Daniel J. Hornbach

Effects of particle concentration and season on the filtration rates of the freshwater clam, Sphaerium striatinum Lamarck (Bivalvia: Pisidiidae)

The effects of particle concentration and season on the filtration rates of the freshwater clam Sphaerium striatinum Lamarck were assessed by measuring clearance rates of small (2.02 µm) latex beads from dilute suspensions. Filtration rates decreased as particle concentration increased over a range of 2–64 mg 1−1, with rates decreasing in similar proportion for clams of all sizes. For a 1-mg clam, rates decreased from approximately 8.4 to 0.57 ml clam −1 h−1. Seasonal filtration rates for adult clams peaked during periods of greatest reproduction. The patterns for smaller clams are similar, though proportional changes in filtration rates differ for various sizes of clams.It is estimated that clams occupying 1 m2 of stream substrate removed about 3.67 gCa−1. This is equivalent to 0.0004% of the carbon that flows past them annually. Filter-feeding provided only 24% of the calculated energy needs of the population, suggesting that another mode of feeding (e.g. deposit-feeding) may provide an important energy source for these forms.

Reproductive strategies in the freshwater sphaeriid clam,Musculium partumeium (say), from a permanent and a temporary pond

SummaryReproduction was studied in two populations ofMusculium partumeium from temporary and permanent ponds. Adults of the single annual generation from the ephemeral pond have an annual selection ratio of 25:1 with 37.03 μgC per newborn, and an intrinsic rate of increase (r) of 0.0084 day-1. Fall-born adults from the permanent pond have an annual selection ratio of 38:1, 21.82 μgC per newborn and anr of 0.0115 day-1; springborn adults have an annual selection ratio of 136:1 (107:1 for their contribution to fall birth and 29:1 for the spring birth period) with newborns of 24.21 μgC and anr of 0.0304. The trade off between quantity and quality of young is discussed in terms of adaptive strategies.

Seasonal variation in the metabolic rates and Q10-values of the fingernail clam, Sphaerium striatinum Lamarck

Abstract 1. 1. Metabolic rates were highest during periods of maximum reproduction. 2. 2. The exponent of the metabolic rate-weight equation varied seasonally, rates of metabolism of small animals exhibited greater annual fluctuations than those of large animals. 3. 3. Absolute and weight-specific Q 10 s (determined at 5–10°C above field temperatures) for smaller clams were greatest in the winter; absolute values of Q 10 were highest for larger individuals in the summer. 4. 4. Small clams had Q 10 Q 10 -values for larger clams were near 1.0 at this time. 5. 5. 38.9% of the total energy assimilated by the population annually was allocated to metabolism, which is near the low end of the range of values reported for freshwater molluscs, suggesting that this species can partition a large amount of energy to growth and reproduction.

Comparative bioenergetics of permanent and temporary pond populations of the freshwater clam, Musculium partumeium (Say)

The population energetics of a temporary and a permanent pond population of Musculium partumeium in Southwest Ohio were studied. In the permanent pond (surface area = 396 m2, maximum depth = 0.7 m) the population was bivoltine and iteroparous whereas in the temporary pond (surface area = 1042 m2, maximum depth = 0.9 m) the population was usually univoltine and semelparous.Growth and biomass were assessed as total organic carbon and total nitrogen to provide estimates of productivity and seasonal changes in C:N for each generation. Productivity (non-respired assimilation = growth + reproduction; N-R.A. = G + R) was 6939 mgC·m−2·a−1 (3858 and 3353 mgC·m−2·a−1 for each generation) and 1661 mgC·m−2·a−1 for the permanent and temporary pond populations respectively. The average standing crop biomass (B) was 606.8 mgC·m−2 (357.5 and 249.3 mgC·m−2 for each generation) and 231.9 mgC·m−2 with overall productivity: biomass ratios of 11.4 and 7.2 for the permanent pond and temporary pond populations respectively.Respiration rates were converted to carbon equivalents (respired assimilation = R.A.) and used to evaluate the components of total assimilation (T.A. = R.A. + N-R.A.) and the efficiency of partitioning this energy to N-R.A. for G and R. When expressed as a percentage, the production efficiencies (100 × N-R.A.:T.A.) were 50.4 and 62%, and the reproductive efficiencies (100 × R:N-R.A.) were 26.4 and 18% for the permanent and temporary pond populations respectively. The reproductive efficiencies for populations of these viviparous clams are greater than those for most oviparous molluscs.The comparative information on the energetics of these populations does not completely fit any theoretical consideration of reproductive effort or life-history strategy. These data are discussed in relation to selection for population success in temporary ponds.

Benthic macroinvertebrate community structure in a backwater lake of Pool 2, Upper Mississippi River

Abstract The benthic community structure of a backwater lake of the upper Mississippi River was examined based on samples taken in July, 1986. The dominant taxa based on density were the midge Tanypus, followed by the naidid and tubificid oligochaetes and the mayfly Hexagenia. Based on biomass, however, Hexagenia was the dominant taxon. The species found were similar to those reported for other backwater lakes of the Mississippi River, although the relative abundances of various taxa were different. A canonical correlation analysis of habitat factors (based on sediment grain size and organic content) with community characters (densities of all taxa found) indicated that the percent sediment organic matter was the most important factor influencing the presence or absence of various taxa. Sediment particle size had a lesser association with the relative abundance of the major taxa.

Life-History Variation in a Stream Population of Musculium partumeium (Bivalvia:Pisidiidae)

This study reports on the life-history traits of a stream population of the clam Musculium partumeium. The population displays two generations per year: a spring-born generation (SG) which reproduces twice (fall and following spring) and a fall-born generation (FG) which reproduces once in the spring. Traits for FG and SG generations are, respectively: maximum shell length, 5.1 and 6.1 mm; annual reproductive output (number of young born per average adult), 16 and 38; larval growth rate, 0.15 and 0.08 mm/wk; larval mortality, 67 and 48%; intrinsic rate of increase (r) 0.011 and 0.019/day. Compared with values for other populations of M. partumeium, our results were generally intermediate between those displayed by permanent pond populations (with 2 generations/year) and those of ephemeral pond populations (1 generation/year). This species appears to display a wide range of phenotypic plasticity in life-history traits.

Comparison of Carbon and Nitrogen-Content of Infected and Uninfected Snails, Succinea-Ovalis, and the Trematode Leucochloridium-Variae

In June, 6.7% of adult Succinea ovalis collected near Urbana, Ohio, were infected with the trematode, Leucochloridium variae. The effects of parasitism were assessed as total organic carbon (equivalent to calorific values) and as total nitrogen. The parasite represents 23.8% of total (parasite + snail tissue) dry tissue weight, 21.4% of total carbon and 19.8% of total nitrogen of infected snails. The higher C : N ratio for parasite tissue indicates a higher proportion of nonproteinaceous compounds (e.g., fats and/or carbohydrates) as compared to host tissue. There is less snail tissue in parasited S. ovalis. The C : N ratios for parasitized and nonparasitized snail tissue suggest identical percentage compositions of proteins, fats, and carbohydrates.