Terrestrial Food Sources Research Articles

Development of food and gastronomy in the sub-Antarctic end of the world

Regional food and gastronomy flourish worldwide driven by unique local foods, the remembrance of old culinary traditions, and the visitors’ desire to taste memorable dishes in an environment evoking cultural heritage and geographical uniqueness. The sub-Antarctic Magellan region of Chile is the southernmost zone of the planet and is unique in centenary food and culinary practices. A detailed description of marine and terrestrial local food sources and biocultural traditions is documented. This article presents a PCF to develop local food and gastronomy in this region. Collection and analysis of bibliometric data led to three pillars supporting the FPC: the nutritional value and uniqueness of local foods and culinary traditions; a booming sustainable tourism that drives the development of gastronomic endeavors, and; lessons from past experiences in other remote places. The proposed PCF may be adapted to different regions worldwide. Recent gastronomic initiatives to implement this PCF at the Cape Horn International Center in Puerto Williams (Chile) are also described.

Habitat use of urban nesting yellow-legged gulls in Croatia during the breeding season

Because of increasing urbanization, some opportunistic birds such as gulls, started to exploit various artificial marine and terrestrial food sources. To better understand urban gull ecology and habitat use, a study was done on a yellow-legged gull (Larus michahellis) during the breeding season in Zadar, a coastal city on the Adriatic Sea. Ten adult breeding yellow-legged gulls (five females and five males) were caught on building rooftops during the late incubation period and were fitted with GPS-GSM solar power transmitters. In total, 2377 trip segments (no. GPS points = 19906) were analyzed, with most of them being classified as nest attendance (56.32 %) and foraging movements (37.10 %). Tracking data showed that the gulls mostly use marine and urban areas, agricultural lands, a dump site, and grasslands. Females were more active while foraging, with a longer duration and trip segment length, travelling further away from the breeding colony, while males tended to rest more than females. Both males and females exploit various habitats for foraging and resting, however females used agricultural lands significantly more than males. Even though gulls are generalists, some individuals showed a preference for certain habitats. After calculating the proportional similarity index, individuals showed high specialization for a certain habitat.

Infant Milk Powder After γ-Irradiation and Accelerated Storage as an Indicator for Space Food Stability

At present, terrestrial food sources are used to provision astronauts for engaged in space missions confined to low Earth orbit. However, in the future, long-duration space exploration is planned for the Moon, and, beyond that, to Mars. Food for such extended missions needs a shelf-life of up to 5 years, a sustained nutritional and product quality. Space radiation can impact on such food, but little is known of what impact this could have on these materials. In this study, we evaluated the impact of radiation dosage and accelerated storage on infant milk powder (a formulated product consisting of proteins, fat, lactose, vitamins, and minerals), to evaluate its potential as an indicator for (chemical) space food stability. The milk powder was irradiated at different dosages (0, 2, 10, and 50 kGy) and underwent different storage conditions (20 or 50 °C for 0, 14, 28, 56, and 77 days), with subsequent color measurement and chemical analysis. It was found that γ irradiation had an impact on the milk powder’s color. It was speculated that this change was related to the Maillard reaction. Some changes were also found with the chemical composition, particularly, vitamins A and C, unexpectedly due to their susceptibility to radiation. Notable differences were not observed though for other components (vitamins, fatty acids, and amino acids). We conclude that infant milk powder shows great promise as an indicator of the impact of γ radiation, and accelerated storage, for (chemical) space food stability.

Impacts of forest harvesting on mercury concentrations and methylmercury production in boreal forest soils and stream sediment

Methylmercury (MeHg) is the most neurotoxic and bioaccumulative form of mercury (Hg) present in the terrestrial and aquatic food sources of boreal ecosystems, posing potential risks to wildlife and human health. Harvesting impacts on Hg methylation and MeHg concentrations in forest soils and stream sediment are not fully understood. In this study, a field investigation was carried out in 4 harvested and 2 unharvested boreal forest watersheds, before and after harvest, to better understand impacts on Hg methylation and MeHg concentration in soils and stream sediment, including their responses to different forest management practices. Changes in total Hg (THg) and MeHg concentrations, first-order potential rate constants for Hg methylation and MeHg demethylation (Kmeth and Kdemeth) as well as total carbon content and carbon-to-nitrogen ratio post-harvest in upland, wetland and riparian soils and stream sediment were assessed and compared. Increases in MeHg production were minimal in upland, wetland or riparian soils after harvest. Sediment in streams with minor buffer protection (∼3 m), greater fractions (>75%) of harvested watershed area and more road construction had significantly increased THg and MeHg concentrations, %-MeHg, Kmeth and total carbon content post-harvest. From these patterns, we infer that inputs of carbon and inorganic Hg into harvest-impacted stream sediment are likely sourced from the harvested upland areas and stimulate in situ MeHg production in stream sediment. These findings indicate the importance of stream sediment as potential MeHg pools in harvested forest watersheds. The findings also demonstrate that forest management practices aiming to mitigate organic matter and Hg inputs to streams can effectively alleviate harvesting impacts on Hg methylation and MeHg concentrations in stream sediment.

Worth the dip? Polar bear predation on swimming flightless greater snow geese and estimation of energetic efficiency

As sea-ice cover is shrinking, polar bears ( Ursus maritimus, Phipps, 1774) face decreased access to seals, their primary prey, resulting in a greater dependence on terrestrial food sources. Whether polar bears can benefit from these terrestrial food sources, however, depends on their ability to find and capture prey items without expending more energy than is acquired. Here, we report one of the northernmost observations of polar bear predation on adult birds. The bear used a dive-hunting technique, which consisted of submerging itself, approaching underwater, and catching flightless greater snow geese ( Anser caerulescens caerulescens (Linnaeus, 1758)) from beneath the surface of a tundra pond. After evaluating energy expenditures during swimming and energy intakes from consuming geese, we estimated that this rarely documented dive-hunting technique could be energetically profitable for a certain range of pursuit durations. This observation highlights the behavioral plasticity that polar bears can deploy to punctually exploit land-based food sources.

Tissue‐ and diet‐dependent stable carbon and nitrogen isotope discrimination: a calibration study in a captive shorebird species

In ecology, stable‐isotope ratios are widely used to determine diets of organisms and reconstruct food webs. This is usually done by analyzing the stable‐isotope ratios of nitrogen (δ15N), which increase with increasing trophic level, and those of carbon (δ13C), which correlate with the δ13C value of food source(s) and generally differ between terrestrial and marine food sources. Assimilation of food changes stable‐isotope ratios, resulting in different values between the food source and its consumer. These differences are known as isotope trophic discrimination factors and, if known, can be used to determine from the stable‐isotope ratios in the consumer's tissue what the consumer has been eating. What is often ignored is that discrimination factors can differ between consumer's food sources and also between tissue types. Therefore, we performed a controlled feeding study in red knots Calidris canutus to determine discrimination factors between different food sources and red knot tissues. We kept two groups of red knots in captivity on a stable diet, one group feeding on mudsnails and the other on Trouvit pellets, for several months, during which the birds molted their feathers. We analyzed δ13C and δ15N in both food sources and in five red knot tissues (blood cells, blood plasma and three feather types) and subsequently calculated the isotope discrimination factors. We confirmed that the discrimination factors differed between tissues, and also between diets. Our values deviated from general averages reported in reviews on a wide range of animals/birds, but were very similar to values from previous red knot and dunlin studies. We therefore think that our discrimination factors can be used in future stable isotope studies, not only on red knots, but also on other marine shorebird species and plea for careful consideration of using the right discrimination factors.Keywords: δ13C, δ15N, discrimination factor, red knot, shorebird, stable isotope

Enculturating Coastal Environments in the Middle Mesolithic (8300–6300 cal BCE) – Site Variability, Human–Environment Relations, and Mobility Patterns in Northern Vestfold, SE-Norway

Abstract The coastal settlement in Middle Mesolithic (MM) Southeast Norway is generally described as a dynamic system of small, short-lived sites and large sites that were visited repeatedly over a long time. It has been suggested that in this period – compared to the preceding Early Mesolithic (EM) – an increased attraction towards the large archipelagos along the Norwegian coast, and their broad spectrum of both marine and terrestrial food sources, took place. This has, however, been debated. An important background for the discussion is the documented population influx and the abrupt shift in tool technology around 8300 cal BCE. The question remains whether this great social and technological upheaval was followed by a transformation or break in the environmental knowledge and changes in the ways of living, such as new human–environment relations, settlement systems, and mobility patterns. We propose that the continuous process of enculturation of the land and environment would have played a decisive role in the societal development. In this article, we therefore investigate details of site construction and mobility patterns, as well as the marking of the land by the establishment of settlement sites and exploitation of lithic raw materials on a larger scale. We concentrate our investigation on the on-site activity, site location, lithic raw material economy, and technological organisation, which brings renewed opportunities for discussing enculturation processes in the period. Our results document a diverse settlement pattern, as well as diachronic variation, suggesting an internal duality within the sociocultural development process in the area. The article presents the new results from the InterCity Vestfold project, situated by the Oslofjord west coast. Our data comprise a total of eight excavated and 69 surveyed sites from 4 municipalities. A strong isostatic land uplift caused continuous and rapid changes in the shoreline configuration and its nearby environments, in the Oslofjord area throughout the Mesolithic. To enable the discussion of human–environment relations, we therefore present a new relative sea level (RSL) curve, supplying detailed data on the shoreline development in the project area.

Broad Whitefish (Coregonus nasus) isotopic niches: Stable isotopes reveal diverse foraging strategies and habitat use in Arctic Alaska.

Understanding the ecological niche of some fishes is complicated by their frequent use of a broad range of food resources and habitats across space and time. Little is known about Broad Whitefish (Coregonus nasus) ecological niches in Arctic landscapes even though they are an important subsistence species for Alaska's Indigenous communities. We investigated the foraging ecology and habitat use of Broad Whitefish via stable isotope analyses of muscle and liver tissue and otoliths from mature fish migrating in the Colville River within Arctic Alaska. The range of δ13C (-31.8- -21.9‰) and δ15N (6.6-13.1‰) across tissue types and among individuals overlapped with isotope values previously observed in Arctic lakes and rivers, estuaries, and nearshore marine habitat. The large range of δ18O (4.5-10.9‰) and δD (-237.6- -158.9‰) suggests fish utilized a broad spectrum of habitats across elevational and latitudinal gradients. Cluster analysis of muscle δ13C', δ15N, δ18O, and δD indicated that Broad Whitefish occupied four different foraging niches that relied on marine and land-based (i.e., freshwater and terrestrial) food sources to varying degrees. Most individuals had isotopic signatures representative of coastal freshwater habitat (Group 3; 25%) or coastal lagoon and delta habitat (Group 1; 57%), while individuals that mainly utilized inland freshwater (Group 4; 4%) and nearshore marine habitats (Group 2; 14%) represented smaller proportions. Otolith microchemistry confirmed that individuals with more enriched muscle tissue δ13C', δD, and δ18O tended to use marine habitats, while individuals that mainly used freshwater habitats had values that were less enriched. The isotopic niches identified here represent important foraging habitats utilized by Broad Whitefish. To preserve access to these diverse habitats it will be important to limit barriers along nearshore areas and reduce impacts like roads and climate change on natural flow regimes. Maintaining these diverse connected habitats will facilitate long-term population stability, buffering populations from future environmental and anthropogenic perturbations.

Dissipation of seabird‐derived nutrients in a terrestrial insular trophic web

AbstractHighly mobile organisms can transport nutrients and energy among distinct ecosystems, such as between oceanic foraging areas and terrestrial breeding sites. Seabirds are great nutrient carriers and potentially play a key role in the maintenance of trophic webs on islands. In this study, we assessed three dimensions of marine nutrient dissipation—horizontal, temporal and vertical—on the tropical Meio Island of Fernando de Noronha Archipelago, Brazil. For this, C3 and C4 plants, ants and spiders found in a 100 m long transect between colonies of masked (Sula dactylatra) and red‐footed boobies (Sula sula) were sampled during the rainy (the masked booby breeding period) and dry seasons (the red‐footed booby breeding period). The marine contribution to the terrestrial trophic web was analysed using Bayesian mixing models from a carbon and nitrogen stable isotope data set. The main findings indicate that marine nutrients in the terrestrial trophic web dissipated horizontally as the distance from the colony increased, which was more marked during the rainy season. On the vertical axis, the relative contribution of marine nutrients in terrestrial consumers was strongly related to food habits but not necessarily to the trophic level, dissipating rather than increasing, due to variable omnivory and the use of terrestrial food sources. The breeding strategy of the masked booby (i.e. incubating eggs on the ground), in addition to a larger body size and larger colony, could produce a more concentrated pulse of nutrients in comparison to seabirds nesting sparsely on trees, contributing more efficiently to the enrichment of marine nutrients on land. The importance of seabirds for the maintenance of interconnected ecosystems has been demonstrated, and the role of marine‐derived nutrients in the enrichment of nutrient‐poor tropical islands.

An assessment of mercury and its dietary drivers in fur of Arctic wolves from Greenland and High Arctic Canada

Mercury has become a ubiquitous hazardous element even ending up in pristine areas such as the Arctic, where it biomagnifies and leaves especially top predators vulnerable to potential health effects. Here we investigate total mercury (THg) concentrations and dietary proxies for trophic position and habitat foraging (δ15N and δ13C, respectively) in fur of 30 Arctic wolves collected during 1869–1998 in the Canadian High Arctic and Greenland. Fur THg concentrations (mean ± SD) of 1.46 ± 1.39 μg g −1 dry weight are within the range of earlier reported values for other Arctic terrestrial species. Based on putative thresholds for Hg-mediated toxic health effects, the studied Arctic wolves have most likely not been at compromised health. Dietary proxies show high dietary plasticity among Arctic wolves deriving nutrition from both marine and terrestrial food sources at various trophic positions. Variability in THg concentrations seem to be related to the wolves' trophic position rather than to different carbon sources or regional differences (East Greenland, the Foxe Basin and Baffin Bay area, respectively). Although the present study remains limited due to the scarce, yet unique historic study material and small sample size, it provides novel information on temporal and spatial variation in Hg pollution of remote Arctic species.

Dietary shifts may underpin the recovery of a large carnivore population.

Supporting the recovery of large carnivores is a popular yet challenging endeavour. Estuarine crocodiles in Australia are a large carnivore conservation success story, with the population having extensively recovered from past heavy exploitation. Here, we explored if dietary changes had accompanied this large population recovery by comparing the isotopes δ13C and δ15N in bones of crocodiles sampled 40 to 55 years ago (small population) with bones from contemporary individuals (large population). We found that δ13C and δ15N values were significantly lower in contemporary crocodiles than in the historical cohort, inferring a shift in prey preference away from marine and into terrestrial food webs. We propose that an increase in intraspecific competition within the recovering crocodile population, alongside an increased abundance of feral ungulates occupying the floodplains, may have resulted in the crocodile population shifting to feed predominantly upon terrestrial food sources. The number of feral pigs consumed to sustain and grow crocodile biomass may help suppress pig population growth and increase the flow of terrestrially derived nutrients into aquatic ecosystems. The study highlights the significance of prey availability in contributing to large carnivore population recovery.

Dietary preferences of brachyuran crabs from Taiwan for marine or terrestrial food sources: evidence based on fatty acid trophic markers

BackgroundTrophic interactions are key processes, which determine the ecological function and performance of organisms. Many decapod crustaceans feed on plant material as a source for essential nutrients, e.g. polyunsaturated fatty acids. Strictly herbivorous feeding appears only occasionally in marine decapods but is common in land crabs. To verify food preferences and to establish trophic markers, we studied the lipid and fatty acid composition of the midgut glands of two marine crab species (Grapsus albolineatus and Percnon affine), one semi-terrestrial species (Orisarma intermedium, formerly Sesarmops intermedius), and one terrestrial species (Geothelphusa albogilva) from Taiwan.ResultsAll species showed a wide span of total lipid levels ranging from 4 to 42% of the dry mass (%DM) in the marine P. affine and from 3 to 25%DM in the terrestrial G. albogilva. Triacylglycerols (TAG) were the major storage lipid compound. The fatty acids 16:0, 18:1(n-9), and 20:4(n-6) prevailed in all species. Essential fatty acids such as 20:4(n-6) originated from the diet. Terrestrial species also showed relatively high amounts of 18:2(n-6), which is a trophic marker for vascular plants. The fatty acid compositions of the four species allow to clearly distinguish between marine and terrestrial herbivorous feeding due to significantly different amounts of 16:0, 18:1(n-9), and 18:2(n-6).ConclusionsBased on the fatty acid composition, marine/terrestrial herbivory indices were defined and compared with regard to their resolution and differentiating capacity. These indices can help to reveal trophic preferences of unexplored species, particularly in habitats of border regions like mangrove intertidal flats and estuaries.

Seaweed-eating sheep show that δ34 S evidence for marine diets can be fully masked by sea spray effects.

Stable sulfur isotope compositions (δ34 S values) are a useful marker of terrestrial (lower δ34 S) versus marine (higher δ34 S) diets. In coastal areas, 34 S-enriched sea spray can obscure these marine/terrestrial differences. We sought to establish whether δ34 S values of sea spray-affected terrestrial fauna can be distinguished from those of marine-feeding terrestrial fauna. We measured bone and dentine collagen δ34 S values, as well as stable carbon (δ13 C) and nitrogen (δ15 N) isotope compositions via continuous flow elemental analysis/isotope ratio mass spectrometry of 21 sheep (Ovis aries) raised on an island (North Ronaldsay, UK) of <7 km2 that had widely divergent access to marine (seaweed) and heavily sea spray-affected terrestrial (grass) food sources. We also analyzed the bone collagen of marine and terrestrial fauna from this island. Sheep bone collagen showed well-defined trends with highly significant correlations between δ13 C and δ15 N values indicative of feeding along a continuum of fully terrestrial to fully marine diets, consistent with other modern baseline data from marine and terrestrial animals in the same area. In contrast, δ34 S values were generally elevated for all sheep and were not significantly correlated with either δ13 C or δ15 N values. Our findings demonstrate that δ34 S values are poorly suited for differentiating marine and terrestrial diets in terrestrial animals in areas with pronounced sea spray effects. Care must be taken to characterize the isotopic compositions of potential food items before δ34 S values are used as a marker for reliance on marine protein in modern and ancient contexts.

Assessment of environmental health based on a complementary approach using metal quantification, oxidative stress and trophic ecology of two gull species (Larus michahellis &Larus audouinii) breeding in sympatry

Metal pollution is currently a major issue in marine ecosystems, as organisms, and particularly seabirds, are exposed and accumulating increased levels from several anthropogenic sources. A set of 13 metals were quantified in two gull species breeding in sympatry, and in two distinct colonies separated by ca. 400 km. Oxidative stress was measured, and stable isotope analyses were used to link metal contamination and oxidative stress with the trophic ecology of each species/population. There was a clear segregation of metal contamination between the two species and to a much lesser extent between colonies. Overall, Audouin's gull was the most contaminated species for most metals, once this species relies mainly on fish and other marine resources. The Yellow-legged gull feeds regularly on terrestrial food sources besides fish, which may dilute contamination levels. Oxidative stress responses were related with birds' trophic ecology and foraging habitat, but apparently not with metal contamination.

Post-glacial hunter-gatherer subsistence patterns in Britain: dietary reconstruction using FRUITS

The diets of 85 individuals from 21 sites were modelled using FRUITS based on their bulk bone collagen C and N isotope ratio signatures. The sites, which occur in a range of environments, group into three distinct periods corresponding to the British ‘Late Upper Palaeolithic’, ‘Early Mesolithic’ and ‘Late Mesolithic’, respectively. The FRUITS models for three LUP sites dated to the Bølling–Allerød Interstadial suggest an emphasis on terrestrial (animal and plant) resources. The FRUITS predictions for the Early and Late Mesolithic suggest there was significant variability in diet between sites and occasionally between individuals from the same site. The Late Mesolithic coastal site of Cnoc Coig in western Scotland shows the expected emphasis on marine resources. In contrast, Early and Late Mesolithic coastal sites in South Wales show greater reliance on terrestrial food sources. In several cases, our model predictions differ from the interpretations of previous authors. A surprising outcome is the lack of evidence for the consumption of freshwater resources at sites near large rivers. We add the caveat that our model predictions are likely influenced by inadequate baseline δ13C and δ15N data for wild terrestrial plant and aquatic resources, in particular.

Carbon δ13C Isotopic Marker Values Correlate with Carotenoid-Based Bill Colouration in Adult Yellow-Legged Gulls Larus michahellis

La coloracion basada en carotenoides que presentan muchas aves puede reflejar honestamente la calidad del individuo, ya que deben ser obtenidos mediante la dieta. Estos pigmentos son importantes para varias funciones fisiologicas y los individuos pueden buscar compensar entre la distribucion de los carotenoides para estos usos y su acumulacion para atributos sexuales secundarios y sociales. La gaviota patiamarilla Larus michahellis es una especie oportunista que se alimenta de una gran variedad de presas. En este trabajo hemos estudiado si la coloracion basada en carotenoides (pico, mancha roja, anillo orbital) esta relacionada con la ecologia trofica inferida a partir de la composicion isotopica de plumas de aves adultas en tres colonias de esta especie. El marcador isotopico del δ13C correlaciono negativamente con la coloracion basada en carotenoides (area de la mancha roja). Contrariamente a la prediccion hecha a priori, el marcador indica que un mayor consumo de presas terrestres y recursos de vertedero podria ayudar a generar una mancha roja del pico mayor en gaviotas de cualquier sexo. En hembras, no se detecto ninguna correlacion entre las signaturas isotopicas y el volumen de los huevos. El resultado de que un consumo mayor de presas marinas implica una mancha roja menor apoya otros descritos en estudios anteriores que muestran efectos aparentemente positivos de comer en ambientes terrestres humanos sobre el fenotipo de aves adultas. Los resultados pueden sugerir que un mayor consumo de presas marinas puede no ser tan positivo como el presentado en estudios previos. Sin embargo, el efecto de los componentes toxicos potenciales que se pueden obtener de algunas fuentes de alimentacion deberia ser estudiado mas a fondo. Deberiamos de considerar tambien los probables efectos subletales retardados asociados a estos habitats y que se ejercerian sobre los adultos y, probablemente tambien, sobre los pollos.

Alligators in the abyss: The first experimental reptilian food fall in the deep ocean.

The high respiration rates of the deep-sea benthos cannot be sustained by known carbon supply pathways alone. Here, we investigate moderately-sized reptilian food falls as a potential alternative carbon pathway. Specifically, three individual carcasses of Alligator mississippiensis were deployed along the continental slope of the northern Gulf of Mexico at depths of ~2000m in early 2019. We posit the tough hide of alligators would impeded scavengers by limiting access to soft tissues of the alligator fall. However, the scavengers began consuming the food fall 43 hours post-deployment for one individual (198.2cm, 29.7kg), and the carcass of another individual (175.3 cm, 19.5kg) was completely devoid of soft tissue at 51 days post-deployment. A third individual (172.7cm, 18.5kg) was missing completely after 8 days, with only the deployment harness and weight remaining drug 8 meters away, suggesting a large elasmobranch scavenger. Additionally, bones recovered post-deployment reveal the first observations of the bone-eating Osedax in the Gulf of Mexico and are confirmed here as new to science. The findings of this study indicate the quick and successful utilization of terrestrial and aquatic-based carbon food sources in the deep marine environment, though outcome variability may be high.

Recently-adopted foraging strategies constrain early chick development in a coastal breeding gull.

Human-mediated food sources offer possibilities for novel foraging strategies by opportunistic species. Yet, relative costs and benefits of alternative foraging strategies vary with the abundance, accessibility, predictability and nutritional value of anthropogenic food sources. The extent to which such strategies may ultimately alter fitness, can have important consequences for long-term population dynamics. Here, we studied the relationships between parental diet and early development in free-ranging, cross-fostered chicks and in captive-held, hand-raised chicks of Lesser Black-backed Gulls (Larus fuscus) breeding along the Belgian coast. This traditionally marine and intertidal foraging species is now increasingly taking advantage of human activities by foraging on terrestrial food sources in agricultural and urban environments. In accordance with such behavior, the proportion of terrestrial food in the diet of free-ranging chicks ranged between 4% and 80%, and consistent stable isotope signatures between age classes indicated that this variation was mainly due to between-parent variation in feeding strategies. A stronger terrestrial food signature in free-ranging chicks corresponded with slower chick development. However, no consistent differences in chick development were found when contrasting terrestrial and marine diets were provided ad libitum to hand-raised chicks. Results of this study hence suggest that terrestrial diets may lower reproductive success due to limitations in food quantity, rather than quality. Recent foraging niche expansion toward terrestrial resources may thus constitute a suboptimal alternative strategy to marine foraging for breeding Lesser Black-backed Gulls during the chick-rearing period.

Increased reliance of stream macroinvertebrates on terrestrial food sources linked to forest management intensity.

Our understanding of how forest management practices affect the relative importance of autochthonous vs. allochthonous resource use by headwater stream food webs is relatively poor. To address this, we used stable isotope (C, N, and H) analyses of food sources and macroinvertebrates from 15 streams in New Brunswick (Canada) and assessed how different catchment conditions arising from the gradient in forest management intensity affect the contribution of autochthonous resources to these food webs. Aquatic primary production contributed substantially to the biomass of invertebrates in these headwater streams, especially for scrapers and collector-gatherers (25-75%). However, the contribution of algae to food webs decreased as forest management intensity (road density and associated sediments, water cations/carbon, and dissolved organic matter humification) increased, and as canopy openness decreased. This trend was probably due to an increase in the delivery of organic and inorganic terrestrial materials (dissolved and in suspension) in areas of greater harvesting intensity and road density, which resulted in more heterotrophic biofilms. Overall, results suggest that, despite the presence of riparian buffers, forest management can affect stream food web structure via changes in energy flows, and that increased protection should be directed at minimizing ground disturbance in areas with direct hydrological connection to streams and at reducing dissolved and particulate matter inputs from roads and stream crossings in catchments with high degrees of management activity.

Terrestrial organic matter increases zooplankton methylmercury accumulation in a brown-water boreal lake

Increases in terrestrial organic matter (tOM) transport from catchments to boreal lakes can affect methylmercury (MeHg) accumulation in aquatic biota both directly by increasing concentrations of aqueous MeHg, and indirectly through effects on MeHg bioavailability and on energy pathways in the lower food web. We carried out a detailed seasonal study of water chemistry, zooplankton diet, and MeHg accumulation in zooplankton in two lakes with contrasting tOM concentrations. Between-lake differences explained 51% of the variability in our water chemistry data, with no observed effect of season or sampling depth, contrary to our expectations. Higher tOM was correlated with higher aqueous Hg concentrations, lower areal pelagic primary productivity, and an increased contribution of terrestrial particles to pelagic particulate organic matter. Based on dietary marker analysis (δ13C, δ15N, and fatty acid [FA] composition), zooplankton diet was strongly linked to feeding mechanism, with dietary reliance on phytoplankton highest in the selective-feeding calanoid copepods, and lowest in filter feeding cladocerans. Zooplankton dietary reliance on phytoplankton and their concentrations of high-quality lipids, including polyunsaturated fatty acids, were higher in the clear-water lake than in the brown-water lake, where bacterial and terrestrial food sources were more prevalent. MeHg was highest in zooplankton from the brown-water lake, with highest concentrations in the 200–500 μm zooplankton size fraction for both lakes. Contrary to our expectations, there was no effect of season on zooplankton dietary markers or MeHg. Our results suggest that, overall, higher tOM results in higher MeHg concentrations in water and zooplankton, and reduces zooplankton dietary reliance on phytoplankton. Increased tOM thus leads to a decrease in the nutritional quality of zooplankton (i.e. higher MeHg concentrations, and lower concentrations of essential fatty acids), which may cascade up the food web with negative implications for higher trophic levels.