Studies on growth rate and grazing mortality rate by microzooplankton of size-fractionated phytoplankton in spring and summer in the Jiaozhou Bay,China

Dilution experiments were performed to examine the growth rate and grazing mortality rate of size-fractionated phytoplankton at three typical stations, inside and outside the bay, in the spring and summer of 2003 in the Jiaozhou Bay, China. In spring, the phytoplankton community structure was similar among the three stations, and was mainly composed of nanophytoplankton, such as, Skeletonema costatum and Cylindrotheca closterium. The structure became significantly different for the three stations in summer, when the dominant species at Stas A, B and C were Chaetoceros curvisetus, Pseudo-nitzschia delicatissima, C. affinis, C. debilis, Coscinodiscus oculus-iridis and Paralia sulcata respectively. Tintinnopsis beroidea and T. tsingtaoensis were the dominant species in spring, whereas the microzooplankton was apparently dominated by Strombidium sp. in summer. Pico- and nanophytoplankton had a relatively greater growth rate than microzooplankton both in spring and summer. The growth rate and grazing mortality rate were 0.18~0.44 and 0.12~1.47 d-1 for the total phytoplankton and 0.20~0.55 and 0.21~0.37 d-1 for nanophytoplankton in spring respectively. In summer, the growth rate and grazing mortality rate were 0.38~0.71 and 0.27~0.60 d-1 for the total phytoplankton and 0.11~1.18 and 0.41~0.72 d-1 for nano- and microphytoplankton respectively. The carbon flux consumed by microzooplankton per day was 7.68~39.81 mg/m3 in spring and 12.03~138.22 mg/m3 in summer respectively. Microzooplankton ingested 17.56%~92.19% of the phytoplankton standing stocks and 31.77%~467.88% of the potential primary productivity in spring; in contrast, they ingested 34.60%~83.04% of the phytoplankton standing stocks and 71.28%~98.80% of the potential primary productivity in summer. Pico- and nanophytoplankton appeared to have relatively greater rates of growth and grazing mortality than microphytoplankton during the experimental period. The grazing rate of microzooplankton in summer was a little bit greater than that in spring because of the relatively higher incubation temperature and different dominant microzooplankton species. Microzooplankton preferred ingesting nanophytoplankton to microphytoplankton in spring, while they preferred ingesting picophytoplankton to nanophytoplankton and microphytoplankton in summer. Compared with the results of dilution experiments performed in various waters worldwide, the results are in the middle range.

In-situ Studies of Microzooplankton Grazing Pressure on Phytoplankton in Jiaozhou Bay, China

Preliminary studies on microzooplankton grazing were conducted with dilution method in Jiaozhou Bay from summer 1998 to spring 1999. Four experiments were carried out at St.5 located at the center of Jiaozhou Bay. Chlorophyll a concentrations were consistently dominated by netphytoplankton(net-,>20μm), except during the autumn 1998 cruise, when they were dominated by nanophytoplankton(nano-,2-20μm). The contribution of picophytoplankton (pico-,<2μm) to total chlorophyll a concentrations(<200μm) varied considerably between cruises. Instantaneous growth coefficients(u) of phytoplankton varied from 0.098 to 1.947d -1 , with mean value of 0.902d -1 . Instantaneous coefficients(g) of microzooplankton grazing on phytoplankton ranged from 0.066 to 0.567d -1 , mean value of 0.265d -1 , which was equivalent to daily loss of 21.9% of the initial standing stock and 58.1% of the daily potential production.

Grazing impact of microzooplankton on phytoplankton in the Xiamen Bay using pigment-specific dilution technique

Phytoplankton group-specific growth and microzooplankton grazing were determined seasonally using the dilution technique with high-performance liquid chromatography （HPLC） in the Xiamen Bay, a subtropical bay in southeast China, between May 2003 and February 2004. The results showed that growth rates of phytoplankton ranged from 0.71 to 2.2 d^-1 with the highest value occurred in the inner bay in May. Mierozooplankton grazing rates ranged from 0.5 to 3.1 d^-1 with the highest value occurred in the inner bay in August. Microzooplankton grazing impact ranged from 39% to 95% on total phytoplankton Chl a biomass, and 65% to 181% on primary production. The growth and grazing rates of each phytoplankton group varied, the highest growth rate （up to 3.3 d^-1 ） was recorded for diatoms in August, while the maximum grazing rate （ up to 2.1 d ^-1 ） was recorded for chlorophytes in February in the inner bay. Among main phytoplankton groups, grazing pressure of microzooplankton ranged from 10% to 83% on Chl a biomass, and from 14% to 151% on primary production. The highest grazing pressure on biomass was observed for cryptophytes （83%） in August, while the maximum grazing pressure on primary production was observed for eyanobacteria （up to 151% ） in December in the inner bay. Net growth rates of larger phytoplanktons （diatoms and dinoflagellates） were higher than those of smaller groups （ prasinophytes, chlorophytes and cyanobacteria）. Relative preference index showed that microzooplankton grazed preferentially on prasinophytes and avoided to harvest diatoms in cold seasons （December and February）.

Preliminary study on different nutrient pools supplies for the phytoplankton growth in the Jiaozhou Bay in China in the fall of 2004

The source and significance of two nutrients, nitrogen and phosphorous, were investigated by a modified dilution method performed on seawater samples from the Jiaozhou Bay, in autumn 2004. This modified dilution method accounted for the phytoplankton growth rate, microzooplankton grazing mortality rate, the internal and external nutrient pools, as well as nutrient supplied through remineralization by microzooplankton. The results indicated that the phytoplankton net growth rate increased in turn from inside the bay, to outside the bay, to in the Xiaogang Harbor. The phytoplankton maximum growth rates and microzooplankton grazing mortality rates were 1.14 and 0.92 d^-1 outside the bay, 0.42 and 0.32 d^ -1 inside the bay and 0.98 and 0.62 d^-1 in the harbor respectively. Outside the bay, the remineralized nitrogen （Kt = 24.49） had heavy influence on the growth of the phytoplankton. Inside the bay, the remineralized phosphorus（Kt = 3.49） strongly affected the phytoplankton growth. In the harbor, the remineralized phosphorus （Kt = 3.73） was in larger demand by phytoplankton growth. The results demonstrated that the dif- ferent nutrients pools supplied for phytoplankton growth were greatly in accordance with the phytoplankton community structure, microzooplankton grazing mortality rates and environmental conditions. It is revealed that nutrient remineralization is much more important for the phytoplankton growth in the Jiaozhou Bay than previously believed.

海蜇养殖港塭微型浮游动物的摄食和生产力研究

通过对山东省靖海湾海蜇养殖港媪定期采样，采用稀释法研究该海蜇养殖港韫水体中浮游植物的生长率、微型浮游动物对浮游植物的摄食率、摄食压力以及微型浮游动物的生产力。研究结果表明，海蜇养殖港韫微型浮游动物组成比较简单，海蜇养殖期间微型浮游动物丰度低于海蜇捕捞结束期。其中，海蜇养殖期间微型浮游动物的优势种为根状拟铃虫（Tintinnopsisradix），为600～2600ind／L，而海蜇捕捞结束后优势种为根状拟铃虫、诺氏麻铃虫（Leprotintinnusnordquisti）和运动类铃虫（Codonellopsismobilis），丰度分别为30006000、15003000、1500～3000ind／L。研究期间，该港韫浮游植物生长率为0．05～1．03d。微型浮游动物的摄食率为0．24～2．37d一，对浮游植物现存量的摄食压力为21．10％～90．61％，对潜在初级生产力的摄食压力为77．08％～583．68％，而微型浮游动物的次级生产力占初级生产力的22．92％～76．92％。本研究表明微型浮游动物在海蜇养殖港媪生态系统物质和能量流动中起着重要作用。