A split flow chamber with artificial sediment to examine the below-ground microenvironment of aquatic macrophytes

We present a new experimental set-up enabling fine-scale examination of how changing environmental conditions affect the below-ground biogeochemical microenvironment of aquatic macrophytes. By means of microsensor and planar optode technology, the influence of plant-mediated radial O₂ release on the below-ground chemical microenvironment of Zostera muelleri and Halophila ovalis was determined in high spatio-temporal resolution. The seagrass specimens were cultured in a new split flow chamber with artificial sediment made of a deoxygenated seawater–agar solution with added sulphide. Microelectrode measurements revealed radial O₂ release from the root–shoot junction of both Z. muelleri and H. ovalis during both light stimulation and darkness, resulting in a rapid decrease in H₂S concentration, and a significant drop in pH was observed within the plant-derived oxic microzone of Z. muelleri. No radial O₂ release was detectable from the below-ground tissue of Z. muelleri during conditions of combined water-column hypoxia and darkness, leaving the plants more susceptible to sulphide invasion. The spatial O₂ heterogeneity within the immediate rhizosphere of Z. muelleri was furthermore determined in two dimensions by means of planar optodes. O₂ images revealed a decrease in the spatial extent of the plant-derived oxic microzone surrounding the below-ground tissue during darkness, supporting the microelectrode measurements. This new experimental approach can be applied to all rooted aquatic plants, as it allows for direct visual assessment of the below-ground tissue surface during microprofiling, while enabling modification of the above-ground environmental conditions.     

Enforcement and price controls in emissions trading

This paper examines how enforcement affects the structure and performance of emissions trading programs with price controls under uncertainty about firms' abatement costs. The analysis highlights how an enforcement strategy can cause abatement-cost risk to be transmitted to enforcement costs via the price of permits. When this occurs, accommodating the effect of abatement-cost risk with an optimal policy results in higher expected emissions and lower expected permit price than their second-best optimal values. However, it is possible to design an enforcement strategy that shields enforcement costs from abatement-cost risk by tying sanctions directly to permit prices. This enforcement strategy stabilizes enforcement effort, the optimal permit supply and price controls are independent of enforcement costs, and the policy produces the second-best optimal outcome.     

Spatial and social connectivity of fish-eating “Resident” killer whales (Orcinus orca) in the northern North Pacific

The productive North Pacific waters of the Gulf of Alaska, Aleutian Islands and Bering Sea support a high density of fish-eating “Resident” type killer whales (Orcinus orca), which overlap in distribution with commercial fisheries, producing both direct and indirect interactions. To provide a spatial context for these interactions, we analyzed a 10-year dataset of 3,058 whale photo-identifications from 331 encounters within a large (linear ~4,000 km) coastal study area to investigate the ranging and social patterns of 532 individually identifiable whales photographed in more than one encounter. Although capable of large-scale movements (maximum 1,443 km), we documented ranges generally <200 km, with high site fidelity across summer sampling intervals and also re-sightings during a winter survey. Bayesian analysis of pair-wise associations identified four defined clusters, likely representing groupings of stable matrilines, with distinct ranging patterns, that combined to form a large network of associated whales that ranged across most of the study area. This provides evidence of structure within the Alaska stock of Resident killer whales, important for evaluating ecosystem and fisheries impacts. This network included whales known to depredate groundfish from longline fisheries, and we suggest that such large-scale connectivity has facilitated the spread of depredation.     

Identifying trophic relationships within the high Arctic benthic community: how much can fatty acids tell?

Multivariate analysis of fatty acids (FA) profiles proved to be a useful tool for demonstrating feeding preferences of Arctic invertebrates belonging to several taxonomic groups collected during summer and winter seasons in the Spitsbergen fjords (Arctic). Within phytodetrivorous taxa, the enhanced proportions of 16:1n-7, C16 polyunsaturated fatty acids (PUFA) and 20:5n-3 in crustaceans clearly reflected selective ingestion of diatoms, while high amounts of 22:6n-3 and C18 FAs found in molluscs indicated flagellate-based nutrition. High levels of C20 PUFA and 16:1n-7 together with the typical bacterial FAs were found in winter specimens of deposit-feeding polychaetes showing their reliance on highly reworked organic matter during this season. Our results suggest that 18:1n-9 may not be a reliable marker of carnivory feeding within benthic taxa. Lipid signatures of omnivores and carnivores/detrivores usually originated from a variety of dietary sources, of which few possess highly characteristic FA features. Still, elevated levels of Calanus markers (20:1 and 22:1 moieties) characterized species linked to the pelagic food chains, while 20:4n-6 proved to be a useful indicator of foraminiferan consumption. We highlight the need for a multimethod approach, since complexity of benthic food webs along with general lack of unambiguous FA trophic markers prevents tracking of trophic relationships with use of FA analysis alone. Based on their FA composition, we showed that benthic species represent a source of essential PUFA and could play a fundamental role in the Arctic food webs transferring energy derived from variable pelagic and benthic resources to upper trophic levels.     

Bootstrap confidence intervals for adaptive cluster sampling design based on Horvitz–Thompson type estimators

Perez and Pontius (J Stat Comput Simul 76:755–764, 2006) introduced several bootstrap methods under adaptive cluster sampling using a Horvitz–Thompson type estimator. Using a simulation study, they showed that their proposed methods provide confidence intervals with highly understated coverage rates. In this article, we first show that their bootstrap methods provide biased bootstrap estimates. We then define two bootstrap methods, based on the method of Gross (Proceeding of the survey research methods section. American Statistical Association, Alexandria, VA, pp 181–184, 1980) and Bootstrap With Replacement, that provide unbiased bootstrap estimates of the population mean with bootstrap variances matching the corresponding unbiased variance estimator. Using a simulation study, we show that the bootstrap confidence intervals based on our proposed methods have better performance than those based on available bootstrap methods, in the sense of having coverage proportion closer to the nominal coverage level. We also compare the proposed intervals to empirical likelihood based intervals in small samples.     

Estimating variation in surface emissivities of intertidal macroalgae using an infrared thermometer and the effects on temperature measurements

Accurate measurements of surface temperatures with an infrared (IR) thermometer require input of the emissivities of the surfaces being measured; however, few determinations of the emissivities of intertidal organisms’ surfaces have been made. Emissivities of intertidal macroalgae were measured to determine whether algal species, measurement angle, hydration, and layering affected them. Emissivities were similar and averaged 0.94 among 11 of 13 species. The species with lower and more variable emissivities (Chondracanthus exasperatus and Desmarestia viridis) differed in morphology from the other species, which were relatively flat thin blades with little surface texture. Measurement angle caused emissivities to decrease significantly in Mazzaella splendens but not in three other species. Hydration and layering of Ulva lactuca also had no effect. At 22 °C, measured temperatures were within 1 °C of actual temperatures when thermometer emissivity settings ranged from 0.75 to 1.00. When emissivities were set lower than actual values, measured temperatures were lower than actual temperatures at 15 °C and higher than actual temperatures at 60 °C. When the IR thermometer was used to measure surface temperatures of nine species of intertidal algae immediately before they were inundated by the incoming tide, temperatures were higher in mid intertidal than low intertidal individuals and higher on a sunnier day than an overcast day. Temperatures of U. lactuca increased with increasing height on the shore, but temperatures of Ulvaria obscura did not. Temperatures were also higher in Fucus distichus blades than receptacles, and lower in U. lactuca and M. splendens occurring in the lower layers of stacks of algae.     

Within- and transgenerational effects of ocean acidification on life history of marine three-spined stickleback (Gasterosteus aculeatus)

Some studies have demonstrated that elevated CO₂ concentrations in ocean waters negatively impact metabolism and development of marine fish. Particularly, early developmental stages are probably more susceptible to ocean acidification due to insufficient regulations of their acid-base balance. Transgenerational acclimation can be an important mechanism to mediate impacts of increased CO₂ on marine species, yet very little is known about the potential of parental effects in teleosts. Therefore, transgenerational effects were investigated on life history in juvenile three-spined sticklebacks Gasterosteus aculeatus by acclimating parents (collected in April 2012, 55°03′N, 8°44′E) and offspring to ambient (~400 µatm) and elevated (~1,000 µatm) CO₂ levels and measured parental fecundity as well as offspring survival, growth and otolith characteristics. Exposure to elevated CO₂ concentrations led to an increase in clutch size in adults as well as increased juvenile survival and growth rates between 60 and 90 days post-hatch and enlarged otolith areas compared with fish from ambient CO₂ concentrations. Moreover, transgenerational effects were observed in reduced survival and body size 30 days post-hatch as well as in enlarged otoliths at the end of the experiment, when fathers or both parents were acclimated to the high-CO₂ environment. These results may suggest that elevated CO₂ concentrations had rather positive effects on life-history traits of three-spined sticklebacks, but that parental acclimation can modify these effects without improving offspring fitness. Although the mechanistic basis of such transgenerational acclimation remains unclear, selective gradients within generations seem to determine the direction of transgenerational effects.     

Amphibian myiasis. Blowfly larvae (Lucilia bufonivora,Diptera: Calliphoridae) coping with the poisonous skin secretion of the common toad (Bufo bufo)

The blowfly Lucilia bufonivora shows high host specificity for toads despite the host’s toxic skin secretion, which consists mainly of bufadienolides. These toxins are effective blockers of the Na⁺, K⁺-ATPase, an enzyme that is essential for many physiological processes in animals. Whereas common toad (Bufo bufo) toxins were identified in the larvae of the fly, few toxins were found in the pupae and empty puparia as trace amounts, while adult flies were entirely free of these toxic compounds. Similar results were obtained when larvae of generalist necrophagous blowflies (L. sericata, Calliphora vicina) fed on toad carcasses. Analysis of the Na⁺, K⁺-ATPase gene revealed no amino acid substitution at positions known to mediate resistance to bufadienolides in other systems. Alternative mechanisms of resistance such as efficient excretion of the compounds may enable the flies to use this poisonous food source.     

Are vocal signals used to recognize individuals during male–male competition in greater prairie-chickens (Tympanuchus cupido)?

Vocal signaling can be an important component of vertebrate communication during social interactions. If vocalizations vary among individuals but are consistent within a given individual, they may be used to discriminate among individuals. In many species, territorial males use vocalizations to discriminate between neighbors and strangers and either respond more aggressively toward strangers relative to neighbors (“dear enemy” effect) or they respond more aggressively toward neighbors relative to strangers (“nasty neighbor” effect). In the greater prairie-chicken (Tympanuchus cupido), male vocalizations are an integral part of the display males produce on leks. We investigated whether male greater prairie-chickens discriminate among familiar individuals on their own territory, familiar individuals outside their normal territory and strangers from a nearby lek. Vocal characteristics varied among males, suggesting that vocalizations may potentially be used by prairie-chickens to identify individuals. Males responded to playback of prairie-chicken calls by vocalizing at a faster rate and approaching the playback speaker, but did not vary in their response to the vocalizations based on the identity of the caller. Our results suggest that variation is present among the vocalizations of individual male greater prairie-chickens, but males do not appear to discriminate among familiar individuals and strangers based solely on their “boom” vocalizations. Greater prairie-chicken vocalization likely functions as a way of announcing that a territory is occupied and defended, but it may also serve as a way of advertising to conspecifics or as a signal that is secondary to other forms of communication.