Advancing interpretations of ¹⁴C-uptake measurements in the context of phytoplankton physiology and ecology

The ¹⁴C-uptake method is the most common approach employed for estimating primary production in the ocean. Normalizing ¹⁴C-uptake to chlorophyll a and time yields a value termed the assimilation number, which is thought to reflect phytoplankton physiology. It is often assumed that the measured rate of ¹⁴C-uptake is between net and gross primary production, depending on the time scale of the incubation. Recent studies employing multiple oxygen and carbon isotopic methods to measure photosynthesis of phytoplankton grown over a range of steady-state division rates have provided mechanistic insights on the relationship between ¹⁴C-uptake and gross-to-net primary production. Results from these studies show that short-term (<12 h) “photosynthesis-irradiance” measurements are not a reliable means of estimating net production, gross production or nutrient limitation, but can provide important information on the photoacclimation state of the phytoplankton. Long-term (24 h) incubations yield assimilation numbers that are in good agreement with net production rates, but are independent of nutrient-limited division rates. Despite complications in interpreting ¹⁴C-uptake data, we suggest that these measurements are important for understanding phytoplankton physiology and carbon cycles while, at the same time, efforts are needed to establish new incubation-free methods for measuring phytoplankton division rate and biomass.This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Oxford University Press. All rights reserved. For permissions, please email: [email protected]. The published article can be found at: http://plankt.oxfordjournals.org/Keywords: primary production, gross production, ¹⁴C metho

A general method to quantify ligand-driven oligomerization from fluorescence-based images

Here, we introduce fluorescence intensity fluctuation spectrometry for determining the identity, abundance and stability of protein oligomers. This approach was tested on monomers and oligomers of known sizes and was used to uncover the oligomeric states of the epidermal growth factor receptor and the secretin receptor in the presence and absence of their agonist ligands. This method is fast and is scalable for high-throughput screening of drugs targeting protein–protein interactions

Who Do We Reach? Campaign Evaluation of Find Thirty every day® Using Awareness Profiles in a Western Australian Cohort

Mass media campaigns are part of a comprehensive, population-based approach to communicate physical activity behavior change. Campaign awareness is the most frequently reported, short-term comparable measure of campaign effectiveness. Most mass media campaigns report those who were aware with those who are unaware of campaigns. Few campaigns follow awareness in the same respondent, over time, during a mass media campaign to track different patterns of awareness or awareness profiles—“never,” “early,” “late,” or “always”—that may emerge. Using awareness profiles, the authors (a) address any demographic differences between groups and (b) assess changes in physical activity. Find Thirty every day® was a populationwide mass media campaign delivered in Western Australia. The cohort comprised 405 participants, who completed periodic telephone interviews over 2 years. Almost one third (30.4%) were “never aware” of the campaign. More than one third recalled the campaign at one or more time points—“early aware.” Ten percent became aware at Time 2 and stayed aware of the campaign across the remaining time. Examining within and across the awareness profiles, only gender was significant. This article provides an approach to profiling awareness, whereby people cycle in and out and few people are “always aware” over a 2-year period. It presents possible implications and considerations for future campaign planners interested in establishing and maintaining campaign awareness with adult populations

Geostationary satellite observations of dynamic phytoplankton photophysiology

Since June 2010, the Geostationary Ocean Color Imager (GOCI) has been collecting the first diurnally resolved satellite ocean measurements. Here GOCI retrievals of phytoplankton chlorophyll concentration and fluorescence are used to evaluate daily to seasonal changes in photophysiological properties. We focus on nonphotochemical quenching (NPQ) processes that protect phytoplankton from high light damage and cause strong diurnal cycles in fluorescence emission. This NPQ signal varies seasonally, with maxima in winter and minima in summer. Contrary to expectations from laboratory studies under constant light conditions, this pattern is highly consistent with an earlier conceptual model and recent field observations. The same seasonal cycle is registered in fluorescence data from the polar-orbiting Moderate Resolution Imaging Spectroradiometer Aqua satellite sensor. GOCI data reveal a strong correlation between mixed layer growth irradiance and fluorescence-derived phytoplankton photoacclimation state that can provide a path for mechanistically accounting for NPQ variability and, subsequently, retrieving information on iron stress in global phytoplankton populations.Keywords: GOCI fluorescence, NPQ effects, Phytoplankto

Satellite-Detected Fluorescence Reveals Global Physiology of Ocean Phytoplankton

Phytoplankton photosynthesis links global ocean biology and climate-driven fluctuations in the physical environment. These interactions are largely expressed through changes in phytoplankton physiology, but physiological status has proven extremely challenging to characterize globally. Phytoplankton fluorescence does provide a rich source of physiological information long exploited in laboratory and field studies, and is now observed from space. Here we evaluate the physiological underpinnings of global variations in satellite-based phytoplankton chlorophyll fluorescence. The three dominant factors influencing fluorescence distributions are chlorophyll concentration, pigment packaging effects on light absorption, and light-dependent energy-quenching processes. After accounting for these three factors, resultant global distributions of quenching-corrected fluorescence quantum yields reveal a striking consistency with anticipated patterns of iron availability. High fluorescence quantum yields are typically found in low iron waters, while low quantum yields dominate regions where other environmental factors are most limiting to phytoplankton growth. Specific properties of photosynthetic membranes are discussed that provide a mechanistic view linking iron stress to satellite-detected fluorescence. Our results present satellite-based fluorescence as a valuable tool for evaluating nutrient stress predictions in ocean ecosystem models and give the first synoptic observational evidence that iron plays an important role in seasonal phytoplankton dynamics of the Indian Ocean. Satellite fluorescence may also provide a path for monitoring climate-phytoplankton physiology interactions and improving descriptions of phytoplankton light use efficiencies in ocean productivity models

Evidence for seasonal cycles in deep-sea fish abundances: A great migration in the deep SE Atlantic?

Animal migrations are of global ecological significance, providing mechanisms for the transport of nutrients and energy between distant locations. In much of the deep sea (>200 m water depth), the export of nutrients from the surface ocean provides a crucial but seasonally variable energy source to seafloor ecosystems. Seasonal faunal migrations have been hypothesized to occur on the deep seafloor as a result, but have not been documented. Here, we analyse a 7.5‐year record of photographic data from the Deep‐ocean Environmental Long‐term Observatory Systems seafloor observatories to determine whether there was evidence of seasonal (intra‐annual) migratory behaviours in a deep‐sea fish assemblage on the West African margin and, if so, identify potential cues for the behaviour. Our findings demonstrate a correlation between intra‐annual changes in demersal fish abundance at 1,400 m depth and satellite‐derived estimates of primary production off the coast of Angola. Highest fish abundances were observed in late November with a smaller peak in June, occurring approximately 4 months after corresponding peaks in primary production. Observed changes in fish abundance occurred too rapidly to be explained by recruitment or mortality, and must therefore have a behavioural driver. Given the recurrent patterns observed, and the established importance of bottom‐up trophic structuring in deep‐sea ecosystems, we hypothesize that a large fraction of the fish assemblage may conduct seasonal migrations in this region, and propose seasonal variability in surface ocean primary production as a plausible cause. Such trophic control could lead to changes in the abundance of fishes across the seafloor by affecting secondary production of prey species and/or carrion availability for example. In summary, we present the first evidence for seasonally recurring patterns in deep‐sea demersal fish abundances over a 7‐year period, and demonstrate a previously unobserved level of dynamism in the deep sea, potentially mirroring the great migrations so well characterized in terrestrial systems

Improbability mapping: a metric for satellite-detection of submarine volcanic eruptions

Submarine volcanic eruptions can result in both real and apparent changes in marine algal communities, e.g., increases in phytoplankton biomass and/or growth rates that can cover thousands of square kilometers. Satellite ocean color monitoring detects these changes as increases in chlorophyll and particulate backscattering. Detailed, high resolution analysis is needed to separate the optical effects of volcanic products from the response of the marine algal community. It is possible to calculate an index, which maps the magnitude of improbable change (relative to long term average conditions) following known volcanic eruptions by using low resolution, initial estimates of chlorophyll and backscatter along with an archived history of satellite data. We apply multivariate probability analysis to changes in global satellite ocean chlorophyll and particulate backscatter data to create a new metric for observing apparent biological responses to submarine eruptions. Several examples are shown, illustrating the sensitivity of our improbability mapping index to known submarine volcanic events, yielding a potentially robust method for the detection of new events in remote locations.Keywords: Improbability mapping index, Submarine volcanic eruptions, Satellite detectio