Annette Van Der Schalie

Bio: Annette Van Der Schalie is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 54 citations.

The Mussels of the Mississippi River

Abstract: There have been a number of mussel surveys (Smith, 1889; Coker, 1914; Grier and Mueller, 1922-23; Grier, 1922, 1926) in the Mississippi River to determine the relative value of these animals as a source of pearl button material. Other studies (Cooper, 1834; Galtsoff, 1924; Wiebe, 1927; Ellis, 1931) were concerned more with general biological problems involving ecology, limnology and fisheries. Several valuable lists (Pratt, 1876; Call, 1885; Grant, 1885; Baker, 1903, 1905; Shimek, 1921; Dawley, 1947) furnish good records of species from various parts of this river. However, there has not been a single published report which gives an account of the distribution of these animals throughout the productive area of the main stream. A comprehensive survey made by Max M. Ellis and his staff during the summers of 1930 and 1931 now makes possible a report on those collections. These records are the only inclusive source of information concerning this unusually rich assemblage of naiades in our largest river.

Impending extinctions of North American freshwater mussels (Unionoida) following the zebra mussel (Dreissena polymorpha) invasion

Abstract: 1. Freshwater mussels (Order Unionoida) are the most imperiled faunal group in North America; 60% of described species are considered endangered or threatened, and 12% are presumed extinct. Widespread habitat degradation (including pollution, siltation, river channelization and impoundment) has been the primary cause of extinction during this century, but a new stress was added in the last decade by the introduction of the Eurasian zebra mussel, Dreissena polymorpha, a biofouling organism that smothers the shells of other molluscs and competes with other suspension feeders for food. Since the early 1990s, it has been spreading throughout the Mississippi River basin, which contains the largest number of endemic freshwater mussels in the world. In this report, we use an exponential decay model based on data from other invaded habitats to predict the long-term impact of D. polymorpha on mussel species richness in the basin. 2. In North American lakes and rivers that support high densities (>3000 m−2) of D. polymorpha, native mussel populations are extirpated within 4–8 years following invasion. Significant local declines in native mussel populations in the Illinois and Ohio rivers, concomitant with the establishment of dense populations of D. polymorpha, suggest that induced mortality is occurring in the Mississippi River basin. 3. A comparison of species loss at various sites before and after invasion indicates that D. polymorpha has accelerated regional extinction rates of North American freshwater mussels by 10-fold. If this trend persists, the regional extinction rate for Mississippi basin species will be 12% per decade. Over 60 endemic mussels in the Mississippi River basin are threatened with global extinction by the combined impacts of the D. polymorpha invasion and environmental degradation.

A review of the effects of heavy metals on freshwater mussels.

Abstract: The widespread recent decline in the species diversity and population density of freshwater mussels in North America may be partly related to chronic, low-level exposure to toxic metals. As benthic filter-feeding organisms, freshwater mussels are exposed to metals that are dissolved in water, associated with suspended particles and deposited in bottom sediments. Thus, freshwater mussels can bioaccumulate certain metals to concentrations that greatly exceed those dissolved in water. In adult mussels, the most common site of metal uptake is the gill, followed by the mantle and the kidney. The toxic effects of metals on freshwater mussels have been examined in a few acute toxicity tests, but the sublethal effects of long-term exposure to low environmental concentrations are little understood. Sublethal exposure to metals can alter growth, filtration efficiency, enzyme activity and behaviour. Sublethal effects are frequently observed at concentrations that are only half the lethal concentrations. However, few toxicity tests have used environmentally realistic exposure concentrations. Total concentrations of Cd, Cu, Hg and Zn in many oxic surface waters are in the ngl(-1) range, yet many toxicity studies have exposed mussels to concentrations in the μgl(-1) or even the mgl(-1) range. An understanding of the processes by which metals affect freshwater mussels would provide insights on the ecotoxicological significance of metal contamination to natural mussel populations and aid in the development of water-quality criteria that adequately protect mussels.

Parasitism and the unionacea (bivalvia)

Abstract: Summary It is proposed that the incorporation of a unique parasitic stage in the life-cycle of unionaceans which involves an obligate relationship between a vertebrate host, usually a fish, and a highly modified larval stage, the glochidium, has had far-reaching consequences with respect to overall morphology, extent of species' geographic ranges, and rate of speciation in the group. Glochidia are separable into three main types with respect to overall shape and attachment features, and are retained in variously modified brood pouches. When mature, glochidia are released in several different ways which reflect various adaptations involved in either attracting the fish host and/or increasing the probability of attachment. Glochidia do not seem capable of host selection, and the reaction of the host to the parasite seems to be the main factor in determining specificity. Release of glochidia is synchronized to correspond to periods of predictable host availability, such as during spawing migrations and nesting behaviour. Other adaptations include modifications of glochidial conglutinates to mimic host food items, and modifications of the unionacean mantle edges to attract hosts. In all cases, a good correlation exists between the type of lure used and host food preferences, but, despite these adaptations, host specificity among unionaceans seems low. Parasitism among unionaceans is postulated to be mainly advantageous in terms of predictability of dispersal by habitat-specific hosts, but parasitism is hypothesized to entail constraints in terms of the degree to which shell shape and life-habit can be diversified among unionaceans. The type of host parasitized is considered to affect the rate of diversification among populations and speciation among unionaceans: those that parasitize strictly freshwater hosts are more likely to exhibit highly individualistic populations in different drainages with respect to molecular genetic and soft-part characters, while those that parasitize anadromous or saltwater-tolerant hosts show little differentiation among widely distributed populations.

Microhabitat use by an assemblage of stream-dwelling unionaceans (Bivalvia), including two rare species of Alasmidonta

Abstract: We studied the microhabitats of six species of freshwater mussels, including two rare species of Alasmidonta, in the Neversink River, New York. In each of 270, 1-m2 quadrats, we measured water depth, current speed, bottom roughness, spatial variation in current speed, distance to shore, presence or absence of macrophytes, presence or absence of an overhead canopy, the extent of patches of fine sediment, and sediment granulometry, as well as recording the mussels present. Mussel populations in the Neversink are dense (mean = 3.2/m2) and highly clumped. Stepwise discriminant analyses showed that current speed and spatial variation in current speed were the most useful predictors of the occurrence of mussels in quadrats. Alasmidonta heterodon was found most frequently at moderate current speeds and in quadrats that contained many patches of fine sediments. Alasmidonta varicosa occurred most frequently at moderate current speeds and in sedi- ments with a high proportion of medium sands (0.25-1 mm). Nevertheless, the predictive power of discriminant models based on microhabitat variables is so low that we question the adequacy of a traditional microhabitat approach to unionacean ecology. We suggest that including geomorpho- logical descriptors of the streambed or working at spatial scales of hundreds of metres might be more useful than a traditional microhabitat approach for predicting the distribution of freshwater mussels in streams.

Distribution, abundance, and roles of freshwater clams (Bivalvia, Unionidae) in the freshwater tidal Hudson River

Abstract: SUMMARY 1. An extensive series of PONAR grabs was used to determine the distribution and abundance of unionid clams in the freshwater tidal Hudson River. 2. The five species of unionids collected were distributed very unevenly within the river. Mean river-wide density and biomass of unionids were 8.0m−2 and 6.2 g DM m−2 (shell-free)., respectively. 3. The environmental variables that we measured (water depth, distance from shore, sediment granulometry and organic content, presence or absence of macrophytes, and the chlorophyll a and particulate organic matter content of the water) explained little of the variation in abundance of unionids. 4. The distributions of the various species of clams did not differ significantly with respect to the environmental variables measured. 5. We estimate that unionids filter a significant amount of water (0.14m3 m−2 day−1, on average) in the Hudson River estuary, roughly equivalent in magnitude to downstream flushing. 6. We project that unionids will serve as a major substratum for the settlement of the zebra mussel (Dreissena polymorpha), which is now invading the estuary. We emphasize that unionids may play important non-trophic roles in large river ecosystems.