ALBERT

Notes: Abstract A method is introduced to determine intermolt stages in Antarctic and boreal euphausiids. The system is based on the classical scheme elaborated by Drach and Tchernigovtzeff. In addition to the definitions of these authors several features unique to euphausiids are described and combined to establish a system of at least 12 easily distinguishable stages. The method can be used to investiate specific cyclical physiological changes as well as answer questions regarding general growth physiology.

Notes: Abstract In the Antarctic krill Euphausia superba two forms of the chitinolytic enzyme N-acetyl-β-d-glucosaminidase (NAGase, EC 3.2.1.52) have been described, previously identified as NAGase B and NAGase C. Here, we demonstrate the organ-specific distribution and physiological relevance of both forms using a polyclonal antibody preparation which allows them to be distinguished immunologically. While NAGase B was localized in the integument and displayed a pattern of activity related to the moult cycle, the activity of NAGase C was independent of the moult cycle and was predominantly found in the gastrointestinal tract. Accordingly, NAGase B played a significant role in chitin degradation during the krill's moult, whereas NAGase C participated in the digestion of chitin-containing dietary components. Chromatographic elution profiles of isolated organs confirmed the immunological results by displaying characteristic organ-specific patterns in NAGase activity. The molecular characteristics of the moulting form, NAGase B, may further indicate a vesicular transport of moulting enzymes from the epidermis into the ecdysial space. Based on our results we develop a hypothesis explaining the concurrent processes of simultaneous chitin degradation and chitin synthesis occurring during moult.

Notes: Abstract Adaptive processes linked to reproduction were studied comparatively for three populations of Northern krill, Meganyctiphanes norvegica (M. Sars, 1857), sampled during winter and summer cruises in the Clyde Sea (W Scotland), the Kattegat (E Denmark), and the Ligurian Sea (NW Mediterranean). The aim was to investigate the functional relationship between egg production and moulting under contrasted climatic and environmental conditions. A staging system for female sexual development established for live krill was complemented by a histological study of the ovary at various developmental steps. During the reproductive season, all adult female krill were engaged in cyclical egg production. During experiments, female krill released one batch of mature oocytes in one or two spawning events. The ovary of postspawn female krill still contained developing oocytes for another egg batch. In the non-reproductive period, all female krill had a resting ovary. Ovarian structure and pattern of egg production were identical in the three populations, but seasonal timing of egg production was different. The model proposed for the Ligurian population of the annual cycle of ovarian development can be extended to the other two populations, taking into account the seasonal characteristics of each site. Random field samples were staged simultaneously for moult cycle and for sexual development. Moult stages and the seasonal variation of the intermoult period were studied for the Kattegat population using multi-year data and compared to data obtained during summer/winter cruises in the Clyde and the Ligurian Sea. At the three sites, intermoult period was shorter and temperature-dependent during the reproductive period, concurrent with the season of greatest food availability. During most of the year and the period of sexual rest, moulting activity was reduced. The relationship between spawning and the moult cycle was studied comparatively for the three populations. Eggs were released during the premoult phase of a “spawning moult cycle”, in one or two spawnings associated with apolysis and Moult Stage D1, respectively. Yolk accumulation for the next egg batch was completed during an alternating “vitellogenic moult cycle”. A model for the timing of cyclical egg production in relation to moulting, as proposed for the Kattegat, can be extended to the other populations, taking into account intermoult period variation with temperature. Temperature appeared to be the principal environmental factor controlling growth (through moulting) and egg production during the reproductive season, in connection with favourable trophic conditions.

Notes: Abstract Meganyctiphanes norvegica (M. Sars)is a pelagic crustacean that plays a key role in marine food webs of North Atlantic Ocean and marginal seas. We studied eight population samples collected in the European Atlantic and Mediterranean Sea. By means of single strand conformation polymorphism analysis (SSCP) and direct sequencing, we investigated a segment of 158 base pairs of the mitochondrial gene coding for the subunit 1 of NADH dehydrogenase. We found 12 sequence variants among the 385 individuals studied. Analysis of molecular variance (AMOVA) showed that 14.75% of the total genetic variability was explained by differences between populations, thus indicating absence of panmixia for these populations. Pairwise comparisons revealed three distinct genetic pools: the first one represented by Cadiz Bay, the second one by the Ligurian Sea, and the third one included all the NE Atlantic samples. We also investigated one population from the Alboran Sea (within the Mediterranean basin, east of the Strait of Gibraltar). This population was found to be genetically intermediate between the NE Atlantic samples and the Ligurian sample, suggesting that the restriction to the gene flow is not associated with the Strait of Gibraltar, but possibly with the Oran–Almeria oceanographic front. The present work indicates that M. norvegica, although endowed with a high dispersal capacity because of its pelagic habit, can develop separate breeding units inside the same oceanic basin (the Atlantic). Furthermore, the Ligurian sample should be considered as a distinct evolutionary entity, separated from the Atlantic population.

Notes: Abstract From 1979 to 1983 a population ofMeganyctiphanes norvegica was regularly found in a confined location in the northern Kattegat. The development of this pelagic population was followed over one complete year-cycle, and is discussed in light of published data on landlocked and oceanic populations. In the Kattegat,M. norvegica mature at the age of 9 to 12 months. Copulation starts in january, but fully developed spermatophores are present in males for at least 9 months. Spawning starts in April and continues until October with a marked peak in July. As only 10 to 15% of the gravid females belong to the II-group, it is concluded that recruitment is due to the I-group. Linear growth is fastest in spring and early summer, rises to a second maximum in October and stagnates during winter. The weight development shows some discontinuties caused by spawning or the accumulation of reserves towards winter. Weight decreases during winter. Growth in length and in weight runs largely parallel in both sexes, and can be closely correlated with the prevailing food supply. Diurnal vertical migration could be demonstrated. The results indicate a continuous development, which suggests the existence of an autonomous palagic population, a well suited subject for long-term investigation.

Notes: Abstract The ultrastructure of malacostracan integument was examined and compared in 11 species collected primarily from the western Baltic Sea in 1989, of which eight species were studied for the first time (indicated below by an asterisk). We attempted to relate cuticle structure and thickness to swimming aptitude. The pelagic euphausiidMeganyctiphanes norvegia and the mysidsPraunus flexuosus * andNeomysis integer * displayed a thin, little-mineralized, and thus light-weight cuticle. Laminae of the endocuticle were very thin (0.1µm) relative to those of the exocuticle (1µm). In contrast, laminae in the procuticles of the benthic amphipodsGammarus locusta, Caprella linearis *,Corophium volutator *,Orchestia gammarellus *, and the isopodIdotea baltica were evenly distributed, comparatively thick (1 to 2µm), and more heavily mineralized. The nektobenthic amphipodHyperia galba *, the cumaceanDiastylis rathkei * and the decapodCrangon crangon * migrate between pelagic and benthic regions. Only near the hypodermis did these organisms exhibit the characteristically pelagic fine-layered endocuticle. A membranous layer was lacking in all species investigated. In contrast to the less-mineralized cuticles of the species analyzed here, a membranous layer appears to be restricted to crustaceans with heavily calcified shells. Ultrastructural results were substantiated by morphometric calculations, which indicated differences in thickness of the total cuticle relative to body volume. In the pelagic malacostracans, thickness of the cuticle did not increase with body volume over the size range investigated.

Notes: Abstract The ultrastructure of euphausiid integument was examined in relation to the moult cycle and supplemented by investigations of chitinase activity in the integument and content of N-acetyl-β-D-glucosamine in the hemolymph. The Antarctic krill, Euphausia superba was collected in 1983 in Admiralty Bay, King George Island, Antarctica. Some specimens of the Northern krill, Meganyctiphanes norvegica, from the Danish Kattegat served for comparison. As a major aim of the study, the moult staging system developed for living tissue could be verified by ultrastructural findings. Under experimental high production conditions of the Antarctic summer, no period of rest or “intermoult” between post- and premoult was observed in subadult E. superba. Neither was a resting phase seen at the cellular level, the epidermis remained active. The epidermal gland cells did not show any cyclical changes, and the organelles of protein synthesis were generally well developed in all moult stages. In order to follow the physiological course of events, structural and biochemical methods were combined and showed as a result that the last moult stage before ecdysis is characterized by massive cuticular resorption. The epicuticle remained ultrastructurally unchanged before and after ecdysis, even though its permeability should alter at ecdysis. The existence of muscle insertions which connect the old and the new cuticle across the exuvial space suggests an answer to the question why E. superba is hardly impaired in swimming almost up to the time of ecdysis.

Notes: Abstract In a 14-d period 38 swarms of Antarctic krill,Euphausia superba Dana, were sampled in an area 55.5 x 55.5 km to the southwest of Elephant Island, at the north of the South Shetland Islands. Moult stage, maturity stage, and size of ca. 100 krill from each swarm were measured. Each of the characteristics varied greatly between swarms. Moulting krill were found in most swarms, but in one swarm all of the krill were just about to moult. Ways in which moulting may act as a possible sorting mechanism are discussed. Data for all the analysed krill (ca. 3000 specimens) were used to investigate the interdependence of moult rate, sexual maturation and growth. While all immature krill moulted at approximately the saine rate in the study, there were significant differences in the moulting rates of mature male and female krill. Gravid female krill continued to moult, although less frequently than mature males. As a consequence males had to attach spermatophores to females after each moult. It is likely that variation in moult rate of females and males was related to the energy expenditure required for ovary development in females and spermatophore production and searching behaviour in males. Spawning and moulting were only partly coupled in gravid females. Spawning appeared to take place predominantly during Moult Stage D2. There was no evidence of intermoult growth by intersegmental dilation.