Wen-Tseng Lo

Identity and abundance of surface-dwelling, coastal copepods of southwestern Taiwan

Day and night abundance of copepods in the coastal waters off southwestern Taiwan was studied during a cruise an 26-28 December 1997. A total of 14 zooplankton samples (7 daytime and 7 nighttime) was taken at seven stations using a one-meter mouth opening net with 333 Pm mesh, and a Hydrobios flowmeter mounted in the centre of the mouth. The mean numerical abundance of copepods was 123 +/- 69 ind./m(3). In all, 67 species of copepods belonging to 16 families and 31 genera were identified. Among these, Paracalanus aculeatus (32% of the numerical total of copepods), Acrocalanus gracilis (31%), and Oncaea venusta (11%) were the most dominant species and occurred at every station. Most species were more abundant during the day than at night. Both the index of species diversity and that of species number of copepods were higher at the northern stations and decreased toward the southern stations at night, but behaved in the opposite manner during the day. From the results of cluster analysis, four station groups were formed: daytime northern stations, daytime southern stations, nighttime northern stations, and nighttime southern stations. The daytime northern station group was most distinct from the others. Four copepod groups were also distinguished and are herein discussed.

Hydrographic processes driven by seasonal monsoon system affect siphonophore assemblages in tropical-subtropical waters (western North Pacific Ocean).

This work is a part of the Taiwan Cooperative Oceanic Fisheries Investigation, the first large scale hydrographic and plankton survey around Taiwan (21–26°N, 119–123°E). The present study examined the influence of hydrodynamic and biological variables driven by monsoon system on the siphonophore assemblages through an annual cycle in 2004. Calycophorans, namely Chelophyes appendiculata, Diphyes chamissonis, Lensia subtiloides, Bassia bassensis, and Muggiaea atlantica, were the most dominant siphonophore species. Maximum abundance of these dominant species generally occurred during the warm period (May and August), while M. atlantica had a significantly peak abundance in February. Although no apparently temporal difference in siphonophore abundance was observed in the study, siphonophore assemblage was more diverse in August than in other sampling times. Result of a cluster analysis indicated that assemblage structure of siphonophores in the waters around Taiwan varied at temporal and spatial scales during the sampling period. The intrusions of the Kuroshio Branch Current and China Coastal Current to the study area play an important role on the transportation of siphonophores. Also, the distribution of siphonophore assemblage was closely related to the hydrographic characteristics, with temperature, chlorophyll a concentration, and zooplankton abundance being the major environmental factors affecting the spatio-temporal variability of siphonophores. This study contributes substantially to the new knowledge of the siphonophore assemblage in the tropical-temperate waters of Taiwan.

COPEPOD ASSEMBLAGES AND DIEL VERTICAL MIGRATION IN THE EAST CHINA SEA, NORTH OF TAIWAN

The western North Pacific north of Taiwan is an area with high oc?anographie complexity, both biological and physicochemical. The northward flowing Kuroshio Current passes here and turns northeastward at the break of the East China Sea continental shelf, inducing an upwelling. We used a NorPac plankton net with opening-closing mechanism to take plankton samples at six depth levels (0, 50, 100, 150, 200, and 250 m) in four time series (00:00, 08:00, 15:00, and 21:00 local time) within 24 hours. Planktonic copepods were identified to species level when possible; depth and time of collecting, and abundance in individuals/nr were recorded. Different patterns of diel vertical migration (DVM) were established for the dominant species, such as normal DVM in Paracalanus aculeatus, Clausocalanus furcatus, Temora dlscaudata, and Canthocalanus pauper, reverse DVM in Olthona atl?ntica, no apparent DVM in Oncaea venusta and Subeucalanus mucronatus, and bimodal vertical distribution in Clausocalanus mastlgophorus and Cosmocalanus darwlnl. Four sampling groups and four copepod species assemblages were defined by using cluster analysis. Each of these sampling groups and species assemblages is characterized by a different DVM pattern.

Influence of monsoon-driven hydrographic features on thaliacean distribution in waters around Taiwan, western North Pacific Ocean

BackgroundThe mesoscale distribution of thaliaceans associated with hydrographic conditions in the waters around Taiwan was investigated during two different monsoon seasons in 2004 in order to elucidate possible influences of hydrological conditions driven by seasonal monsoons on distributional patterns of thaliaceans.ResultsIn total, 18 thaliacean species, belonging to 12 genera and 3 families, were identified in our samples. Thalia rhomboides, Doliolum denticulatum, Doliolum nationalis, Thalia orientalis, Pyrosoma verticillatum, and Thalia democratica were the six predominant species and contributed 93% to the total thaliacean collection by number. Thaliacean assemblages were similar in composition between seasons, but abundances and species numbers were higher in summer than in winter. Spatial distribution patterns of doliolids and salps clearly differed and were closely associated with hydrographic characteristics. Doliolids were mainly found in lower-salinity and nutrient-rich shelf and neritic waters; among them, D. denticulatum could be used as an indicator species of the China Coastal Current. Most salp species showed higher abundances in warm oceanic waters, such as the Kuroshio Current, Kuroshio Branch Current, and South China Sea Surface Current.ConclusionsThis study showed that the succession of water masses driven by monsoons affects seasonal and particularly spatial distributions of abundances of the thaliacean assemblage in the area studied.

Hydrographic characteristics and community structure of epipelagic mesozooplankton in the Dongsha (Pratas) Atoll, South China Sea

The relationship between hydrographic features and the community structure of epipelagic mesozooplankton was examined among 10 stations of the water body within the Dongsha (Pratas) Atoll during April (spring), July (summer) and October (autumn) 2011. The hydrographic conditions of the Dongsha Atoll were likely influenced by air temperature and rainfall due to the semi-enclosed topography. Surface water was warm and less saline, particularly in autumn, apparently due to the passage of Typhoon Nalgae. The highest mean (±s.d.) abundance of mesozooplankton was recorded in spring (1204 ± 336individualsm–3) and the lowest was recorded in autumn (45 ± 9individualsm–3). Twenty-six major mesozooplankton groups were observed across the samples collected. Mesozooplankton communities were dominated by calanoid copepods, crab zoea, fish eggs and foraminiferans, which together comprised 86.01% of the total zooplankton catch. The absence of significant correlation between mesozooplankton abundance and chlorophyll-a concentration indicated that the temporal pattern of the mesozooplankton community seems to be more dependent on physical variables than on primary production.

Temporal and Spatial Occurrence of Mesopelagic Fish Larvae during Epipelagic Drift Associated with Hydrographic Features in the Gaoping Coastal Waters off Southwestern Taiwan

AbstractThis study analyzed the spatiotemporal occurrences of mesopelagic fish larvae in relation to environmental forcing in the Gaoping coastal waters off southwestern Taiwan during August 22–23, 2014 (summer), December 5–6, 2014 (winter), and April 28–29, 2015 (spring). Forty taxa or morphotypes of mesopelagic fish larvae were identified. Skinnycheek Lanternfish Benthosema pterotum (19.1%), Bristlemouth Cyclothone alba (11.6%), Spinycheek Lanternfish B. fibulatum (10.8%), Benthosema spp. (9.4%), and Neoscopelus spp. (9.2%) were the five predominant taxa. Maximum abundance of these taxa generally occurred during the cold period (winter and spring). Although the temporal difference in the abundance of mesopelagic fish larvae was not significant, the assemblage of mesopelagic fish larvae was more diverse in winter than in other seasons. Cluster and distance-based linear model analysis suggested a distinctly structured assemblage of mesopelagic fish larvae. The intrusion of the Kuroshio Branch Current play...