Hein Rune Skjoldal

Summer distribution patterns and biomass estimates of macrozooplankton and micronekton in the nordic seas

Abstract The vertical and horizontal distribution patterns of zooplankton and micronekton were mapped during three research cruises in summers 1993, 1994 and 1995 by pelagic trawl and MOCNESS plankton net sampling. The distribution patterns have been related to the distribution of water masses and the distribution of planktivorous fish such as herring, Clupea harengus. Zooplankton biomass typically revealed a bimodal vertical distribution with high values in the surface layer and at 200-600 m depth. This subsurface maximum contained, among others, several species of macrozooplankton and micronekton such as krill, pelagic shrimps and mesopelagic fish. The dominant krill species Thysanoessa inermis, T. longicaudata and Meganyctiphanes norvegica are widely distributed in the Nordic Seas, extending from the coastal areas of southern Norway in the south to the subarctic and Arctic water masses in the northwest. Though widespread, highest abundances of M. norvegica were restricted to the warmer Atlantic waters....

Dehydrogenase activity and adenosine triphosphate concentration of marine sediments in Lindåspollene, Norway

Abstract Microbial anaerobic metabolism was measured as dehydrogenase activity using 2,3,5-triphenyltetrazolium chloride. Dehydrogenase activity (DHA) per g dry sediment was correlated with adenosine triphosphate (ATP) per g dry sediment as determined by luciferin-luciferase reaction; both generally decreased with depth of sediment layer. The ratio DHA: ATP (ab-sorbance per mole ATP), however, increased significantly with depth of sediment layer. Dehydrogenase activity and oxygen debt of surface sediment and dissolved oxygen of bottom water were interrelated and all related to the depth of water; ATP content of the surface sediment had a similar but statistically insignificant trend as DHA. Data from conversion of ATP to organic carbon per m2 in the surface 4-cm layer at 11 stations showed a significant decrease in microbial biomass with increasing depth of water.

A conceptual model of distribution of capelin in the Barents Sea

Abstract To support an assessment model, we propose a set of numerical models where distribution and growth of capelin (Mallotus villosus) is modelled by biological (evolutionary, ecological) and physical forces. The basics of a dynamic optimization fish distribution model is outlined. This model must be coupled to hydrodynamicallmeteorological (temperature, ice conditions, light regime) and biological (plankton transport and production) models. While modelling capelin distribution is the short term aim, the ultimate goal is to develop management models where understanding (theory) rather than knowledge (empiricism) is the basis for prediction. This will enable sustainable management also in years deviating from past experience.

ANAEROBIC METABOLISM OF THE SCAVENGING ISOPOD CIROLANA BOREALIS LILLJEBORG. ADENINE NUCLEOTIDES

ABSTRACT The oxygen consumption of Cirolana borealis decreased almost proportionally to the ambient oxygen tension, indicating no ability to regulate the rate of oxygen uptake. The concentration of ATP and the adenylate energy charge (EC) showed no change throughout 48 h as the metabolism shifted to anaerobiosis. When transferring C. borealis from oxygen-saturated seawater to deoxygenated water, the ATP concentration remained stable for 24 h, but decreased markedly after 48 h. This was reflected in a drop in EC from about 0.6 to 0.3. After transferring specimens back into oxygen-saturated seawater following 3 days of anaerobiosis, about 10 % of these individuals recovered and regained high ATP content and EC. These results demonstrate the ability of C. borealis to maintain balanced anaerobic metabolism for 1–2 days, after which continued lack of oxygen rapidly leads to death.

Ecological Modelling for Fisheries

Large fluctuations in the fisheries have been a characteristic feature of great importance in the history of the Norwegian people. Herring periods have been times with large fisheries for herring spawning along the west coast of Norway, alternating with periods when the herring was gone. Herring periods and periods without herring appear to have been of cyclic nature with a periodicity of about a century (Devoid 1963, Dragesund & al. 1980, Skjoldal 1990,oiestad 1990). Towards the end of the last century, a common explanation for such fluctuations was that it reflected variable migration routes and therefore variable availability of perceived stable fish stocks to coastal fisheries. When ICES was established in 1902, a standing committee called the Migration Committee was created to deal with such issues (Sinclair & Solemdal 1988). However, in his classical book, JohanHjort (1914) identified large fluctuations in stock size due to variable recruitment as a major source for fluctuations in the fisheries. Variable recruitment is an inherent property related to the reproductive mode of fishes with high fecundity and which produce a high number of larvae that are part of the planktonic system (Skjoldal & Melle 1989).

Fine-scale vertical strucfure of a summer zooplankton community in lindåspollene, Western Norway

Abstract During June 1981 zooplankton composition was investigated in samples collected with Clarke-Bumpus plankton samplers from 0.5, 2, 5, 10, 15, and 20 m depths. Most taxa were limited to specific depth zones. Diel variations in vertical range were observed for the majority of species inhabiting the uppermost part of the water column, whereas diel variations in median depth could be detected for only 3 out of 11 taxa. These were adult Temora longicornis and adult Pseudocalanus elongatus, which ascended during the night, and Evadne nordmanni which tended to descend during the night. A similarity analysis divided the samples into a surface layer group (0.5, 2, and 5 m) and a deeper group (10, 15, and 20 m) separated by the thermocline. The composition and distribution of the zooplankton living deeper down changed little with time, in contrast to the surface-dwelling zooplankton which was more variable. Multivariate analysis indicated that two factors were responsible for 79 % of the total variance in th...

Vertical and small-scale horizontal distribution of chlorophyll a and ATP in subtropical beach sand

The vertical distributions of chlorophyll a and ATP within the uppermost 12 cm of sand were highly correlated (r = 0.97–0.99). The contents of Chl a and ATP decreased only slightly within the uppermost 2–4 cm, while decreasing more rapidly below. There were no differences between the Chl a or ATP contents of samples (0–5 cm) from ridges and depressions of ripple marks. The coefficients of variations of Chl a and ATP for 9 samples taken 1 m apart were about 10 %. These results are interpreted as reflecting a well-mixed upper layer of sand. The average ATP/Chl a ratio for the uppermost 5 cm was 0.6, which is comparable to ratios found for other shallow-water sediments. Due to limited knowledge about the cellular Chl a and ATP levels of sediment biota, it is not possible at present to use Chl a and ATP measurements to distinguish between auto- and heterotrophic biomass components.

Effects of toluene on the survival, respiration, and adenylate system of a marine isopod

Abstract Median times to narcotization (ET 50 ) of Cirolana borealis Lilljeborg by various levels of toluene in seawater were determined. Narcotization quickly became irreversible, and the ET 50 values can be regarded as estimates of median lethal times. Respiratory rate, ATP concentration, and energy charge (E.C.) were not significantly affected by sublethal toluene levels which caused behavioural disturbance. At 12.5 ppm of toluene (nominal concentration; ET 50 :69 h) ATP dropped gradually to less than 1% and E.C. to about 50% of the control values during 8 days, after which time all the individuals were dead. At 125 ppm neither ATP concentration nor E.C. changed significantly during 24 h although the animals were inactive after about 1 h and died within 100 h. Due to the high degree of stabilization of adenine nucleotide levels and E.C. during environmental changes, these parameters do not appear useful as general indices of stress in environmental pollution studies.

Contribution of Calanus species to the mesozooplankton biomass in the Barents Sea

Copepods from the genus Calanus are crucial prey for fish, seabirds and mammals in the Nordic and Barents Sea ecosystems. The objective of this study is to determine the contribution of Calanus species to the mesozooplankton biomass in the Barents Sea. We analyse an extensive dataset of Calanus finmarchicus, Calanus glacialis, and Calanus hyperboreus, collected at various research surveys over a 30-year period. Our results show that the Calanus species are a main driver of variation in the mesozooplankton biomass in the Barents Sea, and constitutes around 80% of the total. The proportion of Calanus decreases at low zooplankton biomass, possibly due to a combination of advective processes (low C. finmarchicus in winter) and size selective foraging. Though the Calanus species co-occur in most regions, C. glacialis dominates in the Arctic water masses, while C. finmarchicus dominates in Atlantic waters. The larger C. hyperboreus has considerably lower biomass in the Barents Sea than the other Calanus species. Stages CIV and CV have the largest contribution to Calanus species biomass, whereas stages CI-CIII have an overall low impact on the biomass. In the western area of the Barents Sea, we observe indications of an ongoing borealization of the zooplankton community, with a decreasing proportion of the Arctic C. glacialis over the past 20 years. Atlantic C. finmarchicus have increased during the same period.

Environmental Impacts - Marine Ecosystems

This chapter presents a review of what is known about the impacts of climate change on the biota (plankton, benthos, fish, seabirds and marine mammals) of the North Sea. Examples show how the changing North Sea environment is affecting biological processes and organisation at all scales, including the physiology, reproduction, growth, survival, behaviour and transport of individuals; the distribution, dynamics and evolution of populations; and the trophic structure and coupling of ecosystems. These complex responses can be detected because there are detailed long-term biological and environmental records for the North Sea; written records go back 500 years and archaeological records many thousands of years. The information presented here shows that the composition and productivity of the North Sea marine ecosystem is clearly affected by climate change and that this will have consequences for sustainable levels of harvesting and other ecosystem services in the future. Multi-variate ocean climate indicators that can be used to monitor and warn of changes in composition and productivity are now being developed for the North Sea.