Description: Abundance, distribution, population structure, lipid content, lipid composition and reproductive and feeding activity of Rhincalanus nasutus were studied in the Gulf of Aqaba and in the northern Red Sea during RV “Meteor”-cruise M 44-2 in February/March 1999. Rhincalanus nasutus occurred in higher numbers in the Gulf of Aqaba (585 ind m−2) than in the northern Red Sea (254 ind m−2). Young developmental stages (nauplii, copepodite stages CI and CII) were absent. In the southern Gulf of Aqaba, the bulk of the population developed from stage CV to adult in the course of the 3-week study period. In contrast, immature CV stages dominated at the adjacent stations in the northern Gulf of Aqaba and in the northern Red Sea. Development was associated with the seasonal vertical migration from wintering mid-water layers and initiation of feeding starting as early as beginning of March in the southern Gulf of Aqaba. No upward migration was observed in the northern parts of the Gulf and in the northern Red Sea, where more than 90% of the females remained immature during our study. Lipids were dominated by wax esters in females and CV. The fatty acid and fatty alcohol compositions of females were very similar throughout the study region and period. Major fatty acids were 18:1(n−9), 16:1(n−7), 16:2(n−4) and 20:5(n−3). Our results support the previous reports of a seasonal dormancy of R. nasutus in the Gulf of Aqaba and suggest that the timing of vertical migration, feeding and maturation is closely coupled to the development of the spring bloom in oligotrophic subtropical waters.

Description: The abundance and vertical distribution of microcopepods sampled by nets with 55 μm mesh size was compared for two neighbouring but hydrographically different areas, the Gulf of Aqaba and the northernmost Red Sea, during spring 1999. The vertical structure of the total microcopepod communities differed considerably between the two regimes: In the stratified waters of the Red Sea, calanoids outnumbered oncaeids as well as oithonids at 0–100 m, whereas oncaeids dominated in all meso- and bathypelagic layers below 100 m deep. In the unusually deep vertically mixed waters of the Gulf of Aqaba, calanoids outnumbered each of the non-calanoid taxa as deep as 250 or 350 m, whereas the oncaeid dominated deep water community was restricted to depth ranges below 400 m. Dominant non-calanoid species in both areas were Oncaea bispinosa, Paroithona pacifica, Oithona simplex, Spinoncaea ivlevi, O. tregoubovi and O. cristata. O. scottodicarloi occurred in exceptionally high numbers in the northern Gulf. Pronounced differences between the two areas were found in the vertical distribution of poecilostomatoid species. By comparing the present results with published data from the central and southern Red Sea and other tropical and warm-temperate oceanic areas, intra- and inter-oceanic differences in the structure of microcopepod communities in oligotrophic areas are discussed. The high abundance and vertically extended range of calanoid copepods during spring appears to be a specific feature of the Gulf of Aqaba, indicating an unusual vertical succession in the trophodynamic structure of the copepod fauna in this area.

Description: Tolerance of organisms towards heterogeneous and variable environments is highly related to physiological flexibility. An effective strategy to enhance physiological flexibility is the expression of polymorphic enzymes. This seems to be the case in the brown shrimp Crangon crangon. It shows high reproduction rates, feeds opportunistically on endo- and epibenthic organisms, and is apparently well adapted to variable environmental conditions. Previous electrophoretic studies revealed a high level of polymorphism and no consistent phenotype of digestive enzymes between individuals. In order to understand the underlying biochemical processes, we carried out a transcriptome-based study of digestive enzymes of C. crangon. Detailed sequence analyses of triacylglycerol lipase, phospholipase A2, alpha amylase, chitinase, trypsin and cathepsin L were performed to identify putative isoforms. The number of isoforms, and thus the degree of polymorphism varied among enzymes: lipases and carbohydrases showed higher numbers of isoforms in enzymes that besides their extracellular function also have diverse intracellular functions. Furthermore, cysteine proteinases showed a lower polymorphism than serine proteinases. We suggest that the expression of enzyme isoforms improves the efficiency of C. crangon in gaining energy from different food sources.

Description: Calanoid copepods in boreal and polar habitats are confronted with a strong variability in food supply. The abundant species in the Southern North Sea, Temora longicornis, cannot accumulate extensive energy stores to buffer longer periods of food paucity. These copepods react immediately to dietary changes and therefore, recent trophic conditions must strongly influence their metabolic and functional responses. To elucidate the implications of feeding history, we collected two cohorts of T. longicornis females, which were characterized by different feeding histories and consequently different physiological backgrounds. In the North Sea in April 2005, females fed at a higher trophic level than in May, were poor in lipids, showed low proteinase activity and produced 41 eggs female-1 d-1. In May, females were significantly smaller than in April, contained more lipids, had a higher proteinase activity and produced 26 eggs female-1 d-1. In the laboratory, females from each group were fed with either autotrophic diatoms or heterotrophic dinoflagellates for three days. Irrespective of different initial conditions, all T. longicornis females incorporated diet-specific fatty acids within 24 h. Also in both experiments and each dietary treatment, egg production increased after 24 h indicating that females were food-limited in situ in April and in May. Responses differed, however, with regard to lipid accumulation and enzyme activities . Total lipid contents increased significantly in females during experiment I (April) but not during experiment II (May), despite higher algal lipid levels during experiment II. Proteolytic activity increased during experiment I, but decreased during experiment II. These deviating responses of T. longicornis females to food conditions suggest that detailed knowledge about the initial physiological state of specimens is required, when investigating adaptive mechanisms and metabolic performances of copepods by means of experiments.