Why do certain species dominate? What we can learn from a rare case of Microdictyon dominance on a Caribbean reef

Many Caribbean reefs have shifted from coral dominance to macroalgal dominance, often by brown algae such as Dictyota and Lobophora. However, the north side of Cayman Brac in the Cayman Islands is dominated seasonally by the green macroalga Microdictyon (percent cover of Microdictyon is 4% in the winter and ~40% of the reef in the summer), although it is absent from the south side of the island and the remainder of the country. Indeed, Microdictyon is rare in much of the Caribbean, so this situation on Cayman Brac provides an opportunity to investigate the conditions that facilitate its distribution and dominance. The impact of herbivory, competition, nutrient input and other abiotic conditions were examined as factors that could influence the distribution and dominance of Microdictyon. While herbivory or nutrient input are frequently found to be key drivers of benthic community composition on coral reefs, here consumption of Microdictyon by herbivores was low, and thus, the alga was not subject to strong top-down control by herbivory. So, in this case, neither herbivore abundance nor feeding preference appeared to influence the distribution of Microdictyon. Nutrient input was also similar to both sides of the island suggesting nutrients played little role in differential distribution. But, in a controlled transplant experiment where Microdictyon was protected from herbivory and competition, it experienced almost complete mortality (93.3%) when transplanted to the south side, compared to only 11.8% mortality on the north. The south side was exposed to the strongest wave action 92% of the days in our study and was on average a slight, but significant 0.2°C warmer. Thus, these data suggest physical forcing (i.e. wave exposure) is the most likely factor dictating Microdictyon distribution. Conversely, a combination of reduced herbivory and increased competitive strength may explain the seasonal dominance of Microdictyon on the north side of Cayman Brac. Microdictyon was a competitive inferior to the other common algae in winter but increased in competitive strength to equal other species in summer. These results add to the literature on Microdictyon and on the forces impacting benthic community structure of coral reefs.     

The role of inflow magnitude and frequency on plankton communities from the Guadalupe Estuary,Texas, USA: Findings from microcosm experiments

Changes in magnitude and frequency of inflow results in subsequent alterations in the delivery of nutrients essential for phytoplankton growth and competition producing variations in community composition and nutritional value of phytoplankton. Zooplankton demographics are likely directly influenced by pulsed inflows due to flushing losses, whereas they are also indirectly affected by changes in prey quality. In this study, we report the potential effect of pulsed inflows on the plankton community of the Guadalupe Estuary. Microcosms were used that allowed control of light intensity and photoperiod, turbulence, temperature, nutrient loading, and flushing magnitude and periodicity. Our microcosm experiments were novel as they utilized natural plankton communities, thereby allowing the simultaneous interaction between hydrology, resource availability and grazing. Results show differences in microcosms according to magnitude and frequency of flushing. For example, copepod population density was greatest at the annual mean inflow magnitude. At half the annual mean inflow a decline in prey quality likely resulted in poorer grazer performance, and at double the annual mean inflow magnitude increased flushing losses prevented the incidence of higher copepod densities. Similarly, pulsed inflows resulted in greater copepod population densities, higher overall phytoplankton biomass, and dominance of centric diatoms (known to be faster growing and more edible). While reduced freshwater inflow associated with increasing anthropogenic demands often strains the needs of estuarine systems, the effects of reduced river input may be alleviated with several management options including manipulation of the timing, frequency, and magnitude of freshwater inflows. Before implications for management can be discerned from these findings, however, larger scale experiments are needed focus on the roles of inflow magnitude and frequency.     

Web 2.0 collaborations address uncertainty in climate reconstructions of the past millennium

Reducing uncertainty in global temperature reconstructions of the past millennium remains the key issue in applying this record to society’s pressing climate change problem. Reconstructions are collaborative, built on the research of hundreds of scientists who apply their diverse scientific expertise and field and laboratory skill to create the individual proxy reconstructions that underlie the multi-proxy, global average temperature time series. Web 2.0 features have enabled collaborative efforts that improve the characterization of uncertainty. Raw data shared via a repository (the World Data Center for Paleoclimatology) enable new reconstructions from the collection of user-generated data. Standards propagated by expert communities facilitate quality control and interoperability. Open access to data and computer code promote transparency and make the science accessible to a broader audience. Blogs, wikis, and listservs share background information and highlight contentious as well as unique aspects of paleo science. A novel approach now underway, titled the Paleoclimate Reconstruction Challenge, and based on the sharing of simulated data (pseudo-proxies) and reconstruction results, seeks to facilitate method development, further reducing uncertainty. Broadly-useful aspects of the Challenge may find application in other fields.     

Gastropod shell repair tracks predator abundance

Predator‐prey interactions can shape biological communities and drive evolutionary change. The assessment of predation rates in modern and ancient ecosystems presents many challenges. We examined the utility of one common predation metric, shell repair frequency, as a proxy for crushing predation on marine gastropod populations. Our six localities near Bamfield, British Columbia, represented two contrasting predation regimes: three high‐wave‐energy (exposed) environments have low predation rates, while three low‐wave‐energy (protected) environments exhibit high predation rates. We measured the occurrence of repair scars for local populations of the gastropod Chlorostoma funebrale, and recorded multiple independent variables (shell measurements, water velocity, predatory crab abundance) at each locality. Fisher's exact test established that the repair frequencies observed in the protected localities were significantly greater than those of the exposed environments. Factors important in predicting the likelihood of an individual having a repair scar were examined using binomial logistic regression. A model containing the main effects of crab abundance, shell height, shell thickness and water velocity provided the best fit in predicting the presence of repair scars, with crab abundance having the largest contribution. The strong relationship between the presence of repair scars and predator abundance indicates that repair frequency is a valid tool for assessing predation intensity in gastropod populations.     

Scales and arrangements of large wood in first- through fifth-order streams of the Blue Ridge Mountains

Large wood frequency and volume were examined as a function of landscape characteristics at different spatial and temporal scales in 50 reaches of the Upper Little Tennessee River basin with drainage areas ranging from 0.3 to 30.1 km². Riparian forest cover was described laterally at the reach scale and longitudinally 1 km upstream in all tributaries. Riparian cover was analyzed with geomorphic and additional landscape variables to isolate factors that most influence wood in streams. Forested area immediately surrounding the reach was the strongest predictor of wood frequency and volume, although upstream riparian cover can explain additional variation in wood distributions. An optimal forested buffer width around the stream for large wood was not evident. The relationship between the riparian forest and wood weakens in bigger channels, as fluvial transport of pieces increases. Resurveys demonstrate that large wood is most dynamic in wide, forested reaches and changes function during floods to store sediment and organic matter.     

Phase relations in silicic systems at one-atmosphere pressure

An important control on magma rheology is the extent to which the magma crystallizes during ascent as a result of the effective undercooling created by volatile exsolution. To assess this undercooling, we need to know the final (anhydrous) one-atmosphere phase relations of silicic magmas. For this reason, we have performed one-atmosphere controlled-fO₂ crystallization experiments on dacitic to rhyolitic melt compositions (67–78 wt% SiO₂) and determined equilibrium phase assemblages, melt fractions, and some phase compositions over a range of temperatures. Experiments were run at oxygen fugacities between NNO+1 and NNO+2 and temperatures of 1,000 to 1,250°C. Constant phase compositions and sample crystallinities in runs longer than 3.5 days suggest that these runs closely approached compositional equilibrium. Additionally, melting experiments with similar compositions yielded results closely resembling those obtained in crystallization experiments. All samples have liquidus temperatures between 1,250 and 1,200 °C, with plagioclase the liquidus phase for the two most mafic samples and quartz for the most silicic sample. When associated glass compositions are projected into the Qz-Ab-Or system they define a revised one-atmosphere quartz-feldspar cotectic 5–10% less quartz normative than previously estimated. Glass compositions from each sample plot along this cotectic between 1,100 and 1,000 °C, consistent with the plagioclase-quartz co-crystallization textures found in runs at these temperatures. This cotectic constrains glass compositions to a maximum silica content of 76±1 wt% SiO₂. Reported glass compositions in excess of 77 wt% SiO₂ in volcanic samples suggest non-equilibrium crystallization, perhaps a consequence of large melt undercoolings.Editorial responsibility: I. Carmichael     

Altered landscapes, altered livelihoods: The shifting experience of informal waste collecting during Hanoi’s urban transition

A growing body of literature is concerned with urbanization processes in contemporary Vietnam and how the country’s globalizing cities of Hanoi and Ho Chi Minh City are increasingly becoming spaces of consumption. However, much less is known about how these changing spaces accommodate labour, and in turn support livelihoods. Using published empirical data on Hanoi’s informal waste collectors from 1992 [DiGregorio, M., 1994. Urban Harvest: Recycling as a Peasant Industry in Northern Vietnam. East–West Center, Hawaii, pp. 1–212] and my own data, including a survey of 575 waste collectors and 44 interviews, collected on Hanoi’s informal waste collectors in 2006, I explore the experiences of informal waste collectors (waste pickers and itinerant junk buyers) in Vietnam’s capital city of Hanoi. I argue that Vietnam’s globalizing economy and urban transition have been a catalyst for the growth of the informal waste collector population in Hanoi as well as a partial player in the gendering of this group and the work they undertake.     

Pollen-inferred vegetation and environmental changes in the central Tibetan Plateau since 8200 yr BP

The ecotone between alpine steppe and meadow in the central Tibetan Plateau is sensitive to climate changes. Here we used the pollen records from three lakes in this region to reconstruct the evolution of local vegetation and climate since 8200 cal. yr BP. The history of temperature and precipitation was reconstructed quantitatively with multi-bioclimatic indexes and a transfer function from pollen records. Results show that the steppe/meadow dominated during the period of 8200–6500 cal. yr BP, especially 8200–7200 cal. yr BP, indicating the central Tibetan Plateau was controlled by strong monsoon. The steppe dominated during the periods of 6000–4900, 4400–3900, and 2800–2400 cal. yr BP. The steppe decreased gradually and the meadow expanded during the period of 4900–4400 cal. yr BP. Three century-scale drought events occurred during 5800–4900, 4400–3900 and 2800 cal. yr BP, respectively. The first time when the regional climate shifted to the present level was at 6500 cal. yr BP in the central Plateau. Since 3000 cal. yr BP, the temperature and precipitation have decreased gradually to the present level. However, the cold climate between 700–300 cal. yr BP likely corresponds to the Little Ice Age. Supported by Chinese Academy of Sciences 100 Talents Project (Grant No. 29082762), National Natural Science Foundation of China (Grant Nos. 40671196, 40372085, 49371068, 49871078), and U.S. National Science Foundation (Grant Nos. ATM-9410491, ATM-008194)     

Intercomparison of snow water equivalent observations in the Northern Great Plains

In the Northern Great Plains, melting snow is a primary driver of spring flooding, but limited knowledge of the magnitude and spatial distribution of snow water equivalent (SWE) hampers flood forecasting. Passive microwave remote sensing has the potential to enhance operational river flow forecasting but is not routinely incorporated in operational flood forecasting. We compare satellite passive microwave estimates from the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR‐E) to the National Oceanic and Atmospheric Administration Office of Water Prediction (OWP) airborne gamma radiation snow survey and U.S. Army Corps of Engineers (USACE) ground snow survey SWE estimates in the Northern Great Plains from 2002 to 2011. AMSR‐E SWE estimates compare favourably with USACE SWE measurements in the low relief, low vegetation study area (mean difference = ?3.8 mm, root mean squared difference [RMSD] = 34.7 mm), but less so with OWP airborne gamma SWE estimates (mean difference = ?9.5 mm, RMSD = 42.7 mm). An error simulation suggests that up to half of the error in the former comparison is potentially due to subpixel scale SWE variability, limiting the maximum achievable RMSD between ground and satellite SWE to approximately 26–33 mm in the Northern Great Plains. The OWP gamma versus AMSR‐E SWE comparison yields larger error than the point‐scale USACE versus AMSR‐E comparison, despite a larger measurement footprint (5–7 km² vs. a few square centimetres, respectively), suggesting that there are unshared errors between the USACE and OWP gamma SWE data.     

Beyond the “fit”: introducing climate forecasts among organic farmers in Georgia (United States)

Organic farmers are a prime clientele for climate services by virtue of their social profile and vulnerability of produce to climate extremes. The study draws on an online survey and in-depth interviews with organic farmers in Georgia (United States). It shows that organic farmers access and act on climate information in ways that reflect their emphasis on diversified and flexible systems. They favor a pluralistic knowledge base that integrates scientific expertise with place-based experience and intuitive understandings. Their management style combines information at multiple temporal scales and draws on a range of technical and social resources. Translating climate forecasts into usable science for organic farming requires attention to the identities, commitments, and relationships that define the organic farming community.