Derivative analysis of spectral absorption by photosynthetic pigments in the western Sargasso Sea

Concurrent measurements of the spectral absorption coefficient and photosynthetic pigmentation of natural particulates were performed to determine the principal pigments responsible for the absorption of spectral irradiance in seawater. The spectral absorption coefficient, Ap(λ), was then analyzed by taking the second and fourth derivatives with respect to wavelength. The wavelength and magnitude of these derivative values provide useful information regarding the identification and quantification of phytoplankton pigments responsible for a given spectral signature. Linear relationships were examined and established between derivative values at selected wavelengths and concentrations of the major tetrapyrrole pigments, specifically chlorophylls a, b, and c. The correlation between derivative values near 526 nm and concentrations of photosynthetic carotenoids was poor and presumably caused by the broad absorption spectra of these pigments. A comparison of the measured particulate absorption coefficient with the absorption coefficient reconstructed for the phytoplankton component revealed that detritus can be a major source of light absorption. The method described here provides a rapid means of obtaining estimates of photosynthetic pigment concentrations in natural samples where absorption can be strongly influenced by detrital matter

Meridional variations of the springtime phytoplankton community in the Sargasso Sea

Meridional distributions of particle, pigment, optical, chemical and physical in situ oceanographic properties, as well as satellite-sensed sea-surface temperature and color imagery, are used to investigate phytoplankton community distributions and their relation to the near-surface water masses of the S bnargasso Sea. 0-H3059 Measurements were made during April of 1985 along a 1200 km transect on 70W (from 24N to 35N). The seasonal evolution of subtropical Mode water (18° water) is shown to be the primary factor controlling the spatial distribution and evolution of the phytoplankton community in the northern Sargasso Sea (31 to 35N). The springtime near-surface restratification of recently ventilated 18° water initiated a diatom-dominated phytoplankton bloom. As the bloom declined, the phytoplankton community evolved into a diverse assemblage. The consequences of these phytoplankton successions were observed both temporally and as spatial variations along the meridional section. South of the region of 18° water wintertime ventilation (south of 31N), phytoplankton concentrations were considerably less and appeared to be regulated by different processes than the northern region. In particular, influences of subtropical convergence fronts were observed. For the northern Sargasso Sea, the wintertime ventilation of 18° water is shown to be the primary new nutrient flux into the euphotic zone, comprising most of the expected annual new production for this region

Bioluminescence of Colonial Radiolaria in the Western Sargasso Sea

Colonial radiolaria (Protozoa: Spumellarida) were a conspicuous feature in surface waters of the Sargasso Sea during the April (1985) Biowatt cruise. The abundance of colonies at the sea surface at one station was estimated to be 23 colonies · m−2. Bioluminescence by colonial radiolaria, representing at least six taxa, was readily evoked by mechanical stimuli and measured by fast spectroscopy and photon-counting techniques. Light emission was deep blue in color (peak emissions between 443 and 456 nm) and spectral distributions were broad (average half bandwidth of 80 nm). Single flashes were 1–2 s in duration at ≈23 °C, with species-dependent kinetics which were not attributed to differences in colony morphology, since colonies similar in appearance could belong to different species (even families) and display different flash kinetics. Although the presence of dinoflagellate symbionts was confirmed by the presence of dinoflagellate marker pigments in the colonies, luminescence in the radiolaria examined most likely did not originate from symbiotic dinoflagellates because of (1) differences in the emission spectra, (2) unresponsiveness to low pH stimulation, (3) differences in flash kinetics and photon emission of light emission, and (4) lack of light inhibition. The quantal content of single flashes averaged 1 × 109 photons flash−1, and colonies were capable of prolonged light emission. The mean value of bioluminescence potential based on measurements of total mechanically stimulated bioluminescence was 1.2 × 1011 photons · colony−1. It is estimated that colonial radiolaria are capable of producing ≈2.8 × 1012 photons · m−2 of sea surface. However, this represented only 0.5% of in situ measured bioluminescence potential

Diversity and productivity of photosynthetic picoeukaryotes in biogeochemically distinct regions of the South East Pacific Ocean

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Limnology and Oceanography 61 (2016): 806–824, doi:10.1002/lno.10255.Picophytoplankton, including photosynthetic picoeukaryotes (PPE) and unicellular cyanobacteria, are important contributors to plankton biomass and primary productivity. In this study, phytoplankton composition and rates of carbon fixation were examined across a large trophic gradient in the South East Pacific Ocean (SEP) using a suite of approaches: photosynthetic pigments, rates of 14C-primary productivity, and phylogenetic analyses of partial 18S rRNA genes PCR amplified and sequenced from flow cytometrically sorted cells. While phytoplankton >10 μm (diatoms and dinoflagellates) were prevalent in the upwelling region off the Chilean coast, picophytoplankton consistently accounted for 55–92% of the total chlorophyll a inventories and >60% of 14C-primary productivity throughout the sampling region. Estimates of rates of 14C-primary productivity derived from flow cytometric sorting of radiolabeled cells revealed that the contributions of PPE and Prochlorococcus to euphotic zone depth-integrated picoplankton productivity were nearly equivalent (ranging 36–57%) along the transect, with PPE comprising a larger share of picoplankton productivity than cyanobacteria in the well-lit (>15% surface irradiance) region compared with in the lower regions (1–7% surface irradiance) of the euphotic zone. 18S rRNA gene sequence analyses revealed the taxonomic identities of PPE; e.g., Mamiellophyceae (Ostreococcus) were the dominant PPE in the upwelling-influenced waters, while members of the Chrysophyceae, Prymnesiophyceae, Pelagophyceae, and Prasinophyceae Clades VII and IX flourished in the oligotrophic South Pacific Subtropical Gyre. Our results suggest that, despite low numerical abundance in comparison to cyanobacteria, diverse members of PPE are significant contributors to carbon cycling across biogeochemically distinct regions of the SEP.Support for this work derived from U.S. National Science Foundation grants to C-MORE (EF-0424599; DMK) and OCE-1241263 (MJC). Additional support was received from the University of Hawai'i Denise B. Evans Research Fellowship in Oceanography (YMR), the Gordon and Betty Moore Foundation (DMK), and the Simons Foundation via the Simons Collaboration on Ocean Processes and Ecology (SCOPE: DJR, MJC, and DMK)

Light driven seasonal patterns of chlorophyll and nitrate in the lower euphotic zone of the North Pacific Subtropical Gyre

The euphotic zone below the deep chlorophyll maximum layer (DCML) at Station ALOHA (a long-term oligotrophic habitat assessment; 22º45′N, 158º00′W) transects the nearly permanently stratified upper thermocline. Hence, seasonal changes in solar radiation control the balance between photosynthesis and respiration in this lightlimited region. Combining profiles of radiance reflectance, algal pigments, and inorganic nutrients collected between January 1998 and December 2000, we explore the relationships between photosynthetically available radiation (PAR), phytoplankton biomass (chlorophyll a), and the position of the upper nitracline in the lower euphotic zone. Seasonal variations in the water-column PAR attenuation coefficient displace the 1% sea-surface PAR depth from approximately 105 m in winter to 121 m in summer. However, the seasonal depth displacement of isolumes (constant daily integrated photon flux strata) increases to 31 m due to the added effect of changes in sea-surface PAR. This variation induces a significant deepening of the DCML during summertime with a concomitant increase in chlorophyll a and the removal of 36 mmol m22 inorganic nitrogen [NO–3 NO–2] in the 90–200-m depth range, equivalent to approximately 34% of the annual flux of particulate nitrogen collected in sediment traps placed at 150 m. We conclude that in this oceanic region the annual light cycle at the base of the euphotic zone induces an increase in the phototrophic biomass analogous to a spring bloom event

The Anti-Inflammatory Effect of Algae-Derived Lipid Extracts on Lipopolysaccharide (LPS)-Stimulated Human THP-1 Macrophages

Algae contain a number of anti-inflammatory bioactive compounds such as omega-3 polyunsaturated fatty acids (n-3 PUFA) and chlorophyll a, hence as dietary ingredients, their extracts may be effective in chronic inflammation-linked metabolic diseases such as cardiovascular disease. In this study, anti-inflammatory potential of lipid extracts from three red seaweeds (Porphyra dioica, Palmaria palmata and Chondrus crispus) and one microalga (Pavlova lutheri) were assessed in lipopolysaccharide (LPS)-stimulated human THP-1 macrophages. Extracts contained 34%–42% total fatty acids as n-3 PUFA and 5%–7% crude extract as pigments, including chlorophyll a, β-carotene and fucoxanthin. Pretreatment of the THP-1 cells with lipid extract from P. palmata inhibited production of the pro-inflammatory cytokines interleukin (IL)-6 (p < 0.05) and IL-8 (p < 0.05) while that of P. lutheri inhibited IL-6 (p < 0.01) production. Quantitative gene expression analysis of a panel of 92 genes linked to inflammatory signaling pathway revealed down-regulation of the expression of 14 pro-inflammatory genes (TLR1, TLR2, TLR4, TLR8, TRAF5, TRAF6, TNFSF18, IL6R, IL23, CCR1, CCR4, CCL17, STAT3, MAP3K1) by the lipid extracts. The lipid extracts effectively inhibited the LPS-induced pro-inflammatory signaling pathways mediated via toll-like receptors, chemokines and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling molecules. These results suggest that lipid extracts from P. lutheri, P. palmata, P. dioica and C. crispus can inhibit LPS-induced inflammatory pathways in human macrophages. Therefore, algal lipid extracts should be further explored as anti-inflammatory ingredients for chronic inflammation-linked metabolic diseases