Tore Høisæter

Physical and biological factors influencing the seasonal variation in disatributrion of zooplanton across the shelfat Nordvestbaskem, northern Norway, 1994

Abstract This paper presents data on species composition, abundance, horizontal and vertical distributions of zooplankton from selected sites across Nordvestbanken, northern Norway, sampled monthly from March to September 1994. The sampling covered three stations: A(closest to shore), C and D (close to the shelf break). There was a distinct succession in species composition over the season, with a shift fro1n a community alrnost entirely dominated by Calanus finmarchicus in May, towards a larger contribution of smaller, neritic species in August and September. Numeiically C finmarchicus made up about 70% of the total zooplankton stock at stations D and C in May (about 90% ifnauplii, which mostly belonged to this species, are included), whereas the proportion of this species was about 50% at station A this month. The population development of the most common species agreed with earlier findings in the area. A CCA analysis was performed including a total of 18 copepod species and 8 environmental variables. ...

Contribution by mezooplankton focal pellets to the carbon flux on Nordvestkbanken, north Norwegian shelf in 1994

Abstract Fecal pellet production rates for mesozooplankton (> 500 µm) were measured monthly at a shelf edge and inshore station in northern Nonvegian coastal waters during Nlarch-September as part of the Ocean Margin Exchange (OMEX) stLrdy. The total potential fecal pellet carbon flux was higher at the inshore station except in May when Calanus finmarchicus (Gunnerus) was more abundant at the shelf edge. Mesozooplankton fecal pellets had the potential to contribute 2.5 % (April & September) to> 100% (May-August) of the POC flux found in sediment traps. This compared with only 5-35 %, when fecal pellet carbon flux was measured from trap pellets suggests that a significant amount of fecal pellet remineralization or coprophagy was occurring in the surface waters. Calanus finmarchicus apparently plays a pivotal role in moderating pellet carbon flux on Nordvestbanken both through its potential fecal pellet production and possibly through coprophagy. Carbon ingestion by the lccrge mesozooplankton at the shelf e...

Seasonal patterns in composition and biomass of autotrophic and heterotrophic nano- and microplankton communities on the north Norwegian shelf

Abstract From monthly transects on the shelf off northern Norway, data describe the size, abundance, and biomass of photosynthetic nano- and picoplankton, heterotrophic (aplastidic) nanoplankton, and ciliates. Samples were analyzed using a state-of-the-art color imaging system. The numerically dominant phytoplankton were pica- and nanoplankton. Highest biomasses occurred in summer, and increased earlier in the year and attained higher values in inshore stations compared to offshore stations. Mean cell sizes were small, 2-5μ.m diameter nanoplankton and 1μm eucaryotic picoplankton; cyanobacteria were comparatively unimportant contributors to biomass. The dominant herbivores appeared to be heterotrophic flagellates, which were generally similar in size, concentration, and biomass to the phototrophic forms. Their temporal and spatial distribution mimicked their putative prey, except that they often occurred in abundance deeper than the photosynthetic nanoplankton. Oligotrich ciliates were also abundant. The r...

Seasonal variaion of nutrients and suspended biomass on a transact across Nordvestbasken, north Norwegian shelf, in 1994

Abstract Nutrient consumption in the uppermost, well-mixed 100m of Nordvestbanken in 1994 started in March across the entire shelf. Significant nitrate reduction in the euphotic zone was reached in June at the inner and middle shelf, but not until September at the shelf edge. The variations of nutrient concentrations were generally similar for nitrate, silicate and phosphate. Increased stratification, giving rise to a pronounced nutricline around 40 m depth, was observed from August to October at the shelf edge., but not on the middle and inner shelf. The maximum carbon equivalent of cumulative nitrate consumption in the upper I 00 mat the inner, middle and outer shelf was about 72, 52, and 55 g C m-2 and occurred in June, August, and July, respectively. The suspended chlorophyll a concentrations were generally low throughout the transect and observed in June and July. Suspended phacopigment concentrations were generally lower than 1 mg m-2 The concentration of suspended organic carbon was moderately high...

The first record of Maeotias marginata (Cnidaria, Hydrozoa) from the Baltic Sea: a Pontocaspian invader

Abstract An exotic hydromedusa, Maeotias marginata (Modeer, 1791) (= M. inexpectata Ostroumoff, 1896) (Limnomedusae, Olindiidae) was observed 1999 in the Væinameri area of the northern Baltic Sea, westem Estonia. The genuine brackishwater species is considered native to the Sea of Azov - Black Sea estuaries. It has earlier been found introduced also in low-salinity habitats in the Netherlands, France, and both coasts of North America. The identity of the Baltic and North American Maeotias was confirmed using molecular characters (sequence of the mitochondrial COI gene).

The burrows of Nephrops norvegicus (L.)

Abstract The highly fluctuating catches of Norway lobster, Nephrops norvegicus (L.), wherever it is exploited, have prompted investigators to postulate that the animal has a burrowing habit. However, no direct observations from the Norway lobsters natural habitat revealing the nature of the burrows or the categories of Norway lobsters making them, have been made so far. — Observations made by divers, combined with aquarium experiments, show that the Norway lobster digs burrows with, usually, two openings in the bottom sediment. These tunnels very often occur in groups of about 5–10, the groups generally being well separated from each other. The dimensions of the burrows are in approximate proportion to the sizes of the animals inhabiting them. Individuals of both sexes and of most size classes (including berried females and large males) are found in such burrows. The decisive factor inducing the animals to retire into and stay in their burrows seems to be light conditions but little is known of the exact...

The first observation of okadaic acid in flounder in the Baltic Sea

Abstract Okadaic acid (OA) is a relatively stable polyether toxin causing diarrhetic shellfish poisoning, DSP. OA is produced by dinoflagellates such as Dinophysis acuminata and D. norvegica, which are common throughout the Baltic Sea. This protein phosphatase (PP) inhibitor can induce toxic effects such as hepatocyte apoptosis after in vitro exposure. The aim of this study was to analyse the liver and muscle of flounder from the Baltic Sea for okadaic acid. 30–50 flounder (Platichthys flesus) were caught at depths between 6 and 20 meter in different areas of the northern Baltic Sea every 3–4 weeks in June– September 1996–1998. The presence of OA was analysed using HPLC. The flounder caught in August 1996 contained OA (222 ng OA g-1 ww, liver tissue). This was the first observation of OA in fish from the northern Baltic Sea.

The shallow-water soft-bottom benthos in lindåspollene, western Norway: 4. Benthig marine diatoms, seasonal density fluctuations

The marine benthic diatoms in a soft-bottom substrate have been studied for about one year at six stations. Diatoms from the uppermost 5 mm of the sediment have been counted. Statistical analyses confirm that there are differences in the number of diatoms from station to station, and also differences in time within stations. The results indicate that most localities have a more or less prominent spring peak and for some stations also a late autumn maximum. Number of diatoms per mm3 varied from about 200 individuals (Stn 5) to about 2000 (Stn 6). Living diatoms were found down to about 16 cm in the sediment, even when there was some hydrogen sulphide at this depth at some of the stations. Arguments are presented for the importance of grazing as a controlling factor of diatom standing crop.

The postraarsupial development of Tanais dulongii (Audouin, 1826) (Crustacea, Tanaidacea) in laboratory culture

Abstract The sequence of postmarsupial stages of Tanais dulongii is described on the basis of separately reared individuals. In addition, gonad differentiation was studied histologically. More postmarsupial stages could be recognised than in previous studies on tanaid development. As in other Tanaidacea, T. dulongii passes two rnanca stages. In females, the manca stages are followed by 2–5 neutrum stages. It is only in the subsequent juvenile stages that female sexual differentiation becomes obvious, females exhibiting the anlagen of oostegites and ovaries. In the following three preparatory stages, the oostegites grow to form a paired ovisac (marsupium). Simultaneously, oocytes develop in the ovaries. With the maturation molt, the marsupium reaches its final size. Males pass through 1–3 neutrum stages only, thereafter presenting genital cones and differentiated gonads. The development of females comprises more instars and takes significantly more time than in males. The development of T. dulongii deviates from the “normal type” of tanaid development.

Biological notes on some Pyramidellidae (Gastropoda: Opisthobranchia) from Norway

Abstract Host-parasite relationships for several species of shallow water pyramidellids from Norwegian waters are described. Pomatoceros reefs were found to be substrate for as many as seven species of pyramidellids simultaneously. Circumstantial evidence for Limaria hians as host for Brachystomia rissoides (Hanley) is provided. Odostomia acuta Jeffreys is shown to be an associate of the sabellid, Myxicola infundibulum. Eggmasses of O. acuta were found embedded in the gelatinous walls of the tube of this polychaete. Eggs and recently hatched larvae of O. acuta are described for the first time. The first Norwegian record of Evalea perezi Dautzenberg & Fischer as an associate of Phascolion strombi is given.