Spatial variability in iron nutritional status of large diatoms in the Sea of Okhotsk with special reference to the Amur River discharge

The Sea of Okhotsk is known as one of the most biologically productive regions among the world's oceans, and its productivity is supported in part by the discharge of iron (Fe)-rich water from the Amur River. However, little is known about the effect of riverine-derived Fe input on the physiology of the large diatoms which often flourish in surface waters of the productive continental shelf region. We conducted diatom-specific immunochemical ferredoxin (Fd) and flavodoxin (Fld) assays in order to investigate the spatial variability of Fe nutritional status in the microplankton-sized (20–200 μm; hereafter micro-sized) diatoms. The Fd index, defined as the proportion of Fd to the sum of Fd plus Fld accumulations in the cells, was used to assess their Fe nutritional status. Additionally, active chlorophyll fluorescence measurements using pulse–amplitude-modulated (PAM) fluorometry were carried out to obtain the maximum photochemical quantum efficiency (<i>F</i>_v/<i>F</i>_m) of photosystem II for the total micro-sized phytoplankton assemblages including diatoms. During our observations in the summer of 2006, the micro-sized diatoms were relatively abundant (> 10 μg C L^&minus;1) in the neritic region, and formed a massive bloom in Sakhalin Bay near the mouth of the Amur River. Values of the Fd index and <i>F</i>_v/<i>F</i>_m were high (>0.9 and >0.65, respectively) near the river mouth, indicating that Fe was sufficient for growth of the diatoms. However, in oceanic waters of the Sea of Okhotsk, the diatom Fd index declined as cellular Fld accumulation increased. These results suggest that there was a distinct gradient in Fe nutritional status in the micro-sized diatoms from near the Amur River mouth to open waters in the Sea of Okhotsk. A significant correlation between dissolved Fe (D-Fe) concentration and the Fd index was found in waters off Sakhalin Island, indicating that D-Fe was a key factor for the photophysiology of this diatom size class. In the vicinity of the Kuril Islands between the Sea of Okhotsk and the Pacific Ocean, micro-sized diatoms only accumulated Fld (i.e., Fd index = 0), despite strong vertical mixing consistent with elevated surface D-Fe levels (>0.4 nM). Since higher Fe quotas are generally required for diatoms growing under low-light conditions, the micro-sized diatoms off the Kuril Islands possibly encountered Fe and light co-limitations. The differential expressions of Fd and Fld in micro-sized diatoms helped us to understand how these organisms respond to Fe availability in the Sea of Okhotsk in connection with the Amur River discharge

Responses of phytoplankton assemblages to iron availability and mixing water masses during the spring bloom in the Oyashio region, NW Pacific

Spring phytoplankton blooms play a major role in the carbon biogeochemical cycle of the Oyashio region, western subarctic Pacific, where the seasonal biological drawdown effect on seawater pCO 2 is one of the greatest among the world\u27s oceans. However, the bloom often terminates before depleting macronutrients, and the initiation and magnitude of the bloom is heterogeneous. We conducted a high resolution taxonomic and physiological assessment of phytoplankton in relation to the different physicochemical water masses of Coastal Oyashio Water (COW), Oyashio water (OYW), and modified Kuroshio water (MKW) in the Oyashio region from April to June 2007. Massive diatom blooms were found in April. Then, chlorophyll a concentration, cell abundance of diatom taxa, and the maximum photosystem II photochemical efficiency (F v /F m ) were positively correlated with the mixing ratios of COW, suggesting that the spring bloom in April was strongly affected by the intrusion of COW. In the OYW, intensive blooms occurred from the middle of May under low dissolved iron (DFe) concentration (\u3c 0.26 nM). Redundancy analysis showed that while diatom blooms accompanied by COW were related to DFe concentration, this was not the case in the OYW. These results indicated that diatoms in the OYW possess different iron adaptation strategies compared with diatoms in the water masses affected by COW. This led to the spatial heterogeneity of the Oyashio spring bloom. The results presented here demonstrate that water mass characterization with detailed assessments of phytoplankton taxonomy and physiological status can improve our understanding of marine ecosystems

Synoptic relationships between surface Chlorophyll-<i>a</i> and diagnostic pigments specific to phytoplankton functional types

Error-quantified, synoptic-scale relationships between chlorophyll-<i>a</i> (Chl-<i>a</i>) and phytoplankton pigment groups at the sea surface are presented. A total of ten pigment groups were considered to represent three Phytoplankton Size Classes (PSCs, micro-, nano- and picoplankton) and seven Phytoplankton Functional Types (PFTs, i.e. diatoms, dinoflagellates, green algae, prymnesiophytes (haptophytes), pico-eukaryotes, prokaryotes and <i>Prochlorococcus</i> sp.). The observed relationships between Chl-<i>a</i> and PSCs/PFTs were well-defined at the global scale to show that a community shift of phytoplankton at the basin and global scales is reflected by a change in Chl-<i>a</i> of the total community. Thus, Chl-<i>a</i> of the total community can be used as an index of not only phytoplankton biomass but also of their community structure. Within these relationships, we also found non-monotonic variations with Chl-<i>a</i> for certain pico-sized phytoplankton (pico-eukaryotes, Prokaryotes and <i>Prochlorococcus</i> sp.) and nano-sized phytoplankton (Green algae, prymnesiophytes). The relationships were quantified with a least-square fitting approach in order to enable an estimation of the PFTs from Chl-<i>a</i> where PFTs are expressed as a percentage of the total Chl-<i>a</i>. The estimated uncertainty of the relationships depends on both PFT and Chl-<i>a</i> concentration. Maximum uncertainty of 31.8% was found for diatoms at Chl-<i>a</i> = 0.49 mg m⁻³. However, the mean uncertainty of the relationships over all PFTs was 5.9% over the entire Chl-<i>a</i> range observed in situ (0.02 &lt; Chl-<i>a</i> &lt; 4.26 mg m^&minus;3). The relationships were applied to SeaWiFS satellite Chl-<i>a</i> data from 1998 to 2009 to show the global climatological fields of the surface distribution of PFTs. Results show that microplankton are present in the mid and high latitudes, constituting only ~10.9% of the entire phytoplankton community in the mean field for 1998–2009, in which diatoms explain ~7.5%. Nanoplankton are ubiquitous throughout the global surface oceans, except the subtropical gyres, constituting ~45.5%, of which prymnesiophytes (haptophytes) are the major group explaining ~31.7% while green algae contribute ~13.9%. Picoplankton are dominant in the subtropical gyres, but constitute ~43.6% globally, of which prokaryotes are the major group explaining ~26.5% (<i>Prochlorococcus</i> sp. explaining 22.8%), while pico-eukaryotes explain ~17.2% and are relatively abundant in the South Pacific. These results may be of use to evaluate global marine ecosystem models

Genetic variants in mannose receptor gene (MRC1) confer susceptibility to increased risk of sarcoidosis

<p>Abstract</p> <p>Background</p> <p>Mannose receptor (MR) is a member of the C-type lectin receptor family involved in pathogen molecular-pattern recognition and thought to be critical in shaping host immune response. The aim of this study was to investigate potential associations of genetic variants in the <it>MRC1 </it>gene with sarcoidosis.</p> <p>Methods</p> <p>Nine single nucleotide polymorphisms (SNPs), encompassing the <it>MRC1 </it>gene, were genotyped in a total of 605 Japanese consisting of 181 sarcoidosis patients and 424 healthy controls.</p> <p>Results</p> <p>Suggestive evidence of association between rs691005 SNP and risk of sarcoidosis was observed independent of sex and age in a recessive model (<it>P </it>= 0.001).</p> <p>Conclusions</p> <p>These results suggest that <it>MRC1 </it>is an important candidate gene for sarcoidosis. This is the first study to imply that genetic variants in <it>MRC1</it>, a major member of the C-type lectin, contribute to the development of sarcoidosis.</p

What Foreclosed Homes Should a Municipality Purchase to Stabilize Vulnerable Neighborhoods?

Housing, Foreclosures, Multi-objective programming, Urban affairs, Affordable housing,