2000～2001年柘林湾浮游动物的群落结构及时空分布

Community Structure and Temporal and Spatial Distribution of Zooplankton in Zhelin Bay, China(2000～2001)

20 0 0年 7月至 2 0 0 0 1年 7月的周年调查结果表明 ,粤东柘林湾浮游动物有桡足类 2 9属 5 7种 ,枝角类 3属 3种 ,及端足类、磷虾、糠虾、多毛类、毛颚类、被囊类、水母和各种浮游幼体。其中 ,强额拟哲水蚤 Paracalanuscrassirostris、短角长腹剑水蚤 Oithona brevicornis和鸟喙尖头 Penilia avirostris为优势种 ,合计占浮游动物总个体数的 6 2 .7%。浮游动物的种类数、生物量和总个体数都表现为湾外大于湾内的平面分布格局 ,周年变化基本上为单峰型 ,高峰期位于 6～ 1 0月份 ,最低谷位于冬季 1月份。因此 ,总个体数与水温成显著正相关关系。柘林湾是一个浮游动物相对丰富的海湾 ,年均生物量为 1 1 5 .7mg· dw / m3 ,总个体数达 6 .8× 1 0 3 ind/ m3 ,但群落结构的小型化趋势比较明显。回归分析结果表明 ,浮游动物总个体数与浮游植物密度成显著正相关关系。

Zhelin Bay is one of the most important bays for marine culture in Guangdong Province of China. Due to the increasing human population and mariculture in the last 10 years, the ecological environment has changed dramatically. Although Phaeocystis blooms of 1997 and 1999 had brought the serious economic loss and ecological damage to this area, few studies were followed. To understand why Phaeocystis blooms frequently hit this area and how the increased marine culture affects this ecosystem, we have investigated the temporal and spatial distribution of phytoplankton, zooplankton, nutrients, and other biochemical parameter since May 2000. This paper describes an annual (7/2000～7/2001) variation of the community structure and temporal and spatial distribution of zooplankton in Zhelin Bay. Water samples were collected from eight stations weekly (March to November) or biweekly (December to February). Sampling was scheduled to cover the period around high tide (±1.5h). In each station, water samples for zooplankton analysis was collected by double vertical hauls of a JP-2 net (200μm) from the bottom to the surface. Two batch samples were collected each time. One batch was fixed immediately with formalin (5% in the samples) in situ and then transferred to laboratory for species identification and biomass analysis. Thereinto, copepod, and cladocera were identified to species, others such as hyperiidea, euphausiacea, mysidacea, polychaeta, chaetognotha, tunicata, medusa were identified to genus. The other batch was used for dry weight measurement. Samples were filtrated through GF without fixation, rinsed with 6.5% isoosmotic ammonium formate, desiccated with the vacuum pump, and dried in the oven at 60℃ for 24 h. Then they were cooled to indoor temperature in the desiccator, and measured with OHAUS analytical balance. Our investigation found 57 copepods, three cladocera, and others such as hyperiidea, euphausiacea, mysidacea, polychaeta, chaetognotha, tunicata, medusa, and planktonic shrimps. In terms of individual biomass, copepod accounted for 66.3%, planktonic larvae accounted for 13.1%, cladocera accounted for 10.7%, and the rest accounted for 9.9%. The dominant species in the Zhelin Bay are Paracalanus crassirostris, Oithona brevicornis, Penilia avirostris, Calocalanus pavoninus and Euterpe acutifrons. Based on their ecological and distributional characteristics, copepod and cladocera can be classified into four ecotypes: estuarine species, nearshore and warm-water species, nearshore and warm-temperature species, and offsea extensive species. Based on the data of copepod and cladocera only, species abundance increased from 26 species in the inner bay (Station 4) to 47 at the outer bay (Station 7). Temporally, the highest abundance was found in August (38 species) and the lowest was in January (17 species). In all identified copepod and cladocera, there were 45 species with body length smaller than 1.3 mm, which accounted for 75.0% of the total species abundance. Particularly, the body lengths of most dominant species were less than 0.6 mm. Therefore, micro-zooplankton dominated the zooplankton community in Zhelin Bay. The annual average dry weight increased from the inner bay (47.3 mg/m 3 at Station 4)to the outer bay (211.8 mg/m 3 at Station 7) . Monthly average dry weight ranged from 19.4 mg/m 3 in January to 264.1 mg/m 3 in May with the annual mean of 115.7 mg/m 3. It also exhibited two peaks during our investigation period: the biomass was low in January (19.4 mg/m 3), but increased from February with water temperature and phytoplankton abundance, and it reached the first peak in May (264.1 mg/m 3), which was associated with the biomass of Noctiluca scientillans, then it decreased until reaching the second peak in September (224.4 mg/m 3). Biomass expressed as individual number increased from 2.4×10 3ind./m 3 in the inner bay (Station 4) to 13.4×10 3ind./m 3 at the outer bay (Station 7). The large-scale filter-feeding oyster culture and marine fish culture were suspected to be the rea