Clinical Validation of an Adult-acquired Buried Penis Classification System Based on Standardized Evaluation of the Penis, Abdomen, and Scrotum

OBJECTIVE

To clinically validate a previously developed adult-acquired buried penis (AABP) classification system that is based on a standardized preoperative physical examination that subtypes patients by their penile skin/escutcheon complex (P), abdominal pannus (A), and scrotal skin (S).

METHODS

The Trauma and Urologic Reconstruction Network of Surgeons (TURNS) database was used to create an AABP cohort. Patients were retrospectively classified using the previously described PAS classification system. The frequency of subtypes, surgical methods utilized for AABP repair, and correlations between PAS classification and surgery subtypes were analyzed.

RESULTS

The final cohort consisted of 101 patients from 10 institutions. Interrater reliability between two reviewers was excellent (κ = 0.95). The most common subtypes were P2c (contributory escutcheon+insufficient penile skin; 27%) and P2a (contributory escutcheon+sufficient penile skin; 21%) for penile subtypes, A0 (no pannus; 41%) and A1 (noncontributory pannus; 39%) for abdominal subtypes, and S0 (normal scrotal skin with preserved scrotal sulcus; 71%) for scrotal subtypes. AABP repair procedures included escutcheonectomy (n = 59, 55%), scrotoplasty (n = 51, 48%), split-thickness skin grafting (n = 50, 47%), penile skin excision (n = 47, 44%) and panniculectomy (n = 7, 7%). P, A, and S subtypes were strongly associated with specific AABP surgical techniques.

CONCLUSION

The PAS classification schema adequately describes AABP heterogeneity, is reproducible among observers, and correlates well with AABP surgery types. Future work will focus on how PAS subtypes affect both surgical and patient-centered outcomes.

Feeding in mixoplankton enhances phototrophy increasing bloom-induced pH changes with ocean acidification

Plankton phototrophy consumes CO₂, increasing seawater pH, while heterotrophy does the converse. Elevation of pH (>8.5) during coastal blooms becomes increasingly deleterious for plankton. Mixoplankton, which can be important bloom-formers, engage in both photoautotrophy and phagoheterotrophy; in theory, this activity could create a relatively stable pH environment for plankton growth. Using a systems biology modelling approach, we explored whether different mixoplankton functional groups could modulate the environmental pH compared to the extreme activities of phototrophic phytoplankton and heterotrophic zooplankton. Activities by most mixoplankton groups do not stabilize seawater pH. Through access to additional nutrient streams from internal recycling with phagotrophy, mixoplankton phototrophy is enhanced, elevating pH; this is especially so for constitutive and plastidic specialist non-constitutive mixoplankton. Mixoplankton blooms can exceed the size of phytoplankton blooms; the synergisms of mixoplankton physiology, accessing nutrition via phagotrophy as well as from inorganic sources, enhance or augment primary production rather than depressing it. Ocean acidification will thus enable larger coastal mixoplankton blooms to form before basification becomes detrimental. The dynamics of such bloom developments will depend on whether the mixoplankton are consuming heterotrophs and/or phototrophs and how the plankton community succession evolves.

Mucus-Trap-Assisted Feeding Is a Common Strategy of the Small Mixoplanktonic Prorocentrum pervagatum and P. cordatum (Prorocentrales, Dinophyceae)

Prorocentrum comprises a diverse group of bloom-forming dinophytes with a worldwide distribution. Although photosynthetic, mixoplanktonic phagotrophy has also been described. Recently, the small P. cf. balticum was shown to use a remarkable feeding strategy by crafting globular mucus traps to capture and immobilize potential prey. Here we present evidence showing that two additional related species, the recently described P. pervagatum and the cosmopolitan bloom-forming P. cordatum, also produce large (80-120 µm) mucus traps supporting their mixoplanktonic activity. Prey are captured within the traps either through passive entanglement upon contact with the outside surface, or through active water movement created by rotating Prorocentrum cells eddying particles to the inside surface where trapped live prey cells became immobilized. Entrapment in mucus assisted deployment into the prey of a peduncle extruded from the apical area of the Prorocentrum cell. Phagotrophy by P. pervagatum supported faster growth compared to unfed controls and time series quantification of food vacuoles revealed ingestion rates of ca. 10-12 Teleaulax prey cells day^-1. Model calculations show clear advantages of deploying a mucus trap for increasing prey encounter rates. This study demonstrates that the large size and immobilization properties of mucus traps successfully increase the availability of prey for small Prorocentrum species, whose peduncle feeding mode impedes consumption of actively moving prey, and that this strategy is common among certain clades of small planktonic Prorocentrum species.

Low rates of bacterivory enhances phototrophy and competitive advantage for mixoplankton growing in oligotrophic waters

With climate change, oceans are becoming increasingly nutrient limited, favouring growth of prokaryotic picoplankton at the expense of the larger protist plankton whose growth support higher trophic levels. Constitutive mixoplankton (CM), microalgal plankton with innate phototrophic capability coupled with phagotrophy, graze on these picoplankton, indirectly exploiting the excellent resource acquisition abilities of the prokaryotes. However, feeding rates can be very low (e.g., a few bacteria d^-1). For the first time, the significance of such low consumption rates has been quantified. We find that while prokaryote-carbon (C) supply to CM grown at non-limiting light was so low that it may appear insignificant (< 10%), contributions of nitrogen (N) and phosphorus (P) from ingestions of 1-12 prokaryotes d^-1 were significant. Under limiting light, contributions of ingested C increased, also raising the contributions of N and P. The order of nutritional importance for CM growth from predation was P > N > C. Further, provision of N through internal recycling of ingested prey-N stimulates C-fixation through photosynthesis. Importantly, coupled photo-phago-mixoplanktonic activity improved CM resource affinities for both inorganic and prey-bound nutrients, enhancing the nutritional status and competitiveness of mixoplankton. With warming oceans, with increased prokaryote abundance, we expect CM to exhibit more phagotrophy.

The Mixoplankton Database - diversity of photo-phago-trophic plankton in form, function and distribution across the global ocean

Protist plankton are major members of open-water marine food webs. Traditionally divided between phototrophic phytoplankton and phagotrophic zooplankton, recent research shows many actually combine phototrophy and phagotrophy in the one cell; these protists are the 'mixoplankton'. Under the mixoplankton paradigm, 'phytoplankton' are incapable of phagotrophy (diatoms being exemplars), while 'zooplankton' are incapable of phototrophy. This revision restructures marine food webs, from regional to global levels. Here we present the first comprehensive database of marine mixoplankton, bringing together extant knowledge of the identity, allometry, physiology and trophic interactivity of these organisms. This Mixoplankton Database (MDB) will aid researchers that confront difficulties in characterizing life traits of protist plankton, and it will benefit modellers needing to better appreciate ecology of these organisms with their complex functional and allometric predator-prey interactions. The MDB also identifies knowledge gaps, including the need to better understand, for different mixoplankton functional types, sources of nutrition (use of nitrate, prey types and nutritional states), and to obtain vital rates (e.g., growth, photosynthesis, ingestion, factors affecting photo' versus phago' -trophy). It is now possible to revisit and re-classify protistan 'phytoplankton' and 'zooplankton' in extant databases of plankton life forms so as to clarify their roles in marine ecosystems.

Thermal Infrared Camera Imaging to Aid Necrotizing Soft Tissue Infections of the Genitalia Management

OBJECTIVE

To determine if imaging with a thermal infrared camera might aid clinicians with diagnosis of equivocal necrotizing soft tissue infections of the genitalia (NSTIG) cases and help surgeons when determining appropriate surgical resection margins.

MATERIALS/METHODS

For twelve months at a single tertiary academic hospital, sequential patients already undergoing exploration for acute scrotum had preoperative photography with an infrared camera (FLIR C5). We compared infrared and standard preoperative photography with operative reports and postoperative photography to investigate if infrared photography corresponded with operative findings in severe scrotal infections - specifically the viability of the skin and the ultimate surgical resection margins.

RESULTS

A total of 16 patients were included. The pre-operative infrared photos directly correlated with resection margins in 13 of 16 (81%) patients. Notably, areas with a relatively lower (cooler) infrared intensity corresponded well to both visibly necrotic tissue when discrete and areas with large underlying fluid collections. Diffuse warm signal relative to surrounding skin correlated with cellulitis and viable skin.

CONCLUSIONS

In this observational study, infrared photography corresponded well with physical exam and operative findings. There may be a role for augmented temperature photography in the diagnosis and triage of scrotal infections. More research with standardized temperature gating of infrared signal and controls with normal or nonacute scrotums are needed to elucidate the clinical utility for infrared photograph.

Favorable Outcomes With Early Component Separation, Primary Closure of Necrotizing Soft Tissue Infections of the Genitalia (Fournier's Gangrene) Debridement Wound Defects

OBJECTIVE

To evaluate the efficacy of early necrotizing soft-tissue infections of the genitalia (NSTIG) component separation, primary wound closure (CSC). We hypothesized that early CSC would be safe, decrease the need for split-thickness skin grafting (STSG) and decrease wound convalescence time.

MATERIALS/METHODS

Management of consecutive NSTIG patients from a single institution were evaluated. Three cohorts emerged: 1) those managed/closed by a reconstructive urologist (URO) using CSC principles (wide genital tissue mobilization with primary closure, when possible, +/- STSG), 2) those managed/closed by the general surgery/burn service, and 3) those managed conservatively with secondary closure. Total NSTIG anatomic extent (AE) was determined by assessing involvement of the penis, scrotum, perineum and suprapubic region, and ranged from 1 (<50% involvement of one area) to 8 (>50% involvement in all 4 areas).

RESULTS

Of 84 FG patients meeting study criteria, 48 (57%) were closed primarily and 36 were left to heal by secondary intention. AE was greatest in patients managed by general surgery/burn service (4.5 ± 1.5), followed by URO (2.7 ± 1.8) and secondary intention cases (1.3 ± 0.5). Secondary procedure rates were similar between closure/non-closure cohorts (6.3% v 11%; P = 0.67). STSG use was predicted by wound size (though not time to closure)-specifically with suprapubic and/or penile wounds of >50% involvement. Wound convalescence time decreased by 64% when wounds were closed versus left open, controlling for AE.

CONCLUSION

Early, same-admission primary closure of stable NSTIG wounds is safe and decreases wound convalescence time by over 60%.

Deuterium in marine organic biomarkers: toward a new tool for quantifying aquatic mixotrophy

The traditional separation between primary producers (autotrophs) and consumers (heterotrophs) at the base of the marine food web is being increasingly replaced by the paradigm that mixoplankton, planktonic protists with the nutritional ability to use both phago(hetero)trophy and photo(auto)trophy to access energy are widespread globally. Thus, many 'phytoplankton' eat, while 50% of 'protozooplankton' also perform photosynthesis. Mixotrophy may enhance primary production, biomass transfer to higher trophic levels and the efficiency of the biological pump to sequester atmospheric CO₂ into the deep ocean. Although this view is gaining traction, science lacks a tool to quantify the relative contributions of autotrophy and heterotrophy in planktonic protists. This hinders our understanding of their impacts on carbon cycling within marine pelagic ecosystems. It has been shown that the hydrogen (H) isotopic signature of lipids is uniquely sensitive to heterotrophy relative to autotrophy in plants and bacteria. Here, we explored whether it is also sensitive to the trophic status in protists. The new understanding of H isotope signature of lipid biomarkers suggests it offers great potential as a novel tool for quantifying the prevalence of mixotrophy in diverse marine microorganisms and thus for investigating the implications of the 'mixoplankton' paradigm.

'Boom-and-busted' dynamics of phytoplankton-virus interactions explain the paradox of the plankton

Rapid virus proliferation can exert a powerful control on phytoplankton host populations, playing a significant role in marine biogeochemistry and ecology. We explore how marine lytic viruses impact phytoplankton succession, affecting host and nonhost populations. Using an in silico food web we conducted simulation experiments under a range of different abiotic and biotic conditions, exploring virus-host-grazer interactions and manipulating competition, allometry, motility and cyst cycles. Virus-host and predator-prey interactions, and interactions with competitors, generate bloom dynamics with a pronounced 'boom-and-busted' dynamic (BBeD) which leads to the suppression of otherwise potentially successful phytoplankton species. The BBeD is less pronounced at low nutrient loading through distancing of phytoplankton hosts, while high sediment loading and high nonhost biomass decrease the abundance of viruses through adsorption. Larger hosts are inherently more distanced, but motility increases virus attack, while cyst cycles promote spatial and temporal distancing. Virus control of phytoplankton bloom development appears more important than virus-induced termination of those blooms. This affects plankton succession - not only the growth of species infected by the virus, but also those that compete for the same resources and are collectively subjected to common grazer control. The role of viruses in structuring plankton communities via BBeDs can thus provide an explanation for the paradox of the plankton.

Mixoplankton interferences in dilution grazing experiments

It remains unclear as to how mixoplankton (coupled phototrophy and phagotrophy in one cell) affects the estimation of grazing rates obtained from the widely used dilution grazing technique. To address this issue, we prepared laboratory-controlled dilution experiments with known mixtures of phyto-, protozoo-, and mixoplankton, operated under different light regimes and species combinations. Our results evidenced that chlorophyll is an inadequate proxy for phytoplankton when mixoplankton are present. Conversely, species-specific cellular counts could assist (although not fully solve) in the integration of mixoplanktonic activity in a dilution experiment. Moreover, cell counts can expose prey selectivity patterns and intraguild interactions among grazers. Our results also demonstrated that whole community approaches mimic reality better than single-species laboratory experiments. We also confirmed that light is required for protozoo- and mixoplankton to correctly express their feeding activity, and that overall diurnal grazing is higher than nocturnal. Thus, we recommend that a detailed examination of initial and final plankton communities should become routine in dilution experiments, and that incubations should preferably be started at the beginning of both day and night periods. Finally, we hypothesize that in silico approaches may help disentangle the contribution of mixoplankton to the community grazing of a given system.

The effect of medication cost transparency alerts on prescriber behavior

OBJECTIVE

The purpose of this study was to determine if medication cost transparency alerts provided at time of prescribing led ambulatory prescribers to reduce their use of low-value medications.

MATERIALS AND METHODS

Provider-level alerts were deployed to ambulatory practices of a single health system from February 2018 through April 2018. Practice sites included 58 primary care and 152 specialty care clinics totaling 1896 attending physicians, residents, and advanced practice nurses throughout western Washington. Prescribers in the randomly assigned intervention arm received a computerized alert whenever they ordered a medication among 4 high-cost medication classes. For each class, a lower cost, equally effective, and safe alternative was available. The primary outcome was the change in prescribing volume for each of the 4 selected medication classes during the 12-week intervention period relative to a prior 24-week baseline.

RESULTS

A total of 15 456 prescriptions for high-cost medications were written during the baseline period including 7223 in the intervention arm and 8233 in the control arm. During the intervention period, a decrease in daily prescribing volume was noted for all high-cost medications including 33% for clobetasol propionate (p < .0001), 59% for doxycycline hyclate (p < .0001), 43% for fluoxetine tablets (p < .0001), and a non-significant 3% decrease for high-cost triptans (p = .65). Prescribing volume for the high-cost medications overall decreased by 32% (p < .0001).

CONCLUSION

Medication cost transparency alerts in an ambulatory setting lead to more cost-conscious prescribing. Future work is needed to predict which alerts will be most effective.

Exploring evolution of maximum growth rates in plankton

Evolution has direct and indirect consequences on species-species interactions and the environment. However, Earth systems models describing planktonic activity invariably fail to explicitly consider organism evolution. Here we simulate the evolution of the single most important physiological characteristic of any organism as described in models-its maximum growth rate (μ_m). Using a low-computational-cost approach, we incorporate the evolution of μ_m for each of the plankton components in a simple Nutrient-Phytoplankton-Zooplankton -style model such that the fitness advantages and disadvantages in possessing a high μ_m evolve to become balanced. The model allows an exploration of parameter ranges leading to stresses, which drive the evolution of μ_m. In applications of the method we show that simulations of climate change give very different projections when the evolution of μ_m is considered. Thus, production may decline as evolution reshapes growth and trophic dynamics. Additionally, predictions of extinction of species may be overstated in simulations lacking evolution as the ability to evolve under changing environmental conditions supports evolutionary rescue. The model explains why organisms evolved for mature ecosystems (e.g. temperate summer, reliant on local nutrient recycling or mixotrophy), express lower maximum growth rates than do organisms evolved for immature ecosystems (e.g. temperate spring, high resource availability).

Future HAB science: Directions and challenges in a changing climate

There is increasing concern that accelerating environmental change attributed to human-induced warming of the planet may substantially alter the patterns, distribution and intensity of Harmful Algal Blooms (HABs). Changes in temperature, ocean acidification, precipitation, nutrient stress or availability, and the physical structure of the water column all influence the productivity, composition, and global range of phytoplankton assemblages, but large uncertainty remains about how integration of these climate drivers might shape future HABs. Presented here are the collective deliberations from a symposium on HABs and climate change where the research challenges to understanding potential linkages between HABs and climate were considered, along with new research directions to better define these linkages. In addition to the likely effects of physical (temperature, salinity, stratification, light, changing storm intensity), chemical (nutrients, ocean acidification), and biological (grazer) drivers on microalgae (senso lato), symposium participants explored more broadly the subjects of cyanobacterial HABs, benthic HABs, HAB effects on fisheries, HAB modelling challenges, and the contributions that molecular approaches can bring to HAB studies. There was consensus that alongside traditional research, HAB scientists must set new courses of research and practices to deliver the conceptual and quantitative advances required to forecast future HAB trends. These different practices encompass laboratory and field studies, long-term observational programs, retrospectives, as well as the study of socioeconomic drivers and linkages with aquaculture and fisheries. In anticipation of growing HAB problems, research on potential mitigation strategies should be a priority. It is recommended that a substantial portion of HAB research among laboratories be directed collectively at a small sub-set of HAB species and questions in order to fast-track advances in our understanding. Climate-driven changes in coastal oceanographic and ecological systems are becoming substantial, in some cases exacerbated by localized human activities. That, combined with the slow pace of decreasing global carbon emissions, signals the urgency for HAB scientists to accelerate efforts across disciplines to provide society with the necessary insights regarding future HAB trends.

Toward a mechanistic understanding of trophic structure: inferences from simulating stable isotope ratios

Stable isotope ratios (SIR) are widely used to estimate food-web trophic levels (TLs). We built systems dynamic N-biomass-based models of different levels of complexity, containing explicit descriptions of isotope fractionation and of trophic level. The values of δ15N and TLs, as independent and emergent properties, were used to test the potential for the SIR of nutrients, primary producers, consumers, and detritus to align with food-web TLs. Our analysis shows that there is no universal relationship between TL and δ15N that permits a robust prognostic tool for configuration of food webs even if all system components can be reliably analysed. The predictive capability is confounded by prior dietary preference, intra-guild predation and recycling of biomass through detritus. These matters affect the dynamics of both the TLs and SIR. While SIR data alone have poor explanatory power, they would be valuable for validating the construction and functioning of dynamic models. This requires construction of coupled system dynamic models that describe bulk elemental distribution with an explicit description of isotope discriminations within and amongst functional groups and nutrient pools, as used here. Only adequately configured models would be able to explain both the bulk elemental distributions and the SIR data. Such an approach would provide a powerful test of the whole model, integrating changing abiotic and biotic events across time and space.

Effects of growth rate, cell size, motion, and elemental stoichiometry on nutrient transport kinetics

Nutrient acquisition is a critical determinant for the competitive advantage for auto- and osmohetero- trophs alike. Nutrient limited growth is commonly described on a whole cell basis through reference to a maximum growth rate (Gmax) and a half-saturation constant (KG). This empirical application of a Michaelis-Menten like description ignores the multiple underlying feedbacks between physiology contributing to growth, cell size, elemental stoichiometry and cell motion. Here we explore these relationships with reference to the kinetics of the nutrient transporter protein, the transporter rate density at the cell surface (TRD; potential transport rate per unit plasma-membrane area), and diffusion gradients. While the half saturation value for the limiting nutrient increases rapidly with cell size, significant mitigation is afforded by cell motion (swimming or sedimentation), and by decreasing the cellular carbon density. There is thus potential for high vacuolation and high sedimentation rates in diatoms to significantly decrease KG and increase species competitive advantage. Our results also suggest that Gmax for larger non-diatom protists may be constrained by rates of nutrient transport. For a given carbon density, cell size and TRD, the value of Gmax/KG remains constant. This implies that species or strains with a lower Gmax might coincidentally have a competitive advantage under nutrient limited conditions as they also express lower values of KG. The ability of cells to modulate the TRD according to their nutritional status, and hence change the instantaneous maximum transport rate, has a very marked effect upon transport and growth kinetics. Analyses and dynamic models that do not consider such modulation will inevitably fail to properly reflect competitive advantage in nutrient acquisition. This has important implications for the accurate representation and predictive capabilities of model applications, in particular in a changing environment.

Oceanic protists with different forms of acquired phototrophy display contrasting biogeographies and abundance

This first comprehensive analysis of the global biogeography of marine protistan plankton with acquired phototrophy shows these mixotrophic organisms to be ubiquitous and abundant; however, their biogeography differs markedly between different functional groups. These mixotrophs, lacking a constitutive capacity for photosynthesis (i.e. non-constitutive mixotrophs, NCMs), acquire their phototrophic potential through either integration of prey-plastids or through endosymbiotic associations with photosynthetic microbes. Analysis of field data reveals that 40-60% of plankton traditionally labelled as (non-phototrophic) microzooplankton are actually NCMs, employing acquired phototrophy in addition to phagotrophy. Specialist NCMs acquire chloroplasts or endosymbionts from specific prey, while generalist NCMs obtain chloroplasts from a variety of prey. These contrasting functional types of NCMs exhibit distinct seasonal and spatial global distribution patterns. Mixotrophs reliant on 'stolen' chloroplasts, controlled by prey diversity and abundance, dominate in high-biomass areas. Mixotrophs harbouring intact symbionts are present in all waters and dominate particularly in oligotrophic open ocean systems. The contrasting temporal and spatial patterns of distribution of different mixotroph functional types across the oceanic provinces, as revealed in this study, challenges traditional interpretations of marine food web structures. Mixotrophs with acquired phototrophy (NCMs) warrant greater recognition in marine research.

Physiology limits commercially viable photoautotrophic production of microalgal biofuels

Algal biofuels have been offered as an alternative to fossil fuels, based on claims that microalgae can provide a highly productive source of compounds as feedstocks for sustainable transport fuels. Life cycle analyses identify algal productivity as a critical factor affecting commercial and environmental viability. Here, we use mechanistic modelling of the biological processes driving microalgal growth to explore optimal production scenarios in an industrial setting, enabling us to quantify limits to algal biofuels potential. We demonstrate how physiological and operational trade-offs combine to restrict the potential for solar-powered algal-biodiesel production in open ponds to a ceiling of ca. 8000 L ha^-1 year^-1. For industrial-scale operations, practical considerations limit production to ca. 6000 L ha^-1 year^-1. According to published economic models and life cycle analyses, such production rates cannot support long-term viable commercialisation of solar-powered cultivation of natural microalgae strains exclusively as feedstock for biofuels. The commercial viability of microalgal biofuels depends critically upon limitations in microalgal physiology (primarily in rates of C-fixation); we discuss the scope for addressing this bottleneck concluding that even deployment of genetically modified microalgae with radically enhanced characteristics would leave a very significant logistical if not financial burden.

Minimising losses to predation during microalgae cultivation

We explore approaches to minimise impacts of zooplanktonic pests upon commercial microalgal crops using system dynamics models to describe algal growth controlled by light and nutrient availability and zooplankton growth controlled by crop abundance and nutritional quality. Losses of microalgal crops are minimised when their growth is fastest and, in contrast, also when growing slowly under conditions of nutrient exhaustion. In many culture systems, however, dwindling light availability due to self-shading in dense suspensions favours slow growth under nutrient sufficiency. Such a situation improves microalgal quality as prey, enhancing zooplankton growth, and leads to rapid crop collapse. Timing of pest entry is important; crop losses are least likely in established, nutrient-exhausted microalgal communities grown for high C-content (e.g. for biofuels). A potentially useful approach is to promote a low level of P-stress that does not adversely affect microalgal growth but which produces a crop that is suboptimal for zooplankton growth.

The role of coccolithophore calcification in bioengineering their environment

Coccolithophorids are enigmatic plankton that produce calcium carbonate coccoliths, which over geological time have buried atmospheric CO2 into limestone, changing both the atmosphere and geology of the Earth. However, the role of coccoliths for the proliferation of these organisms remains unclear; suggestions include roles in anti-predation, enhanced photosynthesis and sun-screening. Here we test the hypothesis that calcification stabilizes the pH of the seawater proximate to the organisms, providing a level of acidification countering the detrimental basification that occurs during net photosynthesis. Such bioengineering provides a more stable pH environment for growth and fits the empirical evidence for changes in rates of calcification under different environmental conditions. Under this scenario, simulations suggest that the optimal production ratio of inorganic to organic particulate C (PIC : POCprod) will be lower (by approx. 20%) with ocean acidification and that overproduction of coccoliths in a future acidified ocean, where pH buffering is weaker, presents a risk to calcifying cells.

Coupling a simple irradiance description to a mechanistic growth model to predict algal production in industrial-scale solar-powered photobioreactors

Various innovative photobioreactor designs have been proposed to increase production of algae-derived biomass. Computer models are often employed to test these designs prior to construction. In the drive to optimise conversion of light energy to biomass, efforts to model the profile of irradiance levels within a microalgal culture can lead to highly complex descriptions which are computationally demanding. However, there is a risk that this effort is wasted if such optic models are coupled to overly simplified descriptions of algal physiology. Here we demonstrate that a suitable description of microalgal physiology is of primary significance for modelling algal production in photobioreactors. For the first time, we combine a new and computationally inexpensive model of irradiance to a mechanistic description of algal growth and test its applicability to modelling biofuel production in an advanced photobioreactor system. We confirm the adequacy of our approach by comparing the predictions of the model against published experimental data collected over a 2 ½-year period and demonstrate the effectiveness of the mechanistic model in predicting long-term production rates of bulk biomass and biofuel feedstock components at a commercially relevant scale. Our results suggest that much of the detail captured in more complicated irradiance models is indeed wasted as the critical limiting procedure is the physiological description of the conversion of light energy to biomass.

Metabolic and physiological changes in Prymnesium parvum when grown under, and grazing on prey of, variable nitrogen:phosphorus stoichiometry

Mixotrophy is found in almost all classes of phytoplankton in a wide range of aquatic habitats ranging from oligotrophic to eutrophic marine and freshwater systems. Few studies have addressed how the nutritional status of the predator and/or the prey affects mixotrophic metabolism despite the realization that mixotrophy is important ecologically. Laboratory experiments were conducted to examine changes in growth rates and physiological states of the toxic haptophyte Prymnesium parvum when fed Rhodomonas salina of varying nutritional status. Haemolytic activity of P. parvum and prey mortality of R. salina were also measured. P. parvum cultures grown to be comparatively low in nitrogen (low-N), phosphorus (low-P) or low in both nutrients (low-NP) were mixed with low-NP, low-N, and low-P R. salina in all possible combinations, i.e., a 3×3 factorial design. N deficiency was obtained in the low-N cultures, while true P deficiency may not have been obtained in the low-P cultures. Mortality rates of R. salina (both due to ingestion and/or cell rupture as a function of grazing or toxic effects) were higher when R. salina cells were low-P, N-rich, regardless of the nutritional state of P. parvum. Mortality rates were, however, directly related to the initial prey:predator cell ratios. On the other hand, growth of the predator was a function of nutritional status and a significant positive correlation was observed between growth rates of P. parvum and cell-specific depletion rates of N, whereas no such relationship was found between P. parvum growth rates and depletion rates of P. In addition, the greatest changes in chlorophyll content and stoichiometric ratios of P. parvum were observed in high N:P conditions. Therefore, P. parvum may show enhanced success under conditions of higher inorganic N:P, which are likely favored in the future due to increases in eutrophication and altered nutrient stoichiometry driven by anthropogenic nutrient loads that are increasingly enriched in N relative to P.

Ocean acidification with (de)eutrophication will alter future phytoplankton growth and succession

Human activity causes ocean acidification (OA) though the dissolution of anthropogenically generated CO₂ into seawater, and eutrophication through the addition of inorganic nutrients. Eutrophication increases the phytoplankton biomass that can be supported during a bloom, and the resultant uptake of dissolved inorganic carbon during photosynthesis increases water-column pH (bloom-induced basification). This increased pH can adversely affect plankton growth. With OA, basification commences at a lower pH. Using experimental analyses of the growth of three contrasting phytoplankton under different pH scenarios, coupled with mathematical models describing growth and death as functions of pH and nutrient status, we show how different conditions of pH modify the scope for competitive interactions between phytoplankton species. We then use the models previously configured against experimental data to explore how the commencement of bloom-induced basification at lower pH with OA, and operating against a background of changing patterns in nutrient loads, may modify phytoplankton growth and competition. We conclude that OA and changed nutrient supply into shelf seas with eutrophication or de-eutrophication (the latter owing to pollution control) has clear scope to alter phytoplankton succession, thus affecting future trophic dynamics and impacting both biogeochemical cycling and fisheries.

Primary renal extra-osseous osteosarcoma

Primary renal extra-osseous osteosarcoma is an exceedingly rare and deadly kidney neoplasm with only 27 reported cases to date. Extra-osseous osteosarcoma is a mesenchymal sarcoma that produces osteoid, but has no skeletal or periosteal involvement and most commonly arises in the lower extremities. Yet, it can arise in other locations such as the kidney. Extra-osseous osteosarcoma behaves as a separate entity from osseous osteosarcoma and should be treated as such. The treatment is surgical resection. Five year overall survival is 46% for local and 10% for metastatic disease. Additionally, 45%-50% of patients experience disease recurrence. We present a 77-year-old woman who underwent work up for recurrent gross hematuria and subsequently underwent radical nephroureterectomy for presumed upper tract urothelial cell carcinoma. However, pathologic analysis revealed a diagnosis of primary renal extra-osseous osteosarcoma. She is alive with no evidence of disease 30 months after surgery.

Feasibility of omitting cortical renorrhaphy during robot-assisted partial nephrectomy: a matched analysis

BACKGROUND AND PURPOSE

To assess the safety of omitting cortical renorrhaphy during robot-assisted partial nephrectomy and measure preliminary functional outcomes.

PATIENTS AND METHODS

Fifteen robot-assisted partial nephrectomies were performed with a running, base-layer suture for the collecting system and vessel hemostasis but without cortical renorrhaphy. The nonrenorrhaphy group was matched 1:2 by R.E.N.A.L. nephrometry score to a running, sliding-clip cortical renorrhaphy group retrospectively. Intraoperative blood loss, urine leaks, postoperative bleeds, and functional outcomes were evaluated. Predictors of %volume loss were evaluated using multivariable regression.

RESULTS

No differences were seen between renorrhaphy and nonrenorrhaphy in sex (P=0.53), age (P=0.14), body mass index (P=0.08), Charlson score (P=0.44), tumor diameter (P=0.55), nephrometry score (P=0.77), preoperative glomerular filtration rate (GFR, P=0.63), or the amount of resected healthy kidney margin (P=0.21). Warm ischemia time was less for the nonrenorrhaphy group (P<0.002). One pseudoaneurysm necessitating embolization (1/30=3%) was seen in the renorrhaphy group compared with none in the nonrenorrhaphy group. No urine leaks occurred in either group. The median %GFR loss was 8.8% for renorrhaphy and 4.4% for nonrenorrhaphy (P=0.14) at a median follow-up of 4.1 months. The median %volume loss was 17 cm(3) for renorrhaphy and 9 cm(3) for nonrenorrhaphy (P=0.003). In a multivariable model, both cortical renorrhaphy (P=0.004) and tumor diameter (P=0.004) were predictors of %volume loss.

CONCLUSION

Omission of cortical renorrhaphy appears feasible with no urine leaks or bleeding complications observed. The percent renal volume loss was improved by omission of cortical renorrhaphy. Reconstruction technique is important to control for when studying renal function after partial nephrectomy.

Have we been underestimating the effects of ocean acidification in zooplankton?

Understanding how copepods may respond to ocean acidification (OA) is critical for risk assessments of ocean ecology and biogeochemistry. The perception that copepods are insensitive to OA is largely based on experiments with adult females. Their apparent resilience to increased carbon dioxide (pCO2 ) concentrations has supported the view that copepods are 'winners' under OA. Here, we show that this conclusion is not robust, that sensitivity across different life stages is significantly misrepresented by studies solely using adult females. Stage-specific responses to pCO2 (385-6000 μatm) were studied across different life stages of a calanoid copepod, monitoring for lethal and sublethal responses. Mortality rates varied significantly across the different life stages, with nauplii showing the highest lethal effects; nauplii mortality rates increased threefold when pCO2 concentrations reached 1000 μatm (year 2100 scenario) with LC50 at 1084 μatm pCO2 . In comparison, eggs, early copepodite stages, and adult males and females were not affected lethally until pCO2 concentrations ≥3000 μatm. Adverse effects on reproduction were found, with >35% decline in nauplii recruitment at 1000 μatm pCO2 . This suppression of reproductive scope, coupled with the decreased survival of early stage progeny at this pCO2 concentration, has clear potential to damage population growth dynamics in this species. The disparity in responses seen across the different developmental stages emphasizes the need for a holistic life-cycle approach to make species-level projections to climate change. Significant misrepresentation and error propagation can develop from studies which attempt to project outcomes to future OA conditions solely based on single life history stage exposures.

Influence of the N:P supply ratio on biomass productivity and time-resolved changes in elemental and bulk biochemical composition of Nannochloropsis sp

This work reports for the first time the detailed impacts of dual nitrogen (N) and phosphorus (P) stress on growth dynamics and biochemical composition in the Eustigmatophyte Nannochloropsis sp. P-stress concurrent with N-stress had subtle effects on culture bulk biochemical composition, but negatively influenced biomass productivity. However, the N:P supply ratio can be raised to at least 32:1 without compromising productivity (yielding a maximum lipid content of 52% of dry weight and volumetric lipid concentration of 233 mg L(-1)). The maximum biomass and lipid yields per unit of cell-P were 1.2 kg DW (gP)(-1) and 0.54 kg lipid (gP)(-1). The P concentration of many common media is thus in surplus for optimal Nannochloropsis sp. biomass and lipid production, offering potential for significant savings in P usage and improving the sustainability of algal cultivation.

Variation in elemental stoichiometry of the marine diatom Thalassiosira weissflogii (Bacillariophyceae) in response to combined nutrient stress and changes in carbonate chemistry

The combined consequences of the multi-stressors of pH and nutrient availability upon the growth of a marine diatom were investigated. Thalassiosira weissflogii was grown in N- or P-limited batch culture in sealed systems, with pH commencing at 8.2 ("extant" conditions) or 7.6 ("ocean acidification" [OA] conditions), and then pH was allowed to either drift with growth, or was held fixed. Results indicated that within the pH range tested, the stability of environmental pH rather than its value (i.e., OA vs. extant) fundamentally influenced biomass accumul-ation and C:N:P stoichiometry. Despite large changes in total alkalinity in the fixed pH systems, final biomass production was consistently greater in these systems than that in drifting pH systems. In drift systems, pH increased to exceed pH 9.5, a level of alkalinity that was inhibitory to growth. No statis-tically significant differences between pH treatments were measured for N:C, P:C or N:P ratios during nutrient-replete growth, although the diatom expre-ssed greater plasticity in P:C and N:P ratios than in N:C during this growth phase. During nutrient-deplete conditions, the capacity for uncoupled carbon fixa-tion at fixed pH was considerably greater than that measured in drift pH systems, leading to strong contrasts in C:N:P stoichiometry between these treatments. Whether environmental pH was stable or drifted directly influenced the extent of physiological stress. In contrast, few distinctions could be drawn between "extant" versus "OA" conditions for cell physiology.

In silico optimization for production of biomass and biofuel feedstocks from microalgae

Optimization of the production rate of biomass rich in N (e.g. for protein) or C (e.g. for biofuels) is key to making algae-based technology commercially viable. Creating the appropriate conditions to achieve this is a challenge; operational permutations are extensive, while geographical variations localise effective methods of cultivation when utilising natural illumination. As an aid to identifying suitable operational envelopes, a mechanistic acclimative model of microalgae growth is used for the first time to simulate production in virtual systems over a broad latitudinal range. Optimization of production is achieved through selection of strain characteristics, system optical depth, nutrient supply, and dilution regimes for different geographic and seasonal illumination profiles. Results reveal contrasting requirements for optimising biomass vs biofuels production. Trade-offs between maximising areal and volumetric production while conserving resources, plus hydrodynamic limits on reactor design, lead to quantifiable constraints for optimal operational permutations. Simulations show how selection of strains with a high maximum growth rate, U_m , remains the prime factor enabling high productivity. Use of an f/2 growth medium with a culture dilution rate set at ~25 % of U_m delivers sufficient nutrition for optimal biomass production. Further, sensitivity to the balance between areal and volumetric productivity leads to a well-defined critical depth at ~0.1 m at which areal biofuel production peaks with use of a low concentration f/4 growth medium combined with a dilution rate ~15 % of U_m . Such analyses, and developments thereof, will aid in developing a decision support tool to enable more productive methods of cultivation.

Monster potential meets potential monster: pros and cons of deploying genetically modified microalgae for biofuels production

Biofuels production from microalgae attracts much attention but remains an unproven technology. We explore routes to enhance production through modifications to a range of generic microalgal physiological characteristics. Our analysis shows that biofuels production may be enhanced ca fivefold through genetic modification (GM) of factors affecting growth rate, respiration, photoacclimation, photosynthesis efficiency and the minimum cell quotas for nitrogen and phosphorous (N : C and P : C). However, simulations indicate that the ideal GM microalgae for commercial deployment could, on escape to the environment, become a harmful algal bloom species par excellence, with attendant risks to ecosystems and livelihoods. In large measure, this is because an organism able to produce carbohydrate and/or lipid at high rates, providing stock metabolites for biofuels production, will also be able to attain a stoichiometric composition that will be far from optimal as food for the support of zooplankton growth. This composition could suppress or even halt the grazing activity that would otherwise control the microalgal growth in nature. In consequence, we recommend that the genetic manipulation of microalgae, with inherent consequences on a scale comparable to geoengineering, should be considered under strict international regulation.

Rapid determination of bulk microalgal biochemical composition by Fourier-Transform Infrared spectroscopy

Analysis of bulk biochemical composition is a key in fundamental and applied studies of microalgae and is essential to understanding responses to different cultivation scenarios. Traditional biochemical methods for the quantification of lipids, carbohydrates and proteins are often time-consuming, often involve hazardous reagents, require significant amounts of biomass and are highly dependent on practitioner proficiency. This study presents a rapid and non-destructive method, utilising Fourier-Transform Infrared (FTIR) spectroscopy for the simultaneous determination of lipid, protein and carbohydrate content in microalgal biomass. A simple univariate regression was applied to sets of reference microalgal spectra of known composition and recognised IR peak integrals. A robust single-species model was constructed, with coefficients of determination r(2)>0.95, high predictive accuracy and relative errors below 5%. The applicability of this methodology is demonstrated by monitoring the time-resolved changes in biochemical composition of the marine alga Nannochloropsis sp. grown to nitrogen starvation.

Cutting the canopy to defeat the "selfish gene"; conflicting selection pressures for the integration of phototrophy in mixotrophic protists

In strict photoautotrophs, and in many mixotrophic protists, growth at low light stimulates the increased content of photopigment. This photoacclimation further elevates cellular Chl:C content through positive feedback (self-shading), until cellular Chl:C attains a maximum (ChlC(max)). This process, driven by the "selfish gene", enhances the fitness of the individual but decreases total population growth potential through community self-shading. However, some mixotrophic protists (generalist non-constitutives; GNC-mixotrophs) acquire their photosystems ready-made from phototrophic prey but they have no regulatory control on the acquired photosystems. When light is limiting, such organisms cannot photoacclimate; their total Chl:C ratio falls as their acquired photosystems are divided amongst daughter cells and also as the photosystems fail. We show that during that process, and with the removal (consumption) of their individually more efficient phototrophic prey, there is potential for populations of GNC-mixotrophs to become more efficient at light harvesting. Through this process these organisms may retain a critical additional period of photosynthetic capacity. Together with the fact that the acquired photosystem biomass can be potentially almost entirely converted into mixotroph biomass (while chloroplasts must remain an important component of biomass in constitutive mixotrophs, with an associated investment), this may help explain the success of GNC-mixotrophs.

Evaluation of topical cysteamine therapy in the CTNS(-/-) knockout mouse using in vivo confocal microscopy

PURPOSE

The purpose of this study was to assess the ability of quantitative in vivo confocal microscopy (CM) to detect changes in cystine crystal volume in the cystinosisn (Ctns(-/-))mouse cornea following topical cysteamine therapy.

METHODS

Fifteen Ctns(-/-) mice were sequentially followed using in vivo CM from 3 to 10 months of age. In a second experiment, five mice receiving topical cysteamine eyedrops (0.55%) for 4 weeks were compared to five untreated mice. The volume of corneal cystine crystals was determined by thresholding and counting high intensity pixels in the in vivo CM scans and dividing by the stromal volume to calculate a crystal volume index (CVI).

RESULTS

Corneal crystals progressively increased in density with age, reaching a peak density at 6-8 months and showing a 70 fold increase in CVI. Eyes treated with cysteamine drops showed significantly less crystal accumulation compared to control eyes (p<0.001) with only a 15% increase in treated eyes (p=ns) compared to 173% increase (p<0.04) for untreated eyes.

CONCLUSIONS

Measurement of CVI shows that there is a progressive increase in cystine crystal volume up to 8 months of age and that cysteamine eyedrops significantly inhibits progression in the Ctns(-/-) mouse. These findings are similar to those seen clinically in patients with cystinosis, and suggest that measurement of CVI in the Ctns(-/-) mouse may be used as a model to develop novel therapeutic strategies for treating corneal cystinosis.

Reducing peak corneal haze after photorefractive keratectomy in rabbits: prednisolone acetate 1.00% versus cyclosporine A 0.05%

PURPOSE

To compare the effects of topical cyclosporine A 0.05% (Restasis) with those of prednisolone acetate 1.00% (Pred Forte) on corneal haze after photorefractive keratectomy (PRK).

SETTING

Gavin Herbert Eye Institute, University of California, Irvine-Orange, California, USA.

DESIGN

Experimental study.

METHODS

After -9.00 diopter PRK, 15 rabbits were divided into 3 groups and treated for 4 weeks with prednisolone acetate 1.00% or cyclosporine A 0.05% or neither (control). Corneal haze was measured by in vivo confocal microscopy preoperatively and 2, 4, 6, 8, and 12 weeks postoperatively. At 12 weeks, the corneas were evaluated for collagen organization by ex vivo 2-photon second-harmonic generation and stromal cell density.

RESULTS

Corneal haze was significantly less in the prednisolone acetate group than in the cyclosporine and control groups during the first 6 weeks postoperatively (P<.02). At 8 weeks, there was no significant difference between the 3 groups. There was no significant difference in haze between the cyclosporine and control groups at any time. The stroma was also significantly thinner in the prednisolone acetate group than in the other groups for the first 4 weeks postoperatively (P<.02). Second-harmonic generation scar thickness measurements at 12 weeks were not significantly different between the groups, although the prednisolone acetate group tended to have lower stromal cell density.

CONCLUSION

Cyclosporine A 0.05% had no effect on wound healing after PRK, while prednisolone acetate 1.00% significantly reduced peak corneal haze but had no effect on long-term corneal haze after discontinuation of the drug.

Placing microalgae on the biofuels priority list: a review of the technological challenges

Microalgae provide various potential advantages for biofuel production when compared with 'traditional' crops. Specifically, large-scale microalgal culture need not compete for arable land, while in theory their productivity is greater. In consequence, there has been resurgence in interest and a proliferation of algae fuel projects. However, while on a theoretical basis, microalgae may produce between 10- and 100-fold more oil per acre, such capacities have not been validated on a commercial scale. We critically review current designs of algal culture facilities, including photobioreactors and open ponds, with regards to photosynthetic productivity and associated biomass and oil production and include an analysis of alternative approaches using models, balancing space needs, productivity and biomass concentrations, together with nutrient requirements. In the light of the current interest in synthetic genomics and genetic modifications, we also evaluate the options for potential metabolic engineering of the lipid biosynthesis pathways of microalgae. We conclude that although significant literature exists on microalgal growth and biochemistry, significantly more work needs to be undertaken to understand and potentially manipulate algal lipid metabolism. Furthermore, with regards to chemical upgrading of algal lipids and biomass, we describe alternative fuel synthesis routes, and discuss and evaluate the application of catalysts traditionally used for plant oils. Simulations that incorporate financial elements, along with fluid dynamics and algae growth models, are likely to be increasingly useful for predicting reactor design efficiency and life cycle analysis to determine the viability of the various options for large-scale culture. The greatest potential for cost reduction and increased yields most probably lies within closed or hybrid closed-open production systems.

Phagotrophy in the origins of photosynthesis in eukaryotes and as a complementary mode of nutrition in phototrophs: relation to Darwin's insectivorous plants

Darwin performed innovative observational and experimental work on the apparently paradoxical occurrence of carnivory in photosynthetic flowering plants. The nutritional use of particulate organic material which also supplies other elements is now known to be widespread in free-living algae as well as in organisms with endosymbiotic algae and with kleptoplastids. In addition to this direct nutritional role, phagotrophy, in the broad sense of internalization of photosynthetic organisms by a eukaryote, is essential for the occurrence of present-day endosymbiotic algae and kleptoplastid-containing protists, and was essential for the origin of plastids themselves. The endosymbiotic phenomena involving photosynthetic organisms clearly played a major role in combining genomes providing different metabolic functions, but, in our opinion, this does not demand a re-appraisal of evolution by natural selection. That the balance of physiological optimization for competition for resources and minimization of losses (e.g. through predation) is a fine one, and thus subject to a complex selective process, is illustrated by the diversity of mixotrophic strategies in extant phytoplankton.

Food-density-dependent inefficiency in animals with a gut as a stabilizing mechanism in trophic dynamics

Animals with a gut, when confronted with food supplied ad libitum, can elevate their ingestion rates and inefficiently use the material they ingest. As a consequence, assimilation efficiency (AE) declines, resulting in food-density-dependent inefficiency (f-DDI). A model describing these processes shows that f-DDI can dampen the consequences of oscillations in food abundance that may occur in response to external stochastic (e.g. climatic) forcing both with respect to production and timing. This response is illustrated with a simple planktonic food chain of a phytoplankter and two consumers. The assumption of a fixed gut transit time, consistent with the traditional model descriptions of a fixed AE, produces predator-prey oscillations. By contrast, simulations using a model showing f-DDI (behaving in accordance with the experimental data) cushion not only the impact of such oscillations but also the effects of the removal of intermediate grazers in the food chain. The operation of f-DDI affects other trophic interactions through changes in the nutrient regeneration and the voiding rates. The extent to which f-DDI operates in nature needs valuation, followed by the appropriate construction of consumer-based ecosystem models.

Allometry and stoichiometry of unicellular, colonial and multicellular phytoplankton

Phytoplankton life forms, including unicells, colonies, pseudocolonies, and multicellular organisms, span a huge size range. The smallest unicells are less than 1 microm3 (e.g. cyanobacteria), while large unicellular diatoms may attain 10(9) microm3, being visible to the naked eye. Phytoplankton includes chemo-organotrophic unicells, colonies and multicellular organisms that depend on symbionts or kleptoplastids for their capacity to photosynthesize. Analyses of physical (transport within cells, diffusion boundary layers, package effect, turgor, and vertical movements) and biotic (grazing, viruses and other parasitoids) factors indicate potential ecological constraints and opportunities that differ among the life forms. There are also variations among life forms in elemental stoichiometry and in allometric relations between biovolume and specific growth. While many of these factors probably have ecological and evolutionary significance, work is needed to establish those that are most important, warranting explicit description in models. Other factors setting limitations on growth rate (selecting slow-growing species) await elucidation.

MODELING THE RELEASE OF DISSOLVED ORGANIC MATTER BY PHYTOPLANKTON(1)

Three models describing dissolved organic matter (DOM) flux and phytoplankton death, each of different levels of complexity, were constructed and tested against experimental data for a cyanobacterium, a chlorophyte, two diatoms, two dinoflagellates, and two prymnesiophytes. The simplest model described only bulk carbon (C) and nitrogen (N) forms of DOM (DOMC and DOMN ) and employed a fixed relationship between phytoplankton nutrient status and DOM release and death rate. The most complex model described fractions of DOM as low molecular weight dissolved organic carbon (DOC; saccharides, low molecular weight carbohydrates [DOCs]), low molecular weight nitrogenous material (comprising C and N as DOC associated with low molecular weight compounds containing amino acids and/or nucleic acids [DOCa] and N associated with DOCa [DONa], which included dissolved free amino acids [DFAA]), and more complex materials (DOC associated with high molecular weight compounds typically requiring extracellular degradation prior to uptake or use by microbes [DOCx] and N associated with DOCx [DONx]). It also employed descriptions of DOM flux and cell death related to nutrient status and growth rates. In all instances, material lysed from dead cells contributed to the DOM pool. All three models captured the gross dynamics of the primary data (dissolved inorganic C [DIC], dissolved inorganic N [DIN], particulate organic carbon [POC], particulate organic N [PON], DOC, dissolved organic N [DON]), but there was little or no improvement of the fit with increasing model complexity. However, the simplest models tended to employ excessively high growth rates to compensate for high fixed death rates. While the proportion of newly fixed C being liberated as DOMC (DOCs plus DOCa) increased as nutrient status declined, the actual rate of release typically did not do so and often declined. The most complex model gave predictions for changes in released saccharides and DFAA in keeping with expectations. The major obstacle to future progress is the lack of suitable, mass balanced data sets for further model testing.

Morphological Controls on Cannibalism in a Planktonic Marine Phagotroph

The ingestion preferences of planktonic protozoa influence the structure and succession of microbial communities and thus biogeochemical cycling within aquatic environments. Some predatory ciliates and flagellates are reported to switch to cannibalism when no suitable non-self prey items are available for consumption. However, the importance of cannibalism as a survival strategy, and its ubiquity within the planktonic protozoa is not known. We report the first attempt to quantify cannibalism in a phagotrophic marine dinoflagellate (Oxyrrhis marina). Cannibalistic Oxyrrhis cells seldom comprised >2% of any experimental population, including those in which all non-self prey items had been grazed to extinction. Such 'prey-deplete' cultures became dominated by homogeneous populations of highly motile Oxyrrhis that were morphologically unable (too similar in size) to cannibalise. That cannibalism can only occur when 'victim' and 'cannibal' cell size-classes of sufficient difference collide, suggests that cannibalism may be of limited use as a long-term survival strategy in phagotrophic protozoa.

Importance of Interactions between Food Quality, Quantity, and Gut Transit Time on Consumer Feeding, Growth, and Trophic Dynamics

Ingestion kinetics of animals are controlled by both external food availability and feedback from the quantity of material already within the gut. The latter varies with gut transit time (GTT) and digestion of the food. Ingestion, assimilation efficiency, and thus, growth dynamics are not related in a simple fashion. For the first time, the important linkage between these processes and GTT is demonstrated; this is achieved using a biomass-based, mechanistic multinutrient model fitted to experimental data for zooplankton growth dynamics when presented with food items of varying quality (stoichiometric composition) or quantity. The results show that trophic transfer dynamics will vary greatly between the extremes of feeding on low-quantity/high-quality versus high-quantity/low-quality food; these conditions are likely to occur in nature. Descriptions of consumer behavior that assume a constant relationship between the kinetics of grazing and growth irrespective of food quality and/or quantity, with little or no recognition of the combined importance of these factors on consumer behavior, may seriously misrepresent consumer activity in dynamic situations.