The complete year—round feeding and growth of the marine snail Polinices duplicatus eating the clam Mya arenaria were directly monitored under field conditions. The major factors affecting feeding rates were food supply, temperature, predator size or weight, and recent feeding experience. Provided with excess prey of differing sizes, Polinices of each size or age ate similar numbers of prey per time (° = 95.5 Mya per snail per yr). Feeding varied directly with temperature, peaking at 0.6 Mya per snail per day in the warmest months, but ceasing (at °5°C) for 4 mo in winter. Energy equivalents for Polinices and size—weight relations for Mya varied seasonally. Only °80% of the tissue weight or energy content of a prey was actually ingested. Because larger predators consistenly ate larger prey, they ingested more (385 kilojoules/yr for a 4th—year snail) than smaller, younger ones (°218 kJ/yr for 2nd—year snails). Wtih a specified food supply, temperature and predator weight together accounted for most ofthe variability in ingestion (milligrams or kilojoules) of Mya by experienced predators. On a year—round basis, ingestion rates of Polinices were only °1% of their own weight per day. Growth rates, unlike feeding rates, were correlated more with a snail's age than its size or weight: 2nd—year Polinices grew nearly 3—fold in diameter or °105 kJ/yr vs. 1.2—fold or °63 kilojoules for a 4th—year nails. Growth creased during the 5 coldest months (<10°C). It was also reduced when snails could interact. Without molluscan prey, Polinices failed to grow. On a Mya diet, gross growth efficiences were high (48%—19% for year—classes 2 to 4). Energy flow through Polinices was comparable to other marine invertebrate predators: annual ingestion and production per square metre were estimated at up to 151 and 71 kilojoules, respectively.

Mature glochidia were stripped from the gills of gravid mussels and exposed to low pH (3 – 6.5), aluminum (150 – 3000 μg/L), aluminum (300 μg/L) at low pH (3–6.5), zinc (5 – 30 000 μg/L), cadmium (50–3000 μg/L), or copper (5 – 1500 μg/L) for 6 days. Viability was tested after 24, 48, 72, and 144 h by observing the ability of the glochidia to close when exposed to an irritant, 2.5 M KCl. Effective concentrations needed to reduce the closure response to 50% (EC50) under the experimental conditions were calculated using probit analysis. The relative toxicities (based on 48-h EC50s) of the metals to Anodonta cygnea glochidia were Cu (EC50 = 5.3 μg/L) > Cd (EC50 = 46.8 μg/L) > Zn (EC50 = 69.1 μg/L) > Al. The EC50 for pH was 4.34 for A. cygnea and 4.69 for Anodonta anatina. In 300 μg/L Al, the EC50 for pH for A. cygnea was 4.46. The ability of glochidia to close their valves is considered a reliable measure of viability, as this action is necessary for the larvae to complete the obligate ectoparasitic stage of their life cycle. Decrease in glochidial viability is suggested as a possible explanation for the disappearance of unionids from acid- and metal-contaminated waters.

This study analyses the histological and cellular morphology of the testis and sperm development in the male Daphnia magna Straus 1820. Due to the rarity of males and predominately parthenogenetic lifecycle of Daphnia, there has been limited detailed information on males in contrast to the well-studied female. Using light and electron microscopy approaches, we describe the morphology of the testis during the progression from an immature to mature testis. The testis has an encasing muscular mesh sheath outside the basal lamina, beneath which is a thin somatic epithelial cell layer. Internal to the epithelium are the spermatogonial stem cells and subsequent syncytial clusters of the germ cells as they progress through spermatogenesis; spermatozoa occupy the entire testis in sexually mature D. magna. We describe the structure of developing and mature spermatozoa; mature spermatozoa are non-flagellated, ovoid in shape with plasmalemma filapodia and are encased in an extracellular capsule.

We examined age-related vulnerability of Daphnia magna to UV-B (ultraviolet-B radiation, 280-320 nm), the age-related relationships between UV-B dosage and reproduction, and the effects of duration of PRR (photorecovery radiation) on survival and fecundity. Animals were exposed to 0, 6, 9 or 12 h UV-B (peak emission 312 nm) at 1, 2, 3 or 4 days of age and followed to 12 days. Survival decreased with increasing exposure to UV-B, but increased with age at exposure. Duration of UV-B, but not age at exposure, decreased offspring production. Survival increased with an increase in duration of PRR for animals of all ages; however, the effect was not age related. Three-day-old animals were exposed to 6 h of UV-B followed by 0-600 min of PRR. Survival was greatest in controls, lowest in the group that received no PRR and similar for all other groups. Most mortality occurred within the first 72 h postirradiation. Offspring production was highest in light controls, lowest in the UV-B-exposed group that received no PRR and not significantly different among other groups. This study demonstrates the need to consider age when examining the effects of UV-B on zooplankton and the need to monitor responses over a sufficient length of time.

We examined the effects of daily (chronic) exposure to artificial UVB radiation on the survival and reproduction of Daphnia magna over two generations. Control and experimental animals in each generation (parental and F1) were exposed to 16 h of UVA radiation and photosynthetically active radiation daily. In addition, experimental animals were exposed to 6 h of UVB during the middle of the light period. Survival and reproduction were followed for 12 days for each individual. Survival and production of F1 were significantly lower in the UVB exposed parental generation Daphnia than in controls. F1 exposure to UVB significantly decreased F1 survival and reproduction. Reproduction was lowest in UVB exposed F1 animals whose parents were also exposed to UVB. Adverse effects of UVB on offspring production may be magnified in successive generations suggesting that short-term experiments could underestimate the impact of increased UVB exposure on populations.