Jason M. Kolts

Variable wind, pack ice, and prey dispersion affect the long‐term adequacy of protected areas for an Arctic sea duck

With changing climate, delineation of protected areas for sensitive species must account for long-term variability and geographic shifts of key habitat elements. Projecting the future adequacy of protected areas requires knowing major factors that drive such changes, and how readily the animals adjust to altered resources. In the Arctic, the viability of habitats for marine birds and mammals often depends on sea ice to dissipate storm waves and provide platforms for resting. However, some wind conditions (including weak winds during extreme cold) can consolidate pack ice into cover so dense that air-breathing divers are excluded from the better feeding areas. Spectacled Eiders (Somateria fischeri) winter among leads (openings) in pack ice in areas where densities of their bivalve prey are quite high. During winter 2009, however, prevailing winds created a large region of continuous ice with inadequate leads to allow access to areas of dense preferred prey. Stable isotope and fatty acid biomarkers indicated that, under these conditions, the eiders did not diversify their diet to include abundant non-bivalve taxa but did add a smaller, less preferred, bivalve species. Consistent with a computer model of eider energy balance, the body fat of adult eiders in 2009 was 33-35% lower than on the same date (19 March) in 2001 when ice conditions allowed access to higher bivalve densities. Ice cover data suggest that the eiders were mostly excluded from areas of high bivalve density from January to March in about 30% of 14 winters from 1998 to 2011. Thus, even without change in total extent of ice, shifts in prevailing winds can alter the areal density of ice to reduce access to important habitats. Because changes in wind-driven currents can also rearrange the dispersion of prey, the potential for altered wind patterns should be an important concern in projecting effects of climate change on the adequacy of marine protected areas for diving endotherms in the Arctic.

Deposit‐feeder diets in the Bering Sea: potential effects of climatic loss of sea ice‐related microalgal blooms

Climate warming in seasonally ice-covered seas is expected to reduce the extent and duration of annual sea ice. Resulting changes in sea ice related blooms of ice algae or phytoplankton may in turn alter the timing, magnitude, or quality of organic matter inputs to the sea floor. If benthic taxa rely differently on direct consumption of settling fresh microalgae for growth and reproduction, altered blooms may lead to reorganization of deposit-feeding assemblages. To assess the potential for such changes, we examined the diets of five abundant deposit-feeders (three infaunal bivalves, a polychaete, and a brittle star) with different feeding modes over the course of the spring bloom in May–June 2007 in the north-central Bering Sea (30–90 m depth). Short-term data from gut contents reflected feeding modes, with the bivalves Macoma calcarea, Ennucula tenuis, and Nuculana radiata, and the brittle star Ophiura sarsi, responding more quickly to deposition of fresh algae than did the head-down polychaete Pectinaria hyperborea. Fatty acid biomarkers also indicated rapid ingestion of settling algae by the bivalves (especially Macoma) and the brittle star, while Pectinaria continued to ingest mainly bacteria. Fatty acid biomarkers did not indicate any unique dietary importance of ice algae released from melting ice. Longer-term inference from stable isotopes suggested that fresh microalgae contributed little to overall carbon assimilated by any of these species. Instead, deposit-feeders appeared to select a consistent fraction from the pool of sediment organic matter, probably heterotrophic microbes, microbial products, and reworked phytodetritus that form a longer-term sediment “food bank.” Redistribution of settled organic matter via scouring and accumulation by currents, as well as the multi-year life spans of macroinvertebrates, may further overwhelm effects of short-term variations in the timing, magnitude, and dispersion of blooms in the water column. More diet data are needed from midsummer to account for any lag in assimilation of fresh microalgae at these cold temperatures. Nevertheless, our results suggest that if annual sea ice cover is reduced, increased production of phytoplankton during longer ice-free periods could replace inputs of ice-associated microalgae to the sediment food bank used by deposit-feeders.

Acute toxicity of copper and silver to Ceriodaphnia dubia in the presence of food

Food is added to exposure solutions in cladoceran chronic toxicity tests and sometimes in acute toxicity tests, but its effects on the bioavailability of toxicants have not been studied extensively. We compared the toxicity of waterborne Ag and Cu to Ceriodaphnia dubia in the presence or absence of food (a mixture of a yeast--Cerophyll--trout chow slurry and a green alga) in two series of acute toxicity tests. In the first series, we added food to Ag or Cu exposure solutions 0, 30, 60, or 120 min before transferring C. dubia into the solutions. In the second series, we exposed C. dubia to waterborne Ag or Cu for 30, 60, and 120 min in the absence of food. Adding food before transferring C. dubia into the exposure solutions greatly decreased the toxicity of Ag, but had less effect on the toxicity of Cu. In contrast, adding food after transferring C. dubia into the exposure solutions did not alter the toxicity of Ag considerably and did not alter the toxicity of Cu as much as the reverse sequence. Median effects concentrations (EC50s) for 30-, 60-, and 120-min unfed Ag tests were within the range of EC50s for 48-h unfed Ag tests, suggesting most uptake that contributes to acute Ag toxicity to C. dubia occurs within the first 30 to 60 min. However, uptake that contributes to acute Cu toxicity to C. dubia appears to occur over more than 2 h. Therefore, standard food decreases the toxicity of waterborne Ag and Cu to C. dubia, and the timing of adding food to exposure solutions is especially important in Ag tests.

Effects of dietborne copper and silver on reproduction by Ceriodaphnia dubia

Recent studies have indicated the potential for dietborne metals as an important exposure pathway for metal toxicity in freshwater organisms. We conducted a study in which freshwater cladocerans (Ceriodaphnia dubia) were fed green algae (either Pseudokirchneriella subcapitata or Chlorella vulgaris) that were grown in Ag- or Cu-contaminated media. In one series of toxicity tests patterned after the U.S. Environmental Protection Agencys three-brood C. dubia chronic toxicity test, we exposed C. dubia to waterborne Ag or Cu while feeding them normal amounts of uncontaminated yeast-Cerophyll-trout chow (YCT) slurry and either algae grown in standard media or algae grown in standard media supplemented with Ag or Cu (added as AgNO3 or CuSO4 x 5H2O). These parallel tests demonstrated that dietborne metal did not contribute to survival or reproduction effects beyond the effects caused by waterborne metal alone. We also conducted dietborne-only toxicity tests patterned after two other recently published experimental designs in which (1) C. dubia were fed only metal-contaminated algae for 4 h, transferred to fresh water, and fed uncontaminated algae and YCT slurry for the duration of the three-brood test or (2) C. dubia were fed standard amounts of metal-contaminated algae and uncontaminated YCT slurry for the entire three-brood test. In contrast to previous studies, we did not find consistent dietborne metal toxicity or standard concentration-response relationships in those two experiments. Instead, among-experiment variation in intracellular partitioning of metals in the algae fed to the C. dubia, among-laboratory differences in experimental procedures, selective feeding by C. dubia to avoid metal-contaminated algae, an interaction between reproductive status of the C. dubia and dietborne metal concentration, or a combination of these might help explain the apparently inconsistent results.

Dissolved fraction of standard laboratory cladoceran food alters toxicity of waterborne silver to Ceriodaphnia dubia

The biotic ligand model (BLM) for the acute toxicity of cationic metals to aquatic organisms incorporates the toxicity-modifying effects of dissolved organic matter (DOM), but the default parameterization (i.e., assuming 10% of DOM is humic acid) does not differentiate DOM from different sources. We exposed a cladoceran (Ceriodaphnia dubia) to Ag in the presence of DOM from filtered YCT (standard yeast–Cerophyll®–trout chow food recommended by the U.S. Environmental Protection Agency [EPA] for cladocerans), from the Suwannee River (GA, USA; relatively little anthropogenic input), and from the Desjardins Canal in Hamilton (ON, Canada; receives treated municipal wastewater effluent). In all three treatments, the dissolved organic carbon (DOC) concentration was 2 mg/L (the concentration following addition of YCT slurry at the U.S. EPA–recommended volume ratio). The average 48-h median effects concentration (EC50) ratios for dissolved Ag in the presence and absence of DOM [i.e., (EC50 with DOM)/(EC50 without DOM)] were as follows: Suwannee River, 1.6; Desjardins Canal, 2.2; and YCT filtrate, 26.8. Therefore, YCT filtrate provided much more protection against Ag toxicity than that provided by DOM from the surface waters. The major spectral characteristic that differentiated YCT filtrate from the other two types of DOM was a strong tryptophan peak in the excitation–emission matrix for YCT. These results have important implications for interpreting Ag toxicity tests in which organisms are fed YCT, and they suggest BLM-calculated toxicity predictions might be improved by incorporating specific chemical constituents or surrogate indices of DOM. Another component of the protective effect against Ag toxicity, however, might be that the dissolved fraction of YCT served as an energy and/or nutrient source for C. dubia.