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

High contributions of sea ice derived carbon in polar bear (Ursus maritimus) tissue.

Polar bears (Ursus maritimus) rely upon Arctic sea ice as a physical habitat. Consequently, conservation assessments of polar bears identify the ongoing reduction in sea ice to represent a significant threat to their survival. However, the additional role of sea ice as a potential, indirect, source of energy to bears has been overlooked. Here we used the highly branched isoprenoid lipid biomarker-based index (H-Print) approach in combination with quantitative fatty acid signature analysis to show that sympagic (sea ice-associated), rather than pelagic, carbon contributions dominated the marine component of polar bear diet (72-100%; 99% CI, n = 55), irrespective of differences in diet composition. The lowest mean estimates of sympagic carbon were found in Baffin Bay bears, which were also exposed to the most rapidly increasing open water season. Therefore, our data illustrate that for future Arctic ecosystems that are likely to be characterised by reduced sea ice cover, polar bears will not only be impacted by a change in their physical habitat, but also potentially in the supply of energy to the ecosystems upon which they depend. This data represents the first quantifiable baseline that is critical for the assessment of likely ongoing changes in energy supply to Arctic predators as we move into an increasingly uncertain future for polar ecosystems

BETTER KNOWLEDGE OF C, N, P ELEMENTS AND STOICHIOMETRY THROUGH THE SECONDARY PRODUCERS CALANOID COPEPODS IN ARCTIC AREAS

participantGeochemical fluxes have received particular attention in marine ecosystems in the context of climate changes and potential CO2 sequestration by the oceans. In addition, areas where changes are expected to be the most important and the fastest are the polar ones and especially the Arctic Ocean. It is thus particularly important to better understand the role played by marine biological pump in regulating the essential elements, which are carbon, nitrogen but also phosphorous, in Arctic seas. Most of the regulation through the biological pump is realised by primary and secondary producers. In the arctic, few data are available on C, N and P elements and ratios of secondary producers. Those ratios can change according to several parameters including species, development stage, feeding mode, etc... Secondary producers are represented by zooplankton, of which 90% are copepods. One result of their feeding activities is the creation of faecal pellets, which can sink out of the euphotic zone and contribute to chemical fluxes. Faecal pellets produced by copepods in the first 50m depth are equivalent to 20% of the particulate carbon flux and 12% of the particulate nitrogen flux in the Arctic seas. Moreover copepods are known to ingest on average 45% of the primary production in Arctic water. It stress the point for an understanding of how stochiometric changes in C, N and P in food sources (primary producers) influence the contents and ratios of these elements in faecal pellets for future predictions of potential changes of the biochemical fluxes

Taking a mass-balance approach to assess marine plastics in the South China Sea

10.1016/j.marpolbul.2021.112708Marine Pollution Bulletin17111270

The blue carbon special edition – Introduction and overview

In May 2010 the United Nations Environment Programme convened a workshop to discuss the opportunities and constraints for developing a marine carbon markets building on experience of the protocols and processes developed for the Reducing Emissions from Deforestation and Forest Degradation (REDD) programme under the United Nations Framework for Climate Change Convention (UNFCCC). The workshop also considered other approaches to realising payment for marine ecosystem services. This special edition of Ocean and Coastal Management presents papers that synthesise the main themes of that workshop and uses the definition of ‘blue carbon’ provided by Herr et al. (2012): ‘carbon stored, sequestered or released from vegetated coastal ecosystems such as tidal salt marshes, mangroves and seagrass meadows’. This definition does not include carbon stored, sequestered or released by the open ocea

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