J. Daniel Farrar

Intraspecific density effects in Nereis (Neanthes) arenaceodentata Moore (Polychaeta: Nereidae)

Effects of intraspecific density on Neanthes arenaceodentata Moore were examined under laboratory conditions by rearing animals for 28 days, in the presence of sediment, at densities of 230, 575, 1150, and 1730 worms/m2. The lowest density examined in this study was similar to the mean reported field density for N. arenaceodentata. Food was allocated to each beaker on a per worm basis to focus the experiment on competition for space. Individual worm growth increased with increasing density. This result contrasts with other studies of intraspecific density effects in this species conducted in the absence of sediment where negative effects on growth were observed. Estimated individual dry weight and ash free dry weight of worms in the highest density treatment were significantly greater (13 and 18%, respectively) than worms in the lowest density treatment at the end of 28 days of growth. This increase in growth was associated with a decrease in the number of ovigerous females, suggesting a delay in reproductive development, and an increase in the number of worms regenerating posterior segments, suggesting an increase in the number of aggressive encounters. At the end of the 28 day growth experiment, mated pairs were established in separate beakers. Intraspecific density did not have a lasting effect on time to egg deposition and juvenile emergence or fecundity. The benefits of larger body size at higher densities may include the fact that larger worms are more successful at defending territories and finding mates. The results of this study emphasize the importance of sediment as a structuring agent in soft substratum habitats and the potential for complex density dependent effects.

Effect of growth on reproduction in the freshwater amphipod, Hyalella azteca (Saussure)

A gradient in H. azteca growth was created by reducing food ration. Tests were initiated with neonates (≤48 h old) and the effects of an altered food ration on survival and growth were examined after 10 and 49 days. Growth rates decreased significantly with reduced food ration (10 day growth rates ranged from 1.2 µg d−1 in the highest feeding regime to 0.5 µg d−1 in lowest feeding regime). Survival after 10 days was not affected by ration, ranging from 86 to 96%. A growth rate of 1.2 µg d−1 at day 10 resulted in mean dry weight (1.0 mg), survival (62%) and reproduction (9.3 neonates/female) at day 49 similar to reported values for this species. Growth rates ≤0.9 µg d−1 at day 10 corresponded to significantly reduced reproduction at day 49 (i.e., < 1 neonate per female). Time to the onset of amplexus increased with decreasing ration suggesting reduced ration may have delayed reproduction.

Assessing the Chronic and Sublethal Aquatic Toxicity of Insensitive Munitions (IM) Compounds Using Aqueous Exposures with the Amphipod Hyalella Azteca : Scientific Operating Procedure Series : Characterization of IMX Ecotoxicological Effects

This document provides a standard method for assessing the aquatic toxicity of insensitive munitions (IM) compounds using the freshwater amphipod Hyalella azteca. The endpoints for the static-renewal test are survival, growth and offspring production. The chronic exposure is conducted for 35 or 42 days at 23 ± 1 °C in 300 mL glass beakers containing 200 mL of test solution. Juvenile amphipods are exposed to decreasing concentrations of IM compounds (e.g., 100%, 50%, 25%, 12.5%, and 6% of the highest concentration) and to a negative control. For each concentration, eight replicate beakers, each containing ten H. azteca are used. Test solutions are renewed three times a week. Water quality parameters are measured at the start, during, and at test termination. The tests are only valid if the mean survival, growth, and reproduction for the control treatment are 80%, 0.35 mg dry weight/individual, and three young/female, respectively, or greater. Instructions and requirements are provided for handling H. azteca before and during the toxicity test, preparing aqueous mixtures, initiating and terminating chronic tests, maintaining appropriate test conditions, making necessary observations and water quality measurements, assessing the survival, growth and reproductive endpoints, and obtaining samples for chemical analysis. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR.

Toxicity Reduction (and Identification) for Dredging Evaluations : Methods for Whole Sediment Elutriate Bioassays

PURPOSE: Physical, chemical, and toxicological characterization of sediment may be required to evaluate dredged material (DM) under the Clean Water Act (CWA) or Marine Protection Research and Sanctuaries Act (MPRSA). When DM evaluations indicate potential for biological effects, it is useful to identify the likely causes of those effects to better inform test interpretation and/or management decisions (USEPA/USACE, 1991). For example, when a non-persistent substance, such as ammonia, is present at elevated levels that are sufficient to alone cause a toxicological effect in laboratory bioassays, it is logical to employ methods to reduce ammonia levels prior to conducting the bioassay to allow toxicological assessment for more persistent contaminants of concern. The primary objective of this Technical Note (TN) was to disseminate methods for conducting toxicity reduction/identification evaluations (TRE/TIE) to be used in select dredging evaluations. While previous documents have discussed the utility of TRE/TIE information for dredging management decisions, this TN provides more specific guidance. In practice, TREs for ammonia in elutriate toxicity tests may be most common and applicable. TRE methods serve as supplementary testing to standard whole sediment and sediment elutriate bioassays in which significant reductions in survival (or other endpoints) are observed, but the primary cause is unknown or suspected to be ammonia, hydrogen sulfide, or other non-contaminant related factors. Through sediment and elutriate manipulations, these methods can generate lines of evidence that a certain chemical class (or specific chemical compound or element when coupled with chemistry data) is primarily responsible for observed biological effects. The drivers of the biological effects may be narrowed to typical contaminants/classes; organic compounds, metals3, ammonia, and/or sulfides (Ankley et al. 1992; Kreitinger et al. 2017). Application of the methods described herein is beneficial to align the type of data generated between different dredging projects, thus allowing greater consistency of robust, scientific data that feed management decisions.

Assessing the sediment toxicity of Insensitive Munitions (IM) compounds using 10-day whole-sediment exposures with freshwater invertebrates; Scientific Operating Procedure series : characterization of IMX ecotoxicological effects

This document provides a standard method for assessing the sediment toxicity of insensitive munitions (IM) compounds using juveniles of the amphipod Hyalella azteca and larvae of the midge Chironomus dilutus. The 10-day test is conducted at 23 ± 1 °C in 300 mL glass beakers containing sediment spiked with an IM formulation or a single constituent. Each beaker receives 100 mL of spiked or control sediment, 175 mL of overlying water, and ten organisms. The endpoints are survival and growth. Five replicate beakers per treatment are used. To prevent excessive loss of IM compounds, the overlying water in the beakers should not be replaced during the 10-day exposure period. Water quality parameters are measured at the start, during, and at test termination. The tests are only valid if the mean survival for the control treatment is 70% or greater for C. dilutus and 80% or greater for H. azteca. Instructions and requirements are provided for handling test organisms before and at the initiation of the toxicity test, initiating and terminating whole-sediment exposures, maintaining appropriate test conditions, making necessary observations and water quality measurements, assessing the survival and growth endpoints, and obtaining samples for chemical analysis. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR.