ALBERT

Description: AbstractThis study describes the annual reproductive cycles of the three dominant Calanus species, C. finmarchicus, C. glacialis and C. hyperboreus, in Disko Bay (West Greenland) in relation to the seasonal phytoplankton development. Relative abundance of females, copepodite stage 5 (CV) and males, and the developmental stage of the female gonad were examined from plankton samples collected at weekly to monthly intervals from May 1996 to June 1997 with a WP2 net or a pump. During spring and summer, egg production rates were determined. Females of all three species were present year round. Maximum relative abundance was reached by C. hyperboreus females at the beginning of February, by C. glacialis in mid February, and by C. finmarchicus in April. All three species reproduced successfully in Disko Bay. Their reproductive cycles were considerably different with respect to the timing of final gonad maturation and spawning, and hence in their relation to the seasonal phytoplankton development. In all three species, early gonad development took place during winter before living food became plentiful suggesting that these processes were largely food independent. Final gonad maturation and spawning in C. finmarchicus was related to the phytoplankton concentration reflecting that final gonad maturation processes are food dependant in this species. C. glacialis females matured and spawned prior to the spring bloom. Our results indicate that first internal lipid stores, and later ice algae grazing, supplied final gonad maturation and egg production. Maximum egg production rates of C. glacialis were found in spring and summer when the chlorophyll a concentration was high. Mature female C. hyperboreus were found from February until mid April when the chlorophyll a concentration was still low. In this species, reproductive activity was decoupled from the phytoplankton development, and final maturation processes and spawning were solely fuelled by internal energy stores.Keywords: Calanus finmarchicus, Calanus glacialis, Calanus hyperboreus, gonad maturation, egg production, West Greenland

Description: Tectonic models predict that, following breakup, rift margins undergo only decaying thermal subsidence during their post-rift evolution. However, post-breakup stratigraphy beneath the NE Atlantic shelves shows evidence of regional-scale unconformities, commonly cited as outer margin responses to inner margin episodic uplift, including the formation of coastal mountains. The origin of these events remains enigmatic. We present a seismic reflection study from the Greenland Fracture Zone – East Greenland Ridge (GFZ-EGR) and the NE Greenland shelf. We doc- ument a regional intra-Miocene seismic unconformity (IMU), which marks the termination of syn-rift deposition in the deep-sea basins and onset of: (i) thermo-mechanical coupling across the GFZ, (ii) basin compression, and (iii) contourite deposition, north of the EGR. The onset of coupling across the GFZ is constrained by results of 2-D flexural backstripping. We explain the thermo-mechanical coupling and the deposition of contourites by the forma- tion of a continuous plate boundary along the Mohns and Knipovich ridges, leading to an accelerated widening of the Fram Strait. We demonstrate that the IMU event is linked to onset of uplift and massive shelf-progradation on the NE Greenland margin. Given an estimated middle-to-late Miocene (ca. 15-10 Ma) age of the IMU, we speculate that the event is synchronous with uplift of the East and West Greenland margins. The correlation between margin uplift and plate-motion changes further indicates that the uplift was triggered by plate tectonic forces, induced perhaps by a change in the Iceland plume (a hot pulse) and/or by changes in intra-plate stresses related to global tectonics.

Description: Here we present a new, pan-Atlantic compilation and analysis of data on Calanus finmarchicus abundance, demography, dormancy, egg production and mortality in relation to basin-scale patterns of temperature, phytoplankton biomass, circulation and other environmental characteristics in the context of understanding factors determining the distribution and abundance of C. finmarchicus across its North Atlantic habitat. A number of themes emerge: (1) the south-to-north transport of plankton in the northeast Atlantic contrasts with north-to-south transport in the western North Atlantic, which has implications for understanding population responses of C. finmarchicus to climate forcing, (2) recruitment to the youngest copepodite stages occurs during or just after the phytoplankton bloom in the east whereas it occurs after the bloom at many western sites, with up to 3.5 months difference in recruitment timing, (3) the deep basin and gyre of the southern Norwegian Sea is the centre of production and overwintering of C. finmarchicus, upon which the surrounding waters depend, whereas, in the Labrador/Irminger Seas production mainly occurs along the margins, such that the deep basins serve as collection areas and refugia for the overwintering populations, rather than as centres of production, (4) the western North Atlantic marginal seas have an important role in sustaining high C. finmarchicus abundance on the nearby coastal shelves, (5) differences in mean temperature and chlorophyll concentration between the western and eastern North Atlantic are reflected in regional differences in female body size and egg production, (6) regional differences in functional responses of egg production rate may reflect genetic differences between western and eastern populations, (7) dormancy duration is generally shorter in the deep waters adjacent to the lower latitude western North Atlantic shelves than in the east, (8) there are differences in stage-specific daily mortality rates between eastern and western shelves and basins, but the survival trajectories for cohort development from CI to CV are similar, and (9) early life stage survival is much lower in regions where C. finmarchicus is found with its congeners, C. glacialis and/or C. hyperboreus. This compilation and analysis provides new knowledge for evaluation and parameterisation of population models of C. finmarchicus and their responses to climate change in the North Atlantic. The strengths and weaknesses of modeling approaches, including a statistical approach based on ecological niche theory and a dynamical approach based on knowledge of spatial population dynamics and life history, are discussed, as well as needs for further research.

Description: To understand the impact of microplastic (MP) pollution to aquatic ecosystems, it is important to identify the mechanisms of interaction with organisms. Exposure experiments, like the study of Sussarellu et al. (1) recently published in PNAS, may provide such insights. However, the results of dose–response experiments must always be interpreted...

Description: Here we compare the functional biology of the sympatric krill species, Meganyctiphanes norvegica and Thysanoessa inermis . For M. norvegica, we investigated functional responses on diatoms and copepods, together with prey size spectra on plankton 〈400 µm and copepods in the size range 500–3220 µm. For T. inermis , only prey size spectrum on plankton 〈400 µm were investigated. The prey size ranges of both species include organisms 〈400 µm, and they consequently graze on several trophic levels. However, T. inermis feed on cells 〈10 µm equivalent spherical diameter (ESD), whereas M. norvegica only feed on cells 〉10 µm. Meganyctiphanes norvegica show maximum predation on 800–1600 µm sized copepods, corresponding to a predator:prey size ratio of 17.0 ± 2.2. Functional response experiments with M. norvegica follow a Holling type III functional response, both when feeding on diatoms and copepods, but with an order of magnitude higher ingestion rate on the copepod prey. The two functional groups, M. norvegica and Thysanoessa spp., overlap in prey size spectra. However, there are differences in their ability to exploit different prey classes. Here, we present clearance rates of both krill species on natural plankton illustrating the two species' wide particle range spectra.

Description: This study investigates whether feeding on the domoic acid (DA)-producing diatom Pseudo-nitzschia seriata affects the faecal pellet (FP) production (proxy for grazing) and fecundity of Calanus finmarchicus and Calanus glacialis. Female copepods were fed a saturating concentration of food (400 µg C L –1 ) in two combinations (i) natural phytoplankton spiked with 50% P. seriata and (ii) only the non-toxic phytoplankton community. The copepods ingested DA, as illustrated by DA accumulation in their FPs, and transferred a share of DA to their eggs and body tissue. DA was mainly excreted through FPs in both species. Compared with C. finmarchicus , C. glacialis accumulated substantially more DA in its body tissue. For both species, egg production and hatching success were unaffected by grazing on the toxic diatom. This suggests that feeding on DA-containing P. seriata does not affect copepod fecundity, despite increasing DA concentrations of P. seriata during the experiment.

Description: Processes governing productivity at the base of the pelagic food web of the southern Indian Ocean are influenced primarily by physical–chemical conditions with implications for the structure and function of the entire pelagic food web. Here, we report observations along a great circle transect from Cape Town, South Africa, to Broome in north western Australia. Primary production was tightly linked to water column stability and nutrient availability, with high productivity (1144 mg C m –2 day –1 ) in the sub-tropical convergence zone, and falling off by an order of magnitude in the sub-tropical gyre and tropical waters off northwest Australia. Primary production was largely confined to the GF/F fraction (GF/F 〉75% of total production and usually much higher) and the photosynthetic parameters showed adaption to the prevailing light levels. Bacterial production ranged from 19 to 155 mg C m –2 day –1 . No relationships were found between bacterial production and primary production or phytoplankton biomass and bacterial production seem more related to the state of the phytoplankton community as high bacterial production was observed in a post-bloom situation. The average BP:PP ratio was 31% (range 3.5–71%).

Description: Disko Bay is a highly productive inlet at the border between high- and low-arctic sectors of west Greenland. The physical/chemical conditions in the bay have changed during recent decades, specifically during an inflow event in 1996–1997 that led to increased deep-water temperatures. To further understand the consequences of physical changes to the plankton community in the bay, we examine findings from a field study on mesozooplankton and fish larvae in the areas of Disko Bay and Disko Bank carried out in 1997. We sampled 31 stations over 5 days along four transects and assessed horizontal and vertical distribution patterns, community composition and plankton trophodynamics. Plankton abundance was enhanced near-coast and across the pycnocline, and communities differed between regions. Polar cod ( Boreogadus saida ) and the sandeel ( Ammodytes sp.) were among the abundant fish larvae. Productivity/growth estimates of key species of copepods and fish larvae showed no apparent relationship to food availability; they reached weight specific values of ~6% day –1 for copepods and ~14% day –1 for fish larvae. Overall, we found a rich and dynamic plankton community, strongly influenced by the complex hydrography of the area. Thus, changes in physical characteristics of the bay could threaten the resilience of its ecosystem.

Description: We investigated the effect of suspended sediments on the vital rates of the copepods Calanus finmarchicus , Pseudocalanus sp. and Metridia longa in a Greenland sub-Arctic fjord. The fjord had a gradient of suspended particulate matter (SPM) with high concentrations (〉50 mg L –1 ) in the inner fjord due to glacial melt water runoff. Laboratory experiments showed that when feeding on the diatom Thalassiosira weissflogii specific ingestion rates were low at high concentrations of suspended sediment for C. finmarchicus (〉20 mg L –1 ) and Pseudocalanus sp. (〉50 mg L –1 ), while no effect was found for M. longa . For C. finmarchicus , a relatively constant fecal pellet production (FPP) and fecal pellet volume suggested ingestion of sediment, which probably led to reduction in egg production rates (EPRs) at high sediment concentrations. For Pseudocalanus sp., FPP decreased with increasing sediment concentrations, while no effect was observed on EPR. No significant difference was observed in FPP for M. longa feeding on the diatom T. weissflogii compared to the ciliate Strombidium sulcatum . The study shows that high sediment concentrations influence the capability of carbon turnover in C. finmarchicus and Pseudocalanus sp., while M. longa appears to be more tolerant to high sediment loads. Therefore, high concentrations of SPM could potentially influence the species composition of glacially influenced fjords.