Decomposition and microbial dynamics for standing,naturally positioned leaves of the salt-marsh grass Spartina alterniflora

Decomposition of leaves of smooth cordgrass (Spartina alterniflora Loisel.) was monitored for two cohorts of leaves from September 1984 to May 1985 (autumn and winterspring) at Sapelo Island (31°23 N; 81°17 W). The leaves were tagged in plance at the ligule, rather than cut and placed in litterbags. Dead leaves were not abscised from shoots. Loss of organic mass from the attached leaves was at least 60 to 68% of the orginal values. Fungal mass, as measured by an enzyme-linked immunosorbent assay, formed > 98% of the microbial standing crops in two of three autumn samples, and in all samples for the colder, drier, winterspring cohort. Fungal mass was probably mostly in the form of the mycelium and pseudothecia of an ascomycete, Phaeosphaeria typharum (Desm.) Holm. Fungal dominance of microbial standing crops declined when autumn leaves bent downward and acquired a large sediment content (ash=35% of dry matter); the bacterial crop then rose to 7% of the total microbial crop. Microphotoautotrophic mass was always measurable, but was never more than 2% of the microbial crop. Carbon-dioxide fixation was much lower than carbon-dioxide release, and a substantial portion of the fixation may have been anaplerotic fungal fixation. Threeto 8 wk net fungal productivity (average per day) was much greater (16 to 26 times) than measured instantaneous bacterial productivity (extrapolated to per-day values) early in each decay period. Fungal productivity was negative late in the decay period. Fungal productivity was negative late in the decay period for autumn leaves, and was approximately equal to bacterial productivity late for winter-spring leaves. Net nitrogen immobilization was observed only late in the decay period for autumn leaves, implying that nearly all dead-leaf nitrogen was scavenged into fungal mass after the first sampling interval. Flux estimates for dead-leaf carbon indicated a flow of 11–15% of the original to fungal mass, 2% to bacterial mass, 15–21% to carbon dioxide, 10–12% to dissolved leachage, and 34–36% to small particles; 32–39% remained attached as shreds at the end of the study periods. Salt-marsh periwinkles (Littorina irrorata Say) appeared to be the major shredders of dead leaves and conveyors of leaf-particulate material to the marsh sediment, at least in those parts of the marsh where the snails are densely concentrated (usually areas of short- and intermediateheight cordgrass shoots).     

Intertidal distribution,population dynamics and production of the amphipod Uhlorchestia spartinophila in a Georgia,USA, salt marsh

The talitrid amphipod Uhlorchestia spartinophila Bousfield and Heard occurs in close association with the smooth cordgrass Spartina alterniflora Loisel in salt marshes along the U.S. Atlantic coast. In order to assess its potential as a prey resource for secondary consumers, we followed the population and production dynamics of this amphipod from 3 November 1990 to 2 October 1991 in a salt marsh on Sapelo Island, Georgia. Semimonthly samples were taken along an intertidal transect, which extended from a vegetated creekbank levee landward 140 m to a site near the upland edge of the marsh. Amphipod densities ranged from 9 to 826 indm^-2 and were greatest in the levee and high marsh habitats at opposite ends of the transect. The highest densities occurred in March to May and the lowest in November and December. Specific growth rates, which ranged from 0.001 to 0.024 mm mm^-1 d^-1 length and 0.003 to 0.068 mg mg^-1 d^-1 AFDW (ash-free dry weight), were least in winter and decreased with increasing amphipod size. Although some reproduction occurred year-round, most of the population's reproductive output was from January to May, when adults had the greatest size-specific mass. Sex ratio usually favored females, which were larger than males. Minimum adult female size was 5.4 mm total length (TL). Broods included from 1 to 28 eggs or young and increased with increasing body size, averaging 7.4 young for an average-size female of 7.6 mm TL. Annual production, which ranged from 0.769 to 1.444 g AFDW m^-2, was least in the low marsh and greatest in the levee habitat. Production:biomass ratios were 15.4 to 17.3 in different habitats. Such high turnover rates, together with the population's broad intertidal distribution, suggest a greater contribution to trophic dynamics than is implied by the relatively low standing stock biomass of U. spartinophila in this marsh system.     

外源氮输入对互花米草生长及叶特征的影响

入侵种互花米草（Spartina alterniflora）是滨海盐沼湿地的多年生草本植物,研究人类活动引起的外源氮输入对其生长的影响有助于了解滨海湿地生态系统结构和功能的未来变化趋势。运用随机区组试验设计方法,模拟海滩水分条件（间歇淹水和持续淹水）,研究了互花米草的地上部生物量、叶片光合特征以及形态特征对外源氮输入的响应。结果表明：互花米草地上部生物量在施氮条件下显著增加,且在土壤处于间歇淹水状态时表现更为明显;施氮条件下植株分蘖数比对照处理分别增加了60.0%和60.2%,是引起地上部生物量增加的主要原因。施加氮素促进了互花米草叶片的生长,叶面积、叶数、叶长和叶宽均显著增加,而叶数的变化是导致植物叶面积增加的主要因素。外源氮输入促进了互花米草叶绿素含量的增加,而对净光合速率的季节变化特征无明显影响。持续淹水处理的植物地上部生物量、生长速率、分蘖数、净光合速率和叶面积均低于间歇淹水处理,说明持续淹水状态对互花米草生长造成了一定的抑制作用。     

Heterotrophic activity associated with particulate size fractions in a Spartina alterniflora salt-marsh estuary,Sapelo Island,Georgia, USA,and the continental shelf waters

An investigation was undertaken to determine the distribution and activity of the heterotrophic microplankton associated with particles from a Georgia salt marshestuarine ecosystem to the western edge of the Sargasso Sea. Heterotrophic activity was determined by the uptake of ¹⁴C-glucose. More than 80% of the activity was associated with detritus greater than 3 m in creek, river and coastal (within 4 km of shore) waters. In the Gulf Stream, approximately 80% of the heterotrophic activity was in the fraction less than 3 m. In the estuary, total heterotrophic activity fluctuated with the tides; the greatest activity occurred near low ebb tide at all locations. The lowest activity was measured at slack low and high tides. In creek water most of the heterotrophic activity was associated with particles between 14 and 180 m, whereas in coastal waters (less than 4 km from shore) most of the activity was in the fraction greater than 180 m.Contribution No. 331 from the University of Georgia Marine Institute, Sapelo Island, Georgia 31327, USA.     

Effect of uranium on growth and reproduction of the marine amphipod Allorchestes compressa

Experiments on growth of the marine amphipod Allorchestes compressa Dana were carried out over four weeks, and both growth and reproduction were studied over three generations, each of which was exposed to uranium for approximately 10 wk. At 0.1 mg l^-1 the uranium increased growth by 23%, as measured by the mean weight after 4 wk, and at 2 mg l^-1 growth was reduced by 28% compared with the control. A. compressa accumulated uranium from sea water with a concentration factor of 10. There was no effect of uranium on the survival of amphipods or their progeny in the multiple-generation experiment, but the numbers of males, the sex ratio, and the respiration rate (measured on males only) at 1mg l^-1 were significantly lower than the control. A. compressa is shown to be a convenient species for the study of toxic effects on growth and reproduction using multiple-generation experiments.     

Importance of grazing on the salt-marsh grassSpartina alterniflora to nitrogen turnover in a macrofaunal consumer,Littorina irrorata,and to decomposition of standing-deadSpartina

Dying leaves ofSpartina alterniflora Loisel (hereafterSpartina) do not undergo abscission and consequently are at least partially degraded while remaining attached to the shoot, i.e., under conditions which may be very different from those occurring in litterbags used to measure decomposition ofSpartina at the sediment surface. Attached living and dead leaves in high-marsh areas are subject to grazing by the abundant gastropodLittorina irrorata Say (hereafterLittorina), a salt marsh periwinkle. In 1986, nitrogen assimilation from living and standing-deadSpartina byLittorina was examined in Sapelo Island (Georgia, USA) salt marshes by labelling plants with the stable nitrogen isotope¹⁵N and measuring the transfer into grazing snails in the field. The initial label of ca 8% total plant nitrogen declined to ca 1% over 5 mo, perhaps due to label dilution by less enriched nitrogen taken up and translocated from below- to above-groundSpartina biomass. Snails incorporatedSpartina-derived nitrogen into tissues at rates equal to 10 to 20% of total snail nitrogen 30-d^–1 in summer and fall, and 2 to 5% 30-d^–1 in winter. In the absence of measurable growth, these high nitrogen incorporation rates may indicate a large reproductive effort, or substantial turnover of somatic tissue nitrogen. The annual total assimilation ofSpartina-derived nitrogen was equal to theLittorina-nitrogen biomass. Assimilation of nitrogen in the presence of livingSpartina material (dead material removed) was reduced substantially below that in the presence of intact plants (living and dead material present).Littorina populations at abundances found in Georgia would assimilate ca 3.4% of above-groundSpartina-nitrogen production annually in high-marsh, short-Spartina areas. Based on preliminary estimates of nitrogen assimilation efficiency, 13.2 to 27.2% of short-Spartina production could be ingested annually by Georgia populations ofLittorina. Most of this ingestion would be concentrated in the summer and early fall, when monthly ingestion could equal 100% of deadSpartina biomass. The impact of grazing byLittorina onSpartina decomposition may be greatest on these early-senescing leaves. Grazing may have little impact on the early stages of decomposition of the bulk of the shoots that senesce later in fall, but may be important in the later stages of decomposition of dead shoots that persist through winter until the following spring and summer.     

Effects of tidally mediated litter moisture content on decomposition of Spartina alterniflora and S. patens

Relationships between flooding frequency, flooding duration, litter moisture levels, and litter decay rates were investigated across the natural hydrologic gradient common to intertidal salt marshes. The effects on litter decay of natural and experimental alterations of litter moisture content were assessed in both field litterbag experiments (conducted in a southern New Jersey salt marsh from 1989 to 1990) and laboratory incubations (1990). Overall, tidally mediated litter moisture content was the dominant factor controlling litter decay throughout the vegetated marsh. Rates of carbon loss were most closely related to litter moisture levels (r=0.84), which were directly related to flooding frequency (r=0.66) and duration (r=0.63). Litter moisture levels were related to elevation within the tidal range due to increasing surface levation from creekbank to high marsh (ca. 54 cm) and height of litter above the sediment surface. Carbon losses from litter of short and tall form Spartina alterniflora Loisel. and S. patens (Aiton) Muhl. along the marsh elevation gradient indicate that while some of the variations in decay rates may be due to litter type, litter moisture accounted for most of the observed variation between marsh zones and within each litter type. Mousture levels are also affected by the water retention capacity of each litter type, which may also secondarily influence decay rates. Short-term incubations of litter indicated that CO₂ evolution was positively related to moisture content with negligible respiration at moisture levels below 15% (fresh mass), increasing to a maximum between 65 and 75% depending upon litter type. Since most Spartina spp. litter remains above the marsh surface where it maintains a lower moisture content than surface litter, the use of surface litterbags may overestimate rates of carbon loss in some systems. In addition, since changes in elevation of only a few centimeters had significant effects on both litter moisture levels and decay rates, slight changes in tidal regime may have important consequences for organic matter cycling in salt marshes by affecting litter decomposition processes.     

Life history and reproduction of the amphipod Synchelidium trioostegitum (Crustacea, Oedicerotidae) on a sandy shore in Korea

The life history and reproductive strategy of the amphipod Synchelidium trioostegitum were studied on a sandy shore at Dolsando, South Korea. Samples were taken once a month for 1 year using a 0.3-mm sledge net on the bottom in 1 m of water at spring tide low water. The highest density of S. trioostegitum occurred from February through March. Ovigerous females were recorded virtually year-round, with a particularly high proportion in fall and early spring, indicating continuous recruitment with two dominant periods. The occurrence of ovigerous females was not correlated with environmental factors, such as temperature and salinity, and no significant difference between the body lengths of females and males was observed. The mean adult body length was greater in the early spring breeding period than in the fall. Brood size and embryo volume were positively correlated with the body length of ovigerous females. Brood size significantly decreased with increases in embryonic developmental stage. Embryo volume was significantly larger in the fall than in the early spring, but brood size was significantly smaller in fall, suggesting a strategy of using the same amount of reproductive energy during breeding periods. This type of reproductive effort is different from that of other Synchelidium amphipods having the same habitat and feeding regime. Our results suggest that interspecific competition for food and territory may be important in defining the reproductive strategy.     

Feeding,growth, and survival of Engraulis mordax larvae reared in the laboratory

Methods are described for the successful rearing of northern anchovy larvae (Engraulis mordax Girard) on cultured foods. Larvae were fed successively on the unarmored dinoflagellate Gymnodinium splendens, the veliger of the gastropod Bulla gouldiana, and nauplii of the brine shrimp Artemia salina. Rearing containers ranging in capacity from 4.5 to 510 l were tested; the smaller ones were found to be most useful for laboratory experimentation. Irreversible starvation occurred when E. mordax were denied food for more than 1.5 days after yolk absorption. Growth rates of larval anchovies fed different diets were compared. Larvae fed G. splendens grew for 1 week at the same rate as animals fed wild plankton, but did not maintain this rate. Laboratory survival of E. mordax larvae on a diet of G. splendens alone, did not differ significantly when veligers supplemented the diet. However, when G. splendens and veligers were fed simultaneously to E. mordax larvae, growth rate was greatly improved, although still not matching the growth attained on a diet of wild plankton. Length (L) versus weight (W) analyses were made for all larvae at all diets. The results showed that weight could be calculated most accurately from length by the relationship log W=3.3237 log L-3.8205, regardless of diet.     

Nitrogen accretion,and the nature and possible significance of N2 fixation (Acetylene reduction) in a Nova Scotian Spartina alterniflora stand

Total aboveground nitrogen accretion through the 1975 growing season at a short Spartina alterniflora stand was estimated as 78 kg N ha^-1, compared to estimated N₂ fixation on the mud surface of 22 kg N ha^-1 and subsurface N₂ fixation of 93 kg N ha^-1. Subsurface N accretion was estimated to be of the order of 77 kg N ha^-1. Mudsurface ARA (acetylene-reducing activity) exhibited a pronounced mid-season maximum, while subsurface ARA exhibited a general trend of increase from May to September, and then a decline as a function of falling temperature. Various experiments suggested that mud-surface ARA was associated largely with non-heterocystous blue-green algae and photosynthetic bacteria, while subsurface ARA was associated mainly with vital activity of S. alterniflora. Counts of various groups of bacteria indicated an enrichment of anaerobic (glucose-utilizing) and microaerophilic (malateutilizing) N₂-fixing bacteria in the rhizosphere in comparison to non-rhizosphere soil. Treatment of roots with chloramine-t for 2 h reduced total numbers (plate count), anaerobic N₂ fixers, and microaerophilic N₂ fixers by factors of 357, 172, and 22, respectively, suggesting a relative enrichment of microaerophiles in the interior or endorhizosphere of the roots. ARA of excised roots was correlated with ¹⁴C-activity for roots from a plant previously exposed to ¹⁴CO₂, and with branching and age of the roots.     

Studies on the growth,reproduction, and life cycle of the supralittoral isopod Ligia pallasii

A two-year study on a field population of Ligia pallasii Brandt has shown that the isopods live for 1.5 to 2 years. Breeding occurs in the spring and early summer, with some females carrying winter broods of eggs. The mean length of breeding females is 22.5±2.2 mm (standard deviation) and the mean brood size is 48±11 eggs. Mature males are larger than mature females (900 and 300 mg live weight, respectively), and are disproportionately broader (31×17 mm and 22.5×9 mm, respectively). The larger size and breadth of the males is an adaptation for copulation, and may be atributed in some measure to slower growth of the female due to the extra energy demands of reproduction. The overall 1:1 ratio of males to females in the population represents the balance between an equal sex ratio in the immature stages, more females in the 18 to 24 mm length category, and more males in the larger length categories. This condition is attributed mainly to the faster growth of the males.     

Effect of selenite and seleniferous fly-ash leachate on growth and viability of the marine amphipod Allorchestes compressa

Juveniles of the amphipod Allorchestes compressa Dana were exposed to sodium selenite and to seleniferous leachate from coal fly-ash. A maximum acceptable toxicant concentration (MATC) for selenite of >44<93 g Se l^-1 is indicated by the results for growth and viability. Leachate:sea water mixtures produced effects which were consistent with selenite toxicity but quantitatively less drastic than expected from the pure selenite work, perhaps because of sulphate antagonism. The results are compared with selenium toxicity data for other aquatic species, and high-light the difficulties of using application factors as the basis for water-quality criteria.     

Growth,reproduction and nutrition of some Barents Sea hydromedusae in natural aggregations

Mass aggregations of the hydromedusae Tiaropsis multicirrata and Rathkea octopunctata have been studied in the Jarnyshnaya Fjord on the Kola Penninsula during the period of domination of the summer neritic plankton complex. The mass aggregations persist at least over periods of 2 months. No hyrometereological parameters could be established that would conceivably favour such aggregations. The factor most likely responsible for creating the aggregations is assumed to be related to the stable level of the summer zooplankton, production in the study area. The vast individual numbers of hydromedusae as well as their polyphageous feeding behaviour and high growth rates suggest that the medusae represent the most substantial consumers of plankton in inshore waters. The low and highly variable percent of medusae individuals which reveal food in their intestinal system lead the authors to assume additional food sources: nannoplankton, bacteria, and dissolved organic matter.     

Effect of temperature on laboratory growth,reproduction and life span of Octopus bimaculoides

Laboratory culture of 40 Octopus bimaculoides from April 1982 to August 1983 through the full life cycle at 18°C vs 23°C provided information on the growth, reproductive biology and life span of this California littoral octopus. At 18°C, the cephalopods grew from a hatchling size of 0.07 g to a mean of 619 g in 404 d; the largest individual was 872 g. Octopuses cultured at 23°C reached their highest mean weight of 597 g in 370 d; the largest individual grown at this temperature was 848 g after 404 d. Growth data revealed a two-phase growth pattern: a 5 mo exponential phase followed by a slower logarithmic (power function) phase until spawning. At 5 mo octopuses grown at 23°C were over three times larger than their 18°C siblings. However, beyond 6.5 mo, growth rates were no higher at 23°C than at 18°C. At 13.5 mo, the mean weight of the 18°C group surpassed that of the 23°C group. The slope of the length/weight (L/W) relationship was significantly different for the two temperature regimes, with the 23°C octopuses weighing 18% less than their 18°C siblings at a mantle length of 100 mm. Females weighed more than males at any given mantle length. Males grew slightly larger and matured before females. The L/W relationship indicated isometric body growth throughout the life cycle. Higher temperature accelerated all aspects of reproductive biology and shortened life span by as much as 20% (from approximately 16 to 13 mo). O. bimaculoides has one of the longest life cycles among species with large eggs and benthic hatchlings. Extrapolations to field growth are made, and the possible effects of temperature anomalies such as El Niño are discussed.     

Feeding, growth and reproduction of sea urchins (Strongylocentrotus droebachiensis) on single and mixed diets of kelp (Laminaria spp.) and the invasive alga Codium fragile ssp. tomentosoides

Since its introduction to Nova Scotia in the early 1990s, the invasive green alga Codium fragile ssp. tomentosoides has spread rapidly to become a dominant and persistent component of seaweed assemblages in the rocky subtidal zone. To examine the potential of sea urchins (Strongylocentrotus droebachiensis) to regulate Codium, and the potential of the alga to support urchin growth and reproduction, we fed urchins Codium and/or kelp (Laminaria spp., a high quality and preferred native food) in the laboratory for 11 months. Urchins showed a strong and active preference for kelp: they consumed more Laminaria than Codium (as dry weight) in single and mixed diet treatments. Urchins fed only Codium consumed 3.5 times more of the alga than those on a mixed diet, but did not increase their feeding rate in winter when kelp consumption was greatest. Laminaria was consumed at the same rate in single and mixed diets, indicating that the presence of an alternative food had no effect on kelp consumption. Survival and growth (change in test diameter) were lowest on the Codium diet, although the differences among diets were not statistically significant. Urchins on the Codium diet showed no gonadal production over the annual reproductive cycle, compared to a marked rise in gonad index on the Laminaria and mixed diets. Our results indicate that Codium is an unattractive, unpalatable and poor quality food, which is not readily consumed by urchins. Thus we predict that urchins at moderate densities will be much more likely to graze kelp than Codium in mixed stands, creating a mosaic of Codium patches and barren areas. At high densities, however, urchins are likely to destructively graze all seaweeds, although dense stands of the invasive alga may prolong the widespread formation of barrens.     

Effect of temperature on growth,sexual maturity and reproduction of<Emphasis Type="Italic"> Acanthomysis robusta</Emphasis> (Crustacea: Mysidacea) reared in the laboratory

The growth, sexual maturity and reproduction of a shallow, temperate-water mysid, Acanthomysis robusta Murano, were investigated by rearing this species through a complete life cycle at 10°C, 15°C, 20°C and 25°C. The average daily growth rate, which ranged from 0.08 to 0.29 mm for immature mysids and from 0.04 to 0.15 mm for mature mysids, increased with increasing temperature. Water temperature had little effect on the molt increment (the increase in body length between successive molts), but clearly shortened the intermolt period (the interval between successive molts) with increasing temperature. Thus, the faster growth rate at higher temperatures is responsible for the shortened intermolt period. External sexual differentiation first became apparent at the 4th or 5th post-marsupial molt, when body length was 4.3–4.9 mm. Thereafter, males reached sexual maturity at the 9th or 10th post-marsupial molt (7.3–9.8 mm in body length), while females reached maturity at the 10th–13th molt (8.2–12.2 mm). In contrast to this small difference in molt number for sexual maturity, the post-marsupial age at first maturity, which ranged from 13 to 57 days for males and from 17 to 78 days for females, decreased markedly with increasing temperature. The incubation time of ovigerous females, which varied from 5 to 24 days, also decreased with increasing temperature. The relationships between water temperature and the three development times, the intermolt period, the age at first sexual maturity and the incubation time conformed to the effective day-degree concept. Although mature females maximally produced four broods in a lifetime, egg-bearing significantly lengthened the intermolt period and consequently functioned as a factor decreasing the growth rate.Communicated by T. Ikeda, Hakodate     

Effect of temperature on growth and reproduction of the epigeic earthworm,Eudrilus Eugeniae (Kinberg)

Influence of temperature on growth and reproduction of Eudrilus eugeniae has been investigated by laboratory culturing at regulated 25.0 degrees C, 30.0 degrees C, 37.5 degrees C and 40.0 degrees C and in fluctuating (22.7-27.3 degrees C) room temperature of prevailing (winter) season over 16 weeks. All worms died during first and tenth week at 40.0 degrees C and 37.5 degrees C respectively. Weight (biomass) and growth of worms cultured at different temperature varied significantly (P<0.01). The mean growth (mg/g live weight/day) at 25.0 degrees C., 30.0 degrees C, 35.0 degrees C, 37.5 degrees C and in fluctuating temperatures was 1,074.04 +/- 6.07, 1,554.01 degrees 192.37, 148.1 +/- 15.28, 192.83 +/- 25.8 and 1450.4 +/- 162.1 respectively. Growth declined after maturity drastically with coccon production. At 25.0 degrees C though worms are sexually mature, they failed to produce cocoons within 16 weeks whereas, at 35.0 degrees C and 37.5 degrees C they did not sexually mature. Worms attained sexual maturity at a mean weight of about 1000 mg/worm. The mean per cent maturity was higher and earlier in fluctuating temperatures and at 30.0 degrees C than at 25.0 degrees C. Cocoon production was observed only at 30.0 degrees C and in fluctuating temperatures with a mean of 0.9 and 1.5 cocoons/ wom/week and the cumulative cocoon number of 10.8 and 14.7/worm over 16th week respectively. The fluctuating temperature of uncontrolled room environment and 30.0 degrees C were favorable for various life activities of the worms. Eudrilus eugeniae appears to have range of temperature optima more than 25.0 degrees C and less than 28 degrees C. The climatic conditions prevailing in whole of the peninsular India during winter season are favourable for employing this worm in intensive field scale vermiculturing practices.     

Effect of cobalt-supplemented diets on bioaccumulation,digestive enzyme activities and growth of Cyprinus carpio

Experiments were conducted to determine the effects of excess dietary cobalt (Co) on bioaccumulation, digestive enzyme activities, and growth in freshwater Cyprinus carpio. Four isonitrogenous diets (average crude protein: 35%) were formulated to prepare a control diet (T₁) with no Co, and three Co-supplemented diets with 1 (T₂), 1.5 (T₃), or 2 (T₄)% Co. The results showed that C. carpio fed with T₃ diet showed maximal apparent protein digestibility, feed conversion, protein utilization, and growth. Protease and lipase activities were maximal in the fish group given T₃ diet. Accumulation of Co in different soft and hard tissues of fish did not correlate with levels of Co in the diet. The concentration of Co in the water increased with dietary level, being at a disturbing adverse effect level at 2% dietary Co. Evidence indicates that an additional supply of dietary Co up to a level of 1.5% is a viable option to augment growth of C. carpio, but at higher levels of Co it may be detrimental to fish health and the aquatic ecosystem.     

Distribution,growth and life cycle of the mesopelagic amphipod Primno abyssalis (Hyperiidea: Phrosinidae) in the southern Japan sea

The vertical distribution, growth, maturation, brood size and life cycle of the hyperiid amphipod Primno abyssalis (formerly P. macropa) were investigated using seasonal samples collected from Toyama Bay, southern Japan Sea, during the period June 1986 to September 1992. Over four different seasons of the year, P. abyssalis was most abundant in the 200 to 350 m strata at night and the 350 to 400 m strata during the day, indicating 100 to 150 m as the general distance of diel vertical movement. Some differences in vertical migrating behavior were noted among juveniles, adult males and females. Population-structure analysis revealed the occurrence of three cohorts aged 0+, 1+ and 2+ yr. Growth as body length in this species is linear with time. Estimated time to complete one life cycle is 1.8 to 2.5 yr for females, but only 0.8 yr for males. Maximum longevity is 2.8 yr. Instar analysis based on the segment number of pleopod rami indicated that newly hatched juveniles molt ten times to reach adult male, and four more times to reach adult female. Adult instar number was found to be only 1 for males and 5 for females. Ovigerous females occurred throughout the year, but the annual peak of release of juveniles from the female's marsupium is estimated to be arly March. Brood size was not correlated with female size, a maximum brood size of 214 eggs was recorded. The dry and ash-free dry weights of instars suggested that juveniles in the female marsupium, adult males, and older adult females are less active feeding or non-feeding stages. Except for the reduced growth rate and the occurrence of small, short-lived males, most characteristics of P. abyssalis are consistent with the present view of the life modes of mesopelagic animals, including linear growth in length, aseasonal reproduction, and smaller brood size coupled with larger eggs.     

Survival and growth of conservation shrubs and trees,with thin-cover reclamation on acid substrate,Iowa, USA

Many abandoned strip-mine sites in midwestern USA are highly acidic and require a separate layer of low-acidity cover materials for successful revegetation. Economics and logistics often constrain this reclamation to a very thin cover. Twenty-two species of shrubs and trees were tested for 6 years of survival and growth on a thin wedge of silt loess (up to 0.75m thick) emplaced over highly acid spoils, in south-central Iowa. No weed control or maintenance was provided. The performance of 21 of the species could be categorized into 3 groups: Group 1-consistent survival (10 species); Group 2-irregular survival and growth (6 species); Group 3-little suitability for survival (5 species). Mouldy nursery stock precluded evaluation of 1 species. For most species, the most favourable survival and growth was not on the thickest loess cover (0.75 meters) because weeds became too well established. In general, the shrubs survived severe weed competition in dwarfed form until they could break through the weed canopy. But the tree species had to penetrate the weed canopy within their first few years of growth or perish. There is evidence that if weed competition were reduced or eliminated, the species in Group 2 would probably have survival and growth equivalent to those in Group 1. The use of “tubelings” for establishing shrubs and trees on thincover reclamation sites is suggested.