This study aims to investigate the spatial and temporal distribution of siphonophores in relation to water temperature, salinity, concentration of chlorophyll a and the abundance of copepods in Tapeng Bay and Kaoping coastal waters from June 1999 to July 2001. In Tapeng Bay, 20 species of siphonophores belonging to 9 genus and 3 families were identified with the mean abundance of 11¡Ó33 ind./100m3. The 5 most dominant siphonophore species in Tapeng Bay were Lensia subtiloides, Chelophyes appendiculata, Lensia subtilis, Bassia bassensis, and Lensia campanella, comprising 85% of the numerical total siphonophores. The siphonophores were mainly found at north station and scarce or even absent at St. N and St. S. Seasonal distribution of siphonophores was inconsistent, but generally had higher abundance in fall and winter. In Kaoping coastal waters, 34 species of siphonophores belonging to 16 genus and 5 families were identified, with the mean abundance of 648¡Ó636 ind./100m3. Seasonal change in numerical abundance of siphonophores was obvious, with higher in spring and autumn. The 5 most dominant species were C. appendiculata, L. subtiloides, Chelophyes contorta, Sulculeolaria chuni and B. bassensis, and comprised 77% of the total counted of siphonophores. The species number, species diversity, and the mean abundance of siphonophores in Kaoping coastal waters were higher than that in Tapeng Bay. The siphonophores found in the present study mostly belong to the widespread oceanic species and widespread coastal species. The distributions of siphonophore were not significantly (p>0.05) correlated to temperature, salinity, concentration of chlorophyll a and the abundance of copepods, except Abylopsis tetragona and Diphyes dispar, that exhibited significant negative correlation with temperature (p<0.01) and chlorophyll a (p<0.01), respectively.

ii Abstract Tapeng Bay has distinct dry (October to May) and wet (June to September) seasons. The salinity was 33‰ in the dry season, but may as low as 21‰ during the wet season. The yearly average temperature, salinity and chlorophyll a of Tapeng Bay are 26.9 ¢J, 29.7 ‰ and 2.24 £gg/L respectively. Thirty-six species of copepods belonging 18 families and three orders plus 16 unidenitified species were found in the materials of this study. The average abundance of copepods was 5.8 ¡Ó8.4 x10 5 ind./100m 3 . The nine most dominant species were Acartia tsuensis , Paracalanidae (copepodites), Acartiidae (copepodites), Parvocalanus crassi rostris , Oithonidae (copepodites), Oithona dissimilis , n auplius, Acrocalanus indicus and Zausodes spp., contibuting to 81% of the total copepods. Majority of the dominant species exhibited clear seasonal changes in abundance, varying positively with temperature. Acartia tsuensis and Acartiidae were dominant species in station N in the wet season, but other dominant species had higher abundance in the dry season. Aurelia aurita (Cnidaria, Scyphozoa) which was dominant in the dry season, may play the role of a keystone species at stations S and C. Species composition was different among stations. Fish-pond species was dominant at station S, copepodite and nauplii, and neritic species at station N. The abundance of copepods may be influenced by tidal action. When inlet species abundance is higher than neritic species, total copepod abundance at high tide is lower than at low tide, but the trend is reverse for neritic species. The grazing impact of copepods on phytoplankton was 0.04 to 40.36 % per day.

none

A 3D numerical model ¡V COHERENS has been applied to construct a coupled hydrodynamic and ecological model for studying Tapeng Bay, which is a coastal lagoon situated in southwest of Taiwan. The simulations have been carried out to study the influences and their interacting mechanisms among the tidal currents, nutrients and micro planktons in the Lagoon. Model results have been compiled for calculating the nutrient fluxes and the primary productions in the Tapeng Bay. Tapeng Bay is a semi-enclosed coastal lagoon, which has only one tidal inlet for exchanging lagoon water with the coastal currents along the Kaoping coast on the narrow shelf in southwest of Taiwan. The study area is situated in the tropical climate zone where has sunshine through out the year except the rainy days concentrated in the summer season, which is influenced by the southwest monsoon. There are several drainage channels that collect the untreated domestic sewerage and wastewater discharged from the fish farms surround the lagoon. The discharges in these channels are usually low during the dry season. The solid contained in the water are mostly settled on the channel beds. During the raining season, high discharges due to the storm rainfalls re-suspend the sediments and carry into the lagoon. These sediments, which contain high concentrations of suspended solids and nutrients, cause the Bay water highly eutrophied. Therefore, the Bay is fully influenced by the seasonal variations. There are a lot of aquaculture, i.e. oyster farming and fish cage, in the Bay area since the water is calm and rich. But the balance between the nature and the anthropogenic disturbance is breaking. Besides the water level variation generated from the tidal inlet, the fresh water inflow from 3 major channels are included in the model to simulate their influences to the hydrodynamics and the density driven circulation due to changing salinities and temperatures from these inlets. Plankton, detritus, dissolved nutrients and dissolved oxygen is taking into account as the model variables for this marine eco-system. The plankton growth is mainly generated due to temperature, light intensity and nutrient level. Only the nitrogen cycle has been considered in the model by assuming there are enough supply of phosphate and silicate. Model runs have been carried out according to different seasonal situations of the boundary conditions. Furthermore, climates (heats, lights, winds, etc) are also included in the model to distinct seasonal characteristics. It is shown, from the model results, that the currents mainly dominate the distribution of nutrients in the Tapeng Bay. The nutrient level controls plankton growth. The nutrient sources are mainly coming from the coastal currents (through tidal inlet) in the wintertime, whereas the summer source was from the drainage channels due to the wash out by the high discharge rates. Beside these, dissolved oxygen concentrations in the Bay water are strongly influenced by the plankton growth rate, faster the photosynthesis higher the DO concentrations. The eutrophication levels of the Tapeng Bay water have been compiled using the plankton carbon level modeled at various situations. According to the Nixon standard (1995), Tapeng Bay has eutrophication through out the year. Mesotrophic condition can be observed during the wintertime, whereas the hypereutrophic level can be concluded during the raining season.

The population dynamics and the feeding of the scyphomedusa Aurelia aurita in Tapeng Bay, southwestern Taiman, were investigated from April, 1999 to April, 2000 and May, 2001 to April, 2002. A. aurita distributed mainly in the inner water of the Bay. The average abundance of A. aurita was 71¡Ó256 ind.100m¡Ð3, with higher abundance in winter and spring than in summer and autumn. The abundance of A. aurita showed no significant correlation with hydrographic features, but it seems to have one or two month¡¦s time lag with the seasonal distribution pattern of copepods. The main reproduction period of A. aurita was form autumn to next spring. The occurrence of ephyra was mainly in winter and spring, with maximum abundance of 328 ind./100m3. The average bell diameter of A. aurita was 13.9¡Ó4.2 cm. The size of bell diameter varied seasonally, generally had larger size in autumn and smaller size in spring. Seventeen zooplankton taxa were found in the stomach contents of A. aurita, copepods were the most dominant (70.3%), followed by copepods nauplius (20.1%), bivalve larva (3.0%) and fish eggs (2.3%). The average ingestion rate of A. aurita was 2165¡Ó2673 prey ind.-1 day-1 , the feeding impact of A. aurita on zooplankton was 14.69 % ~ 40.84 % %, with no significant difference among sizes.