David S. Roper

Freshwater Mussels (Hyriidae) of Australasia

In Australia, New Guinea, Solomon Islands and New Zealand, freshwater mussels are represented by the families Hyriidae and Unionidae. The Hyriidae includes 27 species in 8 genera, in the subfamilies Cucumerunioninae, Hyridellinae, Lortiellinae and Velesunioninae (a fifth subfamily, the Hyriinae, is endemic to South America). Two other species (one genus) from New Guinea are placed tentatively in the Unionidae.

Burial, crawling and drifting behaviour of the bivalve Macomona liliana in response to common sediment contaminants

To investigate the effect of sediment contamination on the tellinid bivalve Macomona liliana, juvenile shellfish (about 1.3 mm long) were exposed to copper- and zinc-dosed sand, and sediments collected from several contaminated sites. The behavioural responses measured included burial rate, crawling and drifting. In copper-dosed sediment, a significant reduction in the number of shellfish burying after 10 min occurred at 25 mg Cu kg−1 (dry wt). After a 96-h exposure, shellfish crawled away from sediment with 10 mg Cu kg−1 (dry wt), and when a weak current was provided they left this 10 mg Cu kg−1 (dry wt) sediment by drifting. Zinc-dosed sediment slowed burial at 80 mg Zn kg−1 (dry wt), and stimulated crawling and drifting at 40 mg Zn kg−1 (dry wt). Some of the field-collected contaminated sediments slowed burial and stimulated drifting, but none affected crawling. It appears that juvenile drifting induced by sediment contamination could play a role in determining M. liliana distributions.

Metal concentrations of resident and transplanted freshwater mussels Hyridella menziesi (Unionacea: Hyriidae) and sediments in the Waikato River, New Zealand

Abstract Heavy metals and metalloids were measured in freshwater mussels ( Hyridella menziesi ) and sediments in the upper Waikato River, New Zealand. Mercury (Hg) concentrations ranged 35-fold in sediments (0.025-0.87 mg kg −1 dry wt) and 144-fold in mussels (0.091-13.1 mg kg −1 dry wt). Arsenic (As) concentrations ranged 190-fold in sediments (7.9–1520 mg kg −1 dry wt) and only 10-fold in mussels (15.0–153 mg kg −1 dry wt). There was no significant correlation between sediment total concentrations of either Hg or As and mussel tissue levels. Sediment quality guidelines were exceeded for Hg and As at most sites and for copper, chromium, iron and manganese at a few sites. Tissue concentrations exceeded levels considered to be safe for human consumption for Hg at Lake Aratiatia and As at several sites. Transplant experiments with caged mussels were used to measure uptake and depuration rates of Hg and As. Half-lives for mussel uptake and depuration of Hg were 6–12 months. Arsenic uptake rates could not be determined but the depuration showed a half-life of about 2.5 months. Physiological measurements were consistent with increased food availability at some sites rather than contaminant effects. These results highlight the need to understand biochemical changes induced by factors that are independent of environmental concentrations of contaminants, such as the influence of food levels and the potential for metabolic adaptation in biomonitoring organisms.

Effects of food and silt on filtration, respiration and condition of the freshwater mussel Hyridella menziesi (Unionacea: Hyriidae): implications for bioaccumulation

The effect of exposure to different concentrations of food and suspended silt on filtration, respiration and condition were studied in the freshwater mussel Hyridella menziesi. Using a milk solids-based food and kaolin to simulate silt, mussels were maintained at different combinations of food and silt concentrations for 3 weeks. Between treatments mean filtration rates ranged from 0.97–1.66 l g−1 h−1, and respiration from 0.50–1.35 mg O2 g−1 h−1. Silt (non-volatile suspended solids up to 35 mg l−1) failed to have a significant effect on filtration rate or condition, but with increasing food levels (volatile suspended solids up to 35 mg l−1) filtration rate was reduced, and condition was reduced at the lowest food concentration (<5 mg l−1). Respiration showed a food × silt interaction between treatment blocks. When food was low respiration increased with increasing silt concentrations, and when silt was low (<5 mg l−1) respiration increased with increasing food concentrations. The observed effects of food and silt on filtration, respiration and condition are discussed in terms of their potential for affecting contaminant bioaccumulation. In low-food situations (i.e., <5 mg l−1), if mussels are pumping large volumes of water, contaminant uptake rates could be enhanced, whereas abundant food would result in lower pumping rates and lower uptake rates. Changes in metabolism with food concentration have implications for contaminant elimination, and changes in biochemical composition associated with changing condition could affect the tissue distribution and retention of contaminants.

Population structure, shell morphology, age and condition of the freshwater mussel Hyridella menziesi (Unionacea: Hyriidae) from seven lake and river sites in the Waikato River system

Populations of the freshwater mussel Hyridella menziesi were compared from six lakes and one river site along the Waikato River system, North Island, New Zealand. Estimated densities ranged from several hundred per square metre in Lake Taupo to less than one per square metre in Lake Karapiro. Length-frequencies were similar at all sites, with unimodal distributions and a notable absence of any individuals less than 20 mm long. The extent of shell erosion varied from sites where most mussels had less than 1% of the right valve affected (i.e., Ohakuri & Karapiro), to Lake Aratiatia where most shells had erosion over 1–20% of their surface. Taupo and Ohakuri mussels showed an unusually high incidence (over 50%) of internal shell abnormalities (including dulling, deformities and protuberances). Canonical discrimination based on shell length, height, width and weight clearly separated Taupo and Ohakuri mussels from all other sites, and ANCOVA on morphological characteristics confirmed significant differences between sites. Physical condition indices (based on dry flesh weight per shell weight and shell volume) showed an increasing downstream trend, but this was not significantly correlated with food availability (i.e., chlorophyll a concentration) because of unexpectedly low condition in lakes Ohakuri and Karapiro. Length v. age relationships contained considerable scatter and did not show between-site differences. Measured differences in external erosion, internal shell abnormalities and morphology were attributed to physical, chemical and biological factors. Use of mussels for environmental monitoring must take these ‘background’ differences into account.

Bleached kraft pulp mill sourced organic chemicals in sediments from New Zealand rivers. Part 1: Waikato River

Abstract The concentrations of resin acids and chlorophenolic compounds were measured in river sediments above and below the effluent discharge point of a New Zealand bleached kraft pulp and paper mill. No significant concentrations of resin acids were found at background sites. Background concentrations of total chlorophenolic compounds ranged from −1 to 35 ng g −1 . Elevated concentrations of both compound classes were observed downstream of the mill. Total concentrations immediately below the discharge point were 76.6 ug g −1 and 30.7 ng g −1 dry weight respectively for the resin acids and chlorophenolic compounds. Chlorophenolic compound concentrations declined to background levels 20 km downstream whereas resin acids reached background concentrations after 38 km. Shallow surficial sediments were shown to contain the majority of the organic compounds.

Growth of an amphipod and a bivalve in uncontaminated sediments: Implications for chronic toxicity assessments

This study assessed the sensitivity of the amphipod Chaetocorophium cf. lucasi, an inhabitant of New Zealand estuarine muddy sediments, and of the bivalve Macomona liliana, commonly found in New Zealand sandflats, to sediment particle-size distribution, total organic carbon, total organic nitrogen and water content. Growth and survival were evaluated after different test exposure times using laboratory-prepared natural sediment mixtures of sand and mud. The results suggest that amphipod survival was affected by the type of sand more than by the concentration of sand in the sediment samples. In samples with high survival rates, amphipod growth was impaired in sediments with higher sand proportions after a 10-day exposure, but after longer periods (28 or 30 days) there were no significant differences among treatments which had ≤76% sand. Bivalve survival and growth were not significantly affected by different natural sediment characteristics. Test duration for chronic toxicity tests with the bivalve M. liliana and the amphipod C. cf. lucasi should be at least 28 days for the detection of significant growth relative to the initial size.