mean depths of the distributions ranging from 99 to 412 m. Results from Sognefjord suggested diel vertical migration. The bulk of the adult colonies in each fjord occurred below sill depth. Siphonophores were not observed at localities known to host persistent populations of Periphylla periphylla.

Primary production enhancement by artificial upwelling in a western Norwegian fjord

To enhance primary production rate for shellfish cultivation in fjords, a large-scale artificial upwelling experiment was carried out in a western Norwegian fjord during the summers of 2004 and 2005. Pumping 2 m3 s–1 brackish surface water to a depth of 30 m created an artificial upwelling of nutrient-rich deeper water. The entrainment of deeper water into the buoyant brackish plume resulted in a transport of about 450 kg d–1 nitrate, 760 kg d–1 silicate and 75 kg d–1 phosphate to an intrusion depth of 8 to 10 m. The artificial upwelling approximately tripled mean chlorophyll a (chl a) concentration and related primary production rate during the summer within an influence area of 10 km2 near the head of the fjord. The size of the area of influence and the relative increase of the algae biomass within it depend on both the water exchange and the photosynthetic effectiveness. The relatively high silicate content of the deeper water stimulated diatom growth inside the area influenced by the artificial upwelling. A higher stable level of phytoplankton biomass, dominated by nontoxic species, would probably increase the carrying capacity of seston-feeding shellfish and could form the basis of more predictable mussel cultivation in fjords.

Swimming and feeding in Periphylla periphylla (Scyphozoa, Coronatae).

Some western Norwegian fjords host extraordinarily abundant and persistent populations of the mesopelagic, coronate scyphomedusa, Periphylla periphylla. In these environments, from late autumn to spring, the medusae undertake regular diel vertical migrations into surface waters. From unique observations obtained with a remotely operated vehicle (ROV), including observations made without artificial light, we observed that 90% of the medusae swam with their tentacles in aboral position. Stomach content analyses of surface-collected specimens revealed that the medusae ate mainly calanoid copepods, but ostracods and large euphausiids were also prominent components of their diets. The clearance rate potential of P. periphylla, assessed from in situ observations and stomach contents, was comparable to that of similar-sized, epipelagic gelatinous species. Our findings suggest that P. periphylla behave as active predators in surface waters.

Seasonal variability in inherent optical properties in a western Norwegian fjord

We present measured seasonal variations in the inherent optical properties (the absorption and scattering coefficients) of water in a deep silled fjord (Samnangerfjorden) in western Norway. These were based on measurements taken at monthly intervals during an annual cycle. The measurements also include concentrations of chlorophyll a and yellow substance, which were assumed to dominate the behaviour of the absorption and scattering coefficients. The stations were at three fixed locations, one being placed in the innermost part of the fjord where there is little mixing of fjord water with water from the coastal current. The other two stations were placed at different distances from the mouth of the fjord, so that the water masses are characterized by different amounts of mixing between fjord water and coastal current water. Our data set shows how the absorption and scattering coefficients vary in a Norwegian fjord during an annual cycle, and how they depend on the concentrations of chlorophyll a and yellow substance. Values of the absorption coefficient at 412 nm varied between 0.1 and 2.0 m , and scattering coefficients were also found to vary within this range. Little variation over the spectral range was found for the scattering coefficients, but the absorption coefficient had larger spectral variations. The chlorophyll a concentrations varied from 0.01 to 6.3 mg m , and the concentration of yellow substance, as expressed by its absorption coefficient at 310 nm, was within the range 0.7–7.8 m .

Climatic factors governing plant phenological phases along a Norwegian fjord.

In the present project, the time of leaf budding and flowering, and partly also of fruit ripening, was studied over 3 years in different cultivated and native plants on a gradient along a western Norwegian fjord about 300 km long, from oceanic to relatively continental regions. In the plants investigated, flowering of the red currant was most strongly favoured by oceanic conditions in the outermost part of the fjord. On the other hand, flowering of the apple was earliest in the middle district, as were flowering of the common lilac and raspberry, while differences were small between the districts for flowering of the plum and pear. In the inner district, leaf budding of the apple was about 1.5 weeks earlier than flowering of the red currant, while these two phenophases, on average, occurred on the same day in the oceanic district. The time from 1 April to flowering was generally lengthened by increased precipitation in the pear, apple, lilac and raspberry, but not in the red currant and plum. By contrast, the period from leaf budding to flowering was significantly shortened in the plum by high precipitation. The present studies also indicated that leaf budding of the birch was favoured by the high minimum temperature and the relatively high precipitation normally found in the oceanic district. Partial correlations showed that increased precipitation delayed the flowering of both rowan and bird cherry trees; there was also a week effect on bud break in the same two species. The clear conclusion of the present study, therefore, is that various plant species react differently to various climatic factors ("phenological interception"), even in different phenophases within the same species. This means that the various species are best fitted to certain climatic regions and should preferably be planted there if other growth factors are satisfactory.

Parameterization and analysis of the optical absorption and scattering coefficients in a western Norwegian fjord: a case II water study.

Based on statistical analyses of optical properties measured during a whole year of monthly cruises in a Norwegian fjord, we constructed a two-component model for the absorption and scattering coefficients for visible light. The input to the model is the concentrations of yellow substance and chlorophyll a. Because of the presence of a significant amount of nonalgal particles in coastal water, we assume that the absorption and scattering coefficients approach constant background values when the concentration of chlorophyll a approaches zero. The model works reasonably for a variety of optical conditions encountered throughout the year, with a possible exception during a bloom of the Emiliania huxleyi algae in June.

Stage‐specific mortality of Calanus spp. under different predation regimes

We have applied the population surface method to estimate the mortality rates of eggs, nauplii, and copepodids of Calanus spp. in two Norwegian fjords with contrasting predator guilds. Efforts were concentrated in Lurefjorden on the western coast (sampled weekly from late February to mid‐June), an unusual fjord dominated by invertebrate (tactile) planktivores. In addition, monthly sampling in Sørfjorden was carried out for comparisons. The latter fjord resembles most Western Norwegian fjords in that it contains populations of vertebrate (visual) planktivores but lower abundance of the invertebrate planktivores. In Lurefjorden, mortality of Calanus spp. was high early in life (~0.35 d−1), but significantly lower (~0.00 d−1) in the early copepodid stages. In Sørfjorden, mortality was rather uniform throughout ontogeny (~0.08 d−1). The noted differences are consistent with different patterns of selective predation between the two fjords. Visual predation in SÄrfjorden gave rise to persistent high mortality over the life cycle. Tactile predation in Lurefjorden gave rise to a concave mortality curve for the later developmental stages. Our results indicate that mortality patterns suffered by natural zooplankton populations may differ greatly over short geographical distances, and we suggest that the predator community and mortality patterns must be considered when addressing the spatial and temporal dynamics of zooplankton populations.

Importance of food quantity to structural growth rate and neutral lipid reserves accumulated in Calanus finmarchicus

Growth and developmental rates were determined for copepodids of Calanus finmarchicus (Gunnerus) from experimental seawater mesocosms in a western Norwegian fjord. The instantaneous growth rates (g) from copepodid stage I (CI) to adult ranged from 0.08 to 0.10 d−1. Daily per capita mortality rate of the cohorts was as low as 0.012 d−1 (1.2% d−1). At local increasing temperatures (5.1 to 8.3 °C), development was equiproportional, and the cumulative median development time from egg to CV was approximately 65 d. CV moulted to males and females, and egg production was initiated. Enhancement of food resources by nutrient addition caused a 23.4% increase in growth rates from CI to adult. Additionally, copepodid stages showed a generally larger body size, carbon and nitrogen content and total storage lipid content (wax esters + triacylglycerols) in response to enhanced resources. Our data support an elsewhere proposed exponential-growth hypothesis; growth of the structural compartments and store lipids (mostly wax esters) was exponential during the copepodid stages. However, a sigmoidal pattern of growth best described growth of adult stages if reared at high resources, and depot lipid accumulation in late CVs and adults at high resources. Body nitrogen growth increased exponentially, however, no significant changes in nitrogen specific growth rates were found between individuals from low and high resources. CV and adults seem to have reached near-maximal weights at high resources, whereas structural weight continued to increase at low resources. Despite the differences in structural growth dynamics, cohort development was similar until the end of CV. During the onset of sexual differentiation, the male:female ratio and the adult:CV ratio were highest at high food resources, suggesting that the time used for the final moult depends on the feeding history of the copepods in relation to food quality and quantity. It appears that relatively small changes in food availability strongly influence the biochemical composition of C. finmarchicus copepodids.

Growth and development rates of Calanus finmarchicus nauplii during a diatom spring bloom

Growth and development rates were determined for nauplii of Calanus finmarchicus (Gunnerus) in the near-shore waters of a western Norwegian fjord from in situ mesocosm incubations. The major food source for the nauplii was diatoms, but Phaeocystis sp., dinoflagellates and ciliates were also part of the diet. At local temperatures ranging from 4.8 to 5.2 °C the cumulative median development time from hatching to Nauplius VI was 19 d. The time taken to molt to the next naupliar stage was approximately constant (3 d) from Stages IV to VI, but Stage III needed the longest development time (5 d). The instantaneous growth rate in terms of body carbon was negative from hatching to Nauplius Stage II, but as high as 0.25 to 0.30 d−1 from Stage III to V. Enhancement of food resources by nutrient addition led to no significant change in specific growth rates. Additionally, the cohorts from different nutrient regimes showed almost equal development time, size and body carbon within stages. Length–weight relationships of nauplii from the two different food resources were: Wlow resources = 4.17 × 10−6 × L2.03 (r2 = 0.84) and Whigh resources = 4.29 × 10−6 × L2.05 (r2 = 0.92), where weight (W) is in micrograms of C and body length (L) in micrometers. The natural body morphology of naupliar stages I to VI is illustrated with digital images, including the final molt from Nauplius VI to Copepodid Stage I. In general, development of the nauplii was faster than that of the copepodids of C. finmarchicus, and structural growth was exponential from naupliar stages III to VI. This study validates our earlier results that nauplii of C. finmarchicus can obtain high growth and nearly maximal developmental rates at relatively low food levels (∼50 μg C l−1), suggesting that nauplii exhibit far less dependence on food supply than copepodids.

Zooplankton Distribution in Four Western Norwegian Fjords

A multi-instrumental array constructed in the Laboratoire d'Ecologie du Plancton Marin in Villefranche sur mer, France, named the Underwater Video Profiler (UVP), was used to investigate the vertical distribution of zooplankton in four western Norwegian fjords in the summer 1996. Six distinct zoological groups were monitored. The fauna included: (a) small crustaceans (mainly copepods), (b) ctenophores (mainly lobates), (c) siphonophores (mainly physonects), (d) a scyphomedusa Periphylla periphylla, (e) chaetognaths and (f) appendicularians. The use of the non-disturbing video technique demonstrated that the distribution of large zooplankton is heterogeneous vertically and geographically. Furthermore, the abundance of non-migrating filter feeders in the deep basins of the fjords indicates that there is enough food (living and non-living particulate organic matter) to support their dietary needs. This adaptation may be considered as a strategy for survival in fjords. Specifically, living in dark, deep water reduces visual predation and population loss encountered in the upper layer due to advective processes.

Morphometry and Taxonomy of Hexacontium Species from Western Norwegian Fjords

Morphometry and Taxonomy of Hexacontium Species from Western Norwegian Fjords

Western Norwegian fjord sediments: age, volume, stratigraphy, and role as temporary depository during glacial cycles

The sediments in the western Norwegian fjords are described chronologically, qualitatively and quantitatively by means of seismic profiling and correlation with dated terrestrial sediments along the fjords. Five chronostratigraphic units (I–V) are proposed for the fjord sediments using the well established Quaternary stratigraphy in the area. Sediment volumes of the main fjords are calculated using a dense seismic grid combined with map analyses. Approximately 150 km 3 of sediments are present in the fjords between 59–63 °N. Ninety percent of this material is considered to be deposited during deglaciation of the last (Weichselian) ice sheet. Less than ten percent of the fjord sediments in this area is older than the last glacial (Weichselian) maximum. Both glacial and glaciofluvial processes are active in emptying the fjord basins and transporting the sediments to the continental shelf and slope during glaciations.