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: The intertidal Asian shore crab H. sanguineus was initially found on the French coast in the late 1990’s. It rapidly extended its range further north and is now well established in the German Wadden Sea. Recently, it was also found in western Sweden. In its intertidal habitat, it co-occurs with the European green crab C. maenas. The ecophysiology of H. sanguineus is virtually unknown. In this study, the physiological capacities of both species and their potential for intra-guild competition were investigated. We specifically compared the energy deposition and dietary preferences of ovigerous females of both species. Females of both species carrying immature or mature eggs were collected in April, June, August and October 2015 in an intertidal site on the Island of Helgoland, North Sea, Germany. Total lipid levels of midgut glands and eggs were acquired via extraction. Subsequently, fatty acid compositions were determined through gas chromatography. Total lipid levels of H. sanguineus midgut glands were clearly higher than those of C. maenas (40% vs. 10% dry mass, DM). Immature eggs of both species were quite lipid-rich with 30% and 25%DM, respectively. In mature eggs, lipid levels decreased to ~15%DM each. A Principal Component Analysis of the fatty acid compositions of midgut glands and eggs revealed separate clusters for both species. Lipids of C. maenas were characterized more by membrane fatty acids. Fatty acids of C. maenas midgut glands and eggs clustered together. They were largely dominated by carnivory biomarkers. Contrastingly, fatty acids of midgut glands and all eggs of H. sanguineus formed separate clusters and trophic markers indicated a more herbivorous diet. Higher lipid levels and thus more pronounced energy deposition in H. sanguineus midgut glands indicate higher starvation tolerance for females, a potential competitive advantage over C. maenas. Direct food competition, however, seems negligible, as H. sanguineus prefers a more herbivorous diet than C. maenas. Deviating fatty acid compositions among H. sanguineus midgut glands and eggs suggests that this species may represent an income breeder, utilizing energy from both the midgut gland and dietary input. In contrast, most brachyuran crabs are capital breeders, relying exclusively on internal reserves.