Food Chain Dynamics Research Articles

The Behavioral Response Race Between Predator and Prey

On tente de preciser par la methode de regression lineaire ce qui determine les rapports de force relatifs en ce qui concerne les relations predateur-proie (on donne comme exemple Notonectidae-Culicidae)

The spawning habitat of the Peruvian anchovy, Engraulis ringens

Individual larvae of the anchovy Engraulis ringens appear to survive better off the northern coast of Peru during the austral winter season when a motile algal food supply is available. Concentrations of the dinoflagellate food of the first feeding anchovy larvae may be reduced less often by wind events in the north than in the south. Under El Nino conditions, more of the adult anchovy are found south within a less favorable spawning habitat, in terms of dilution and food quality, where there is evidently less larval survival and subsequent recruitment to adult stocks. Increased mortality of the larvae during 1965, 1972, and 1976 El Ninos and of the adults during the 20-year fishery has reduced the present stock to less than 20% of its biomass in times of peak yield. Such a change in food chain dynamics is reflected in transients of oxygen demand at the decadal scale of variability. Associated with an increase in zooplankton biomass and a decline of the anchovy fishery, the sardine species of the clupeid pair off Peru may also be increasing in number, implying that natural oscillations of clupeoids may be accelerated by overfishing.

Detritus and Juvenile Salmon Production in the Nanaimo Estuary: I. Production and Feeding Rates of Juvenile Chum Salmon (Oncorhynchus keta)

Theories of food chain dynamics have important implications for the management of marine resources. As yet, however, there are few empirical studies of the food chain dynamics of resource species against which these theories can be judged. This paper compares the food requirements of juvenile chum salmon (Oncorhynchus keta) in the Nanaimo Estuary with the productivity of their principal food species. Chum were present in the estuary from March until June and the estuary population ranged up to 4.1 million in May 1975 and 2.4 million in April 1976. The average weight of chum was 0.66 g in 1975 and 0.65 g in 1976, and their rate of growth averaged ~6% body weight per day in both years. Food intake estimated by three independent methods ranged 4.4–18% body weight per day and was assumed to average 15% body weight per day. Annual fry production was 2381 kg in 1975 and 1122 kg in 1976. Food intake was 6184 kg in 1975 and 2815 kg in 1976. The principal dietary item in both years was harpacticoid copepods. In 1975 Harpacticus uniremis made up 50% of the diet overall, and >80% of the diet when fry were most abundant. The seasonal pattern of abundance of fry and H. uniremis on the estuary was the same, and the fry consumed most of the estimated production of H. uniremis. Juvenile chum production was potentially limited by food supply. Food chain dynamics were, therefore, important in the productivity of the chum population, but since both chum and its chief food were rare and ephemeral elements of the estuarine fauna, their interaction probably had little impact on the dynamics of the estuary as a whole. Key words: chum salmon, estuaries, food chains, populations, feeding rates

Wind events and food chain dynamics within the New York Bight 1, 2

Time series of wind, current, nutrients, chlorophyll, and zooplankton are used to examine the effect of storm events on the food chain dynamics of the New York Bight. Storms cause dilution of phytoplankton concentration in the vertical plane, but lead to aggregation of chlorophyll in the horizontal field. Nutrients are made available with onshore flow in response to wind events favorable for upwelling. A series of nutrient budgets suggest that storm‐induced mixing and upwelling of nitrate may satisfy at least 33% of the productivity demand of this system. Examples of the biological response to storms are drawn from 20 cruises during January, March, April–May, and August–September 1974, 1975, 1976, and 1977 under mixed and stratified conditions of the water column. The interaction of storms and seasonal stratification suggests predictable structure and frequency of chlorophyll distribution across the shelf which may influence both the survival strategies of herbivores and the loci of energy transfer to the rest of the food chain.

Vertical and Seasonal Distribution of Chlorophyll a in Lake Michigan

Vertical and seasonal distribution of chlorophyll a was observed for 2 yr at an offshore station in Lake Michigan. Chlorophyll a concentrations increased uniformly at all depths during spring reaching 3–4 mg/m3 by late May. Thermal stratification was followed by development of a subthermocline chlorophyll peak between 10 and 30 m that reached 8.5 mg/m3 by late July. The major subthermocline peak collapsed in mid-August but was followed by two lesser peaks at depths of 10 and 30 m. Autumn mixing dispersed these peaks in the mixed layer, increasing the chlorophyll content of the epilimnion at a time when integral chlorophyll levels were declining. At fall overturn chlorophyll concentrations were uniformly distributed at approximately 1 mg/m3, where they remained throughout the winter. The presence of a deep chlorophyll maximum in Lake Michigan adds a new dimension to limnological studies of the Great Lakes. The influence of this peak must be considered in future investigations of food chain dynamics and eutrophication processes in the Great Lakes system. Key words: Laurentian Great Lakes, limnology, chlorophyll a, spatial distribution, phytoplankton dynamics

Utilization of aged detritus derived from different sources by the polychaete Capitella capitata

Because the rate of microbial degradation differs for the various sources contributing to the detrital pool in marine systems, their availability to detritivores might also vary. Carbon-14 tracer experiments were used to compare differences in the oxidation and net incorporation by the polychaete Capitella capitata of a nitrogenrich, easily-decomposable detritus derived from the red macrophytic algae Gracilaria sp. versus a nitrogen-poor, decay-resistant detritus derived from the eelgrass Zostera marina. The net incorporation of Gracilaria sp. detritus by C. capitata reached a maximum (91 μg dry weight of detritus/mg dry weight of worm/day) after only 14 days of decomposition, whereas that of z. marina detritus equaled this level after 30 days of aging, but continued to increase to 375 μg at 180 days. The oxidation rate of Gracilaria sp. detritus was consistently higher (peak of 61 mg dry weight of detritus/day at 30 day-aging) than z. marina detritus, which reached this level only after 180 days of aging. The presence or absence of C. capitata did not significantly alter the oxidation rate. The above difference might be attributed to a rapid exploitation and mineralization by bacteria of the more available Gracilaria sp. detritus, but a slow, “controlled” utilization by the microbes of the less available Z. marina detritus, especially during the early stage of decomposition. This would allow maximum exploitation of the substrate by macroconsumers, resulting in more of the detrital resource being tied up in detritivore biomass rather than being rapidly mineralized to CO2. Difference in the length of aging at which various detrital sources become available to detritivores could result in a temporal partitioning of food resources and should be considered in attempting to understand the dynamics of detrital-based food chains.

The effect of food concentration on cumulative ingestion and growth efficiency of two small marine planktonic copepods

A knowledge of the growth rates and feeding behaviour of planktonic copepods at natural food concentrations is important for an understanding of food-chain dynamics in the sea. In many areas of the open oceans average concentrations of particulate organic carbon rarely exceed 100 µ carbon 1-1, and even in coastal regions the maximum levels are probably only one or two orders of magnitude higher (Parsons, 1975). Thus, most herbivorous marine copepods live in a nutritionally dilute environment (Conover, 1968). In contrast to natural conditions, many laboratory investigations have been carried out at unnaturally high food concentrations, often more than one order of magnitude higher than those which might be expected in the sea.

Food chain dynamics of abalone in a polyculture system

The food chain dynamics of three species of commercially important abalone — the red abalone ( Haliotis rufescens), the green ( H. fulgens) and the Japanese ( H. discus) — were measured to determine their relative success in the multispecies aquaculture system at Woods Hole Oceanographic Institution. The abalone were fed sea lettuce ( Ulva lactuca) used in the polyculture system to remove nutrients regenerated by the bivalves. This polyculture system was operated on a moderate-sized scale during the summer of 1973. Growth and feeding rates of the abalone were measured during a 112-day period and net growth efficiency was calculated (net production/food ingested). All three species grew during the experiment but H. rufescens had the lowest efficiency of 10.2%, and H. fulgens had the highest efficiency of 22.7%. These differences might be due to the temperature regime (16–23°C) during the experiment. H. rufescens is typically found in colder waters whereas H. fulgens is common in warmer Southern California waters. The results suggest the feasibility of the browsing role of abalone in polyculture systems.

Dynamics and Energetics of Three Deposit‐Feeding Benthic Invertebrate Populations in Puget Sound, Washington

The dynamics and energetics of subpopulations of a numerically dominant deposit—feeding polychaete species, Pectinaria californiensis Hartman, were studied and compared with crude determinations of the same for the larger but rarer coexisting species of the same feeding mode, the heart urchin Brisaster latifrons (Agassiz) and the sea cucumber Molpadia intermedia (Ludwig). Monthly samples, taken for 1 yr at five stations in Puget Sound representing different habitats, were used in conjunction with laboratory measurements of respiration to assess the effects of seasonal and spatial variation in growth, mortality, and respiration on estimates of energy flow through these species populations. Pectinaria larval settlement (2,900—24,000 animals/m2) occurred at all locations in June 1970. Two of three age classes or cohorts were present simultaneously. Pectinaria represented 4%—26% of macrofaunal (> 1 mm) biomass, and 9%—47% of numbers at the five locations, based on the mean of four seasonal estimates. At the two stations where Brisaster and Molpadia coexisted with Pectinaria they contributed, respectively, 79% and 4% of macrofaunal biomass at one station and 13% and 63% at the other. Recruitment and growth of the two echinoderms appeared negligible, as neither numbers nor mean size changed during the study period. Annual production of Pectinaria, not including excretion or mucus production, varied 1.4—48 g C/m2°yr (14—49 kcal/m2°yr). The ratio of annual production to mean annual biomass, varying in the study area 3.3—5.5m provided a better estimate of turnover than the more commonly used ratio based on the lifetime of a cohort because of the difficulty of determining lifespan, a problem with most long—lived organisms. Pectinaria contributed 14%—42% of macrofaunal respiration in the area studied. But these numbers were shown to be affected by the failure to reproduce in the laboratory in situ oxygen—tension conditions. Such overestimates of population respiration from laboratory measurements were most marked for Brisaster and Molpadia. These latter estimates, while reflecting biomass data, unrealistically overshadowed the respiration of all other organisms. The sum of Pectinaria production and respiration (corrected for in situ oxygen tension) varied 2.6—9.2 g C/m2°yr (27—98 kcal/m2°yr), reflecting differences in rates of growth and mortality among stations. At two stations where primary production data were available, Pectinaria assimilated at least 1.3% and 3.3% of the carbon fixed by phytoplankton. Subsequently, 0.6% and 1.7%, respectively, were made available to predators and decomposers in the form of Pectinaria flesh. Because of its greater turnover of assimilated energy, Pectinaria contributed more to metabolic processes and to foodchain dynamics of the seabed than did the coexisting echinoderms. The echinoderms, on the other hand, may exert important influences on the structure of the community not accounted for in normal energetic assessments. Spatial and temporal variations in energy flow through species subpopulations can be large, and thus may limit the usefulness of a stability assumption in the development of predictive models for organic matter budgets.

The food chain dynamics of the oyster, clam, and mussel in an aquaculture food chain

The food chain dynamics of the edible mussel Mytilus edulis L., the American oyster Crassostrea virginica (Gmelin) and the hard clam Mercenaria mercenaria (L.) were investigated in large experimental tanks with flowing, filtered sea water and controlled addition of phytoplankton. The feeding rate of the mussel (5.36 μg carbon removed/l/g C animal was higher than that of the oyster (3.92) and clam (3.03) but the ecological efficiencies (net production/ingested food) × 100 of the clam (23.69 %) and the oyster (18.38 %) were higher than that of the mussel (10.01 %). The food chain efficiencies (net production/available food) were lower than the ecological efficiencies, suggesting under-exploitation of the available food. The clam, although having a lower feeding rate, was more efficient in utilizing the food it filtered and so showed the highest net production. The rates (μg-at/l/g C animal) of regeneration of nutrients, especially total inorganic nitrogen (mussel, 2.1723 × 10 −3; oyster, 7.4270 × 10 −3; and clam, 8.1750 × 10 −3) along with reported high biodeposition rates of bivalves suggest that multi-species aquaculture systems would be more efficient and productive than one-species systems.

Comparison of rates of feeding and biodeposition of the American oyster, Grassostrea virginica Gmelin, fed different species of phytoplankton

The feeding and biodeposition rates of small (2.4 cm) and large (5.2 cm) Crassostrea virginica were differently affected in experiments using flowing systems by moderate (292 μ C/1 sea water) and high (487 μ C/1 sea water) concentrations of the following phytoplankton: the diatoms, Thalassiosira pseudonana (Hasle & Heindal) ( Cyclotella nana), Skeletonema costatum (Greville) Cleve, Nitzschia closterium (Ehrenberg) Wm. Smith, and the green alga, Dunaliella tertiolecta Butcher. The average feeding rate of the oysters on the different phytoplankton was: Dunaliella < Nitzschia < Skeletonema < Thalassiosira. In contrast, oysters fed on Thalassiosira had the lowest rate of biodeposition (1.626 × 10 −3 g ash-free dry wt/g dry flesh wt per day) but oysters cultured on Nitzschia showed the highest rate of biodeposition (2.952 × 10 −3 units). The response of the feeding rate of the two sizes of oysters to food concentration differed according to the algal food source. Oysters fed on Thalassiosira and Skeletonema exhibited a higher feeding rate at a higher food level: in contrast, oysters fed on Nitzschia showed no significant differences and those cultured on Dunaliella a depressed feeding rate at the higher food concentration. We observed no differences in feeding rate between small and large oysters fed on Skeletonema and Dunaliella, but small oysters had a higher feeding rate than large oysters when cultured on Thalassiosira and a lower feeding rate when fed on Niitzschia. The smaller size of Thalassiosira and larger size of Nitzschia might account for these differences in the feeding efficiency of small oysters. The biodeposition rates of both sizes of oysters were also affected by food concentration of the different algae. At the high food concentration with Skeletonema, Nitzschia, and Dunaliella, all oysters showed a marked increase in the rate of biodeposition, but oysters fed on Thalassiosira exhibited no great change. On all species of phytoplankton, the larger oysters produced greater biodeposition than the smaller oysters. These differences in response of feeding and biodeposition rates are important to our knowledge of food chain dynamics and may be used to optimize aquaculture systems.