Role In Energy Cycles Research Articles

Assessment of acute toxicity and developmental transformation impacts of polyethylene microbead exposure on larval daggerblade grass shrimp (Palaemon pugio)

Due to the ubiquity of microplastic contamination in coastal waters, there is potential for adverse impacts to organism development. One organism of interest is the daggerblade grass shrimp, Palaemon pugio, an ecologically important species in estuaries along the east coast of North America. We exposed larval grass shrimp to virgin polyethylene microbeads (35 and 58 µm) at a high (0.375 and 1.95 mg/L), medium (0.0375 and 0.195 mg/L), and a low concentration (0.00375 and 0.0195 mg/L), respectively for 23 days to assess mortality, transformation time from larval to juvenile stage, and weight. Average percent mortality was 3.7 to 4.8 times higher in the experimental treatments compared to controls. The greatest proportion of mortality was observed in the first 11 days. Median time for transformation ranged from 20.2 to 20.8 days. Shrimp exposed to the 35 µm beads in the high treatment (20.2 days) transformed significantly faster than the control shrimp (20.8 days). Although development was not delayed and size of the shrimp did not differ, the acute toxicity of microplastics on grass shrimp is a concern due to their role in energy cycling within tidal-creeks. These findings suggest potential population and community level effects following microplastic exposure.

Marine Microbial Polysaccharides Environmental role and Applications: An Overview

Marine habitat represents about 70% of our planet. Microbial populations including bacteria, fungi and algae represent a base of food pyramids in this environment. The exudates of microbial cells (like polysaccharide) in the marine environment play an important role in energy cycling between the surface and the bottom in the sea by aggregation of small molecules causing them to sink. So it plays an important role in carbon sequestration and re emission through what called biologic pump. On the other hand, microbial polysaccharides help the microbial cell itself to colonize hydrophobic surfaces forming biofilms and tolerate drastic conditions like heat, salinity and cold stresses. Marine microbial polysaccharides are characterized by unique properties making them a good source of bioactive agents that can be used in many fields as anti-tumor, antiviral, antioxidant, anticoagulant, food and feed applications. An overview of the role of polysaccharide in the marine environment, its advantages and applications will be presented.

Yellow Perch Research and Management in Lake Michigan

Yellow perch (Perca flavescens) is an important component of near-shore freshwater fish communities. It plays an important role in energy cycling and transfer, and is available to nearly all segments of the angling public and to commercial fisheries. Beginning around 1990, yellow perch population density declined in Lake Michigan due in part to an almost complete lack of recruitment. In response to this dramatic decline, the Lake Michigan Yellow Perch Task Group (YPTG) was formed (under the auspices of the Great Lakes Fishery Commission's Lake Michigan Committee) to develop a multi-agency research initiative to identify the likely cause(s) for yellow perch recruitment failure. The multi-agency effort has made substantial progress in addressing this question, and serves as a model for agencies to work collaboratively to address important management questions with a sound research strategy. We highlight the work conducted during 1997–2001 to address five factors (predation, zooplankton availability, temperature, mass water movement, spawning stock characteristics) potentially influencing recruitment of yellow perch. Thus far, work to address influence of forage availability and stock characteristics on yellow perch recruitment has yielded significant results. The YPTG continues work to quantify the relative importance of (and interaction among) the factors described above in determining yellow perch survival and recruitment. The cooperative approach used by the YPTG to address these issues holds great promise, and can be used by agencies managing shared resources regardless of the system in question.

Impacts of trawling on the diversity, biomass and structure of meiofauna assemblages

Disturbance due to trawling reduces the biomass and production of macro-infaunal invertebrate communities, implying that their total food-consumption rate will fall, and that production (carbon) reaching the sea floor will be processed by other animals that can withstand the effects of trawling. Meiofauna may be resistant to disturbance by trawling because they are likely to be resuspended rather than killed by trawls and because their short generation times would allow them to withstand elevated mortality. We used a BACI experimental approach to investigate the short-term effects of beam trawling on the diversity, biomass and community structure of meiofauna on real fishing grounds in the southern North Sea. Experiments at two locations showed that there were no short- to medium-term (1–392 days after experimental trawling) trawling impacts on meiofaunal diversity or biomass, but that there were mild effects on community structure. Any impacts due to trawling were minor in relation to seasonal changes in the meiofaunal communities. We assessed the power of our experiments to detect the effects of trawling and recorded a 44–85% chance of detecting a 50% change in species richness and a 65% chance of detecting an order-of-magnitude change in biomass. The power to detect changes in total abundance, however, was low (between 11% and 12% power for detecting a change of 50%). We suggest that meiofauna are more resistant to disturbance by beam trawling than are macrofauna and that they have the potential to withstand the effects of chronic trawling on real fishing grounds and to retain a key role in energy cycling.

Development of Eodiaptomus japonicus Burckhardt (Copepoda, Calanoida) reared on different sized fractions of natural plankton

The nutritional value of different sized fractions of natural plankton was investigated for the growth of Eodiaptomus japonicus Burckhardt by comparing the development of its naupliar and copepodid stages fed on differentially fractionated planktonic assemblages of a eutrophic pond, at 20°C. Water filtered through a 0.8 urn Nuclepore filter, containing mainly small coccoid bacteria (0.45-0.6 jim in cell diameter), at a concentration of 82.7 p.g C could not support the development of E.japonicus. The 3 p.m filtered water, containing bacteria and picoalgae. at a total concentration of 259 jig C I, supported development but not egg production. The 20 jim filtered water, containing bacteria, picoalgae and large algae, at a total concentration of 2600 u.g C I, supported rapid development of the juveniles and continuous egg production by the adults. The separated 3-20 (j.m fraction, containing only large algae, could not support the development at concentrations of 131 and 196 |xg C I. However, the same rapid development of the juveniles and continuous egg production by adults occurred at all of the tested concentrations between 261 and 3920 M-g C I of the large algae. The results suggest that E.japonicus favours algae larger than 3 \im during its complete lifespan, and that the threshold food concentration for its development varies between 200 and 250 |j.g C I '. Introduction Adult calanoids are usually characterized as macrofiltrators, preferentially selecting the 5-20 u-m size faction (65-800 u,m in biovolume), containing phytoplankton, heterotrophic nanoflagellates and protozoans (e.g. Gras etai, 1971; Meskova, 1975; Infante, 1981; Ferguson etai, 1982; Price etai, 1983; Paffenhofer, 1984; Horn 1985a,b; Hartmann, 1991; Gifford, 1993). Bacteria are considered to be food for adult calanoids only if the cells are attached to larger particles or aggregated (Pedr6s-AH6 and Brock, 1983a,b; Nagata and Okamoto, 1988). Calanoids pass through six naupliar (Nl-NVI) and five copepodid (CI-CV) developmental stages before they become adults. Since juveniles usually constitute 60-80% of the natural populations, they are supposed to play a significant role in energy cycling in the plankton community (Fryer, 1987; Zinkai, 1991, 1994). However, our knowledge of the feeding habits of these immature stages is very limited and contradictory. Some authors demonstrated that NI-NII nauplii of calanoids do not usually ingest external food (they use energy stored in the yolk) and they start feeding in the NIII instar on phytoplankton larger than 4-5 u.m (PaffenhOfer and Knowles, 1978; Infante, 1981; Sastry, 1983; Burns, 1985,1988). In contrast to this, other experimental evidence has suggested that the early naupliar development of some calanoids is limited by the external food supply, and nauplii ingest bacteriaand picoalga-sized plastic beads (Dagg, 1977; Fernandez, 1979; Hamburger and Boetius, 1987; Zdnkai, 1991, 1994; Santer, 1994). Thus, it is still uncertain whether NI-NII nauplii do or do not require external food and whether © Oxford University Press 819

Nutrient Deposition in Cattail Stands by Communally Roosting Blackbirds and Starlings

Nutrient additions to five cattail (Typha spp.) stands in central New York State from droppings of roosting red-winged blackbirds (Agelaius phoeniceus), common grackles (Quiscalus quiscula), brown-headed cowbirds (Molothrus ater) and European starlings (Sturnus vulgaris) are reported. Bird numbers were estimated by counting birds as they left their roosts in the morning. Red-winged blackbirds were mistnetted as they entered a roost and were held until morning in cages lined with aluminum foil of known mass to determine the quantity of droppings excreted per bird-night. These data were used to develop a regression model to predict, from existence energy, the quantity of excreta input per bird per night. The amounts of nitrogen (N), phosphorus (P) and potassium (K) in the excreta were measured for red-winged blackbirds fed a simulated August diet and a simulated October diet. Red-winged blackbird droppings averaged 9.2% N, 1.41% P and 1.35% K. Nightly excretions of N, P and K averaged 59, 9.0 and 8.7 mg for a 39.0-g female and 75, 12 and 11 mg for a 56.0-g male. Nutrient loadings from blackbirds and starlings to the most densely populated roosts ranged up to 28, 4.3 and 4.1 kg*ha'eyear'I of N, P and K, respectively. These nutrient loadings are greater than those coming into the stands via precipitation and may be of similar magnitude to runoff loadings in some systems. INTRODUCTION Little is known about the role birds play in nutrient cycling (Sturges et al., 1974; Wiens and Dyer, 1977). Wiens (1973) suggested three possible roles for birds in ecosystems: (1) they may directly affect an ecosystem through a major influence on the flow of energy or nutrients; (2) they may act as controlling factors helping to maintain stability in the system without playing a major role in energy or nutrient cycling, or (3) they may be frills in the ecosystem living off its excess production and having no influence on the system. Population bioenergetics has been the primary means of assessing the role of birds in ecosystems. In general, this approach has shown that birds act only as frills, or at most play only a minor role in energy cycling (Holmes and Sturges, 1973; Wiens, 1973; Weiner and Glowacinski, 1975). Because of the necessary link between energy and nutrient cycling in birds, one might conclude that birds play at most a minor role in nutrient cycling. We present evidence to the contrary. Few rigorous studies have directly examined the role of birds in nutrient cycling. Bedard et al. (1980) found that nutrient importation by seabirds to an area of the St. Lawrence estuary was negligible relative to nutrients already present in the water or nutrients flowing into the estuary from the Mitis River. Likewise, Sturges et al. (1974) reported that birds played only a minor role in the nutrient budget of a northern hardwoods ecosystem. These studies support the idea that birds are of little consequence in nutrient cycling, but studies by Manny et al. (1975) and McColl and Burger (1976) came to different conclusions. Manny et al. (1975) suggested that inputs of N (12.9 kgeha-lyearA1) and P (3.9 kgeha-lyear-l) from migrant Canada geese (Branta canadensis) were the principal cause of hypereutrophic conditions in Wintergreen Lake, Michigan. McColl and Burger (1976) found that Franklin's gulls (Larus pipixcan) contributed 36% of the total annual P inputs to a cattail (Typha spp.) pool in Minnesota. These studies indicated that birds were potentially important nutrient cyclers. 1 Present address: Dept. of Biology, University of California-Riverside, Riverside, California 92521