Impact of microzooplankton and copepods on the growth of phytoplankton in the Yellow Sea and East China Sea

Dilution and copepod addition incubations were conducted in the Yellow Sea (June) and the East China Sea (September) in 2003. Microzooplankton grazing rates were in the range of 0.37-0.83 d(-1) stopin most of the experiments (except at Station A3). Correspondingly, 31-50% of the chlorophyll a (Chl a) stock and 81-179% of the Chl a production was grazed by microzooplankton. At the end of 24 h copepod addition incubations, Chl a concentrations were higher in the copepod-added bottles than in the control bottles. The Chl a growth rate in the bottles showed good linear relationship with added copepod abundance. The presence of copepods could enhance the Chl a growth at a rate (Z) of 0.03-0.25 (on average 0.0691) d(-1) ind(-1) l. This study, therefore parallels many others, which show that microzooplankton are the main grazers of primary production in the sea, whereas copepods appear to have little direct role in controlling phytoplankton.

Feeding and growth on bivalve biodeposits by the deposit feeder Stichopus japonicus Selenka (Echinodennata : Holothuroidea) co-cultured in lantern nets

Suspension aquaculture of filter-feeding bivalves has been developing rapidly in coastal waters in the world, especially in China. Previous studies have demonstrated that dense populations of filter-feeding bivalves in shallow water can produce a large amount of faeces and pseudofaeces (biodeposits) that may lead to negative impacts on the benthic environment. To determine whether the deposit feeder Stichopus (Apostichopus) japonicus Selenka can feed on bivalve biodeposits and whether the sea cucumber can be co-cultured with bivalves in suspended lantern nets, three experiments were conducted, two in tanks in the laboratory and one in the field. In a 3-month flow-through experiment, results showed that sea cucumbers grew well with specific growth rate (SGR) reaching 1.38% d(-1), when cultured in the bottom of tanks (10 m(3) water volume) where scallops were cultured in suspension in lantern nets. Moreover, results of another laboratory experiment demonstrated that sea cucumbers could survive well on bivalve biodeposits, with a feeding rate of 1.82 +/- 0.13 g dry biodeposits ind(-1) d(-1), absorption efficiency of organic matter in biodeposits of 17.2% +/- 5.5%, and average SGR of 1.60% d(-1). Our longer-term field experiments in two coastal bays (Sishili Bay and Jiaozhou Bay, northern China) showed that S. japonicus co-cultured with bivalves also grew well at growth rates (0.09-0.31 g wet weight ind(-1) d(-1)) depending on individual size. The results suggest that bivalve lantern nets can provide a good habitat for sea cucumbers; and the co-culture of bivalve molluscs with sea cucumbers may provide an additional valuable crop with no additional inputs. (c) 2006 Elsevier B.V. All rights reserved.

Growth and survival of reciprocal crosses between two bay scallops, Argopecten irradians concentricus Say and A-irradians irradians Lamarck

A complete diallel cross between two bay scallop populations, Argopecten irradians concentricus Say (M) and A. irradians irradians Lamarck (C), was carried out. Growth and survival were compared among hybrids and pure populations. No significant difference in the shell length was found among the four groups on the first day of D-larvae. On day 10, shell lengths of the two reciprocal crosses (CM, MC)(female x male ) were significantly greater than those of the CC (141.97 mu m) and MM (146.20 mu m) groups, with the growth rate of the MC (156.14 mu m) cross greater than that of the CM (155.35 mu m) cross. Also, heterosis for survival was significantly larger than that for growth. Both maternal origin and mating strategy had significant effects on growth and survival throughout the whole larval stage. Heterosis was also observed in later spat and adult stages. On day 170, the mean shell length, shell height and total weight of the CM cross were significantly larger than those of the other crosses (P<0.05). The results from this study indicate that hybridization between A. irradians concentricus and A. irradians irradians may be a promising way for genetic improvement of existing bay scallop brood stocks in China. (c) 2007 Elsevier B.V. All rights reserved.

Effect of Tannic Acid on the Growth and Survival of Root Vles (Micortus oeconomus)

The objective of this study was to investigate the effects of tannic acid on the gworth and survival of small mammalian berbirvores. Measurements were conducted with weaned root voles fed with 3% or 6% tannic acid and 10% or 20% protein in their diets. The results indicated that the effect of tannic acid on growth rate of weaned root voles was greater when given a lower protein diet than a higher protein diet. After 20 d, with 10% protein diets, mean growth rates of the weaned voles fed with 3% or 6% tannic acid were -0.135 g/d and -0.25 g/d, respectively. When given 20% protein diet, mean growth rates of weaned root voles fed with 3% and 6% tannic acid for 20 d were 0.134 g/d and -0.116 g/d, respectively. Food utilization efficiencies of the voles fed with 3% and 6% tannic acid diets were significantly lower than that of the control diet at the level of 10% protein. When given the 20% protein diet, food utilization efficiencies of weaned voles fed with 6% tannic acid were significantly lower than that of the voles fed with 3% tannic acid diet or the control diet with the 10% protein diets, the average survival days of the weaned voles fed with 3% and 6% tannic acid diets decreased 26.23% and 49.36% compared to controls at the end of trial period, respectively. With 20% protein diets, the average survival of weaned voles given 6% tannic acid diet decreased 39.41% compared to controls at the end of trial period, although weaned voles given 3% tannic acid had a slight decrease of average survival days. The results of study suggested that tannins could substanitially affect the individual performance of weaned root voles.

Host sex and ectoparasite infections of plateau pika (Ochotona curzoniae, Hodgson) on the Qinghai-Tibetan Plateau

A total of 449 plateau pika (Ochotona curzoniae Hudgson) individuals were sampled with rattraps from 21 plots (size 1 ha) randomly scattered over the area of the species distribution at the altitude 3275-4807 in a.s.l. in the Qinghai-Tibetan Plateau (West China). Two main ectoparasite species Hypoderma satyrus Brauer and Ixodes crenulatus Neumann of plateau pika were surveyed, and the relations between host sex and parasitism were analyzed. The results were: (i) although not significantly, the infection rate of female young was close to zero and lower than that of male young (6%), while the infection rate of female sub-adults (19%) was contrarily - higher than that of male sub-adults (11%); adult females had significantly higher (41%) infection rate than that of males (18%) (P<0.001); (ii) the parasite infection rates for both males and females increased with increasing age, but female age-groups had obviously steeper slope. We suggested that the differences of body mass, growth rate and home range between males and females had mainly caused the sex-biased parasitism (SBP) of plateau pika at each age stage. Also, due to the higher increases of body mass and maybe as well as of the home range differences between consecutive age-groups, the parasite infections of females became more sensitive to the influences of age than that of males.