Estimating the Diets of Animals Using Stable Isotopes and a Comprehensive Bayesian Mixing Model

Using stable isotope mixing models (SIMMs) as a tool to investigate the foraging ecology of animals is gaining popularity among researchers. As a result, statistical methods are rapidly evolving and numerous models have been produced to estimate the diets of animals—each with their benefits and their limitations. Deciding which SIMM to use is contingent on factors such as the consumer of interest, its food sources, sample size, the familiarity a user has with a particular framework for statistical analysis, or the level of inference the researcher desires to make (e.g., population- or individual-level). In this paper, we provide a review of commonly used SIMM models and describe a comprehensive SIMM that includes all features commonly used in SIMM analysis and two new features. We used data collected in Yosemite National Park to demonstrate IsotopeR's ability to estimate dietary parameters. We then examined the importance of each feature in the model and compared our results to inferences from commonly used SIMMs. IsotopeR's user interface (in R) will provide researchers a user-friendly tool for SIMM analysis. The model is also applicable for use in paleontology, archaeology, and forensic studies as well as estimating pollution inputs

Seasonal inorganic nitrogen distributions and dynamics in the southeastern Bering Sea

The annual cycle of the distribution of nitrate and ammonium concentrations in the PROBES area of the southeastern Bering Sea was highly interactive with the physical and biological processes. Nitrate concentrations were replenished over the shelf during the autumn and winter at a very uniform rate until the spring bloom commenced. In the middle shelf after nitrate concentrations were depleted in the upper mixed layer during the spring bloom, large quantities of ammonium were produced in the bottom layer. Cross-shelf diffusion, vertical diffusion, vertical mixing by storms, benthic release, and possibly nitrification interacted to supply nitrogen utilized by primary production. Nitrogen uptake by photosynthetic processes as estimated by nitrate depletion and nitrogen isotope measurements agreed with primary production estimates made by radiocarbon uptake rate measurements and ∑CO2 budgets. © 1985

Phytoplankton production from melting ponds on Arctic sea ice

Recently, the areal extent of melt ponds within sea ice has rapidly increased during the Arctic Ocean summer. However, the biological impacts of melt ponds on the Arctic marine ecosystem have rarely been studied. Carbon and nitrogen uptake rates of phytoplankton were measured at 26 different melt ponds in 2005 and 2008, using a C-13-N-15 dual stable isotope tracer technique. Generally, the open ponds had relatively higher nutrients than closed ponds, but the nutrient concentrations in the open ponds were within a range similar to those in surrounding surface seawaters. Chlorophyll a (Chl a) concentrations in melt ponds ranged from 0.1 to 2.9 mg Chl a m(-3) with a mean of 0.6 mg Chl a m(-3) (SD = +/- 0.8 mg Chl a m(-3)) in the Canada Basin in 2005, whereas the range of the Chl a concentrations was from 0.1 to 0.3 mg Chl a m(-3) with a mean of 0.2 mg Chl a m(-3) (SD = +/- 0.1 mg Chl a m(-3)) in the central Arctic Ocean in 2008. The average annual carbon production in sea ice melt ponds was 0.67 g C m(-3) (SD = +/- 1.03 g C m(-3)) in the Arctic Ocean. Based on this study, recent annual carbon production of all melt ponds was roughly estimated to be approximately 2.6 Tg C, which is less than 1% of the total production in the Arctic Ocean.X1123sciescopu

Characteristics and variability of the inner front of the southeastern Bering Sea

The inner front of the southeastern Bering Sea shows marked spatial variability in frontal characteristics created by regional differences in forcing mechanisms. Differences in forcing mechanisms (sea ice advance/retreat and storm strength and timing) and early spring water properties result in strong interannual variability in biological, chemical, and physical features near the front. We have developed a simple model based on surface heat flux and water-column mixing to explain the existence of cold belts (Cont. Shelf Res. 19(14) (1999) 1833) associated with such fronts. Hydrography, fluorescence and nutrient observations show that pumping of nutrients into the euphotic zone occurs, and this can prolong primary production at the inner front. The effectiveness of this process depends on two factors: the existence of a reservoir of nutrients in the lower layer on the middle shelf and the occurrence of sufficient wind and tidal energy to mix the water column. © 2002 Elsevier Science Ltd. All rights reserved

Anomalous conditions in the south-eastern Bering Sea, 1997: Nutrients, phytoplankton and zooplankton

Anomalies in the regional weather over the southeastern Bering Sea during spring and summer of 1997 resulted in significant differences in nutrient availability, phytoplankton species composition, and zooplankton abundance over the continental shelf as compared with measurements in the 1980s. Calm winds and the reduction of cloud cover in spring and summer produced a very shallow mixed layer in which nitrate and silicate were depleted after an April diatom bloom. High submarine light levels allowed subsequent phytoplankton growth below the pycnocline and eventual depletion of nitrate from the water column to depths of 70 m or more. Thus, total new production during 1997 may have exceeded that of previous years when nitrate was not depleted below the pycnocline. A bloom of the coccolithophorid, Emiliania huxleyi, was observed in early July in the warm, nutrient-depleted waters over the middle and inner shelf. Emiliania huxleyi concentrations reached 4.5 × 106 cells L-1 by September, and the bloom persisted through the autumn. There was evidence for increased abundance of some species of copepods in 1997 as compared with data from the middle domain in June 1981. The abundance of adult and juvenile euphausiids in 1997 was statistically similar to values measured in 1980 and 1981. However, near-surface swarms were rarely observed on the inner shelf in August-September 1997. Lack of euphausiid availability in the upper water column may partially explain the August-September mass mortality of planktivorous short-tailed shearwaters (Puffinus tenuirostris) observed on the inner shelf

Contribution of small phytoplankton to total primary production in the Chukchi Sea

Given a projection of thriving small phytoplankton in the Arctic Ocean under climate-induced environmental changes, it is important to estimate the contribution of small phytoplankton (0.7-5 mu m) to the total primary production in the Chukchi Sea, which is an important conduit of organic matter from the North Pacific to the Arctic Ocean. Based on a C-13-N-15 dual isotope tracer technique, small phytoplankton productivity measurements were taken during two consecutive cruises in the Chukchi Sea in 2004. The total phytoplankton carbon uptake rates ranged from 0 to 25.38 mg C m(-3) h(-1), whereas the uptake rates of small phytoplankton ranged from 0 to 2.87 mg C m(-3) h-1. In comparison with the carbon uptake rates, total phytoplankton nitrate uptake rates ranged from 0 to 4.40 mg N m(-3) h-1 while small phytoplankton nitrate uptake rates ranged from 0 to 0.39 mg N m(-3) h(-1). Ammonium uptake rates ranged from 0 to 8.34 mg N m(-3) h(-1) and from 0.01 to 2.18 mg N m(-3) h(-1), for total and small phytoplankton, respectively. Small phytoplankton contributed 24.80% (S.D.= +/- 23.0%) to the total chlorophyll-a concentration, and 59.41% (S.D.= +/- 52.12%) to the total carbon biomass due to its higher particulate organic carbon per chlorophyll-a unit during the two cruises in 2004. In the Chukchi Sea, the average contributions of small phytoplankton to carbon and total nitrogen (nitrate +ammonium) uptake rates were 31.72% (S.D.= +/- 23.59%) and 3731% (S.D.= +/- 26.06%), respectively. (C) 2013 Elsevier Ltd. All rights reserved.111713sciescopu

Holes in Progressively Thinning Arctic Sea Ice Lead to New Ice Algae Habitat

The retreat and thinning of Arctic sea ice associated with climate warming is resulting in ever-changing ecological processes and patterns. One example is our discovery of myriad new "marine aquaria" formed by melt holes in the perennial sea ice. In previous years, these features were closed, freshwater melt ponds on the surface of sea ice. Decreased ice thickness now allows these ponds to melt through to the underlying ocean, thus creating a new marine habitat and concentrating a food source for the ecosystem through accumulation of algae attached to refreezing ice in late summer. This article describes the formation of these late-season algal masses and comments on their overall contribution to Arctic ecosystems and the consequences of a continued decline in sea ice.open113434sciescopu