Uniform bathymetric zonation of marine benthos on a Pan-Arctic scale

While numerous regional studies of bathymetric zonation of benthic fauna globally have been done, few large-scale analyses exist, and no ocean-scale studies have focused on the Arctic Ocean to date. In the present work we, hence, examined bathymetric zonation of macro- and megabenthos over a depth range spanning from the shelf to the abyssal plain (14 – 5416 m) and regionally extending from the Fram Strait to the Beaufort Sea (as a whole hereafter called the Central Arctic). Based on 104 quantitative (box-corers and grabs) and 37 semi- quantitative (trawls) samples compiled from different studies we evaluated bathymetric zonation patterns in abundance, biomass and diversity, and also compared species composition among samples. Abundance and biomass decreased with depth from > 3000 ind. m−2 and > 40 g ww m−2 to ∼ 130 ind. m−2 and −2 corroborating previous studies. Diversity showed a parabolic pattern, peaking at ∼ 100–600 m. Cluster analysis revealed four (macrofauna) and five (megafauna) groups of benthic assemblages, including three that covered the upper and lower continental slope and the abyssal plains with relatively little overlap (named the Lower Shelf – Upper Slope 1, the Lower Slope and the Abyss). Substantial changes in benthic community composition were observed at depths 650–950 m (between the Lower Shelf – Upper Slope 1 and the Lower Slope) and 2600–3000 m (between the Lower Slope and the Abyss), so we interpreted these two depth horizons as major bathymetric boundaries. The first boundary (650–950 m) corresponds to the transition from sublittoral to bathyal fauna consistent with previous studies. The second boundary (2600–3000 m) reflects a decrease in benthic abundance, biomass and diversity within the Central Arctic abyssal plain. Bathymetric patterns and species overturn of benthos were relatively uniform throughout the entire Central Arctic continental slope and abyssal plain. For some regions of the Arctic Ocean, foremost for the area north from Greenland and Canadian Archipelago, benthic data are still unavailable and further research is needed

Tibetan sheep are better able to cope with low energy intake than Small-tailed Han sheep due to lower maintenance energy requirements and higher nutrient digestibilities

Tibetan sheep are indigenous to the Qinghai-Tibetan Plateau (QTP) and are well-adapted to and even thrive under the harsh alpine conditions. Small-tailed Han sheep were introduced to the plateau because of their high prolificacy and are maintained mainly in feedlots. Because of their different backgrounds, we hypothesised that Tibetan and Small-tailed Han sheep would differ in their utilization of energy intake and predicted that Tibetan sheep would cope better with low energy intake than Small-tailed Han sheep. To test this prediction, we determined nutrient digestibilities, energy requirements for maintenance and blood metabolite and hormone concentrations involved in energy metabolism in these breeds. Sheep of each breed (n = 24 of each, all wethers and 1.5 years of age) were distributed randomly into one of four groups and offered ad libitum diets of different digestible energy (DE) densities: 8.21, 9.33, 10.45 and 11.57 MJ DE/kg Dry matter (DM). Following 42 d of measuring feed intake, a 1-week digestion and metabolism experiment was done. DM intakes did not differ between breeds nor among treatments but, by design, DE intake increased linearly in both breeds as dietary energy level increased (P < 0.001). The average daily gain (ADG) was significantly greater in the Tibetan than Small-tailed Han sheep (P = 0.003) and increased linearly in both breeds (P < 0.001). In addition, from the regression analysis of ADG on DE intake, daily DE maintenance requirements were lower for Tibetan than for Small-tailed Han sheep (0.41 vs 0.50 MJ/BW0.75, P < 0.05). The DE and metabolizable energy (ME) digestibilities were higher in the Tibetan than Small-tailed Han sheep (P < 0.001) and increased linearly as the energy level increased in the diet (P < 0.001). At the lowest energy treatment, Tibetan sheep when compared with Small-tailed Han sheep, had: 1) higher serum glucose and glucagon, but lower insulin concentrations (P < 0.05), which indicated a higher capacity for gluconeogenesis and ability to regulate glucose metabolism; and 2) higher non-esterified fatty acids (NEFA) and lower very low density lipoprotein (VLDL) and triglyceride (TG) concentrations (P < 0.05), which indicated a higher capacity for NEFA oxidation but lower ability for triglyceride (TG) synthesis. We concluded that our prediction was supported as these differences between breeds conferred an advantage for Tibetan over Small-tailed Han sheep to cope better with low energy diets

Effect of air temperature and energy intake on body mass, body composition and energy requirements in sheep

Body mass was measured and body composition and energy requirements were estimated in sheep at four air temperatures (0°C to 30°C) and at four levels of energy offered (4715 to 11785 kJ/day) at a time when the sheep reached a constant body mass. Final body mass was affected mainly by metabolizable energy intake and, to a lesser extent, by air temperature, whereas maintenance requirements were affected mainly by air temperature. Mean energy requirements were similar and lowest at 20°C and 30°C (407.5 and 410.5 kJ/kg , respectively) and increased with a decrease in air temperature (528.8 kJ/kg at 10°C and 713.3 kJ/kg at 0°C). Absolute total body water volume was related positively to metabolizable energy intake and to air temperature. Absolute fat, protein and ash contents were all affected positively by metabolizable energy intake and tended to be related positively to air temperature. In proportion to body mass, total body water volume decreased with an increase in metabolizable energy intake and with an increase in air temperature. Proportionate fat content increased with an increase in metabolizable energy intake and tended to increase with an increase in air temperature. In contrast, proportionate protein content decreased with an increase in metabolizable energy intake and tended to decrease with an increase in air temperature. In all cases, the multiple linear regression using both air temperature and metabolizable energy intake improved the fit over the simple linear regressions of either air temperature or metabolizable energy intake and lowered the standard error of the estimate. The fit was further improved and the standard error of the estimate was further lowered using a polynomial model with both independent variables to fit the data, since there was little change in the measurements between 20°C and 30°C, as both air temperatures were most likely within the thermal neutral zone of the sheep. It was concluded that total body energy content, total body water volume, fat and protein content of sheep of the same body mass differed or tended to differ when kept at different air temperatures