scholarly journals Seasonal variability and vertical distribution of autotrophic and heterotrophic picoplankton in the Central Red Sea

PeerJ ◽  
2020 ◽  
Vol 8 ◽  
pp. e8612 ◽  
Author(s):  
Najwa Al-Otaibi ◽  
Tamara M. Huete-Stauffer ◽  
Maria Ll. Calleja ◽  
Xabier Irigoien ◽  
Xosé Anxelu G. Morán

The Red Sea is characterized by higher temperatures and salinities than other oligotrophic tropical regions. Here, we investigated the vertical and seasonal variations in the abundance and biomass of autotrophic and heterotrophic picoplankton. Using flow cytometry, we consistently observed five groups of autotrophs (Prochlorococcus, two populations of Synechococcus separated by their relative phycoerythrin fluorescence, low (LF-Syn) and high (HF-Syn), and two differently-sized groups of picoeukaryotes, small (Speuk) and large (Lpeuk)) and two groups of heterotrophic prokaryotes of low and high nucleic acid content (LNA and HNA, respectively). Samples were collected in 15 surveys conducted from 2015 to 2017 at a 700-m depth station in the central Red Sea. Surface temperature ranged from 24.6 to 32.6 °C with a constant value of 21.7 °C below 200 m. Integrated (0–100 m) chlorophyll a concentrations were low, with maximum values in fall (24.0 ± 2.7 mg m−2) and minima in spring and summer (16.1 ± 1.9 and 1.1 mg m−2, respectively). Picoplankton abundance was generally lower than in other tropical environments. Vertical distributions differed for each group, with Synechococcus and LNA prokaryotes more abundant at the surface while Prochlorococcus, picoeukaryotes and HNA prokaryotes peaked at the deep chlorophyll maximum, located between 40 and 76 m. Surface to 100 m depth-weighted abundances exhibited clear seasonal patterns for Prochlorococcus, with maxima in summer (7.83 × 104 cells mL−1, July 2015) and minima in winter (1.39 × 104 cells mL−1, January 2015). LF-Syn (0.32 – 2.70 × 104 cells mL−1 ), HF-Syn (1.11 – 3.20 × 104 cells mL−1) and Speuk (0.99 – 4.81 × 102 cells mL−1) showed an inverse pattern to Prochlorococcus, while Lpeuk (0.16 – 7.05 × 104 cells mL−1) peaked in fall. Synechococcus unexpectedly outnumbered Prochlorococcus in winter and at the end of fall. The seasonality of heterotrophic prokaryotes (2.29 – 4.21×105 cells mL−1 ) was less noticeable than autotrophic picoplankton. The contribution of HNA cells was generally low in the upper layers, ranging from 36% in late spring and early summer to ca. 50% in winter and fall. Autotrophs dominated integrated picoplankton biomass in the upper 100 m, with 1.4-fold higher values in summer than in winter (mean 387 and 272 mg C m–2, respectively). However, when the whole water column was considered, the biomass of heterotrophic prokaryotes exceeded that of autotrophic picoplankton with an average of 411 mg C m–2. Despite being located in tropical waters, our results show that the picoplankton community seasonal differences in the central Red Sea are not fundamentally different from higher latitude regions.

2021 ◽  
Vol 8 ◽  
Author(s):  
Najwa Al-Otaibi ◽  
Francisca C. García ◽  
Xosé Anxelu G. Morán

The diel variability of the abundance and cell size of picoplanktonic groups in the central Red Sea was monitored every 2 h in situ on 4 occasions (once per season) from 2015 to 2016. We distinguished Prochlorococcus, low (LF-Syn) and high (HF-Syn) fluorescence Synechococcus, small (Speuk) and large (Lpeuk) picoeukaryotes and two groups of heterotrophic prokaryotes of low (LNA) and high (HNA) nucleic acid content. The diel variability in abundance was less marked than in cell size and more apparent in autotrophs than heterotrophs. Specific growth rates were estimated by an empirical relationship from measurements obtained in bottle incubations of surface and deep samples collected in the winter compared with in situ variations in cell size over 24 h. Autotrophic picoplankton groups generally grew faster (0.23–0.77 d–1) than heterotrophic prokaryotes (0.12–0.50 d–1). Surface to 100 m depth-weighted specific growth rates displayed a clear seasonal pattern for Prochlorococcus, with maxima in winter (0.77 ± 0.07 d–1) and minima in fall (0.52 ± 0.07 d–1). The two groups of Synechococcus peaked in spring, with slightly higher growth rates of LF-Syn (0.57 ± 0.04 d–1) than HF-Syn (0.43 ± 0.04 d–1). Speuk and Lpeuk showed different seasonal patterns, with lower values of the former (0.27 ± 0.02 and 0.37 ± 0.04 d–1, respectively). HNA consistently outgrew LNA heterotrophic prokaryotes, with a higher growth in the epipelagic (0–200 m, 0.36 ± 0.03 d–1) than in the mesopelagic (200–700 m, 0.26 ± 0.03 d–1), while no differences were found for LNA cells (0.19 ± 0.03 d–1 and 0.17 ± 0.02 d–1, respectively). With all data pooled, the mean diel abundances of autotrophic picoplankton in the upper epipelagic and of HNA cells in the epipelagic and mesopelagic layers were significantly correlated with the specific growth rates estimated from cell size variations. Our high-resolution sampling dataset suggests that changes in growth rates underlie the noticeable seasonality of picoplankton recently described in these tropical waters.


Agronomy ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 2253
Author(s):  
Myrish Pacleb ◽  
O-Young Jeong ◽  
Jeom-Sig Lee ◽  
Thelma Padolina ◽  
Rustum Braceros ◽  
...  

Temperate japonica rice is mainly cultivated in temperate regions. Many temperate japonica varieties have a superior grain quality that is preferred in Northeast Asian countries such as Japan, Korea, and China. The changes in consumers’ preferences in Southeast Asia and Western countries has contributed to increasing the demand for temperate japonica. Most temperate japonica varieties developed in temperate regions typically exhibit extra-early flowering under the short-day conditions in the tropics, which usually results in severely reduced yields. Since 1992, we have been developing temperate japonica varieties that can adapt to tropical environments to meet the increasing demand for temperate japonica rice, having released six varieties in the Philippines. Especially, the yield of one of the temperate japonica varieties, Japonica 7, was comparable to the yields of leading indica varieties in the Philippines. Here, we discuss the current breeding initiatives and future plans for the development of tropical-region-bred temperate japonica rice.


Author(s):  
Jacqueline Scotcher

<p>Walking and the tropical Far North Queensland landscape of Australia have had a major influence on the author’s creative research. In this paper, immersive practice, which includes walking, is examined as a means to form connections with the natural environment and stimulate imaginative thought. These attributes have developed the author’s painting processes, which endeavour to enrich understandings of the landscapes of tropical far north Queensland. An immersive approach responds to the complexities of increasingly sedentary lifestyles and the tendency to engage with digital distractions in our high speed media-connected world. In this fast-paced realm, meaningful relationships with the natural environment can be reduced, with meandering and imaginative pursuits often becoming neglected. Living in Far North Queensland provides easy access to unique tropical landscapes to engage with. Walking receptively in such natural environments can provide a physical and mental counterpoint to  contemporary fastpaced lifestyles. Furthermore, walking provides opportunities to engage in ‘mindwandering’ and embodied experience that can enrich painting practice.</p><p><br />The research presented in this paper celebrates life in tropical Far North Queensland and highlights the artist’s experience in this particular part of the world. Recently, the 29th of June was designated the International Day of the Tropics by the UN General Assembly, a day founded to raise  awareness and consideration of both the challenges and opportunities faced by tropical regions of the world. (stateofthetropics.org). This designated day provides space for the author/artist to reflect upon the diverse culture and ecosystems of the region and position her artistic practice within a broader context of ideas relating to tropical environments.</p>


2018 ◽  
Vol 5 ◽  
Author(s):  
Maria L. Calleja ◽  
Mohd I. Ansari ◽  
Anders Røstad ◽  
Luis Silva ◽  
Stein Kaartvedt ◽  
...  

2007 ◽  
Vol 73 (7) ◽  
pp. 2101-2109 ◽  
Author(s):  
Audrey Caro ◽  
Olivier Gros ◽  
Patrice Got ◽  
Rutger De Wit ◽  
Marc Troussellier

ABSTRACT We investigated the characteristics of the sulfur-oxidizing symbiont hosted in the gills of Codakia orbicularis, a bivalve living in shallow marine tropical environments. Special attention was paid to describing the heterogeneity of the population by using single-cell approaches including flow cytometry (FCM) and different microscopic techniques and by analyzing a cell size fractionation experiment. Up to seven different subpopulations were distinguished by FCM based on nucleic acid content and light side scattering of the cells. The cell size analysis of symbionts showed that the symbiotic population was very heterogeneous in size, i.e., ranging from 0.5 to 5 μm in length, with variable amounts of intracellular sulfur. The side-scatter signal analyzed by FCM, which is often taken as a proxy of cell size, was greatly influenced by the sulfur content of the symbionts. FCM revealed an important heterogeneity in the relative nucleic acid content among the subclasses. The larger cells contained exceptionally high levels of nucleic acids, suggesting that these cells contained multiple copies of their genome, i.e., ranging from one copy for the smaller cells to more than four copies for the larger cells. The proportion of respiring symbionts (5-cyano-2,3-ditolyl-terazolium chloride positive) in the bacteriocytes of Codakia revealed that around 80% of the symbionts hosted by Codakia maintain respiratory activity throughout the year. These data allowed us to gain insight into the functioning of the symbionts within the host and to propose some hypotheses on how the growth of the symbionts is controlled by the host.


1978 ◽  
Vol 56 (6) ◽  
pp. 1420-1429 ◽  
Author(s):  
M. J. Pybus ◽  
L. S. Uhazy ◽  
R. C. Anderson

Field data from two populations of Lampetra lamottenii (Lesueur, 1827) in Ontario, combined with informattion from experimental studies, have provided the following explanation of the transmission of Truttaedacnitis stelmioides (Vessichelli, 1910). Eggs hatch on the stream bed in spring and early summer. Newly hatched larvae are ingested by filter-feeding ammocoetes and remain in the intestine throughout the summer. After developing to the third stage, larvae migrate via the bile duct to cystic ducts of the liver where they remain in a state of arrested development for up to 4 years. During transformation of the host, third-stage larvae apparently moult at least once in the liver, reenter the intestine, and develop to maturity in transformers and adult lampreys. Eggs are released into the lamprey intestine and eventually passed from the anus. Transmission occurs mainly in early summer. Truttaedacnitis stelmioides never becomes encapsulated in the gut wall of L. lamottenii although it may in other lamprey species. Lampetra lamottenii may be the most suitable host among the lampreys. The biology of the parasite is closely linked to the metamorphosis and maturation of the lamprey. Other cucullanids may have a similar relationship with their hosts. Possibly the cucullanids are basically heteroxenous in that they use the immature stage of the host (e.g. the ammocoete) as an intermediate host.


1986 ◽  
Vol 16 (4) ◽  
pp. 761-771 ◽  
Author(s):  
L. Kullman

The recent history of Piceaabies (L.) Karst. at its altitudinal tree limit has been studied in the southern Swedish Scandes. Altitudinal transects (131) were evenly distributed over a tract of mountains of ca. 40 × 200 km. The age of spruces growing at the tree limit and downhill were estimated by annual ring counts. The spruce tree limit had risen (on average by ca. 50 m altitudinally) in ca. 70% of the studied transects as a result of the subsequent growth in height of old, established, formerly stunted individuals. Their growth in height accelerated during the 1930's, in response to the general climatic warming. A rise in the tree limit because of the establishment of new individuals (after 1915) was noted in only 7% of the studied transects. Most of the spruces growing in the tree-limit ecotone established around the 1860's and the 1940's, which were epochs with relatively snowy winters. After 1860, spruce establishment was not correlated with the summer mean temperature. Successful regeneration of spruce at the tree limit is dependent of a deep and stable snow cover and the requisite balance between precipitation–meltwater and evaporation being maintained in the early summer. The importance of air temperatures in May for successful growth and natural regeneration was evident. High air temperature in May is detrimental, since it promotes a too early initiation of growth and a consequent increased risk of frost damage. The spruce populations at the tree limit are recruited both from local seed parents and from long distance dispersal of seed from trees growing at lower altitudes.


2015 ◽  
Vol 19 (1) ◽  
pp. 583-599 ◽  
Author(s):  
R. G. Anderson ◽  
D. Wang ◽  
R. Tirado-Corbalá ◽  
H. Zhang ◽  
J. E. Ayars

Abstract. Standardized reference evapotranspiration (ET) and ecosystem-specific vegetation coefficients are frequently used to estimate actual ET. However, equations for calculating reference ET have not been well validated in tropical environments. We measured ET (ETEC) using eddy covariance (EC) towers at two irrigated sugarcane fields on the leeward (dry) side of Maui, Hawaii, USA in contrasting climates. We calculated reference ET at the fields using the short (ET0) and tall (ETr) vegetation versions of the American Society for Civil Engineers (ASCE) equation. The ASCE equations were compared to the Priestley–Taylor ET (ETPT) and ETEC. Reference ET from the ASCE approaches exceeded ETEC during the mid-period (when vegetation coefficients suggest ETEC should exceed reference ET). At the windier tower site, cumulative ETr exceeded ETEC by 854 mm over the course of the mid-period (267 days). At the less windy site, mid-period ETr still exceeded ETEC, but the difference was smaller (443 mm). At both sites, ETPT approximated mid-period ETEC more closely than the ASCE equations ((ETPT-ETEC) < 170 mm). Analysis of applied water and precipitation, soil moisture, leaf stomatal resistance, and canopy cover suggest that the lower observed ETEC was not the result of water stress or reduced vegetation cover. Use of a custom-calibrated bulk canopy resistance improved the reference ET estimate and reduced seasonal ET discrepancy relative to ETPT and ETEC in the less windy field and had mixed performance in the windier field. These divergences suggest that modifications to reference ET equations may be warranted in some tropical regions.


2018 ◽  
Vol 20 (8) ◽  
pp. 2990-3000 ◽  
Author(s):  
Francisca C. García ◽  
Maria L. Calleja ◽  
Najwa Al-Otaibi ◽  
Anders Røstad ◽  
Xosé Anxelu G. Morán

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