A Comparative study on the temporal and spatial variation of micro-zooplankton in the coastal and estuarine ecosystems
Date Issued
2008
Date
2008
Author(s)
Chung, Jia-Lu
Abstract
The estuary and coastal water have sufficient nutrients that support high phytoplankton biomass and primary production. Higher nutrients and organic particle by river input indicate that the estuaries supply more food to copepods than the coastal water. One would easily predict copepods would not limited by food supply in estuary. On the other hand, verity of copepod abundance would control by temperature and predator in estuary. Fish larvae, Chaetognatha and jellyfish are common predators in estuary and coastal water, and also affect the variety of copepod abundance. Our hypotheses are as followed: first, copepod abundance was higher in estuary than in coastal water, because the differences of food supply conditions. Second, the copepod grazing rate and grazing impact in estuary are higher than in coastal water. Finally, copepod abundance is not controlled by food supply in estuary. ampling sites are in Tan-Shui River estuarine (as estuary site, TSR) and the inlet of Taiwan Nuclear Power Plant II (as coastal site, TPII). A 100 um mesh size of plankton net were employed to collect the smaller copepods and other zooplankton. A 330 um size net were collected the larger plankton and compare the abundance to smaller copepods. Temperature, salinity, nutrients, Chl-a concentrations and predator abundance were also measured. The linear regression was used to the relation between measurements. Copepod abundance is positive correlation with temperature indicating copepods are not in food limited condition. Under this condition, we could discuss the predation effect by negative correlation between copepods and predators abundance. e sampled weekly or bi-weekly during November 2001 to May 2004 in TPII. Temperature (17.9 to 29.9 ^oC), nitrate concentration (0.01 to 19.0 uM) showed strong seasonal fluctuation. Chl-a concentration (0.03~2.02 mg Chl-a m^-3) were positive correlation with temperature and negative correlation with nitrate. Paracalanus parvus, Acrocalanus gibber and Temora turbinata were most dominant species. Copepod abundance (42~29902 ind. m^-3) were positive correlation with temperature, indicating food is sufficient. Copepod specific grazing rate (SGR, 0.02 to 0.66 ugC Chl-a d^-1) and mean copepod grazing impact (2.68 ±11.0 Chl-a d^-1) were lower than others study, indicating phytoplankton was not the major food to copepods. The higher dissolve organic carbon concentration was obtained in TPII, which may support another carbon source from microbial loop. The jellyfish and Chaetognatha abundance were showed positive correlation with copepods, showed predators were not affected to copepod abundance. he large copepods were collected using 330 um mesh size net in 19 sampling stations, while small copepods were also collected by using 100 um mesh size net in 5 stations. During four seasons in 2006 in TSR, temperature (18.4~29.9 ^oC) varied seasonally with lowest and highest values recorded in winter and summer, respectively. Nitrate concentrations (0.3~8.8 uM) showed a significant seasonal trend with higher values in winter and lower values in summer. Chl-a concentration (0.3~8.5 mg Chl-a m^-3) varied with temperature, and recorded higher values near the river mouth. The neritic species were dominant in TSR, that including Parvocalanus crassirostris, Acrocalanus indicus, Oithona attenuata and O. nana. The species composition showed significant different by Cluster Analysis. Small copepods abundance (275~7088 ind. m^-3) varied with temperature, but large copepods (2~3272 ind. m^-3) were decreased from spring to summer. Medusae abundance (0~32584 ind. 1000m^-3) were significant decreased from winter to spring, and increased almost 444-folds of abundance in summer. The significant negative correlation between large copepod and medusa abundance indicated the strong predation appeared during spring to summer. The significant decouple of spatial pattern also support large copepods were under the strong predation effect by medusae. But small copepod abundance did not affect by medusae. It suggested that small copepods have higher growth rate and reproductive rate. mall copepod abundance in TPII were significant high than in TSR. According to the similar temperature variation and the sufficient foods in both areas, it is suggested that predator effect by medusae played the key factor that explain the difference of copepod abundance. The medusa bloom is occurred in many of estuary, small copepods may play more important role in secondary production when in a medusa bloom. It is also obtained the decreasing DOC in TPII in 2003, indicating it may be in food limited condition in 2004 or following years. The role of small copepods in microbial loop and secondary production may be important in study trophodymanics and carbon cycling.
Subjects
estuary
coastal water
copepods
seasonal variation
food limited
predator effect
Type
thesis
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