Li-Chun Tseng

Copepod communities related to water masses in the southwest East China Sea

The East China Sea is characterized by a complex hydrographic regime and high biological productivity and diversity. This environmental setting in particular challenged a case study on the use of mesozooplankton community parameters as indicators of water masses. In order to reveal spatial patterns of zooplankton communities during summer, a large scale oceanic transect study was conducted. Two transects were taken in the southwest East China Sea region, covering for the first time the China shelf, slope, and the estuaries of the Yangtze river and of the Minjiang river, the northern Taiwan Strait, and the Kuroshio Current region. A total of 77 copepod species were quantified. Copepod abundance was significantly higher in the estuary of the Yangtze River runoff mixture waters and lowest at the Kuroshio Current Region. The calanoid Parvocalanus crassirostris was the most frequently occurring and abundant species retrieved from 27 samples of a total of 39 samples. The use of multivariate cluster analysis separated the Mainland China Shelf from the northern Taiwan Strait and the Kuroshio Current Region at the first hierarchical level. The use of an indicator value method (IndVal) associated with each cluster of stations revealed characteristic species assemblages. Two hierarchical levels defined 4 assemblages within geographical sectors representing copepod assemblages of the Kuroshio Current Region, of the northern Taiwan Strait and the southern China Shelf near the estuary of the Minjiang River and northern stations near the estuary of the Yangtze River. Overall, there was a strong correspondence between the distribution of certain copepod species and water masses. Differences between the Mainland China shelf, the northern Taiwan Strait and the Kuroshio Current Region were characterized by differences in species composition and abundance. Water mass boundaries in the study area were exclusively indicated by distinct differences in species composition, emphasizing a correlation between copepod communities and water masses of the southwest East China Sea in summer.

Copepod community structure over a marine outfall area in the north-eastern South China Sea

This study focuses oil the dynamics of copepod abundances and species composition in the upper water column of a marina outfall area Tso-Ying (T-Y) in the boundary waters of the north-eastern South China Sea and the Taiwan Strait as all example. Zooplankton samples were collected in March, June and September 2002. Mean copepod abundance at all stations ranged from a minimum Of 9.4 (individuals m(-3)) ill March to a maximum of 1685 (individuals m(-3)) in June. A total of 66 copepod species belonging to 31 genera and 19 families were identified during three cruises. Copepod assemblages were dominated by Temora turbinata which occurred in >97% samples with a relative abundance Of 75-46% combining all three sampling cruises. The ordination diagram derived from non-metric multidimensional scaling separated samples oil the basis of season and revealed that different sampling stations clustered differently during each cruise. The second and third most dominant species were Acrocalanus gracilis and Acrocalanus gibber, representing 1.73% and 1.65% of the total copepod abundance respectively. The outfall area studied here correlates with lower copepod densities represented by a few species that show a higher relative abundance in comparison with non-affected areas. We provide here the first example where plankton assemblages indicate useful information about environmental changes in the course of selvage disposal all a stable outlet site.

Copepod assemblages of the northern South China Sea

We studied copepod assemblages in the northern South China Sea during October 2004. A total of 78 copepod species was identified from 24 families and 42 genera that include the four orders Calanoida, Cyclopoida, Harpacticoida, and Poecilostomatoida. The high copepod diversity in the study area may mainly be caused by both the year-round Kuroshio Current intrusion and the SW monsoon, prevailing in the South China Sea during summer. Water currents in the region transport marine planktonic fauna, that comprises predominantly Copepoda from subtropical and tropical water masses. Calanus sinicus did not appear, indicating that there was no cold water mass intrusion in that area during October 2004. Clansocalanus furcatus and C. arcuicornis were most dominant, occurring in 27 of a total of 28 samples (occurrence rate (OR): 96.43%). Thirteen copepod species were found once in all samples. The three most dominant copepods considering all samples were Clausocalanus furcatus (RA: 15.32%), C. arcuicornis (RA 13.52%), and Paracalanus nanus (RA: 9.28%). Most species of copepods performed a common diel vertical migration, descending during daytime and ascending at night at different rates to different depth zones. There were smaller numbers of species and lower diversity indices in surface waters (1-2 m depth) as compared to depths below 50 m.

Mesh size affects abundance estimates of Oithona spp. (Copepoda, Cyclopoida)

Retrieval by different mesh-sized plankton nets is compared, using the abundance and distribution patterns of cyclopoid copepods of the genus Oithona W. Baird, 1843 as a case study. Mesozooplankton was sampled during spring, summer, and autumn of 2000-2002 in the South China Sea. Plankton samples were collected by surface tows (5-0 m) and by oblique tows in three different depth layers (0-50 m, 0-100 m, and 0-150 m), with Norpac zooplankton nets of 333 and 100 mu m mesh size. The oithonid density and diversity in the plankton samples collected through a 100 mu m mesh was about one order of magnitude higher than those collected through a 333 mu m mesh. The mean occurrence frequency of Oithona spp. in the plankton samples collected through a 100 mu m mesh net was > 85% and > 60% through a 333 mu m mesh net, with a mean total density of 45.86 +/- 206.97 m(-3) for the 100 mu m mesh net compared to 2.28 +/- 21.94 m(-3) for the 333 mu m mesh net [which indicates the enormous patchiness in occurrence of these copepods]. The density of smaller mesozooplankton, as evidenced by Oithona spp., has thus been underestimated by previous researchers using larger meshed nets. Samples collected through a 100 mu m mesh net demonstrated the numerical importance of the genus Oithona and its distinct seasonal and interannual patterns of abundance and distribution in the South China Sea.

Potential of three aquatic predators to control mosquitoes in the presence of alternative prey: a comparative experimental assessment

Predator-induced control of pests depends on the predator’s preference for the target pest over naturally co-occurring prey species. We compared the larvivorous efficiency of three common freshwater predators: mosquitofish (Gambusia affinis; Baird and Girard, 1854), dragonfly naiads (Zyxomma petiolatum; Rambur, 1842) and copepods (Mesocyclops aspericornis; Daday, 1906) on different instars and the relative abundances of the mosquito Anopheles stephensi (Liston, 1901) in the presence of alternative cladoceran prey, either Moina macrocopa (Straus, 1820) or Daphnia similoides (Hudec, 1991). Larval removal rate decreased with increasing larval size and instar stage. The maximum consumption rate was by mosquitofish, followed by dragonfly naiads and copepods. The presence of either of the alternative prey significantly reduced larval consumption by all three predators, except in the D. similoides–mosquito larvae combination for naiads. Mosquitofish and copepods preferred early instars of the mosquito. Prey selectivity indices for early mosquito instars against D. similoides did not differ between mosquitofish and copepods, whereas naiads had significantly lower index values than the other two predators. Considering the negative impacts of mosquitofish on native assemblages, that is, its invasiveness and its lower selectivity for mosquito larvae, our results suggest that the feasibility of using copepods in large-scale control programs needs to be evaluated.

Summer distribution of Noctiluca scintillans and mesozooplankton in the Western and Southern East China Sea prior to the Three Gorges Dam operation

This research investigated the distribution and abundance of Dinoflagellate Noctiluca scintillans and mesozooplankton along two transect lines covering the China shelf, slope, the estuaries of the Yangtze River and the Minjiang River, the Northern Taiwan Strait, and the Kuroshio Current region during the summer of 2001. In addition to the regular sampling, 24-h high-frequency sampling at four fixed stations (estuary of the Yangtze River, estuary of the Minjiang River, the Northern Taiwan Strait, and the Kuroshio Current region stations) were also conducted to understand the diurnal vertical migration behavior of zooplankton. Mesozooplankton were dominated by Calanoida (relative abundance, RA 15.74%), Cyclopoida (RA 5.10%), Pteropoda (RA 3.88%), and copepod nauplii (RA 3.42%). Chaetognaths and calanoid copepods were recorded in all samples. Noctiluca scintillans was abundant (RA 51.04%) among all identified organisms in samples at low-salinity stations, particularly in the estuarine region of the Yangtze River. Copepods were the dominant group of mesozooplankton at most stations of the Southwest East China Sea. Our 24-h high-frequency sampling did not reveal any clear diurnal vertical migration behavior of zooplankton. The cluster analysis indicates that differential patterns of the zooplankton community structure in the Southwest East China Sea were related to different water masses. Our results provide useful information on zooplankton community structure in the estuarine region of the Yangtze River and the Southwest East China Sea prior to operation of the Three Gorges Dam.

Geospatial variability in the autumn community structure of epipelagic zooplankton in the upper layer of the northern South China Sea

BackgroundFor the present study, we collected mesozooplankton in the upper layer (above 100 m in depth) of four stations in the northern South China Sea (SCS) to determine the influence of different water masses on their distribution and abundance from 27 September to 2 October 1999.ResultsIn total, 18 major zooplankton taxa were recovered from the samples. Calanoid copepods, Noctilucales, and chaetognaths were dominant and together comprised 65.90% of the overall zooplankton counts. Zooplankton densities ranged from 102.19 to 1,285.24 individuals per cubic meters (ind./m3) (average, 306.38 ± 435.71). Noctilucales were abundant at stations located in the Kuroshio Current (KC) intrusion area. Integrating all samples, 32 copepod species were identified consisting of 23 genera belonging to 16 families. Total copepod abundances ranged from 30.24 to 311.17 ind./m3 (average, 99.14 ± 97.84). Numerically, Pleuromamma gracilis, Nannocalanus minor, and Lucicutia flavicornis were the most dominant species. The most frequently occurring species in all samples were Acartia (Acartia) negligens and Corycaeus (Farranula) gibbula. Results of a cluster analysis indicated that community structures of zooplankton and copepods of the northern SCS varied at geospatial scales during the sampling period.ConclusionsResults of the present study suggest that the composition and community structure of zooplankton and copepods were influenced by intrusion of the KC in the shallow layer above 100 m in depth in the northern SCS. Some indicator species characteristic of the KC indicated that the study area received water masses from the northern SCS and the KC.

Comparison of metal accumulation in the azooxanthellate scleractinian coral (Tubastraea coccinea) from different polluted environments

The response of metal accumulation in coral Tubastraea coccinea to various degrees of metal enrichment was investigated from the Yin-Yang Sea (YYS) receiving abandoned mining effluents, the Kueishan Islet (KI) hydrothermal vent field, and the nearshore area of remoted Green Island (GI). The concentrations of most dissolved metals were highest in seawater at YYS, followed by KI, and then GI, showing the effects of anthropogenic and venting inputs on metal levels. Five metals (Co, Fe, Mn, Ni, and Zn) yielded significant differences (p<0.05) among the skeleton samples. We identified similar patterns in the metal-Ca ratios, indicating that the elevated metals in skeletons was a consequence of external inputs. The coral tissues were relatively sensitive in monitoring metal accumulation, showing significant differences among three locations for Cd, Co, Cu, Fe, Pb, Ni, and Zn. Specific bioconcentration factors provided strong support for the differential metal accumulation in skeletons and tissues.

Bioaccumulation of trace elements in dominant mesozooplankton group inhabiting in the coastal regions of Indian Sundarban mangrove wetland.

Mesozooplankton (Body size 20-200 μm) along with the surface water were collected from coastal regions of Sundarban, northeastern part of Bay of Bengal considering three seasons, namely premonsoon, monsoon and postmonsoon. Samples were analyzed for community structure and the dominant copepod species were further analyzed for trace metal concentration. In total, 50 copepods were identified (22 families and 43 genera). The dominant mesozooplankton species included 9 copepods and an epipelagic chaetognath, exhibited both spatial and seasonal variations. Metal concentration exhibited considerable inter-specific variations for the copepods and the mean concentrations were: Fe, 1350.2-51118.3 μg/g; Al, 647.2-73019.1 μg/g; Ni, 32.4-110.3 μg/g; Mn, 122.8-1066.5 μg/g; Pb, 0.04-97.5 μg/g; Pb, 10.6-97.5 μg/g; Cd, 4.2-21.6 μg/g; Cu, 17.4-145.1 μg/g; Zn, 225.7-1670.9 μg/g; Cr, 21.7-194.3 μg/g; Co, 1.32-111.1 μg/g. Metal concentrations showed the following order: Sagitta bedoti>Coryceas danae>Oithona sp.>Eucalanus subcrassus>Labidocera euchaeta>Paracalanus parvus>Acartiella tortaniformis>Acartia spinicauda>Pseudocalanus serricaudatus.

Ciliate (Euplotes sp.) predation by Pseudodiaptomus annandalei (Copepoda: Calanoida) and the effects of mono-algal and pluri-algal diets

BackgroundPseudodiaptomus annandalei is an estuarine species and being cultured as live feed for grouper fish larvae and other planktivores. We examined the predation behavior of P. annandalei adults when preying on ciliated protists (Euplotes sp.) and the effects of mono- and pluri-algal diets on ciliate predation by P. annandalei under laboratory conditions. The algal food comprised the pigmented flagellate Isochrysis galbana (4 ~ 5 μm) and Tetraselmis chui (17 ~ 20 μm).ResultsMales and females of P. annandalei consumed 8 ~ 15 ciliate cells/h. The probability of ciliate ingestion following an attack was a direct function of the copepods hunger level. Conversely, the probability of prey rejection after capture was a negative function of the copepods hunger level. Starved and poorly fed females showed a significantly lower rate of prey rejection compared to similarly treated males. The duration of handling a ciliate prey did not significantly differ between males and females of P. annandalei. Starved copepods spent less time handling a ciliate prey than fed copepods. Prey ingestion rates showed a negative relation with the feeding duration, whereas the prey rejection rate increased as the feeding duration increased. The ciliate consumption rate of P. annandalei was significantly lower in the presence of mixed algae. Neither I. galbana nor T. chui alone had any significant effect on ciliate consumption by P. annandalei.ConclusionsThe results confirmed that P. annandalei ingests bacterivorous heterotrophic protists even in the presence of autotrophic protists. Therefore, our results point to the role of P. annandalei in the transfer of microbial carbon to the classical food chain in estuarine and brackish water ecosystems.