Abstract The brown macroalga Ascophyllum nodosum is a foundation species on intertidal rocky shores, where its perennial canopy and high productivity support key ecological functions. However, its population dynamics near the northern edge, where low temperatures and sea ice may challenge stability, are largely unknown. We followed the population structure, dynamics, and nutrient status of A. nodosum in the sheltered, subarctic Kobbefjord, Greenland from 2012 to 2019. Despite the northern location, population biomass (16–27 kg FW · m −2 ) was within the upper known range and was dominated by few large (max length: 109 cm), old individuals (observed age: up to 19 years; estimated mean lifespan: 37.5 years based on intrinsic mortality rate). Population density remained stable because of low mortality (0.019 · year −1 ) and recruitment rates (0.010 · year −1 ), sustained by an understory of small juveniles. Biomass increased 1.5‐fold over the 8‐year study, supported by high biomass productivity (3.3–8.1 kg FW · m −2 · year −1 ) that balanced branch loss and reflected a moderate biomass turnover time (2.6–6.3 years) of organic matter, underlying the apparent stability. Such overall population stability reflects a “biomass storer” strategy typical of environments with low disturbance and nutrient levels. The stability is remarkable given seasonal ice cover (2–7.5 months per year), large variation in average daily temperature (−3.9 to 15.4°C), and low nutrient supply. While ice breakup poses a risk of shoot abrasion, the ice cover likely provides protection against ice scouring. Enhanced growth during warmer summers and earlier ice break‐up suggests faster turnover rates in the future to the extent nutrient availability can support it.
The effect of warming on the oxygen requirements and the survival of benthic organisms under hypoxia was tested using a meta-analysis of published results of experiments evaluating the effects of temperature on the median lethal time and median lethal concentration of benthic macrofauna under hypoxia. The meta-analysis confirmed that survival times under hypoxia were reduced by on average 74% and that median lethal concentration increased by on average 16% when marine benthic organisms were exposed to warmer temperatures. Warming reduced survival times of marine benthic macrofauna under hypoxia by a median of 3.95±1.67 h °C−1 and increased the oxygen thresholds for hypoxia-driven mortality by a median of 1.02±0.15% saturation °C−1 or 0.07±0.01 mg O2 L−1 °C−1. The corresponding Q10 values averaged 3.01±0.29 for the median survival time and 2.09±0.20 for the median lethal oxygen concentration. Use of these Q10 values predicts that the 4 °C warming expected during the 21st century will lead to survival times 35.6% lower under hypoxia and that the threshold oxygen concentrations for high mortality to occur will increase by, on average, 25.5% if bottom water temperature increased by 4 °C. Hence, ocean warming is expected to increase the vulnerability of benthic macrofauna to reduced oxygen concentrations and expand the area of coastal ecosystems affected by hypoxia.
Abstract In this paper we describe for the first time the use of astable multivibrator circuits for computer-less control of solenoid micropumps and application for analytical flow techniques. Triggering and powering were accomplished using the NE555 integrated circuit. The activation and deactivation time intervals were adjusted using 10-turn trimmer potentiometers. The potential and characteristics of the instrumentation were studied on a two-channel flow system injecting an indigo carmine indicator solution. Subsequently, a three-channel flow system was assembled and successfully applied to the determination of nitrite in well waters. One circuit was used to control the activation time intervals of three further circuits used for the control of the flow rates or pulsation of solenoid micropumps. These were used for driving carrier, reagent, and sample in an analytical flow system. In the present work, the utility of the circuits for the construction of simple multipumping flow systems was demonstrated. A main feature to be highlighted was the simplicity and very low costs of the controlling circuits, favouring economic and miniaturised flow analysers. Second, no expenses or knowledge are required for the usual software control of the solenoid micropumps. This allows working with every existing detector without considering any problems of software and control compatibility. Third, owing to these features, the proposed assembly is especially suited for simple monitoring analysers, sample provision from an environmental or industrial process, or chemical education. Keywords: computer-less controlastable multivibratorsolenoid micropumpmultipumpingnitrite Acknowledgements BH was funded by a JAE Postdoctoral fellowship from CSIC. The work was supported by the project CTQ2007-64331 funded by the MEC (Spanish Ministry of Education and Science).
Abstract Mangroves forests of A vicennia marina occupy about 135 km 2 in the Red Sea and represent one of the most important vegetated communities in this otherwise arid and oligotrophic region. We assessed the soil organic carbon (C org ) stocks, soil accretion rates (SAR; mm y −1 ) and soil C org sequestration rates (g C org m −2 yr −1 ) in 10 mangrove sites within four locations along the Saudi coast of the Central Red Sea. Soil C org density and stock in Red Sea mangroves were among the lowest reported globally, with an average of 4 ± 0.3 mg C org cm −3 and 43 ± 5 Mg C org ha −1 (in 1 m-thick soils), respectively. Sequestration rates of C org , estimated at 3 ± 1 and 15 ± 1 g C org m −2 yr −1 for the long (millennia) and short (last century) temporal scales, respectively, were also relatively low compared to mangrove habitats from more humid bioregions. In contrast, the accretion rates of Central Red Sea mangroves soils were within the range reported for global mangrove forests. The relatively low C org sink capacity of Red Sea mangroves could be due to the extreme environmental conditions such as low rainfall, nutrient limitation and high temperature, reducing the growth rates of the mangroves and increasing soil respiration rates.
This live data set reports gross primary production (GPP), community respiration (CR) and net community production (NCP) of oceanic plankton communities. The methods used to measure GPP, CR, and NCP varied; these include oxygen evolution in dark-light bottles (Carpenter 1965; Carrit and Carpenter 1966),tracer additions (14C additions, SteemanNielsen 1952, and 18O-labeled H2O, Bender etal. 1987), incubation-free methods, including analyses of triple oxygen isotopes (Luz etal. 2000), O2:Ar ratios (Emerson 1987; Spitzer and Jenkins 1989; Emerson et al. 1993),non-intrusivebio-optical (OPT) methods (Claustre et al. 2008), fast repetition rate fluorometry (FRRF, Kolber and Falkowski 1993), and oxygen sensors mounted on gliders (Tengberg et al. 2006; Nicholson et al. 2008) and buoys (Boutin and Merlivat2009). Characteristics of each method are discussed by Robinson and Williams (2005)and Duarte et al.(2013). The article Global patterns in oceanic planktonic metabolism by Regaudie de Gioux, A. and Duarte, C.M. is currently in press to be published in Limnology and Oceanography in 2013. This dataset is subject to a Creative Commons License Attribution-Noncommercial-ShareAlike 3.0 Unported.
Abstract Few studies have investigated ultraviolet (UV) radiation in the open ocean besides its harmful effects on organisms and influence on biogeochemical processes. Here, we assessed UV attenuation, with particular focus on UV‐B, across the (sub)tropical ocean during the Malaspina 2010 Circumnavigation. Vertical UV radiometer profiles together with Chl‐ a concentration, and UV absorption by CDOM ( a CDOM ( λ )) and by suspended particulate matter ( a p ( λ )) were measured at 117 stations. At photosynthetically active radiation (PAR) and across UV‐A and UV‐B wavelengths, the lowest downwelling attenuation coefficients ( K d ) during the expedition were recorded in ultra‐oligotrophic regions at 5°–15°S (mean K d (305 nm): 0.129 m −1 , mean K d (313 nm): 0.107 m −1 ) in the Indian and South Pacific Oceans. The waters here were comparatively more transparent than at 5°–15°N (mean K d (305 nm): 0.239 m −1 , mean K d (313 nm): 0.181 m −1 ) where equatorial upwelling occurs. K d was highest near the Costa Rica Dome ( K d (313 nm): 0.226 m −1 ) and at the confluence of the Benguela and Agulhas currents ( K d (313 nm): 0.251 m −1 ). The contribution of a p ( λ ) toward nonwater absorption ( a nw ( λ )) was significantly lower at 305 nm than at 313 and 320 nm, suggesting the contribution of absorption by detritus and phytoplankton particles decreases compared with that of CDOM absorption as UV‐B wavelength decreases. Both a CDOM ( λ ) and a p ( λ ) at UV‐B wavelengths were lowest in the Indian Ocean whereas K d was lowest in the South Pacific. This finding emphasizes that other factors besides absorption, such as scattering by reflective phytoplankton or inorganic particles, strongly influence UV‐B attenuation in open ocean waters.
A survey of 330 phytoplankton communities in Florida lakes shows the range of populations (i.e. from sparse to dense) developed by 63 phytoplankton genera to increase with increasing size plasticity of the genera. The average size of individuals within genera tended to increase as the 1/2 power of their biomass in the community, the strength and nature of these relationships depending on the potential for size plasticity of the genera. These patterns provide evidence of the important adaptative value of algal size and support the notion that algal biomass is an important vector constraining the structure of phytoplankton communities.
Abstract. Planktonic gross community production (GPP), net community production (NCP) and community respiration (CR) across the Mediterranean Sea was examined in two cruises, THRESHOLDS 2006 and 2007, each crossing the Mediterranean from West to East to test for consistent variation along this longitudinal gradient. GPP averaged 2.4±0.4 mmol O2m−3 d−1, CR averaged 3.8±0.5 mmol O2m−3 d−1, and NCP averaged -0.8&amp;plusmn0.6 mmol O2m−3 d−1across the studied sections, indicative of a tendency for a net heterotrophic metabolism, prevalent across studied sections of the Mediterranean Sea as reflected in 70% of negative NCP estimates. The median P/R ratio was 0.58, also indicating a strong prevalence of heterotrophic communities (P/R<1) along the studied sections of the Mediterranean Sea. The communities tended to be net heterotrophic (i.e. P/R<1) at GPP less than 3.5 mmol O2m−3 d−1. Although the Western Mediterranean supports a higher gross primary production than the Eastern basin does, it also supported a higher community respiration. The net heterotrophy nature of the studied sections of the Mediterranean Sea indicates that allochthonous carbon should be important to subsidise planktonic metabolism, and that the planktonic communities in the Mediterranean Sea acted as CO2 sources to the atmosphere during the study.
