Oyster-sea nettle interdependence and altered control within the Chesapeake Bay ecosystem

Research on the effects of declining abundances of the Eastern oyster (Crassostrea virginica) in Chesapeake Bay and other estuaries has primarily focused on the role of oysters in filtration and nutrient dynamics, and as habitat for fish or fish prey. Oysters also play a key role in providing substrate for the overwintering polyp stage of the scyphomedusa sea nettle,Chrysaora quinquecirrha, which is an important consumer of zooplankton, ctenophores, and icthyoplankton. Temporal trends in sea nettle abundances in visual counts from the dock at Chesapeake Biological Laboratory, trawls conducted in the mesohaline portion of the Patuxent River, and published data from the mainstem Chesapeake Bay indicate that sea nettles declined in the mid 1980s when overfishing and increased disease mortality led to sharp decreases in oyster landings and abundance. Climate trends, previously associated with interannual variation in sea nettle abundances, do not explain the sharp decline. A potentially important consequence of declining sea nettle abundances may be an increase in their ctenophore prey (Mnemiopsis leidyi), and a resultant increase in predation on icthyoplankton and oyster larvae. Increased predation on oyster larvae by ctenophores may inhibit recovery of oyster populations and reinforce the current low abundance of oysters in Chesapeake Bay.     

The role of organochlorines in cancer-associated mortality in California sea lions (Zalophus californianus)

Wild California sea lions (Zalophus californianus) have an unusually high prevalence of neoplasms (18% of stranded dead adults) and high levels of contaminants. The contribution of organochlorine (OC) tissue burdens to the probability of sea lions dying from carcinoma was explored using a logistic regression model. Levels of PCBs and DDTs were determined in blubber of sea lions diagnosed with metastatic carcinoma and animals that had died from non-carcinoma-related incidents (e.g., gunshot, domoic acid poisoning). Animals with carcinoma had higher mean concentrations (based on wet weight) of PCBs and DDTs (more than 85% and 30% higher, respectively) in blubber than did sea lions without carcinoma; the highest concentrations of OCs in the sea lions affected with carcinoma were measured in the males. Blubber thickness was significantly different between the two groups of sea lions, but after controlling for this difference, there was still a significant effect of PCBs, but not DDTs, on the probability of sea lions dying with carcinoma. Age, sex, mass and length did not affect the probability of dying from carcinoma.     

Weather Forecasts are for Wimps: Why Water Resource Managers Do Not Use Climate Forecasts

Short-term climate forecasting offers the promise of improved hydrologic management strategies. However, water resource managers in the United States have proven reluctant to incorporate them in decision making. While managers usually cite poor reliability of the forecasts as the reason for this, they are seldom able to demonstrate knowledge of the actual performance of forecasts or to consistently articulate the level of reliability that they would require. Analysis of three case studies in California, the Pacific Northwest, and metro Washington DC identifies institutional reasons that appear to lie behind managers reluctance to use the forecasts. These include traditional reliance on large built infrastructure, organizational conservatism and complexity, mismatch of temporal and spatial scales of forecasts to management needs, political disincentives to innovation, and regulatory constraints. The paper concludes that wider acceptance of the forecasts will depend on their being incorporated in existing organizational routines and industrial codes and practices, as well as changes in management incentives to innovation. Finer spatial resolution of forecasts and the regional integration of multi-agency functions would also enhance their usability.The title of this article is taken from an advertising slogan for the Oldsmobile Bravura SUV.     

Carbon isotopic compositions of Recent planktonic foraminifera of the Indian Ocean

Carbon and oxygen isotopic determinations have been made of 29 species of Recent Indian Ocean planktonic foraminifera. Fourteen core-top samples were used and as many as 18 species were chosen from a single core-top sample. The δ¹³C of the foraminifera was compared with that of total dissolved CO₂ (ΣCO₂) and of calcite precipitated in isotopic equilibrium with ΣCO₂. The foraminiferal calcite is always at least 1.2‰ less than the value estimated for equilibrium calcite. This carbon isotopic disequilibrium suggests the partial utilization of¹³C-depleted metabolic CO₂. The calcite tests of several species, however, have δ¹³C values which are similar to the δ¹³C of ΣCO₂ in seawater. This relationship suggests that important paleohydrographic information may be obtained from carbon isotope records based on analyses of several foraminiferal species from single deep-sea sediment samples.     

The impact of solution chemistry on Mytilus edulis calcite and aragonite

Magnesium/calcium, Sr/Ca, and Na/Ca atom ratios were determined in the calcite and aragonite regions of Mytilus edulis shells which were grown in semi-artificial ‘seawater’ solutions having varying Mg/Ca, Sr/Ca, and Na/Ca ratios. These ratios were measured by instrumental neutron activation, atomic absorption, and electron microprobe analytical techniques. Strontium/calcium ratios in both calcite and aragonite were linearly proportional to solution Sr/Ca ratios. Magnesium/calcium ratios in calcite increased exponentially when solution Mg/Ca ratios were raised above the normal seawater ratio; whereas in aragonite, Mg/Ca ratios increased linearly with increases in solution Mg/Ca ratios. Sodium/calcium and sulfur/calcium ratios in calcite covaried with Mg/Ga solution ratios. Conversely, in aragonite, Na/Ca ratios varied linearly with solution Na/Ca ratios.Magnesium is known to inhibit calcite precipitation at its normal seawater concentration. We infer from the results of the work reported here that Mytilus edulis controls the Mg activity of the outer extrapallial fluid, thus facilitating the precipitation of calcitic shell. Increases in sulfur content suggest that changes in shell organic matrix content occur as a result of environmental stress. Certain increases in Mg content may also be correlated to stress. Sodium/calcium variations, and their absolute amounts in calcite and aragonite, are best explained by assuming that a substantial amount of Na is adsorbed on the calcium carbonate crystal surface. Strontium/calcium ratios show more promise than either Mg/Ca or Na/Ca ratios as seawater paleochemistry indicators, because the Sr/Ca distribution coefficients for both aragonite and calcite are independent of seawater Ca and Sr concentrations.     

A high-resolution pigment and productivity record from the varved Ponte Tresa basin (Lake Lugano,Switzerland) since 1919: insight from an approach that combines hyperspectral imaging and high-performance liquid chromatography

Eutrophication, prompted by anthropogenic activities and climate change has led to multiple adverse effects in freshwater systems across the world. As instrumental measurements are typically short, lake sediment proxies of aquatic primary productivity (PP) are often used to extend the observational record of eutrophication back in time. Sedimentary pigments provide specific information on PP and major algal communities, but the records are often limited in the temporal resolution. Hyperspectral imaging (HSI) data, in contrast, provide very high seasonal (sub-varve-scale) resolution, but the pigment speciation is limited. Here, we explore a combined approach on varved sediments from the Ponte Tresa basin, southern Switzerland, taking the advantages of both methods (HSI and high performance liquid chromatography, HPLC) with the goal to reconstruct the recent eutrophication history at seasonal to interannual resolution. We propose a modified scheme for the calibration of HSI data (here: Relative Absorption Band Depth between 590 and 730 nm RABD_590–730) and HPLC-inferred pigment concentrations (here: ‘green pigments’ {chlorophyll a and pheophytin a}) and present a calibration model (R²?=?0.82; RMSEP?~?12%). The calibration range covers >?98% of the spectral index values of all individual pixels (68 µm?×?68 µm) in the sediment core. This allows us to identify and quantify extreme pigment concentrations related to individual major algal blooms, to identify multiple algal blooms within one season, and to assess interannual variability of PP. Prior to the 1930s, ‘green pigment’ concentrations and fluxes (~?50 µg g^?1;?~?2 µg cm^?2a^?1, chlorophyll a and pheophytin a) and interannual variability was very low. From the 1930s to 1964, chlorophyll a and pheophytin a increased by a factor of ~?4, and ββ-carotene appeared in substantial amounts (~?0.4 µg cm^?2a^?1). Interannual variability increased markedly and a first strong algal bloom with ‘green pigment’ concentrations as high as 700 µg g^?1 is observed in 1958. Peak eutrophication (~?12 µg cm^?2a^?1 chlorophyll a and pheophytin a) and very high interannual variability with extreme algal blooms (‘green pigment’ concentrations up to 1400 µg g^?1) is observed until ca. 1990, when eutrophication decreases slightly. Maximum PP values after 2009 are likely the result of internal nutrient cycling related to repeated deep mixing of the lake.     

“Doing Good Work”: Feminist Dilemmas of Volunteering in the Field

In this article, I argue that there is a need to examine the feminist ethics of volunteering in the field, specifically as it relates to issues of positionality, power and reciprocity, and participatory methods. Reflecting on dilemmas I experienced as a volunteer with the Girl Scouts of San Diego while conducting research on their annual Girl Scout cookie sale, I debate the relationship between volunteerism and fieldwork more broadly and question the effectiveness of volunteerism within a feminist geographic methodological framework. In light of the dilemmas that arose in the field as a volunteer and researcher, I question whether we can consider volunteering as “good work.”