Tracking seasonal changes in North Sea zooplankton trophic dynamics using stable isotopes

Trophodynamics of meso-zooplankton in the North Sea (NS) were assessed at a site in the southern NS, and at a shallow and a deep site in the central NS. Offshore and neritic species from different ecological niches, including Calanus spp., Temora spp. and Sagitta spp., were collected during seven cruises over 14 months from 2007 to 2008. Bulk stable isotope (SI) analysis, phospholipid-derived fatty acid (PLFA) compositions, and δ 13CPLFA data of meso-zooplankton and particulate organic matter (POM) were used to describe changes in zooplankton relative trophic positions (RTPs) and trophodynamics. The aim of the study was to test the hypothesis that the RTPs of zooplankton in the North Sea vary spatially and seasonally, in response to hydrographic variability, with the microbial food web playing an important role at times. Zooplankton RTPs tended to be higher during winter and lower during the phytoplankton bloom in spring. RTPs were highest for predators such as Sagitta sp. and Calanus helgolandicus and lowest for small copepods such as Pseudocalanus elongatus and zoea larvae (Brachyura). δ 15NPOM-based RTPs were only moderate surrogates for animals’ ecological niches, because of the plasticity in source materials from the herbivorous and the microbial loop food web. Common (16:0) and essential (eicosapentaenoic acid, EPA and docosahexaenoic acid, DHA) structural lipids showed relatively constant abundances. This could be explained by incorporation of PLFAs with δ 13C signatures which followed seasonal changes in bulk δ 13CPOM and PLFA δ 13CPOM signatures. This study highlighted the complementarity of three biogeochemical approaches for trophodynamic studies and substantiated conceptual views of size-based food web analysis, in which small individuals of large species may be functionally equivalent to large individuals of small species. Seasonal and spatial variability was also important in altering the relative importance of the herbivorous and microbial food webs

Food webs under changing biodiversity - Top-down control

Report on effects of changing predation pressure on benthic and pelagic specie

Spring-to-summer changes and regional variability of benthic processes in the western Canadian Arctic

Seasonal dynamics in the activity of Arctic shelf benthos have been the subject of few local studies, and the pronounced among-site variability characterizing their results makes it difficult to upscale and generalize their conclusions. In a regional study encompassing five sites at 100–595 m water depth in the southeastern Beau- fort Sea, we found that total pigment concentrations in surficial sediments, used as proxies of general food supply to the benthos, rose significantly after the transition from ice-covered conditions in spring (March–June 2008) to open-water conditions in summer (June–August 2008), whereas sediment Chl a concentrations, typical markers of fresh food input, did not. Macrobenthic biomass (including agglutinated foraminifera [500 lm) varied significantly among sites (1.2–6.4 g C m-2 in spring, 1.1–12.6 g C m-2 in summer), whereas a general spring-to-summer increase was not detected. Benthic carbon remineralisation also ranged significantly among sites (11.9–33.2 mg C m-2 day-1 in spring, 11.6–44.4 mg C m-2 day-1 in summer) and did in addition exhibit a general significant increase from spring-to-summer. Multiple regression analysis suggests that in both spring and summer, sediment Chl a concentration is the prime determinant of benthic carbon remineralisation, but other factors have a significant secondary influence, such as foraminiferan biomass (negative in both seasons), water depth (in spring) and infaunal biomass (in summer). Our findings indicate the importance of the combined and dynamic effects of food supply and benthic community patterns on the carbon remineralisation of the polar shelf benthos in seasonally ice-covered seas

Sea ice cover, and bottom water and sediment characteristics at stations in the Amundsen Gulf, Canada

Seasonal dynamics in the activity of Arctic shelf benthos have been the subject of few local studies, and the pronounced among-site variability characterizing their results makes it difficult to upscale and generalize their conclusions. In a regional study encompassing five sites at 100-595 m water depth in the southeastern Beaufort Sea, we found that total pigment concentrations in surficial sediments, used as proxies of general food supply to the benthos, rose significantly after the transition from ice-covered conditions in spring (March-June 2008) to open-water conditions in summer (June-August 2008), whereas sediment Chl a concentrations, typical markers of fresh food input, did not. Macrobenthic biomass (including agglutinated foraminifera >500 µm) varied significantly among sites (1.2-6.4 g C/m**2 in spring, 1.1-12.6 g C/m**2 in summer), whereas a general spring-to-summer increase was not detected. Benthic carbon remineralisation also ranged significantly among sites (11.9-33.2 mg C/m**2/day in spring, 11.6-44.4 mg C/m**2/day in summer) and did in addition exhibit a general significant increase from spring-to-summer. Multiple regression analysis suggests that in both spring and summer, sediment Chl a concentration is the prime determinant of benthic carbon remineralisation, but other factors have a significant secondary influence, such as foraminiferan biomass (negative in both seasons), water depth (in spring) and infaunal biomass (in summer). Our findings indicate the importance of the combined and dynamic effects of food supply and benthic community patterns on the carbon remineralisation of the polar shelf benthos in seasonally ice-covered seas

Interspecific and nutrient-dependent variations in stable isotope fractionation: experimental studies simulating pelagic multitrophic systems

Stable isotope signatures of primary producers display high inter- and intraspecific variation. This is assigned to species-specific differences in isotope fractionation and variable abiotic conditions, e.g., temperature, and nutrient and light availability. As consumers reflect the isotopic signature of their food source, such variations have direct impacts on the ecological interpretation of stable isotope data. To elucidate the variability of isotope fractionation at the primary producer level and the transfer of the signal through food webs, we used a standardised marine tri-trophic system in which the primary producers were manipulated while the two consumer levels were kept constant. These manipulations were (1) different algal species grown under identical conditions to address interspecific variability and (2) a single algal species cultivated under different nutrient regimes to address nutrient-dependent variability. Our experiments resulted in strong interspecific variation between different algal species (Thalassiosira weissflogii, Dunaliella salina, and Rhodomonas salina) and nutrient-dependent shifts in stable isotope signatures in response to nutrient limitation of R. salina. The trophic enrichment in 15N and 13C of primary and secondary consumers (nauplii of Acartia tonsa and larval herring) showed strong deviations from the postulated degree of 1.0‰ enrichment in δ13C and 3.4‰ enrichment in δ15N. Surprisingly, nauplii of A. tonsa tended to keep “isotopic homeostasis” in terms of δ15N, a pattern not described in the literature so far. Our results suggest that the diets’ nutritional composition and food quality as well as the stoichiometric needs of consumers significantly affect the degree of trophic enrichment and that these mechanisms must be considered in ecological studies, especially when lower trophic levels, where variability is highest, are concerned

Principles for integrated island management in the tropical Pacific

We propose a new approach for island-wide planning and implementation of ecosystem management in the Pacific, recognizing a lack of replicability, sustainability and cost-effectiveness in other approaches. 'Integrated island management' (IIM) operates through coordinated networks of institutions and communities focused on sustainable and adaptive management of natural resources. IIM enables simultaneous and cost-effective achievement of ecosystem-based management, climate change adaptation and disaster risk reduction while conserving biodiversity, maintaining ecosystem services and securing human health and well-being. We present ten guiding principles for IIM, and then use these to evaluate 36 case studies from the Pacific islands. Most case studies were pilot or demonstration projects with little evidence of planning to ensure long-term financial and human capacity needs were sustained, beyond the life of the projects, or could be replicated at significant scales. Management outcomes in the Pacific will be enhanced by: (1) building on foundations of customary management practice and social networks; (2) working holistically across relevant ecological and governance scales, through coordinated but decentralized and nested institutions; (3) empowering local communities to participate in integrated planning and implementation; and (4) embedding IIM practice into national systems for long-term sustainability and replication. These also ultimately depend on the context and externalities, beyond the control of practitioners. Cost-effectiveness and appropriateness are also critical for successful IIM in the Pacific islands but ultimately there is little alternative for effective biodiversity conservation

Principles for integrated island management in the tropical Pacific

We propose a new approach for island-wide planning and implementation of ecosystem management in the Pacific, recognizing a lack of replicability, sustainability and cost-effectiveness in other approaches. \u27Integrated island management\u27 (IIM) operates through coordinated networks of institutions and communities focused on sustainable and adaptive management of natural resources. IIM enables simultaneous and cost-effective achievement of ecosystem-based management, climate change adaptation and disaster risk reduction while conserving biodiversity, maintaining ecosystem services and securing human health and well-being. We present ten guiding principles for IIM, and then use these to evaluate 36 case studies from the Pacific islands. Most case studies were pilot or demonstration projects with little evidence of planning to ensure long-term financial and human capacity needs were sustained, beyond the life of the projects, or could be replicated at significant scales. Management outcomes in the Pacific will be enhanced by: (1) building on foundations of customary management practice and social networks; (2) working holistically across relevant ecological and governance scales, through coordinated but decentralized and nested institutions; (3) empowering local communities to participate in integrated planning and implementation; and (4) embedding IIM practice into national systems for long-term sustainability and replication. These also ultimately depend on the context and externalities, beyond the control of practitioners. Cost-effectiveness and appropriateness are also critical for successful IIM in the Pacific islands but ultimately there is little alternative for effective biodiversity conservation