Search

Phytoplankton alter their biochemical composition according to nutrient availability, such that their bulk elemental composition varies across oceanic provinces. However, the links between plankton biochemical composition and variation in biogeochemical cycling of nutrients remain largely unknown. In a survey of phytoplankton phosphorus stress in the western North Atlantic, we found that phytoplankton in the phosphorus-depleted subtropical Sargasso Sea were enriched in the biochemical polyphosphate (polyP) compared with nutrient-rich temperate waters, contradicting the canonical oceanographic view of polyP as a luxury phosphorus storage molecule. The enrichment in polyP coincided with enhanced alkaline phosphatase activity and substitution of sulfolipids for phospholipids, which are both indicators of phosphorus stress. Further, polyP appeared to be liberated preferentially over bulk phosphorus from sinking particles in the Sargasso Sea, thereby retaining phosphorus in shallow waters. Thus, polyP cycling may form a feedback loop that attenuates the export of phosphorus when it becomes scarce, contributes bioavailable P for primary production, and supports the export of carbon and nitrogen via sinking particles. [ABSTRACT FROM AUTHOR]

The European eel migrates 5,000–6,000 km to the Sargasso Sea to reproduce. Because they venture into the ocean in a pre-pubertal state and reproduce after swimming for months, a strong interaction between swimming and sexual maturation is expected. Many swimming trials have been performed in 22 swim tunnels to elucidate their performance and the impact on maturation. European eels are able to swim long distances at a cost of 10–12 mg fat/km which is 4–6 times more efficient than salmonids. The total energy costs of reproduction correspond to 67% of the fat stores. During long distance swimming, the body composition stays the same showing that energy consumption calculations cannot be based on fat alone but need to be compensated for protein oxidation. The optimal swimming speed is 0.61–0.67 m s, which is ~60% higher than the generally assumed cruise speed of 0.4 m s and implies that female eels may reach the Sargasso Sea within 3.5 months instead of the assumed 6 months. Swimming trials showed lipid deposition and oocyte growth, which are the first steps of sexual maturation. To investigate effects of oceanic migration on maturation, we simulated group-wise migration in a large swim-gutter with seawater. These trials showed suppressed gonadotropin expression and vitellogenesis in females, while in contrast continued sexual maturation was observed in silver males. The induction of lipid deposition in the oocytes and the inhibition of vitellogenesis by swimming in females suggest a natural sequence of events quite different from artificial maturation protocols. [ABSTRACT FROM AUTHOR]

Abstract: Potential biogenic sources of ultrafiltered dissolved and suspended particulate organic matter (UDOM and POM, respectively) from the Sargasso Sea (SS) and North Central Pacific (NCP) Ocean were investigated using lipid biomarker compounds. Organic carbon (OC) concentrations were ~20–40 times greater in UDOM than POM and decreased with depth. However, total OC-normalized lipid concentrations were 2–3 orders of magnitude higher in POM than in UDOM. Particulate total lipids decreased 3–10-fold with depth, compared to 10–20% for dissolved total lipids. Total fatty acids (FA), the most abundant lipids, showed similar patterns as total lipids, comprising ~62–88% of the total lipids analyzed in UDOM and ~57–84% in POM. FA were dominated by straight-chain saturated compounds followed by monounsaturated, polyunsaturated, and branched FA. Polyunsaturated FA were enriched in POM vs. UDOM and in surface vs. deep waters for both UDOM and POM, likely reflecting the algal origins and greater reactivity of surface-derived materials. In both UDOM and POM, sterols of planktonic origin dominated, including cholest-5-en-3β-ol (C27Δ5), 24-methylcholesta-5,24(28)E-dien-3β-ol (C28Δ5,24(28)) and 24-ethylcholest-5-3β-ol (C29Δ5), with varying contributions from cholesta-5,22E-3β-ol (C27Δ5,22), 24-methylcholesta-5,22E-3β-ol (C28Δ5,22) and 24-ethylcholesta-5,22E-3β-ol (C29Δ5,22). Factor analysis of lipid biomarkers showed major differences between the UDOM and POM pools and for each pool as a function of depth, but not between the SS and NCP. While UDOM and POM biomarkers were both dominated by autochthonous sources, differences between the two pools suggest potential effects from some combination of source and diagenetic factors. The lipid biomarker data are further evaluated relative to previous studies of radiocarbon (14C) and elemental (C:N:P) characteristics of UDOM and POM in the SS and NCP. [Copyright &y& Elsevier]