AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 12:71-83 (1997) - doi:10.3354/ame012071 Dynamics of ciliate abundance, biomass and community composition in an oligotrophic coastal environment (NW Mediterranean) Vaqué D, Blough HA, DuarteCM The importance of ciliates as components of the microbial community of the oligotrophic coastal area of the Bay of Blanes (NW Mediterranean Sea) was examined based on a 3 yr, high resolution study focused on the composition, abundance and biomass of the ciliate community. The most abundant components of the ciliate community were 'oligotrich' ciliates. Naked oligotrichs included heterotrophic genera represented by Halteria, Strombidium, Strobilidium, and Lohmaniella, as well as mixotrophic genera represented by Laboea and Tontonia and loricate ciliates represented by the group of tintinnids. Autotrophic ciliates were represented by the genus Mesodinium. Other, less abundant groups encountered throughout the study period included the orders Scuticociliatida, Pleurostomatida and Prorodontida. Ciliate community abundance and biomass did not show a simple seasonal pattern. Maximum values were observed in spring, following the winter phytoplankton blooms, throughout the study period. Ciliate communities showed significant interannual differences in abundance and cell size. However, total ciliate biomass (μg C l-1) was similar among years. Changes in ciliate abundance and biomass were independent of temperature. Periods with persistent, heavy rainfall, which promotes pulses of allochthonous material from flushed rivers, were characterized by a reduced abundance of ciliates, and increased pico- and nanoplanktonic populations. Cross correlation analysis revealed that bacterial abundance and chlorophyll a (chl a) concentration were both significantly negatively correlated with ciliate abundance, with time lags of 15 d, suggesting a role for ciliates in the control of these communities. Examination of the variability of ciliate abundance and biomass at different time scales revealed a dominant scale of temporal variation in ciliate abundance at about 50 d, similar to that of chl a in the Bay of Blanes, whereas total ciliate biomass (μg C l-1) did not show any dominant scale of variation. Coastal area · Ciliate abundance and biomass · Community composition · Rainfall · Temporal variabilty Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 12, No. 1. Publication date: January 30, 1997 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1997 Inter-Research.
A perceived recent increase in global jellyfish abundance has been portrayed as a symptom of degraded oceans. This perception is based primarily on a few case studies and anecdotal evidence, but a formal analysis of global temporal trends in jellyfish populations has been missing. Here, we analyze all available long-term datasets on changes in jellyfish abundance across multiple coastal stations, using linear and logistic mixed models and effect-size analysis to show that there is no robust evidence for a global increase in jellyfish. Although there has been a small linear increase in jellyfish since the 1970s, this trend was unsubstantiated by effect-size analysis that showed no difference in the proportion of increasing vs. decreasing jellyfish populations over all time periods examined. Rather, the strongest nonrandom trend indicated jellyfish populations undergo larger, worldwide oscillations with an approximate 20-y periodicity, including a rising phase during the 1990s that contributed to the perception of a global increase in jellyfish abundance. Sustained monitoring is required over the next decade to elucidate with statistical confidence whether the weak increasing linear trend in jellyfish after 1970 is an actual shift in the baseline or part of an oscillation. Irrespective of the nature of increase, given the potential damage posed by jellyfish blooms to fisheries, tourism, and other human industries, our findings foretell recurrent phases of rise and fall in jellyfish populations that society should be prepared to face.
Atmospheric methane (CH4) is the second strongest greenhouse gas and it is emitted to the atmosphere naturally by different sources. It is crucial to define the dimension of these natural emissions in order to forecast changes in atmospheric CH4 mixing ratio in future scenarios. However, CH4 emissions by seagrass ecosystems in shallow marine coastal systems have been neglected although their global extension. Here we quantify the CH4 production rates of seagrass ecosystems in the Red Sea. We measured changes in CH4 concentration and its isotopic signature by cavity ring-down spectroscopy on chambers containing sediment and plants. We detected CH4 production in all the seagrass stations with an average rate of 85.09 ± 27.80 µmol CH4 m-2 d-1. Our results show that there is no seasonal or daily pattern in the CH4 production rates by seagrass ecosystems in the Red Sea. Taking in account the range of global estimates for seagrass coverage and the average seagrass CH4 production, the global CH4 production and emission by seagrass ecosystems could range from 0.09 to 2.7 Tg yr-1. Because CH4 emission by seagrass ecosystems had not been included in previous global CH4 budgets, our estimate would increase the contribution of marine global emissions, hitherto estimated at 9.1 Tg yr-1, by about 30%. Thus, the potential contribution of seagrass ecosystems to marine CH4 emissions provides sufficient evidence of the relevance of these fluxes as to include seagrass ecosystems in future assessments of the global CH4 budgets.
Long‐term and experimental approaches were used to examine the metabolic balance of the planktonic community in the Bay of Blanes (Spanish Mediterranean). Incubation measurements at weekly intervals for 6 yr revealed that community respiration, R, was consistently larger than gross primary production (GPP) by a factor of 2. The plankton community was net heterotrophic for 2/3 of the study period, with a median P/R ratio of 0.65. The biomass of autotrophs comprised, on average, 41% ± 3% of the planktonic biomass, and the total microplankton biomass was about 2.5‐fold greater than that of the primary producers. The monthly average GPP and R were positively correlated with day length, and the planktonic respiration and gross production per unit microplankton biomass increased with increasing water temperature. Experimental nutrient additions had a greater effect on GPP than respiration rates; the increase in R along the nutrient gradient was 7.8% (± 0.4%) of the increase in GPP. As a result, net community production increased in parallel with GPP, shifting from net heterotrophic at low GPP to net autotrophic when GPP increased because of nutrient additions. Our results show that the R that would be supported by llocthonous inputs was 3.83 ± 0.67 µmol O 2 L −1 d −1 , and the average GPP required to shift the community from net heterotrophic to net autotrophic was about 4 µmol O 2 L −1 d −1 . This is well above the average GPP recorded in the Bay of Blanes along this study (2.56 ± 0.13 µmol O 2 L −1 d −1 ), explaining the net heterotrophic nature of the community.
The most highly conserved nucleotides in D5, an essential active site component of group II introns, consist of an AGC triad, of which the G is invariant. To understand how this G participates in catalysis, the mechanistic contribution of its functional groups was examined. We observed that the exocyclic amine of G participates in ground state interactions that stabilize D5 binding from the minor groove. In contrast, each major groove heteroatom of the critical G (specifically N7 or O6) is essential for chemistry. Thus, major groove atoms in an RNA helix can participate in catalysis, despite their presumed inaccessibility. N7 or O6 of the critical G could engage in critical tertiary interactions with the rest of the intron or they could, together with phosphate oxygens, serve as a binding site for catalytic metal ions.
Les mesures de conservation de la vie marine portent leurs fruits : elles ont déjà permis d’enrayer le déclin de certaines espèces et de rétablir des écosystèmes marins dégradés. Mais pour restaurer la santé de l’océan à grande échelle, il faut lutter plus activement contre la pollution, la surpêche et les effets du changement climatique.
MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 169:283-288 (1998) - doi:10.3354/meps169283 Oxygen dynamics in the rhizosphere of Cymodocea rotundata Ole Pedersen1,*, Jens Borum1, Carlos M. Duarte2, Miguel D. Fortes3 1The Freshwater Biological Laboratory, University of Copenhagen, Helsingørsgade 51, DK-3400 Hillerød, Denmark 2Centro de Estudios Avanzados de Blanes, CSIC, Camí de Santa Bárbara s/n, E-17300 Blanes, Girona, Spain 3Marine Science Institute, CS, University of The Philippines, Diliman, Quezon City, The Philippines *E-mail: olep@ibm.net ABSTRACT: The spatial distribution of oxygen and the dynamics of the oxic microzone around roots of Cymodocea rotundata were studied using oxygen microelectrodes under constant light conditions and during light-dark transitions. Under daylight steady state conditions, oxygen was present at concentrations up to 75% of air saturation at the root surface, and the oxic microzone around the roots was 80 µm thick. Steady state oxygen concentrations were reached within 1.5 h after light-dark shifts. Under darkness, free oxygen, at about 20% of air saturation, was still present on the root surface at steady state, but the thickness of the oxic microzone shrank to 50 µm. The oxygen present in the rhizosphere during darkness was supplied from the water column to roots via, primarily, gas-phase diffusion in leaves and rhizomes. The oxic microzone around roots comprised about 0.5o/oo of the total volume of the seagrass rhizosphere, and the root-mediated oxygen supply was estimated to be insignificant for the whole sediment oxygen budget contributing about 1% of total oxygen consumption only. However, the continuous oxygen supply may ensure a persistent oxic environment for below-ground tissues of C. rotundata and, hence, protect the plant from reduced phytotoxins. KEY WORDS: Seagrasses · Roots · Sediments · Oxygen · Respiration Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 169. Publication date: August 06, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.
