Factors aff ecting lipid and fatty acid composition of Calanus sinicus in the Yellow Sea and the East China Sea in spring

The factors aff ecting lipid and fatty acid composition of copepod Calanus sinicus in the Yellow Sea(YS)and the East China Sea(ECS)were examined in this study.In spring,there were signifi cant diff erences between these two regions for both environmental conditions and food availability.Such regional diff erence signifi cantly infl uenced the lipid and fatty acid profi les of C.sinicus.Our results show that C.sinicus has a higher lipids content in ECS,especially for wax ester and triglyceride lipids,indicating a more active and effi cient predation.According to BIO-ENV analysis,the variation of lipids profi les may be infl uenced majorly by water temperature.Moreover,the fatty acids(FAs)profi les of C.sinicus were also diff erent between YS and ECS,especially in the four major contributors,C22꞉1ω11,eicosapentaenoic acid(EPA),docosahexenoic acid(DHA),and C20꞉1ω9.The considerable amounts of self-biosynthesized FAs of herbivorous copepod(C22꞉1ω11 and C20꞉1ω9)and low DHA/EPA ratio may indicate that C.sinicus in ECS feed mainly on phytoplankton comparing to those in YS.The fatty acid profi les of C.sinicus were aff ected by the diff erences in food availability.

Feeding strategies of Euphausia superba in the eastern South Shetland Islands in austral summer

Euphausia superba is a key species in the Southern Ocean that serves as a link between primary production and higher trophic levels.To investigate the feeding strategies of E.superba from the eastern South Shetland Islands,fatty acid biomarkers,stable isotope signatures,and an incubation experiment were conducted.The results of the incubation experiment proved that adult E.superba mainly fed on 2–20μm particles,demonstrating the importance of nanoplankton in their diet.Moreover,significant positive relationships betweenδ15N and body size demonstrated that size-related dietary shifts were present in E.superba.Evidence from principal component analysis and the C16:1ω7/C18:4ω3 ratio showed that juveniles preferentially fed on dinoflagellates and adults were more likely to feed on diatoms.Fatty acid profiles in adult E.superba roughly mirrored the different trophic conditions and feeding strategies between stations.Adult E.superba at Stas D2-07,D5-07,DA-01 and DA-02 exhibited elevated levels of C16:1ω7,C18:4ω3,C18:1ω9 and C18:1ω9/C18:1ω7,indicating higher levels of feeding on both phytoplankton and higher trophic diets.In contrast,adult E.superba at Stas D1-03 and D1-04 were characterized by high levels of polyunsaturated fatty acids/saturated fatty acids ratios and low levels of C16:1ω7,C18:1ω7,C18:4ω3,C18:1ω9 and total fatty acids.We inferred that adult krill at Stas D1-03 and D1-04 still suffered from difficult dietary conditions after overwintering.The different dietary conditions between stations suggest a highly plastic feeding strategy of E.superba in the eastern South Shetland Islands.

Dietary preferences and potential ecological impact on the zooplankton community of Nemopilema nomurai based on stable isotope and fatty acid analyses

Information on the dietary composition and food preferences of the giant jellyfish Nemopilema nomurai is important for understanding the trophic drivers of jellyfish outbreaks and their ecological consequences.We used fatty acid(FA)and stable isotope(SI)biomarkers to analyze the diet of N.nomurai from the Yellow Sea in August 2016.N.nomurai was found at all sampling stations,with abundances ranging from 59 inds./km^(2) to 1651 inds./km^(2).There were no significant differences between large(>80 cm in diameter)and small(20–30 cm in diameter)medusae,either in FA compositions or in SI values,which suggests that large and small jellyfi sh have the same food composition and similar trophic levels.Compared to other zooplanktons,the relatively high levels of C20꞉4n-6 in total FAs(~12%)indicates that organic detritus contributes considerably to the food composition of the jellyfish.The mixed model Stable Isotope Analysis in R(SIAR)revealed that N.nomurai tended to prey on smaller organisms(<1000μm in diameter)which comprised about 70%of its diet.This means the N.nomurai blooms will put high feeding pressure on the small plankton.The similar SI values and FA composition indicates that krill may share the same food resources with N.nomurai,which suggests that the jellyfi sh blooms may affect krill populations as a result of food competition.

Distribution,ecology,and oxygen and carbon isotope characteristics of modern planktonic foraminifers in the Makarov Basin of the Arctic Ocean

The Arctic region, with magnificent ice cover on the surface of the Arctic Ocean and adjacent seas, is not only extremely sensitive to but also has strong amplification effects on climate change. Observations during the past decades have documented substantial retreat and thinning of the Arctic sea-ice cover, a process that is accelerating. Its feedback and impact on the global climate has become an important subject of current climate change research. Calcite tests of planktonic foraminifers are major constituents in pelagic sediments, and they provide valuable materials for the reconstruction of past oceanographic conditions. However, research is still sparse in the Arctic sea area because of limited availability of the materials for investigation. Here, we present a study of modern foraminifers from the plankton tow samples taken in the Makarov Basin of the Arctic Ocean during the fourth Arctic expedition of China. We have analyzed ecological information stored in the modern planktonic foraminifers and in their stable isotope signals, and established a relationship between the distribution of the main taxa and the environment. Our main observations are as follows:(1) in the Makarov Basin, the polar species Neogloboquadrina pachyderma(sinistral coiling) dominates the [150 lm planktonic foraminiferal assemblages.(2) The planktonic foraminifers live mainly in the upper halocline at a water depth of 50–100 m and less in the depth interval of 100–200 m.(3) Temperature change in the halocline can affect the absolute abundance of planktonic foraminifers and their distribution in the water column. The warmer halocline is more favorable to the development of planktonic foraminifers.(4) A lighter d18O value(2.11 %) of N. pachyderma(sin.) is recorded in the depth interval of 100–200 m, which is likely related to the isotopically light brines separated out during sea ice freezing. The relatively heavy d18O value(1.68 %–2.68 %, average 2.27 %) in the depth interval of 50–100 m may be influenced by the low salinity water with the relatively heavy d18O value formed during the sea-ice melting in the surface layer.