Astrid N. Schwalb

Horizontal and vertical movements of unionid mussels in a lowland river

Abstract Freshwater mussels are important constituents of freshwater ecosystems, yet much of their basic biology remains to be examined. The behavior of 3 species of unionid mussels (Unio tumidus, Unio pictorum, and Anodonta anatina) was examined in the lowland River Spree (Germany). Mussels were marked individually, and their positions on the sediment surface and depth below the sediment surface were recorded weekly between May and October 2004. The average rate of horizontal movement was 11 ± 15 cm/wk (mean ± 1 SD). The direction of the movements seemed erratic; however, a significant net shoreward displacement of ~17 cm, possibly caused by rising water levels, was observed during the study. A surprisingly high percentage of the mussels (74 ± 7%) was burrowed entirely in the sediment to depths as great as 20 cm during the summer. Smaller mussels and individuals not infested by the zebra mussel, Dreissena polymorpha, burrowed deeper in the sediments than larger or infested mussels. Burrowing reduced infestation densities in a laboratory experiment. Significantly more U. tumidus individuals were found on the sediment surface during the reproductive period in early summer than in late summer, suggesting that reproductive activity may influence burrowing. Burrowing was significantly related to current velocity (discharge), day length, and water temperature (multiple linear regression, R2 = 0.74, p < 0.001), but current velocity appeared to be the dominant factor driving vertical movements (R2 = 0.53, p < 0.01). We propose that movement behaviors are important adaptations of unionid mussel populations to the flow and food conditions in rivers. Movement behavior also may help unionids escape predators and control infestation by D. polymorpha.

Sensitivity of the glochidia (larvae) of freshwater mussels to copper : Assessing the effect of water hardness and dissolved organic carbon on the sensitivity of endangered species

The assessment of the potential impact of waterborne contaminants on imperilled freshwater mussels is needed. Acute copper toxicity was assessed in a standardized soft water (hardness 40-48 mg CaCO(3)equivalents L(-1)) using the larvae (glochidia) from three common and six (Canadian) endangered mussel species. The resulting 24h EC50s ranged from 7 to 36 microg Cu L(-1), with the EC50s of two endangered species <10 microg Cu L(-1). Acute copper sensitivity was also determined in Ptychobranchus fasciolaris, a species that employs conglutinates (packets of glochidia) in its reproductive strategy. Conglutinates were found to provide significant protection from acute copper exposure as the EC50 of the encased glochidia was more than four-fold higher than freed glochidia (72.6 microg Cu L(-1) vs. 16.3 microg Cu L(-1)). The glochidia from two endangered species, Epioblasma triquetra and Lampsilis fasciola, were used to examine the influence of water hardness and dissolved organic carbon (DOC) on copper sensitivity. Exposures in moderately-hard water (165 mg CaCO(3) L(-1)) demonstrated that an increase in water hardness resulted in a significant reduction in copper sensitivity. For example, in L. fasciola the 24 h EC50s were 17.6 (14.2-22.6) microg Cu L(-1) and 50.4 (43.5-60.0) microg Cu L(-1) in soft water and moderately-hard water, respectively. The addition of DOC (as Aldrich Humic Acid) also resulted in a significant decrease in Cu sensitivity, such that a 10-fold increase in the EC50 of E. triquetra was observed when the reconstituted soft water was augmented with 1.6 mg DOC L(-1). To determine if current water quality regulations for copper would protect all glochidia, the USEPAs Biotic Ligand Model (BLM) was used to derive water quality criteria for these exposures. While BLM-derived criteria for the soft water exposures indicate that protection would be marginal for the sensitive endangered species, the criteria derived for the DOC exposures suggest that the natural complexity of most natural waters in Southern Ontario (Canada) will provide glochidia with protection from acute copper exposure.

The state of Lake Simcoe (Ontario, Canada): the effects of multiple stressors on phosphorus and oxygen dynamics

Abstract Lake Simcoe, the largest lake in southern Ontario outside of the Laurentian Great Lakes, is affected by numerous stressors including eutrophication resulting from total phosphorus (TP) loading, climate change, and invasions of exotic species. We synthesized the long-term responses of Lake Simcoe to these stressors by assessing trends in water quality and biological composition over multiple trophic levels. Evidence for climate change included increasing thermal stability of the lake and changes in subfossil diatom communities over time. Although the deep water dissolved oxygen (O2) minimum has increased significantly since TP load reductions, it is still below estimated historical values and the Lake Simcoe Protection Plan end-of-summer target level of 7 mg O2 L-1. Low deep water O2 concentrations corresponded with a decline in coldwater fish abundance. Since 1980, some nutrient concentrations have decreased (spring TP) while others have increased (silica), but many show no obvious changes (ice-free TP, nitrate, ammonium). Increases in water clarity, combined with declines in chlorophyll a and phytoplankton biovolumes in Cook’s Bay, were temporally consistent with declines in TP loading and the lake-wide establishment of dreissenid mussels as a major component of the Lake Simcoe ecosystem. Using an investigative tool, we identified 2 periods when abrupt shifts potentially occurred in multiple parameters: 1986 and 1995-1997. Additional ecosystem level changes such as declines in zooplankton, declines in offshore benthic invertebrate abundance, and increased nearshore invertebrate abundance likely reflect the effects of invasive species. The interaction of these multiple stressors have significantly altered the Lake Simcoe ecosystem.

Morphology and Development of Blue Whale Baleen: An Annotated Translation of Tycho Tullberg's Classic 1883 Paper

Herein we present an annotated translation of the classic paper by Tycho Tullberg on the structure and development of baleen in blue whales. The three blue whale fetuses on which this study was based were obtained from a whaling station in Norway during a time when blue whales were still abundant enough to support a whaling industry. The value of this text for the modern reader is that it provides a glimpse into the mechanisms of development of baleen in the largest rorqual whale, which is something that modern biologists are unlikely to be able to replicate for a long time. Tullberg’s careful morphology, histology, and developmental thinking provide a coherent account of how the elaborate baleen racks develop from simple epidermal and dermal origins. The figures, which we have reproduced here, are superb and provide a rare window into the morphology of blue whale baleen at three fetal stages. The histology is excellent for its time and provides insights into the various keratin tissue phases that make up the baleen plates and bristles as well as the enigmatic Zwischensubstanz that acts as a spacer and possible shock-absorber between plates.

Impacts of hydrodynamics and benthic communities on phytoplankton distributions in a large, dreissenid-colonized lake (Lake Simcoe, Ontario, Canada)

Abstract We quantified the vertical and horizontal variation of chlorophyll a (Chl-a) to test how benthic filter feeders (dreissenid mussels), rooted macrophytes, and hydrodynamics influence phytoplankton distributions in a large lake (Lake Simcoe, Canada). Water column Chl-a did not differ significantly among sites of different depth, distance offshore, or rooted macrophyte biomass, but among the nearshore sites (7.5–10 m deep) it was higher where mussel biomass was greater. This counterintuitive result may be explained by wind-driven horizontal circulation during our specific study periods together with the patchy distribution of the mussels in the lake. Information on mixing depths, vertical eddy diffusivity, and mussel biomass was used to predict when and where the grazing pressure of mussels would likely deplete near-bottom phytoplankton. Chl-a depletion was frequently predicted at sites with moderate or high mussel biomass and sufficient thermal stratification to impede vertical mixing but never at sites without thermal stratification. Observations were consistent with predictions in most cases. The results suggested that mussels at depths of 7.5–15 m (a depth range of generally high mussel biomass in the lake) may frequently suffer food limitation due to near-bottom depletion during the early and middle stratified season. A deep Chl-a maximum was documented and may be important for mussel nutrition at such times.

Potential medicinal value of some South African seaweeds

Eleven macroalgae were collected from the KwaZulu-Natal coast and nineteen species from the cooler Western Cape coast in March and April 2000. Ethanolic and aqueous extracts were made and tested for biological activity in the Cox-1 anti-inflammatory assay, in a nematode mortality bioassay for anthelminthic activity, an IC 50 anticancer assay and a MIC antimicrobial assay. The ethanolic extracts were very active in the Cox-1 anti-inflammatory assay for almost all of the species tested. The aqueous extracts were not active. No anthelminthic mortality was detected in extracts from any of the species tested. Many of the extracts had cytotoxic activity against three cancer cell lines tested, with those from representative species of the Chlorophyta and Rhodophyta being the most effective. The extracts had much lower cytotoxic activity when tested on normal mouse fibroblasts (NIH3T3). Extracts from only a few species had antimicrobial activity with those of the Chlorophyta tested being the most effective against both the Gram-positive and Gram-negative bacteria.

Distribution of unionid freshwater mussels and host fishes in Texas. A study of broad-scale spatial patterns across basins and a strong climate gradient

Unionid freshwater mussels are a threatened fauna, and understanding their distribution is essential to aid and promote conservation efforts. Therefore, we (1) compared patterns of species richness and endemism of Texas mussel and fish species, as mussels depend on fish for their reproduction and dispersal; (2) examined how distribution and community composition of mussels and fishes varies across river basins; and (3) how much variation in mussel community composition could be explained by the distribution of potential host fish, river basin (as a spatial component), ecoregion (as proxy for large-scale environmental differences), and flow variability. Mussel and fish community compositions in rivers differed significantly between river basins with an east-to-west gradient of decreasing species richness following the transition from sub-humid to arid climate. River basin explained 25% of the variation in mussel community composition, and potential host fish presence explained 20%. The total variation explained by both variables was 34%, as part of the variation in host fish presence (11.5%) was spatially structured by differences in river basins. Flow variability explained an additional 14% of the variation in mussel community composition, and ecoregion an additional 9% compared with river basin alone. Locations of significantly higher mussel species richness and/or endemism were present in rivers from all regions of Texas. These locations should be protected, especially as human population continues to expand and urbanize in these regions. A better understanding of mussel–host fish relationships and the impact of flow variation on the distribution of mussels will be needed to inform conservation efforts.