Vertical distribution and diurnal migration of some Cyclopoida (Copepoda) in the tropical region of the Pacific Ocean

The material was collected in the western equatorial part of the Pacific Ocean at a 24 h station on December 21 to 23, 1968. Collections were made by means of 2 Juday nets from 2 winches simultaneously. A series of hauls was made at 2 h intervals. The vertical distribution of 17 Cyclopoida species, belonging to 3 families (Oithonidae, Oncaeidae and Corycaeidae) was studied. From 0 to 300 m, the absolute number of Cyclopoida individuals was practically constant throughout the 24 h period. The bulk of the species performed no diurnal vertical migration, or migrated with low intensity in the usual way (i.e. moved upward at night and downward during the day). Only 2 Oncaeidae species performed significant diuranl vertical migration. No reversed migration in Cyclopoida was discovered. To characterize the vertical distribution of Cyclopoida, the distribution of the cores of populations (abundancies between 25 and 75%) was examined. During the 24 h period, the cores of populations of various Cyclopoida species were found at different depths; this steplike distribution was not disturbed in migrating species. The cores of populations differed both with habitat depth and time of ascent of the migrating species to the surface layer. This peculiarity, probably, tends to lessen the intensity of food competition between Cyclopoida species with similar nutritional habits.     

Eine Apparatur zur kontinuierlichen Respirationsmessung an marinen Organismen

Measurements were made with a Clark electrode in a closed system under conditions of different, regulatable water current velocities. Six simultaneous parallel measurements are possible with only one electrode. The volume of respiration chambers amounts to 80 ml for small animals and 300 ml for larger ones. Technical details of the apparatus and measuring procedures are described. The accuracy amounts to 0.5 μl O₂ for the 80 ml chamber, and 2 μl O₂ for the 300 ml chambers. The apparatus has been successfully used on various marine evertebrates and algae.     

Effect of the spionid polychaeteBoccardia syrtis on the distribution and survival of juvenileMacomona liliana (Bivalvia: Tellinacea)

The tellinid bivalveMacomona liliana (Iredale) occurs at relatively low densities on a sandbank (Te Tau bank) in Manukau Harbour, New Zealand. Te Tau bank is dominated by polychaetes, including the tube-building spionidBoccardia syrtis (Rainer). JuvenileM. liliana are known to disperse as post-settlement juveniles by byssus-drifting. Laboratory experiments were conducted to assess whether the low abundance ofM. liliana on Te Tau bank was due to the presence ofB. syrtis, or to some reaction to the sediment itself. In particular, we, examined how juvenileM. liliana survived after exposure to Te Tau bank sediments with and without the spionid tube-mat for 1 mo in still-water conditions, and how they responded when given a choice of different sediment/tube-mat treatments in moving water. JuvenileM. liliana did not appear to have a strong aversion to settling and burrowing in sediments from Te Tau bank. Sediments without the tube-mat did not adversely affect the survivorship of the bivalves, but survival was significantly lower amongst theB. syrtis tube-mat. In the presence of a current, the juvenile bivalves settled in Te Tau bank sediments without a tube-mat, but avoided settling amongst liveB. syrtis. An artificial tube-mat enhanced settlement. Avoidance of liveB. syrtis appears to be an avoidance of the worms themselves rather than a response to the physical presence of their tubes.     

Allozyme and colour differences between two sibling species of the heteronemertean Lineus torquatus from the Sea of Japan

Brown and cherry colour morphs of the heteronemertean Lineus torquatus Coe, 1901 from the Vostok Bay of the Sea of Japan were compared using allele frequencies at 18 isozyme loci. These morphs shared no common alleles at 9 of the 18 loci. The observed genetic differences are strong evidence that the brown and cherry colour morphs, which occur sympatrically, are different species. Nei's genetic distance between these species (D=1.135) is considerably higher than typical D values for congeneric animal species. As with much previous work on nemerteans, intraspecific allozymic variability in both species was high, with mean expected heterozygosity values 0.286±0.049 and 0.159±0.051 for L. torquatus (brown) and L. torquatus (cherry) species, respectively.     

Mate sampling behaviour of black grouse females (Tetrao tetrix)

We studied female mate sampling behaviour in lekking black grouse (Tetrao tetrix). Females mainly visited males occupying territories in the centre of the lek with relatively large territories. They were also more likely to visit males that had high attendance. The same factors were also correlated with male mating success. A multiple regression model including these factors explained more of the variance in female visits per male (53%) than in mating success (33%). The pattern of female sampling conformed with a pool comparison (best-of-n) tactic. Such a tactic is expected if the costs of sampling are low. Females of high body mass visited more males than lighter females, however, which indicates that females may vary in their search tactics and suggests that there may be search costs. The existence of costs is further suggested by the fact that if the mate from a previous year was still present, females always mated with the same male in the following year. Though search costs were not measured directly, our findings suggest that some costs are negligible (e.g. energetic exhaustion or predation) whereas others (timing of mating) may be more important.     

Comparison of Zn, Cu, Pb, Ni, Cr, Sn, Mo Concentrations in Tissues of Fish (Roach and Perch) from Lake Baikal and Bratsk reservoir, Russia

Data on Zn, Cu, Pb, Ni, Cr, Sn, Mo concentrations in some food fish in Baikal Lake and Bratsk reservoir have been compared. The muscles, skin and gills of roach and perch (Rutilus rutilus and Perca fluviatis L.) were analysed. The conditions of atomic-emission analysis, detection limits, reproducibility, coefficients of transformation from the wet to dry mass and to an ash residue are reported. To verify accuracy, the results of reference samples OK-1 (Baikal perch) and OM-1 (Baikal roach) were used along with atomic-absorption and neutron-activation results of ashed and dried samples. The observed range of concentrations in tissues exceeds the probable analytical errors and reflects natural variability. The content of Zn, Cu, Pb, Ni and Cr in tissues of fish collected in the Bratsk reservoir from the conventionally uncontaminated and polluted sites correspond to the concentrations in tissues of similar fish from Lake Baikal. The latter are normal for fish of weakly mineralised oligotrophic reservoirs. The ranges of concentration in studied fish (roach and perch) consist of mg kg^–1 dry wt: in muscles-Zn(14–28), Cu(2.2–4.7), Pb(0.30–0.61); in skin-Zn(94–119), Cu(1.2–1.4), Pb(0.16–0.08); in gills-Zn(70–280), Cu(2.0–7.4), Pb(0.19–1.2).     

The inactive temporary component: an unexplored fraction of meiobenthos

Numerous morphotypes and great abundances of resting stages falling within the meiobenthic size-range were found in meiobenthos samples collected in a coastal lagoon of the North Adriatic Sea. Biodiversity, abundances and energetic values of both active and inactive meiobenthic organisms were analysed by the traditional techniques of meiobenthology. Inactive stages were represented by more than 100 morphotypes and formed 52% of the meiobenthos in terms of numbers of individuals. Inactive meiobenthos came mostly from plankton: the second and third most abundant groups of all meiobenthic organisms were the eggs of a rotifer and the cysts of a dinophyte, respectively. Resting stages of plankters fit the definition of temporary meiobenthos, making up the “inactive temporary meiobenthos”, but they are usually not considered in meiobenthology. The diversity and abundance of the meiobenthos is, thus, currently underestimated; this leads to neglect of the role of meiobenthos in several processes linking different ecosystems. It is hypothesised, for instance, that the meiobenthic resting stages of planktonic organisms (besides being the “seeds” for the perpetuation of planktonic communities) might also be the prey of meiofaunal organisms with piercing mouth parts. If this proves correct, a regulatory role might be proposed for the meiofauna in respect to plankters with benthic stages. Received: 10 September 1998 / Accepted: 12 April 1999