R. Douglas Hunter

Changes in carbon and nitrogen content during decomposition of three macrophytes in freshwater and marine environments

AbstractThree species of aquatic plants were analyzed for their ash, organic carbon and nitrogen content both fresh and after decomposition using the mesh bag method Chara contraria A. Br. ex Kütz in a small freshwater pond and Lemna minor L. in a shallow swamp were examined over a 70 day period of in situ decomposition. Fucus vesiculosus L. was examined over a 63 day period of decomposition in a rocky shore and a salt marsh environment.During decomposition Chara showed a decrease in carbon and an increase in nitrogen content while Lemna increased in carbon and decreased in nitrogen, all on an ash-free dry weight basis. Although the C : N ratio of Chara was high initially and that of Lemna relatively low, after decomposition the C : N ratio for the remains of the two plants was nearly the same. Fucus decomposing in the salt marsh showed no significant change in carbon but increased in nitrogen content while that at the rocky shore decreased in carbon and increased in nitrogen content. Much of the loss in total dry weight in the first few hours of submergence could be attributed to solubilization of ash and of some high C : N ratio organic material. Consistent and significant differences in the C : N ratio of decomposing Fucus at the two marine sites may be attributable to the nature of the decomposer organisms that inhabit these environments. The accumulation of a high proportion of autotrophic microbial biomass (such as purple sulfur bacteria) in the structural carbohydrates of the salt marsh Fucus may have caused these differences.This study suggests that initial differences in nutritional value of aquatic macrophytes diminish during decomposition and that the ultimate C : N ratio attained may be more dependent on the nature of the decomposer organisms present than on the nature of the organic material undergoing decomposition.

Plant and animal species composition and heavy metal content in fly ash ecosystems

Plant and animal species present on a coal fly ash slurry pond site and a dry deposit site were surveyed and sampled during a two-day period in October. Elemental analyses were determined for most of the species encountered. A total of 48 plant species were observed on the two sites, with 35 species on the wet site, and 20 on the dry site. Eighteen terrestrial and 7 aquatic animal species were found on the wet site, exclusive of vertebrates which were not studied with the exception of a carp (Cyprinus carpio). Eleven terrestrial invertebrates and one aquatic species were observed on the dry site. Neutron activation analysis was carried out for: Se, Hg, Cr, Ni, Zn, Co, Sb, Cd, and As. Using literature values for phytotoxicity, we conclude that, in general, plants did not accumulate toxic levels of metals. Only one plant (Impatiens biflora Willd.) showed a significant level of Cd. Of 20 plants analyzed on the wet site, 10 had excessive Se concentrations (>5 ppm); on the dry site 6 out of 18 had high Se values. In animals (Gryllus sp.; Melanoplus sp.; Trachelipus sp.; Lumbricus terrestris; Physa integra; Cyprinus carpio) the trace metal concentration was generally in between that of control animals and that of the fly ash itself. One exception included Zn, which, although the most variable element examined, was concentrated in all the terrestrial animals to levels higher than in fly ash. Crickets are the most consistent bioconcentrators with Cr, Se, and Zn at higher levels than for control animals. All animal species studied accumulated Se compared to controls.

Physiologic and environmental factors influencing the calcium-to-tissue ratio in populations of three species of freshwater pulmonate snails

SummaryA study of three species of freshwater pulmonate snails, Physa gyrina (11 populations), Physa integra (17 populations), and Helisoma anceps (18 populations) was carried out from 1973 to 1976, primarily in Michigan.The ratio of whole animal calcium content to tissue dry weight (Ca: tissue ratio) changes with age, but these changes are largely restricted to early growth and do not significantly affect individuals over 40 mg total dry weight, regardless of species.Parasitization by larval trematodes was found to have no significant effect on the Ca: tissue ratio in the populations examined regardless of species.Ca: tissue ratio of P. gyrina did not vary greatly between populations and showed a narrow range over a wide range of environmental calcium concentrations. Shell mass in P. gyrina is therefore either physiologically regulated in all populations (at a species specific ‘constant’ level) or interpopulation variation is minimized by moderately high levels of gene flow between populations.There was no relationship between Ca: tissue ratio and environmental calcium for either P. integra or H. anceps over a wide range of snail and environmental calcium values. In both of the foregoing species, shell calcium content varied greatly between populations. This variation did not conform to any apparent geographic cline.In 7 of the population sites studied, P. integra and H. anceps coexist, and when these sites are listed from highest to lowest Ca: tissue ratios, the rank orders for the two species are nearly identical. This suggests that there is some environmental factor (possibly trophic conditions) at these localities that influences shell mass.In 8 other species of pulmonates briefly examined, differences in Ca: tissue ratio between populations of the same species were often as great as or greater than differences between species.While the patterns of shell mass and environmental calcium for these species are not unlike those previously reported, the proposed causal factors for these patterns are clearly distinct from those suggested for other freshwater pulmonates.

Dreissenids in Lake St. Clair in 2001: Evidence for Population Regulation

Zebra mussel (Dreissena polymorpha [Pallas]) density was surveyed at 12 stations in Lake St. Clair in September 2001. Lake-wide mean density was 1,824 individuals/m2; whole wet biomass was 148 g/m2; and dry tissue biomass was 1.23 g/m2. Compared to historical data, density did not change significantly, whereas biomass showed a significant downward trend. Our data support the assertion that the zebra mussel population in Lake St. Clair has undergone important changes since the mid-1990s. Some areas of the lake are now juvenile-dominated, others are adult-dominated, and some have a balanced size distribution. These data are consistent with the hypothesis that zebra mussels have changed the lake ecosystem in two ways that have contributed to their own population limits in a density-dependent manner. First is the reduction of adult microhabitat due to the elimination of native mussels from the lake proper. Second is the massive redirection of larval settlement onto a greatly expanded aquatic macrophyte community which senesces and dies at the end of each season, thus decreasing survivorship of juvenile D. polymorpha. If sustained, these recent changes, especially biomass reduction, suggest that the impact of dreissenids on the Lake St. Clair ecosystem will be more moderate in the future.

Lake St. Clair Zooplankton: Evidence for Post-Dreissena Changes

ABSTRACT We surveyed the zooplankton of Lake St. Clair at 12 sites over ten dates from May to October 2000. Mean zooplankton density by site and date was 168.6 individuals/L, with Dreissena spp. veligers the most abundant taxon at 122.7 individuals/L. Rotifers, copepods, and cladocerans were far lower in mean abundance than in the early 1970s (rotifers, 20.9/L; copepods, 18.1/L; and cladocerans, 6.8/L). Species richness of zooplankton taxa in 2000 was 147, which was virtually unchanged from that of the first reported survey in 1894. Overall, the decline in abundance was greatest for rotifers (-90%) and about equal for cladocerans (-69%) and copepods (-66%). The decrease in abundance of Daphnia spp. was especially dramatic in Canadian waters. The decline in the southeastern region was significant for all three major groups of zooplankton, whereas in the northwestern region the decline was significant only for rotifers. From June to August 2000, Lake St. Clair open waters were numerically dominated by Dreissena spp. veligers, with a reduced abundance of rotifers and crustaceans compared to pre-Dreissena spp. surveys. Mean nutrient concentrations were not different from the 1970s, but Secchi depth (greater) and chlorophyll a concentration (lower) were. Disproportionate reduction in rotifer abundance is consistent with hypotheses implicating direct consumption by settled Dreissena spp. Reduction of crustaceans is likely due to more complex interactions including removal of nauplii as well as resource competition for phytoplankton.

The effect of artificial photoperiod on growth and reproduction in the land snail Cepaea nemoralis

Summary Specimens of Cepaea nemoralis were raised from egg to adult in the laboratory for 15.5 months in two artificial photoperiods: short-day (LD 8:16) and long-day (LD 16:8). Over 20% of the snails in each photoperiod were functional adults by the end of the experiment and had fully developed male and female reproductive systems as determined both by dissection and by oviposition. A total of 925 eggs were laid by animals reared in a long-day photoperiod, whereas animals in a short-day photoperiod laid 677 eggs. Animals reared in a long-day photoperiod grew slightly faster (2.04 mg/day compared to 1.73 mg/day), began laying eggs about 18 days sooner, and suffered higher mortality (19% compared to 11%) than animals reared in a short-day photoperiod. These results clearly establish for C. nemoralis that gametogenesis and the development of a functional hermaphroditic reproductive system are neither prevented nor significantly retarded by exposing the animals to a short-day photoperiod for their entire pre...

Effects of Acid Water on Shells, Embryos, and Juvenile Survival of Planorbella trivolvis (Gastropoda: Pulmonata): A Laboratory Study

ABSTRACT Adults of the freshwater pulmonate snail Planorbella trivolvis were maintained in aquaria at four pH levels of approximately 4.9, 5.9, 6.8 and 7.8. Adult mortality was moderate over 82 days (10–32%) and not related to the magnitude of pH reduction. Decrease in both shell calcium per unit tissue dry weight and shell calcium per unit maximum shell diameter were significantly related to both time of exposure and pH level. Both measures were significantly reduced after 53 days of exposure to acid water such that for mean Ca mg−1, pH 4.9=5.9 < 6.8 < 7.8 and for mean Ca mm−1, pH 4.9=5.9 < 6.8=7.8. Empty (ashed) shells without a periostracum lost CaCO3 about 4.6 times faster than did shells of live snails with periostracum intact. Fecundity per snail did not differ greatly from one pH treatment to another although at pH 4.9 the embryos developed slowly and showed a high incidence (38.5%) of abnormality compared to embryos reared at pH 7.8 (4.8% abnormality). Juvenile survival at pH 5.1 was poor with 100...

Methylcellulose: An alternative medium for the study of burrowing aquatic invertebrates

Methylcellulose mixed with sea water forms a highly transparent, viscous solution which is palpably similar to certain natural marine sediments such as oozes and flocculent muds. Two species of invertebrates, a polychaete and a priapulid, have been observed burrowing in methylcellulose/sea water solution. Such a medium is superior to other artificial substrata (e.g. cryolite and glass particles) in terms of transparency and penetrability which are especially critical when observing soft‐bodied invertebrates and when quantification of the relative advance of individual appendages or segments is required.

Seasonal changes in organic carbon and C:N ratio in the major storage organs of Cepaea nemoralis (Mollusca: Pulmonata)

Abstract 1. 1. The carbon content and C:N composition of certain major storage organs of Cepaea nemoralis changes seasonally. 2. 2. The digestive and mature albumen glands can be characterized as high carbon, low nitrogen tissues having C:N ratios of 6.6:1 and 9.0:1 respectively compared to 3.7:1 for the tissues less the digestive gland. 3. 3. Both digestive gland and tissue less gland increase in carbon content before hibernation then decline gradually through winter and spring. 4. 4. In mature albumen glands, C:N ratio as well as dry weight increases before the reproductive period, then decreases thereafter.