The influx of large numbers of alewife, Alosa pseudoharengus, into relatively small freshwater systems may have a considerable impact upon pre—established food chains and nutrient cycles. We estimate the total nutrient input to Pausacaco Pond, Rhode Island, USA, from alewives amounted to 0.43 g P, 2.7 g N, and 16.8 g/Cm2 over a 2—mo period. This is largely through mortality of the spawning fish, and to a lesser extent through excretion. These inputs were much greater than the eventual nutrient loss to the system through emigration of juvenile fish. In tank experiments using pond microcosms, the initial response to the addition of the fish was a large phytoplankton bloom and an increase in litter respiration. The phytoplankton bloom was short—lived, and the most lasting effort was an increase in production and respiration in the leaf litter. This increased production in the litter community would support a long lasting supply of insect and benthic invertebrate food for young fish. The respiration rate of autumn leaves incubated in alewife streams during the migration was significantly higher than that of leaves incubated simultaneously in a stream which had no alewife run. Respiration rates of leaves incubated in the same streams before the arrival of alewives did not differ significantly. The increase in litter respiration, an indication of microbial and invertebrate activity on the leaf surface, was attributed to the additional nutrients supplied by the fish.
Egg production, dry weight, cephalothorax length, and condition factor were measured for adult Acartia tonsa females collected twice weekly from Narragansett Bay, R
Changes in the cephalothorax length and dry weight of Formalin-preserved copcpodite and adult Acartia clausi were followed from 12 March-l June 1976 and naupliar weights and lengths determined for one sample. Preservation in Formalin caused a significant loss of dry weight, carbon, and nitrogen in adult females, mostly during the first 24 h, but did not significantly affect the C:N ratio or the cephalothorax length of the animals. Length and weight were inversely related to seawater temperature at the time of sampling. As the animals became older this relationship was increasingly affected by their past temperature history. Separate linear relationships between log length and log weight were observed for the nauplii, the CIs, the CII-CVs, and the adults, making it possible to estimate the weight of individual stages from measurcmcnts of length. Animals collected on the same day frorn different stations sometimes showed significant differences in weight for a given length. Such differences could be more clearly expressed by calculation of a condition factor relating weight to the cube of cephalothorax length. The differences in the condition factor appeared to be related to food availability and such differences may be even more apparent when weights of live animals are examined.
Ingestion and short-term weight change in adult female Acartia hudsonica were investigated at 4. 5", 8", 12", and 16°C with the solitary diatom Thalassiosira constricta as food. Narragansett Bay copepods were preadapted to the desired temperature and saturating food level for 3 d to standardize feeding history before the experiments. Maximal ingestion rates at the four temperatures were 16,460, 14,120, 2 1,470, and 29,960 cells copepod-'d-l or 43.9, 37.2, 67.9, and 92.9% body C (Q10 = 2.3) and 34.2, 30.7, 42.6, and 74.7% body N d-' (Q10 = 2.4). The critical concentration varied between 840 and 1,900 cells ml-' (0.17-0.23 pg C ml-l) and was not significantly related to temperature. Maximal clearance rate was similar at all temperatures (20.8-23.9 ml copepod-Id-l), but .on a weight-specific basis increased from 3.3 to 6.0 ml (pg copepod C)-'d -I between 4.5" and 16°C (Q10 = 1.8). Feeding rates at 4.5" and 8°C were similar; the seemingly low ingestion rates at 8°C were interpreted as evidence for a senescent population of adult copepods in the bay from late April to early May.During preadaptation at high food, A. hudsonica body C and N either stayed constant (indicating saturating food in the field) or increased (indicating food limitation in situ). Body weight was sensitive to variation in food supply; during the 24-h feeding experiments weight remained stable at the two highest food levels, but declined significantly at lower levels. Maximal observed weight loss was temperature-dependent, increasing from -15% C and 12% N d-l at 4.5"C to 25% C and 17% N d-l at 16°C. The relationship between temperature and feeding rate in marine copepods has seldom been investigated, although temperature effects on respiration, reproduction, growth and development, and gut evacuation are relatively well known (e.g. Mullin and Brooks 1970; Vidal 1980~;Dam and Peterson 1988;McLaren et al. 1989). Of particular interest are the effects of temperature on the maximum rates of feeding (I,,,) and clearance (E,,,), and the food concentrations associated with the lower feeding threshold (C,) and the attainment of Imax (the critical concentration Cc), as these parameters define the functional relationship between food abundance and feeding rate Acknowledgments We thank Robert G. Campbell for assistance in the field and laboratory work, Einar Hjorleifsson for advice concerning computer analysis of the data, R. Choudary Hanumara for statistical advice, Theodore J. Smayda for permission to use the C-N analyzer in his laboratory, and Marilyn Maley for assistance in manuscript preparation. We also thank three reviewers for their comments on the manuscript.
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